海原断裂带干盐池拉分盆地的沉积演化
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摘要
干盐池拉分盆地为青藏高原东北边界海原断裂带内最大的拉分盆地,对揭示青藏高原NE向生长、海原断裂的运动变形及古环境演变有着重要的意义。前人主要开展了区域地质填图和古地震方面的研究,而该盆地的地层、年龄、形成演化等皆不清楚。针对以上问题,在干盐池盆地开展了浅层人工地震勘探、深孔钻探及样品测试等工作。深孔剖面显示,干盐池盆地大约形成于距今2. 76Ma前,盆地内堆积了3段地层,第Ⅰ、Ⅱ、Ⅲ段地层分别约于距今2. 76Ma、2. 33Ma和1. 78Ma前开始堆积,沉积物的粒度呈现出"向上逐渐变细"的趋势,表现为1个典型的"退积型"沉积序列;磁化率结果表明,干盐池盆地大约于距今1. 78Ma前进入积水期,湖相层记录了多个高磁化率区间,这有可能是因为自生的亚铁磁性硫化铁矿物所致;钻孔及浅层人工地震勘探资料表明,干盐池盆地主要受南-西华山与唐家坡-干盐池断层的控制,其沉降中心介于这2条断层之间,最深处可能超过了550m。干盐池拉分盆地的沉积过程经历了由残积相(距今约2. 76Ma前)—扇根相(距今2. 76～2. 33Ma)—扇中相(距今2. 33～1. 78Ma)—盐湖相(距今约1. 78Ma—现今)的演变。盐湖相期以B/M界线为界又可细分为2个阶段,其中,第2阶段(距今约0. 78Ma—现今)的沉积速率急剧加快,高达232. 5m/Ma,这有可能是受盆地中央断层的活动影响所致。
Ganyanchi( Salt Lake) basin,located in the central part of the Haiyuan Fault,northeastern corner of the Tibetan plateau,is the largest pull-apart basin along this fault. Due to its location in northeastern Tibet,the Ganyanchi Basin preserves an important sedimentary record of tectonism and climate change associated with progressive growth of the Tibetan plateau. The sediments of this basin also contain abundant information regarding the deformational history of the bounding strike-slip fault,i.e.,the Haiyuan Fault. Therefore,a detailed study on the depository history of the Ganyanchi Basin is of great importance. Earlier studies only focused on regional geological mapping and paleoseismic research,however,no sedimentologic or chronological work has been done in the Ganyanchi pull-apart basin. To address this problem,we drilled a 328 m-deep borehole,named HYC8, at the south of the cross-basin fault and near the active depocenter, and employ magnetostratigraphic analyses and seismic reflection data to constrain the age and to deduce the evolving history of the basin. The deep borehole profile shows that the stratigraphy of the basin can be divided into three main units( Unit Ⅰ,Ⅱ and Ⅲ),which began to deposit at about 2. 76,2. 33 and1. 78 Ma,respectively. The grain size of the deposits manifests an upward thinning trend,which probably implies the profile is a characteristic retrogradational sequence. The magnetic susceptibility results indicate that the playa lake probably was formed at about 1. 78 Ma ago,the corresponding playa-lake deposits recorded more than eight high susceptibility sections,which are most likely due to the iron sulfides( such as melnikovite,pyrrhotine etc.) that were usually produced in high-lake-level and reduction conditions. A combination of boreholes and shallow seismic reflection data indicates that the Ganyanchi Basin is mainly controlled by the cross-basin fault and its northern boundary fault,and the depocenter, probably deeper than 550 m, lies in between these two faults. Finally, the sedimentary facies of the Ganyanchi Basin experienced a four-stage evolving history: eluvial facies( before～2. 76 Ma) to alluvial fan facies( about 2. 76 ～ 2. 33 Ma) to distal alluvial fan facies( 2. 33 ～1. 78 Ma) to playa lake facies( 1. 78 Ma ～ present). Based on accumulation rates,the stage of playa lake can be divided into two subchrons,and the depositional rates of subchrons 2( about 0. 78 Ma ～present) is as high as 232. 5 m/Ma,which probably was caused by the activity along the cross-basin fault in the Ganyanchi Basin.
