摘要
超高压变质岩的折返过程是陆陆碰撞边界演化的关键问题。南倾的花凉亭-弥陀剪切带位于南大别低温-超高压变质带和中大别中温-超高压变质带之间,矿物拉伸线理倾伏向为SE,逆冲和走滑分量大致相等。电子背散射衍射分析表明:花凉亭-弥陀剪切带大多数样品的石英组构记录了上盘向NW的剪切变形,反映了中大别超高压变质岩向SE的快速折返,而部分样品的石英具有上盘向SE的剪切指向,与早白垩世花岗岩穹隆发育导致的区域伸展有关。对前人的岩石学和年代学成果进行总结,发现大别山进变质和超高压变质峰期/退变质的锆石U-Pb年龄从南往北逐渐变新,南大别和中大别在215～225 Ma同时经历了高压榴辉岩相退变质作用,在191～195 Ma经历了绿片岩相变质作用。超高压变质岩的白云母和黑云母的40Ar/39Ar年龄靠近郯庐断裂时偏年轻,可能受到郯庐断裂活动的影响。南大别和中大别变质峰期温压的等值线与花凉亭-弥陀剪切带的走向斜交,反映了超高压变质岩的斜向折返。因此,南大别低温-超高压变质带在～236 Ma最先开始折返,之后中大别和北大别依次发生快速折返,具有不同折返速率和折返角度的构造岩片通过韧性剪切带调节相对运动。
Exhumation processes of ultrahigh-pressure(UHP) metamorphic rocks are critical for evolution of continental collision boundaries. The south-dipping Hualiangting-Mituo shear zone is the boundary between the South Dabie low-temperature/UHP zone and the Central Dabie mid-temperature/UHP zone. It is characterized by SE-trending stretching lineation, and nearly equal thrust and strike slip components. The lattice-preferred orientation of quartz from the Hualiangting-Mituo shear zone was determined using the electronic backscatter diffraction(EBSD) technique. Most samples show the top-to-NW shear sense due to the fast SE-ward exhumation of the Central Dabie mid-temperature/UHP zone. However, some samples developed the top-to-SE shear sense because of intrusion of granitic domes and regional extension in the Early Cretaceous. A summary of petrological and geochronological data in the Dabie Mountains reveals the decreasing U-Pb zircon ages of the prograde metamorphism and UHP peak metamorphism from south to north. The South and Central Dabie UHP zones experienced coeval high-pressure eclogite facies metamorphism at 215～225 Ma and greenschist facies metamorphism at 191～195 Ma. The relatively younger40 Ar/39 Ar ages of muscovite and biotite near the Tanlu fault may be affected by ductile activation of the Tanlu fault. The isobaric and isothermal contours of the peak metamorphism in the South and Central Dabie UHP zones are oblique to the trend of the Hualiangting-Mituo shear zone, suggesting oblique exhumation of UHP rocks. We proposed that the South Dabie low-temperature/UHP zone was first exhumed towards SE as a tectonic slice at ～236 Ma, which was followed by fast exhumation of the Central and North Dabie UHP zones. The relative motion(i.e., different exhumation rates and oblique exhumation angels) between these UHP metamorphic slices was adjusted by ductile shear zones.
引文
林伟,王清晨,Faure M,等.2005.从北淮阳构造带的多期变形透视大别山构造演化[J].中国科学(D辑),35:127-139.
林伟,冀文斌,石永红,等.2008.高压-超高压变质岩石多期构造折返:以桐柏-红安-大别造山带为例[J].科学通报,58:2259-2265.
石永红,王次松,康涛,等.2012.安徽省宿松变质杂岩岩石学特征和锆石U-Pb年龄研究[J].岩石学报,28:3389-3402.
石永红,王娟,聂峰,等.2016.宿松变质杂岩中石榴石-蓝晶石-硬绿泥石片岩形成条件及时限研究[J].岩石学报,32(2):493-504.
魏春景,单振刚.1997.安徽省大别山南部宿松杂岩变质作用研究[J].岩石学报,13(3):356-368
谢智,郑永飞,闫峻,等.2004.大别山沙村中生代A型花岗岩和基性岩的源区演化关系[J].岩石学报,20(5):1175-1184.
