西南天山柯坪逆冲推覆构造带的地壳缩短分析
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摘要
柯坪逆冲推覆构造带是西南天山山前晚新生代以来形成的活动逆断裂-褶皱带,由5~6排近平行的弧形褶皱带组成,出露地层为寒武系—第四系。背斜形态多为复式箱状背斜和不对称的斜歪背斜,分别与断层弯曲背斜和断层扩展背斜的几何形态一致。地震勘探资料显示,各褶皱带前缘活动逆断裂在深部归并于统一的、由寒武系中的石膏层组成的滑脱面。滑脱面深度具有南浅北深、东浅西深的特点,皮羌断裂西侧滑脱面深度约为9km,东侧滑脱面深度为5km。在柯坪逆冲推覆构造中部的皮羌断裂东西两侧各5km和8km的位置,以断层弯曲褶皱和断层扩展褶皱构造模型为指导,用线长平衡的方法完成了2条长度分别为78km和73km的平衡地质剖面,恢复到变形前的形态后计算出这2条剖面上的地壳缩短量分别为40km和45km,缩短率为33%和37%。由于对柯坪逆冲推覆构造开始形成时间的证据较少,所以要计算长期的缩短速率是比较困难的。对比天山南麓库车活动逆断裂-褶皱带的形成时代,以及柯坪逆冲推覆构造与印干断裂的关系,认为柯坪逆冲推覆构造形成于第四纪早期的西域砾岩沉积阶段,按距今2.5Ma计算,柯坪逆冲推覆构造的地壳缩短速率是15.4~17.3mm/a。
Kalpin thrust tectonic is an active reverse fault fold zone at the southwestern Tianshan front piedmont, it consists of five to six rows of arc fold zones which are formed by Cambrian-Quaternary sedimentary rocks. The major morphology of the anticline is multiple box-shaped or asymmetry inclined, mostly, and it is similar to that of fault-bend fold and fault-propagation fold. Depending on the seismic reflection surveys data, the reverse faults on the front of the nappe in Kalpin thrust tectonic zone form an integrate detachment surface in the deep along the gypsum stratum in Cambrian. The depth of the detachment is shallower in the southeast and deeper in the northwest. The depth of the detachment fault is deeper in the west part (about 9km deep) and shallower in the east part (about 5km deep) of the Piqiang fault. In the middle part of the Kalpin reverse fault-fold zone, we have made two balanced cross-sections at the two sides of Piqiang fault. On the two geological cross-sections, we construct the structure mode at depth using fault-bend fold or fault-propagation fold model. The length of the two sections is 73km and 78km, respectively. The restored sections yield a crustal shortening of 40km to 45km, the shortening rate is 33% and 37%, respectively. Calculating the long-term shortening rate from these two across-sections is difficult, because the time of initiation of deformation is poorly known. Geological evidence suggests that most of the shortening began in the beginning of the deposition of the thick conglomerate unit in lower Quaternary. If the initiation time is about 2.5Ma, the shortening rate of Kalpin thrust tectonic zone is 15.4～17.3mm/a.
Kalpin thrust tectonic is an active reverse fault fold zone at the southwestern Tianshan front piedmont, it consists of five to six rows of arc fold zones which are formed by Cambrian-Quaternary sedimentary rocks. The major morphology of the anticline is multiple box-shaped or asymmetry inclined, mostly, and it is similar to that of fault-bend fold and fault-propagation fold. Depending on the seismic reflection surveys data, the reverse faults on the front of the nappe in Kalpin thrust tectonic zone form an integrate detachment surface in the deep along the gypsum stratum in Cambrian. The depth of the detachment is shallower in the southeast and deeper in the northwest. The depth of the detachment fault is deeper in the west part (about 9km deep) and shallower in the east part (about 5km deep) of the Piqiang fault. In the middle part of the Kalpin reverse fault-fold zone, we have made two balanced cross-sections at the two sides of Piqiang fault. On the two geological cross-sections, we construct the structure mode at depth using fault-bend fold or fault-propagation fold model. The length of the two sections is 73km and 78km, respectively. The restored sections yield a crustal shortening of 40km to 45km, the shortening rate is 33% and 37%, respectively. Calculating the long-term shortening rate from these two across-sections is difficult, because the time of initiation of deformation is poorly known. Geological evidence suggests that most of the shortening began in the beginning of the deposition of the thick conglomerate unit in lower Quaternary. If the initiation time is about 2.5Ma, the shortening rate of Kalpin thrust tectonic zone is 15.4～17.3mm/a.
