We integrated new and existing bedrock and detrital zircon dates from the Zealandia Cordillera to explore the tempo of Phanerozoic arc magmatism along the paleo-Pacific margin of southeast Gondwana. We found that episodic magmatism was dominated by two high-magma-addition-rate (MAR) events spaced ∼250 m.y. apart in the Devonian (370–368 Ma) and the Early Cretaceous (129–105 Ma). The intervening interval between high-MAR events was characterized by prolonged, low-MAR activity in a geographically stable location for more than 100 m.y. We found that the two high-MAR events in Zealandia have distinct chemistries (S-type for the Devonian and I-type for the Cretaceous) and are unlikely to have been related by a repeating, cyclical process. Like other well-studied arc systems worldwide, the Zealandia Cordillera high-MAR events were associated with upper-plate deformation; however, the magmatic events were triggered by enhanced asthenospheric mantle melting in two distinct arc-tectonic settings—a retreating slab and an advancing slab, respectively. Our results demonstrate that dynamic changes in the subducting slab were primary controls in triggering mantle flare-up events in the Phanerozoic Zealandia Cordillera.Phanerozoic continental arcs are factories for the growth and refinement of modern continental crust (e.g., Rudnick, 1995; Hawkesworth and Kemp, 2006). In most well-studied continental arcs, the tempo of magmatism is episodic, and there is abundant evidence for alternating high-magma-addition-rate (MAR) events (or flare-ups) and magmatic lulls. These flare-ups are significant because they are responsible for the generation of the bulk of plutonic arc crust (∼85%–90%) in geologically brief intervals (<20 m.y.; DeCelles et al., 2009; Ducea et al., 2015).In continental arcs where long-lived records are available, high-MAR events are sometimes shown to have occurred at intervals of 30–70 m.y., with cycles repeating as many as three times over the course of ∼150–250 m.y. (Ducea et al., 2015; Paterson and Ducea, 2015; Kirsch et al., 2016). However, there is currently no consensus regarding the mechanisms responsible for this episodic behavior and the causes of high-MAR events (e.g., Chapman and Ducea, 2019; Collins et al., 2020). In the case of the Sierra Nevada batholith and other segments of the American Cordillera, some researchers have proposed that plutonic rocks produced during repeated high-MAR events are linked to upper-plate compression leading to underthrusting of retroarc crust and widespread crustal melting beneath the arc (e.g., DeCelles et al., 2009; Ducea et al., 2015). However, others have noted that many arc segments do not display patterns of 30–70 m.y. high-MAR events (e.g., Kirsch et al., 2016), and in these cases, episodic magmatic surges may be driven instead by enhanced mantle melting rather than upper-plate deformation (e.g., Cecil et al., 2018). These conflicting views on the significance of episodic magmatic surges create an important and unresolved question in arc petrology: what processes drive the initiation