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首页> 外文期刊>Journal of Asian earth sciences >Reworked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intrusion, Nanling Range, South China
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Reworked restite enclave: Petrographic and mineralogical constraints from the Tongshanling intrusion, Nanling Range, South China

机译：重做的重晶岩飞地：华南南岭山脉铜山岭侵入岩的岩石学和矿物学约束

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摘要

Microgranular enclaves, which can provide important petrogenetic indications for the host granitoids, are commonly observed in the Middle-Late Jurassic Cu-Pb-Zn-bearing granodiorites in the Nanling Range of South China. The origin of these Cu-Pb-Zn-bearing granodiorites is still controversial, with two different hypotheses: crust-mantle mixing and partial melting of the mafic lower crust, primarily based on geochemistry and geochronology. Detailed petrographic and mineralogical studies have been carried out on the Tongshanling granodiorite and its microgranular enclaves to provide new textural and compositional constraints on the petrogenesis. The microgranular enclaves have dioritic compositions with a mineralogy dominated by plagioclase, amphibole, and biotite. Abundant residual materials, such as mafic mineral clots, inherited and metamorphic zircon, and Ca-rich core plagioclase, occur in the enclaves and are in favor of a restite origin. The amphibole-rich clots are considered as vestiges of residual pyroxene-rich precursors from the source. Three different types of amphibole, i.e., magmatic, metamorphic, and magma reworked metamorphic amphibole, have been recognized in the granodiorite and its enclaves. The magmatic amphibole occurs as enclosed and idiomorphic isolated crystals in the granodiorite with Al and Si contents of 1.34-2.12 apfu (atoms per formula unit) and 6.25-6.88 apfu, respectively, and a Sigma REE content of 307-764 ppm. The metamorphic amphibole, with a granoblastic triple-junction texture, occurs as aggregated crystals dominantly in the enclaves and a few in the granodiorite. It has actinolitic compositions (Al: 0.31-0.81 apfu, Si: 7.33-7.72 apfu) and distinctly lower contents of incompatible elements (Sigma REE: 99-146 ppm). The magma reworked amphibole has intermediate compositions (Al: 0.81-1.59 apfu, Si: 6.71-7.35 apfu, Sigma REE: 317-549 ppm) between the magmatic and metamorphic amphibole. The zonal amphibole-rich clots exhibit increasing Al and decreasing Si contents from interior amphibole to exterior amphibole and also from core to rim in amphibole grains, and the outer parts of enclave magmatic zircon have higher ThO2 + UO2 contents and lower Zr/Hf ratios than the inner parts, showing the process of magma reworking of the restite enclaves. Based on the textural and compositional evidence, these microgranular enclaves are thought to be reworked restite enclaves. This is also supported by thermobarometric calculation. A model illustrating the formation process of reworked restite enclave has been proposed. Combined with previous experimental studies of partial melting, the Tongshanling granodiorite is deduced to be derived from dehydration melting of amphibolite in the mafic lower crust. The fertile amphibolitic source is beneficial to the formation of Cu-Pb-Zn-bearing granodiorites in the Nanling Range.
机译：在中国南方南岭地区晚侏罗世含铜-铅-锌的花岗闪长岩中普遍观察到微粒飞地，可以为宿主类花岗岩提供重要的成岩指示。这些含铜，铅，锌的花岗闪长岩的起源仍存在争议，有两个不同的假设：地壳幔混合和铁镁质下壳的部分熔融，这主要是基于地球化学和地球年代学。已经对铜山岭花岗闪长岩及其微细颗粒飞地进行了详细的岩石学和矿物学研究，从而为岩石成因提供了新的构造和成分约束。微颗粒的飞地具有闪长岩的成分，其矿物学以斜长石，闪石和黑云母为主。飞地中存在大量的残留物质，例如铁镁质矿物凝块，继承的和变质的锆石以及富含Ca的核心斜长石，它们有利于重晶石的起源。富含闪石的凝块被认为是来源中残留的富含辉石的前体的痕迹。在花岗闪长岩及其飞地中已认识到三种不同类型的闪石，即岩浆，变质和岩浆再造变质闪石。岩浆闪石在花岗闪长岩中以封闭的和同形的分离晶体出现，Al和Si含量分别为1.34-2.12 apfu（原子/公式单位）和6.25-6.88 apfu，Sigma REE含量为307-764 ppm。变质的闪石，具有颗粒状的三结结构，以聚集晶体的形式主要存在于飞地，少数存在于花岗闪长岩中。它具有光化树脂组成（Al：0.31-0.81 apfu，Si：7.33-7.72 apfu）和不相容元素的含量明显降低（Sigma REE：99-146 ppm）。岩浆重做的闪石在岩浆和变质闪石之间具有中间组成（Al：0.81-1.59 apfu，Si：6.71-7.35 apfu，Sigma REE：317-549 ppm）。从闪石内部到闪石的外部，以及闪石中从核心到边缘，带状闪石丰富的凝块显示出增加的Al和降低的Si含量，飞地岩浆锆石的外部具有较高的ThO2 + UO2含量和较低的Zr / Hf比内部部分，显示了重晶岩飞地的岩浆改造过程。根据质地和成分证据，这些微细颗粒飞地被认为是重做的重辉石飞地。热压计算也支持这一点。提出了一个模型，说明重做的重晶岩飞地的形成过程。结合以前的部分熔融实验研究，推断铜山岭花岗闪长岩是由镁铁矿下部地壳中闪石的脱水熔融而得。肥沃的两性来源有利于南岭山脉含铜铅锌花岗闪长岩的形成。

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