南海东北部居里面特征及其石油地质意义
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摘要
居里面是岩石中铁磁性矿物因温度升高达到居里点而由铁磁性变为顺磁性时的温度界面,在这个面以下的岩石由于温度超过居里点而被认为几乎无磁性。1985年中美双船地震扩展排列东剖面(ESPE)和1993年中日合作海底地震仪剖面(OBS93)均穿越南海东北部各主要构造带和盆地,获得了完整的地震及重、磁资料。通过上述剖面的磁测异常反演出其磁居里面,同时由热流探测资料计算其地温场并从中获取了热居里面(575℃等温面)数据(热居里面是笔者相对于磁居里面而提出的一个新概念,即指由海底热流探测资料经地温场模拟而获得的居里面)。研究结果表明,两种方法得到的居里面深度在很多地区并不一致,表现出显著的差异。笔者认为造成这种差异的主要原因在于,在有可能存在未知热事件的地区,计算稳态地温场的前提条件并不成立,因而由这种方法计算出来的热居里面在这些地区并不能真正反映居里面的深度,从而形成了它与磁居里面的显著差异。通过计算研究区磁及热居里面并根据其差异可以快速判定该区下部是否存在10Ma以来的热侵事件以及是否有浅层热源,这对于研究南海东北部新生代含油气盆地深部结构及沉积充填特征与烃源岩成熟生烃作用以及油气运聚成藏规律和油气资源潜力评价等,均具有重要的油气地质意义和地球科学意义。
Curie point isotherm is the temperature isotherm where ferromagnetic minerals in the rocks change from ferromagnetism into paramagnetism because the temperature increases to the Curie point. Below this isotherm,the rocks are thought to be almost non-magnetism because their temperature is higher than the Curie point. Sino-US two-ship expanding spread profiles eastern transect (ESPE) in 1985 and Sino-Japan Ocean Bottom Seismography profile in 1993 (OBS93) crossed the major structural belts and basins in the northeastern South China Sea. Integral gravity,magnetic,heatflow and seismic data were acquired along these profiles. Magnetic Curie point isotherm was obtained by inversion of the magnetic anomalies,and thermal Curie point isotherm (the 575℃ isotherm) was obtained according to the geothermal temperature field calculated from the heatflow survey data. The results showed that the two Curie point isotherms derived respectively from the prior two methods were inconsistent with significant differences in many regions. After analyzing their calculation principle,the authors believed that the reason for these differences was that the prerequisite calculating the stable-state geothermal temperature filed was untenable in some areas with possible unknown underground heat events,then the thermal Curie point isotherm derived from this method would not show the actual Curie point isotherm in such areas. In order to explain these differences more clearly,the authors introduced the concept of thermal equilibrium,which showed that the two types of Curie point isotherm were consistent in thermal equilibrium region and inconsistent in thermal disequilibrium region. As a result,they could achieve the magnetic and thermal Curie point isotherm first in some areas and distinguish the unknown underground heat events from their differences,which has important instructional significance and reference value for the study on regional tectonics,oil and gas geological conditions and resource predictions.
Curie point isotherm is the temperature isotherm where ferromagnetic minerals in the rocks change from ferromagnetism into paramagnetism because the temperature increases to the Curie point. Below this isotherm,the rocks are thought to be almost non-magnetism because their temperature is higher than the Curie point. Sino-US two-ship expanding spread profiles eastern transect (ESPE) in 1985 and Sino-Japan Ocean Bottom Seismography profile in 1993 (OBS93) crossed the major structural belts and basins in the northeastern South China Sea. Integral gravity,magnetic,heatflow and seismic data were acquired along these profiles. Magnetic Curie point isotherm was obtained by inversion of the magnetic anomalies,and thermal Curie point isotherm (the 575℃ isotherm) was obtained according to the geothermal temperature field calculated from the heatflow survey data. The results showed that the two Curie point isotherms derived respectively from the prior two methods were inconsistent with significant differences in many regions. After analyzing their calculation principle,the authors believed that the reason for these differences was that the prerequisite calculating the stable-state geothermal temperature filed was untenable in some areas with possible unknown underground heat events,then the thermal Curie point isotherm derived from this method would not show the actual Curie point isotherm in such areas. In order to explain these differences more clearly,the authors introduced the concept of thermal equilibrium,which showed that the two types of Curie point isotherm were consistent in thermal equilibrium region and inconsistent in thermal disequilibrium region. As a result,they could achieve the magnetic and thermal Curie point isotherm first in some areas and distinguish the unknown underground heat events from their differences,which has important instructional significance and reference value for the study on regional tectonics,oil and gas geological conditions and resource predictions.