引文
[1]新疆维吾尔自治区地质局,1965,1/20万苏巴什、赞比勒幅地质图及说明书
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沈军,汪一鹏,李莹甄,等.2003.中国新疆天山博阿断裂晚第四纪右旋走滑运动特征[J].地震地质,25(2):183—194.SHENJun,WANGYi-peng,LIYing-zhen,etal.2003.LateQuaternaryright-lateralstrike-slipfaultingalongtheBo-lokenu-AqikekudukeFaultinChineseTianshan[J].SeismologyandGeology,25(2):183—194(inChinese).
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王琪,张培震,牛之俊,等.2001.中国大陆现今地壳运动和构造变形[J].中国科学(D辑),31(7):529—536.WANGQi,ZHANGPei-zhen,NIUZhi-jun,etal.2001.PresentcrustmovementandtectonicdeformationofChinamainland[J].ScienceinChina(SerD),31(7):529—536(inChinese).
杨庚.2003.塔里木西北缘北西向古隆起的存在及油气勘探前景[J].新疆地质,21(2):157—162.YANGGeng.2003.TheanalysesonNW-strikingpaleoupliftandthehydrocarbonpotential,northwestTarim[J].XinjiangGeology,21(2):157—162(inChinese).
杨晓平,沈军.2000.天山内部博罗可努断裂精河-阿拉山口段晚更新世以来的活动特征[J].地震地质,22(3):305—315.YANGXiao-ping,SHENJun.2000.LateQuaternaryactivityofJinghe:AlashankousectionoftheBoluokenufault,interiorTianshan[J].SeismologyandGeology,22(3):305—315(inChinese).
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AbdrakhmatovKY.1996.RelativerecentconstructionoftheTienshaninferredfromGPSmeasurementsofpresent-daycrustdeformation[J].Nature,384:450—453.
AllenMB,VincentSJ.1999.LateCenozoictectonicsoftheKepingtagethrustzone:InteractionsoftheTienShanandTarimBasin,northwestChina[J].Tectonics,18(4):639—654.
AvouacJP,TapponierP,BaiM,etal.1993.,ActivethrustingandfoldingalongthenorthernTienshanandlateCe-nozoicrotationoftheTarimrelativetoDzungariaandKazakhstan[J].JournalofGeophysicalResearch,98(B4):6755—6804.
BilhamR,LarsonK,FreymuellerJ,etal.1997.GPSmeasurementsofpresent-dayconvergenceacrosstheNepelHi-malaya[J].Nature,386:61—64.
BurchfielBC,BrownET,DengQ,etal.1999.CrustalshorteningonthemarginsoftheTienShan,Xinjiang,China[J].InternationalGeologyReview,41:665—700.
BurtmanVS,SkolelevSF,MolnarP.1996.LateCenozoicslipontheTalas-Ferghanafault,theTienshan,centralA-sia[J].GeolSocAmerBull,108(8):1004—1021.
ChenJ,BurbankDW,ScharerKM,etal.2002.MagnetochronologyoftheupperCenoziocstrataintheSouthwesternChineseTianShan:ratesofPleistocenefoldingandthrusting[J].EarthandPlanetaryScienceLetters,195:113—130.
HendrixMS,DumitruTA,GrahamSA.1994.LateOligocene-earlyMioceneunroofingintheChineseTianShan:anearlyeffectoftheIndia-Asiacollision[J].Geology,22:487—490.
JamisonWR.1987.Geometricanalysisoffolddevelopmentinoverthrustterraces[J].JournalofStructureGeology,9:207—219.
MolnarP,TapponnierP.1977.ThecollisionbetweenIndiaandEurasia[J].SciAmer,236:30—41.
SobelER,DumitruTA.1997.ThrustingandexhumationaroundthemarginsofthewesternTarimbasinduringtheIn-dia-Asiacollision[J].JournalofGeophysicalResearch,102:5043—5063.
