大别山黄石-六安反射地震剖面新的地质解释
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摘要
在大别山黄石至六安反射地震剖面上有很多近水平的反射体,表明大别山中心部位的中、下地壳内也有近水平的分层性,反映有流变性和动力学方面的差异,与大型薄皮构造理论对岩石圈性质的认识一致,因而在其运动过程中应服从薄皮构造的运动规律。结合以往对大别山区划分的岩石-构造组合,在前人对此反射地震剖面所作的地质解释的基础上,对反射地震剖面作了较为详细的地质解释,并建立了大别山造山带在此剖面上的两维几何结构。剖面南部为造山过程中形成的背斜构造,地表15km深度内为由碰撞混杂岩组成的扬子与中-朝大陆之间的主滑脱带。剖面中部为造山期后的侵入体。剖面北部为主滑脱带的根带(通常认为的缝合带),根带被中生代形成的晓天磨子潭断裂带切割。剖面最北端为变质复理石中略晚于主滑脱带的反向冲断带。推测下地壳的断开距离在扬子大陆俯冲时(三叠纪前)规模较大,然后逐渐缩小,直至保留到今天的规模。
There are many subhorizontal reflectors in the Huangshi-Liu′an migrated seismic reflection profile across the Dabie Mountains, which suggests that subhorizontal stratification also occurs in the middle and lower crust below the central part of the Dabie Mountains and shows the difference in rheology and kinematics. This agrees with the understanding of the nature of the lithosphere based on the concept of"thin skin tectonics". On the basis of the previous geological interpretation of this seismic reflection profile, combined with the classification of the petrologic-tectonic associations of the Dabie Mountains, a more detailed geological interpretation of this profile is made and a 2D geometric architecture of the Dabie orogen along the profile is established in the present paper. In the southern part of the profile, an antiform was formed in the orogenic process, and within 15 km below the surface there occurs the main detachment between the Yangtze block and Sino-Korean block, composed of collisional mélanges. The middle part of the profile is occupied by a post-orogenic intrusion. The northern part is the root zone of the main detachment, cut by the Xiaotian-Mozitan fault formed in the Mesozoic;it is commonly regarded as a suture between the two blocks. The northernmost part is the back thrust belt formed slightly later than the main detachment. It is inferred that the offset of the lower crust and Moho was large during the subduction of the Yangtze block before the Triassic and then was reduced to the present magnitude.
There are many subhorizontal reflectors in the Huangshi-Liu′an migrated seismic reflection profile across the Dabie Mountains, which suggests that subhorizontal stratification also occurs in the middle and lower crust below the central part of the Dabie Mountains and shows the difference in rheology and kinematics. This agrees with the understanding of the nature of the lithosphere based on the concept of"thin skin tectonics". On the basis of the previous geological interpretation of this seismic reflection profile, combined with the classification of the petrologic-tectonic associations of the Dabie Mountains, a more detailed geological interpretation of this profile is made and a 2D geometric architecture of the Dabie orogen along the profile is established in the present paper. In the southern part of the profile, an antiform was formed in the orogenic process, and within 15 km below the surface there occurs the main detachment between the Yangtze block and Sino-Korean block, composed of collisional mélanges. The middle part of the profile is occupied by a post-orogenic intrusion. The northern part is the root zone of the main detachment, cut by the Xiaotian-Mozitan fault formed in the Mesozoic;it is commonly regarded as a suture between the two blocks. The northernmost part is the back thrust belt formed slightly later than the main detachment. It is inferred that the offset of the lower crust and Moho was large during the subduction of the Yangtze block before the Triassic and then was reduced to the present magnitude.
引文
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[7]《大别山超高压变质作用与碰撞造山动力学》编写组.大别山超高压变质作用与碰撞造山动力学[M].北京:科学出版社,2005:210.
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[10]李曙光,黄方,周红英,等.大别山双河超高压变质岩及北部片麻岩的U-Pb同位素组成——对超高压岩石折返机制的制约[J].科学通报,2001,31:977-984.
[11]Xu Shutong,Liu Yican,Wu Weiping.A paradox:The ultramafic rock belt(UMRB)as a metamorphic tectonic mélange in northern Dabie Mountains eastern central China[C]//Ueli Briegel,Wenjiao Xiao.Paradox in Geology.The Netherlands,Elsevier Science B V,2001:323-342.
[12]Li S,Jagoutz E,Chen Y,et al.Sm-Nd and Rb-Sr isotope chronology of ultrahigh-pressure metamorphic rocks and their country rocks at Shuanghe in the Dabie Mountains,central China[J].GCA,2000,64:1077-1093.