引文
[1]何家雄,刘海龄,姚永坚,等.南海北部边缘盆地油气地质及资源前景[M].北京:石油工业出版社,2008:4,34-63,68-70.
[2]龚再生,李思田,等.南海北部大陆边缘盆地分析与油气聚集[M].北京:科学出版社,1997:1-5,9-26,96-106,251-256,385-405.
[3]刘昭蜀,赵焕庭,范时清,等.南海地质[M].北京:科学出版社,2002:255-260.
[4]夏戡原,黄慈流,张毅祥,等.南海东北部与台湾间的构造及海洋地球物理研究[R].广州:中国科学院南海海洋研究所,2004.
[5]何家雄,施小斌,阎贫,等.南海北部边缘盆地油气地质特征与勘探方向[J].新疆石油地质,2007,28(2):129-135.
[6]李平鲁,梁慧贤.新生代岩浆活动与盆地演化、油气聚集的关系[J].广东地质,1994,9(2):23-34.
[7]NISSEN S S,HAYES D E,YAO BOCHU,et al.Gravity,heat flow,and seismic constraints on the processes of crustal extension:Northern margin of the South China Sea[J].JGeophys Res,1995,100(B11):22447-22483.
[8]阎贫.海底地震仪记录中的横波.海洋地质与第四纪地质.1998,18(1):115-118.
[9]刘天佑,等.海洋重磁资料处理系统[D].武汉:中国地质大学(武汉),2000.
[10]赵俊峰.南海东北部高磁带及磁静区地球物理场特征与南海构造演化的关系[D].上海:同济大学海洋学院,2006.
[11]施小斌,丘学林,夏戡原,等.南海热流特征及其构造意义.热带海洋学报,2003,22(2):63-73.
[12]何家雄,陈胜红,刘海龄,等.南海北部边缘盆地区域地质与油气运聚成藏规律及特点[J].西南石油大学学报,2008,30(5):91-98.
[13]何家雄,夏斌,王志欣,等.南海北部边缘盆地西区油气运聚成藏规律与勘探领域及方向[J].石油学报,2006,27(4):12-18.
[14]何家雄,李明兴,陈伟煌,等.莺歌海盆地热流体上侵活动与天然气运聚富集关系探讨[J].天然气地球科学,2000,11(6):29-43.
[2]龚再生,李思田,等.南海北部大陆边缘盆地分析与油气聚集[M].北京:科学出版社,1997:1-5,9-26,96-106,251-256,385-405.
[3]刘昭蜀,赵焕庭,范时清,等.南海地质[M].北京:科学出版社,2002:255-260.
[4]夏戡原,黄慈流,张毅祥,等.南海东北部与台湾间的构造及海洋地球物理研究[R].广州:中国科学院南海海洋研究所,2004.
[5]何家雄,施小斌,阎贫,等.南海北部边缘盆地油气地质特征与勘探方向[J].新疆石油地质,2007,28(2):129-135.
[6]李平鲁,梁慧贤.新生代岩浆活动与盆地演化、油气聚集的关系[J].广东地质,1994,9(2):23-34.
[7]NISSEN S S,HAYES D E,YAO BOCHU,et al.Gravity,heat flow,and seismic constraints on the processes of crustal extension:Northern margin of the South China Sea[J].JGeophys Res,1995,100(B11):22447-22483.
[8]阎贫.海底地震仪记录中的横波.海洋地质与第四纪地质.1998,18(1):115-118.
[9]刘天佑,等.海洋重磁资料处理系统[D].武汉:中国地质大学(武汉),2000.
[10]赵俊峰.南海东北部高磁带及磁静区地球物理场特征与南海构造演化的关系[D].上海:同济大学海洋学院,2006.
[11]施小斌,丘学林,夏戡原,等.南海热流特征及其构造意义.热带海洋学报,2003,22(2):63-73.
[12]何家雄,陈胜红,刘海龄,等.南海北部边缘盆地区域地质与油气运聚成藏规律及特点[J].西南石油大学学报,2008,30(5):91-98.
[13]何家雄,夏斌,王志欣,等.南海北部边缘盆地西区油气运聚成藏规律与勘探领域及方向[J].石油学报,2006,27(4):12-18.
[14]何家雄,李明兴,陈伟煌,等.莺歌海盆地热流体上侵活动与天然气运聚富集关系探讨[J].天然气地球科学,2000,11(6):29-43.
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