菲律宾海盆磁条带特征及61 Ma以来的海底扩张过程重建

菲律宾海盆是西太平洋最大的边缘海盆地,作为地球上最壮观的“沟-弧-盆”体系的重要组成部分,其成因及构造演化可有效约束西太平洋洋陆过渡带的复杂动力学过程。海底磁异常条带是海底扩张的重要依据,其几何形态能够反映海底扩张的时间、方向及速率,为研究海盆的海底扩张过程提供重要信息。菲律宾海盆的次级海盆—西菲律宾海盆、四国海盆地磁异常表现为明显的条带状异常特征,帕里西维拉海盆内的磁条带特征虽不明显,但仍能看出南北向的分带现象。对海盆内的磁异常条带进行系统的分析、对比与解释,将菲律宾海盆划分为7个扩张阶段,构建了菲律宾海盆61 Ma以来的阶段性扩张模型。揭示了边缘海盆构造演化的一般规律及扩张过程为岛弧裂解、高速弧后扩张、慢速弧后扩张和扩张后作用4个阶段。     

鲍威尔海盆的重磁场特征及其构造意义

鲍威尔海盆位于南极半岛东北和南奥克尼微大陆之间,是南半球典型的高纬度边缘海。通过搜集鲍威尔海盆的相关重磁资料、历史文献,以及总结前人的相关研究成果,介绍了鲍威尔海盆的重磁场基本特征以及张开历史。结果表明鲍威尔海盆中部存在着约NW30°方向倾斜的埋藏扩张中心,两侧残存基底高地,在靠近陆架边缘存在着裂谷海盆。根据线性的对称磁异常分布模式及年代的限定,鲍威尔海盆的扩张历史可以被重建为40 Ma的闭合期,29.7 Ma的断裂后期,27 Ma的中脊扩张时期。     

Basin development subsequent to ridge-trench collision: the Jane Basin,Antarctica

The Jane Arc and Basin system is located at the eastern offshore prolongation of the Antarctic Peninsula, along the southern margin of the South Orkney Microcontinent. Three magnetic anomaly profiles orthogonal to the main tectonic and bathymetric trends were recorded during the SCAN97 cruise by the Spanish R/V Hespérides. In our profiles, chron C6n (19.5 Ma) was identified as the youngest oceanic crust of the Northern Weddell Sea, whose northern spreading branch was totally subducted. The profiles from the Jane Basin allow us to date, for the first time, the age of the oceanic crust using linear sea floor magnetic anomalies. The spreading in the Jane Basin began around the age of the oldest magnetic anomaly at 17.6 Ma (chron C5Dn), and ended about 14.4 Ma (chron C5ADn). The distribution of the magnetic anomalies indicate that the mechanism responsible for the development of Jane Basin was the subduction of the Weddell Sea spreading centre below the SE margin of the South Orkney Microcontinent, suggesting a novel mechanism for an extreme case of backarc development.     

Seafloor spreading anomalies and crustal ages of the Clarion-Clipperton Zone

The Clarion-Clipperton Zone (CCZ) of the central Pacific is one of the few regions in the world’s oceans that are still lacking full coverage of reliable identifications of seafloor spreading anomalies. This is mainly due to the geometry of the magnetic lineations’ strike direction sub-parallel to the Earth’s magnetic field vector near the equator resulting in low amplitude magnetic anomalies, and the remoteness of the region which has hindered systematic surveying in the past. Following recently granted research licenses for manganese nodules in the CCZ by the International Seabed Authority, new magnetic data acquired with modern instrumentation became available which combined with older underway data make the identification of seafloor spreading anomalies possible for large parts of the CCZ and adjacent areas. The spreading rates deduced from the seafloor spreading patterns show a sharp increase at the end of Chron 21 (47.5 Ma) which corresponds to the age of the bend in the Hawaii-Emperor seamount chain and an associated plate tectonic reorganisation in the Central Pacific. An accurate map of crustal ages for the central-eastern Pacific based on our anomaly picks may provide a basis for improved plate tectonic reconstructions of the region.     

