地质学报2016，Vol.90Issue(2)：383-397,15.
内蒙古锡林浩特早石炭世构造环境：来自变质基性火山岩的年代学和地球化学证据
Late Paleozoic Subduction of the Paleo-Asian Ocean:Geochronological and Geochemical Evidence from the Meta-basic Volcanics of Xilinhot,Inner Mongolia
摘要
Abstract
The meta-basic volcanics,lying at the Southeast of Xilinhot area,distributed in the east of the Hinggan-Mongolian orogenic belt in Inner Mongolia,are the amphibolite part of Xilin Gol complex.From the amphibolite,by LA-MC-ICP-MS Zircon U-Pb Dating technique,this paper gets two formation ages:(334.5±3.5)Ma and (323.4±2.4)Ma,which belong to late Carboniferous epoch.Geochemical ananlysis shows that the meta-basic volcanics are characterized by relatively high Fe (TFeO=6.07% ~10.55%), high Mg (MgO =3.90% ~11.29%),high Al (Al2 O3 =12.68% ~17.22%),low Ti (TiO2 =0.56% ~1.69%),high Na low K (K2 O+Na2 O=2.12%~7.37%,K2 O/Na2 O=0.02 ~0.59),belonging to calc-alkaline basalt or andesite.These metabasic volcanics are also characterized by relatively low in REE content(ΣREE=15.97 ×10 -6 ~176.0 ×10 -6 ),relatively light fractionation between LREE and HREE (LREE/HREE=0.77~6.26),no obvious Eu negative anomaly(δEu=0.48~1.13)and particular strong enrichment in large-ion lithophile elements (Rb,Th,U and K )and depletion in high-field-strength elements (Zr,Hf,Nb and Ta),showing an affinity to MORB,suggesting that their original rock mostly are island-arc basalt or andesite.Further,The I sr andεNd (t)values are 0.701828~0.704096 and +2.83~+6.61,which implies that they could be derived from the depleted lithospheric mantle.In a word,it is presumedly determined that their primary magma may originate from depleted mantle wedge which was metasomatosed due to the subduction of plate.They may result from island arc magmatism.Based on these results,it is inferred that these volcanics were melting products of the metasomatized mantle wedge formed during the Paleo-Asian Ocean subduction northward.And therefore in late Carboniferous the Paleo-Asian Ocean was not closed in study area but was in its subduction stage.关键词
变质基性火山岩/早石炭世/锆石 U-Pb 年龄/俯冲作用/古亚洲洋Key words
meta-basic volcanics/Early Carboniferous/zircon U-Pb age/subduction/Paleo-Asian Ocean引用本文复制引用
康健丽,肖志斌,王惠初,初航,任云伟,刘欢,高知睿,孙义伟..内蒙古锡林浩特早石炭世构造环境：来自变质基性火山岩的年代学和地球化学证据[J].地质学报,2016,90(2):383-397,15.基金项目
本文为中国地质调查“华北克拉通变质基底大地构造分区及其对成矿作用的制约研究（编码12120114034201）”、“华北地区古生代变质作用和动力学（编码1212011121077）”“华北克拉通对哥伦比亚超大陆事件的响应及大地构造格架（编码1212011120154）”项目资助的成果。 （）
