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引用本文:王增振,陈宣华,李冰,张义平,徐盛林. 甘肃合黎山古元古代正长岩的发现及其对阿拉善地块大地构造属性的启示[J]. 中国地质, 2019, 46(5): 1094-1104.
WANG Zengzhen,CHEN Xuanhua,LI Bing,ZHANG Yiping,XU Shenglin. The discovery of the Paleoproterozoic syenite in Helishan, Gansu Province, and its implications for the tectonic attribution of the Alxa Block[J]. Geology in China, 2019, 46(5): 1094-1104(in Chinese with English abstract).
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甘肃合黎山古元古代正长岩的发现及其对阿拉善地块大地构造属性的启示
王增振1,2, 陈宣华1,2, 李冰1,2, 张义平1,2, 徐盛林1,2
1.中国地质科学院, 北京 100037;2.中国地质调查局-中国地质科学院地球深部探测中心, 北京 100037
摘要:
阿拉善地块的大地构造属性是近年来地质界激烈争论的科学问题:是华北克拉通的一部分,还是在前寒武纪尚未与华北克拉通拼合?研究阿拉善地块的基底并与华北克拉通主体进行对比,对探讨这一问题具有重要启示。阿拉善地块的基底仅在其东部和西南缘零星出露,且前人的研究主要集中在地块东部。在阿拉善地块西部的合黎山地区,有正长岩侵入龙首山群,并被震旦系不整合覆盖。该正长岩强烈富钾(K2O=13.77%),轻、重稀土明显分异((La/Yb)N=46.62),显示Nb-Ta负异常和Pb-Zr-Hf正异常,并具有高Sr低Nd的同位素特征(εNdt)=-5.05),表明该岩体源于玄武质下地壳的部分熔融。LA-ICP-MS锆石U-Pb定年表明,该正长岩形成于(1872 ±12)Ma,即古元古代,并记录了~2.7 Ga的地壳生长以及~2.5 Ga和~1.95 Ga的岩浆活动。合黎山古元古代正长岩的发现补充了阿拉善地块前寒武纪基底的组成,进一步完善了阿拉善地块新太古代-古元古代基底和构造热事件的时代格架,且与华北克拉通主体十分相似,指示二者具有明显的亲缘性。
关键词:  前寒武纪基底  古元古代  阿拉善地块  大地构造属性  深地探测工程
DOI:10.12029/gc20190510
分类号:P588.12+2;P597
基金项目:中国地质调查局项目(DD20160083)和中国地质科学院基本科研业务费项目(YWF201708)联合资助。
The discovery of the Paleoproterozoic syenite in Helishan, Gansu Province, and its implications for the tectonic attribution of the Alxa Block
WANG Zengzhen1,2, CHEN Xuanhua1,2, LI Bing1,2, ZHANG Yiping1,2, XU Shenglin1,2
1.Chinese Academy of Geological Sciences, Beijing 100037, China;2.SinoProbe Center, Chinese Academy of Geological Sciences and China Geological Survey, Beijing, 100037, China
Abstract:
The tectonic affinity of the Alxa block has long been in debate. It may be part of the North China Craton (NCC), or independent from the NCC during the Precambrian. The comparison of basements between the Alxa block and the NCC would be helpful to solving this dispute, but the Alxa basement is relatively poorly studied due to limited outcrops, with most of available data reported in eastern Alxa. Recently, a syenite that intruded into the Longshoushan Group has been sampled in Helishan area, western Alxa, and both of them are unconformably covered by Sinian strata. The Helishan syenite is characterized by extremely enriched K2O (13.77%) and LREE[(La/Yb)N=46.62], and shows distinct negative and positive anomalies of Nb-Ta and Pb-Zr-Hf, respectively, with EM-I type Sr-Nd isotope features (εNd(t)=-5.05), implying partial melting of basaltic lower crust. Moreover, LA-ICP-MS zircon U-Pb data indicate that this syenite was formed during Paleoproterozoic (1872 ±12) Ma and display records of~2.7 Ga crustal growth and~2.5, 2.1 and 1.95 Ga magmatic activities. According to data from this study and previously published data, the Neoarchean-Pelaoproterozoic basements and tectono-thermal events of the Alxa block and the NCC are geochronologically consistent, indicating very close affinity between them.
Key words:  Precambrian basement  Paleoproterozoic  Alxa block  tectonic affinity  deep earth exploration engineering