薛怀民,马芳,赵逊,等.2011.大别山造山带东南部天柱山花岗岩类侵入体的特征及其LA-ICP-MS锆石U-Pb年龄[J].岩石矿物学杂志,30(5):935-950.
张超,马昌前.2008.大别山晚中生代巨量岩浆活动的启动:花岗岩锆石U-Pb年龄和Hf同位素制约[J].矿物岩石学报,28(4):71-79.
Ayers J C,Dunkle S,Gao S,et al.2002.Constraints on timing of peak and retrograde metamorphism in the Dabie Shan ultrahigh pressure metamorphic belt,east-central China,using U-Th-Pb dating of zircon and monazite[J].Chemical Geology,186:315-331.
Bohlen S R,Montana A and Kerrick D M.1991.Precise determinations of the equilibria kyanite-reversible-sillimanite and kyanite-reversibleandalusite and a revised triple point for Al2SiO5polymorphs[J].American Mineralogist,76:677-680.
Bundy F P.1980.The P,T phase and reaction diagram for elemental carbon,1979[J].Journal of Geophysical Research,85:6930-6936.
Carswell D A,O’Brien P J,Wilson R N,et al.1997.Thermobarometry of phengite-bearing eclogites in the Dabie Mountains of central China[J].J.Metamorph.Geol.,15:239-252.
Chopin C.1984.Coesite and pure pyrope in high-grade blueschists of the western Alps:a first record and some consequences[J].Contrib.Mineral.Petrol.,86:107-118.
Dai L Q,He H Y and Zhao Z F.2016.Postcollisional mafic igneous rocks record recycling of noble gases by deep subduction of the continental crust[J].Lithos,252-253:135-144.
Faure M,Lin W,Sch?rer U,et al.2003.Continental subduction and exhumation of UHP rocks:structural and geochronological insights from the Dabieshan(East China)[J].Lithos,70:213-241.
Faure M,Lin W,Shu L S,et al.1999.Tectonics of the Dabieshan(eastern China)and possible exhumation mechanism of ultrahigh-pressure rocks[J].Terra Nova,11:251-258.
Gao X Y,Zheng Y F,Chen Y X,et al.2015.Zircon geochemistry records the action of metamorphic fluid on the formation of ultrahigh-pressure jadeite quartzite in the Dabie orogen[J].Chemical Geology,419:158-175.
Gao X Y,Zheng Y F and Chen Y X.2011.U-Pb ages and trace elements in metamorphic zircon and titanite from UHP eclogite in the Dabie orogen:constraints on P-T-t path[J].Journal of Metamorphic Geology,29:721-740.
Grove M and Harrison T M.1996.40Ar diffusion in Fe-rich biotite[J].American Mineralogist,81:940-951.
Hacker B R,Ratschbacher L,Webb L E,et al.1998.Zircon ages constrain the architecture of the ultrahigh-pressure Qinling-Dabie orogen,China[J].Earth and Planetary Science Letters,161:215-230.
Hacker B R,Ratschbacher L,Webb L E,et al.2000.Exhumation of ultrahigh-pressure continental crust in east central China:Late Triassic-early Jurassic tectonic unroofing[J].Journal of Geophysical Research,105:13,339-13,364.
Harrison T M,Célérier J,Aikman A B,et al.2009.Diffusion of40Ar in muscovite[J].Geochim.Cosmochim.Acta,73:1039-1051.
Harrison T M,Duncan I and McDougall I.1985.Diffusion of40Ar in biotite:temperature,pressure,and compositional effects[J].Geochimica et Cosmochimica Acta,49:2461-2468.
Harrison T M.1981.Diffusion of40Ar in hornblende[J].Contributions to Mineralogy and Petrology,78:324-331.
Hemingway B S,Bohlen S R,Hankins W B,et al.1998.Heat capacity and thermodynamic properties for coesite and jadeite,reexamination of the quartz-coesite equilibrium boundary[J].American Mineralogist,83:409-418.
