Role of subduction-plate boundary forces during the initial stages of Gondwana break-up: evidence from the proto-Pacific margin of Antarctica
Role of subduction-plate boundary forces during the initial stages of Gondwana break-up: evidence from the proto-Pacific margin of Antarctica
复制标题
冈瓦纳大陆破裂初始阶段俯冲板块边界力的作用：来自南极洲原太平洋边缘的证据
DOI：
10.1144/gsl.sp.1992.068.01.10
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
H. Wever
中科院分区：
文献类型：
--
作者：
B. Storey;T. Alabaster;M. Hole;R. Pankhurst;H. Wever
在南极西部冈瓦纳板块，早期裂解与大的舌状-卡鲁-塔斯曼玄武岩区有关。这个板块内省的形成与活动边缘构造和沿南极半岛沿着的原太平洋边缘岩浆岩套以及与南美洲南部和南格鲁吉亚的Rocas Verdes边缘盆地系统相关的广泛Tobífera火山岩套的发展同步。拉张作用与俯冲和岩浆中心向海洋的迁移同时发生，导致弧后和弧内背景下形成了一个广泛的拉张区。高地温梯度和玄武岩底侵作用导致南极半岛东海岸地壳熔融，形成双峰式玄武岩-流纹岩套。富含大离子亲石元素的初始裂陷岩浆至少在罗卡斯维迪斯盆地的部分地区被过渡化学的早期漂移岩浆继承，然后被代表岩石圈破裂和海底扩张的整个软流圈MORB岩浆继承。提出了一个板块相互作用模型的冈瓦纳大陆解体的初始阶段有关的地幔熔融的广泛区域减少俯冲板块边界力。在侏罗纪从冈瓦纳挤压岩石圈伸展的变化可能与从浅俯冲到陡俯冲的变化，以及板块边界带参数变化引起的俯冲速率减缓有关。压缩边界应力的可能减少可能使无侧限的、过厚的二叠-三叠纪地壳由于重力不稳定而伸展，从而促进了破裂。我们认为，破裂不是羽流相关的，但由于在区域应力场变化与不断变化的板块边界力。大陆地壳被置于张力下，岩石圈大量减薄，富集地幔源减压熔融，形成板内岩浆活动的广泛线性带。卡鲁省下的地幔柱的存在可能已经热弱化了岩石圈，并引起了局部裂谷，导致了东冈瓦纳和西冈瓦纳的最终分离。
Abstract In the West Antarctic sector of Gondwana, early stages of break-up are associated with the large Antarctic-Karoo-Tasman basalt province. Formation of this within-plate province was synchronous with active margin tectonics and development of both a proto-Pacific margin magmatic suite along the Antarctic Peninsula and the extensive Tobífera volcanic suite associated with the Rocas Verdes marginal basin system of southern South America and South Georgia. Extension, concurrent with subduction and oceanward migration of the magmatic focus, resulted in a broad extensional province in a back-arc and intra-arc-setting. High geothermal gradients and basalt underplating caused crustal melting on the east coast of the Antarctic Peninsula and formation of bimodal basalt-rhyolite suites. Large-ion lithophile element enriched initial rifting magmas were succeeded, at least in part of the Rocas Verdes basin, by early drift magmas of transitional chemistry and then by entirely asthenospheric MORB magmas representing lithospheric rupture and sea-floor spreading. A plate interaction model is proposed for the initial stages of Gondwana break-up relating the broad zone of mantle melting to a reduction in subduction-plate boundary forces. The change from Gondwanide compression to lithospheric extension in the Jurassic may be linked to a change from shallow to steeply dipping subduction, and to a slowing of subduction rates caused by a change in plate boundary zone parameters. A possible reduction of compressive boundary stresses may have enabled unconfined, overthickened Permo-Triassic crust to extend because of gravitational instability, thus facilitating break-up. We suggest that break-up was not plume-related, but was due to variations in the regional stress field associated with changing plate-boundary forces. The continental crust was placed under tension with substantial lithospheric thinning and decompression melting of an enriched mantle source forming the broad linear zone of within-plate magmatism. The presence of a plume beneath the Karoo province may have thermally weakened the lithosphere and induced local rifting, contributing to, but not causing the eventual separation of East and West Gondwana.