Raumid地块(S. Pamir)高分选花岗岩:氧同位素与地球化学研究

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
E. O. Dubinina, A. S. Avdeenko, V. N. Volkov, S. A. Kossova, E. V. Kovalchuk
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引用次数: 1

摘要

以Raumid地块始新世花岗岩为例,研究了其结晶分异、逆向同位素交换和自变质作用的过程。Raumid地块由8个侵入期组成,是一个“天然实验室”。这项工作是基于对该地块每个侵入期的代表性样品的氧同位素、岩石学和地球化学研究。对所有造岩矿物(Qz、Pl、Kfs、Bt)及其蚀变品种进行了同位素和地球化学研究。根据地球化学特征,Raumid花岗岩既属于a型花岗岩,也属于高分异的i型花岗岩。我们的研究结果表明,Raumid地块的岩石并不像之前假设的那样,是西藏中部羌塘地块或Vanj杂岩的始新世花岗岩类的地球化学模拟物(Chapman et al., 2018)。我们估计Raumid岩体的长硅熔体分异发生在T = 750 ~ 800℃,P = 4.5 ~ 7.8 kbar,主要受Pl结晶控制。熔体侵入浅成带至少分为两个阶段:早期(γ - 1 - γ - 3)和晚期(γ - 4 - γ - 8),尽管γ - 7和γ - 8相的岩石可能形成另外一个单独的阶段。石英氧同位素体系的封闭温度(TQz)为420 ~ 610℃。考虑了熔体多次侵入对TQz和表观冷却速率的影响。对蚀变和未蚀变矿物的研究表明,自变质作用与冷却岩石中的逆行氧同位素交换有部分重叠。模拟的Pl和Kfs蚀变δ18О值很好地描述了在Raumid岩浆结晶过程中释放的有限含量的水流体(W/M = 0.3 ~ 0.05)发生结晶时观测到的同位素数据。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Highly Fractionated Granites of the Raumid Massif (S. Pamir): Oxygen Isotope and Geochemical Study

Highly Fractionated Granites of the Raumid Massif (S. Pamir): Oxygen Isotope and Geochemical Study

The processes of crystallization differentiation, retrograde isotopic exchange, and autometamorphism are considered with reference to the Eocene granites of the Raumid massif, which consists of eight intrusive phases and serves as an example of a “natural laboratory”. The work is based on oxygen isotope, petrographic, and geochemical study of representative samples from each intrusive phase of the massif. The isotopic and geochemical studies were carried out for all rock-forming minerals (Qz, Pl, Kfs, Bt) and their altered varieties. Based on geochemical features, the Raumid granites correspond both to A-type granites and to highly fractionated I-type granites. Our results show that the rocks of the Raumid massif are not the geochemical analog of the Eocene granitoids from the Qiangtang terrane of the Central Tibet or the Vanj complex, as it previously assumed (Chapman et al., 2018). We estimated that differentiation of felsic melts of the Raumid pluton occurred at T = 750–800°C, and P = 4.5–7.8 kbar and was mainly controlled by Pl crystallization. The melts were intruded into the hypabyssal zone in at least two stages: early (γ1–γ3) and late (γ4–γ8), although it is possible that the rocks of the γ7 and γ8 phases formed an additional separate stage. The closure temperature of the oxygen isotopic system of quartz (TQz) ranges from 420 to 610°C. The effect of the multiple intrusions of the melts on the TQz and apparent cooling rates is considered. The study of altered and unaltered minerals showed that autometamorphism partially overlapped with the retrograde oxygen isotope exchange in the cooling rock. The modelled δ18О values during Pl and Kfs alteration describes well the observed isotope data when the crystallization takes place at limited content of water fluid (W/M = 0.3–0.05) which could release during the Raumid’s magmas crystallization.

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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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