Ji W B,Lin W,Faure M,et al.2017.The early Cretaceous orogen-scale Dabieshan metamorphic core complex:implications for extensional collapse of the Triassic HP-UHP orogenic belt in east-central China[J].International Journal of Earth Sciences,106:1311-1340.
Law R D.2014.Deformation thermometry based on quartz c-axis fabrics and recrystallization microstructures:A review[J].Journal of Structural Geology,66:129-161.
Li S G,Huang F,Zhou H Y,et al.2003.U-Pb isotopic compositions of the ultrahigh pressure metamorphic(UHPM)rocks from Shuanghe and gneisses from Northern Dabie zone in the Dabie Mountains,central China:constraint on the exhumation mechanism of UHPM rocks[J].Science in China(Series D),46:200-209.
Li S G,Jacoutz E,Chen Y Z,et al.2000.Sm-Nd and Rb-Sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at Shuanghe in the Dabie Mountains,Central China[J].Geochimica et Cosmochimica Acta,64(6):1077-1093.
Li S G,Jacoutz E,Lo C H,et al.1999.Sm/Nd,Rb/dSr,and40Ar/39Ar isotopic systematics of the ultrahigh-pressure metamorphic rocks in the Dabie-Sulu belt,Central China:A retrospective view[J].International Geology Review,41:1114-1124.
Li S G,Wang C X,Dong F,et al.2009.Common Pb of UHP metamorphic rocks from the CCSD project(100-5000 m)suggesting decoupling between the slices within subducting continental crust and multiple thin slab exhumation[J].Tectonophysics,475:308-317.
Li X P,Zheng Y F,Wu Y B,et al.2004.Low-T eclogite in the Dabie terrane of China:petrological and isotopic constraints on fluid activity and radiometric dating[J].Contrib Mineral Petrol.,148:443-470.
Lin W,Ji W B,Faure M,et al.2015.Early Cretaceous extensional reworking of the Triassic HP-UHP metamorphic orogen in Eastern China[J].Tectonophysics,662:256-270.
Liou J G,Ernst W G,Zhang R Y,et al.2009.Ultrahigh-pressure minerals and metamorphic terranes-the view from China[J].Journal of Asian Earth Sciences,35:199-231.
Liu D Y,Jian P,Kr?ner A and Xu S T.2006.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,250:650-666.
Liu J B,Ye K,Maruyama S,et al.2001.Mineral inclusions in zircon from gneisses in the ultrahigh-pressure zone of the Dabie Mountains,China[J].The Journal of Geology,109:523-535.
Liu P L,Wu Y,Liu Q,et al.2014.Partial melting of UHP calc-gneiss from the Dabie Mountains[J].Lithos,192-195:86-101.
Liu Y C,Gu X F,Rolfo F,et al.2011a.Ultrahigh-pressure metamorphism and multistage exhumation of eclogite of the Luotian dome,North Dabie Complex Zone(central China):evidence from mineral inclusions and decompression textures[J].Journal of Asian Earth Sciences,42:607-617.
Liu Y C,Gu X F,Li S G,et al.2011b.Multistage metamorphic events in granulitized eclogites from the North Dabie complex zone,central China:Evidence from zircon U-Pb age,trace element and mineral inclusion[J].Lithos,122:107-121.
Liu Y C,Li S G,Gu X F,et al.2007b.Ultrahigh-pressure eclogite transformed from mafic granulite in the Dabie orogen,east-central China[J].Journal of Metamorphic Geology,25:975-989.
Liu Y C,Li S G and Xu S T.2007a.Zircon SHRIMP U-Pb dating for gneisses in northern Dabie high T/P metamorphic zone,central China:Implications for decoupling within subducted continental crust[J].Lithos,96:170-185.
Mainprice D,Bouchez J L,Blumenfeld P,et al.1986.Dominant C slip in naturally deformed quartz:Implications for dramatic plastic softening at high temperature[J].Geology,14:819-822.
Mainprice D.1990.A Fortran program to calculate seismic anisotropy from the lattice preferred orientation of minerals[J].Computer Geosciences,16:385-393.
