A crucial geologic test of Late Jurassic exotic collision versus endemic re-accretion in the Klamath Mountains Province, western United States, with implications for the assembly of western North America
A crucial geologic test of Late Jurassic exotic collision versus endemic re-accretion in the Klamath Mountains Province, western United States, with implications for the assembly of western North America
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DOI：
10.1130/b35981.1
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发表时间：
2021-07
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通讯作者：
Todd A. LaMaskin;Jonathan A. Rivas;D. Barbeau;J. Schwartz;J. A. Russell;A. Chapman
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作者：
Todd A. LaMaskin;Jonathan A. Rivas;D. Barbeau;J. Schwartz;J. A. Russell;A. Chapman
对地球物理和地质数据的不同解释导致了关于大陆尺度板块构造、俯冲极性和前白垩纪中期北美板块边缘碰撞事件发生时间的争论。一套模型涉及遥远的“外来”碎屑岩沿着沿着西倾俯冲带与大陆边碰撞和增生，而第二套模型涉及大陆边下长期存在的东倾俯冲，以及北美板块西部边缘许多中生代碎屑岩的边缘或“地方性”起源。在这里，我们提出了新的碎屑锆石U-Pb年龄从碎屑岩的响尾蛇溪和西部克拉马斯山的克拉马斯北方加州和南部俄勒冈州，这些对比模型提供了一个测试。我们的数据表明，部分响尾蛇溪盖层序列（盐溪组合）的年龄不超过约。170-161 Ma（中-早侏罗世），含62-83%前寒武纪碎屑锆石颗粒。Galice组的浊积岩砂岩样品的年龄不超过约。158-153 Ma（中晚侏罗世），含15-55%前寒武纪碎屑锆石颗粒。基于我们的数据发表的岩浆和碎屑岩年龄的外来和地方性模型（一个重要的地质测试）预测的种源情景的比较，我们表明，我们的样品可能来自以前增生的，较老的火山的克拉马斯山脉和内华达州山脉，以及活动弧源，与一定程度的贡献在大陆内部的回收来源。我们的观察结果与基于北美近海形成的外来洋内弧的古地理重建不一致。与此相反，纳入回收的碎屑从旧的克拉马斯山脉和内华达州山脉，以及北美，到响尾蛇溪和西部克拉马斯山脉前晚侏罗世变形增加了大量的支持地方性模型。我们的研究结果表明，在长期的，东倾俯冲，开放和随后关闭的边缘Galice/约瑟芬盆地发生在原地伸展和随后的收缩的结果。我们的研究结果表明，构造模型调用异国情调，洋内群岛组成的科迪勒拉弧火山岩失败的关键地质测试的火山岩的建议异国情调的起源，并支持发生东倾，前中白垩纪俯冲下北美大陆边缘。
Differing interpretations of geophysical and geologic data have led to debate regarding continent-scale plate configuration, subduction polarity, and timing of collisional events on the western North American plate margin in pre–mid-Cretaceous time. One set of models involves collision and accretion of far-traveled “exotic” terranes against the continental margin along a west-dipping subduction zone, whereas a second set of models involves long-lived, east-dipping subduction under the continental margin and a fringing or “endemic” origin for many Mesozoic terranes on the western North American plate margin. Here, we present new detrital zircon U-Pb ages from clastic rocks of the Rattlesnake Creek and Western Klamath terranes in the Klamath Mountains of northern California and southern Oregon that provide a test of these contrasting models. Our data show that portions of the Rattlesnake Creek terrane cover sequence (Salt Creek assemblage) are no older than ca. 170–161 Ma (Middle–early Late Jurassic) and contain 62–83% Precambrian detrital zircon grains. Turbidite sandstone samples of the Galice Formation are no older than ca. 158–153 Ma (middle Late Jurassic) and contain 15–55% Precambrian detrital zircon grains. Based on a comparison of our data to published magmatic and detrital ages representing provenance scenarios predicted by the exotic and endemic models (a crucial geologic test), we show that our samples were likely sourced from the previously accreted, older terranes of the Klamath Mountains and Sierra Nevada, as well as active-arc sources, with some degree of contribution from recycled sources in the continental interior. Our observations are inconsistent with paleogeographic reconstructions that are based on exotic, intra-oceanic arcs formed far offshore of North America. In contrast, the incorporation of recycled detritus from older terranes of the Klamath Mountains and Sierra Nevada, as well as North America, into the Rattlesnake Creek and Western Klamath terranes prior to Late Jurassic deformation adds substantial support to endemic models. Our results suggest that during long-lived, east-dipping subduction, the opening and subsequent closing of the marginal Galice/Josephine basin occurred as a result of in situ extension and subsequent contraction. Our results show that tectonic models invoking exotic, intra-oceanic archipelagos composed of Cordilleran arc terranes fail a crucial geologic test of the terranes’ proposed exotic origin and support the occurrence of east-dipping, pre–mid-Cretaceous subduction beneath the North American continental margin.