Ganyanchi( Salt Lake) basin,located in the central part of the Haiyuan Fault,northeastern corner of the Tibetan plateau,is the largest pull-apart basin along this fault. Due to its location in northeastern Tibet,the Ganyanchi Basin preserves an important sedimentary record of tectonism and climate change associated with progressive growth of the Tibetan plateau. The sediments of this basin also contain abundant information regarding the deformational history of the bounding strike-slip fault,i.e.,the Haiyuan Fault. Therefore,a detailed study on the depository history of the Ganyanchi Basin is of great importance. Earlier studies only focused on regional geological mapping and paleoseismic research,however,no sedimentologic or chronological work has been done in the Ganyanchi pull-apart basin. To address this problem,we drilled a 328 m-deep borehole,named HYC8, at the south of the cross-basin fault and near the active depocenter, and employ magnetostratigraphic analyses and seismic reflection data to constrain the age and to deduce the evolving history of the basin. The deep borehole profile shows that the stratigraphy of the basin can be divided into three main units( Unit Ⅰ,Ⅱ and Ⅲ),which began to deposit at about 2. 76,2. 33 and1. 78 Ma,respectively. The grain size of the deposits manifests an upward thinning trend,which probably implies the profile is a characteristic retrogradational sequence. The magnetic susceptibility results indicate that the playa lake probably was formed at about 1. 78 Ma ago,the corresponding playa-lake deposits recorded more than eight high susceptibility sections,which are most likely due to the iron sulfides( such as melnikovite,pyrrhotine etc.) that were usually produced in high-lake-level and reduction conditions. A combination of boreholes and shallow seismic reflection data indicates that the Ganyanchi Basin is mainly controlled by the cross-basin fault and its northern boundary fault,and the depocenter, probably deeper than 550 m, lies in between these two faults. Finally, the sedimentary facies of the Ganyanchi Basin experienced a four-stage evolving history: eluvial facies( before～2. 76 Ma) to alluvial fan facies( about 2. 76 ～ 2. 33 Ma) to distal alluvial fan facies( 2. 33 ～1. 78 Ma) to playa lake facies( 1. 78 Ma ～ present). Based on accumulation rates,the stage of playa lake can be divided into two subchrons,and the depositional rates of subchrons 2( about 0. 78 Ma ～present) is as high as 232. 5 m/Ma,which probably was caused by the activity along the cross-basin fault in the Ganyanchi Basin.
引文
邓成龙,刘青松,潘永信,等. 2007.中国黄土环境磁学[J].第四纪研究,27(2):193—209.DENG Cheng-long,LIU Qing-song,PAN Yong-xin,et al.2007.Environmental magnetism of Chinese Loess paleosol sequence[J].Quaternary Sciences,27(2):193-209(in Chinese).
邓起东,张维岐,张培震,等.1989.海原走滑断裂带及其尾端挤压构造[J].地震地质,11(1):1-14.DENG Qi-dong,ZHANG Wei-qi,ZHANG Pei-zhen,et al.1989.Haiyuan strike-slip fault zone and its compressional structures of the end[J].Seismology and Geology,11(1):1-14(in Chinese).
郭鹏,韩竹军,安艳芬,等.2017.冷龙岭断裂系活动性与2016年门源6.4级地震构造研究[J].中国科学(D辑),47:617-630.GUO Peng,HAN Zhu-jun,AN Yan-fen,et al.2017.Activity of the Lenglongling fault system and seismotectonics of the 2016 MS6.4 Menyuan earthquake[J].Science in China(Ser D),60:929-942.
国家地震局地质研究所,宁夏回族自治区地震局.1990.海原活动断裂带[M].北京:地震出版社.Institute of Geology of State Seismological Bureau,Seismological Bureau of Ningxia Hui Autonomous Region.1990.Haiyuan Active Fault Zone[M].Seismological Press,Beijing(in Chinese).
国家地震局兰州地震研究所.1980.一九二○年海原大地震[M].地震出版社.Lanzhou Institute of Seismology,State Seismological Bureau.1980.The 1920 Haiyuan Earthquake[M].Seismological Press,Beijing(in Chinese).
胡守云,邓成龙,Appel E,等.2001.湖泊沉积物磁学性质的环境意义[J].科学通报,46(17):1491-1494.HU Shou-yun,DENG Cheng-long,Appel E,et al.2001.Environmental magnetic studies of lacustrine sediments[J].Chinese Science Bulletin,46(17):1491-1494(in Chinese).
胡守云,王苏民,Appel E,等.1998.呼伦湖湖泊沉积物磁化率变化的环境磁学机制[J].中国科学(D辑),28(4):334-339.HU Shou-yun,WANG Su-min,Appel E,et al.1998.Environmental magnetism in magnetic susceptibility of Hulun lake sediments[J].Science in China(Ser D),28(4):334-339(in Chinese).