Massonne H J.2012.Formation of amphibole and clinozoisite-epidote in eclogite owing to fluid infiltration during exhumation in a subduction channel[J].Journal of Petrology,53(10):1969-1998.
Nicolas A and Poirier J P.1976.Crystalline Plasticity and Solid State Flow in Metamorphic Rocks[M].New York:Wikey,444.
Okay A I,Sengor A and Satir M.1993.Tectonics of an ultrahigh-pressure metamorphic terrane:the Dabie Shan/Tongbieshan orogen,China[J].Tectonics,12:1320-1334.
Okay A I,Xu S T and Sengor A M C.1989.Coesite from the Dabie Shan eclogites,central China[J].European Journal of Mineralogy,1:595-598.
Qiu H N,Wijbrans J R,Brouwer F M,et al.2010.Amphibolite facies retrograde metamorphism of the Zhujiachong eclogite,SE Dabieshan:Ar/Ar age constraints from argon extraction using UV,laser microprobe,in vacuo crushing and stepwise heating[J].Journal of Metamorphic Geology,28:477-487.
Ratschbacher L,Hacker B R,Webb L E,et al.2000.Exhumation of the ultrahigh-pressure continental crust in east central China:Cretaceous and Cenozoic unroofing and the Tan-Lu fault[J].Journal of Geophysical Research,105:13303-13338.
Rolfo F,Compagnoni R,Wu W,et al.2004.A coherent lithostratigraphic unit in the coesite-eclogite complex of Dabie Shan,China:geologic and petrologic evidence[J].Lithos,73:71-94.
Rolfo F,Compagnoni R,Xu S T,et al.2000.First report of felsic whiteschist in the ultrahigh-pressure metamorphic belt of Dabie Shan,China[J].European Journal of Mineralogy,12:883-898.
Shi Y H,Lin W,Ji W B,et al.2014.The architecture of the HP-UHP Dabie massif:New insights from geothermobarometry of eclogites,and implication for the continental exhumation processes[J].Journal of Asian Earth Sciences,86:38-58.
Smith D C.1984.Coesite in clinopyroxene in the Caledonides and its implications for geodynamics[J].Nature,310:641-644.
Tsujimori T and Ernst W G.2014.Lawsonite blueschists and lawsonite eclogites as proxies for palaeo-subduction zone processes:A review[J].Journal of Metamorphic Geology,32:437-454.
Wang R C,Xu S J,Fang Z,et al.2004.Protolith age and exhumation history of metagranites from the Dabie UHP metamorphic belt in east-central China:A multi-chronological study[J].Geochemical Journal,38:345-362.
Wang X M and Liou J G.1991.Regional ultrahigh-pressure coesite-bearing eclogite terrane in central China:evidence from country rocks,gneiss,marble and metapelite[J].Geology,19:933-936.
Wang Y S,Xiang B W,Zhu G,et al.2011.Structural and geochronological evidence for Early Cretaceous orogen-parallel extension of the ductile lithosphere in the northern Dabie orogenic belt,East China[J].Journal of Structural Geology,33:362-380.
Wang Y.2006.The onset of the Tan-Lu fault movement in eastern China:constraints from zircon(SHRIMP)and40Ar/39Ar dating[J].Terra Nova,18:423-431.
Wu Y B.,Zheng Y F.,Zhao Z F,et al.2006.U-Pb,Hf and O isotope evidence for two episodes of fluid-assisted zircon growth in marble-hosted eclogites from the Dabie orogen[J].Geochimica et Cosmochimica Acta,70:3743-3761.
Xia Q X,Zheng Y F and Chen Y X.2013.Protolith control on fluid availability for zircon growth during continental subduction-zone metamorphism in the Dabie orogen[J].Journal of Asian Earth Sciences,67-68:93-113.
Xia Q X,Zheng Y F and Hu Z C.2010.Trace elements in zircon and coexisting minerals from low-T/UHP metagranite in the Dabie orogen:implications for fluid regime during continental subduction-zone metamorphism[J].Lithos,114:385-412.
Xia Q X,Zheng Y F,Yuan H L,et al.2009.Contrasting Lu-Hf and U-Th-Pb isotope systematics betweenmetamorphic growth and recrystallization of zircon from eclogite-facies metagranites in the Dabie orogen,China[J].Lithos,112:477-496.
