The Olympic Peninsula is the uplifted portion of the Cascadia accretionary wedge and forms the core of a 200 km scale oroclinal bend on the west coast of Washington State. The accretionary wedge started forming 45 million years ago following the accretion of the Siletzia igneous province along the Cascadia subduction margin. Low-temperature thermochronology studies have shown that the core of the peninsula has been continuously exhumed for the last 14 million years. The earlier onset of oroclinal bending, uplift, and emergence remains poorly documented. Here, we explore the Cenozoic drainage history of the Cascadia forearc and accretionary wedge to reconstruct the deformation history of the Olympic Peninsula. We use detrital zircon provenance and grain petrography data from modern rivers draining the Cascades, the Cascadia forearc and accretionary wedge, as well as from Eocene to late middle Miocene sedimentary units from the same areas. We first show a clear difference of sedimentary provenance between sedimentary units in the accretionary wedge, with older units reflecting mélange and imbricated strata that began as part of Siletzia, and younger units reflecting trench-fill material sourced from the Cascades and accreted to the wedge. We show that the accretionary wedge was directly fed from the Cascade arc until at least 16.5±0.5 Ma⁠, providing a maximum age for the emergence of the Olympic Peninsula. Fluvial deposits in the Cascadia forearc basin dated at 13.3±1.3 Ma display zircon age spectra and sedimentary grain petrography features typical of recycled accretionary wedge material. Although these deposits may also reflect local input, middle Miocene exhumation rates suggest the Olympic Peninsula was an active sediment source. Our results bracket the timing of emergence of the Olympic Peninsula to a narrow window in the late middle Miocene. We suggest that the initial onset of accretionary wedge deformation and oroclinal bending predates this by at least 10 million years, in the upper Oligocene, and is marked by flexural subsidence and high sedimentation rates recorded in strata of the Seattle Basin. Our results support a composite history for the development of the Cascadia accretionary wedge rather than models predicting a gradual and steady build-up.The Olympic Peninsula of Western Washington State is the subaerially exposed portion of the Cascadia accretionary wedge [1, 2], which developed following the Eocene accretion of the Siletzia igneous province along the west coast of North America [3, 4]. Substantial deformation and uplift of the Cascadia accretionary wedge have resulted in a large oroclinal bend with the Olympic Mountain range at its core [5]. These mountains are unique in that they are larger and higher than all other coast mountain ranges formed by accretionary wedges on the Pacific Coast of North America. Low-temperature thermochronology studies have shown that the core of the peninsula has been continuously exhumed for the last 14 million years, though the tempo and evolution of exhumation rates through recent times remain debated [1, 6–10]. Rock uplift has been proposed to be driven by crustal thickening related either to margin-parallel shortening [11], frontal accretion [7, 10], or underplating at the trench [12]. High precipitation rates along the coast enhance exhumation, contributing to the shape and rate of uplift [13].The actual timing of surface uplift of the accretionary wedge remains virtually undocumented. It is unclear when the accretionary wedge started forming a submarine high, creating a topographic barrier between the Cascadia trench and the forearc, and when the peninsula finally emerged. Documenting the chronology of these events is essential to reconstruct sedimentary fluxes into the trench, to understand how fast exhumational steady state was reached in the Olympic Mountains, and to identify the main drivers of rock uplift [12].Here, we use detrital zircon provenance and sandstone petrography to place age constraints on the uplift and subaerial exposure of the Olympic Mountains. We use U-Pb zircon ages and petrographic data from modern rivers of the Olympic Peninsula and the North Cascades to determine the provenance character of modern drainages. We then use the same methods on Cenozoic sedimentary rocks of the Cascadia forearc and accretionary wedge to reconstruct the regional drainage history and track the emergence of the Olympic Mountains as a topographic high.The Cascadia accretionary wedge, Cascadia forearc, and the Cascade Range run parallel to the Cascadia subduction zone, where the Gorda and Juan de Fuca Plates subduct beneath the North American Continental Plate. The Olympic Peninsula is the portion of the Cascadia accretionary wedge that sits on the west coast of Washington State, separating the Puget Lowland from the Pacific Ocean with a high mountain range. The Puget Lowland is the portion of the Cascadia forearc in Washington, which is bounded by the Olympic Peninsula to the West and the Cascade Range to the East, draining sediment from both. In Canada, the forearc forms the Georgia Basin, bounded by Vancouver Island to the West and the Coast Mountains to the East, the northward continuation of the Cascade Range (Figure 1). Reference to “the Cascades” in this manuscript specifically regards the North Cascades that extend from Central Washington to southern British Columbia. The Cascades comprise an exhumed metamorphic core, Mesozoic to Eocene plutons—the Coast Mountains Batholith—and an Andean-type volcanic arc that has been active since the middle Eocene—the Cascade Arc [14].The seminal study of Tabor and Cady [2] provides detailed structural and geological description of the Olympic Peninsula and has guided all other studies to follow. The peninsula is composed of two primary terrains: peripheral rocks that comprise early Eocene basalts of the Crescent Formation overlain by little-deformed Eocene to Miocene, mostly marine sedimentary rocks, and a core of extensively deformed marine sedimentary rocks called the Olympic subduction complex (OSC) by Brandon and Calderwood [1].The Crescent Formation is in fault contact with the OSC along the Hurricane Ridge Fault, wrapping around the east of the Olympic Peninsula to form a crescent shape (Figures 1 and 2; [15]). The Crescent Formation comprises primarily thick basal pillow and columnar basalts overlain by felsic volcaniclastic sandstones, lignite, and mudstones [16]. K-Ar hornblende dating, 40Ar/39Ar whole rock ages, and U-Pb dating of felsic tuffs constrain the eruption of the Crescent Formation to between 53.2 and 48.4 Ma [4, 17]. Some have proposed slab window volcanism as a result of ridge subduction to be the source of the Crescent Basalt [18, 19]. An alternative hypothesis has linked the Crescent Formation to a flare-up of the long-lived Yellowstone hotspot that resulted in the eruption of a marine large igneous province [4, 20, 21]. The latter model groups together contemporary basalts from Oregon, Washington, and British Columbia, including the Crescent Formation, into the Siletzia terrane; the Siletzia terrane would have erupted as a marine large igneous province, forming a submarine plateau on the Farallon plate before being accreted to North America in the early Eocene [4, 17]. Regardless of which model for the origin of the Crescent Formation is the most accurate, the grouping of the Siletzia terrane and accretion timing are well agreed upon. In this manuscript, “Siletzia” is used to refer to the entire accreted terrane, and “Crescent Formation” is used in reference to rocks of the Siletzia terrane that crop out in Western Washington.The first marine sediments were accreted to the Cascadia accretionary wedge beneath the Siletzia terrane in the Eocene, following the initiation of the Cascadia subduction zone, which caused significant slip along the Hurricane Ridge Fault (tens of kilometers; [7]). The initiation of the Cascadia subduction zone is dated at ca. 42-45 Ma based on the age of the oldest post-Siletzia accretion magmatic rocks in the Cascade Arc [14, 22]. The accreted sedimentary rocks that have been underthrust beneath the Crescent Formation form the core of the Olympic Peninsula today, and they have been thoroughly mapped [2, 15]. These rocks were initially divided into five informal lithic assemblages: the Hoh, Elwha, Western Olympic, Grand Valley, and Needles-Gray Wolf assemblages (Figure 2; [2]). Although these rocks have been mapped with high precision, the extreme amount of deformation and displacement has made it difficult to discern stratigraphic relationships between the five assemblages; in general, the rocks become younger from East to West [2, 15, 23]. Brandon and Vance [23] grouped rocks of the Cascadia accretionary wedge into the Olympic subduction complex (OSC) and reorganized the five lithic assemblages into three structural units using thermochronological and structural data: the coastal OSC, equating to the Hoh assemblage; the lower OSC, grouping the Western Olympic and Grand Valley assemblages; and the upper OSC, grouping the Needles-Gray Wolf and Elwha assemblages (Figure 2; [23]). Stratigraphic and chronologic relationships between these structural units are not clearly defined; biostratigraphic ages for the OSC range from Eocene to upper Miocene, and generally the oldest ages are found in the upper OSC and the youngest in the coastal OSC [24].The upper OSC is the structurally highest unit of the OSC, and it is interpreted to be the oldest [23]. The upper OSC locally contains pillow basalts that are compositionally similar to the Crescent Formation and are interbedded with fossiliferous limestones that yield latest Paleocene to middle Eocene fossil ages [15, 24]. Detrital