StephenCT,WelsonRJ,RubinCM,etal.2002.LateQuaternaryslipratesacrossthecentralTienShan,Kyrgy-zstan,centralAsia[J].JournalofGeophysicalResearch,107(B9):ETG7-1-7-32.
SuppeandMedweff.1990.Geometryandkinematicsoffault-propagationfolding[J].EcologueGeolHelv,83(30):409—454.
SuppeJ.1983.Geometryandkinematicsoffaultbendfolding[J].AmericanJournalofScience,283:684—721.
YinA,NieP,HarrisonTM,etal.1998.LateCenozoictectonicevolutionofthesouthernChineseTianShan[J].Tectonics,17(1):1—27.
陈杰,尹金辉,曲国胜,等.2000.塔里木盆地西缘西域组的底界、时代、成因与变形过程的初步研究[J].地震地质,22(增刊):104—116.CHENJie,YINJin-hui,QUGuo-sheng,etal.2000.Timing,lowerboundary,genesis,anddeformationofXiyufor-mationaroundthewesternmarginsoftheTarimbasin[J].SeismologyandGeology,22(suppl):104—116(inChinese).
陈杰,丁国瑜,BurbankDW,等.2001.中国西南天山山前的晚新生代构造与地震活动[J].中国地震,17(2):134—155.CHENJie,DINGGuo-yu,BurankDW,etal.2001.LateCenozoictectonicsandseismicityinthesouthwesternTian-shan,China[J].EarthquakeResearchinChina,17(2):134—155(inChinese).
邓起东,冯先岳,张培震,等.2000.天山活动构造[M].北京:地震出版社.188—265.DENGQi-dong,FANGXian-yue,ZHANGPei-zhen,etal.2000.ActiveTectonicsintheTianshan[M].Seismologi-calPress,Beijing(inChinese).
郭召杰,吴泰然,王东,等.2004.塔里木西北缘晚新生代印干断层及其与帕米尔构造结的关系[J].自然科学进展,14(9):1072—1076.GUOZhao-jie,WUTai-ran,WANGDong,etal.2004.TherelationbetweentheYinganfaultandPamierstructureinLateCenozoic,northwesternTarimbasin[J].NaturalScienceProgress,14(9):1072—1076(inChinese).
贾承造.1997.中国塔里木盆地构造特征与油气[M].北京:石油工业出版社.1—5.JIACheng-zao.1997.TectonicCharacteristicsandPetroleumofTarimBasin,China[M].PetroleumIndustryPub-lishingHouse,Beijing(inChinese).
曲国胜,李亦刚,陈杰,等.2003.柯坪塔格推覆构造几何学、运动学及其构造演化[J].地学前缘,10(特刊):142—152.QUGuo-sheng,LIYi-gang,CHENJie,etal.2003.Geometry,kinematicsandtectonicsevolutionofKepingtagethrustsystem[J].EarthScienceFrontier,10(suppl):142—152(inChinese).
沈军,赵瑞斌,李军,等.2001.塔里木盆地西北缘河流阶地变形测量与地壳缩短速率[J].科学通报,46(4):334—337.SHENJun,ZHAORui-bin,LIJun,etal.2001.SurveyingofthedeformedterracesandcrustshorteningrateinthenorthwesternTarimbasin[J].ChineseScienceBulletin,46(4):334—337(inChinese).
沈军,汪一鹏,李莹甄,等.2003.中国新疆天山博阿断裂晚第四纪右旋走滑运动特征[J].地震地质,25(2):183—194.SHENJun,WANGYi-peng,LIYing-zhen,etal.2003.LateQuaternaryright-lateralstrike-slipfaultingalongtheBo-lokenu-AqikekudukeFaultinChineseTianshan[J].SeismologyandGeology,25(2):183—194(inChinese).
王琪,丁国瑜,乔学军,等.2000.用GPS研究天山(伽师)地区现今地壳变形[J].地震学报,22(3):263—270.WANGQi,DINGGuo-yu,QIAOXue-jun,etal.2000.ResearchonpresentcrustdeformationinthesouthernTians-han(Jiashi),ChinabyGPSgeology[J].ActaSeismologicaSinica,22(3):263—270(inChinese).
