扬子地块西部新发现的a型花岗岩及其地球化学特征:华南克拉通下脊俯冲的证据

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
Awei Mabi, Yanlong Li, Mingchun Zhang, Zhengxi Yang, Niuben Yu
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引用次数: 0

摘要

在扬子地块西部,有大量的新元古代花岗质侵入岩,其南北长度超过700公里。本文利用锆石U-Pb年龄、Lu-Hf同位素及全岩地球化学资料,表明该区石绵花岗岩体由原来认为的s型花岗岩体为a型花岗岩体。本研究选取的新鲜样品主要为斑状黑云母二长花岗岩。弱过铝质a2亚型花岗岩,SiO2、K2O含量高,CaO、Na2O含量低,具有高硅、富钾、低钠的特征。富不相容微量元素,富镁基硅酸盐和长石中不相容微量元素,具有REE、Ga丰度高,Al、Ni、Ba、Sr、Eu丰度低的化学特征。主微量元素行为表明,该花岗岩经历了超前的分异结晶过程,可能是由地壳部分熔融形成的。锆石U-Pb年龄显示石冕花岗质岩体侵位时间为728±20 Ma。花岗岩的平均176Hf/177Hf值为0.282363 (εHf = 0.8), 94%的置信区间为0.282334 ~ 0.282384 (εHf = - 0.1 ~ 1.7),表明花岗岩来源于幼年大陆地壳的重熔。本文认为,石绵新发现的a型花岗岩更可能是在隆起俯冲形成的板块窗的拉张背景下形成的,这不仅可以解释大量花岗岩类的形成,也可以解释扬子地块西部玄武岩、珠光枕状熔岩和ssz型蛇绿岩的形成。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Newly Identified A-type Granite in Western Yangtze Block and Its Geochemistry Characteristics: Evidence for Ridge Subduction beneath the South China Craton

Newly Identified A-type Granite in Western Yangtze Block and Its Geochemistry Characteristics: Evidence for Ridge Subduction beneath the South China Craton

Numerous Neoproterozoic granitic intrusions occur over a north-south distance of more than 700 km in the western Yangtze Block. In this paper, we use zircon U-Pb age, Lu-Hf isotopic, and whole-rock geochemical data to show that the Shimian granitic pluton, which was previously thought to be S-type granite in the area, is actually A-type granite. The selected fresh samples for this study are mainly porphyritic biotite monzogranites. They are weak peraluminous, A2-subtype granites, displaying high contents of SiO2 and K2O, low CaO, and Na2O, with the characteristics of high silica, rich potassium, and low sodium. They are enriched in incompatible trace elements, but low in trace elements compatible in mafic silicates and feldspars, and they are chemically characterized by having high REE and Ga abundances and low Al, Ni, Ba, Sr, and Eu abundances. The major and trace element behavior suggests that the granites underwent the process of advanced fractional crystallization and were likely generated by crustal partial melting. Zircon U-Pb age shows the Shimian granitic pluton was emplaced at 728 ± 20 Ma. The studied granites yield an average 176Hf/177Hf value of 0.282363 (εHf = 0.8) with a 94% confidence interval of 0.282334 to 0.282384 (εHf = −0.1 to 1.7), indicating that they are derived from the remelting of juvenile continental crust. We suggest that this newly identified A-type granite at Shimian, southwestern China, was more plausibly generated in an extensional setting as a result of slab window caused by ridge subduction, which can account not only for the formation of voluminous granitoids, but also for the basalts, boninitic pillow lavas, and SSZ-type ophiolites in western Yangtze Block.

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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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