zircons from this unit have yielded fission-track maximum depositional ages ranging from early Eocene to early Oligocene (48-32 Ma; [23]). Some localities attributed to the upper OSC yield upper Eocene to lower Miocene microfossils [25, 26].The lower OSC is distinguished from the upper OSC by the absence of pillow basalts, and only comprises marine clastic sedimentary rocks including turbidite sequences and highly deformed mudstone-rich mélanges. It structurally underlies the upper OSC. Detrital zircons from this unit have yielded fission-track maximum depositional ages ranging from 27 to 19 Ma [23, 27].The coastal OSC is the structurally lowest unit of the OSC and is lithologically similar to the lower OSC [23]; the two units are differentiated by the higher degree of metamorphism observed in the lower OSC [2, 23]. Detrital zircons from turbidites of the coastal OSC have yielded fission-track maximum depositional ages ranging from 26 to 11 Ma; mélange blocks have yielded maximum depositional ages ranging from 39 to 15 Ma [27]. The youngest fission-track ages, however, display high uncertainties (⁠2 s±3 to 4 Ma; [27]).The three units of the OSC have been attributed different sediment sources and accretionary histories, though little work has been done to quantify these differences [23]. It has been interpreted that the lower OSC represents sediment drained from the Cascades into the subduction trench, while the coastal OSC represents mass wasting of material from the continental slope, with these two units constituting the true accretionary wedge [23, 27]. Brandon and Vance [23] propose that early Eocene deposits of the upper OSC originated as the westernmost clastic strata of the Siletzia terrane. These strata were imbricated and underthrust beneath the Crescent Formation following the initiation of the Cascadia subduction zone. Brandon and Vance [23] also propose that this imbrication could not have occurred until after deposition of the youngest strata of the upper OSC (~33 Ma), which is several million years later than the proposed slip event along the Hurricane Ridge Fault and initiation of subduction (~45 Ma; [7, 14]).Detrital apatite and zircon fission-track and (U-Th)/He ages from the core of the peninsula show continuous exhumation since at least 14 Ma [7–9, 23, 28]. The exhumation of the OSC has created a wide oroclinal bend, resulting in the arcuate shape of the Crescent Formation [5]. It has been proposed, based on regional-scale plate motion and GPS data, that this oroclinal bend and the unusual elevation of the OSC is caused by margin-parallel motion, which contributes to uplift, with the Olympic Peninsula caught between the northward motion of the Oregon Coast Range and the relatively stable Vancouver Island [11, 29–31]. This margin-parallel motion is evidenced by the numerous southeast- and northeast-striking oblique-slip faults that accommodate trench-parallel shortening and westward block extrusion within the Olympic Peninsula [32–34].Alternatively, it has been proposed that uplift and oroclinal bending are generated by margin-normal deformation resulting from accretion along the wedge [10, 28]. It has been estimated that 80 to 100% of the sediment from the subducting Juan de Fuca Plate is accreted to the wedge front, and that this accretionary flux is in equilibrium with exhumation rates, with accreted material horizontally traversing most of the wedge before being exhumed [1, 28]. The presence of low-grade metamorphic rocks at high elevations in the Olympic Mountains shows that accretion is likely complemented by underplating of accreted sediment driving material flow upwards within the wedge [1, 7]; however, the contribution of this underplating component remains debated [10, 12]. For these scenarios, the greater elevation of the Olympic Peninsula compared to southern parts of the Cascadia wedge is explained by the concavity of the North American margin where the Juan de Fuca plate subducts beneath Washington; the curvature of this contact forces the underriding slab into an antiformal configuration, shallowing the slab dip beneath the Olympic Peninsula and driving margin-normal shortening and underplating [1, 35, 36]. High sedimentation rates at the trench in the Pacific Northwest could also have amplified accretion rates and underplating [7].Margin-normal and margin-parallel drivers on oroclinal bending are nonexclusive and both could have contributed to shaping the Olympic Peninsula, either at the same time or at different periods. For both types of drivers, the onset of deformation is commonly associated with the beginning of basin and range extension in the middle Miocene; this extension would have changed block motion along the North American margin and enhanced its curvature [1]. Early low-temperature thermochronology studies have suggested that exhumation in the core of the peninsula has been fairly constant at a rate of 0.75 to 1 mm/yr since 14 Ma and is at accretionary steady state [7, 23, 28]. More recent studies have highlighted a more complex exhumation story, with initially high (>2 mm/yr) exhumation rates followed by a sharp decrease to values<0.3mm/yr at ~5-7 Ma, coeval to a lowering in convergence rates [9]. Exhumation rates were later increased with the onset of Plio-Pleistocene glaciation [8, 9].While it is established that the core of the peninsula has been steadily exhumed since at least 14 Ma, the timing of the initiation of uplift remains poorly understood. It is unknown when the accretionary wedge started forming a submarine topographic high, which is critical to understand sediment transfer from the arc to the trench and the distribution of deformation along the subduction margin [37]. It is also unclear when the Olympic Peninsula became subaerially exposed, confining the Puget Lowland and allowing fluvial erosion to significantly increase exhumation rates.Brecciation and quartz veining in low-grade metamorphic rocks in the Olympic core dated at 17 Ma may be associated with early exhumation [38]. Using an assumption of a depth of accretion at 14.5 km, a constant exhumation rate of 0.75 km/Myr, and a geothermal gradient of 4.4°C/km, Brandon et al. [7] combined zircon and apatite fission-track ages to calculate that exhumation of the core of the Olympic Mountains should have begun at ca. 18 Ma. Uplift of the Olympic Peninsula resulted in the deformation and further partitioning of the Cascadia forearc basin into smaller subbasins, a process that had begun after collision with the Siletzia terrane [17]. This uplift could be reflected in the angular unconformity between 22 and ~13 Ma found in the Seattle Basin [39, 40], or the younger angular unconformity between 7.5 and 6 Ma in the Astoria Basin [41]. Bigelow [42] used sedimentary grain petrography to characterize the provenance of the upper Miocene Montesano Formation of Southwest Washington and Northwest Oregon to support the claim that the Olympic core and Crescent Formation had been uplifted and emerged by 10 Ma. There are no other, more precise constraints for the age of uplift and emergence of the Olympic Mountains, particularly in Northwest Washington near the highest peaks of the range.Before the accretion of Siletzia, Western Washington hosted the Swauk Basin, a large nonmarine sedimentary basin into which the several kilometer-thick Chuckanut Formation was deposited between 60 and 51 Ma (Figure 3; [17]). Well exposed along the coast near Bellingham, Washington, the Chuckanut Formation consists of 6 members: the Bellingham Bay, Slide, Governer’s Point, Padden, Warnick, and Maple Falls Members, in stratigraphic order [43]. The Chuckanut Formation consists of coarse sandstones and conglomerates, mudstones and siltstones, and abundant coal [43–45]. The sedimentary provenance of the Chuckanut Formation has been thoroughly studied and shows a composite history for the unit. The Bellingham Bay and Slide Members have been proposed to be sourced by sediment from the metamorphic core of Eastern Washington, transported by large, competent fluvial systems, which decreased in size through time [43]. The Padden Member contains abundant chert pebbles and is likely derived from the Western mélange belt (WMB)—a large belt of Jurassic to Cretaceous mélange that was accreted to North America in the Late Cretaceous and today is exposed in the foothills of the Cascades [46]. The Warnick and Maple Falls Members are more likely sourced from uplift at the northern portion of the Swauk Basin, and they comprise interfingered alluvial fan deposits [17, 44]. Strike-slip faulting in the Swauk Basin began at 51 Ma resulting from collision of Siletzia with North America [4, 17]. Subsequent faulting caused large-scale deformation of the Chuckanut Formation and partitioning of the Swauk Basin throughout the Eocene [43]. The faulting and deformation of the Chuckanut Formation have obscured the top of the section, and stratigraphic relationships with adjacent strata are difficult to discern.Middle Eocene to early Miocene forearc deposits that postdate deposition of the Chuckanut Formation and accretion of Siletzia have been given various local names; they are grouped under the Puget Group within the Puget Lowland [47], and under the Northern and Southern Peripheral sequences north and south of the Olympic Peninsula, respectively [48]. The Puget Group commonly comprises lignite-bearing fluviodeltaic and shallow marine deposits, interfingered with volcaniclastic sandstones [49]. In the Lake McMurray area near Mt. Vernon, Washington, 1500 m of these deposits have been given the informal name of the Bulson Creek assemblage (Figure 3; [45]). The northern and southern Peripheral Sequences are dominated by deeper marine facies [48].Further South in Puget