北斐济海盆的构造特征与演化

北斐济海盆位于西南太平洋边缘,近半个世纪以来,针对该海盆地质和地球物理特征的调查研究取得了丰硕的成果。现今海盆内活动的构造带主要包括北斐济断裂带以及北部、中部、斐济西侧3组扩张中心,北斐济断裂带以左行走滑作用为主,扩张中心具有不稳定性。北斐济海盆形成于约10 Ma,早期主要受控于瓦努阿图岛弧的顺时针旋转,后期在以近NS和EW向的扩张作用控制下逐渐张开。扩张中心的迁移和多期构造运动的叠加是造成现今海盆内复杂构造和磁异常特征的主要原因。北斐济海盆扩张活动的深部动力学机制仍需进一步研究。     

南海西北海盆的构造特征及南海新生代的海底扩张

分析了南海西北海盆及其邻区的地形地貌、重磁场异常和地壳结构特征,并对穿过西北海盆和中央海盆的地震剖面进行精细解释。结果发现,西北海盆的地球物理场异常、地质构造和地壳厚度均呈ＮＥ走向展布,而中央海盆则表现为ＥＷ向特征;西北海盆中的新生代沉积比中央海盆多一套地层（Ｔ４－Ｔｇ）,说明西北海盆的年龄比中央海盆老。联系到南海西南海盆和西北海盆在区域构造、地球物理场异常和地形地貌特征等方面的相似,以及西南海盆和中央海盆由磁异常条带对比得出的年龄差异,我们认为,西北海盆和西南海盆是在第一次海底扩张时（４２－３５ＭａＢ．Ｐ．）形成的,中央海盆是在第二次海底扩张时形成的。     

冲绳海槽中段地球物理场及对其新生洋壳的认识

通过对冲绳海槽中的磁场进行分析，在海槽轴部追踪到了线性磁条带异常。另外，在扩张轴附近也拖到了新鲜拉斑玄武岩。重力自由空气异常值较低。根据这是由于深部地幔大幅上升所致。地震剖面及磁力资料显示在海槽轴部有强磁性浅层侵入体及海底山，这些侵入体很可能来自于深部地幔。高温地幔物质上涌在海槽轴部形成高热流、强磁异常、多火山以及热液活动。上述现象说明冲绳海槽中段张裂轴部大陆岩石圈已经破裂，并可能已有新生洋壳形成。     

Evolution of the Malvinas Plate South of Africa

We confirm that a Malvinas Plate is required in the Agulhas Basin during the Late Cretaceous because: (1) oblique Mercator plots of marine gravity show that fracture zones generated on the Agulhas rift, as well as the Agulhas Fracture Zone, do not lie on small circles about the 33o-28y South America-Africa stage pole and were therefore not formed by South America-Africa spreading, (2) the 33o-28y South America-Africa stage rotation does not bring 33o magnetic anomalies on the Malvinas Plate into alignment with their conjugates on the African Plate, and (3) errors in the 33o-28y South America-Africa stage rotation cannot account for the misalignment. We present improved Malvinas-Africa finite rotations determined by interpreting magnetic anomaly data in light of fracture zones and extinct spreading rift segments (the Agulhas rift) that are clearly revealed in satellite-derived marine gravity fields covering the Agulhas Basin. The tectonic history of the Malvinas Plate is chronicled through gravity field reconstructions that use the improved Malvinas-Africa finite rotations and more recent South America-Africa and Antarctica-Africa finite rotations. Newly-mapped triple junction traces on the Antarctic, South American, Malvinas, and African Plates, combined with geometric and magnetic constraints observed in the reconstructions, enable us to investigate the locations of the elusive western and southern boundaries of the Malvinas Plate. This revised version was published online in November 2006 with corrections to the Cover Date.     

A New Scenario of the Parece Vela Basin Genesis

A new high density geophysical data set in the Parece Vela Basin north of 15°N has been obtained through surveys conducted by the Hydrographic Department of Japan. The combined analyses of the swath bathymetry, magnetic and gravity anomalies from these surveys reveal a new scenario for the genesis of this basin. The evolutionary process is as follows: rifting and crust thinning (29–26 Ma), northward propagation of east-west opening (26-23 Ma) , east-west opening together with the Shikoku Basin (23–21 Ma), and the northeast-southwest opening (20/19–15 Ma). The western part of the basin is complicated, displaying some traces of northward propagation of the spreading center. The change between early east-west opening and the final stage of northeast-southwest spreading is marked by a distinct north-south boundary in both structural and magnetic patterns. Deep and rough topography of the extinct Parece Vela Rift is due to magma starvation in the terminal phase of the spreading.     

