Cooling history of the St. Elias syntaxis, southeast Alaska, revealed by geochronology and thermochronology of cobble‐sized glacial detritus
Cooling history of the St. Elias syntaxis, southeast Alaska, revealed by geochronology and thermochronology of cobble‐sized glacial detritus
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通过鹅卵石大小的冰川碎屑的地质年代学和热年代学揭示了阿拉斯加东南部圣埃利亚斯构造的冷却历史
作者：
Falkowski;Enkelmann;Pfänder;Stübner;Ehlers
我们使用鹅卵石大小的冰川碎屑中的多个温度计时器和地质计时器研究了阿拉斯加东南部冰盖圣埃利亚斯构造地区的折返作用的时空演化。多个温度计时器揭示了来自两个最大的构造集水区的27个冰川运输的鹅卵石从500°C到60°C的冷却历史。研究了鹅卵石岩性和21个锆石U-Pb年龄(~277~31 Ma)，以确定样品的来源。此外，利用8个角闪石和7个生物陨石40Ar/39Ar年龄(分别为~276~16 Ma和~50~42 Ma)、4个锆石和6个磷灰石(U-Th)/He年龄(分别为~35~4.8 Ma和~4.2~0.6 Ma)和4个磷灰石裂变径迹年龄(~17~1.6 Ma)重建了鹅卵石个体的冷却历史。另外四个来自费尔韦瑟山脉的基岩样品获得了三个40Ar/39Ar年龄，年龄在~42至5 Ma之间。汇编了圣埃利亚斯山脉和费尔韦瑟山脉已发表的基岩和新的鹅卵石冷却历史，揭示了区域新生代冷却和折返历史，强调了圣埃利亚斯构造作为挤压和俯冲环境之间的过渡带的位置。新的鹅卵石和基岩数据表明，在~5 Ma开始了快速折返，但在联结区的持续时间(2-3Myr)和数量(~10 Km)有限。这项研究还证明了鹅卵石在揭示原本难以接近的地区的热历史方面的有效性，因为鹅卵石分析结合了基岩和碎屑热年代学的优点。
We investigate the spatiotemporal evolution of exhumation in the ice‐covered St. Elias syntaxis area, southeast Alaska, using multiple thermochronometers and geochronometers from cobble‐sized glacial detritus. Multiple thermochronometers reveal the cooling histories from 500 to 60°C of 27 glacially transported cobbles from the two largest catchments of the syntaxis. Cobble lithologies and 21 zircon U‐Pb ages (~277–31 Ma) were examined to determine sample provenance. Furthermore, eight amphibole and seven biotite40Ar/39Ar ages (~276–16 Ma and ~50–42 Ma, respectively), four zircon and six apatite (U‐Th)/He ages (~35–4.8 Ma and ~4.2–0.6 Ma, respectively), and four apatite fission track ages (~17–1.6 Ma) were used to reconstruct the individual cobble cooling histories. An additional four bedrock samples from the Fairweather Range yielded three biotite40Ar/39Ar ages between ~42 and 5 Ma. A compilation of published bedrock and new cobble cooling histories from the St. Elias Mountains and Fairweather Range reveals the regional Cenozoic cooling and exhumation history, emphasizing the position of the St. Elias syntaxis as a transitional zone between transpression and subduction settings. The new cobble and bedrock data indicate an onset of rapid exhumation at ~5 Ma that was limited in duration (2–3 Myr) and amount (~10 km) in the syntaxial region. This study also demonstrates the usefulness of cobbles for revealing thermal histories of otherwise inaccessible regions as cobble analysis combines advantages of bedrock and detrital thermochronology.
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