拉萨地块保吉地区晚侏罗世吐卡日组灰岩岩石磁学特征研究
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摘要
班公湖—怒江缝合所代表的中特提斯洋盆的属性及其构造演化过程仍在争论之中.多年来,地质工作者们不断在班公湖—怒江缝合带以南的拉萨地块寻找新的地质证据以求厘清这一关键问题.2016年,地质学家先后在拉萨地块北缘保吉地区新识别出了晚侏罗世碳酸岩地层吐卡日组,这一发现为我们获得古地磁证据提供了新的地层基础.为了进一步明确该地层中载磁矿物的组合类型和特征,本文对采自班戈县保吉地区晚侏罗世吐卡日组灰岩样品进行了饱和等温剩磁曲线获得实验、累计高斯模型线性和梯度曲线分析、三轴等温系统热退磁实验、k-T曲线测试、磁滞回线实验.实验结果表明,保吉地区晚侏罗世吐卡日组灰岩地层中的载磁矿物组合可以分为两类:第一类以高矫顽力的针铁矿、磁赤铁矿`以及赤铁矿为主,含少量低矫顽力矿物;第二类以低矫顽力的磁铁矿以及贫钛的钛磁铁为主,含少量高矫顽力矿物.此外,吐卡日组样品中的磁性矿物颗粒粒径普遍较小,以单畴和假单畴颗粒为主.
The properties of the Central Tethys ocean basin represented by the Bangong-Nujiang suture zone are still in dispute. Over the years, geologists have been searching for new geological evidence in the Lhasa terrane south of the Bangong-Nujiang suture zone in an attempt to clarify this key issue. In 2016, geologists successively identified the late Jurassic Carbonate Tukari formation in the Baoji area on the northern margin of the Lhasa terrane. This discovery provided a new stratigraphic foundation for the paleomagnetic evidence. In order to further clarify the types, combinations, and characteristics of the magnetic minerals contained in this stratum, this paper presents a saturated isothermal remanence curve from the late Jurassic Tukari formation limestone samples from the Bangor region to obtain experiments and cumulative Gaussian model linearity and gradients. Curve analysis, three-axis isothermal thermal demagnetization test, k-T curve test, hysteresis loop experiment. The experimental results show that the magnetic mineral components in the limestone strata of the Late Jurassic Tukari formation in the Baoji area can be divided into two categories: The first type is high-coercivity goethite, maghemite, and hematite It is dominated by a small amount of low-coercivity minerals; the second type is dominated by low-coercivity magnetite and titanium-depleted titanium magnets, containing a small amount of high-coercivity minerals. In addition, the particle size of magnetic minerals in the Tukari formation sample is generally small, mainly mono-domain and pseudo-domain particles.
The properties of the Central Tethys ocean basin represented by the Bangong-Nujiang suture zone are still in dispute. Over the years, geologists have been searching for new geological evidence in the Lhasa terrane south of the Bangong-Nujiang suture zone in an attempt to clarify this key issue. In 2016, geologists successively identified the late Jurassic Carbonate Tukari formation in the Baoji area on the northern margin of the Lhasa terrane. This discovery provided a new stratigraphic foundation for the paleomagnetic evidence. In order to further clarify the types, combinations, and characteristics of the magnetic minerals contained in this stratum, this paper presents a saturated isothermal remanence curve from the late Jurassic Tukari formation limestone samples from the Bangor region to obtain experiments and cumulative Gaussian model linearity and gradients. Curve analysis, three-axis isothermal thermal demagnetization test, k-T curve test, hysteresis loop experiment. The experimental results show that the magnetic mineral components in the limestone strata of the Late Jurassic Tukari formation in the Baoji area can be divided into two categories: The first type is high-coercivity goethite, maghemite, and hematite It is dominated by a small amount of low-coercivity minerals; the second type is dominated by low-coercivity magnetite and titanium-depleted titanium magnets, containing a small amount of high-coercivity minerals. In addition, the particle size of magnetic minerals in the Tukari formation sample is generally small, mainly mono-domain and pseudo-domain particles.
引文
AO H,DENG C L.2007.Review in the identification of magnetic minerals [J].Progress in geophysics (in Chinese),22(2):432- 442,doi:10.3969/j.issn.1004-2903.2007.02.015.
Bai Q H,Yan Y G,Huang B C,et al.2015.Preliminary rock magnetic study of Permo-Triassic limestones from the Shan state block of Myanmar,SE Asia [J].Progress in Geophysics (in Chinese),30(3):1177-1184,doi:10.6038/pg20150323.