of high-MAR events in continental arcs? Are they triggered by upper-plate compression and related phenomena, or are they triggered by mantle processes such as changes in subduction zone dynamics related to lower-plate geometry (e.g., slab rollback, slab tear, slab advance) and/or changes in volatile or melt contributions?We addressed these questions by integrating >380 new and existing bedrock zircon ages with >2280 detrital zircon ages from 46 samples deposited on the Zealandia Cordillera to investigate the tempo of arc magmatism and the causes of high-MAR events (Figs. 1A and 1B). The Zealandia Cordillera, located along the Pacific margin of southeast Gondwana, was active for much of the Phanerozoic and encompasses an area that is 700 km long and 200 km wide (Fig. 2), comparable in scale to other well-studied arcs worldwide (e.g., the Sierra Nevada and Coast Mountains batholiths of North America). On the South Island of New Zealand, and Stewart Island, this paleo arc consists of lower-, middle-, and upper-crustal rocks from ∼5 to 65 km paleodepth (Tulloch and Kimbrough, 2003; Allibone et al., 2009; De Paoli et al., 2009; Scott et al., 2011; Schwartz et al., 2017). These exposures offer a unique perspective from which to examine Phanerozoic arc magmatic tempos in southeast Gondwana for over 400 m.y.The Zealandia Cordillera was a Phanerozoic orogenic belt that extended over much of the 4.9 × 106 km2 Zealandia continent, then part of southeast Gondwana (Figs. 1A and 1B) (Mortimer et al., 2017; Tulloch et al., 2019). Arc-related magmatism was nearly continuous from ca. 500 Ma to 100 Ma (Kimbrough et al., 1994; Tulloch and Kimbrough, 2003; Schwartz et al., 2017; Tulloch et al., 2009, 2019), and igneous and metamorphic rocks are best exposed in Fiordland, Nelson-Westland, and Stewart Island (Fig. 2). Studies of offshore samples have shown that the arc continues underwater for more than 1000 km eastward to the Bounty and Antipodes Islands (Tulloch et al., 2019), to the north and west of Nelson (Mortimer et al., 2017), and to likely correlatives in Queensland (Tulloch et al., 2010), for a total arc length of ∼4500 km (Fig. 1B). Prebatholithic rocks of the Zealandia Cordillera consist of variably metamorphosed and deformed rocks of the early Paleozoic Takaka and Buller terranes (Cooper, 1989), which are suggested to have amalgamated at ca. 387 ± 3 Ma (Turnbull et al., 2016). Construction of the Zealandia Cordillera primarily involved emplacement of arc-related igneous rocks into both terranes over >250 m.y. and included three main magmatic phases: (1) Devonian to Carboniferous plutons from 370 to 305 Ma, (2) Permian to Cretaceous Darran and Longwood Suite plutons from 260 to 130 Ma, and (3) Cretaceous Separation Point Suite and Rahu Suite plutons from 129 to 105 Ma (Fig. 2) (Kimbrough et al., 1994; Muir et al., 1998; Tulloch et al., 2009; Milan et al., 2017; Schwartz et al., 2017).We compiled >380 U-Pb zircon ages, including 24 new dates, and we calculated new pluton area and volume estimates using digitized geologic maps of New