中国大陆科学钻探主孔100～2000米超高压变质岩岩相学特征与变质变形史
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摘要
中国大陆科学钻探工程的实施,为超高压变质带的研究打开了新的生面,加深了对苏鲁超高压变质带的认识。从100-2000米获得的岩心的岩石学观察,得知主要岩石类型有:(1)榴辉岩及石榴辉石岩;(2)榴辉岩质片麻岩;(3)石榴橄榄岩;(4)黑云(角闪)二长片麻岩和(5)碎裂岩等。榴辉岩可分幔源和壳源两类,壳源榴辉岩在钻孔中分布较广,上部最为集中;幔源榴辉岩,包括石榴辉石岩,在空间上与超镁铁岩有密切共生关系。榴辉岩质的片麻岩是一种中酸性的超高压岩石,与壳源的榴辉岩共生,显微镜下可以追索出它们之间的结构演化关系。石榴橄榄岩以石榴单辉橄榄岩为主,是俯冲带上部地幔楔加入于俯冲板片变质而成。石榴橄榄岩中的石榴子石富镁,单斜辉石为绿辉石并常含钛斜硅镁石,说明其经过超高压变质的过程。从变质岩石的组合,面理和线理产状的差异,地震反射面和构造角砾岩带的发育,发现以1600米为界,可大致分为2个岩片。上部岩片中多金红石榴辉岩而且出现频率很高,下部岩片中多为多硅白云母榴辉岩出现频率较低。由于隆升进入中下地壳,超高压变质岩普遍发生退变质。榴辉岩的早期退变质成为具后成合晶结构的石榴角闪岩,榴辉岩质片麻岩退变质形成绿帘黑云(角闪)斜长片麻岩,变质条件为角闪岩相,它可以部分熔融或受到钾交代作用而转变为?
The implementation of the Chinese Continental Scientific Drilling ( CCSD) has made a new breakthrough in the study of ultrahigh-pressure metamorphic (UHPM) belt and has deepened the understanding of evolution of this orogenic belt. The close study of the core rocks from 100 - 2000m of the main hole of the Drilling has revealed that the major lithological types are: (1) Eclogites and garnet pyroxenites; (2) Eclogitic gneiss; (3) Garnet peridotites; (4) Biotite(hornblende) two-feldspar gneiss and (5) Fault breccia and mylonites. The eclogites are of two types: crustal and mantle-derived eclogites. The crustal eclogites are widely developed and are much more concentrated in the upper part of the mainhole. The mantle derived eclogites are closely related with the ultramafic rock unit. The eclogitic gneiss are UHPM rocks of intermediate acidic composition and are associated with crustal eclogites. There are distinct textural relationships between them which can be traced under the petrographic microscope. Garnet peridotites are mainly garnet wehrlites. They were incorporated into the subducted slab from the overlying mantle wedge. The garnets in the peridotite are high in Pyp mol % , and Cpx in them are omphacites, besides , there are wide-spread titanoclinohumites. All of these indicate that the garnet peridotites had undergone ultrahigh-pressure metamorphism. Judging from the differences in metamorphic rock association , in dip and plunging direction and angles of foliation and lineation of the rocks, in the existence of seismic reflection plane and fault breccia in the depth of 1600 m, it is obvious that there are 2 different rock slices across the 1600m surface. In the upper slice the rutile eclogites are abundant and with high frequency, in the lower the phengite eclogites are common but are sporadically occurred. Due to the uplift of the subducted slab into the mid-lower crust, most of the UHPM rocks had undergone retrogressive metamorphism in various degree. In the earlier stage of retrogression eclogite was turned to be symplectic garnet amphibolites. The eclogitic gneiss was retrograded to be biotite (hornblende) plagioclase gneiss . The metamorphic condition belonged to amphibolite facies and can subsequently be remelted or due to K-metasomatism be replaced by biotite hornblende two feldspar gneiss ( granite gneiss). In the later stage the crustal extension had resulted in local cataclasis forming tectonic breccia with the development of chlorite, calcite, hematite and epidote indicating the epidote amphibolite facies or greenschist facies of metamorphism. The ultrahigh-pressure metamorphism of the 100 -2000m core from the CCSD main hole reveals that voluminous crustal materials can deeply subducted to mantle depth and rapidly returned back to the surface. The UHPM rocks had recorded the processes of subduction and exhumation of the continental crust, therefore they are good information carriers of the tectonics beneath plate and mantle dynamics.