李彦宝,冉勇康,王虎,等.2016.干盐池拉分盆地盆内新生断层大地震记录与海原断裂带级联破裂地震事件[J].地震地质,38(4):830-843.doi:10.3969/j.issn.0253-4967.2016.04.003.LI Yan-bao,RAN Yong-kang,WANG Hu,et al.2016.Paleoseismic records of large earthquakes on the cross-basin fault in the Salt Lake pull-apart basin and cascade rupture events on the Haiyuan Fault[J].Seismology and Geology,38(4):830-843(in Chinese).
刘青松,邓成龙.2009.磁化率及其环境意义[J].地球物理学报,52(4):1041-1048.LIU Qing-song,DENG Cheng-long.2009.Magnetic susceptibility and its environmental significances[J].Chinese Journal of Geophysics,52(4):1041-1048(in Chinese).
王心源,吴立,张广胜,等.2008.安徽巢湖全新世湖泊沉积物磁化率与粒度组合的变化特征及其环境意义[J].地理科学,28(4):548-553.WANG Xin-yuan,WU Li,ZHANG Guang-sheng,et al.2008.Characteristics and environmental significance of magnetic susceptibility and grain size of lake sediments since Holocene in Chaohu Lake,Anhui Province[J].Scientia Geographica Sinica,28(4):548-553(in Chinese).
张俊辉,杨太保,李永国,等.2010.柴达木盆地察尔汗盐湖CH0310钻孔沉积物磁化率及其影响因素分析[J].沉积学报,28(4):790-797.ZHANG Jun-hui,YANG Tai-bao,LI Yong-guo,et al.2010.Analysis on the magnetic susceptibility and its influence factors of the lake sediments in the CH0310 core of Qarhan paleolake,Qaidam Basin[J].Acta Sedimentologica Sinica,28(4):790-797(in Chinese).
Basile C,Brun J P.1999.Transtensional faulting patterns ranging from pull-apart basins to transform continental margins:An experimental investigation[J].Journal of Structure Geology,21:23-37.
Burchfiel B C,Zhang P Z,Wang Y P,et al.1991.Geology of the Haiyuan fault zone,Ningxia-Hui Autonomous Region,China,and its relation to the evolution of the northeastern margin of the Tibetan plateau[J].Tectonics,10:1091-1110.
Deng Q,Song F,Zhu S,et al.1984.Active faulting and tectonics of the Ningxia Hui Autonomous Region,China[J].Journal of Geophysic Research:Solid Earth,89:4427-4445.
Ding G Y,Chen J,Tian Q J,et al.2004.Active faults and magnitudes of left-lateral displacement along the northern margin of the Tibetan plateau[J].Tectonophysics,380:243-260.
Gaudemer Y,Tapponnier P,Meyer B,et al.1995.Partitioning of crustal slip between linked,active faults in the eastern Qilian Shan,and evidence for amajor seismicgap,the“Tianzhu gap”,on the western Haiyuan Fault,Gansu(China)[J].Geophysical Journal International,120:599-645.
Heller F,Evans M E.1995.Loess magnetism[J].Review of Geophysics,33:211-240.
Lei S X,Li Y B,Cowgill E,et al.2018.Magnetostratigraphy of the Ganyanchi(Salt Lake)basin along the Haiyuan Fault,NE Tibet[J].Geosphere,14(4),in press.
Li C Y,Zhang P Z,Yin J H,et al.2009.Late Quaternary left-lateral slip rate of the Haiyuan Fault,northeastern margin of the Tibetan plateau[J].Tectonics,28:TC5010.doi:10.1029/2008TC002302.
Li Y,Ran Y,Wang H,et al.2014.Paleoseismic records of large earthquakes on the cross-basin fault in the Ganyanchi pull-apart basin,Haiyuan Fault,northeastern Tibetan plateau[J].Natural Hazards,71:1695-1713.
Liu Z J,Shao Y X,Klinger Y,et al.2015.Variability in magnitude of paleoearthquakes revealed by trenching and historical records,along the Haiyuan Fault,China[J].Journal of Geophysical Research:Solid Earth,120:8304-8333.
Mann W P,Hempton M R,Bradley D C,et al.1983.Development of pull-apart basins[J].Journal of Geology,91:529-554.
Rahe B,Ferrill D A,Morris A P.1998.Physical analog modeling of pull-apart basin evolution[J].Tectonophysics,285:21-40.
Shi W,Dong S,Liu Y,et al.2015.Cenozoic tectonic evolution of the south Ningxia region,northeastern Tibetan plateau inferred from new structural investigations and fault kinematic analyses[J].Tectonophysics,649:139-164.
