Geochemistry and petrogenesis of the Cretaceous A‐type granites in the Laoshan granitic complex, eastern China
Geochemistry and petrogenesis of the Cretaceous A‐type granites in the Laoshan granitic complex, eastern China
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DOI：
10.1111/iar.12070
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发表时间：
2014-09
期刊：
影响因子：
1.5
通讯作者：
Q. Yan;Xuefa Shi
中科院分区：
文献类型：
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作者：
Q. Yan;Xuefa Shi
测定了华南和华北构造块体之间三叠纪缝合线东侧崂山花岗杂岩碰撞后花岗岩的主量、微量元素组成及Sr、Nd、Pb同位素组成。花岗岩为碱性A型花岗岩，可进一步划分为A1型花岗岩。这些花岗岩的微量元素组成介于洋岛玄武岩和富洋中脊玄武岩之间，Ba、Sr、P和Ti的富集可能归因于矿物分馏作用，Cs、Rb、Th和U的富集可能是由于板块流体的参与。崂山花岗岩的同位素特征为富地幔1型（EMI）样端元与下大陆地壳（LCC）的混合。我们认为，形成崂山A1花岗岩的岩浆是来自类似EMI的脱层榴辉岩（随后被中生代太平洋俯冲板块释放的流体富集）和来自LCC的岩浆的混合物，后者由该地区上一代I型花岗岩的麻粒岩或变质残留物组成。混合岩浆在进入崂山花岗岩体形成a型花岗岩之前，经历了以强碱长石为主的分选作用。
Major element and trace element compositions, and Sr, Nd and Pb isotopic compositions for postcollisional granites from the Laoshan granitic complex, in the eastern side of the Triassic suture between the South China and North China tectonic blocks were determined. The granites are alkaline, A‐type and can be further classified as A1 granites. The trace element composition of these granites is transitional between those of oceanic island basalt and enriched mid‐oceanic ridge basalt, with depletions in Ba, Sr, P, and Ti that can be ascribed to mineral fractionation and enrichments in Cs, Rb, Th and U possibly resulted from the involvement of slab fluids. The isotopic signature of Laoshan granites represent a mixture between an enriched mantle type 1 (EMI)‐like end‐member and lower continental crust (LCC). We propose that the magmas that formed the Laoshan A1 granites are a mixture between those derived from the EMI‐like delaminated eclogitic rocks (subsequently enriched by fluids released from Mesozoic Pacific subducted slab) and those derived from the LCC, which consists of granulites or metamorphic residues from the prior generation of I‐type granites in the region. The mixed magmas then experienced a strongly alkali feldspar‐dominated fractionation prior to their emplacements as A‐type granites in the Laoshan granitic complex.