南沙地块内破裂不整合与碰撞不整合的构造分析
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摘要
廷贾断裂以东的南沙地块与南海北部陆缘共轭,因此其构造过程研究对认识整个南海的构造演化具有重要意义.地震资料和区域构造背景分析揭示,破裂不整合面(BU)和碰撞不整合面(CU)是控制南沙地块内盆地演化的骨架界面;为了揭示南沙地块内的主要构造过程,本文利用地震剖面分析和数值模拟的方法,侧重对两个重要界面开展构造分析.结果显示:南沙地块内的破裂不整合面(BU)存在穿时现象,在地块东侧的礼乐盆地时代为T60(约23.8 Ma),而在地块西侧的北康和南薇西盆地内,BU时代为T40(约16 Ma),与碰撞不整合面重合.碰撞不整合面在南沙地块东部也为1 6 Ma左右.碰撞之后的几个构造界面时代比较一致,而之前的张裂事件界面可能也有穿时性.深度与空盆构造沉降速率一阶拟合结果显示,南沙地块中西部从Tg以后就表现出伴随前陆作用的岩石圈挠曲,90N09剖而和94N07剖面上,前隆的高度逐渐增高,并在16 Ma的层面上表现出最大的前隆高度,之后减弱;整体上挠曲程度西强东弱,且挠曲形态也存在很大差异,推测与岩石圈强度、俯冲的古南海洋壳宽度和陆陆接触的先后顺序等因素有关.
Nansha block on the east of Tinjar fault(or called Baram Line) is the conjugate counterpart of the Northern continental margin.A research on Nansha block will contribute greatly to the study of the South China Sea evolution.Seismic profiles interpretation and regional tectonic analysis suggested that two unconformities as Breakup Unconformity(BU) and Collision Unconformity(CU) are two most important boundaries,which constitute the evolutionary frame of the Nansha area.In order to reveal the main tectonic process in Nansha block,seismic profiles constrained with drilling data and mathematical modeling were carried out,the main results are as follows.BU is revealed to be a diachronic boundary and dated early Miocene in Liyue basin to the east,while to the west the Beikang and Nanweixi basin is dated middle Miocene around 16 Ma, where B.U.is synchronous with CU.The CU in the east of Nansha block is around 16 Ma.The boundaries after CU are also synchronous,but the rifting boundaries before BU might also be diachronic.Compared the depth as well as the Empty Basin Subsiding Rate(EBSR) simulation, we found that Nansha block experienced deflection since Tg in the middle and west part accompanied with the subduction and the collision thereafter.On 90N09 and 94N07,the top of the forebulge rose to the highest around 16 Ma.The deflection is strong in the west and weak in the east,the position of the forebulge migrates differently.We conjecture that the deflection of the block might be controlled by factors as collision time,lithospheric strength,or oceanic width of the subducted proto South China Sea.
Nansha block on the east of Tinjar fault(or called Baram Line) is the conjugate counterpart of the Northern continental margin.A research on Nansha block will contribute greatly to the study of the South China Sea evolution.Seismic profiles interpretation and regional tectonic analysis suggested that two unconformities as Breakup Unconformity(BU) and Collision Unconformity(CU) are two most important boundaries,which constitute the evolutionary frame of the Nansha area.In order to reveal the main tectonic process in Nansha block,seismic profiles constrained with drilling data and mathematical modeling were carried out,the main results are as follows.BU is revealed to be a diachronic boundary and dated early Miocene in Liyue basin to the east,while to the west the Beikang and Nanweixi basin is dated middle Miocene around 16 Ma, where B.U.is synchronous with CU.The CU in the east of Nansha block is around 16 Ma.The boundaries after CU are also synchronous,but the rifting boundaries before BU might also be diachronic.Compared the depth as well as the Empty Basin Subsiding Rate(EBSR) simulation, we found that Nansha block experienced deflection since Tg in the middle and west part accompanied with the subduction and the collision thereafter.On 90N09 and 94N07,the top of the forebulge rose to the highest around 16 Ma.The deflection is strong in the west and weak in the east,the position of the forebulge migrates differently.We conjecture that the deflection of the block might be controlled by factors as collision time,lithospheric strength,or oceanic width of the subducted proto South China Sea.