[13]Liu X C,Jahn B M,Liu D,et al.SHRIMP U-Pb zircon dating ofa metagabbro and eclogites from western Dabieshan(Hong′an Block),China,anditstectonicimplications[J].Tectonophysics,2004,394:171-192.
[14]Liu D Y,Jian P,Kr(ner A,et al.Dating of prograde metamorphic events deciphered from episodic zircon growth in rocks of the Dabie-Sulu UHP complex,China[J].Earth and Planetary Science Letters,2006,250:650-666.
[15]Seeber L.Large scale thin-skin tectonics[J].Reviews of Geophysics and Space Physics,1983,21(6):1528-1538.
[16]Cowan D S,Silling R M.A dynamic model of accretion at trench and its implications for the tectonic evolution of subduction com-plex[J].J.Geophys.Rev.,1978,83:5389-5396.
[17]简平,杨巍然,李志昌,等.大别山西部熊店加里东期榴辉岩:同位素年代学证据[J].地质学报,1997,71(2):133-140.
[18]李曙光,Jagoutz E,肖益林,等.大别山-苏鲁地体超高压变质年代学:I.Sm-Nd同位素体系[J].中国科学(D辑),1996,26:249-257.
[19]Tompson R I.The nature and significance of large“blind”thrusts within the northern Rocky Mountains of Canada[C]//McClay Price N J.Thrust and Nappe Tectonics.Published for The Geological Society of London by Blackweii Scientific Publications Oxford London Edinburgh Boston Moelbourne,1981:539.
[20]Ramsay J G,Huber M I.The techniques of modern geology,vol-ume2,folds and fractures[M].Academic Press INC,(London)LDT,1987:700.
[21]Coney P J,Jones D L,Monger J W H.Cordilleran suspect terrans[J].Nature,1980,288:329-333.
[22]Ma C,Ehlers C,Xu C,et al.The roots of the Dabieshan ultrahigh pressure metamorphic terrane:constrains from geochemistry and Nd-Sr isotope systems[J].Precambrian Research,2000,102:279-301.
[23]Davis G A,郑亚东.变质核杂岩的定义、类型及构造背景[J].地质通报,2002,21(4/5):185-192.
[24]宋鸿林.关于变质核杂岩构造特征的几个问题[J].地质通报,2002,21(4/5):193-197.
[25]Bryant D L,Ayers J C,Gao S,et al.Geochemical,age,and isotopic constrains on the location of the Sino-Korean/Yangtze Suture and evolution of the Northern Dabie Complex,east central China[J].GSA Bulletin,2004,116(5/6):698-717.
[26]王强,许继峰,赵振华,等.大别山燕山期亏损重 稀土元素花岗岩类的成因及动力学意义[J].岩石学报,2001,17:551-564.
[27]马昌前,扬坤光,许长海,等.大别山中生代钾质岩浆作用与超高压变质地体的剥露机制[J].岩石学报,1999,15(3):379-395.
[28]Liu Y,Li S,Xu S.Zircon SHRIMP U-Pb dating for gneisses in northern Dabie high T/P zone,central China:implications for de-coupling within subducted continental crust[J].Lithos,2007,96:170-185.
[29]徐树桐,刘贻灿,江来利,等.大别山的构造格局和演化[M].北京:科学出版社,1994:174.
①安徽省地质矿产局.杨柳湾镇幅(1∶5万)地质调查报告及地质图.2005.
[2]Wang X,Liou J,Mao H.Coesite-bearing eclogites from the Dabie Mountains in central China[J].Geology,1989,17:1085-1088.
[3]Xu S,Okay A I,Ji S,et al.Diamond from the Dabie Shan meta-morphicrocksanditsimplicationfortectonicsetting[J].Science,1992,256:80-82.
[4]Condie.Plate tectonics and crustal evolution(third edition)[M].Pergamon Press,1989:476.
[5]HsüK J.Thin-skinned plate tectonic model for collision-type oro-genesis[J].Science in China,1981,24(1):100-110.
[6]Yuan Xue-cheng,Simon L K,Teng Wen-bong,et al.Crustal structure and exhumation of the Dabie Shan ultrahigh pressure oro-gen,eastern China,from seismic reflectio profiling[J].Geology,2003,31:435-438.
[7]《大别山超高压变质作用与碰撞造山动力学》编写组.大别山超高压变质作用与碰撞造山动力学[M].北京:科学出版社,2005:210.
[8]徐树桐,刘贻灿,江来利,等.大别山造山带的构造几何学和运动学[M].合肥:中国科学技术大学出版社,2002:133.