Zealand, and paleocrustal thickness estimates after Mantle and Collins (2008) (see the Supplemental Material1 for methods). Plutonic samples spanned the entire age range of magmatism in the Zealandia Cordillera, and we focused exclusively on arc-related magmatic rocks and excluded small-volume dikes and nonsubduction (i.e., alkaline intraplate) rocks. Our compilation of existing dates revealed a paucity of age information from the Mesozoic Darran Suite, and so we conducted additional U-Pb zircon geochronology to refine the tempo of Zealandia magmatism during this interval. Because the plutonic record is sometimes incompletely preserved, we also compared our bedrock zircon ages to >2280 detrital zircon dates from 46 samples (6 new) from sediments deposited on Zealandia for the purpose of examining the magmatic record preserved in detrital sediments. Analytical procedures, pluton and detrital zircon data, sample locations, standard information, and an explanation of age calculations are provided in the Supplemental Material.Our compilation of bedrock zircon dates allowed us to refine the tempo of arc magmatism over the ∼400 m.y. life span of the Zealandia Cordillera, providing a complete history of a Phanerozoic arc outside the heavily studied North and South American Cordillera. Our data and volume addition rate calculations revealed that magmatism was nearly continuous for most of the Phanerozoic (Fig. 3A) and was dominated by two high-MAR pulses (Fig. 3B): one high-MAR event occurred in the Cretaceous (the Separation Point Suite pulse from 129 to 105 Ma; Tulloch and Kimbrough, 2003; Milan et al., 2017; Schwartz et al., 2017), and the other occurred in the Paleozoic (the Karamea Suite pulse from 370 to 368 Ma; Tulloch et al., 2009; Turnbull et al., 2016). Although Darran Suite and related magmatism (e.g., Longwood Suite) lasted for >100 m.y., we observed no high-MAR events during this time (see the discussion below). For the Cretaceous and Paleozoic high-MAR events, their duration was ∼24 m.y. and 2 m.y., respectively, and estimated volume addition rates are as high as 40,000–45,000 km3/m.y. (Fig. 3B). Milan et al. (2017) reached a similar conclusion for the Cretaceous event. These high-MAR durations are similar to other events in well-studied Cordilleran arcs, and the volume addition rates are comparable to some of the highest MAR events ever recorded (cf. Paterson and Ducea, 2015).A unique aspect of the Zealandia Cordillera is that the time interval between high-MAR events (∼250 m.y.) was characterized by an extended period of near-continuous, low-MAR subduction-related magmatism involving emplacement of minor late Paleozoic plutons, the Darran and Longwood Suites, along with minor accretion of fringing-arc terranes at ca. 270–265 Ma (Dun Mountain and Brook Street terranes) (Fig. 3A). The detrital record of sediments deposited on the Zealandia Cordillera also shows near-continuous magmatism throughout the Phanerozoic despite gaps in the plutonic record. This prolonged low-MAR interval is especially unique when compared to other