The implementation of the Chinese Continental Scientific Drilling ( CCSD) has made a new breakthrough in the study of ultrahigh-pressure metamorphic (UHPM) belt and has deepened the understanding of evolution of this orogenic belt. The close study of the core rocks from 100 - 2000m of the main hole of the Drilling has revealed that the major lithological types are: (1) Eclogites and garnet pyroxenites; (2) Eclogitic gneiss; (3) Garnet peridotites; (4) Biotite(hornblende) two-feldspar gneiss and (5) Fault breccia and mylonites. The eclogites are of two types: crustal and mantle-derived eclogites. The crustal eclogites are widely developed and are much more concentrated in the upper part of the mainhole. The mantle derived eclogites are closely related with the ultramafic rock unit. The eclogitic gneiss are UHPM rocks of intermediate acidic composition and are associated with crustal eclogites. There are distinct textural relationships between them which can be traced under the petrographic microscope. Garnet peridotites are mainly garnet wehrlites. They were incorporated into the subducted slab from the overlying mantle wedge. The garnets in the peridotite are high in Pyp mol % , and Cpx in them are omphacites, besides , there are wide-spread titanoclinohumites. All of these indicate that the garnet peridotites had undergone ultrahigh-pressure metamorphism. Judging from the differences in metamorphic rock association , in dip and plunging direction and angles of foliation and lineation of the rocks, in the existence of seismic reflection plane and fault breccia in the depth of 1600 m, it is obvious that there are 2 different rock slices across the 1600m surface. In the upper slice the rutile eclogites are abundant and with high frequency, in the lower the phengite eclogites are common but are sporadically occurred. Due to the uplift of the subducted slab into the mid-lower crust, most of the UHPM rocks had undergone retrogressive metamorphism in various degree. In the earlier stage of retrogression eclogite was turned to be symplectic garnet amphibolites. The eclogitic gneiss was retrograded to be biotite (hornblende) plagioclase gneiss . The metamorphic condition belonged to amphibolite facies and can subsequently be remelted or due to K-metasomatism be replaced by biotite hornblende two feldspar gneiss ( granite gneiss). In the later stage the crustal extension had resulted in local cataclasis forming tectonic breccia with the development of chlorite, calcite, hematite and epidote indicating the epidote amphibolite facies or greenschist facies of metamorphism. The ultrahigh-pressure metamorphism of the 100 -2000m core from the CCSD main hole reveals that voluminous crustal materials can deeply subducted to mantle depth and rapidly returned back to the surface. The UHPM rocks had recorded the processes of subduction and exhumation of the continental crust, therefore they are good information carriers of the tectonics beneath plate and mantle dynamics.
