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中亚造山系中南段早中生代花岗岩类时空分布特征及构造环境
Spatial-temporal distribution and tectonic settings of Early Mesozonic granitoids in the middle-south segment of the Central Asia Orogenic System
  
中文关键词:花岗岩  锆石年龄  同位素特征  构造环境  早中生代  中亚造山系
英文关键词:granitoids  zircon U-Pb age  isotope characteristics  tectonic setting  Early Mesozoic  Central Asian Orogenic System
基金项目:国家重点基础研究发展规划资助项目(2007CB411307);中国地质调查局资助项目(1212010611803);中俄国际合作基金(40472101)
作者单位E-mail
李 舢 中国地质科学院 地质研究所 北京 100037 lishan428@163.com 
王 涛 中国地质科学院 地质研究所 北京 100037 taowang@cags.net.cn 
童 英 中国地质科学院 地质研究所 北京 100037  
摘要点击次数: 2318
全文下载次数: 1982
中文摘要:
      依据锆石U-Pb年龄,中亚造山系中南段早中生代花岗岩类大致可以划分出早中三叠世(251~227 Ma)和晚三叠世—早侏罗世(226~195 Ma)两个阶段。早中三叠世花岗岩类,主要分布于东天山造山带中东部、北山造山带中北部、中蒙古地块、阿尔泰造山带西段及内蒙古-吉林造山带中西部地区,多沿板块缝合带及附近展布,具有准铝质-弱过铝质的钙碱性-高钾钙碱性或弱碱性花岗岩的特点,I型、S型和A型或I-A型花岗岩均有出露,且同期的超镁铁质-镁铁质岩少见。晚三叠世—早侏罗世花岗岩类,较广泛分布于全区各造山带,具有准铝质-弱过铝质的高钾钙碱性-碱性花岗岩的特点,大都为A型和I-A型花岗岩,部分具有高分异Ⅰ型花岗岩的特点,且同期的超镁铁质-镁铁质岩较发育。早期花岗岩类的稀土元素总量(ΣREE)高于晚期,但晚期较早期具显著负铕异常,晚期花岗岩Ba、Nb、Sr、P和Ti的亏损程度较早期更明显一些。花岗岩Sr-Nd同位素特征显示,华北北缘具有非常低的εNd(t)值(-19.6~-5.4)和老的tDM值(1.23~2.09 Ga),以古老陆壳为其主要源区;北蒙古-西外贝加尔造山带和内蒙古-吉林造山带主体以年轻物源为主;中蒙古地块、阿尔泰造山带、东天山造山带和北山造山带在以古老微陆块为花岗岩源区的构造背景下,有部分年轻幔源组分的贡献,总体显示出早期以壳源和幔源的双源为特点,晚期以幔源为主,从早期到晚期有年轻幔源组分递增的趋势。大量新生地壳主要分布在鄂霍茨克带及其邻区,但在一些老的微陆块上,后造山或后碰撞阶段也有较多年轻幔源岩浆的底侵而导致地壳垂向生长。早中三叠世花岗岩类在中亚造山系西部地区为后造山构造背景,东部地区为同造山作用的晚期阶段;晚三叠世—早侏罗世花岗岩类为后造山或非造山或板内伸展构造背景。
英文摘要:
      The Central Asian Orogenic System (CAOS) is one of the largest accretionary orogenic belts characterized by the highest rate of Phanerozoic continental growth in the world. In recent years, extensive studies of the orogenic belts have been conducted, focused mainly on Paleozoic accretionary processes and granitic magmatism. By contrast, Mesozoic magmatism and tectonism are poorly understood. This paper tries to analyze and discuss temporal-spatial distribution and tectonic setting of the early Mesozoic granite magmatism. According to zircon U-Pb ages, the Early Mesozoic granitoids in the middle-south segment of the Central Asian Orogenic System can be roughly divided into two stages, i.e., early-middle Triassic (251~227 Ma) and late Triassic-early Jurassic (226~195 Ma). The early-middle Triassic rocks consist mainly of the monzogranite-granodiorite_syenite assemblage. These granitoids are distributed in such areas as the east-middle part of the East Tianshan orogenic belt, the north-middle part of the Beishan orogenic belt, the central Mongolian block, the western part of the Altay orogenic belt and the middle-western region of the Inner Mongolia-Jilin orogenic belt. They are spread along or near the suture zones. The granitoids have metaluminous-weakly peraluminous, calc-alkaline-high-K calc-alkaline or weak alkaline features. I-, S- and A-type or I-A type granites are all exposed. Some ultramafic-mafic rocks are associated with these granitoids. The late stage rocks widely occurring in every orogenic belt are composed of the alkali feldspar granite-K-feldspar granite-monzogranite-alkali feldspar quartz syenite assemblage. They are characterized by metaluminous-wealy peraluminum, high-K calc-alkaline or alkaline granites. Most of them are of A-type and I-A type. Some of them have the characteristics of highly fractionated I-type granites. There exist voluminous coeval ultramafic-mafic rocks. The early-middle Triassic granitoids have a higher ΣREE content, while the late ones have a significant negative Eu anomaly and are more depleted in Ba, Nb, Sr, P and Ti. The Sr-Nd isotopic characteristics reveal that the granitoids in the northern margin of the North China Craton show very low εNd(t) values (-19.6~-5.4) and the old tDM values (1.23~2.09 Ga), suggesting derivation from an ancient continental crust: those in the north Mongolia-west Transbaikalia orogenic belt and Inner Mongolia-Jilin orogenic belt were derived from a young source, whereas those in central Mongolian block, Altay orogenic belt, East Tianshan orogenic belt and Beishan orogenic belt were derived from an ancient micro-continental crust with some contributions of young mantle-derived components. In general, the early-middle Triassic granitoids were derived from dual-sources, while the late Triassic-early Jurassic granitoids mainly from the mantle source. Mantle-derived components have an increasing trend from early to late ones. Juvenile compositions of major sources for the granitoids were distributed in the Okhotsk belt and its adjacent areas, and also contributed by the ancient continental crust through underplating of young mantle-derived magma, leading to vertical continental growth in the post-orogenic or post-collision stage. According to recent researches, the early-middle Triassic granitoids in the eastern and western regions show some differences in tectonic settings. The north Mongolia-west Transbaikalia orogenic belt seems to show an intraplate tectonic setting of the continental rift. The central Mongolian block may represent the late stage of the syn-orogenic setting. The Altay orogen and the East Tianshan orogen are described as a post-orogenic extensional setting. The Beishan orogen reflects the late orogenic collision or post-orogenic tectonic setting. The Inner Mongolia-Jilin orogenic belt has the syn-orogenic characteristics. The late Triassic granitoids mainly reflect a post-orogenic, non-orogenic or intraplate extensional tectonic setting.
李 舢,王 涛,童 英,2010,中亚造山系中南段早中生代花岗岩类时空分布特征及构造环境[J].岩石矿物学杂志,29(6):642~662.
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