Lowland, in the Seattle Basin, Oligocene to Miocene deposits are particularly thick (>7 km). Thickening in this region is explained by local flexural loading along the Seattle Fault Zone (SFZ; [50, 51]). The SFZ consists of multiple east-trending, north-verging thrust faults, which accommodate northward shortening inboard of the Olympic massif [52]; it merges further west with the northeast-striking oblique-slip fault system that accommodates trench-parallel shortening within the Olympic Peninsula [33, 34]. The timing of onset of SFZ activity and associated flexural loading is debated. Johnson et al. ([50], 1998) propose a late Eocene to Oligocene age for the initiation of the Seattle Fault; this interpretation is supported by a single apatite fission-track age of 32±5 Ma obtained from the Green Mountain area in the Seattle Fault hanging wall [53]. By contrast, ten Brink et al. [51] date the onset of the Seattle Fault to the early to middle Miocene based on seismic reflection data.The upper Oligocene-lower Miocene Blakeley Formation in the Seattle Basin is commonly distinguished from the Puget Group as it is dominated by deeper marine facies [54]. Deposited between 32 and 22 Ma, the Blakeley Formation is divided into two members: the lower Orchard Point and the upper Restoration Point Members [39], both representing submarine fan deposition [54]. The Orchard Point Member, which is well exposed along the Sinclair Inlet and along Alki Beach in Seattle, is a coarse clastic sandstone with local siltstones and fine sandstones, and one layer of tuffaceous clay-shale [39]. The Restoration Point Member is well exposed on the south of Bainbridge Island and is finer grained, with fine sandstones, abundant siltstones and shales, and rare pebbly sandstone layers [39]. The top of the Blakeley Formation is marked by an angular unconformity [55].Sitting atop the unconformity that caps the Blakeley Formation is the Blakely Harbor Formation, which is well exposed along the Southern beaches of Bainbridge Island [39, 55]. While this contact is not expressed at the surface, it has been well documented with subsurface imaging [51]. A zircon fission-track age at 13.3±1.3 Ma from a tephra layer near the base of the Blakely Harbor Formation and a middle Miocene pollen assemblage give a late middle Miocene age for the base of the unit [40]. The Blakely Harbor Formation is made of coarse fluvial and overbank deposits, composed of clastic, basalt-rich sandstones and conglomerates interbedded with claystone and siltstone, and is locally rich in organic matter [39]. The numerous basalt clasts found in the Blakely Harbor Formation have been attributed to erosion of the Crescent Formation as a sediment source [39].Further east within the Seattle Basin, a sequence of sedimentary rocks, contemporary with the Blakely Harbor Formation, crops out in ravines within Vasa Park [56]. Some have considered these strata part of the Blakely Harbor Formation [40]; however, we refer to this section informally as the Vasa Park assemblage. The Vasa Park assemblage contains two lithofacies: pebbly conglomerate containing andesitic and felsic volcanic cobbles, and tuffaceous sandy siltstone and silty sandstone rich in organic matter [56]. K-Ar ages of tuffs constrain deposition of the assemblage to between 14.7 and 9.3 Ma, though the extremely low radiogenic argon content of these samples (8%) leaves high uncertainty [57]. A more recently acquired 40Ar/39Ar age dates the middle of the assemblage to 11.40±0.61 Ma [58].Sediment samples were collected from several modern rivers in the Washington Cascades and Olympic Peninsula as well as sedimentary rock samples from turbidites and fluvial sandstones in the Puget Lowland and on the Olympic Peninsula. Sample locations, determined with a handheld GPS, are shown in Figure 1 and labeled in Table 1. We collected samples of 1 to 5 kg of medium to coarse sand from sand bars of the following modern rivers: the Skykomish, Puyallup, Skagit, and Snoqualmie rivers, which drain the Cascades into Puget Sound; the Hoh, Elwha, Bogachiel, and Queets rivers, which drain the Olympic Peninsula into the Pacific Ocean and the Strait Juan de Fuca; and the Columbia River, which drains Eastern Washington State into the Pacific Ocean.Sedimentary rock samples were collected from medium to coarse fluvial sandstones and turbidites, and samples were cleaned to avoid contamination from nearby quaternary alluvium. In the Olympic Peninsula, we collected two samples of the coastal OSC from Kalaloch Beach, mapped as lower to middle Miocene [25]. We collected one sandstone from the upper OSC at Shi Shi Beach, just South of a block of Eocene pillow basalt that correlates to the Crescent Formation, in turbidites attributed to the upper Eocene-Oligocene [26]. We collected a second sandstone of the upper OSC at Second Beach just south of La Push, Washington, from a local mélange attributed to diapirism and considered as being upper Eocene to lower Miocene in age [25].In the Puget Lowland, we collected two samples in the Bellingham Bay Member of the Chuckanut Formation. We collected two samples of the Bulson Creek assemblage from the upper lithofacies described by Marcus [45]; one sample of the Blakeley Formation from the Restoration Point Member on Bainbridge Island; two samples from the Orchard Point Member where it crops out on Alki Beach in Seattle [39, 55]; four samples from the Blakely Harbor Formation on Bainbridge Island near the 13.3±1.3 Ma tephra layer reported by Sherrod [40]; and three samples from the Vasa Park assemblage close to or at the locality described by Dillhof et al. [56], where a 40Ar/39Ar age of 11.4±0.6 Ma is reported [58].In total, we collected samples from 9 modern rivers and 18 rock outcrops. All samples but two were analyzed for grain petrography. For each modern river sample, a small fraction of collected sediment was mounted in synthetic resin. For each hard-rock sample, a small (⁠~1.5×3 cm⁠) fragment was cut and prepared as a thin section. Petrographic results were acquired on these thin sections using the Gazzi-Dickinson method to discern the relative abundance of quartz, feldspar, and lithic grains in each sample [59]. All petrographic data and GPS locations of the samples are available in Supplementary Table 1.All samples were analyzed for detrital zircon provenance; analytical set-up is presented by Licht et al. [60], and the complete procedure is detailed in Supplementary File 1. Zircons were extracted by traditional methods of heavy mineral separation, including concentration with a Holman-Wilfley™ gravity table, density separation with methylene iodide, and magnetic separation with a Frantz™ Magnetic Barrier Separator. U-Pb ages were generated using laser-ablation inductively coupled-plasma mass-spectrometry (LA-ICP-MS), using an iCAP-RQ Quadrupole ICP-MS coupled to an Analyte G2 excimer laser at the University of Washington, using a spot diameter of 25 microns and Plešovice zircons as calibration reference material [61]. Data reduction was conducted with Iolite (Version 3.5), using their U_Pb_Geochron4 Data Reduction Scheme to calculate U-Pb dates uncorrected for common lead [62]. In addition, date uncertainties for all samples were calculated using a modified version of the method of Matthew and Guest [63], implemented in MATLAB, that takes into account the impact of 207Pb beam intensity on date uncertainties [64]. The dates used for plotting and in the discussion are 206Pb/238U for dates<1400 Ma and 207Pb/206Pb for dates>1400 Ma⁠. Dates>300 Ma were screened for concordance using a discordance filter at >20% discordance (<80% concordance) and >5% reverse discordance (>105% concordance); we used the 206Pb/238U vs. 207Pb/235U ratio to calculate discordance for dates<1300 Ma⁠, and the 206Pb/238U vs. 207Pb/206Pb ratio for older dates. These parameters are detailed and justified in Supplementary File 1.The ten zircon validation reference materials used during these sessions yielded offset around TIMS ages<1% in most cases, <2% otherwise. In total, our new dataset includes 1478 zircon ages from modern rivers and 2713 zircon ages from sedimentary units; detailed data are available in Supplementary Table 2.The maximum depositional age for detrital samples is the weighted average of the youngest zircon dates when the youngest three or more dates overlap [65], calculated with TuffZirc [66]; if there is no overlap between youngest zircons, we used the youngest zircon date as maximum depositional age. The final age uncertainty around maximum depositional ages is the quadratic sum of the uncertainty of TuffZirc age calculation or youngest zircon date and of the systematic uncertainty (∼2.67% for the 238U/206Pb ratios). Age distributions are given in the form of kernel density estimate (KDE) diagrams and age histograms obtained with MATLAB.Figure 4 displays detrital zircon age distributions for each of the samples processed over the 0-300 Myr interval; complete age distributions over the 0-3000 Myr interval are displayed in Supplementary Figure 1. Few samples yield zircons older than Mesozoic in age; these older zircons are present in small proportions (⁠commonly<20%⁠) and display the same age populations: 1.05-1.2 Ga, 1.3-1.4 Ga, 1.5-1.8 Ga, 1.9-2.1 Ga, 2.3-2.4 Ga, and 2.5-2.8 Ga. Older populations are significant (>5%) in the sands of the Elwha and Columbia rivers and in samples of the OSC (sample #27), the Chuckanut Formation (samples #22 and 23), and the Blakely Harbor Formation (Samples #15-18). Maximum depositional ages are displayed in Table 1.Samples #1-4 from Cascade rivers are rich in quartz and volcanic lithic fragments, plotting in the “recycled orogen” domain on the QFL plot. Age distributions from modern Cascade rivers