赤峰-库伦地区石炭-二叠系沉积体系、物源组成及其构造意义

North China Block (NCB) is located in the south of Solonker suture along the eastern part of Central Asian Orogenic Belt (CAOB), also called Xing-Meng Orogenic Belt by Chinese geologists. NCB amalgamated with South Gobi block by the northern margin in late Paleozoic time, whose tectonic nature has long been debated on a passive continental margin or an active continental margin. Actually the point to the debates is the nature of Inner Mongolia Paleo-Uplift(IMPU), which lies across the northern margin of NCB. There are some late Paleozoic - early Mesozoic plutons exposed in IMPU, thought to be formed in an Andes-type magmatic arc or by linear lithospheric delamination within a post-collisional transtensional regime. A Permo-Carboniferous strata assemblage was developed across Chifeng and Kulunqi area in the north of IMPU, recording the magmatic activity of IMPU and surfacial response to dynamic process of the continental margin. This job combines sedimentary interpretation, detrital framework petrography, isotope geochemistry and U-Pb ages of detrital zircons, aims to restore the basin-filling process, to determine the source lithology and buildup a chronosequence of the source rocks, to disscuss the coupling relationship between basin evolution and structural activity of IMPU, and finally to disccuss tectonic history of the northern margin of NCB.

华北地块位于中亚造山带(CAOB)的东段--兴蒙造山带内索伦缝合线的南侧，其北缘与南蒙地块在晚古生代期间发生了重要的拼合过程。华北地块北缘在石炭-二叠纪存在活动陆缘与被动陆缘的争论，争论的关键在于内蒙古隆起的性质。内蒙古隆起现今出露了一些晚古生代-早中生代的侵入岩体，对于这些岩体的成因，目前存在安第斯型陆缘弧与碰撞后岩石圈线性拆沉的不同认识。在内蒙古隆起以北的赤峰-库伦地区发育了一套石炭-二叠纪的沉积地层，不仅保存了"陆缘弧"岩浆活动的重要信息，而且记录了大陆边缘动力过程的地表响应。本项目拟通过对野外露头的沉积体系恢复、碎屑矿物组分、元素地球化学与碎屑锆石年代学等方面的研究，以盆地沉积体系与物源组成为切入点，恢复盆地的充填过程，反演源区的岩性组成和时代序列，建立盆地演化与内蒙古隆起构造活动之间的耦合关系，从沉积盆地角度为华北地块北缘石炭-二叠纪大陆边缘构造演化提供证据。

华北北缘在石炭-二叠纪的大地构造属性存在活动陆缘与被动陆缘的争论。项目对内蒙古隆起以北的赤峰—库伦地区石炭-二叠系进行地层年代学、沉积学和物源等方面的综合研究，恢复了研究区不同阶段的沉积体系、物源以及盆地充填序列，探讨华北北缘石炭-二叠纪盆地性质、内蒙古隆起隆升事件以及它们与古亚洲洋构造演化的关系。.通过火山岩和碎屑锆石U-Pb年龄，建立了地层时代格架，白家店组-酒局子组时代下限为331Ma；青凤山组、额里图组和于家北沟组为同期异相，时代为284~263Ma；铁营子组角度不整合于300±1Ma的花岗岩体和于家北沟组之上，为晚二叠世产物。.赤峰—库伦地区石炭-二叠系发育三个充填序列：第一序列白家店组-酒局子组，是一套滨海碎屑岩和浅海灰岩，在垂向上是一个进积序列，从浅海相灰岩到滨海相碎屑岩。盆地相带展布和指向北的古水流，指示南高北低的古地理格局，物源来自内蒙古隆起；第二序列早-中二叠世青凤山组、额里图组和于家北沟组是一套陆源碎屑与火山岩-火山碎屑岩序列，在靠近内蒙古隆起的南侧发育滨海相石英砂岩夹火山岩-火山碎屑岩，物源来自古隆起。在远离隆起的翁牛特旗—克什克腾旗广兴源一线发育火山溢流-喷发相的火山岩-火山碎屑岩，物源来自同期火山活动；晚二叠世是一套陆相沉积，物源来自下伏地层于家北沟组和侵入岩体。.白家店组-酒局子组进积序列记录了内蒙古隆起在石炭纪持续挤压隆升，以结晶基底和少量火山岩为源岩；青凤山组、额里图组和于家北沟组青凤山组序列的双向物源和相带展布指示了火山岛弧和弧后盆地的构造配置，青凤山组属于弧后盆地沉积，额里图组和于家北沟组属于岛弧火山岩；铁营子组序列是一套山间盆地沉积。各充填序列分别记录了华北北缘石炭纪初始俯冲挤压、早中二叠世板片回卷下的伸展沉降和晚二叠世碰撞挤压的构造演化历史。