Xu S T,Liu Y C,Chen G,et al.2003.New finding of micro-diamonds in eclogites from Dabie-Sulu region in central-eastern China[J].Chinese Science Bulletin,48:988-994.
Xu S T,Liu Y C,Chen G,et al.2005.Architecture and kinematics of the Dabie orogen,central eastern China[J].Acta Geologica Sinica,79:356-371.
Xu S T,Okay A I,Ji S Y,et al.1992.Diamond from the Dabie Shan metamorphic rocks and its implication for tectonic setting[J].Science,256:80-82.
Xu Z Q,Wang Q,Tang Z M,et al.2009.Fabric kinematics of ultrahigh-pressure metamorphic rocks from the main borehole of the Chinese Continental Scientific Drilling Project:implications for continental subduction and exhumation[J].Tectonophysics,475:235-250.
Xu Z Q,Zeng L S,Liu F L,et al.2006.Polyphase subduction and exhumation of the Sulu high-pressure-ultrahigh-pressure metamorphic terrane[J].In:Hacker,B.R.,McClelland,W.C.,Liou,J.G.(Eds.),Ultrahigh-pressure Metamorphism:Deep Continental Subduction.GSASpecial Paper,403:93-113.
Ye K,Cong B and Ye D.2000.The possible subduction of continental material to depths greater than 200 km[J].Nature,407:734-736.
Zhao X X and Coe R S.1987.Palaeomagnetic constraints on the collision and rotation of North and South China[J].Nature,327:141-144.
Zhao Z F,Zheng Y F,Wei C S,et al.2005.Zircon U-Pb age,element and C-O isotope geochemistry of post-collisional mafic-ultramafic rocks from the Dabie orogen in east-central China[J].Lithos,83:1-28.
Zhao Z F,Zheng Y F,Wei C S,et al.2007.Post-collisional granitoids from the Dabie orogen in China:Zircon U-Pb age,element and O isotope evidence for recycling of subducted continental crust[J].Lithos,93:248-272.
Zheng Y F,Fu B,Li Y L,et al.1998.Oxygen and hydrogen isotope geochemistry of ultrahigh pressure eclogites from the Dabie Mountains and the Sulu terrane[J].Earth and Planetary Science Letters,155:113-129.
Zheng Y F,Xia Q X,Chen R X,et al.2011a.Partial melting,fluid supercriticality and element mobility in ultrahigh-pressure metamorphic rocks during continental collision[J].Earth-Science Reviews,107:342-374.
Zheng Y F,Gao X Y,Chen R X,et al.2011b.Zr-in-rutile thermometry of eclogite in the Dabie orogen:Constraints on rutile growth during continental subduction-zone metamorphism[J].Journal of Asian Earth Sciences,40:427-451.
Zheng Y F,Gong B,Zhao Z F,et al.2003.Two types of gneisses associated with eclogite at Shuanghe in the Dabie terrane:carbon isotope,zircon U-Pb dating and oxygen isotope[J].Lithos,70:321-343.
Zheng Y F,Wu Y B,Zhao Z F,et al.2005a.Metamorphic effect on zircon Lu-Hf and U-Pb isotope systems in ultrahigh-pressure eclogite-facies metagranite and metabasite[J].Earth and Planetary Science Letters,240:378-400.
Zheng Y F,Zhou J B,Wu Y B,et al.2005b.Low-grade metamorphic rocks in the Dabie-Sulu orogenic belt:a passive-margin accretionary wedge deformed during continent subduction[J].International Geology Review,47:851-871.
Zheng Y F.2008.A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt[J].Chinese Science Bulletin,53:3081-3104.
Zheng Y F.2012.Metamorphic chemical geodynamics in continental subduction zones[J].Chemical Geology,328:5-48.
Zhu G,Xie C,Chen W,et al.2010.Evolution of the Hongzhen metamorphic core complex:Evidence for Early Cretaceous extension in the eastern Yangtze craton,eastern China[J].GSA Bulletin,122:506-516.