contain >97% zircons younger than 250 Ma, with >90% of the zircons younger than 110 Ma. Two main age populations can be distinguished, with their contribution varying between samples: 15-40 Ma and 85-100 Ma. Samples #3 (Puyallup River, draining Mount Rainier) and #4 (Skagit River, draining two active volcanoes, Mount Baker and Glacier Peak) yield recent (<5 Ma) zircons.Samples #5-8 from Olympic rivers are rich in quartz and sedimentary lithic fragments, plotting in the “recycled orogen” domain on the QFL plot. Age distributions from modern Olympic rivers contain >85% zircons younger than 250 Ma, but the contribution of older Cretaceous and Jurassic ages (110-250 Ma) is higher (~23% of zircons), with two prominent age populations at 140-170 Ma (all samples) and 180-220 Ma (Hoh and Elwha rivers). All Olympic rivers display the 85-100 Ma age peak found in modern Cascade rivers; samples #5 and #7, from the Elwha and Queets rivers, display a well-defined population centered at 50 Ma. The 15-40 Ma population found in Cascade river sands is barely expressed in Olympic rivers (<4% of zircons). The youngest grains for all Olympic rivers span from 20 to 24 Ma (Table 1).Sample #9 from the Columbia River is rich in quartz and volcanic lithic fragments, plotting in the “recycled orogen” domain on the QFL plot. Sample #9 yields ages spanning the last 180 Ma, with few (~5% of zircons) pre-Mesozoic ages, despite its wide drainage basin covering Precambrian strata near its sources. Two age populations are particularly well marked: 45-55 Ma and <5 Ma.Samples #26 and 27 of the Miocene coastal OSC display petrographic assemblages similar to modern Olympic rivers, dominated by quartz and lithic fragments, plotting in the “recycled orogen” field. The two samples also display age distributions similar to those of samples from modern Olympic rivers. They contain a major population at 85-100 Ma and subordinate populations at 45-55 Ma and 140-170 Ma. Samples #26 and #27 both display a significant population of early Miocene ages with maximum depositional ages at 16.5 and 16.7±0.5 Ma (2 s; Table 1).Samples #24 and 25 from the upper OSC (late Eocene to Oligocene/early Miocene) display the same petrographic results as coastal OSC samples, but significantly different age distributions. Both age distributions are dominated by one single 170-230 Ma peak, with only few younger and older grains. The characteristic 0-110 Ma age range of the modern Cascade rivers is notably absent, with most of the zircons significantly older than the depositional ages of the samples.Samples #22 and 23 from the Chuckanut Formation are distinct from other samples as they are particularly rich in quartz and metamorphic lithic fragments, with sample #22 plotting in the “continental block domain” on the QFL plot (Figure 5). Their age distributions are rich in pre-Mesozoic grains (30 to 40% of zircons); younger grains cover the 55-200 Ma range, with a significant Late Cretaceous-Paleocene population centered around 70 Ma (Figure 4).Samples #10 and 11 from the Bulson Creek assemblage are notably different from each other. Sample #10 is rich in quartz, metamorphic and sedimentary lithic clasts; it displays one population of younger grains clustered at 50 Ma, with most ages ranging between 115 and 280 Ma (>90% of zircons). Sample #11 consists entirely of volcaniclastic lithic grains and rare quartz grains; its age distribution shows a single prominent population between 28 and 35 Ma, with rare older accessory grains. Sample #11 yields a 29.0±0.8 Ma maximum depositional age (2 s; Table 1).Samples of the Blakeley Formation can be divided into two groups. Samples #19 and #21 are rich in quartz and volcanic lithic fragments, and plot in the “recycled orogen” domain; most zircons are in the 20-110 Ma age range with an important Cretaceous population, and a secondary population around 50 Ma for sample #19. Sample #20 is rich in volcanic lithic grains, with rare quartz grains; its age distribution show a characteristic zircon population between 20 and 35 Ma, with a 26.1±0.7 Ma maximum depositional age (2 s; Table 1).Samples #15-17 of the late middle Miocene Blakely Harbor Formation display similar age distributions to one another, and mirror age distributions of modern Olympic rivers; ages cover the full 20-230 Ma range with a major population around 85-100 Ma and a subordinate population at 45-55 Ma. Sample #18 spans a similar age range, though it has a primary age peak at ~30 Ma and contains only rare accessory grains between ~120 and 230 Ma. In contrast to the Olympic river sands, samples #15-17 are mostly made of basaltic lithic clasts, a feature recognized by Fulmer [39]. Maximum depositional ages are all similar to those of the Blakeley Formation samples (22-30 Ma; Table 1) and much older than the depositional age of the Blakely Harbor Formation (⁠13.3±1.3 Ma⁠; [40]).Samples #12-14 of the Vasa Park assemblage show distinctive characteristics in their petrography and age distributions. All three samples contain primarily quartz grains and lithic clasts with roughly the same amount of volcanic and sedimentary lithic fragments. Samples #12 and #14 show a single, late middle Miocene population and maximum depositional ages at 12.3±0.3 and 11.1±0.3 Ma (Table 1); this second age is statistically similar to the 11.4±0.6 Ma40Ar/39Ar age that is reported at the same locality [56, 58]. Sample #13 shows a similar maximum depositional age at 11.8±0.3 Ma⁠, but with an age range spanning 10-50 Ma (Table 1; Figure 4).The age distributions of samples #1-4 from modern Cascade river sands are a combination of young zircon populations derived from the Cascade Arc (⁠ages<45 Ma⁠) and minor, older populations derived from the Coast Mountains Batholith (clusters at 65-75 Ma, 85-105 Ma, 140-165 Ma, and 200-210 Ma; Figure 6). Below, we use these age distributions as a signature for zircons derived from the Cascades; sedimentary rocks that were sourced from the Cascades should contain similar zircon populations and are expected to incorporate young volcanic zircons from the Cascade Arc that are coeval or only slightly delayed in age with the deposition of the unit.Our study highlights two distinct provenances for the OSC. Samples #24 and 25 of the upper OSC (early Eocene to early Miocene in age) are dominated by a single Late Triassic to Early Jurassic population (170-220 Ma) that is absent in every other sample, including modern Cascade rivers (Figure 4). There are Late Triassic-Early Jurassic plutons in the crystalline core of the Cascades [67, 68], but they barely contribute to the zircon load of modern Cascade rivers, as highlighted here. Thermochronological data show that the crystalline core of the Cascades remained mostly unexhumed until the Miocene: rocks from the west flank of the Cascades yield apatite-He cooling ages between 12 and 6 Ma; rocks from the east flank show a broader range of apatite-He cooling ages between 60 and 18 Ma, though they also display far slower exhumation rates throughout the Cenozoic [69]. Mesozoic strata from the Methow Valley, east of the Cascades, contain abundant Late Jurassic and Early Cretaceous zircon populations, but zircons older than 200 Ma are either entirely absent, as seen in the Boston Bar and Twisp Formations [70], or they are extremely rare (>2%), as in the Winthrop, Harts Pass, and Midnight Peak Formations and the Jackass Mountain Group [71].Another potential source for the 170-220 Ma age peak found in samples #24 and 25 is the Bonanza Arc of the Wrangellia Terrane, which is exposed on Southern and Western Vancouver Island [72]. Rocks of the Bonanza Arc yield U-Pb ages ranging from 168 to 202 Ma; associated volcaniclastic strata indicate that magmatic activity had started earlier in the Triassic, potentially as early as 230 Ma [73]. A similar 170-220 Ma zircon population is found in the age distribution of samples from Cretaceous forearc strata in the Georgia Basin, east of Vancouver Island [74]. This population is particularly prominent in samples from the Comox Formation of the lower Nanaimo Group in the southern part of the Georgia Basin, and is interpreted by Huang et al. [74] as reflecting sediment sourced from the Bonanza Arc (Figure 7). Other age populations found in samples of the Comox Formation include age clusters at 344-364 Ma and 450-455 Ma, and ages younger than 170 Ma; these populations are interpreted as reflecting sediment drained from the Coast Mountains and the metamorphic and igneous basement of Vancouver Island [74]. However, these ages are absent from our samples of the upper OSC. Rocks of the Bonanza Arc crop out on extensively along the southern and western slope of Vancouver Island; this makes it possible for sediment from the Bonanza Arc to drain into the Pacific Ocean without incorporating zircons from other basement rocks, from forearc strata, or from the Coast Mountains [75]. We interpret the 170-220 Ma age population in our samples of the upper OSC as also reflecting sediment drained form the Bonanza Arc on Vancouver Island. Major exhumation of the Wrangellia Terrane is recorded between 50 and 40 Ma, which is contemporary with deposition of the upper OSC and shows that the Bonanza Arc is a viable source of sediment to the upper OSC [76]. We suggest that our samples originated as turbiditic events generated along the Vancouver Island slope during this period of exhumation.The Late Triassic-Early Jurassic population identified in upper OSC samples is barely expressed in samples of the coastal OSC and modern Olympic rivers. The composite age distribution of the (Miocene) samples from the coastal OSC contains the same zircon populations that are found in the composite age distribution of modern Cascade rivers, aside from the