Cao Y,Sun Z M,Li H B,et al.2017.New Late Cretaceous paleomagnetic data from volcanic rocks and red beds from the Lhasa terrane and its implications for the paleolatitude of the southern margin of Asia prior to the collision with India [J].Gondwana Research,41:337-351,doi:10.1016/j.gr.2015.11.006.
Chen W W,Zhang S H,Ding J K,et al.2017.Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane,central Tibet [J].Gondwana Research,41:373-389,doi:10.1016/j.gr.2015.07.004.
Day R,Fuller M,Schmidt V A.1977.Hysteresis properties of titanomagnetites:Grain-size and compositional dependence [J].Physics of the Earth and Planetary Interiors,13(4):260-267,doi:10.1016/0031-9201(77)90108-X.
Dekkers A J V.1999.The incorporation of thermal methods in mineral magnetism of loess-paleosol sequences:a brief overview [J].China.Sci.Bull.,44:53- 63.
Ding L,Kapp P,Yue Y H,et al.2007.Postcollisional calc-alkaline lavas and xenoliths from the southern Qiangtang terrane,central Tibet [J].Earth and Planetary Science Letters,254(1-2):28-38,doi:10.1016/j.epsl.2006.11.019.
Hrouda F.1994.A technique for the measurement of thermal changes of magnetic susceptibility of weakly magnetic rocks by the CS-2 apparatus and KLY-2 Kappabridge [J].Geophysical Journal Internation,118(3):604- 612,doi:10.1111/j.1365-246X.1994.tb03987.x.
Huang B C,Wei Q Y,Zhu R X.1995.Magnetic features of early paleozoic rockunits in north china block [J].Chinese Journal Of Geophysics (in Chinese),38(6):796-805.
Huang Q-T,Liu W-L,Xia B,et al.2017.Petrogenesis of the Majiari ophiolite (western Tibet,China):Implications for intra-oceanic subduction in the Bangong-Nujiang Tethys [J].Journal of Asian Earth Sciences,146:337-351,doi:10.1016/j.jseaes.2017.06.008.
Kapp P,Decelles P G,GehrelS G E,et al.2007.Geological records of the Lhasa-Qiangtang and Indo-Asian collisions in the Nima area of central Tibet [J].Geological Society of America Bulletin,119(7-8):917-933,doi:10.1130/B26033.1.
Kapp P,Murphy M A,YIN A,et al.2003.Mesozoic and Cenozoic tectonic evolution of the Shiquanhe area of western Tibet [J].Tectonics,22(4):n/a-n/a,doi:10.1029/2001TC001332.
King J W,Channell J E T.1991.Sedimentary magnetism,environ-mental magnetism,and magnetostratigraphy [J].Reviews Of Geophysics,29(S1):358-370,doi:10.1002/rog.1991.29.s1.358.
Kruiver P P,Dekkers M J,Heslop D.2001.Quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation [J].Earth and Planetary Science Letters,189(3- 4):269-276,doi:10.1016/S0012-821X(01)00367-3.
Kruiver P P.,Passier H F.2001.Coercivity analysis of magnetic phases in sapropel S1 related to variations in redox conditions,including an investigation of the S ratio [J].Geochemistry,Geophysics,Geosystems,2(12):35 articles,doi:10.1029/2001GC000181.
Lippert P C,Zhao X X,Coe R S,et al.2011.Palaeomagnetism and 40Ar/39Ar geochronology of upper Palaeogene volcanic rocks from Central Tibet:implications for the Central Asia inclination anomaly,the palaeolatitude of Tibet and post-50 Ma shortening within Asia [J].Geophysical Journal International,184(1):131-161,doi:10.1111/j.1365-246X.2010.04833.x.
Otofuji Y-I,MU C L,TanakA K,et al.2007.Spatial gap between Lhasa and Qiangtang blocks inferred from Middle Jurassic to Cretaceous paleomagnetic data [J].Earth and Planetary Science Letters,262(3- 4):581-593,doi:10.1016/j.epsl.2007.08.013.
Pan G T,Wang L Q,LI R S,et al.2012.Tectonic evolution of the Qinghai-Tibet Plateau [J].Journal of Asian Earth Sciences,53:3-14,doi:10.1016/j.jseaes.2011.12.018.
Stockhausen H.1998.Some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log Gaussian functions [J].Geophysical Research Letters,25(12):2217-2220,doi:10.1029/98gl01580.
