Genesis of LCT Pegmatites during Early Paleozoic Orogeny of the North Qinling Orogenic Belt, China: Emplacement Conditions and Structural Control

IF 3.5 3区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY
Jubiao CEN, Yonggang FENG, Ting LIANG, Mengxi WANG, Jianxin ZHANG, Xijuan TAN, Jie ZHANG, Jinggang GAO, Lei HE
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Abstract

The Guanpo pegmatite field in the North Qinling orogenic belt (NQB), China, hosts the most abundant LCT pegmatites. However, their emplacement conditions and structural control remain unexplored. In this contribution, we investigated it combining pegmatite orientation measurement with oxygen isotope geothermometry and fluid inclusion study. The orientations of type A1 pegmatites (Pf < σ2) are predominantly influenced by P- and T-fractures due to simple shearing in Shiziping dextral thrust shear zone during D2 deformation, whereas type A2 pegmatites (contemporaneous with D4) are governed by hydraulic fractures aligned with S0 and S0+1 stemming from fluid pressure (Pf2). Additionally, type B pegmatites (Pfσ2) exhibit orientations shaped by en echelon extensional fractures in local ductile shear zones (contemporaneous with D3). The albite-quartz oxygen isotope geothermometry and microthermometric analysis of fluid inclusions in elbaites from the latest pegmatites (including types B and A2) suggest that the crystallization P-T for late magmatic and hydrothermal stages are 527.5–559.2°C, 320°C, 3.1–3.6 kbar and 2.0 kbar, respectively. Our observations along with previous studies suggest that the genesis of the LCT pegmatites was a long-term, multi-stage event during early Paleozoic orogeny (including the collision stage) of the NQB, and was facilitated by various local fractures.

Abstract Image

中国北秦岭造山带早古生代造山运动中LCT伟晶岩的成因:成岩条件与构造控制
中国北秦岭造山带(NQB)的关坡伟晶岩区拥有最丰富的LCT伟晶岩。然而,它们的成矿条件和构造控制仍未得到探索。在本文中,我们结合伟晶岩方位测量、氧同位素地热测量和流体包裹体研究对其进行了研究。A1型伟晶岩(Pf <σ2)的取向主要受D2变形过程中石子坪向斜推力剪切带的简单剪切导致的P型和T型断裂的影响,而A2型伟晶岩(与D4同期)的取向则受流体压力导致的S0和S0+1型水力断裂的影响(Pf <σ2)。此外,B 型伟晶岩(Pf ≤ σ2)的走向是由局部韧性剪切带(与 D3 同时发生)中的梯状延伸断裂形成的。最新伟晶岩(包括 B 型和 A2 型)中的白云石-石英氧同位素地热测定法和埃洛石中流体包裹体的微热分析表明,岩浆晚期和热液阶段的结晶 P-T 分别为 527.5-559.2°C、320°C、3.1-3.6 千巴和 2.0 千巴。我们的观察结果与之前的研究结果表明,喇嘛塘伟晶岩的成因是古生代造山运动早期(包括碰撞阶段)的一个长期、多阶段事件,并受到各种局部断裂的促进。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Acta Geologica Sinica ‐ English Edition
Acta Geologica Sinica ‐ English Edition 地学-地球科学综合
CiteScore
3.00
自引率
12.10%
发文量
3039
审稿时长
6 months
期刊介绍: Acta Geologica Sinica mainly reports the latest and most important achievements in the theoretical and basic research in geological sciences, together with new technologies, in China. Papers published involve various aspects of research concerning geosciences and related disciplines, such as stratigraphy, palaeontology, origin and history of the Earth, structural geology, tectonics, mineralogy, petrology, geochemistry, geophysics, geology of mineral deposits, hydrogeology, engineering geology, environmental geology, regional geology and new theories and technologies of geological exploration.
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