complete absence of middle Miocene and younger zircons in the coastal OSC (Figure 6). These features indicate that the coastal OSC was likely derived from Cascade material. The composite age distribution of modern Olympic rivers is also similar to the composite output of Cascade rivers (Figure 6), with some differences. Olympic rivers contain a relatively low proportion of 0-50 Ma grains (~6.5% of zircons) and display a 110-200 Ma population, which is underrepresented in modern Cascade rivers. The four modern Olympic rivers we sampled all drain the core of the Olympic Peninsula, which is dominated by the oldest (Eocene) OSC rocks; this drainage is consistent with an underrepresentation of 0-50 Ma grains and a higher representation of older populations. We suggest that despite these differences, the majority of the sedimentary rocks in the core of the Olympic Peninsula were sourced by drainage of the Cascades.The presence of zircons as young as 20 Ma in Olympic rivers draining the core of the peninsula indicates that the Olympics remained topographically low prior to the early Miocene. The maximum depositional ages of 16.5 and 16.7±0.5 Ma in samples #26 and #27 of the coastal OSC indicate that the OSC was fed by Cascade-derived sediment until at least that time.Samples #22 and 23 of the Chuckanut Formation display a significant population of pre-Mesozoic grains and, in addition to the well-marked 90 Ma population found in all forearc samples, a distinct 75 Ma population, which is not well expressed in the modern Cascade rivers. The age distributions of these samples are remarkably similar to those of Maastrichtian strata of the upper Nanaimo Group in the Georgia Basin, which also display two Cretaceous age peaks centered at 75 and 90 Ma, and older age populations centered at 1380 Ma and 1650-1800 Ma (Figure 7; [77, 78]). The age clusters at 90 Ma, 1380 Ma, and 1650-1800 Ma found in upper Nanaimo samples have been interpreted as derived from Idaho [79] and the younger ages from the Coast Mountains Batholith. Alternatively, Mathews et al. [63] showed that these ages are also found in the Mojave-Sonoran Region (MSR) of the Southwestern United States, advocating for a much lower paleolatitude for Vancouver Island at the time of deposition of the Nanaimo Group followed by a large coastwise translation of the Wrangellia Terrane during the Cretaceous [80]. The paleolatitude of the Wrangellia Terrane and the distinction between the two possible sediment source regions for the Nanaimo Group are both topics of ongoing debate. The age distributions of our samples suggest that either the Chuckanut Formation and the Maastrichtian strata of the Nanaimo Group share the same sediment source, or that the Chuckanut Formation was sourced from reworking of the Nanaimo Group. A direct provenance from the MSR is unlikely for the Chuckanut Formation as the proposed coastwise translation of accreted terranes would have been achieved several millions of years prior to deposition of the Chuckanut Formation in the early Eocene [80]. At present, our provenance data do not allow us to distinguish between a sediment source for the Chuckanut Formation either in northern Idaho or from reworking of the Nanaimo group. A potential reworking of the Nanaimo group at that time requires further validation as thermochronological data do not show major exhumation of the Nanaimo Group until 50 Ma [76].The source of the Bulson Creek assemblage is also problematic. The volcaniclastic nature and age distribution of sample #11 indicates a direct sourcing from the Cascade Arc. By contrast, sample #10 displays a dominant, broad age population ranging between 115 and 280 Ma, which is barely expressed in any other sample. This broad population overlaps with the ages of magmatism found in the Eastern Magmatic Belt of the Coast Mountains Batholith in British Columbia, though it is unclear how sediment derived from this region could have been transported far enough southwest to become incorporated into the Bulson Creek assemblage [81]. The Western mélange melt (WMB) crops out in close vicinity to our sampling site; age distributions of samples from the WMB are heterogeneous, with some samples displaying a well-marked 100-200 Ma age population while others do not [82–84]. It is possible that sample #10 is locally derived from the reworking of WMB material.Samples #19 and 21 of the Oligocene to early Miocene Blakeley Formation are volcaniclastic or quartz-rich, and the composite age distribution of the Blakeley Formation shows prominent age peaks at 30 Ma and 90 Ma, and a small population at 140-160 Ma (Figures 5 and 6). The same peaks are found in the same proportions in the composite age distribution of modern Cascade rivers (Figure 6). The provenance and petrography data of the Blakeley Formation are consistent with drainage of the Cascades as the sediment source.Both the Vasa Park assemblage and the Blakely Harbor Formation are fluvial, lithic sedimentary units that were deposited into the Cascadia Forearc in the late middle Miocene, with the Vasa Park assemblage deposited in the east of the forearc basin and the Blakely Harbor Formation deposited further west (Figures 1 and 3). Samples #12-14 of the Vasa Park assemblage are entirely volcaniclastic and likely have a source in the Cascade Arc. By contrast, samples #15-18 of the Blakely Harbor Formation show significant (7-22 million years) offset between their maximum depositional ages and their true depositional ages (Figure 8). This offset indicates that the Cascade arc did not supply sediment to the Blakely Harbor Formation. The maximum depositional ages of samples #15-18 (22-30 Ma; Table 1) are the same as those of samples #19-21 of the Blakeley Formation (22.8-30 Ma; Table 1). The composite age distribution of the Blakely Harbor Formation very closely resembles the composite distributions of the modern Olympic rivers and the Blakeley Formation, with the exception of a prominent age peak at 50 Ma that is only well expressed in the Blakely Harbor Formation and the Columbia River (Figure 6). This 50 Ma peak is consistent with the age of the Crescent Formation, and the Blakely Harbor Formation contains abundant basaltic lithic clasts, which have been attributed to the incorporation of felsic and basaltic material from the Crescent Formation [39, 54]. These provenance and petrographic data show that the Blakely Harbor Formation was sourced by sediment that was eroded from the Crescent Formation and from older sedimentary units including the Blakeley Formation. There are two potential source areas where the Crescent Formation, the Blakeley Formation, and associated units of the Puget Group are exposed in close vicinity: (1)The eastern flank of the Olympic Peninsula, approximately 30 km away from our sample location, where these units are exposed over thousands of square kilometers(2)The hanging wall of the SFZ in the Green Mountain area, approximately 20 km away from our sample location, where exposure is much more limited (<100 km2; [15, 53])The eastern flank of the Olympic Peninsula, approximately 30 km away from our sample location, where these units are exposed over thousands of square kilometersThe hanging wall of the SFZ in the Green Mountain area, approximately 20 km away from our sample location, where exposure is much more limited (<100 km2; [15, 53])Everywhere else in the Puget Lowland, the hanging wall of the SFZ is covered by Puget Group sediment and does not expose the Crescent Formation [50, 51, 85–87]Our petrographic and detrital zircon data are insufficient to distinguish between these two source areas as they display the same geological units. However, we suggest that a single contribution from the SFZ hanging wall is unlikely. Both the Blakely Harbor Formation and the Vasa Park assemblage are in the footwall of the SFZ [51, 86]; our samples of the Vasa Park assemblage do not show evidence for reworking of Puget Group material, which is immediately adjacent in the SFZ hanging wall.The only thermochronological data available for the SFZ is an apatite fission-track age from the Green Mountain area dated at 32±5 Ma [53]. This age dates the onset of exhumation of the SFZ hanging wall 10 to 25 Myr earlier than deposition of the Blakely Harbor Formation. Assuming a geothermal gradient of 20°C/km in the forearc [88, 89] and a functional closure temperature of 120°C for the apatite fission-track system [90], this fission-track age limits average exhumation to ~0.2 km/Myr since the Oligocene. Exhumation was to 4-10 times higher in the Olympic Peninsula during the late middle Miocene, with rates estimated between 0.75 and 2 km/Myr [7, 9]. The Olympic Peninsula is a more likely source as it was actively denuded during the period of deposition of the Blakely Harbor Formation. Though further thermochronological work on the SFZ is needed to confirm this interpretation, the plausible presence of material derived from the Olympic Peninsula in the Blakely Harbor Formation suggests that the peninsula had already been subaerially exposed and sufficiently uplifted to form a local topographic high and supply sediment to eastward draining rivers. The tuff dated at 13.3±1.3 Ma at the base of the unit [40] gives a minimum age for the emergence of the Olympic Peninsula (Figure 9).All the samples interpreted here as flowing directly from the Cascades display a short lag time between their depositional age and the age of their youngest zircon population, commonly <5 Myr (Figure 8). Samples interpreted as coming from Vancouver Island (upper OSC) or mostly made from the reworking of older material (Chuckanut Formation, Bulson Creek assemblage, and Blakely Harbor Formation) display much longer lag times (9 to 60 Myr), which corroborates