Sun Z M,Yang Z Y,Pei J L,et al.2006.New Early Cretaceous paleomagnetic data from volcanic and red beds of the eastern Qaidam Block and its implications for tectonics of Central Asia [J].Earth and Planetary Science Letters,243(1-2):268-281,doi:10.1016/j.epsl.2005.12.016.
Tauxe L,Mullender T A T,Pick T.1996.Potbellies,wasp-waists,and superparamagnetism in magnetic hysteresis [J].Journal of Geophysical Research:Solid Earth,101(B1):571-583,doi:10.1029/95jb03041.
Wu S,Song C H,Yan M D,et al.2015.Rock magnetic study on the middle-late Jurassic Yanshiping strata:implication of the sedimentary environment of the northern Qiangtang basin [J].Progress in Geophysics (in Chinese),30(2):571-580,doi:10.6038/pg20150213.
Yan M D,Zhang D W,Fang X M,et al.2016.Paleomagnetic data bearing on the Mesozoic deformation of the Qiangtang Block:Implications for the evolution of the Paleo-and Meso-Tethys [J].Gondwana Research,39:292-316,doi:10.1016/j.gr.2016.01.012.
Zhang P,Ao H,An Z S,et al.2015.Rock magnetism properties of Oligocene sediments in the Lanzhou Baisn [J].Chinese Journal Of Geophysics (in Chinese),58(7):2445-2459,doi:10.6038/cjg20150721.
敖红,邓成龙.2007.磁性矿物的磁学鉴别方法回顾[J].地球物理学进展,22(2):432- 442,doi:10.3969/j.issn.1004-2903.2007.02.015.
柏千惠,闫永刚,黄宝春,等.2015.缅甸掸邦地块二叠纪-三叠纪灰岩的岩石磁学初步研究结果[J].地球物理学进展,30(3):1177-1184,doi:10.6038/pg20150323.
陈国荣,陈玉禄,张宽忠,等.2004.班戈县幅地质调查新成果及主要进展[J].地质通报,23(5):520-524.
程鑫,吴汉宁,刁宗宝,等.2013.藏东地区晚石炭-晚二叠世古地磁新结果:对羌北-昌都地块构造演化的制约[J].中国科学:地球科学,43(8):1312-1323.
程鑫,周亚楠,郭强,等.2015.青藏高原拉萨地块西段三叠纪古地磁结果及其构造意义[J].地质通报,34(2):306-317.
丁林,李震宇,宋培平.2017.青藏高原的核心来自南半球冈瓦纳大陆[J].中国科学院院刊,1(9):945-950.
黄宝春,谭承泽.1994.古地磁多磁成分的分离技术[J].地球物理学进展,9(1):125-134.
黄宝春,魏青云,朱日祥.1995.华北地块早古生代地层单元的岩石磁学特征研究[J].地球物理学报,38(6):796-805.
纪占胜,姚建新,武桂春.2007.西藏冈底斯西段措勤地区海相三叠系的划分[J].地质通报,26(8):947-952.
梁寿生,夏金宝.1979.藏北班戈地区海相白垩系[J].青藏高原地质文集,5(6):181-193.
刘振宇,贾海明,黄维平,等.2015.西藏1:5万班戈县西南地区四幅区调成果与展望[J].中国地质调查,2(7):8-12.
孟亚洲,纪占胜,廖卫华,等.2016.西藏保吉地区晚侏罗世珊瑚动物群的发现及其意义[J].地质学报,90(05):833-847.
任海东,颜茂都,陈毅,等.2015.羌塘地块中生代时期的漂移演化及其成钾条件[J].地质学报,89(11):2002-2015.
吴松,宋春晖,颜茂都,等.2015.北羌塘盆地雁石坪地区中-上侏罗统岩石磁学特征与沉积环境[J].地球物理学进展,30(2):571-580,doi:10.6038/pg20150213.
肖序常,王军.1998.青藏高原构造演化及隆升的简要评述[J].地质论评,44(4):372-381.
叶祥华,李家福.1987.古地磁与西藏板块及特提斯的演化[J].成都地质学院学报,14(1):65-79.
张鹏,敖红,安芷生,等.2015.兰州盆地渐新世沉积物岩石磁学性质探究[J].地球物理学报,58(7):2445-2459,doi:10.6038/cjg20150721.
赵文津,刘葵,蒋忠惕,等.2004.西藏班公湖—怒江缝合带——深部地球物理结构给出的启示[J].地质通报,23(7):623- 635.
Bai Q H,Yan Y G,Huang B C,et al.2015.Preliminary rock magnetic study of Permo-Triassic limestones from the Shan state block of Myanmar,SE Asia [J].Progress in Geophysics (in Chinese),30(3):1177-1184,doi:10.6038/pg20150323.
