The Jinchuan Ultramafic Intrusion: Cumulate of a High-Mg Basaltic Magma
The Jinchuan Ultramafic Intrusion: Cumulate of a High-Mg Basaltic Magma
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DOI：
10.1093/petrology/33.2.277
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发表时间：
1992-04
影响因子：
3.9
通讯作者：
G. Chai;A. J. Naldrett
中科院分区：
文献类型：
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作者：
G. Chai;A. J. Naldrett
金川岩体是侵位于中朝地台西南缘龙首山隆起区的超基性岩墙状岩体。侵入体长6公里，宽350米，并拥有一个主要的镍-铜硫化物存款。它包括三个分庭：西部、中西部和东部。两个西部亚室是狭窄而深，都是从纯橄榄岩的核心通过二辉橄榄岩向边缘的橄榄辉石岩横向分带。东部亚室浅而宽，垂直分层从底部的纯橄榄岩到上部的二辉橄榄岩和斜长二辉橄榄岩，再回到上部的二辉橄榄岩。所有样品含有> 24重量% MgO，当重新计算为100%无水时，大部分具有> 35%。MgO与其他成分呈负线性相关（除Na 2 O、K2 O、Sr和Rb等少数可能受蚀变影响的成分外），表明岩石基本上是由堆积橄榄石和原生岩浆混合而成。电子探针分析表明，橄榄石成分范围为Fo 79 ~ Fo 86，大部分介于Fo 83 ~ Fo 85之间。原始岩浆的MgO/（MgO + FeO）值计算为1.64，MgO含量估计为≤ 12 wt.%。因此，金川岩体可能是与大陆裂谷作用有关的高镁玄武质岩浆侵入体的超镁铁质堆晶部分，金川岩体西部的两个次级岩浆房是通向原始岩浆房的主要通道，它们的分带是由岩浆流动分异作用形成的。东部亚室可能代表了岩浆房的较高水平，在那里，结晶的特点是对流和定期补充。固结后，金川岩体向东倾斜，因此西部副室的较深部分现在暴露于与东部副室的较浅部分相同的侵蚀水平。
The Jinchuan intrusion, situated in Gansu province, China, is an ultramafic dyke-like body emplaced in the Longshoushan uplifted terrain on the southwest margin of the Sino-Korea platform. The intrusion is 6 km long, 350 m wide and hosts a major Ni-Cu sulfide deposit. It comprises three subchambers: the west, west-central, and east. The two western subchambers are narrow and deep, and both are laterally zoned from dunite in the core through Iherzolite to olivine pyroxenite toward the margins. The eastern subchamber is shallow and wide, and it shows vertical stratification grading from dunite at the base upward into Iherzolite and plagioclase Iherzolite, then back to Iherzolite at the top.Sixty rock samples from the Jinchuan intrusion have been analyzed for major and trace elements, and 54 samples were also analyzed for the REE. All samples contain > 24 wt.% MgO, with the majority having > 35% when recalculated to 100% anhydrous. Negative linear correlations are observed between MgO and most other constituents (except for a few such as Na2O, K2O, Sr, and Rb, which may have been affected by alteration), and it appears that the rocks were essentially formed as mixtures of cumulus olivine and primary magma.Electron microprobe analyses show olivine compositions from Fo79to Fo86, with most between Fo83and Fo85. The MgO/(MgO + FeO) value of the primary magma is calculated to have been Ü 0.64, and its MgO content is estimated to have been Ü12 wt.%. Thus, the Jinchuan igneous body is probably the ultramafic cumulate portion of an intrusion of a high-magnesium basaltic magma related to continental rifting.We suggest that the two western subchambers of the Jinchuan intrusion represent the main conduit to the original magma chamber and that their zoning was formed by flow differentiation. The eastern subchamber probably represents a higher level of the magma chamber, where crystallization was marked by convection and periodic replenishment. After consolidation, the Jinchuan intrusion was tilted to the east so the deeper parts of the western subchambers are now exposed to the same erosion level as the shallower part of the eastern subchamber.