贺兰山滚钟口花岗岩岩石成因和构造背景  

Petrogenesis and tectonic setting of the Gunzhongkou granite in the Helanshan Mountains,North China

作　　者：张鑫[1] 谢晖[1] ZHANG Xin;XIE Hui(School of Geography and Planning,Ningxia University,Yinchuan Ningxia Hui Autonomous Region 750021,China)

机构地区：[1]宁夏大学地理科学与规划学院,宁夏回族自治区银川750021

出　　处：《矿物学报》2024年第2期188-199,共12页Acta Mineralogica Sinica

基　　金：宁夏回族自治区重点研发计划项目(引才专项)(2019BEB04016)。

摘　　要：华北克拉通(NCC)由多个地体或微陆在古元古代拼合形成,是探知地球演化历史的重要窗口。目前,NCC孔兹岩带中古元古代的S型花岗岩的岩石成因尚存争议。针对此,本文开展了孔兹岩带中贺兰山滚钟口花岗岩的岩石学、年代学和地球化学研究,重点利用锆石Hf-O多同位素体系限定其岩浆来源,以期获得准确成岩信息。结果显示,滚钟口花岗岩的w(SiO_(2))介于63.83%~67.95%之间,w(Na_(2)O)介于1.75%~2.75%之间,w(K_(2)O)介于4.37%~6.20%之间,w(Al_(2)O_(3))较高,介于13.80%~16.76%之间,铝饱和指数较高,介于1.48~1.58之间,为典型的S型花岗岩。样品的30个锆石U-Pb年代学测点得到上交点年龄(1914±26)Ma,为滚钟口花岗岩的成岩年龄。样品具有较高的ε_(Hf)(t)值(-1.97~+5.90),较高的δ^(18)O值(6.40‰~10.46‰),较老的T_(DM1)年龄(2415.72~2088.70 Ma)和较老的TDm^(2)年龄(2672.74~2187.88 Ma),说明初始岩浆来源于古老地壳物质的熔融,形成于同碰撞的构造环境。结合已发表的研究区内花岗岩和沉积岩的Hf-O同位素数据,本文认为在约1950 Ma时岩浆岩的源区性质发生了显著的变化,这标志着区域由板块俯冲构造环境向陆-陆碰撞构造环境的转换。由此,本次研究建立了区域2200~1800 Ma的构造演化模型,该模型揭示了鄂尔多斯陆块与阴山陆块的碰撞造山过程及其深部岩浆作用的响应,为恢复孔兹岩带和NCC古元古代构造演化历史提供新的制约。The North China Craton(NCC)was formed by the assemblage of multiple terranes or micro-continents in the Paleoproterozoic.It is an important window for us to explore evolution history of the earth.At present,there is still controversy over the petrogenesis of the Paleoproterozoic S-type granite in the NCC Khondalite belt.In this paper,we have conducted petrological,chronological,and geochemical studies on the Kunzhongkou granite in the Khondalite belt,especially by using the zircon Hf-O multi isotope system to constrain its magma source,in order to obtain accurately its petrogenetic information.The results show that contents of SiO_(2),Na_(2)O,K_(2)O and Al_(2)O_(3) of samples from the Gunzhongkou granite are 63.83%~67.95%,1.75%~2.75%,4.37%~6.20%,and 13.80%~16.76%,respectively,indicating that the Gunzhongkou granite belongs to a typical S-type granite.The U-Pb dating data of 30 zircon grains of the granite sample yielded an upper intercept age of 1914±26 Ma which is the emplacement age of the Gunzhongkou granite.Zircon grains of the sample have highε_(Hf)(t)values varying from-1.97 to+5.90,relatively highδ^(18)O values varying from 6.40‰to 10.46‰,relatively old T_(DM1) ages varying from 2415.72 Ma to 2088.70 Ma,and old T_(DM2) ages varying from 2672.74 Ma to 2187.88 Ma,indicating that the initial magma was originated from the partial melting of ancient crustal materials under the syncollisional tectonic setting.Combined with published Hf-O isotope data of zircons of granites and sedimentary rocks in the study area,we found that the source nature of magmatic rocks had changed significantly at about 1950 Ma when the tectonic setting of the area was transformed from a plate subduction setting to a continental collision setting.Therefore,we have established a model for tectonic evolution of the area during 2200~1800 Ma.The model reveals the collision orogenic process of the Ordos and Yinshan blocks and its response to the magmatism in depth,and will provide new constraints for restoring the Paleoproterozoic tec

关 键 词：S型花岗岩 孔兹岩带 岩石成因 构造背景 

分 类 号：P597[天文地球—地球化学]