Cao Y,Sun Z M,Li H B,et al.2017.New Late Cretaceous paleomagnetic data from volcanic rocks and red beds from the Lhasa terrane and its implications for the paleolatitude of the southern margin of Asia prior to the collision with India [J].Gondwana Research,41:337-351,doi:10.1016/j.gr.2015.11.006.
Chen W W,Zhang S H,Ding J K,et al.2017.Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane,central Tibet [J].Gondwana Research,41:373-389,doi:10.1016/j.gr.2015.07.004.
Day R,Fuller M,Schmidt V A.1977.Hysteresis properties of titanomagnetites:Grain-size and compositional dependence [J].Physics of the Earth and Planetary Interiors,13(4):260-267,doi:10.1016/0031-9201(77)90108-X.
Dekkers A J V.1999.The incorporation of thermal methods in mineral magnetism of loess-paleosol sequences:a brief overview [J].China.Sci.Bull.,44:53- 63.
Ding L,Kapp P,Yue Y H,et al.2007.Postcollisional calc-alkaline lavas and xenoliths from the southern Qiangtang terrane,central Tibet [J].Earth and Planetary Science Letters,254(1-2):28-38,doi:10.1016/j.epsl.2006.11.019.
Hrouda F.1994.A technique for the measurement of thermal changes of magnetic susceptibility of weakly magnetic rocks by the CS-2 apparatus and KLY-2 Kappabridge [J].Geophysical Journal Internation,118(3):604- 612,doi:10.1111/j.1365-246X.1994.tb03987.x.
Huang B C,Wei Q Y,Zhu R X.1995.Magnetic features of early paleozoic rockunits in north china block [J].Chinese Journal Of Geophysics (in Chinese),38(6):796-805.
Huang Q-T,Liu W-L,Xia B,et al.2017.Petrogenesis of the Majiari ophiolite (western Tibet,China):Implications for intra-oceanic subduction in the Bangong-Nujiang Tethys [J].Journal of Asian Earth Sciences,146:337-351,doi:10.1016/j.jseaes.2017.06.008.
Kapp P,Decelles P G,GehrelS G E,et al.2007.Geological records of the Lhasa-Qiangtang and Indo-Asian collisions in the Nima area of central Tibet [J].Geological Society of America Bulletin,119(7-8):917-933,doi:10.1130/B26033.1.
Kapp P,Murphy M A,YIN A,et al.2003.Mesozoic and Cenozoic tectonic evolution of the Shiquanhe area of western Tibet [J].Tectonics,22(4):n/a-n/a,doi:10.1029/2001TC001332.
King J W,Channell J E T.1991.Sedimentary magnetism,environ-mental magnetism,and magnetostratigraphy [J].Reviews Of Geophysics,29(S1):358-370,doi:10.1002/rog.1991.29.s1.358.
Kruiver P P,Dekkers M J,Heslop D.2001.Quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation [J].Earth and Planetary Science Letters,189(3- 4):269-276,doi:10.1016/S0012-821X(01)00367-3.
Kruiver P P.,Passier H F.2001.Coercivity analysis of magnetic phases in sapropel S1 related to variations in redox conditions,including an investigation of the S ratio [J].Geochemistry,Geophysics,Geosystems,2(12):35 articles,doi:10.1029/2001GC000181.
Lippert P C,Zhao X X,Coe R S,et al.2011.Palaeomagnetism and 40Ar/39Ar geochronology of upper Palaeogene volcanic rocks from Central Tibet:implications for the Central Asia inclination anomaly,the palaeolatitude of Tibet and post-50 Ma shortening within Asia [J].Geophysical Journal International,184(1):131-161,doi:10.1111/j.1365-246X.2010.04833.x.
Otofuji Y-I,MU C L,TanakA K,et al.2007.Spatial gap between Lhasa and Qiangtang blocks inferred from Middle Jurassic to Cretaceous paleomagnetic data [J].Earth and Planetary Science Letters,262(3- 4):581-593,doi:10.1016/j.epsl.2007.08.013.
Pan G T,Wang L Q,LI R S,et al.2012.Tectonic evolution of the Qinghai-Tibet Plateau [J].Journal of Asian Earth Sciences,53:3-14,doi:10.1016/j.jseaes.2011.12.018.
Stockhausen H.1998.Some new aspects for the modelling of isothermal remanent magnetization acquisition curves by cumulative log Gaussian functions [J].Geophysical Research Letters,25(12):2217-2220,doi:10.1029/98gl01580.