盆地深层火山岩磁异常的增强方法

通过模型正演分析发现,盆地深层火山岩产生的磁异常不是很大,表现为叠加在强背景之上的次级异常。 基于积分迭代延拓方法提出了增强盆地深层火山岩磁异常信息的新方法—积分迭代延拓平化曲。该方法不仅能起到增强盆地深层火山岩磁异常的作用,而且还能起到消除火山岩埋深不同对磁异常形态和大小的影响,以达到均衡磁异常的目的。将该方法应用到松辽盆地的深层火山岩预测中见到了明显的应用效果。     

Age of the Solomon Sea Basin from magnetic lineations

Magnetic anomalies measured in the central to western half of the Solomon Sea, when considered with other magnetic data, reveal the existence of linear patterns. Magnetic lineation anomaly models of the Cenozoic, 65 to 0 Ma, suggest that an age between 34 and 28 Ma and a half-rate spreading speed of 5.8 cm/yr for the northern flank of a former spreading center best fits our present magnetic data in the Solomon Sea Basin. Heat flow and bathymetry data support this preferred model.     

Age of the Solomon Sea Basin from magnetic lineations

Magnetic anomalies measured in the central to western half of the Solomon Sea, when considered with other magnetic data, reveal the existence of linear patterns. Magnetic lineation anomaly models of the Cenozoic, 65 to 0 Ma, suggest that an age between 34 and 28 Ma and a half-rate spreading speed of 5.8 cm/yr for the northern flank of a former spreading center best fits our present magnetic data in the Solomon Sea Basin. Heat flow and bathymetry data support this preferred model.     

Fault patterns on the outer wall of the Peru—Chile trench

Faults on the outer wall of the northern Peru—Chile trench, seaward of the Lima Basin, Arica Bight, and Iquique Basin, parallel the trend of Nazca plate magnetic anomalies. Where the Nazca Ridge enters the subduction zone, faulting parallels the trench, probably reflecting a lack of spreading fabric on the ridge. Seaward of the Yaquina Basin, faulting does not parallel the trench or the spreading fabric, possibly reflecting stress changes caused by N—S extension across the nearby Mendaña fracture zone. These results generally agree with a previous review of subduction-related faulting, which concluded that faults parallel the spreading fabric where it differs from the strike of the dipping slab by less than 30°.     

南海双峰盆地的形成演化及其对构造样式的约束

南海北部深水区已逐渐成为我国南海北部油气资源调查的热点区域,开展南海北部双峰盆地构造样式及成因分析研究对进一步认识南海北部沉积盆地的形成演化和评价油气资源潜力具有重要的借鉴意义。利用广州海洋地质调查局已有的二维地震资料,在对双峰盆地地震层序和构造精细解释的基础上,厘定了双峰盆地主要的构造样式;采用平衡剖面技术,重建了双峰盆地的构造演化史;结合南海北部区域构造背景,分析了双峰盆地的性质和成因。研究认为,双峰盆地为与洋壳热沉降有关的坳陷沉积盆地。从神狐运动开始,双峰盆地经历了大陆破裂—大陆裂解—海底扩张完整的构造演化旋回,在持续伸展构造应力场的作用下,形成了双峰盆地,主要发育伸展构造样式、转换-伸展构造样式、重力滑动构造样式和火成构造样式4类,其中伸展构造和火成构造较为发育。     

Evaluation of tectonic structure of İskenderun Basin (Turkey) using steerable filters

In this paper, we demonstrate the effectiveness of steerable filters as a method of delineating the boundaries of subsurface geological structures. Steerable filters, generally used for edge detection on 2-D images, have the properties of band pass filters with certain directions and are applied to many image processing problems. We first tested the method on synthetic data and then applied it to the aeromagnetic data of İskenderun Basin and adjacent areas.İskenderun Basin is located in the Northeastern Mediterranean where African–Arabian and Anatolian plates are actively interacting. The basin fill records a complex tectonic evolution since the Early Miocene, involving ophiolite emplacement, diachronous collision of Eurasian and Arabian plates and subsequent tectonic escape related structures and associated basin formation. Geophysical investigations of the tectonic framework of İskenderun Basin of Turkey provide important insights on the regional tectonics of the Eastern Mediterranean and Middle East. In this study we show geological structures, which are responsible for the magnetic anomalies in İskenderun Basin and enlighten the structural setting of the Northeastern Mediterranean triple junction using steerable filters. We obtained a magnetic anomaly map of the region from the General Directorate of Mineral Research and Exploration as raw data and then evaluated this by steerable filters. We determined the magnetic anomaly boundaries for İskenderun Basin by using various types of steerable filters and correlated these to drilling data and seismic profiles from the Turkish Petroleum Corporation. The result of the steerable filter analysis was a clarified aeromagnetic anomaly map of İskenderun Basin. The tectonic structure of İskenderun Basin is divided into regions by an N–S trending oblique-slip fault defined by the steerable filter outputs. We propose a new tectonic structure model of İskenderun Basin and modify the direction of the East Anatolian Fault Zone. In our model, East Anatolian Fault Zone cross-cuts the basin as a narrow fault zone and continues towards the Cyprus arc.     