引文
Cui JW, Wang LJ, Li PW, Xu DH and Wu HY. 2004． Tectonic stress field of brittle deformation within 2000m of the main borehole Chinese Continental Scientific Drilling. Acta Petrologica Sinica, 20 (1) :73-80 (in Chinese with English abstract)
Irvine T N and Baragar W R A. 1971． A gqide to the chemical classification of the common volcanic rocksk. Canadian J. Earth Sci. , 8:523-548
Jin ZM, Ou XG, Xu HJ, Jin SY, Hou GJ and Kern H. 2004． Elastic wave velocities of the 2000m depth at Chinese Continental Scientific Drilling: Constraints on deep seismic reflection. Acta Petrologica Sinica, 20(1) :81-96 (in Chinese with English abstract)
Lasaga A C. 1997． Kinetic theory in the Earth Sciences Princeton series in geochemistry Princeton university press, Princeton New Jersey: 515-520
Liu FL, Zhang ZM, Xu ZQ. 2003． Three dimensional distribution of ultrahigh-pressure minerals in Sulu terrane. Acta Geologica Sinica, 77(1) :69-84 (in Chinese with English abstract)
Liu FL, Xu ZQ, Yang JS, Zhang ZM, Xu HM and Li TF. 2004． Geochemical characteristics and UHP metamorphism of granitic gneisses in the main drilling hole of Chinese Continental Scientific Drilling Project and its adjacent area. Acta Petrologica Sinica, 20 (1) : 9-26 (in Chinese with English abstract)
Spear F S. 1995． Metamorphic phase equilibria and Pressure-Temperature-Time paths, mineralogical Society of America monograph(second printing) :425-427
Suo ST, Zhong ZQ, Zhou HW. 2002． Reclined folds within the UHP metamorphic belt in the Donghai area, northern Jiangsu, China. Geological Science and Technology Information, 21 (2) :1-7 (in Chinese with English abstract)
Suo ST, Zhong ZQ, You ZD. 2001． Extensional tectonic framework of the Dabie-Sulu UHP-HP metamorphic belt, Central China, and its geodynamical significance. Acta Geologica Sinica, 75 (1) : 14-24 (in Chinese with English abstract)
Wang CY, Zeng RS, Mooney WD and Hacker BR. 2000． A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling. Journal of Geophysical Research, 105 :10857-10869
Wang X, Liou JG and Mao HK. 1989． Coesite-bearing eclogite from the Dabie mountains in Central China. Geology, 17:1085-1088
Xu PF, Liu FT, Wang QC et al. 2001． Slab-like high velocity anomaly in the uppermost mantle beneath the Dabie-Sulu orogen. Geophysical Research Letters, 28:1847-1850
Xu S, Okay A I, Ji S, Sengor AMC, Su W, Liu Y and Jiang L. 1992． Diamond from the Dabie Shan metamorphic rocks and its implication for tectonic setting. Science, 256:80-82
Xu ZQ, Yang WC, Zhang ZM and Yang TN. 1998． Scientific significance and site selection researches of the first Chinese continental scientific deep drillhole. Continental Dynamics, 3 :1-13
Xu ZQ, Zhang ZM, Liu FL et al. 2003a. Exhumation structure andmechanism of the Sulu ultrahigh-pressure metamorphic belt, centralChina. Acta Geologica Sinica, 77(4) :433-450 (in Chinese withEnglish abstract)
Xu ZQ, Zhao ZX, Yang JS et al. 2003b. Tectonics beneath plates andmantle dynamics. Geological Bulletin of China, 22(3) : 149-159(in Chinese with English abstract)
Xu ZQ. 2004． The scientific goals and investigation progresses of theChinese Continental Scientific Drilling Project. Acta PetrologicaSinica, 20(1) :1-8
Yang JJ. 2003． Titanian Clinohumite-garnet-pyroxene rock from theSulu UHP metamorphic terrane, China: Chemical evolution andtectonic implications. Lithos, 70:359-379
Yang Qijun, Zhong Zengqiu, Zhou Hanwen. 2003． Geochemistryconstraints on rock association of UHP terrane during exhumation.Earth Science-Journal of China University of Geosciences, 28(3) :241-249 (in Chinese with English abstract)
Yang WC, Yang WY and Chen ZY. 2004． Interpretation of 3D seismicreflection data in the Chinese Continental Scientific Drilling site.Acta Petrologica Sinica 20(1) : 127-137 ( in Chinese with Englishabstract)
Ye K, Cong B and Ye D. 2000． The possible subduction of continentalmaterial to depths greater than 200km. Nature, 407 :734-736
