Middle Jurassic within-plate granites in West Antarctica and their bearing on the break-up of Gondwanaland
Middle Jurassic within-plate granites in West Antarctica and their bearing on the break-up of Gondwanaland
复制标题
西南极洲中侏罗世板内花岗岩及其对冈瓦纳大陆分裂的影响
DOI：
--
复制
发表时间：
1988
影响因子：
2.7
通讯作者：
W. Vennum
中科院分区：
文献类型：
--
作者：
B. Storey;M. Hole;R. Pankhurst;I. Millar;W. Vennum
西南极洲埃尔斯沃-惠特莫尔山地块中部的五个构造后花岗岩体形成了一套独特的地球化学组合。它们都具有S型花岗岩的某些特征，是不典型的活动大陆边缘。它们的成分范围从板内花岗岩（WPG）端员，具有最低的87 Sr/86 Sr初始比值（0.707），花岗岩具有更显着的地壳签名和高初始比值（0.722）。花岗质岩套侵位于中侏罗世一个有限的时间间隔内，与广泛的Ferrar-Karoo-塔斯曼镁铁质岩套同时，就在冈瓦纳超大陆解体之前。岩石成因模型表明，WPG端员可能已经完全衍生的富集幔源Ferrar岩浆的分化，和端员具有最高的初始比例的部分熔融的地壳源。较低的初始143 Nd/144 Nd比和元古代模式年龄与前寒武纪地壳成分相容，但也可能反映了自前寒武纪分异以来与下地壳地球化学耦合的富集岩石圈地幔的部分继承，例如费拉尔超群岩浆的情况。从这些花岗岩的数据是一致的大规模底侵的镁铁质岩浆和地壳熔融的热扰动在冈瓦纳大陆岩石圈在某种程度上有关的超大陆的解体。
Five post-tectonic granitic plutons isolated within the central Ellsworth-Whitmore mountains crustal block in West Antarctica form a distinctive geochemical suite. All have some characteristics of S-type granites and are atypical of active continental margins. They range in composition from a within-plate granite (WPG) end member, with the lowest 87Sr/86Sr initial ratio (0.707), to granites with a much more marked crustal signature and high initial ratios (0.722). The granitic suite was emplaced over a restricted Middle Jurassic time interval at the same time as the extensive Ferrar-Karoo-Tasman mafic suite and just prior to the disintegration of the supercontinent Gondwanaland. Petrogenetic modelling suggests that the WPG end member could have been derived entirely by differentiation of the enriched mantle-derived Ferrar magma, and the end member with the highest initial ratio by partial melting of a crustal source. Low initial 143Nd/144Nd ratios and Proterozoic model ages are compatible with a Precambrian crustal component but may alternatively, as in the case of Ferrar Supergroup magmas, reflect partial inheritance from enriched lithospheric mantle geochemically coupled to the lower crust since Precambrian differentiation. Data from these granites are consistent with large-scale underplating of mafic magma and crustal melting in response to a thermal disturbance in the Gondwanaland lithosphere related in some way to break-up of the supercontinent.