well-studied magmatic arc segments; it is 3–4× longer than average magmatic cycles recognized in the Mesozoic American Cordillera (∼60–70 m.y.) and 8–13 × longer than those recognized in the Cenozoic American Cordillera (∼20–30 m.y.) (Haschke et al., 2006; DeCelles et al., 2009; DeCelles and Graham, 2015; Ducea et al., 2015; Paterson and Ducea, 2015; Kirsch et al., 2016).Our new bedrock zircon ages also show that the relatively steady-state Darran Suite involved three low-MAR events (peaks at ca. 230, 148, and 138 Ma), but no high-MAR events are observed (Fig. 3B). This period of low-MAR activity is also documented in formerly adjacent sections of the southeast Gondwana margin in West Antarctica (Tulloch et al., 2019) and eastern Australia, including within the Tasmanides (e.g., Jessop et al., 2019). In this along-strike arc segment, Paleozoic plutonic rocks show evidence for repeated patterns of slab advance and slab rollback behind a retreating arc (e.g., Collins, 2002). Estimated crustal addition rates for this period resemble average magmatic productivity at modern convergent plate boundaries (Kemp et al., 2009) and are lower than those estimated for the high-MAR events in the Zealandia Cordillera (Turnbull et al., 2016; Milan et al., 2017; Schwartz et al., 2017; this study). Therefore, the integrated record of both the Zealandia Cordillera and Paleozoic eastern Australia preserves evidence for only two high-MAR events with an intervening period of enigmatically prolonged, subduction-related, low-MAR events and minor terrane accretions (Fig. 3A).The presence of two high-MAR events spaced ∼250 m.y. apart in the Zealandia Cordillera raises the question: what drivers were responsible for the two arc-magmatic surges? In both cases, there is strong evidence that lower-plate–triggered mantle-melting processes have dominated the Zealandia Cordillera for >400 m.y. In the case of the first documented high-MAR event in Zealandia (the Karamea Suite event), high-precision U-Pb geochronology and whole-rock geochemistry indicate that magma generation and batholith emplacement occurred during a period of extensional activity caused by slab rollback that occurred ∼10 m.y. after an episode of orogenic crustal thickening at ca. 387 Ma (Figs. 3B, 4A, and 4B) (Tulloch et al., 2009; Turnbull et al., 2016). Slab rollback is interpreted to have triggered an episode of upper-plate extension, whereby thinning of the crust enabled hot asthenosphere to rise to shallow depths and facilitate rapid, widespread, and voluminous crustal melting (Fig. 4B). Whole-rock isotopic compositions indicate a crustal contribution between 35% and 90% and some contribution from a mantle source (Tulloch et al., 2009). Cessation of the brief high-MAR, S-type event by ca. 368 Ma is inferred to have been the result of depletion of the fertile metasedimentary source rocks due to significant partial melting and crustal thinning (Turnbull et al., 2016).Structural and geochemical data from the Early Cretaceous Separation Point Suite also suggest that lower-plate processes were responsible