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西准噶尔地区最晚期岩浆侵入活动——来自早二叠世–早三叠世接特布调岩体的证据
投稿时间:2019-01-09  修订日期:2019-04-25  点此下载全文
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作者单位E-mail
徐盛林 中国地质大学(北京)
中国地质科学院 
xushenglindizhi@163.com 
陈宣华 中国地质科学院 xhchen@cags.ac.cn 
李廷栋 中国地质大学(北京)中国地质科学院  
丁伟翠 中国地质科学院  
李冰 中国地质科学院  
张垚垚 中国地质科学院  
马飞宙 中国地质科学院  
基金项目:国家重点基础研究发展计划(973计划)
中文摘要:西准噶尔地区晚古生代构造运动复杂,岩浆侵入活动强烈,地壳生长显著,处在洋陆构造转换的关键时期。接特布调岩体位于连接西准噶尔地区、天山造山带和准噶尔盆地的重要位置,岩石类型以碱长花岗岩、二长花岗岩和花岗闪长岩为主。碱长花岗岩矿物组成以碱性长石(55%~60%)、斜长石(15%~20%)和石英(23%~25%)为主,几乎不含暗色矿物,岩石内部无暗色微粒包体;二长花岗岩和花岗闪长岩矿物组成以斜长石(30%~40%和~16%)、碱性长石(30%~40%和~50%)和石英(20%~25%和~18%)为主,含少量黑云母和角闪石,内部存在不同数量和规模的暗色微粒包体。通过高精度锆石U–Pb定年,将接特布调岩体的成岩年龄限定为287~250 Ma,岩体内早三叠世250.4Ma)二长花岗岩是迄今为止在整个西准噶尔地区发现的最年轻的侵入岩,该期花岗岩的就位标志着西准噶尔地区深成岩浆侵入活动的终结。接特布调岩体整体具有高硅(SiO2 = 67.04%~77.01%)、富碱(K2O = 3.45%~4.63%,Na2O = 3.62%~4.18%),贫钙(CaO = 0.45%~0.3.05%)、贫镁(MgO = 0.16%~1.51%)、低铁(Fe2O3 = 0.99%~4.40%)的特征,属于高钾钙碱性系列,准铝质–弱过铝质(A/CNK=0.93~1.03)。球粒陨石标准化稀土元素配分图具有明显的右倾海鸥型特征,富集轻稀土元素和Rb、Th、K元素,亏损重稀土元素和Eu、Ba、Nb、Sr、P、Ti元素。碱长花岗岩具有比A性花岗岩低的岩浆结晶温度,属于高分异的I型花岗岩,来源于新生地壳部分熔融;二长花岗岩和花岗闪长岩整体具有较高的岩浆结晶温度,属于壳幔混源的I型花岗岩。接特布调地区在早二叠–早三叠世处于高温、低压、地壳减薄的后造山伸展的陆内演化阶段。
中文关键词:接特布调岩体  地球化学  U-Pb年代学  Lu-Hf同位素  I型花岗岩  后造山  西准噶尔
 
The Latest Magma Intrusion Activities in the West Junggar: Constraints from Early Permian–Early Triassic Jietebutiao Pluton
Author NameAffiliationE-mail
Xu Shenglin China University of Geosciences, BeijingChinese Academy of Geological Sciences xushenglindizhi@163.com 
Chen Xuanhua Chinese Academy of Geological Sciences xhchen@cags.ac.cn 
Li Tingdong China University of Geosciences, BeijingChinese Academy of Geological Sciences  
Ding Weicui Chinese Academy of Geological Sciences  
Li Bing Chinese Academy of Geological Sciences  
Zhang Yaoyao Chinese Academy of Geological Sciences  
Ma Feizhou Chinese Academy of Geological Sciences  
Abstract:The West Junggar of the Central Asian Orogenic Belt, known as complex tectonic movements, extensive magmatic activities and remarkable crustal growth, was in a critical period of ocean-continent transition in the Late Paleozoic. Jietebutiao pluton, located in the West Junggar area, Tianshan Orogenic Belt and Junggar Basin, is mainly composed of alkali feldspar granite, monzogranite and granodiorite in the southwest of the West Junggar. The alkali feldspar granite, whose mineral composition consists of potassium feldspar (60%~65%), plagioclase (10%~15%), quartz (23%~25%) and few dark minerals, has no mafic microgranular enclaves. The monzonitic granite and granodiorite, whose mineral composition respectively consists of potassium feldspar (30%~40% and ~16%), plagioclase (30%~40% and ~50%), quartz (20%~25% and ~18%) and a small amount of dark minerals, has visible mafic microgranular enclaves .Jietebutiao pluton were formed during 287~250 Ma by high-precision zircon U-Pb dating, which indicates the multi-stage magmatic activity events during the Early Permian–Early Triassic. The Early-Triassic (250.4Ma) monzogranite is the youngest intrusive magmatic rock that has been found in the West Junggar so far and its intrusion means the end of Late Paleozoic magmatic intrusion activitie. Jietebutiao plutons are characterized by high silica (SiO2 = 67.04%~77.01%), high-K Calc-alkaline (K2O = 3.45%~4.63%, Na2O = 3.62%~4.18%, CaO = 0.45%~0.3.05%), poor magnesium (MgO = 0.16%~1.51%), low iron (FeOT = 0.99%~4.40%), quasi aluminum–weak peraluminum (Al2O3 = 12.60%~15.01%). Trace elements of the Jietebutiao pluton have obvious right-leaning seagull type characteristics with distinct negative Eu anomalies in the chondrite-normalized Rare Earth Elements distribution patterns diagram, enriched in Light Rare Earth Elements and Rb, Th, K, depleted in Heavy Rare Earth Elements and Eu, Ba, Nb, Sr, P and Ti. The pluton shows the similar characteristics as I-type granite in terms of major and trace element, but there are also some differences between alkali feldspar granite and other granites. The alkali feldspar granite, characterized by low crystallization temperature compared with A-type granite, belongs to highly fractionated I-type granite. The monzonitic granite and granodiorite, characterized by high crystallization temperature, belong to Magmatic mixed I-type granite. Compared with the existing research results, we convinced that Jietebutiao pluton evolved into the stage of the intracontinental tectonic activity under the post-orogenic extensional environment with high temperature, low pressure and crust thinning during the Early Permian–Early Triassic.
keywords:Jietebutiao pluton  geochemistry  U-Pb dating  Lu-Hf isotopic composition  I-type granite  post-orogenic intracontinental evolution  West Junggar
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