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甘肃龙首山—合黎山晚志留世—早泥盆世花岗岩类的成因及其对阿拉善地块西南缘早古生代构造演化的约束
投稿时间:2019-04-26  修订日期:2019-09-10  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020027
摘要点击次数: 115
全文下载次数: 110
作者单位E-mail
王增振 中国地质科学院 pkuwzz@163.com 
陈宣华 中国地质科学院  
邵兆刚 中国地质科学院  
李冰 中国地质科学院  
丁伟翠 中国地质科学院  
张义平 中国地质科学院  
王永超 中国地质科学院  
张垚垚 中国地质科学院  
徐盛林 中国地质科学院  
秦翔 中国地质科学院  
中文摘要:阿拉善地块西南缘在中志留世—早泥盆世究竟是处于古亚洲洋俯冲的构造环境,还是受控于祁连造山带而处于后碰撞伸展环境?这是探讨该区早古生代构造演化不可回避的重要科学问题。阿拉善地块西南缘出露的早古生代岩浆岩是探讨该问题的重要研究对象,但前人的工作集中于北大山和龙首山的东段。本文在龙首山西段及更西部的合黎山地区选择三个花岗岩体进行了LA-ICP-MS锆石U–Pb定年和元素及同位素地球化学研究。结果表明,龙首山西段的大佛寺碱性长石花岗岩形成于晚志留世(426 ± 2 Ma),主量元素具有高SiO2(78.03%)、富碱(ALK = 7.96%)、低CaO(0.60%)、贫MgO(0.13%)的特征,稀土分布呈明显的“V”型,大离子亲石元素(LILEs)高度富集而高场强元素(HFSEs)中等富集,Ba、Sr、Eu负异常显著,属于铝质A2型花岗岩。合黎山地区的五坝黑云母花岗岩和张家窑花岗闪长岩分别形成于晚志留世(421 ± 2 Ma)和早泥盆世(406 ± 4 Ma),都属于高钾钙碱性I型花岗岩,轻、重稀土分异(La/YbN = 10.69~13.79),Eu负异常显著(δEu = 0.56~0.77),LILEs富集,HFSEs亏损,Nb、Ta负异常和Zr、Hf正异常同时出现。此外,三个岩体均具有富集型Sr-Nd同位素特征和中元古代二阶段Nd模式年龄,可能源于中元古代地壳物质在不同温度下的部分熔融。结合区域资料,阿拉善地块西南缘中志留世—早泥盆世具有钙碱性—高钾钙碱性I型花岗岩、铝质A2型花岗岩和碱性—过碱性花岗岩的岩石组合,指示后碰撞伸展环境,而该区早古生代俯冲阶段(中奥陶世—早志留世;ca. 461~441 Ma)和后碰撞阶段(中志留世—早泥盆世;ca. 432~397 Ma)的识别与祁连造山带的构造演化是可对比的。
中文关键词:阿拉善地块西南缘  早古生代  花岗岩  岩石成因  大地构造背景
 
Petrogenesis of the Late Silurian–Early Devonian granites in the Longshoushan–Helishan area, Gansu Province, and its tectonic implications for the Early Paleozoic evolution of the southwestern Alxa Block
Author NameAffiliationE-mail
WANG Zengzhen Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
pkuwzz@163.com 
CHEN Xuanhua Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
SHAO Zhaogang Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
LI Bing Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
DING Weicui Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
ZHANG Yiping Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
WANG Yongchao Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
ZHANG Yaoyao Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
XU Shenglin Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
QIN Xiang Chinese Academy of Geological Sciences,Beijing,100037
SinoProbe Center,Chinese Academy of Geological Sciences and China Geological Survey,Beijing,100037 
 
Abstract:The Alxa Block is located in between the Central Asian Orogenic Belt to the north and the Qilian Orogenic Belt to the southwest, but the tectonic setting of its southwestern margin during Early Paleozoic has long been in debate. Researchers who studied the Early Paleozoic plutons in eastern Beidashan believe the subduction of Paleo-Asian Ocean had reached the southwestern Alxa Block. But others proposed the post-collision extensional setting for this area based on Early Paleozoic magmatic rocks in eastern Longshoushan. It is noteworthy that there is no large fault in between the eastern Beidashan and Longshoushan, and the distances between the western Longshoushan and the two orogenic belts are the same as those for the eastern Beidashan and Longshoushan, indicating same tectonic setting. In order to discuss the Early Paleozoic tectonic setting of the western Longshoushan, the Dafosi alkali-feldspar granite, Wuba biotite granite and Zhangjiayao granodiorite were sampled for LA-ICP-MS zircon U–Pb dating and element and isotope geochemical analyses. The results indicate that the Dafosi alkali-feldspar granite was formed during Late Silusian (426 ± 2 Ma), and its major elements are characterized by high SiO2 (78.03%) and total alkali (7.96%) and low CaO (0.60%) and MgO (0.13%), with prominent V-type rare earth element pattern and negative Ba, Sr, and Eu anomalies, belonging to aluminous A2-type granite. The Wuba biotite granite and Zhangjiayao granodiorite were formed during Late Silurian (421 ± 2 Ma) and Early Devonian (406 ± 4 Ma), respectively, and both are high K calc-alkaline I-type granites. They have enriched LREEs (La/YbN = 10.69~13.79) and depleted Eu (δEu = 0.56~0.77), and exhibit apparently negative Nb-Ta anomalies and positive Zr-Hf anomalies at the same time. Moreover, all the three plutons have enriched Sr-Nd isotopic features and Mesoproterozoic two-stage Nd model ages. Therefore, they may be originated from the partial melting of Mesoproterozoic crust and indicate post-collisional tectonic setting. Besides, according to the statistic analysis and comparison, the tectonic evolution of southwestern Alxa Block could be divided into the subduction stage of Middle Ordovician–Early Silurian (ca. 461~441 Ma) and the post-collision stage of Middle Silurian–Early Devonian (ca. 432~397 Ma), and this process is comparable with the evolution of Qilian Orogenic Belt, indicating a genetic relationship.
keywords:Southwestern Alxa Block  Early Paleozoic  Granite  Petrogenesis  Tectonic setting
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