their provenance from areas without coeval volcanism.Our data confirm that the upper OSC has a different origin from other structural units of the Olympic Peninsula, which has important implications for the build-up of the Cascadia accretionary wedge. Age distributions and sedimentary grain petrography of the Miocene coastal OSC and modern Olympic rivers indicate that they are derived from the Cascades; this is consistent with deposition and incorporation in a typical accretionary wedge, with Cascade material transported through the forearc and into the subduction trench [27]. By contrast, our samples of the Eocene upper OSC are derived from Vancouver Island and do not include Cascade-derived zircons; this suggests that parts of the upper OSC were deposited offshore at a significant distance from the Cascadia trench. These data support the interpretation of Brandon et al. [7] who proposed that the upper OSC was deposited as the western continuation of the Siletzia terrane, and was later imbricated and underthrust beneath the eastern strata of Siletzia following the initiation of the Cascadia subduction zone (Figure 9: middle Eocene to middle Miocene). Despite the Cretaceous and middle Eocene maximum depositional ages of our two samples (Table 1), the upper OSC has yielded biostratigraphic ages as young as the lower Miocene, and our two samples are mapped as post-middle Eocene [25, 26]. It is very likely that our samples represent older strata of the upper OSC that have been reprised into a mélange and are part of broken formations, integrating younger foraminifera, as seen in many places in the upper OSC [7, 15].There is quasicontinuous volcanism within the Cascade Arc since 45 Ma, despite periods of lower flux and varying composition [14]; it is expected that we would observe the presence of continually younger zircons within the OSC until uplift of the Olympic Peninsula precluded Cascade material from entering the accretionary wedge. As such, the presence of the youngest zircon population within the coastal OSC at 16.5±0.5 Ma provides the maximum age at which the Peninsula was not uplifted and had not yet formed a topographic barrier. There are two mechanisms that could bring zircons of postuplift age into the Olympic accretionary wedge. First, younger zircons brought to the sea by the Columbia River, or an older analogue, south of the peninsula could have been transported 150 km northward along the Olympic Coast by longshore drift to eventually arrive at the trench in front of the OSC, at the northernmost end of the modern deep-sea Astoria Fan. Today, Columbia River sediment is transported up to 100 km northwards into the Quinault Canyon along the southern part of the Olympic Coast [91]; this has also been observed for Mount Saint Helens ash material [92]. However, most of the modern sediment reaching the Quinault Canyon is very fine grained (silty clay; [93]), well below the grain size of the zircons we analyzed (25-micron minimum laser beam diameter). An alternative way that postuplift zircons could have been transported into the Cascadia trench and subsequently into the accretionary wedge is conveyance via a proto-Strait of Juan de Fuca around the north of the peninsula followed by a 100 km southward transit either by longshore drift or, less likely, deeper trench-parallel turbidity currents. Today, there is almost no southward longshore drift along the Washington coast due to the dominance of southwesterly winds in the winter [92]. Additionally, the age distribution of the coastal OSC is not consistent with either sediment supply from the Columbia River or from Vancouver Island, so it is unlikely that these mechanisms supplied fresh zircons to the OSC after uplift of the Olympic Peninsula cut off drainage from the Cascade Arc (Figure 9).The late middle Miocene Blakely Harbor Formation in the Washington forearc displays age distributions and grain petrography that are consistent with a direct supply from the Olympic Peninsula. Our data cannot exclude that this formation was sourced by material from the hanging wall of the Seattle Fault, as proposed by ten Brink et al. [51], but we suggest that this source is less likely due to the low exhumation rates of the SFZ at that time and the absence of hanging wall reworking in the Vasa Park assemblage. While thrust loading along the SFZ likely contributed to the subsidence of the Seattle Basin and the deposition of the Blakely Harbor Formation in the late middle Miocene [50, 51], a contribution of the SFZ hanging wall to the sedimentary supply remains to be shown. We show that the Olympic Peninsula very likely contributed sediment to the Blakely Harbor Formation, making the age of the base of the Blakely Harbor Formation a maximum constraint on the emergence of the peninsula and formation of a topographic high.Our sedimentary provenance data bracket the timing of the emergence of the Olympic Peninsula to a narrow window in the late middle Miocene, after 16.5±0.5 Ma and likely before 13.3±1.3 Ma (2 s), though this latter age remains to be confirmed by a more thorough study of the exhumation of the SFZ. Brandon et al. [7] estimated that sediment accreted to the base of the accretionary wedge would take ~4.4 Myr to rise from the depth of accretion to the α-damaged zircon closure depth of 10 km, assuming a constant exhumation rate of 0.75 km/Myr as observed for the last 14 Ma, and they show that this 10 km depth was reached ca. 13.7 Ma. These estimates date the onset of exhumation to ca. 18.1 Ma, at least two million years before our proposed window for the emergence of the peninsula. Michel et al. [9] proposed a faster rate (2 km/Myr) for the initial phase of exhumation, decreasing to bellow modern rates at 5-7 Ma. Using this faster initial exhumation rate, and the same model as Brandon et al. [7], we estimate exhumation to begin at ca. 15.3 Ma, which falls within our proposed time window for the emergence of the Olympic Peninsula. These estimates are based on a simple model for the trajectory and temperature history of material accreted to the wedge and should be assessed with caution. In the framework of this simple model, and assuming that there was little preemergence erosion and exhumation in the accretionary wedge, our timing for the emergence of the peninsula is in agreement with models arguing for an early phase of high exhumation [9] and a composite deformation history for the accretionary wedge.Our work constrains the initial subaerial exposure of the Olympic Peninsula and the formation of a topographic barrier to the late middle Miocene, but we do not exclude the possibility of earlier deformation and uplift of the accretionary wedge. Deformation predating the emergence of the peninsula may have occurred in the Oligocene to early Miocene, and this deformation may be recorded in the strata of the Blakeley Formation. The Blakeley Formation is dominated by submarine fan deposits, some of which have yielded foraminifera found at bathyal to abyssal depths (deeper than 1 km; [39]). The presence of such depths in a forearc basin requires a mechanism to create high subsidence. Johnson et al. [50] linked this subsidence to an early phase of thrusting along the SFZ, the timing of which is supported by apatite fission-track data [53]. More thermochronological work along the SFZ is needed to confirm this early phase of deformation; if confirmed, this Oligocene episode of thrusting on the SFZ provides evidence for margin-parallel shortening and initiation of the Olympic orocline that predates emergence of the Olympic Peninsula by at least ten million years.Our combined detrital zircon provenance and grain petrography data from the Olympic Peninsula and the Puget Lowland allow us to reconstruct the Cenozoic history of the Cascadia subduction zone. We first show a distinct sedimentary provenance of the upper OSC that differs from other structural units of the Olympic Peninsula. Upper OSC samples comprise only material from Vancouver Island and show no mixing with young (post-40 Ma) zircons. These results indicate that the upper OSC was deposited as part of the Siletzia terrane before its accretion to the Cascadia margin, and was later imbricated and underthrust beneath the Crescent Formation. Other units of the OSC represent accreted Cascadia trench sediment and show input from the Cascades into the accretionary wedge until at least 16.5±0.5 Ma⁠, providing an older age limit for the emergence of the Olympic Peninsula. The fluvial deposits of the late middle Miocene Blakely Harbor Formation record the first input of recycled Crescent Formation and OSC/forearc material into the Seattle Basin. Though we cannot exclude some contribution from the hanging wall of the Seattle Fault Zone, we suggest that the Blakely Harbor Formation provides a minimum age for input of eroded material from the Olympic Peninsula into the Puget Lowland; this gives a younger age limit of 13.3±1.3 Ma for the emergence of the peninsula. We finally propose that the initial onset of deformation and oroclinal bending in the Olympic Peninsula predates emergence by at least 10 Myr, marked by flexural subsidence along the Seattle Fault Zone and the deposition of the Blakeley Formation in the Oligocene.The authors declare that there is no conflict of interest regarding the publication of this article.This research was primarily funded by the University of Washington. Samples in the Olympic National Park were collected under the permit OLYM-2018-SCI-0036. We thank Susie Winkowski from Vasa Park Resort to have allowed us access to their property. We also thank M. Mueller, Tamas Ugrai, Ralph Haugerud, Hope Sisley, Eric Cheney, Alexandre Delga, Matthew Dubeau, the Olympic National Park Service, and Darrel Cowan for prolific discussions and assistance in the field and in the lab. We also thank Ralph Haugerud, William Matthews, Sarah Roeske, and Stephen Johnston for their insightful and constructive reviews of this manuscript.Supplementary File 1: complete analytical procedure for detrital zircon provenance analysis. Supplementary Table 1: grain-counting data. Supplementary Table 2: U-Pb data. Supplementary Figure 1: histograms and kernel density estimate diagrams for detrital zircon age distributions of all samples. River samples are grouped by drainage region, and rock samples are grouped by formation. All ages are displayed in 20 Myr bins.

