Whole-lithosphere shear during oblique rifting
Whole-lithosphere shear during oblique rifting
复制标题
倾斜裂谷期间的全岩石圈剪切
DOI：
10.1130/g49603.1
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发表时间：
2021
期刊：
影响因子：
5.8
通讯作者：
Phillips, Fred M.
中科院分区：
文献类型：
--
作者：
Lutz, Brandon M.;Axen, Gary J.;van Wijk, Jolante W.;Phillips, Fred M.
控制大陆全岩石圈剪切带形成的过程是有争议的，但它们的存在要求岩石圈从底部到顶部是机械耦合的。我们的文件形成的右旋，整个岩石圈剪切带在死亡谷地区（DVR），美国西南部。岩石圈-软流圈边界和莫霍面深度梯度的右旋偏转垂直叠加，确定了一个20-50 km宽的岩石圈下部剪切带，剪切力约为60 km。这些偏转是上地壳断裂带的基础，该断裂带自大约1980年以来累积了约60公里的右旋滑动。8-7马，当我们推断整个岩石圈剪切开始时。这种右旋偏移量小于上地壳断裂带（约90 km，约100 km）的净右旋偏移量。13-0 Ma）和总上地壳伸展（~ 250公里，约。16-0 Ma）。我们表明，在CA。8-7 Ma时，弱中地壳的上地壳变形与下地壳和地幔岩石圈的变形不耦合。在16和7马之间，拆离滑动减薄，隆起，冷却，从而加强了中地壳，这是在变质核杂岩与整个岩石圈剪切带搭配暴露。中地壳强化耦合层状岩石圈垂直，因此使整个岩石圈右旋剪切。在厚地壳存在（如在前16马DVR），中地壳加强可能是一个必要条件，整个岩石圈剪切。
Processes controlling the formation of continental whole-lithosphere shear zones are debated, but their existence requires that the lithosphere is mechanically coupled from base to top. We document the formation of a dextral, whole-lithosphere shear zone in the Death Valley region (DVR), southwest United States. Dextral deflections of depth gradients in the lithosphere-asthenosphere boundary and Moho are stacked vertically, defining a 20–50-km-wide, lower lithospheric shear zone with~ 60 km of shear. These deflections underlie an upper-crustal fault zone that accrued~ 60 km of dextral slip since ca. 8–7 Ma, when we infer that whole-lithosphere shear began. This dextral offset is less than net dextral offset on the upper-crustal fault zone (~ 90 km, ca. 13–0 Ma) and total upper-crustal extension (~ 250 km, ca. 16–0 Ma). We show that, before ca. 8–7 Ma, weak middle crust decoupled upper-crustal deformation from deformation in the lower crust and mantle lithosphere. Between 16 and 7 Ma, detachment slip thinned, uplifted, cooled, and thus strengthened the middle crust, which is exposed in metamorphic core complexes collocated with the whole-lithosphere shear zone. Midcrustal strengthening coupled the layered lithosphere vertically and therefore enabled whole-lithosphere dextral shear. Where thick crust exists (as in pre–16 Ma DVR), midcrustal strengthening is probably a necessary condition for whole-lithosphere shear.