Wang W T,Zhang P Z,Kirby E,et al.2011.A revised chronology for Tertiary sedimentation in the Sikouzi Basin:Implications for the tectonic evolution of the northeastern corner of the Tibetan plateau[J].Tectonophysics,55:100-114.
Zhang P Z,Burchfiel B C,Chen S F,et al.1989.Extinction of pull-apart basins[J].Geology,17:814-817.
Zhang P,Burchfiel B C,Molnar P,et al.1991.Amount and style of late Cenozoic deformation in the Liupan Shan area,Ningxia Autonomous Region,China[J].Tectonics,10:1111-1129.
Zheng D,Zhang P,Wan J,et al.2006.Rapid exhumation at 8Ma on the Liupan Shan thrust fault from apatite fissiontrack thermochronology:Implications for growth of the northeastern Tibetan plateau margin[J].Earth and Planetary Science Letters,248:198-208.
Zheng W J,Zhang P Z,He W G,et al.2013.Transformation of displacement between strike-slip and crustal shortening in the northern margin of the Tibetan plateau:Evidence from decadal GPS measurements and late Quaternary sliprates on faults[J].Tectonophysics,584:267-280.
(1)利源钻井队,2015,内部资料。
邓起东,张维岐,张培震,等.1989.海原走滑断裂带及其尾端挤压构造[J].地震地质,11(1):1-14.DENG Qi-dong,ZHANG Wei-qi,ZHANG Pei-zhen,et al.1989.Haiyuan strike-slip fault zone and its compressional structures of the end[J].Seismology and Geology,11(1):1-14(in Chinese).
郭鹏,韩竹军,安艳芬,等.2017.冷龙岭断裂系活动性与2016年门源6.4级地震构造研究[J].中国科学(D辑),47:617-630.GUO Peng,HAN Zhu-jun,AN Yan-fen,et al.2017.Activity of the Lenglongling fault system and seismotectonics of the 2016 MS6.4 Menyuan earthquake[J].Science in China(Ser D),60:929-942.
国家地震局地质研究所,宁夏回族自治区地震局.1990.海原活动断裂带[M].北京:地震出版社.Institute of Geology of State Seismological Bureau,Seismological Bureau of Ningxia Hui Autonomous Region.1990.Haiyuan Active Fault Zone[M].Seismological Press,Beijing(in Chinese).
国家地震局兰州地震研究所.1980.一九二○年海原大地震[M].地震出版社.Lanzhou Institute of Seismology,State Seismological Bureau.1980.The 1920 Haiyuan Earthquake[M].Seismological Press,Beijing(in Chinese).
胡守云,邓成龙,Appel E,等.2001.湖泊沉积物磁学性质的环境意义[J].科学通报,46(17):1491-1494.HU Shou-yun,DENG Cheng-long,Appel E,et al.2001.Environmental magnetic studies of lacustrine sediments[J].Chinese Science Bulletin,46(17):1491-1494(in Chinese).
胡守云,王苏民,Appel E,等.1998.呼伦湖湖泊沉积物磁化率变化的环境磁学机制[J].中国科学(D辑),28(4):334-339.HU Shou-yun,WANG Su-min,Appel E,et al.1998.Environmental magnetism in magnetic susceptibility of Hulun lake sediments[J].Science in China(Ser D),28(4):334-339(in Chinese).
李彦宝,冉勇康,王虎,等.2016.干盐池拉分盆地盆内新生断层大地震记录与海原断裂带级联破裂地震事件[J].地震地质,38(4):830-843.doi:10.3969/j.issn.0253-4967.2016.04.003.LI Yan-bao,RAN Yong-kang,WANG Hu,et al.2016.Paleoseismic records of large earthquakes on the cross-basin fault in the Salt Lake pull-apart basin and cascade rupture events on the Haiyuan Fault[J].Seismology and Geology,38(4):830-843(in Chinese).
刘青松,邓成龙.2009.磁化率及其环境意义[J].地球物理学报,52(4):1041-1048.LIU Qing-song,DENG Cheng-long.2009.Magnetic susceptibility and its environmental significances[J].Chinese Journal of Geophysics,52(4):1041-1048(in Chinese).
王心源,吴立,张广胜,等.2008.安徽巢湖全新世湖泊沉积物磁化率与粒度组合的变化特征及其环境意义[J].地理科学,28(4):548-553.WANG Xin-yuan,WU Li,ZHANG Guang-sheng,et al.2008.Characteristics and environmental significance of magnetic susceptibility and grain size of lake sediments since Holocene in Chaohu Lake,Anhui Province[J].Scientia Geographica Sinica,28(4):548-553(in Chinese).
