Tibetan dichotomy exposed in the Canadian Shield: A lower crustal perspective
Tibetan dichotomy exposed in the Canadian Shield: A lower crustal perspective
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加拿大地盾中暴露的西藏二分法：下地壳视角
DOI：
10.1016/j.epsl.2020.116375
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发表时间：
2020
影响因子：
5.3
通讯作者：
Dumond, Gregory
中科院分区：
文献类型：
--
作者：
Dumond, Gregory
这种行为需要下地壳的弱和强流变二分法。这种行为的证据来自于加拿大地盾西部一个深挖的麻粒岩地体（> 0.6-1.6 GPa）。数据支持了1.95 ~ 1.90 Ga时，长约400 km的脂河剪切带西北部的下地壳处于熔融弱化状态，而东南部的下地壳处于脱水强韧状态。应变局部化和右旋压剪切发生在1.91-1。研究表明，下大陆地壳流变学在<1 m2 ~ 100 m2尺度上具有空间不均匀性。深部地壳流变学也取决于肥力：在无流体熔融（bb0 - 750°C）和麻粒级变质作用中有利于“第一旋回”变质沉积的富含黑云母的原岩，尽管熔体提取会降低这种肥力。较老的和先前脱水的多变质麻粒岩往往较强，不容易受到普遍的下地壳流动的影响。
It has been hypothesized that much of central and eastern Tibet coincides with gravitationally driven flow of weak lower continental crust. Magnetotelluric profiles throughout Tibet reveal several deep crustal zones of high conductivity inferred to represent either melt-weakened channelized flow of deep crust or alternatively, migration of fluids or melts along shear zone-fault systems. In eastern Tibet, some workers suggest that deep crustal flow is diverted around cratonic lithosphere beneath the Sichuan basin. This behavior requires a weak versus strong rheological dichotomy in the lower crust. Evidence for this behavior is presented from a deeply exhumed granulite terrane (>0.6–1.6 GPa) in the western Canadian Shield. Data support the hypothesis that at 1.95–1.90 Ga, lower crust northwest of the >400 km-long Grease River shear zone was melt-weakened while lower crust southeast of the Grease River shear zone was dehydrated and strong. Strain localization and dextral transpressive shearing occurred at 1.91–1.90 Ga along the Grease River shear zone – the locus of a rheological dichotomy that represents a field-based analog for lower crust beneath the eastern Tibetan plateau. This work demonstrates that rheology of the lower continental crust can be spatially heterogeneous at <1 m2to 100s of km2scales. Deep crustal rheology also depends on fertility: melt weakening and flow during fluid-absent melting (>750 °C) and granulite-grade metamorphism is favored in “first-cycle” metasedimentary biotite-rich protoliths, though melt extraction can decrease this fertility. Older and previously dehydrated poly-metamorphic granulites tend to be stronger and less prone to pervasive lower crustal flow.
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DOI：
--
发表时间：
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DOI：
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DOI：
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