引文
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[22]Turcotte D L,Schubert G.Geodynamics.Cambridge: Cambridge University Press,1982
[23]赵中贤,孙珍,陈广浩等.南沙海域新生代构造特征和沉降演化.地球科学,2011,36(5):815-822 Zhao Z X,Sun Z,Chen GH.Cenozoicstructural characteristics and subsidence evolution in Nansha.Journal of Earth Sciences(in Chinese),2011,36(5):815-822
[24]Fuller M,Ali J R,Moss S J,et al.Paleomagnetism of Borneo.J.Asian Earth Sci.,1999,17(1-2):3-24
[25]Morley C K.A tectonic model for the Tertiary evolution of strike-slip faults and rift basins in SE Asia.Tectonophysics, 2002,347(4):189-215
[2]Hutchison C S.The 'Rajang accretionary prism' and 'Lupar Line' problem of Borneo.In:Hall R,Blundell D J,eds. Tectonic Evolution of South-East Asia.Geol Soc Special Publication,1996,106.247-261
[3]Taylor B,Hayes D E.The tectonic evolution of the South China Sea Basin.In:Hayes D E,ed.The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands. American Geophysical Union,Geophysical Monograph, 1980,23:89-104
[4]Hutchison CS.Marginal basin evolution:the southern South China Sea.Marine and Petroleum Geology,2004,21(9): 1129-1148
[5]Franke D,Barckhausen U,Heyde I,et al.Seismic images of a collision zone offshore NW Sabah/Borneo.Marine and Petroleum Geology,2008,25(7):606-624
[6]Kudrass H R,Wiedicke M,Cepek P,et al.Mesozoic and Cainozoic rocks dredged from the South China Sea(Reed Bank area) and Sulu Sea and their significance for platetectonic reconstructions.Marine and Petroleum Geology, 1986,3(1):19-30
[7]Hinz K,Fritsch J,Kempter E H K,et al.Thrust tectonics along the north-western continental margin of Sabah/Borneo. Geologische Rundschau,1989,78(3):705-730
[8]Schlliter H U,Hinz K,Block M.Tectono-stratigraphic terranes and detachment faulting of the south China Sea and Sulu sea.Marine Geology,1996,130(1-2):39-51
[9]Cullen A B.Transverse segmentation of the Baram-Balabac Basin,NW Borneo:refining the model of Borneo's tectonic evolution.Petroleum Geoscience,2010,16(1):3-29,DOI, 10.1144/1354-079309-828
[10]孙珍,赵中贤,周蒂等.南沙海域盆地的地层系统与沉积结构.地球科学,2011,36(5):798-806 Sun Z,Zhao Z X,Zhou D,et al.The stratigraphy and the sequence achitecture of the Basins in Nansha Region.Journal of Earth Sciences(in Chinese),2011,36(5):798-806
[11]李平鲁.珠江口盆地构造结构及演化.中国海上油气(地质),1989,3(1):11-18 Li P L.The tectonic and evolution of the Pearl River Mouth basin.China Offshore Oil and Gas(Geology)(in Chinese), 1989,3(1):11-18
[12]陈长民,施和生,许仕策等.珠江口盆地(东部)第三系油气藏形成条件.北京:科学出版社,2003 Chen C M,Shi H S,Xu S C,et al.The Condition of Tertiary Oil and Gas Formation in the East of Pearl River Mouth Basin(in Chinese).Beijing:Science Publishing House,2003
[13]Hesse S,Back S,Franke D.The deep-water fold-and-thrust belt offshore NW Borneo:Gravity-driven versus basement-driven shortening.Geological Society of America Bulletin, 2009,121(5-6):939-953
[14]庞雄,陈长民,彭大钧等.南海珠江深水扇系统及油气.北京:科学出版社,2007 Pang X,Chen C M,Peng D J,et al.The Pearl River Deepwater Fan System and Petroleum in South China Sea(in Chinese).Beijing:Science Publishing House,2007
[15]Wang P,Prell W L,Blum P,et al.Proc.ODP,Init. Repts.,184.Available from:Ocean Drilling Program, Texas A&M University,2000,College Station TX 77845-9547,USA
[16]金庆焕.南海地质与油气资源.北京:地质出版社,1989 Jin Q H.The Geology and Petroleum Resources of South China Sea (in Chinese).Beijing:Geological Publishing House,1989
[17]姚伯初.南沙群岛万安盆地构造演化史再探讨.热带海洋, 1997,16(3):15-22 Yao B C.A rediscussion on the tectonic evolutional history of the Wanan basin in Nansha area.Tropical Oceanology(in Chinese),1997,16(3):15-22
[18]Dietz R S,Menard H W,Hamilton E L.Echograms of the Mid-Pacific expedition.Deep-Sea Research,1954,1(4):258-272
[19]Allen P A,Allen J R.Basin Analysis:Principles and Applications.London:Blackwell Scientific Press,1990.451
[20]Sclater J G,Christie P A F.Continental stretching:An explanation of the post-mid-Cretaceous subsidence of the central North Sea Basin.Journal of Geophysical Research, 1980,85(B7):3711-3739
[21]Watts A B,Talwani M.Gravity anomalies seaward of deepsea trenches and their tectonic implications.Geophys.J.R. Astron.Soc.,1974,36(1):57-90
[22]Turcotte D L,Schubert G.Geodynamics.Cambridge: Cambridge University Press,1982
[23]赵中贤,孙珍,陈广浩等.南沙海域新生代构造特征和沉降演化.地球科学,2011,36(5):815-822 Zhao Z X,Sun Z,Chen GH.Cenozoicstructural characteristics and subsidence evolution in Nansha.Journal of Earth Sciences(in Chinese),2011,36(5):815-822
[24]Fuller M,Ali J R,Moss S J,et al.Paleomagnetism of Borneo.J.Asian Earth Sci.,1999,17(1-2):3-24
[25]Morley C K.A tectonic model for the Tertiary evolution of strike-slip faults and rift basins in SE Asia.Tectonophysics, 2002,347(4):189-215
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