for this high-MAR event (Figs. 3B, 4C, and 4D). Geochemical and in situ zircon Hf- and O-isotopic results show that the Cretaceous flare-up was primarily sourced from the underlying mantle, with limited contributions (0%–20%) from radiogenic crustal material (Muir et al., 1998; Decker et al., 2017; Milan et al., 2017; Schwartz et al., 2021). While the preceding low-MAR phase was geographically fixed and focused into a narrow 10–20-km-wide zone for over 100 m.y., the Separation Point Suite surge represents an abrupt and transient change in arc dynamics coincident with continentward migration of arc magmatism and widening of the active Early Cretaceous arc axis to ≥70 km (Scott et al., 2011; Schwartz et al., 2021). Evidence for underthrusting of melt-fertile continental crust beneath the arc is absent even in the lower crust (De Paoli et al., 2009), and the lack of evidence for a thick lithospheric root prior to the flare-up suggests that lithospheric foundering was an unlikely triggering mechanism for the Cretaceous high-MAR event (Klepeis et al., 2016; Chapman et al., 2017). Similarly, the strongly mantle-like O-isotope data in the lower crust preclude significant involvement of melt-fertile continental crust (Decker et al., 2017; Schwartz et al., 2021). The abrupt advance of the arc points to a fundamental change in the arc-tectonic setting from an extensional flare-up setting in the Paleozoic to a strongly contractional and advancing slab in the Early Cretaceous. Moreover, the mantle-dominated chemistry of the Early Cretaceous arc melts and their high zircon crystallization temperatures (>850 °C; Schwartz et al., 2017) indicate that asthenospheric mantle melting was the driver for the Early Cretaceous high-MAR event, and this enhanced melting event was likely triggered by a slab-tear or slab-window event (Fig. 4D).Our compilation of new and existing zircon dates from the Phanerozoic Zealandia Cordillera demonstrates that magmatism was episodic and characterized by two high-MAR events spaced ∼250 m.y. apart. We observed no evidence for magmatic cyclicity, and geochemical data from the high-MAR events are difficult to attribute to similar, intra-arc processes in the upper plate because the dominant triggering mechanisms appear to have been different. Instead, our data point to external controls related to changes in lower-plate dynamics (slab retreat, slab advance, and/or slab tear) as the driving factors behind the two events. We conclude that the >400 m.y. magmatic record of the Zealandia Cordillera illustrates the importance of mantle-dominated processes in controlling magmatic flare-ups in some long-lived continental arcs.We thank the New Zealand Department of Conservation for access and sampling in Fiordland; Richard Jongens, Keith Klepeis, Nick Mortimer, and Harold Stowell for insightful discussions; and Jay Chapman, Bob Miller, Scott Paterson, and Moritz Kirsch, as well as two anonymous reviewers, for significantly improving our manuscript. Financial support for this work was provided by U.S. National Science Foundation grant EAR-1352021 (to J.J. Schwartz) and Marsden Fund grant GNS1701 (to R.E. Turnbull).