中文翻译：

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沉积源显示的中半岛中新世晚期

奥林匹克半岛是卡斯卡迪亚增生楔的隆起部分，是华盛顿州西海岸200公里规模的口弯的核心。沿着卡斯卡迪亚俯冲带增加了西雷兹亚火成岩省之后，在四千五百万年前开始形成增生楔。低温热年代学研究表明，在过去的1400万年中，一直在不断挖掘半岛的核心。早期的眼眶弯曲，隆起和出现的证据仍然很少。在这里，我们探索卡斯卡迪亚前臂和增生楔的新生代排水史，以重建奥林匹克半岛的变形历史。我们使用了排泄小瀑布的现代河流中的碎屑锆石物源和谷物岩石学数据，卡斯卡迪亚前缘和增生楔形物，以及同一地区从始新世到中新世中期晚期的沉积单元。我们首先显示出增生楔形中各沉积单元之间的沉积物产地存在明显差异，较旧的单元反映了混杂岩和成辫状地层（始于Siletzia的一部分），而较年轻的单元则反映了源自喀斯喀特山脉并增生至楔形物的沟槽填充物。我们证明增生楔块是直接从喀斯喀特弧中馈送的，直到至少16.5±0.5Ma⁠，为奥林匹克半岛的出现提供了最大年龄。卡斯卡迪亚前陆盆地中的河流沉积物的年代为13.3±1.3 Ma，显示出锆石年龄谱，沉积颗粒岩相特征是再生增生楔形材料的典型特征。尽管这些存款也可能反映了本地投入，中新世中部的出土率表明，奥林匹克半岛是活跃的沉积物来源。我们的研究结果表明，中新世中期晚期，奥林匹克半岛出现的时间很短。我们认为，在渐新世上部，增生楔形变形和斜向弯曲的开始至少要早于这一点，至少要有一千万年，并且其特征是在西雅图盆地地层记录了弯曲沉降和高沉积速率。我们的结果支持了卡斯卡迪亚增生楔形发展的综合历史，而不是预测逐渐稳定建立的模型。西华盛顿州的奥林匹克半岛是卡斯卡迪亚增生楔形在地下暴露的部分[​​1、2]，它是在北美西海岸的Siletzia火成岩省始新世增生后形成的[3，4]。卡斯卡迪亚增生楔的大量变形和隆升导致了一个大的以奥林山山脉为核心的大斜面弯曲[5]。这些山脉的独特之处在于，它们比北美太平洋海岸增生楔形形成的所有其他沿海山脉更大，更高。低温热年代学研究表明，在最近的1400万年中，一直在不断挖掘半岛的核心地带，尽管人们仍在争论着最近的挖掘速度和速度[1，6-10]。有人提出岩石隆起是由与边缘平行缩短[11]，额积[7、10]有关的地壳增厚驱动的，或在沟槽处进行底镀[12]。沿海岸的高降水率增强了发掘活动，从而促进了隆升的形状和速率[13]。增生楔形地表隆升的实际时机几乎没有记载。目前尚不清楚增生楔何时开始形成海底高地，从而在卡斯卡迪亚海沟和前臂之间形成地形障碍，以及半岛何时最终出现。记录这些事件的时间顺序对于重建进入海沟的沉积通量，了解奥林匹克山达到快速的采掘稳定状态并确定岩石隆升的主要驱动力[12]至关重要。在这里，我们使用碎屑锆石物源和砂岩岩相学，将年龄限制放在奥林匹克山的隆升和空中暴露方面。我们使用U-Pb锆石年龄和来自奥林匹克半岛和北部小瀑布的现代河流的岩石学数据来确定现代排水系统的起源特征。然后，我们对卡斯卡迪亚前缘和增生楔的新生代沉积岩使用相同的方法来重建区域排水历史并跟踪奥林匹克山的地形高处。卡斯卡迪亚增生楔，卡斯卡迪亚前缘和喀斯喀特山脉平行到卡斯卡迪亚俯冲带，那里的戈尔达和胡安·德富卡板块在北美大陆板块下方俯冲。奥林匹克半岛是卡斯卡迪亚增生楔的一部分，坐落在华盛顿州西海岸，将普吉低地与太平洋隔开，山脉高。普吉低地是华盛顿卡斯卡迪亚前臂的一部分，西部是奥林匹克半岛的边界，而东部则是喀斯喀特山脉的边界，从这两个地带排出沉积物。在加拿大，前臂形成了乔治亚盆地，西部是温哥华岛，东部是沿海山脉，是喀斯喀特山脉的北向（图1）。本手稿中的“瀑布”一词特别提到了从中央华盛顿延伸到不列颠哥伦比亚省南部的北部瀑布。喀斯喀特山脉包括一个发掘出的变质岩心，即中新世至始新世的岩体-沿海山脉基岩-以及自始新世中期以来一直活跃的安第斯式火山弧-喀斯喀特山脉[14]。塔博尔和卡迪[2]的开创性研究提供了对奥林匹克半岛的详细结构和地质描述，并指导了其他所有研究的进行。半岛由两个主要地形组成：外围岩石包括新月形地层的早期始新世玄武岩，由几乎未变形的始新世至中新世覆盖，大部分是海洋沉积岩，以及被广泛变形的海洋沉积岩心，称为奥林匹克俯冲复合体（OSC） ）（Brandon and Calderwood [1]）。新月形地层沿飓风岭断裂与OSC断层接触，环绕奥林匹克半岛东部，形成月牙形（图1和2； [15]）。新月形地层主要由厚厚的基底枕和柱状玄武岩覆盖，上面长有长英质火山碎屑砂岩，褐煤和泥岩[16]。K-Ar角闪闪测年，40Ar / 39Ar整个岩龄和长英质凝灰岩的U-Pb测年将新月形层的喷发限制在53.2-48.4 Ma之间[4，17]。由于脊俯冲的缘故，有人提出板状窗口火山作用是新月玄武岩的来源[18，19]。另一种假设是，新月形地层与长期存在的黄石热点爆发，导致了一个火成岩大省的爆发[4，20，21]。后一种模型将来自俄勒冈州，华盛顿州和不列颠哥伦比亚省的当代玄武岩（包括新月形地层）组合到Siletzia地层中。Siletzia地带本来是一个火成的大火成岩省，在Farallon板块上形成了一个海底高原，然后在始新世早期被吸纳到北美[4，17]。无论哪种新月形地层的模型是最准确的，Siletzia地层的分组和增生的时间都已达成共识。在本手稿中，“ Siletzia”是指整个增生的地貌，“新月形”是指在华盛顿西部种植的Siletzia地貌的岩石。最早的海洋沉积物是在Cascadia增生楔中增生的。在始新世的卡斯卡迪亚俯冲带开始后，在始新世的西勒齐亚地层以下，这导致沿着飓风岭断裂带的明显滑动（数十公里； [7]）。卡斯卡迪亚俯冲带的起始时间大约为。根据级联弧中最古老的Siletzia吸积岩浆岩的年龄，得出42-45 Ma [14，22]。在月牙形地层以下已被推覆的沉积岩构成了今天奥林匹克半岛的核心，并已对其进行了彻底测绘[2，15]。这些岩石最初分为五个非正式的石器组合：可可，Elwha，西方奥林匹克运动会，大山谷和Needles-Gray Wolf组合（图2； [2]）。尽管这些岩石的测绘精度很高，但变形和位移的极大程度使其难以辨别这五个组合之间的地层关系。通常，岩石从东到西变得更年轻[2，15，23]。Brandon和Vance [23]将卡斯卡迪亚增生楔的岩石归为奥林匹克俯冲带（OSC），并使用热年代学和结构数据将五个岩性组合重组为三个结构单元：沿海OSC，等同于Hoh组合；较低的OSC，将西方奥林匹克运动会和大峡谷运动组合在一起；和上层OSC，将Needle-Gray Wolf和Elwha组合在一起（图2； [23]）。这些结构单元之间的地层学和年代学关系尚不清楚。OSC的生物地层年龄范围从始新世到中新世，通常最老的年龄出现在OSC的上部，而沿海OSC的年龄最小[24]。OSC的上部是OSC的结构最高单元，可以解释为成为最老的[23]。上部OSC局部含有枕形玄武岩，其成分与新月形地层相似，并与化石质石灰岩互层，产生最新的古新世至中新世化石年龄[15，24]。该单元的碎屑锆石产生了裂变径迹的最大沉积年龄，范围从始新世到渐新世（48-32 Ma； [23]）。某些区域归因于上部OSC产生了上始新世至下部中新世微化石[25，26]。下部OSC与上部OSC的区别在于没有枕形玄武岩，仅包括海相碎屑沉积岩，包括浊积岩层序和高度变形的泥岩。丰富的混杂语。它在结构上是上层OSC的基础。该单元的碎屑锆石产生了裂变径迹的最大沉积年龄，范围从27到19 Ma [23，27]。沿海OSC是OSC的结构最低单元，在岩性上类似于下部OSC [23]。通过在较低的OSC中观察到较高的变质程度，可以区分这两个单元[2，23]。沿海OSC浊度的碎屑锆石产生的裂变径迹最大沉积年龄为26到11 Ma。混杂岩块的最大沉积年龄为39到15 Ma [27]。然而，最年轻的裂变径迹年龄显示出很高的不确定性（⁠2 s±3至4 Ma； [27]）。OSC的三个单元被赋予了不同的沉积物来源和增生历史，尽管对于量化这些差异[23]。已有解释认为，下部OSC代表从级联流排入俯冲沟的沉积物，而沿海OSC则代表大陆坡地物质的大量浪费，这两个单元构成了真正的增生楔[23，27]。布兰登和万斯[23]提出，上OSC的始新世沉积起源于Siletzia地层的最西面碎屑岩层。在卡斯卡迪亚俯冲带开始后，这些地层在新月形地层下被盘根和下伏。布兰登和万斯[23]还提出，只有在上层OSC最年轻的地层（〜33 Ma）沉积之后才发生这种胶结作用，这比拟议的沿着飓风山脊断裂的滑移事件晚了几百万年。的俯冲作用（〜45 Ma； [7，14]）。从半岛中心开始的碎屑磷灰石和锆石裂变径迹和（U-Th）/ He年龄显示出不断的尸体化，因为至少14 Ma [7–9，23 ，28]。OSC的发掘产生了宽的眼眶弯曲，形成了新月形的弧形形状[5]。根据区域尺度的板块运动和GPS数据，有人提出这种眼眶弯曲和OSC异常抬高是由边缘平行运动引起的，这导致隆起，而奥林匹克半岛陷入了北向运动之间。俄勒冈海岸山脉和相对稳定的温哥华岛[11，29–31]。这种平行运动是由东南向和东北向倾斜的滑坡断层所证实的，这些断层可以适应奥林匹克半岛内平行于沟槽平行缩短和向西挤压的断裂[32-34]。或者，有人提出隆起和口斜沿楔形[10，28]积聚产生的边缘法向变形会产生弯曲。据估计，来自俯冲胡安德富卡板块的沉积物有80％至100％积聚在楔形前缘，并且该增生通量与发掘速率处于平衡状态，在挖出之前，增粘材料水平横穿了大部分楔形物[1，28]。奥林匹克山高海拔地区存在低品位变质岩，这表明增生很可能是由沉积的底泥带动底盘所驱动的物质在楔块内向上流动的补充[1，7]。然而，该底层组件的贡献仍存在争议[10，12]。在这些情况下，与卡斯卡迪亚楔形山脉南部相比，奥林匹克半岛的海拔更高，可以用胡安·德·富卡板块俯冲到华盛顿以下的北美边缘凹陷来解释。这种接触的曲率迫使下面的平板变成反形式结构，使奥林匹克半岛下方的板块倾角变浅，并驱使边缘法线正常缩短和压下[1，35，36]。西北太平洋海沟的高沉积速率也可能会增加积聚速率和下沉[7]。口缘弯曲的边缘法线和边缘平行驱动器不是唯一的，并且两者都可能对奥林匹克半岛的塑造有所贡献。时间或不同时期。对于这两种类型的驱动器，变形的开始通常与中新世中期盆地的开始和范围扩展有关。该扩展将改变沿北美边缘的块运动并增强其曲率[1]。早期的低温热年代学研究表明，半岛核心的尸体发掘一直相当稳定，比率为0。自14 Ma以来为75到1 mm / yr / yr，处于稳定状态[7，23，28]。最近的研究强调了更复杂的挖掘活动，最初的挖掘活动速率较高（> 2毫米/年），然后在〜5-7 Ma时急剧降低至<0.3毫米/年，同时收敛速率降低[ 9]。后来随着上新世更新世冰期的开始，尸体的发掘率增加了[8，9]。虽然已经确定了半岛的核心自至少14 Ma以来就被稳定地发掘了，但隆起的开始时间仍然知之甚少。增生楔形物何时开始形成海底地形高点仍是未知的，这对于了解沉积物从弧到沟的转移以及沿俯冲带的变形分布是至关重要的[37]。还不清楚奥林匹克半岛何时暴露于地下，限制了普吉低地并允许河流冲刷显着增加了尸体的发掘率。奥林匹克岩心中低品位变质岩中17Ma的破裂和石英脉可能与早期尸体化有关。 [38]。布兰登（Brandon）等人假设在14.5 km处有积聚深度，恒定的掘尸速率为0.75 km / Myr，地热梯度为4.4°C / km。[7]结合锆石和磷灰石的裂变径迹年龄来计算，奥林匹克山核心的发掘工作应在大约公元前开始。18 Ma。奥林匹克半岛的隆起导致卡斯卡迪亚前臂盆地变形并进一步划分为更小的子盆地，这一过程是在与Siletzia地形碰撞后开始的[17]。这种隆起可能反映在西雅图盆地[39，40]中发现的22至13 Ma之间的角度不整合面中，或者阿斯托里亚盆地[7.5]中的7.5和6 Ma之间的年轻角度不整合面中。Bigelow [42]使用沉积岩相学来描述华盛顿西南部和俄勒冈西北部的中新世蒙塔萨诺地层的物源，以支持有关奥林匹克核心和新月形地层抬升并出现10 Ma的说法。对于隆起和奥林匹克山脉的出现，没有其他更精确的限制条件，尤其是在该范围最高峰附近的西北华盛顿地区。在锡列兹亚（Siletzia）增生之前，西华盛顿州曾是Swauk盆地的东道主，一个大型的非海洋沉积盆地，在60至51 Ma之间沉积了几公里厚的Chuckanut组（图3； [17]）。Chuckanut组在华盛顿贝灵汉附近的海岸沿线暴露良好，按地层顺序包括6个成员：贝灵汉湾，滑坡，总督府，帕登，沃尼克和枫树瀑布成员[43]。Chuckanut组由粗砂岩和砾岩，泥岩和粉砂岩以及丰富的煤组成[43-45]。Chuckanut组的沉积物源已被彻底研究，并显示了该单元的综合历史。贝林汉姆湾和滑动成员被认为是来自华盛顿东部变质岩心的沉积物，这些沉积物是由强大的，有能力的河流系统运移的，并随着时间的流逝而减小[43]。帕登（Padden）成员含有丰富的石卵石，很可能来自西部混杂带（WMB），这是侏罗纪至白垩纪混杂带的大带，早在白垩纪就已汇聚到北美，如今暴露在喀斯喀特山脉的山麓地区[46]。 ]。Warnick和Maple Falls的成员更有可能来自Swauk盆地北部的隆升，并且它们由带手指的冲积扇沉积物组成[17，44]。Swauk盆地的走滑断层始于Siletzia与北美的碰撞，始于51 Ma [4，17]。随后的断层导致了始新世的Chuckanut组大规模变形和整个始新世的Swauk盆地分区[43]。Chuckanut组的断层和变形遮盖了该段的顶部，很难识别与相邻地层的关系。在始新世的Chuckanut组沉积和Siletzia的增生之后，中始新世至中新世前陆前沉积被赋予了各种当地名称。它们分别归入Puget低地内的Puget组[47]以及奥林匹克半岛北部和南部的北部和南部外围序列[48]。普吉特集团通常包括含褐煤的氟三角洲和浅海沉积物，与火山碎屑岩夹杂[49]。在山附近的麦克默里湖地区。华盛顿州弗农，其中1500 m的矿床已被非正式命名为Bulson Creek组合体（图3； [45]）。北部和南部外围层序由较深的海相主导[48]。在普吉特低地的更南部，在西雅图盆地，渐新世至中新世的沉积特别厚（> 7 km）。该区域的增厚是由西雅图断层带（SFZ； [50，51]）上的局部挠性荷载引起的。SFZ由多个向东，向北延伸的逆冲断层组成，可以适应奥林匹克断层向北缩短的现象[52]。它进一步向西与东北向的斜滑断层系统合并，该系统适应了奥林匹克半岛内部平行于沟槽的缩短[33，34]。SFZ活动的发作时机和相关的弯曲负荷受到争议。约翰逊等。（[50]，1998）提出了晚始新世至渐新世的时代，以引发西雅图断层；从西雅图断层悬墙的格林山区地区获得的单个磷灰石裂变径迹年龄为32±5 Ma来支持这种解释[53]。相比之下，十个Brink等人。[51]根据地震反射数据，将西雅图断层的发生日期定为中新世早期至中期。西雅图盆地的上渐新世-下中新世布雷克利组通常与普吉特群区分开，因为它以较深的海相为主[ 54]。布莱克利组沉积在32至22 Ma之间，分为两个成员：果园下层和恢复点上层成员[39]，都代表了海底扇沉积[54]。沿Sinclair入口和西雅图Alki海滩暴露的Orchard Point成员是一种粗碎屑砂岩，其中含有局部粉砂岩和细砂岩，以及一层凝灰质泥页岩[39]。恢复点成员在班布里奇岛的南部非常裸露，且颗粒更细，上有细砂岩，丰富的粉砂岩和页岩，以及稀有的卵石砂岩层[39]。布莱克利组的顶部有一个角度不整合[55]。布莱克利港组位于布雷克利组的不整合顶部，在班布里奇岛的南部海滩上暴露得很好[39，55]。虽然这种接触没有在表面上表达出来，但已被地下成像[51]很好地证明了。布雷克利港组底部附近的特非拉层的锆石裂变径迹年龄为13.3±1.3 Ma，中新世花粉组合为该单元底部的中新世中期[40]。布莱克利港组是由较粗的河流和岸上沉积物组成的，由碎屑，富含玄武岩的砂岩和夹有粘土岩和粉砂岩的砾岩组成，并且在当地富含有机质[39]。布莱克利港组中发现的大量玄武岩碎屑归因于新月形层作为沉积源的侵蚀[39]。在西雅图盆地的更东部，一系列沉积岩，与布雷克利港组形成现代，在瓦萨公园内的沟壑[56]。一些人认为这些地层是布雷克利港组的一部分[40]。但是，我们将此部分非正式地称为“瓦萨公园”组合。瓦萨公园组合包含两个岩相：卵石砾岩包含安第斯山脉和长笛山脉的火山卵，以及凝灰质的砂质粉砂岩和富含有机质的粉质砂岩[56]。凝灰岩的K-Ar年龄将组合物的沉积限制在14.7至9.3 Ma之间，尽管这些样品的极低的放射性氩含量（8％）留下了很高的不确定性[57]。最近获得的40Ar / 39Ar年龄可追溯到组合体的中部，达到11.40±0.61 Ma [58]。沉积物样品是从华盛顿喀斯喀特山脉和奥林匹克半岛的几条现代河流中采集的，以及从浊积岩和河流相砂岩中的沉积岩样品中采集的。普吉低地和奥林匹克半岛上。用手持式GPS确定的采样位置如图1所示，并在表1中进行了标记。我们从以下现代河流的沙洲（Skykomish，Puyallup，Skagit和斯诺夸尔米（Snoqualmie）河流将小瀑布排入普吉特海湾（Puget Sound）；呼和浩特河，博加奇厄尔河和奎特河，将奥林匹克半岛排入太平洋和胡安德富卡海峡；华盛顿河和将华盛顿东部地区排入太平洋的哥伦比亚河。从中等到粗大的河流砂岩和浊石中收集沉积岩样品，并对样品进行清洁以避免附近的第四纪冲积层造成污染。在奥林匹克半岛，我们从Kalaloch海滩收集了两个沿海OSC样本，这些样本被绘制为中新世中低层[25]。我们从石炭海滩上OSC上部收集了一个砂岩，该岩石位于与新月形成有关的始新世枕形玄武岩块的南部，处于始新世-渐新世上层的浊积岩中[26]。我们在华盛顿州拉普什市以南的第二海滩采集了OSC上层的第二块砂岩，[25]。这是在普吉低地，我们从Chuckanut组的Bellingham湾成员中采集了两个样本。我们从Marcus描述的上部岩相中收集了两个Bulson Creek组合的样本[45]；来自班布里奇岛恢复点成员的布莱克利组的一个样本；来自果园点成员的两个样本，在西雅图的Alki海滩上种植[39，55]；Sherrod [40]报道了来自班布里奇岛布雷克利港组的4个样品，靠近13.3±1.3 Ma tephra层。以及在Dillhof等人描述的位置附近或附近的瓦萨公园集合中的三个样本。[56]，据报道40Ar / 39Ar年龄为11.4±0.6 Ma [58]。我们从9条现代河流和18条岩石露头收集了样本。除两个样品外，所有样品均进行了颗粒岩石学分析。对于每个现代河流样本，将一小部分收集的沉积物安装在合成树脂中。对于每个硬岩样品，将其切成小块（⁠〜1.5×3cm⁠），并切成薄片。使用Gazzi-Dickinson方法在这些薄片上获得了岩相学结果，以辨别每个样品中石英，长石和石屑颗粒的相对丰度[59]。补充表1中提供了样品的所有岩石学数据和GPS位置。分析了所有样品的碎屑锆石产地。分析设置由Licht等提出。[60]，完整程序在补充文件1中有详细说明。锆石是通过传统的重矿物分离方法提取的，包括使用Holman-Wilfley™重力表进行浓缩，使用二碘甲烷进行密度分离以及使用Frantz™电磁屏障分离器进行磁分离。U-Pb年龄是通过激光烧蚀电感耦合等离子体质谱（LA-ICP-MS），iCAP-RQ四极杆ICP-MS与华盛顿大学的Analyte G2准分子激光耦合并使用斑点产生的直径25微米，并以Plešovice锆石作为校准参考材料[61]。使用Iolite（版本3.5）进行数据归约，使用他们的U_Pb_Geochron4数据归约方案来计算未针对普通铅校正的U-Pb日期[62]。此外，使用MATLAB和Guest [63]方法的修改版，可以计算出所有样品的日期不确定性。考虑到207Pb束强度对日期不确定性的影响[64]。用于绘图和讨论的日期对于<1400 Ma的日期是206Pb / 238U，对于> 1400 Ma的日期是207Pb / 206Pb。使用不一致性过滤器，以> 20％不一致（<80％一致性）和> 5％反向不一致（> 105％一致性）的方式筛选> 300 Ma的日期是否具有一致性；我们使用206Pb / 238U与207Pb / 235U的比率来计算小于1300Ma⁠的日期的不一致，而使用206Pb / 238U与207Pb / 206Pb的比率来计算较旧的日期。这些参数在补充文件1中进行了详细说明和论证。在这些会议期间使用的十种锆石验证参考材料在大多数情况下在TIMS年龄<1％左右产生了偏移，否则<2％。总共，我们的新数据集包括来自现代河流的1478​​个锆石年龄和来自沉积单位的2713个锆石年龄。补充表2中提供了详细数据。碎屑样品的最大沉积年龄是三个或三个以上最年轻的日期重叠时最年轻的锆石日期的加权平均值[65]，用TuffZirc [66]计算；如果最小的锆石之间没有重叠，我们将最小的锆石日期作为最大沉积年龄。在最大沉积年龄附近的最终年龄不确定性是TuffZirc年龄计算或最小锆石日期的不确定性与系统不确定性（238U / 206Pb比率约为2.67％）的二次加总。年龄分布以内核密度估计（KDE）图和使用MATLAB获得的年龄直方图的形式给出。图4显示了在0-300 Myr间隔内处理的每个样品的碎屑锆石年龄分布。补充图1显示了0-3000 Myr间隔内的完整年龄分布。很少有样品能产生比中生代年龄大的锆石。这些年龄较大的锆石所占比例很小（通常<20％⁠），并且显示相同的年龄群体：1.05-1.2 Ga，1.3-1.4 Ga，1.5-1.8 Ga，1.9-2.1 Ga，2.3-2.4 Ga和2.5 -2.8 Ga。