阿拉善东部波罗斯坦庙杂岩含石榴子石黑云斜长片麻岩的p-t演化及独居石U-Pb年龄

Metamorphic p-t evolution and tectonic implications of garnet-bearing biotite-plagioclase gneiss from the Boluositanmiao Complex of the eastern Alxa Block

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DOI 10.20086/j.cnki.yskw.2025.4202
刊名
Acta Petrologica et Mineralogica
年,卷(期) 2025, 44(4)
作者
作者单位

西北大学地质学系, 大陆演化与早期生命全国重点实验室, 陕西 西安 710069

摘要
波罗斯坦庙杂岩是阿拉善地块东部高级变质杂岩之一,对研究阿拉善地块晚古生代构造演化具有重要的地质意义。本研究对阿拉善地块东部波罗斯坦庙杂岩中的长英质片麻岩进行了详细的野外地质调查、岩相学、LA-ICP-MS独居石U-Pb定年和变质相平衡模拟工作,用于揭示其变质演化特征,进而阐明其形成的构造背景。长英质片麻岩主要由含石榴子石黑云斜长片麻岩和黑云斜长片麻岩两类岩石组成,岩相学观察显示2个含石榴子石黑云斜长片麻岩样品ALS2202和ALS2204记录的峰期变质矿物组合为石榴子石+黑云母+白云母+钛铁矿+斜长石+钾长石+石英+熔体,结合相平衡模拟计算得到2个样品的峰期变质温压条件分别为727~751℃/820~1 030 MPa和730~751℃/930~1 070 MPa。通过石榴子石-黑云母-斜长石-石英(GBPQ)地质温压计计算得到退变质冷却阶段的温压条件为629~672℃/410~490 MPa和620~657℃/330~400 MPa。综合以上变质温压结果, 2个样品均显示顺时针的p-t演化轨迹。LA-ICP-MS独居石U-Pb定年得到含石榴子石黑云斜长片麻岩样品ALS2207和黑云斜长片麻岩ALS2210样品的206Pb/238U加权平均年龄分别为268±4 Ma和255±2 Ma,代表峰期变质作用或深熔作用的时代。根据矿物组合推测波罗斯坦庙杂岩中长英质片麻岩应为副变质岩,结合该岩石记录的变质温压条件和顺时针轨迹,表明波罗斯坦庙杂岩在二叠纪中晚期经历了一次显著的地壳加厚过程,该过程可能与古亚洲洋的闭合有关。
Abstract
The Boluositanmiao Complex in the eastern part of the Alxa Block, is one of the high-grade metamorphic complexes, which has important geological significance for the late Paleozoic tectonic evolution of the Alxa Block. In this paper, a combined study of detailed geological investigation, petrography, LA-ICP-MS monazite U-Pb dating and phase equilibrium modeling, were carried out for felsic gneisses of the Boluositanmiao Complex, which is used to reveal their metamorphic evolution and tectonic implications. Felsic gneisses are mainly composed of garnet-bearing biotite-plagioclase gneiss and biotite-plagioclase gneiss. The garnet-bearing biotite-plagioclase gneiss samples ALS2202 and ALS2204 record peak mineral assemblage of garnet+biotite+muscovite+ilmenite+plagioclase+K-feldspar+quartz+melt. Combined with phase equilibrium modeling, the peak p-t conditions of two samples were constrained at 727~751℃/820~1 030 MPa and 730~751℃/930~1 070 MPa, respectively. In addition, the garnet-biotite-plagioclase-quartz (GBPQ) geothermobarometry yields relatively low metamorphic p-t conditions of 629~672℃/410~490 MPa and 620~657℃/330~400 MPa, which correspond to the retrograde cooling. Based on the above results, a clockwise p-t evolution was obtained for the garnet-bearing biotite-plagioclase gneiss samples ALS2202 and ALS2204. LA-ICP-MS monazite U-Pb analyses obtained the weighted mean 206Pb/238U ages of 268±4 Ma and 255±2 Ma for the garnet-bearing biotite-plagioclase gneiss sample ALS2207 and the biotite-plagioclase gneiss sample ALS2210, respectively, which may represent the timing of peak metamorphism or anatexis. Based on the mineral assemblage, it suggests that the protolith of these felsic gneisses should be sedimentary rocks. Combined with the clockwise p-t path and previously published data in the region, this indicates a significant crustal thickening process in the middle and late Permian, which may be related to the closure of the Paleo-Asian Ocean.
关键词
波罗斯坦庙杂岩;LA-ICP-MS独居石U-Pb定年;相平衡模拟;顺时针p-t轨迹;中亚造山带
KeyWord
the Boluositanmiao Complex; LA-ICP-MS monazite U-Pb dating; phase equilibrium modeling; clockwise p-t path; Central Asian Orogenic Belt
基金项目
页码 870-894
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马椰婷,苟龙龙*,周峰,田智博. 阿拉善东部波罗斯坦庙杂岩含石榴子石黑云斜长片麻岩的p-t演化及独居石U-Pb年龄 [J]. 岩石矿物学杂志. 2025; 44; (4). 870 - 894.

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