中文翻译：

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西兰科迪勒拉以地幔为主的弧岩浆涌动的显生宙记录

我们整合了西兰西亚科迪勒拉的新的和现有的基岩和碎屑锆石年代，以探索冈瓦纳东南部古太平洋边缘显生宙弧岩浆活动的节奏。我们发现，在泥盆纪（370-368 Ma）和早白垩世（129-105 Ma）中，间歇性岩浆活动由两个相距约 250 米的高岩浆添加率（MAR）事件主导。高 MAR 事件之间的间隔的特点是在地理稳定的位置长时间的低 MAR 活动超过 100 my 我们发现西兰西亚的两个高 MAR 事件具有不同的化学性质（泥盆纪和 I 型为 S 型） -类型为白垩纪）并且不太可能通过重复的周期性过程相关联。与全球其他经过充分研究的电弧系统一样，西兰科迪勒拉高 MAR 事件与上板块变形有关；然而，岩浆事件是由两个不同的弧形构造环境中增强的软流圈地幔熔化引发的——分别是后退板块和前进板块。我们的结果表明俯冲板块的动态变化是触发显生宙西兰西亚山脉地幔爆发事件的主要控制因素。显生宙大陆弧是现代大陆地壳生长和细化的工厂（例如，Rudnick，1995；Hawkesworth and Kemp , 2006)。在大多数经过充分研究的大陆弧中，岩浆活动的速度是间歇性的，并且有大量证据表明高岩浆添加率 (MAR) 事件（或爆发）和岩浆停滞交替出现。这些爆发很重要，因为它们在地质上短暂的间隔（<20 my; DeCelles et al., 2009; Ducea et al., 2015 ). 在有长期记录可用的大陆弧中，有时显示高 MAR 事件以 30-70 my 的间隔发生，在 ~150-250 my 的过程中循环重复多达 3 次（Ducea等，2015；Paterson 和 Ducea，2015；Kirsch 等，2016）。然而，目前对于导致这种偶发行为的机制和高 MAR 事件的原因尚未达成共识（例如，Chapman 和 Ducea，2019 年；Collins 等人，2020 年）。在内华达山脉的基石和美国科迪勒拉山脉的其他部分，一些研究人员提出，在重复的高 MAR 事件期间产生的深成岩与导致弧后地壳下冲和弧下地壳广泛熔化的上板块压缩有关（例如，DeCelles 等人，2009 年；Ducea 等人，2015 年） ）。然而，其他人已经注意到，许多弧段不显示 30-70 my high-MAR 事件的模式（例如，Kirsch 等，2016），在这些情况下，幕式岩浆涌动可能是由增强的地幔熔化而不是驱动比上板变形（例如，Cecil 等人，2018 年）。关于间歇性岩浆涌动意义的这些相互矛盾的观点在弧形岩石学中创造了一个重​​要且未解决的问题：是什么过程驱动了大陆弧中高 MAR 事件的发生？它们是否由上板压缩和相关现象触发，或者它们是由地幔过程触发的，例如与下板块几何形状相关的俯冲带动力学变化（例如，板坯回滚、板坯撕裂、板坯推进）和/或挥发性或熔融贡献的变化？我们通过积分>380解决了这些问题新的和现有的基岩锆石年龄大于 2280 个碎屑锆石年龄，来自 46 个沉积在西兰西亚山脉的样品，以研究弧岩浆活动的节奏和高 MAR 事件的原因（图 1A 和 1B）。位于冈瓦纳东南部太平洋边缘的西兰西亚科迪勒拉在显生宙的大部分时间都很活跃，包括一个长 700 公里、宽 200 公里的区域（图 2），其规模可与世界范围内其他研究良好的弧相媲美（例如，北美的内华达山脉和海岸山脉的基石）。在新西兰南岛，和斯图尔特岛，这个古弧由约 5 至 65 公里古深度的下地壳、中地和上地壳岩石组成（Tulloch 和 Kimbrough，2003 年；Allibone 等人，2009 年；De Paoli 等人，2009 年；Scott等人，2011 年；施瓦茨等人，2017 年）。这些暴露提供了一个独特的视角，从中可以检查冈瓦纳东南部的显生宙弧岩浆速度超过 400 米西兰科迪勒拉是一个显生宙造山带，延伸到 4.9 × 106 平方公里西兰西亚大陆的大部分地区，然后是冈瓦纳东南部的一部分（图 1A）和 1B)（Mortimer 等人，2017 年；Tulloch 等人，2019 年）。与弧有关的岩浆活动从大约开始几乎是连续的。500 Ma 到 100 Ma（Kimbrough 等，1994；Tulloch 和 Kimbrough，2003；Schwartz 等，2017；Tulloch 等，2009，2019），火成岩和变质岩在 Fiordland-Welson 出露最好, 和斯图尔特岛（图 2）。对近海样本的研究表明，该弧向东延伸至 Bounty 和 Antipodes 群岛（Tulloch 等人，2019 年）、纳尔逊北部和西部（Mortimer 等人，2017 年），并在水下持续超过 1000 公里。昆士兰的可能相关物（Tulloch 等人，2010 年），总弧长约为 4500 公里（图 1B）。西兰科迪勒拉 (Zealandia Cordillera) 的潜伏期岩石由早期古生代 Takaka 和 Buller 地体 (Cooper, 1989) 的可变变质和变形岩石组成，这些岩石被认为在约 387 ± 3 Ma（特恩布尔等人，2016 年）。西兰科迪勒拉山脉的建造主要涉及在超过 250 米的两个地体中植入与弧相关的火成岩，包括三个主要的岩浆阶段：(1) 泥盆纪到石炭纪岩体，从 370 到 305 Ma，(2) 二叠纪至白垩纪 Darran 和 Longwood 组岩体 260 至 130 Ma，以及 (3) 白垩纪分离点组和 Rahu 组岩体 129 至 105 Ma（图 2）（Kimbrough 等人，1994；Muir 等人） ., 1998; Tulloch et al., 2009; Milan et al., 2017; Schwartz et al., 2017). 我们汇编了 > 380 U-Pb 锆石年龄，包括 24 个新日期，我们计算了新的岩体面积和体积估计使用新西兰的数字化地质图，以及 Mantle 和 Collins (2008) 之后的古地壳厚度估计（方法参见补充材料 1）。深成岩样品跨越了西兰西亚科迪勒拉岩浆活动的整个年龄范围，我们只关注与弧相关的岩浆岩，排除了小体积岩脉和非俯冲（即碱性板内）岩石。我们对现有日期的汇编揭示了来自中生代 Darran Suite 的年龄信息的缺乏，因此我们进行了额外的 U-Pb 锆石年代学研究，以细化该区间内西兰蒂亚岩浆活动的节奏。由于深成岩记录有时保存不完整，我们还将我们的基岩锆石年龄与来自西兰迪亚沉积物的 46 个样品（6 个新样品）的 >2280 个碎屑锆石年龄进行了比较，目的是检查碎屑沉积物中保存的岩浆记录。补充材料中提供了分析程序、岩体和碎屑锆石数据、样本位置、标准信息和年龄计算的解释。我们对基岩锆石日期的汇编使我们能够改进大约 400 年的弧岩浆活动节奏西兰西亚科迪勒拉，提供了大量研究的北美和南美科迪勒拉之外的显生宙弧的完整历史。