Yuan XC, Klemperer SL, Teng WB et al. 2003． Crustal structure
Irvine T N and Baragar W R A. 1971． A gqide to the chemical classification of the common volcanic rocksk. Canadian J. Earth Sci. , 8:523-548
Jin ZM, Ou XG, Xu HJ, Jin SY, Hou GJ and Kern H. 2004． Elastic wave velocities of the 2000m depth at Chinese Continental Scientific Drilling: Constraints on deep seismic reflection. Acta Petrologica Sinica, 20(1) :81-96 (in Chinese with English abstract)
Lasaga A C. 1997． Kinetic theory in the Earth Sciences Princeton series in geochemistry Princeton university press, Princeton New Jersey: 515-520
Liu FL, Zhang ZM, Xu ZQ. 2003． Three dimensional distribution of ultrahigh-pressure minerals in Sulu terrane. Acta Geologica Sinica, 77(1) :69-84 (in Chinese with English abstract)
Liu FL, Xu ZQ, Yang JS, Zhang ZM, Xu HM and Li TF. 2004． Geochemical characteristics and UHP metamorphism of granitic gneisses in the main drilling hole of Chinese Continental Scientific Drilling Project and its adjacent area. Acta Petrologica Sinica, 20 (1) : 9-26 (in Chinese with English abstract)
Spear F S. 1995． Metamorphic phase equilibria and Pressure-Temperature-Time paths, mineralogical Society of America monograph(second printing) :425-427
Suo ST, Zhong ZQ, Zhou HW. 2002． Reclined folds within the UHP metamorphic belt in the Donghai area, northern Jiangsu, China. Geological Science and Technology Information, 21 (2) :1-7 (in Chinese with English abstract)
Suo ST, Zhong ZQ, You ZD. 2001． Extensional tectonic framework of the Dabie-Sulu UHP-HP metamorphic belt, Central China, and its geodynamical significance. Acta Geologica Sinica, 75 (1) : 14-24 (in Chinese with English abstract)
Wang CY, Zeng RS, Mooney WD and Hacker BR. 2000． A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling. Journal of Geophysical Research, 105 :10857-10869
Wang X, Liou JG and Mao HK. 1989． Coesite-bearing eclogite from the Dabie mountains in Central China. Geology, 17:1085-1088
Xu PF, Liu FT, Wang QC et al. 2001． Slab-like high velocity anomaly in the uppermost mantle beneath the Dabie-Sulu orogen. Geophysical Research Letters, 28:1847-1850
Xu S, Okay A I, Ji S, Sengor AMC, Su W, Liu Y and Jiang L. 1992． Diamond from the Dabie Shan metamorphic rocks and its implication for tectonic setting. Science, 256:80-82
Xu ZQ, Yang WC, Zhang ZM and Yang TN. 1998． Scientific significance and site selection researches of the first Chinese continental scientific deep drillhole. Continental Dynamics, 3 :1-13
Xu ZQ, Zhang ZM, Liu FL et al. 2003a. Exhumation structure andmechanism of the Sulu ultrahigh-pressure metamorphic belt, centralChina. Acta Geologica Sinica, 77(4) :433-450 (in Chinese withEnglish abstract)
Xu ZQ, Zhao ZX, Yang JS et al. 2003b. Tectonics beneath plates andmantle dynamics. Geological Bulletin of China, 22(3) : 149-159(in Chinese with English abstract)
Xu ZQ. 2004． The scientific goals and investigation progresses of theChinese Continental Scientific Drilling Project. Acta PetrologicaSinica, 20(1) :1-8
Yang JJ. 2003． Titanian Clinohumite-garnet-pyroxene rock from theSulu UHP metamorphic terrane, China: Chemical evolution andtectonic implications. Lithos, 70:359-379
Yang Qijun, Zhong Zengqiu, Zhou Hanwen. 2003． Geochemistryconstraints on rock association of UHP terrane during exhumation.Earth Science-Journal of China University of Geosciences, 28(3) :241-249 (in Chinese with English abstract)
Yang WC, Yang WY and Chen ZY. 2004． Interpretation of 3D seismicreflection data in the Chinese Continental Scientific Drilling site.Acta Petrologica Sinica 20(1) : 127-137 ( in Chinese with Englishabstract)
Ye K, Cong B and Ye D. 2000． The possible subduction of continentalmaterial to depths greater than 200km. Nature, 407 :734-736
Yuan XC, Klemperer SL, Teng WB et al. 2003． Crustal structure
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