Laxmi Ridge – A continental sliver in the Arabian Sea

Identification by Bhattacharya et al. (1994) of seafloor spreading type magnetic anomalies in the basin lying between Laxmi Ridge in the Arabian Sea and the Indian continent necessitates a change in plate tectonic reconstruction. Naini and Talwani (1982) named this basin the Eastern Basin and we will continue to use this term in this paper. Others, in the literature, have called this the Laxmi Basin. Previous reconstructions had assumed that the Eastern Basin is underlain by continental crust. The new reconstruction moves Seychelles' original location closer to India and ameliorates a space problem in the Mascarene Basin. A new rotation pole between anomaly 28 and 34 times avoids skipping of fracture zones resulting from rotation poles described earlier. The negative gravity anomaly over the Eastern Basin is a necessary consequence of a continental sliver lying between oceanic crust on either side. Seismic velocities that are slightly greater than 7 km s^–1 under the Eastern need not be necessarily interpreted as material that underplates continental crust.     

台西南盆地的构造演化与油气藏组合分析

本文根据台西南盆地的地质、地球物理资料，对台西南盆地的地壳结构、基底特征、沉积厚度、断裂构造等基本地质构造特征＾［１］作了研究，探讨了台西南盆地的构造发展演化及及油气藏组合。认为该盆地的构造演化为幕式拉张。幕式拉张可分为三大张裂幕，相应的热沉降作用使盆地在不同的张裂幕时期发展为断陷，裂陷，裂拗－拗陷。它们分别与板块作用下的区域构造运动阶段相对应，说明区域构造运动不但控制了盆地的发展演化，同时也制约     

从南海与大洋磁异常的相关性探讨南海的成因

对南海与大洋盆地条带状磁异常的相关分析表明，相关系数为０．１１—０．６５９，存在弱线性关系。这从一个侧面反映出边缘海洋壳与大洋壳本质上的差异。边缘海洋壳是玄武岩浆侵入并吞蚀破碎的大陆边缘地壳后形成的不同于大洋壳的新型洋壳。南海盆地磁异常显示其洋壳是新老不一、厚薄不匀的新洋壳的拼合叠覆体。     

南海东北部陆缘地壳结构特征及下地壳高速层成因

南海东北部陆缘构造演化信息丰富,对于理解南海的演化过程至关重要。本文收集了南海东北部的深反射地震和海底广角地震成果剖面,提取地壳和下地壳高速层的厚度结果,并结合水深、重磁异常和岩石圈的流变学等地质地球物理资料,对南海东北部的地壳减薄特征、吕宋-琉球转换板块边界的性质和下地壳高速层的分布及成因进行了分析和讨论。南海东北部的地壳减薄在横向和垂向上都存在不均匀性,以下地壳减薄为主,在台西南盆地存在极端减薄地壳;南海北缘的白云凹陷、西沙海槽和西缘的中建南盆地也存在类似的极端减薄地壳,且都与刚性地块共轭或邻近,推测刚性地块的存在导致地壳初始破裂时下地壳流动和地幔上隆是局部出现地壳极端减薄的主要原因。吕宋-琉球转换板块边界两侧在海底地形、新生代反射和重磁异常等方面均存在差异,与中生代岛弧引起的高磁异常大角度相交,其可能是中生代古特提斯构造域向太平洋构造域转换的边界断裂。下地壳高速层在南海东北部广泛发育,结合其分布特征和波速比V_p/V_s的分布区间,认为其是多期次岩浆底侵形成的铁镁质基性岩。