我们的数据和体积添加率计算表明，大部分显生宙的岩浆活动几乎是连续的（图 3A），并以两个高 MAR 脉冲为主（图 3B）：一个高 MAR 事件发生在白垩纪（分离Point Suite 脉冲从 129 到 105 Ma；Tulloch 和 Kimbrough，2003；Milan 等，2017；Schwartz 等，2017），另一个发生在古生代（Karamea Suite 脉冲从 370 到 368 Ma；Tulloch 等2009 年；特恩布尔等人，2016 年）。尽管 Darran Suite 和相关的岩浆活动（例如 Longwood Suite）持续了 100 my 以上，但我们在这段时间内没有观察到高 MAR 事件（见下面的讨论）。对于白垩纪和古生代高 MAR 事件，它们的持续时间为~24 my 和 2 my，和估计的体积增加率高达 40,000-45,000 km3/my（图 3B）。米兰等人。(2017) 对白垩纪事件得出了类似的结论。这些高 MAR 持续时间与经过充分研究的 Cordilleran 弧中的其他事件相似，并且体积增加率与有史以来记录的一些最高 MAR 事件相当（参见 Paterson 和 Ducea，2015）。Zealandia Cordillera 的一个独特方面是高 MAR 事件之间的时间间隔（~250 my）的特点是长时间的近乎连续的、低 MAR 俯冲相关的岩浆作用，涉及较小的晚古生代岩体、Darran 和 Longwood 岩体的侵位，以及较小的边缘弧地体在约 。270-265 Ma（Dun Mountain 和 Brook Street 地体）（图 3A）。沉积在西兰西亚山脉上的沉积物的碎屑记录也显示了整个显生宙近乎连续的岩浆作用，尽管在深成岩记录中存在间隙。与其他经过充分研究的岩浆弧段相比，这种延长的低 MAR 间隔尤其独特；它比中生代美国科迪勒拉 (~60-70 my) 中识别的平均岩浆周期长 3-4 倍，比新生代美国科迪勒拉 (~20-30 my) 中识别的平均岩浆周期长 8-13 倍（Haschke 等人，2007 年）。 , 2006; DeCelles et al., 2009; DeCelles and Graham, 2015; Ducea et al., 2015; Paterson and Ducea, 2015; Kirsch et al., 2016).我们新的基岩锆石年龄也表明相对稳态Darran Suite 涉及三个低 MAR 事件（峰值在大约 230、148 和 138 Ma），但没有观察到高 MAR 事件（图 3B）。这段低 MAR 活动期也记录在南极洲西部冈瓦纳大陆东南边缘（Tulloch 等人，2019 年）和澳大利亚东部（包括塔斯马尼德群岛内）以前相邻的部分（例如，Jessop 等人，2019 年）。在这个沿走向的弧段中，古生代深成岩显示出在后退弧后面板片前进和板片后退的重复模式的证据（例如，Collins，2002）。这一时期估计的地壳添加率类似于现代会聚板块边界的平均岩浆生产力（Kemp 等人，2009 年），低于西兰科迪勒拉高 MAR 事件的估计值（Turnbull 等人，2016 年；米兰等人） al.，2017 年；Schwartz 等人，2017 年；本研究）。所以，西兰科迪勒拉山脉和澳大利亚东部古生代的综合记录仅保留了两次高 MAR 事件的证据，其间有一段神秘延长的、与俯冲相关的低 MAR 事件和次要地体增生（图 3A）。在西兰西亚山脉中相距约 250 米的两次高 MAR 事件提出了一个问题：是什么驱动因素导致了两次弧岩浆涌动？在这两种情况下，有强有力的证据表明，下板块触发的地幔熔化过程在西兰西亚科迪勒拉占主导地位超过 400 米。高精度 U-Pb 年代学和全岩地球化学表明，岩浆生成和基岩侵位发生在由板块回滚引起的伸展活动期间，该活动发生在大约 10 年左右的造山地壳增厚事件后约 10 年。387 Ma（图 3B、4A 和 4B）（Tulloch 等人，2009 年；Turnbull 等人，2016 年）。板块回滚被解释为触发了上板块伸展的情节，由此地壳变薄使热软流圈上升到浅层并促进快速、广泛和大量的地壳熔化（图 4B）。全岩同位素组成表明地壳贡献介于 35% 和 90% 之间，部分贡献来自地幔源（Tulloch 等，2009）。大约在 20 年前停止了短暂的高 MAR、S 型事件。推断 368 Ma 是由于显着的部分熔融和地壳减薄导致肥沃的变质沉积烃源岩枯竭的结果（Turnbull 等人，2016 年）。来自早白垩世分离点套件的结构和地球化学数据也表明低-板块过程是造成这种高 MAR 事件的原因（图 3B、4C 和 4D）。地球化学和原位锆石 Hf 和 O 同位素结果表明，白垩纪的爆发主要来自下伏地幔，放射成因地壳物质的贡献有限（0%–20%）（Muir 等人，1998 年；Decker等人，2017 年；米兰等人，2017 年；施瓦茨等人，2021 年）。虽然之前的低 MAR 阶段在地理上是固定的，并且集中在一个 10-20 公里宽的狭窄区域内，但超过 100 米，Separation Point Suite 浪涌代表了弧动力学的突然和瞬态变化，同时伴随着弧岩浆向大陆迁移和活动的早白垩世弧轴加宽至≥70 km（Scott 等人，2011 年；Schwartz 等人，2021 年）。即使在下地壳中也不存在弧下熔体肥沃的大陆地壳下冲的证据（De Paoli 等人，2009 年），并且缺乏爆发前厚岩石圈根部的证据表明岩石圈沉没是白垩纪高 MAR 事件不太可能的触发机制（Klepeis 等人，2016 年；Chapman 等人，2017 年）。同样，下地壳中强烈的类似地幔的 O 同位素数据排除了熔体肥沃的大陆地壳的显着参与（Decker 等人，2017 年；Schwartz 等人，2021 年）。弧的突然推进表明弧构造环境发生了根本性变化，从古生代的拉张爆发环境到早白垩世的强烈收缩和推进的板块。此外，早白垩世弧熔体以地幔为主的化学性质及其高锆石结晶温度（>850 °C；Schwartz et al., 2017）表明软流圈地幔熔化是早白垩世高 MAR 事件的驱动因素，和这种增强的熔化事件可能是由板片撕裂或板片窗事件引发的（图 4D）。我们对显生宙西兰西亚山脉新的和现有的锆石日期的汇编表明，岩浆活动是偶发性的，其特征是两个高 MAR 事件间隔开〜250我分开。我们没有观察到岩浆循环的证据，来自高 MAR 事件的地球化学数据和地球化学数据很难归因于上板块类似的弧内过程，因为主要的触发机制似乎不同。相反，我们的数据指向与下板动力学变化（板坯退缩、板坯推进和/或板坯撕裂）相关的外部控制是这两个事件背后的驱动因素。我们得出的结论是，西兰西亚山脉的 >400 my 岩浆记录说明了地幔主导过程在控制某些长寿命大陆弧中岩浆爆发方面的重要性。Richard Jongens、Keith Klepeis、Nick Mortimer 和 Harold Stowell 进行了富有洞察力的讨论；和杰伊查普曼、鲍勃米勒、斯科特帕特森和莫里茨基尔希，以及两位匿名审稿人，显着改善了我们的手稿。这项工作的财政支持由美国国家科学基金会资助 EAR-1352021（给 JJ Schwartz）和马斯登基金资助 GNS1701（给 RE Turnbull）提供。