摘要
厘清大陆深部地壳形成、演化及其动力学过程,对于了解板块构造、揭示壳幔相互作用至关重要.针对华北深部地壳物质组成、结构及演化等问题,本研究在限定其地震学结构特征基础上,结合深部地壳岩石捕虏体的来源深度(定深)、化学和物理性质(定性)和形成年龄(定年)的研究成果,构建了华北深部地壳多维度物理、化学结构模型.结果表明:华北陆块地壳厚度变化于30~48 km,全地壳和地壳内部各层均呈现东薄西厚特征.东、西部地壳虽然厚度上有明显差异,但内部结构特征有一致性,即整体上较少典型的高速基性下地壳,平均P波波速(~6.3 km/s)、密度(2.72~2.78 g/cm^(3))并呈中性岩石特征.深部地壳岩石捕虏体除斜长角闪岩外主要成分包括基性和酸性的麻粒岩.中生代时期华北陆块部分地区地壳存在榴辉岩捕虏体,指示了当时局部地区曾存在厚达45 km的地壳,但现今地震学剖面并未显示;此外,有些地区(如汉诺坝)基性岩石捕虏体揭示出新生代基性岩浆底侵,难以在地震学模型中识别.因此,岩石探针与地震探测结果的结合,将更有助于全面认识深部地壳结构组成和演化.
Deep continental crust archives critical information on the bulk crustal composition as well as its formation.It is commonly the inherent zone for complex crust-mantle interaction.Unlike the shallow crust,the deep crust is generally inaccessible for direct geological sampling.Instead,knowledge of the deep crust can be obtained from a combination study of geophysical techniques and"lithoprobe"(deep crustal fragments entrained in magmatic outcrops).Wide-angle reflection/refraction seismic profiles have the highest resolution on crustal velocity structure and provide information on the averaged presentday nature of large deep crust domains;"lithoprobe",instead,give detailed information of locality-specific deep crustal sections through determining the physical and chemical properties,dating the formation and alteration ages and constraining the melting and equilibration depths of the xenoliths.Here,the two methodologies are integrated to constrain the crustal structure on the North China Block.The seismic crustal structure model of the block is compiled from all available seismic wide-angle reflection/refraction profiles and receiver function results.The model parameters include Moho depth,Vp velocity and thicknesses for four crustal layers(sedimentary cover,and the upper,middle and lower crust).The crust as a whole is thin(<36 km)in the eastern part relative to the western part(38-44 km).In addition,the crust is shown to have a thick upper and middle crust and a relatively thin(typically<5 km)lower mafic crust;no spatial variations in average crustal Vp velocity and densities are observed.The average crustal Vp and density for the whole North China Block are 6.33-6.37 km/s and 2.72-2.78 g/cm^(3),respectively.The overall absence of high P-wave velocity layer and the relatively low average Vp and density indicate that the block has an intermediate to felsic bulk crustal composition.In contrast,regional crustal xenoliths include mafic to felsic granulites and amphibolites and rare eclogite xenoliths(e.g.,Xinyang and Xuhuai),indicating the presence of thick lower crust(e.g.,>45 km)at that time.Meanwhile,mafic xenoliths in Hannuoba and Nüshan show strong mafic underplating at the lower crust in the Meso-Cenozoic while no high-velocity layer is shown in the seismic crustal model.These inconsistences can be explained by the fact that the two methodologies tap the crustal information at different timeslices and dimensions and be complementary to understand the chemical and physical structure of the deep crust.Therefore,the combination study of petrological and geochemical of the crustal xenoliths and geophysical observations can provide essential information on making and destroying the deep continental crust through time.
作者
郑建平
夏冰
平先权
魏颖
汤华云
苏玉平
马强
Jianping Zheng;Bing Xia;Xianquan Ping;Ying Wei;Huayun Tang;Yuping Su;Qiang Ma(State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2021年第23期3018-3031,共14页
Chinese Science Bulletin
基金
国家自然科学基金(41930215)
国家重点基础研究发展计划(2006CB403503)资助。
关键词
地壳结构
地震学
深部地壳
捕虏体
岩石探针
华北陆块
crustal structure
seismology
deep crust
xenoliths
rock probes
North China Block
作者简介
联系人:郑建平,E-mail:jpzheng@cug.edu.cn。