Sun Z M,Yang Z Y,Pei J L,et al.2006.New Early Cretaceous paleomagnetic data from volcanic and red beds of the eastern Qaidam Block and its implications for tectonics of Central Asia [J].Earth and Planetary Science Letters,243(1-2):268-281,doi:10.1016/j.epsl.2005.12.016.
Tauxe L,Mullender T A T,Pick T.1996.Potbellies,wasp-waists,and superparamagnetism in magnetic hysteresis [J].Journal of Geophysical Research:Solid Earth,101(B1):571-583,doi:10.1029/95jb03041.
Wu S,Song C H,Yan M D,et al.2015.Rock magnetic study on the middle-late Jurassic Yanshiping strata:implication of the sedimentary environment of the northern Qiangtang basin [J].Progress in Geophysics (in Chinese),30(2):571-580,doi:10.6038/pg20150213.
Yan M D,Zhang D W,Fang X M,et al.2016.Paleomagnetic data bearing on the Mesozoic deformation of the Qiangtang Block:Implications for the evolution of the Paleo-and Meso-Tethys [J].Gondwana Research,39:292-316,doi:10.1016/j.gr.2016.01.012.
Zhang P,Ao H,An Z S,et al.2015.Rock magnetism properties of Oligocene sediments in the Lanzhou Baisn [J].Chinese Journal Of Geophysics (in Chinese),58(7):2445-2459,doi:10.6038/cjg20150721.
敖红,邓成龙.2007.磁性矿物的磁学鉴别方法回顾[J].地球物理学进展,22(2):432- 442,doi:10.3969/j.issn.1004-2903.2007.02.015.
柏千惠,闫永刚,黄宝春,等.2015.缅甸掸邦地块二叠纪-三叠纪灰岩的岩石磁学初步研究结果[J].地球物理学进展,30(3):1177-1184,doi:10.6038/pg20150323.
陈国荣,陈玉禄,张宽忠,等.2004.班戈县幅地质调查新成果及主要进展[J].地质通报,23(5):520-524.
程鑫,吴汉宁,刁宗宝,等.2013.藏东地区晚石炭-晚二叠世古地磁新结果:对羌北-昌都地块构造演化的制约[J].中国科学:地球科学,43(8):1312-1323.
程鑫,周亚楠,郭强,等.2015.青藏高原拉萨地块西段三叠纪古地磁结果及其构造意义[J].地质通报,34(2):306-317.
丁林,李震宇,宋培平.2017.青藏高原的核心来自南半球冈瓦纳大陆[J].中国科学院院刊,1(9):945-950.
黄宝春,谭承泽.1994.古地磁多磁成分的分离技术[J].地球物理学进展,9(1):125-134.
黄宝春,魏青云,朱日祥.1995.华北地块早古生代地层单元的岩石磁学特征研究[J].地球物理学报,38(6):796-805.
纪占胜,姚建新,武桂春.2007.西藏冈底斯西段措勤地区海相三叠系的划分[J].地质通报,26(8):947-952.
梁寿生,夏金宝.1979.藏北班戈地区海相白垩系[J].青藏高原地质文集,5(6):181-193.
刘振宇,贾海明,黄维平,等.2015.西藏1:5万班戈县西南地区四幅区调成果与展望[J].中国地质调查,2(7):8-12.
孟亚洲,纪占胜,廖卫华,等.2016.西藏保吉地区晚侏罗世珊瑚动物群的发现及其意义[J].地质学报,90(05):833-847.
任海东,颜茂都,陈毅,等.2015.羌塘地块中生代时期的漂移演化及其成钾条件[J].地质学报,89(11):2002-2015.
吴松,宋春晖,颜茂都,等.2015.北羌塘盆地雁石坪地区中-上侏罗统岩石磁学特征与沉积环境[J].地球物理学进展,30(2):571-580,doi:10.6038/pg20150213.
肖序常,王军.1998.青藏高原构造演化及隆升的简要评述[J].地质论评,44(4):372-381.
叶祥华,李家福.1987.古地磁与西藏板块及特提斯的演化[J].成都地质学院学报,14(1):65-79.
张鹏,敖红,安芷生,等.2015.兰州盆地渐新世沉积物岩石磁学性质探究[J].地球物理学报,58(7):2445-2459,doi:10.6038/cjg20150721.
赵文津,刘葵,蒋忠惕,等.2004.西藏班公湖—怒江缝合带——深部地球物理结构给出的启示[J].地质通报,23(7):623- 635.
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