张俊辉,杨太保,李永国,等.2010.柴达木盆地察尔汗盐湖CH0310钻孔沉积物磁化率及其影响因素分析[J].沉积学报,28(4):790-797.ZHANG Jun-hui,YANG Tai-bao,LI Yong-guo,et al.2010.Analysis on the magnetic susceptibility and its influence factors of the lake sediments in the CH0310 core of Qarhan paleolake,Qaidam Basin[J].Acta Sedimentologica Sinica,28(4):790-797(in Chinese).
Basile C,Brun J P.1999.Transtensional faulting patterns ranging from pull-apart basins to transform continental margins:An experimental investigation[J].Journal of Structure Geology,21:23-37.
Burchfiel B C,Zhang P Z,Wang Y P,et al.1991.Geology of the Haiyuan fault zone,Ningxia-Hui Autonomous Region,China,and its relation to the evolution of the northeastern margin of the Tibetan plateau[J].Tectonics,10:1091-1110.
Deng Q,Song F,Zhu S,et al.1984.Active faulting and tectonics of the Ningxia Hui Autonomous Region,China[J].Journal of Geophysic Research:Solid Earth,89:4427-4445.
Ding G Y,Chen J,Tian Q J,et al.2004.Active faults and magnitudes of left-lateral displacement along the northern margin of the Tibetan plateau[J].Tectonophysics,380:243-260.
Gaudemer Y,Tapponnier P,Meyer B,et al.1995.Partitioning of crustal slip between linked,active faults in the eastern Qilian Shan,and evidence for amajor seismicgap,the“Tianzhu gap”,on the western Haiyuan Fault,Gansu(China)[J].Geophysical Journal International,120:599-645.
Heller F,Evans M E.1995.Loess magnetism[J].Review of Geophysics,33:211-240.
Lei S X,Li Y B,Cowgill E,et al.2018.Magnetostratigraphy of the Ganyanchi(Salt Lake)basin along the Haiyuan Fault,NE Tibet[J].Geosphere,14(4),in press.
Li C Y,Zhang P Z,Yin J H,et al.2009.Late Quaternary left-lateral slip rate of the Haiyuan Fault,northeastern margin of the Tibetan plateau[J].Tectonics,28:TC5010.doi:10.1029/2008TC002302.
Li Y,Ran Y,Wang H,et al.2014.Paleoseismic records of large earthquakes on the cross-basin fault in the Ganyanchi pull-apart basin,Haiyuan Fault,northeastern Tibetan plateau[J].Natural Hazards,71:1695-1713.
Liu Z J,Shao Y X,Klinger Y,et al.2015.Variability in magnitude of paleoearthquakes revealed by trenching and historical records,along the Haiyuan Fault,China[J].Journal of Geophysical Research:Solid Earth,120:8304-8333.
Mann W P,Hempton M R,Bradley D C,et al.1983.Development of pull-apart basins[J].Journal of Geology,91:529-554.
Rahe B,Ferrill D A,Morris A P.1998.Physical analog modeling of pull-apart basin evolution[J].Tectonophysics,285:21-40.
Shi W,Dong S,Liu Y,et al.2015.Cenozoic tectonic evolution of the south Ningxia region,northeastern Tibetan plateau inferred from new structural investigations and fault kinematic analyses[J].Tectonophysics,649:139-164.
Wang W T,Zhang P Z,Kirby E,et al.2011.A revised chronology for Tertiary sedimentation in the Sikouzi Basin:Implications for the tectonic evolution of the northeastern corner of the Tibetan plateau[J].Tectonophysics,55:100-114.
Zhang P Z,Burchfiel B C,Chen S F,et al.1989.Extinction of pull-apart basins[J].Geology,17:814-817.
Zhang P,Burchfiel B C,Molnar P,et al.1991.Amount and style of late Cenozoic deformation in the Liupan Shan area,Ningxia Autonomous Region,China[J].Tectonics,10:1111-1129.
Zheng D,Zhang P,Wan J,et al.2006.Rapid exhumation at 8Ma on the Liupan Shan thrust fault from apatite fissiontrack thermochronology:Implications for growth of the northeastern Tibetan plateau margin[J].Earth and Planetary Science Letters,248:198-208.
Zheng W J,Zhang P Z,He W G,et al.2013.Transformation of displacement between strike-slip and crustal shortening in the northern margin of the Tibetan plateau:Evidence from decadal GPS measurements and late Quaternary sliprates on faults[J].Tectonophysics,584:267-280.
(1)利源钻井队,2015,内部资料。