[9]Zhang H,Gao S,Zhong Z,et al.Geochemical and Sr-Nd-Pb iso-topic compositions of Creteceous granotoids:constrains on tectonic framework and crustal stracture of the Dabieshan ultrahigh-pressure metamorphic belt,China[J].Geochemical Geology,2002,186:281-199.
[10]李曙光,黄方,周红英,等.大别山双河超高压变质岩及北部片麻岩的U-Pb同位素组成——对超高压岩石折返机制的制约[J].科学通报,2001,31:977-984.
[11]Xu Shutong,Liu Yican,Wu Weiping.A paradox:The ultramafic rock belt(UMRB)as a metamorphic tectonic mélange in northern Dabie Mountains eastern central China[C]//Ueli Briegel,Wenjiao Xiao.Paradox in Geology.The Netherlands,Elsevier Science B V,2001:323-342.
[12]Li S,Jagoutz E,Chen Y,et al.Sm-Nd and Rb-Sr isotope chronology of ultrahigh-pressure metamorphic rocks and their country rocks at Shuanghe in the Dabie Mountains,central China[J].GCA,2000,64:1077-1093.
[13]Liu X C,Jahn B M,Liu D,et al.SHRIMP U-Pb zircon dating ofa metagabbro and eclogites from western Dabieshan(Hong′an Block),China,anditstectonicimplications[J].Tectonophysics,2004,394:171-192.
[14]Liu D Y,Jian P,Kr(ner A,et al.Dating of prograde metamorphic events deciphered from episodic zircon growth in rocks of the Dabie-Sulu UHP complex,China[J].Earth and Planetary Science Letters,2006,250:650-666.
[15]Seeber L.Large scale thin-skin tectonics[J].Reviews of Geophysics and Space Physics,1983,21(6):1528-1538.
[16]Cowan D S,Silling R M.A dynamic model of accretion at trench and its implications for the tectonic evolution of subduction com-plex[J].J.Geophys.Rev.,1978,83:5389-5396.
[17]简平,杨巍然,李志昌,等.大别山西部熊店加里东期榴辉岩:同位素年代学证据[J].地质学报,1997,71(2):133-140.
[18]李曙光,Jagoutz E,肖益林,等.大别山-苏鲁地体超高压变质年代学:I.Sm-Nd同位素体系[J].中国科学(D辑),1996,26:249-257.
[19]Tompson R I.The nature and significance of large“blind”thrusts within the northern Rocky Mountains of Canada[C]//McClay Price N J.Thrust and Nappe Tectonics.Published for The Geological Society of London by Blackweii Scientific Publications Oxford London Edinburgh Boston Moelbourne,1981:539.
[20]Ramsay J G,Huber M I.The techniques of modern geology,vol-ume2,folds and fractures[M].Academic Press INC,(London)LDT,1987:700.
[21]Coney P J,Jones D L,Monger J W H.Cordilleran suspect terrans[J].Nature,1980,288:329-333.
[22]Ma C,Ehlers C,Xu C,et al.The roots of the Dabieshan ultrahigh pressure metamorphic terrane:constrains from geochemistry and Nd-Sr isotope systems[J].Precambrian Research,2000,102:279-301.
[23]Davis G A,郑亚东.变质核杂岩的定义、类型及构造背景[J].地质通报,2002,21(4/5):185-192.
[24]宋鸿林.关于变质核杂岩构造特征的几个问题[J].地质通报,2002,21(4/5):193-197.
[25]Bryant D L,Ayers J C,Gao S,et al.Geochemical,age,and isotopic constrains on the location of the Sino-Korean/Yangtze Suture and evolution of the Northern Dabie Complex,east central China[J].GSA Bulletin,2004,116(5/6):698-717.
[26]王强,许继峰,赵振华,等.大别山燕山期亏损重 稀土元素花岗岩类的成因及动力学意义[J].岩石学报,2001,17:551-564.
[27]马昌前,扬坤光,许长海,等.大别山中生代钾质岩浆作用与超高压变质地体的剥露机制[J].岩石学报,1999,15(3):379-395.
[28]Liu Y,Li S,Xu S.Zircon SHRIMP U-Pb dating for gneisses in northern Dabie high T/P zone,central China:implications for de-coupling within subducted continental crust[J].Lithos,2007,96:170-185.
[29]徐树桐,刘贻灿,江来利,等.大别山的构造格局和演化[M].北京:科学出版社,1994:174.
①安徽省地质矿产局.杨柳湾镇幅(1∶5万)地质调查报告及地质图.2005.
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