Abstract Xenolith and seismic studies provide evidence for tectonic erosion and eastward displacement of lower crust-subcontinental mantle lithosphere (LC-SCML) underlying the Mojave Desert Region (i.e. southern California batholith (SCB)). Intensified traction associated with the Late Cretaceous flattening of the subducting Farallon plate, responsible for deforming the SW U.S., likely played a key role in “bulldozing” the tectonically eroded LC-SCML ∼500 km eastwards, to underneath the Colorado Plateau Transition Zone (CPTZ) and further inboard. The garnet clinopyroxenite xenoliths from two CPTZ localities, Chino Valley and Camp Creek (central Arizona), provide a rare glimpse of the material underlying the CPTZ. Thermodynamic modeling, in addition to major and trace element thermobarometry, suggests that the xenoliths experienced peak conditions of equilibration at 600-900 °C and 12-28 kbar. These peak conditions, along with the composition of the xenoliths (type “B” garnet and diopsidic clinopyroxene) strongly suggest a continental arc residue (“arclogite”), rather than a lower plate subduction (“eclogite”), origin. A bimodal zircon U-Pb age distribution with peaks at ca. 75 and 150 Ma, and a Jurassic Sm-Nd garnet age (154 ± 16 Ma, with initial eNd value of +8) overlaps eastern SCB pluton ages and suggests a consanguineous relationship. Cenozoic zircon U-Pb ages, REE geochemistry of zircon grains, and partially re-equilibrated Sm-Nd garnet ages indicate that displaced arclogite remained at elevated PT conditions (>700 °C) for 10s of Myr following its dispersal until late Oligocene entrainment in host latite. With a ∼100 Myr long thermal history overlapping that of the SCB and the CPTZ, these assemblages also contain evidence for late-stage hydration (e.g. secondary amphibole), potentially driven by de-watering of the Laramide slab. In light of these results, we suggest that the CPTZ arclogite originates from beneath the eastern half of the SCB, where it began forming in Late Jurassic time as mafic keel to continental arc magmas. The displacement and re-affixation of the arclogites further inboard during the Late Cretaceous flat slab subduction, might have contributed to the tectonic stability of the Colorado Plateau relative to adjacent geologic provinces through Laramide time and likely preconditioned the region to Cenozoic tectonism, e.g. present-day delamination beneath the plateau, high-magnitude extension and formation of metamorphic core complexes.

中文翻译：

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寻找南加州基石缺失的弧根：科罗拉多高原过渡带上地幔包体的PTt演化

摘要 捕虏体和地震研究为下地壳-次大陆地幔岩石圈（LC-SCML）的构造侵蚀和东移提供了证据，该岩石圈位于莫哈韦沙漠地区（即南加州基岩（SCB））之下。与晚白垩世俯冲的 Farallon 板块变平相关的强烈牵引力，导致美国西南部变形，可能在“推倒”构造侵蚀的 LC-SCML 向东约 500 公里到达科罗拉多高原过渡带 (CPTZ) 下方的过程中发挥了关键作用) 并进一步向内侧。来自两个 CPTZ 地区 Chino Valley 和 Camp Creek（亚利桑那州中部）的石榴石斜辉石捕虏体提供了 CPTZ 下物质的罕见一瞥。热力学建模，除了主要和微量元素热气压测量法，表明捕虏体在 600-900 °C 和 12-28 kbar 下经历了平衡的峰值条件。这些峰值条件以及捕虏体的组成（“B”型石榴石和透辉石单斜辉石）强烈表明是大陆弧残留物（“arclogite”），而不是下板块俯冲（“榴辉岩”）的起源。双峰锆石 U-Pb 年龄分布，峰值位于约 75 和 150 Ma，侏罗纪 Sm-Nd 石榴石年龄（154 ± 16 Ma，初始 eNd 值为 +8）与东部 SCB 岩体年龄重叠，表明存在近亲关系。新生代锆石 U-Pb 年龄、锆石颗粒的 REE 地球化学和部分重新平衡的 Sm-Nd 石榴石年龄表明，置换的弧长岩在其扩散后的 10 秒内仍处于升高的 PT 条件（>700 °C），直到晚渐新世主机拉铁。大约 100 Myr 的长热历史与 SCB 和 CPTZ 重叠，这些组合还包含后期水合的证据（例如二级闪石），可能是由 Laramide 板的脱水驱动的。根据这些结果，我们认为 CPTZ 弧辉岩起源于 SCB 东半部下方，它在晚侏罗世开始形成为大陆弧岩浆的镁铁质龙骨。在晚白垩世平板俯冲期间，弧长岩在更内侧的位移和重新附着，可能有助于科罗拉多高原在拉拉米德时间期间相对于相邻地质省的构造稳定性，并可能将该地区预处理为新生代构造作用，例如现在-高原下的日间分层，