在Elwha和Columbia河流的沙地以及OSC（27号样品），Chuckanut组（22号样品和23号样品）和Blakely Harbour组的样品中，老年人口数量较大（> 5％）。 （样品＃15-18）。最大沉积年龄见表1。喀斯喀特河的1-4号样品富含石英和火山岩碎屑，在QFL图上的“再生造山带”域中绘制。现代喀斯喀特河的年龄分布中，年龄小于250 Ma的锆石> 97％，年龄小于110 Ma的锆石> 90％。可以区分两个主要年龄种群，它们的贡献在样本之间有所不同：15-40 Ma和85-100 Ma。样品＃3（普亚洛普河，排泄雷尼尔山）和＃4（斯卡吉特河，排泄两个活火山，贝克山和冰川峰）产生最近的锆石（<5 Ma）。奥林匹克河的样品＃5-8富含石英。和沉积岩屑碎片，在QFL图上的“再生造山带”域中绘制。现代奥林匹克河的年龄分布中，年龄小于250 Ma的锆石> 85％，但年龄较大的白垩纪和侏罗纪年龄（110-250 Ma）的贡献更大（约占锆石的23％），在140-170 Ma（所有样本）和180-220 Ma（和河和Elwha河流）有两个突出的年龄种群。所有奥林匹克河流都显示出现代喀斯喀特河流中85-100 Ma的年龄高峰。来自Elwha和Queets河的5号和7号样本显示了以50 Ma为中心的明确定义的种群。在喀斯喀特河砂中发现的15-40 Ma人口在奥林匹克河中几乎没有表达（不到锆石的4％）。所有奥林匹克河流中最年轻的谷粒介于20至24 Ma之间（表1）。哥伦比亚河的9号样品富含石英和火山岩碎屑，位于QFL图的“再生造山带”域中。样品＃9产生的年龄跨越最后一个180 Ma，中生代之前的年龄很少（约锆石的5％），尽管其流域宽阔，覆盖了其源头附近的前寒武纪地层。两个年龄段的人群特别明显：45-55 Ma和< 中新世沿岸OSC的5 Ma.26号和27号样品显示出与现代奥林匹克河类似的岩相组合，其中石英和石屑碎片占主导地位，分布在“再生造山带”场中。这两个样本还显示出与现代奥林匹克河样本相似的年龄分布。它们的主要种群为85-100 Ma，次要种群为45-55 Ma和140-170 Ma。样品＃26和＃27均显示出大量的中新世早期年龄，最大沉积年龄为16.5和16.7±0.5 Ma（2 s;表1）。样品24和25来自上OSC（始新世晚期至渐新世/早期）中新世）的岩相学结果与沿海OSC样品相同，但年龄分布差异显着。两种年龄的分布都以一个170-230 Ma的峰值为主导，只有少一些的早老谷物。现代喀斯喀特河的0-110 Ma年龄段明显不存在，大多数锆石都明显早于样品的沉积年龄.Chuckanut组的22号和23号样品与其他样品截然不同，因为它们特别如此富含石英和变质岩屑，22号样品位于QFL图的“大陆块域”中（图5）。他们的年龄分布富含前中生代谷物（锆石的30％至40％）；较年轻的谷粒覆盖55-200 Ma范围，晚白垩世古新世人口集中在70 Ma左右（图4）。来自Bulson Creek组合的10号和11号样品彼此显着不同。10号样品富含石英，变质岩和沉积岩屑。它显示了一群聚集在50 Ma的年轻谷物，大多数年龄介于115至280 Ma之间（>锆石的90％）。11号样品完全由火山碎屑岩和稀有石英颗粒组成。它的年龄分布显示出一个单一的重要种群，介于28至35 Ma之间，并具有稀有的较旧的副粒。11号样品的最大沉积年龄为29.0±0.8 Ma（2 s;表1）.Blakeley组样品可分为两组。＃19和＃21样品富含石英和火山岩碎屑，并绘制在“再生造山带”域中。大多数锆石的年龄在20-110 Ma之间，其中有重要的白垩纪种群，而19号样本的次生种群约为50 Ma。20号样品富含火山岩粒，稀有石英粒。其年龄分布显示出特征性锆石种群在20至35 Ma之间，为26.1±0。最大沉积年龄为7 Ma（2 s；表1）。中新世中期布雷克利海港组的15-17号样品显示了相似的年龄分布，并反映了现代奥林匹克河的年龄分布。年龄覆盖20-230 Ma的整个范围，主要人口在85-100 Ma左右，从属人口在45-55 Ma。样本＃18的年龄范围相似，尽管它的主要年龄峰值为〜30 Ma，并且仅包含〜120至230 Ma之间的稀有辅助晶粒。与奥林匹克河沙相反，样品15-17主要由玄武岩碎屑制成，这是富尔默认识到的特征[39]。最大沉积年龄都与布莱克利组样品的沉积年龄相似（22-30 Ma；表1），并且比布莱克利港组的沉积年龄（13.3±1.3Ma⁠； [40]）大得多。瓦萨公园组合的样本＃12-14在岩石学和年龄分布方面显示出鲜明的特征。所有这三个样品主要包含石英颗粒和碎屑岩，火山岩和沉积性碎屑岩含量大致相同。样品＃12和＃14显示出一个中晚期中新世种群，最大沉积年龄为12.3±0.3 Ma和11.1±0.3 Ma（表1）。第二个年龄在统计学上与在同一地区报道的11.4±0.6 Ma40Ar / 39Ar年龄相似[56，58]。13号样品显示了相似的最大沉积年龄，为11.8±0.3Ma⁠，但年龄范围为10-50 Ma（表1;图4）。现代喀斯喀特河砂的1-4号样品的年龄分布是来自级联弧（年龄小于45Ma⁠）和未成年锆石的年轻锆石种群的组合，较老的人口来自沿海山脉岩床（集群在65-75 Ma，85-105 Ma，140-165 Ma和200-210 Ma；图6）。下面，我们将这些年龄分布用作从小瀑布中提取的锆石的特征。来自喀斯喀特山脉的沉积岩应该包含相似的锆石种群，并且预计将合并来自喀斯喀特弧的年轻火山锆石，这些锆石是同卵的，或者随着年龄的增长而略有延迟。我们的研究突出了OSC的两个不同来源。上部OSC的第24号和第25号样品（年龄为始新世至中新世早期）由一个晚三叠世至侏罗纪早期种群（170-220 Ma）所占优势，而其他所有样本（包括现代喀斯喀特河）均不存在（图4） ）。在喀斯喀特山脉的晶体核心中有晚三叠世-早侏罗世岩体[67，68]，但它们几乎不能促进现代喀斯喀特河流的锆石负荷，如此处突出显示。热年代学数据表明，直到中新世为止，喀斯喀特山脉的晶体核心一直没有被挖掘出来：从喀斯喀特山脉西侧的岩石产生的磷灰石-He冷却年龄为12-6Ma。东面的岩石显示出范围更广的磷灰石-He冷却年龄，在60至18 Ma之间，尽管它们在整个新生代也显示出慢得多的发掘速率[69]。喀斯喀特山脉以东的Methow谷中生代地层中含有丰富的侏罗纪晚期和白垩纪早期锆石，但是，如在Boston Bar和Twisp地层中所见[70]，锆石要么完全不存在，要么极为稀少。稀有（> 2％），如温思罗普，哈茨山口和午夜峰地层以及Jackass山群[71]。样品24和25中发现的170-220 Ma年龄峰的另一个潜在来源是兰格利亚的Bonanza弧。 Terrane，暴露在南温哥华岛和西温哥华岛[72]。Bonanza弧岩的U-Pb年龄范围从168到202 Ma。相关的火山碎屑岩层表明岩浆活动早于三叠纪开始，可能早在230 Ma [73]。在温哥华岛以东的乔治亚盆地，白垩纪前臂地层样品的年龄分布中发现了相似的170-220 Ma锆石种群[74]。该种群在格鲁吉亚盆地南部纳纳莫莫群下部的Comox组的样本中尤为突出，由Huang等人解释。[74]反映了来自Bonanza弧的沉积物（图7）。在Comox地层样品中发现的其他年龄种群包括344-364 Ma和450-455 Ma的年龄群，以及170 Ma以下的年龄。这些人口被解释为反映了从海岸山脉和温哥华岛变质和火成岩基底排出的沉积物[74]。但是，我们的上层OSC样本中没有这些年龄段。Bonanza Arc的岩石广泛地沿着温哥华岛的南坡和西坡生长；这使得来自Bonanza弧的沉积物可以排入太平洋，而无需合并来自其他基底岩石，前臂地层或海岸山脉的锆石[75]。我们将上OSC样本中的170-220 Ma年龄人口解释为也反映了温哥华岛Bonanza弧排放的沉积物。Wrangellia Terrane的主要掘出记录在50到40 Ma之间，这与上层OSC的沉积是当代的，表明Bonanza弧是上层OSC的可行沉积物来源[76]。我们建议我们的样本起源于此发掘期间在温哥华岛斜坡上产生的湍流事件。在沿海OSC和现代奥林匹克河的样本中几乎没有发现上部OSC样本中识别的晚三叠世-早侏罗世种群。来自沿海OSC的（中新世）样本的复合年龄分布包含与现代喀斯喀特河的复合年龄分布相同的锆石种群，除了沿海OSC中完全没有中新世和年轻的锆石外（图6）。这些特征表明，沿海OSC可能是从Cascade资料衍生而来的。现代奥林匹克河流的综合年龄分布也与喀斯喀特河流的综合产出相似（图6），但有一些差异。奥林匹克河流含有相对较低的0-50 Ma谷物（约占锆石的6.5％），并显示110-200 Ma的人口，这在现代喀斯喀特河中所占的比例不足。我们采样的四条现代奥林匹克河流全部排泄了奥林匹克半岛的核心，而奥林匹克半岛的核心则是最古老的（始新世）OSC岩石。这种排水与0-50 Ma谷物的代表性不足和老年人口的代表性更高有关。我们建议，尽管存在这些差异，奥林匹克半岛核心地带的大部分沉积岩都来自小瀑布的排水。在奥林匹克河流中排泄半岛核心地带的锆石年龄最小为20 Ma，这表明奥运会在早期之前仍处于地形低谷。中新世 沿海OSC的26号和27号样品的最大沉积年龄为16.5和16.7±0.5 Ma，这表明OSC至少是在这段时间之前是由级联沉积物供料的.Chuckanut组的22号和23号样品显示除了在所有前臂样本中发现的显着的90 Ma种群外，还有明显的中生代谷物种群，另外还有75 Ma种群，这在现代喀斯喀特河中并未得到很好的表达。这些样品的年龄分布与佐治亚盆地纳纳莫组上层的马斯特里赫特地层非常相似，它们还显示了两个白垩纪的年龄峰，分别集中在75和90 Ma处，年龄较大的人群则集中在1380 Ma和1650-1800年之间。 Ma（图7; [77，78]）。在纳奈莫上部样本中发现的年龄群分别为90 Ma，1380 Ma和1650-1800 Ma，这被解释为源自爱达荷州[79]，而较年轻的年龄则来自沿海山脉岩基。另外，Mathews等。[63]表明，这些年龄也出现在美国西南部的莫哈韦-索诺兰地区（MSR），主张在纳奈莫群沉积时温哥华岛的古夷度要低得多，然后对白垩纪时期的Wrangellia Terrane [80]。Wrangellia Terrane的古纬度和Nanaimo组的两个可能的泥沙源区之间的区别都是正在进行辩论的话题。我们样品的年龄分布表明，纳奈莫集团的Chuckanut组和Maastrichtian地层共享相同的沉积物来源，或者Chuckanut组来自Nanaimo组的返工。对于Chuckanut组来说，MSR的直接来源是不太可能的，因为拟议的地层沿海岸的平移将在始新世早期的Chuckanut组沉积之前几百万年就已经实现[80]。目前，我们的出处数据无法区分爱达荷州北部Chuckanut组的沉积物来源还是Nanaimo组的返工。当时的Nanaimo组可能会进行改造，因为热年代学数据直到50 Ma才显示Nanaimo组的主要尸体[76]。BulsonCreek组合的来源也有问题。样品＃11的火山碎屑性质和年龄分布表明直接从喀斯喀特弧来。相比之下，第10号样本显示的主要年龄段人群介于115到280 Ma之间，这在其他任何样本中都很少表达。这一广泛的人口与在不列颠哥伦比亚省沿海山脉岩基的东部岩浆带发现的岩浆作用时代重叠，尽管目前尚不清楚该地区产生的沉积物如何能够向西南移动得足够远，从而可以整合到Bulson Creek组合中[ 81]。西部混杂棉（WMB）在我们采样点附近播种。WMB样本的年龄分布是异类的，有些样本显示出明显的100-200 Ma年龄人口，而另一些则没有[82-84]。样品＃10可能是从WMB材料的返修中获得的。渐新世至早中新世布雷克利组的样品＃19和21富含火山碎屑岩或石英，并且布雷克利组的复合年龄分布显示出明显的年龄峰。在30 Ma和90 Ma处，少数在140-160 Ma之间（图5和6）。在现代喀斯喀特河的综合年龄分布中，以相同的比例发现相同的峰（图6）。布雷克利组的物源和岩石学数据与作为沉积源的喀斯喀特山脉的排水相一致。瓦萨帕克组合和布雷克利港组都是中新世中期晚期沉积到卡斯卡迪亚前臂的河床石质沉积单元，瓦萨帕克组合物位于前盆地东部，布雷克利港组更西端（图1和3）。Vasa Park组合的＃12-14样本完全是火山碎屑的，可能在喀斯喀特弧中有来源。相比之下，布莱克利港组的15-18号样品显示出其最大沉积年龄与真实沉积年龄之间存在明显的偏移（7至2200万年）（图8）。该偏移量表明，喀斯喀特弧没有向布雷克利港组提供沉积物。样品＃15-18的最大沉积年龄（22-30 Ma; 表1）与Blakeley组的样品＃19-21（22.8-30 Ma；表1）相同。布莱克利港组的复合年龄分布与现代奥林匹克河流和布雷克利组的复合分布非常相似，唯一不同的是，在50 Ma处有一个突出的年龄高峰，只有在布莱克利港组和哥伦比亚河中才能很好地表达。 （图6）。这个50 Ma的峰值与新月岩层的年龄相符，布莱克利港组含丰富的玄武岩碎屑岩，这归因于新月岩层中的长英质和玄武岩物质的结合[39，54]。这些物证和岩石学数据表明，布雷克利港组的沉积物来自新月形和包括布雷克利组在内的较早沉积单元的侵蚀。新月组，布莱克利组和普吉特集团的相关单位有两个潜在的震源区，这些震源区很靠近：（1）奥林匹克半岛的东翼，距我们的采样点约30公里，单位暴露在数千平方公里（2）格林山区SFZ的吊墙，距离我们的样本位置约20公里，那里的暴露程度受到限制（<100 km2； [15，53]）。距我们样本位置约30公里的奥林匹克半岛东翼，这些单位暴露在数千平方公里的地方绿山区SFZ的吊墙，距我们的样本位置约20公里，那里的暴露要有限得多（<100 km2; [15，53]）在普吉低地，南极洲自由区的吊壁被普吉特集团沉积物覆盖，没有露出新月形地层[50，51，85–87]我们的岩相和碎屑锆石数据不足以区分这两个源区相同的地质单位。但是，我们建议SFZ吊墙不可能有任何贡献。布莱克利海港组和瓦萨公园的集合体都在SFZ的下盘[51，86]。我们在Vasa Park组合中的样本没有显示对Puget Group材料进行返工的证据，SFZ唯一可用的热年代学数据是绿山地区的磷灰石裂变径迹时代，其年龄为32±5 Ma [53]。这个年龄比布雷克利港组的沉积早10到25 Myr的SFZ悬墙掘尸开始。假设前臂的地热梯度为20°C / km [88，89]，而磷灰石裂变径迹系统的有效闭合温度为120°C [90]，则该裂变径迹的年龄将平均发掘限制在〜0.2 km /自渐新世以来的年纪。中新世中期晚期，奥林匹克半岛的尸体发掘高出4-10倍，估计速率在0.75至2 km / Myr之间[7，9]。奥林匹克半岛是一个更可能的来源，因为它在布雷克利港组沉积期间被积极剥夺。尽管需要在SFZ上进行进一步的热年代学工作来证实这一解释，但在布雷克利港组中可能存在源自奥林匹克半岛的物质，这表明该半岛已经暴露在地下，并且已经充分抬升以形成局部地形高处并提供沉积物。向东排水的河流。在单元底部的凝灰岩为13.3±1.3 Ma [40]，为奥林匹克半岛的出现提供了最小年龄（图9）。这里解释为直接从喀斯喀特河流出的所有样本都显示出较短的滞后时间。它们的沉积年龄和最年轻的锆石种群年龄，通常<5 Myr（图8）。样品被解释为来自温哥华岛（OSC上层）或大部分是由旧材料（Chuckanut组，Bulson Creek组合和Blakely Harbour组显示出更长的滞后时间（9到60 Myr），这证实了它们在没有中世纪火山爆发地区的出处。我们的数据证实，上层OSC与奥林匹克半岛其他结构单元的起源不同，这对卡斯卡迪亚增生楔的建立具有重要意义。中新世沿海OSC和现代奥林匹克河流的年龄分布和沉积颗粒岩石学表明，它们是从喀斯喀特山脉中衍生而来的。这与典型的增生楔中的沉积和结合是一致的，级联材料通过前臂传输到俯冲沟中[27]。相比之下，我们的始新世上层OSC样本是从温哥华岛获得的，不包括层叠的锆石。这表明上部OSC的部分沉积在离卡斯卡迪亚海沟很远的海上。这些数据支持对布兰登等人的解释。[7]提出将上层OSC沉积为Siletzia地层的西部延续，随后在卡斯卡迪亚俯冲带开始后，在Siletzia东部地层下盘根和下冲（图9：中始新世至中新世） 。尽管我们两个样品的白垩纪和中始新世的最大沉积年龄（表1），高OSC的生物地层年龄都与中新世的年龄一样年轻，并且我们的两个样品被绘制为中新世后[25，26]。我们的样品很有可能代表了上层OSC的较旧地层，已被重新混入混杂岩中，并且是破碎地层的一部分，整合了年轻的有孔虫，如在OSC上部的许多地方所见[7，15]。尽管有较低的通量和变化的时期[14]，但自45 Ma以来，级联弧内仍存在准连续的火山活动[14]。预计我们会观察到OSC内锆石不断年轻化，直到奥林匹克半岛隆起阻止了Cascade材料进入增生楔形。因此，沿海OSC内最年轻的锆石种群存在于16.5±0.5 Ma处，提供了半岛没有抬升且尚未形成地形障碍的最大年龄。有两种机制可以将隆升后的锆石带入奥林匹克增生楔块。首先，哥伦比亚河将较年轻的锆石带到海中，或更古老的类似物，该半岛以南可能是通过长岸漂流沿着奥林匹克海岸向北运送150公里，最终到达OSC前方的海沟，即现代深海Astoria Fan最北端。今天，哥伦比亚河的沉积物沿奥林匹克海岸的南部向北输送了100公里，进入奎诺特峡谷[91]；在圣海伦火山灰材料中也观察到了这一点[92]。但是，到达奎诺特峡谷的大多数现代沉积物的颗粒都很细（粉质粘土； [93]），远低于我们分析的锆石的粒径（最小25微米激光束直径）。隆升后的锆石本来可以运到卡斯卡迪亚海沟然后又运到增生楔上的另一种方式是通过胡安·德·富卡原始海峡绕半岛北部运输，然后通过长岸漂流或向南运输100公里。较小的可能性，是更深的平行于沟槽的浊流。如今，由于冬季西南风的主导，华盛顿沿岸几乎没有向南的长岸漂移[92]。此外，沿海OSC的年龄分布与哥伦比亚河或温哥华岛的沉积物供应均不一致，因此，在奥林匹克半岛隆起切断喀斯喀特山脉的排水之后，这些机制不太可能向OSC提供新鲜的锆石。电弧（图9）。华盛顿前中部的中新世布雷克利港中部晚期显示了年龄分布和谷物岩相学，这与奥林匹克半岛的直接供应是一致的。我们的数据不能排除这种地层是由西雅图断层的悬挂壁上的物质提供的，这是十位Brink等人提出的。[51]，但我们建议该来源的可能性较小，因为当时SFZ的尸体发掘率较低，并且在Vasa Park组合中没有悬挂式墙体返工。尽管沿着SFZ的推力载荷可能导致了西雅图盆地的沉降和中新世中期后期的布雷克利港组沉积[50，51]，但SFZ悬挂壁对沉积物供应的贡献仍有待显示。我们发现，奥林匹克半岛极有可能为布雷克利港形成了沉积物，使布雷克利港形成基部的年龄成为半岛出现和地形高点形成的最大限制因素。 16.5±0.5 Ma之后，可能在13.3±1.3 Ma（2 s）之前，中新世晚期奥林匹克半岛出现到一个狭窄的窗口，尽管这个年龄尚待更深入的发掘研究来证实SFZ。布兰登等。[7]估计，假设观测到的恒定掘尸速率为0.75 km / Myr，则从增生深度上升到10 km的α损坏锆石封闭深度将需要约4.4 Myr，才能从增生楔上升到沉积物。在最后14 Ma 结果表明，大约10公里的深度已达到 13.7马 这些估计将尸体发掘的时间定为大约。18.1 Ma，距离我们提出的半岛出现窗口至少提前了两百万年。Michel等。[9]提出了一个更快的速率（2 km / Myr）用于掘尸的初始阶段，在5-7 Ma时降低到波纹管的现代速率。使用这种更快的初始尸体发掘率，并使用与Brandon等人相同的模型。[7]，我们估计尸体发掘始于约。15.3马，它在我们建议的奥林匹克半岛出现时间范围内。这些估计是基于一个简单的模型，该模型是楔形物所吸积材料的轨迹和温度历史记录，应谨慎评估。在这个简单模型的框架中，并且假设增生楔几乎没有出土前的侵蚀和发掘，我们半岛出现的时间与模型有关，即高发掘的早期阶段[9]和增生楔的复合变形历史。这项工作限制了奥林匹克半岛的初始空中暴露以及对中新世中期晚期的地形障碍的形成，但我们并未排除增生楔形物早期变形和抬升的可能性。早于中新世到中新世可能发生了半岛出现的变形，这种变形可能记录在布雷克利组的地层中。布雷克利编队以海底扇状沉积为主，其中一些已经产生了有孔虫，发现于海底至深渊（深于1 km； [39]）。前臂盆地中这种深度的存在需要一种产生高沉降的机制。约翰逊等。[50]将这种沉降与沿SFZ推进的早期阶段联系起来，磷灰石裂变径迹数据支持了这一时机[53]。沿着SFZ需要更多的热年代学工作来确认变形的早期阶段。如果得到证实，则这种渐新世冲入SFZ的事件为边距平行缩短和开始奥林匹克奥林匹克线提供了证据，这比奥林匹克半岛的出现早了至少一千万年。来自奥林匹克半岛和普吉低地的碎屑锆石物源和谷物岩石学数据相结合，使我们能够重建卡斯卡迪亚俯冲带的新生代历史。我们首先显示上层OSC的独特沉积物源，与奥林匹克半岛的其他结构单元不同。上部OSC样品仅包含来自温哥华岛的材料，并且未与年轻（40 Ma后）锆石混合。这些结果表明，上层OSC在Siletzia地层增加到Cascadia边缘之前已作为Siletzia地层的一部分沉积，后来又在新月形地层下盘化和下推。OSC的其他单位表示已积聚的卡斯卡迪亚海沟沉积物，并显示从小瀑布到增生楔的输入，直到至少16.5±0.5Ma⁠，为奥林匹克半岛的出现提供了更高的年龄限制。中新世中期布雷克利港组的河床沉积记录了回收的新月组和OSC /前臂材料向西雅图盆地的首次输入。尽管我们不能排除西雅图断层带悬壁的某些贡献，但我们建议布雷克利港组为从奥林匹克半岛进入普吉低地的侵蚀物质输入提供了最低年龄。半岛出现的年龄限制为13.3±1.3 Ma。我们最后提出，奥林匹克半岛的形变和眼眶弯曲的初始发作至少要早于10 Myr出现，其特征是沿西雅图断层带的弯曲沉降和渐新世Blakeley组的沉积。作者声明，本文的发表没有利益冲突。这项研究主要由华盛顿大学资助。奥林匹克国家公园的样本是在OLYM-2018-SCI-0036许可下收集的。感谢Vasa Park Resort的Susie Winkowski允许我们使用他们的财产。我们还感谢M. Mueller，Tamas Ugrai，Ralph Haugerud，Hope Sisley，Eric Cheney，Alexandre Delga，Matthew Dubeau，奥林匹克国家公园管理局和Darrel Cowan在现场和实验室中进行了多方讨论和协助。我们还要感谢拉尔夫·豪格鲁德（Ralph Haugerud），威廉·马修斯（William Matthews），莎拉·罗斯基（Sarah Roeske）和斯蒂芬·约翰斯顿（Stephen Johnston）对这份手稿的见解和建设性的评论。补充文件1：碎屑锆石物源分析的完整分析程序。补充表1：谷物计数数据。补充表2：U-Pb数据。补充图1：所有样品碎屑锆石年龄分布的直方图和核密度估计图。河流样本按流域分组，岩石样本按地层分组。所有年龄均显示在20个Myr箱中。