Deciphering garnet genesis in meta-igneous rocks: An example from the Jiao-Liao-Ji Belt, North China Craton.
Deciphering garnet genesis in meta-igneous rocks: An example from the Jiao-Liao-Ji Belt, North China Craton.
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破译变火成岩中石榴石的成因：以华北克拉通胶辽吉带为例。
DOI：
10.1016/j.precamres.2020.105871
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发表时间：
2020
影响因子：
3.8
通讯作者：
Palin Richard
中科院分区：
文献类型：
--
作者：
Huang Guangyu;Guo Jinghui;Cui Weilong;Palin Richard
石榴石在变质岩中很常见，可以用来有效地约束造山过程中经历的压力-温度条件；然而，它也可能在许多类型的岩浆中结晶为主相，这可能会使破译变质火成岩的岩石成因变得复杂。本研究结合石榴石和锆石的年代学和地球化学分析，对北中国克拉通胶辽冀带无斜长镁铁质麻粒岩中石榴石的成因进行了综合研究。稀土元素配分模式显示石榴石与变质锆石之间存在平衡关系，表明石榴石具有变质成因。U-Pb测年结果表明，石榴石的全晶年龄为1.83Ga，核区和边区年龄基本一致，略低于锆石记录的变质年龄(1.87Ga)。石榴石和锆石的年龄差异可能是由于它们在U-Pb同位素体系中的闭合温度不同所致。石榴石+单斜辉石+钾长石+钛铁矿的矿物组合具有结构平衡特征，确定了830-880°C的峰值压温条件为0.8-1.2 Gpa。考虑到本文计算的高压变质作用年龄(c.1.87Ga)比前人研究提出的西辽东半岛的c.1.95-1.90Ga要早，我们认为c.1.95-1.87Ga代表了龙岗地块与南缘地块的递进碰撞时间，西部的碰撞略早于东部。
Garnet is common in metamorphic rocks and can be used to efficiently constrain pressure–temperature conditions experienced during orogenesis; however, it may also crystallize as a primary phase in many types of magma, which can complicate deciphering the petrogenesis of meta-igneous rocks. In this study, geochronological and geochemical analyses of garnet and zircon were integrated to constrain garnet genesis in plagioclase-absent mafic granulite from the Jiao-Liao-Ji Belt, North China Craton. The rare earth element patterns show an equilibrium relationship between garnet and metamorphic zircon, indicating that garnet has a metamorphic origin. U–Pb dating shows that garnet has a whole-grain age of c. 1.83 Ga, with no difference between core and rim domains, which is slightly younger than metamorphic ages recorded by zircon (c. 1.87 Ga). The age difference between garnet and zircon is likely a result of differences in their closure temperature for the U–Pb isotope system. The mineral assemblage garnet + clinopyroxene + K-feldspar + titanite shows textural equilibration and was used to determine peak pressure–temperature conditions of 0.8–1.2 GPa at 830–880 °C. Given the age of high-pressure metamorphism (c. 1.87 Ga) calculated here being younger than c. 1.95–1.90 Ga proposed by previous studies for the west Liaodong peninsula, we suggest that c. 1.95–1.87 Ga represents the timing of progressive collision between the Longgang Block and the Nangrim Block, with the western part having collided slightly earlier than the eastern part.