王琪,张培震,牛之俊,等.2001.中国大陆现今地壳运动和构造变形[J].中国科学(D辑),31(7):529—536.WANGQi,ZHANGPei-zhen,NIUZhi-jun,etal.2001.PresentcrustmovementandtectonicdeformationofChinamainland[J].ScienceinChina(SerD),31(7):529—536(inChinese).
杨庚.2003.塔里木西北缘北西向古隆起的存在及油气勘探前景[J].新疆地质,21(2):157—162.YANGGeng.2003.TheanalysesonNW-strikingpaleoupliftandthehydrocarbonpotential,northwestTarim[J].XinjiangGeology,21(2):157—162(inChinese).
杨晓平,沈军.2000.天山内部博罗可努断裂精河-阿拉山口段晚更新世以来的活动特征[J].地震地质,22(3):305—315.YANGXiao-ping,SHENJun.2000.LateQuaternaryactivityofJinghe:AlashankousectionoftheBoluokenufault,interiorTianshan[J].SeismologyandGeology,22(3):305—315(inChinese).
张培震,邓起东,杨晓平,等.1996.天山的晚新生代构造变形及其地球动力学问题[J].中国地震,12(2):127—140.ZHANGPei-zhen,DENGQi-dong,YANGXiao-ping,etal.1996.LateCenozoictectonicdeformationandmechanismalongtheTianshanMountains,NorthwesternChina[J].EarthquakeResearchinChina,12(2):127—140(inChinese).
AbdrakhmatovKY.1996.RelativerecentconstructionoftheTienshaninferredfromGPSmeasurementsofpresent-daycrustdeformation[J].Nature,384:450—453.
AllenMB,VincentSJ.1999.LateCenozoictectonicsoftheKepingtagethrustzone:InteractionsoftheTienShanandTarimBasin,northwestChina[J].Tectonics,18(4):639—654.
AvouacJP,TapponierP,BaiM,etal.1993.,ActivethrustingandfoldingalongthenorthernTienshanandlateCe-nozoicrotationoftheTarimrelativetoDzungariaandKazakhstan[J].JournalofGeophysicalResearch,98(B4):6755—6804.
BilhamR,LarsonK,FreymuellerJ,etal.1997.GPSmeasurementsofpresent-dayconvergenceacrosstheNepelHi-malaya[J].Nature,386:61—64.
BurchfielBC,BrownET,DengQ,etal.1999.CrustalshorteningonthemarginsoftheTienShan,Xinjiang,China[J].InternationalGeologyReview,41:665—700.
BurtmanVS,SkolelevSF,MolnarP.1996.LateCenozoicslipontheTalas-Ferghanafault,theTienshan,centralA-sia[J].GeolSocAmerBull,108(8):1004—1021.
ChenJ,BurbankDW,ScharerKM,etal.2002.MagnetochronologyoftheupperCenoziocstrataintheSouthwesternChineseTianShan:ratesofPleistocenefoldingandthrusting[J].EarthandPlanetaryScienceLetters,195:113—130.
HendrixMS,DumitruTA,GrahamSA.1994.LateOligocene-earlyMioceneunroofingintheChineseTianShan:anearlyeffectoftheIndia-Asiacollision[J].Geology,22:487—490.
JamisonWR.1987.Geometricanalysisoffolddevelopmentinoverthrustterraces[J].JournalofStructureGeology,9:207—219.
MolnarP,TapponnierP.1977.ThecollisionbetweenIndiaandEurasia[J].SciAmer,236:30—41.
SobelER,DumitruTA.1997.ThrustingandexhumationaroundthemarginsofthewesternTarimbasinduringtheIn-dia-Asiacollision[J].JournalofGeophysicalResearch,102:5043—5063.
StephenCT,WelsonRJ,RubinCM,etal.2002.LateQuaternaryslipratesacrossthecentralTienShan,Kyrgy-zstan,centralAsia[J].JournalofGeophysicalResearch,107(B9):ETG7-1-7-32.
SuppeandMedweff.1990.Geometryandkinematicsoffault-propagationfolding[J].EcologueGeolHelv,83(30):409—454.
SuppeJ.1983.Geometryandkinematicsoffaultbendfolding[J].AmericanJournalofScience,283:684—721.
YinA,NieP,HarrisonTM,etal.1998.LateCenozoictectonicevolutionofthesouthernChineseTianShan[J].Tectonics,17(1):1—27.
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