Structural differences between the western and eastern Qiongdongnan Basin: evidence of Indochina block extrusion and South China Sea seafloor spreading

Located at the intersection between a NW-trending slip system and NE-trending rift system in the northern South China Sea, the Qiongdongnan Basin provides key clues for us to understand the proposed extrusion of the Indochina Block along with Red River Fault Zone and extensional margins. In this paper we for the first time systematically reveal the striking structural differences between the western and eastern sector of the Qiongdongnan Basin. Influenced by the NW-trending slip faults, the western Qiongdongnan Basin developed E–W-trending faults, and was subsequently inverted at 30–21 Ma. The eastern sector was dominated by faults with NE orientation before 30 Ma, and thereafter with various orientations from NE, to EW and NW during the period 30–21 Ma; rifting display composite symmetric graben instead of the composite half graben or asymmetric graben in the west. The deep and thermal structures in turn are invoked to account for such deformation differences. The lithosphere of the eastern Qiongdongnan Basin is very hot and thinned because of mantle upwelling and heating, composite symmetric grabens formed and the faults varied with the basal plate boundary. However, the Southern and Northern Uplift area and middle of the central depression is located on normal lithosphere and formed half grabens or simple grabens. The lithosphere in the western sector is transitional from very hot to normal. Eventually, the Paleogene tectonic development of the Qiongdongnan Basin may be summarized into three stages with dominating influences, the retreat of the West Pacific subduction zone (44–36 Ma), slow Indochina block extrusion together with slab-pull of the Proto-South China Sea (36–30 Ma), rapid Indochina block extrusion together with the South China Sea seafloor spreading (30–21 Ma).     

台湾海峡及其两岸地震和地热特征

本文主要论述了台湾海峡及其两岸地震和地热的各自特征以及它们之间的关系。该地区的4个北东向地震带刻划了各个块体的相互关系。台东地震带的震源机制解表明台湾纵谷具有复杂的过渡性构造。台湾西部和台湾海峡的地震活动也受到菲律宾海板块的控制。福建沿海的地震活动与巴士断层活动有关。在自东向西各地震带的活动能量急剧下降的同时,相应的地热流异常值有一个上升趋势,海峡西岸的地热异常高值多分布在NE与NW向断裂的交汇点上。     

Preliminary Analysis of Seismic Risk in Taiwan Strait and Study on Feasibility of Construction of Tunnel Across the Strait

The collision between Eurasian and Pacific plates along the eastern margin of the Asian continent resulted in formation of a series of island-arcs, one of which is the Taiwan Island-arc, and the Taiwan Straits is a foreland basin in the continent-arc collision zone. The Quaternary fine-grained sediments occur evenly in the upper part of the basin, and the Pliocene deposits in the lower part. The stepped faults run in the deposits, indicating that the tectonic movement tended to weaken after the Pliocene. Strong seismic zones of Taiwan Island released large amount of plate overthrust-collision compressive stress and have their screen and prevention roles for the straits. Only the intersections between offshore NW-trending transform-like faults and seashore NE-trending faults on the southern and northern terminations of the Island are prone to strong earthquakes. The possibility of occurrence of M ≥ 6 earthquake should be very low in the area for the planned future tunnel. Moreover, the seismic intensity is rapidly attenuated from the surface downward. Thus, the seismic intensity for the tunnel under the seabed will be much lower. In seismotectonic view, the construction of tunnel is feasible.     

南海西南次海盆被动陆缘构造单元划分及伸展演化过程

南海西南次海盆被动陆缘洋陆转换带位于陆缘强烈伸展区,蕴含着岩石圈临界伸展破裂和洋盆扩张过程的丰富信息。本文利用多道地震剖面和重力异常数据,对西南次海盆被动陆缘构造单元进行划分,研究陆缘南、北部洋陆转换带结构构造特征,探讨陆缘伸展演化过程。多道地震剖面资料显示,北部洋陆转换带发育有裂陷期断陷和向海倾斜的掀斜断块;南部发育有低角度正断层控制的裂陷期断陷、海底火山以及局部隆起;从陆到洋方向,重力异常值变化明显。根据上述结果南海西南次海盆被动陆缘划分为近端带、洋陆转换带和洋盆三个构造单元,分别对应了其伸展演化过程的三个阶段：前裂谷阶段、陆缘裂陷阶段和海底扩张阶段。     

Preliminary Analysis of Seismic Risk in Taiwan Strait and Study on Feasibility of Construction of Tunnel Across the Strait

The collision between Eurasian and Pacific plates along the eastern margin of the Asian continent resulted in formation of a series of island-arcs, one of which is the Taiwan Island-arc, and the Taiwan Straits is a foreland basin in the continent-arc collision zone. The Quaternary fine-grained sediments occur evenly in the upper part of the basin, and the Pliocene deposits in the lower part. The stepped faults run in the deposits, indicating that the tectonic movement tended to weaken after the Pliocene. Strong seismic zones of Taiwan Island released large amount of plate overthrust-collision compressive stress and have their screen and prevention roles for the straits. Only the intersections between offshore NW-trending transform-like faults and seashore NE-trending faults on the southern and northern terminations of the Island are prone to strong earthquakes. The possibility of occurrence of M?≥?6 earthquake should be very low in the area for the planned future tunnel. Moreover, the seismic intensity is rapidly attenuated from the surface downward. Thus, the seismic intensity for the tunnel under the seabed will be much lower. In seismotectonic view, the construction of tunnel is feasible.     

Evolution of the South China Sea: Revised ages for breakup and seafloor spreading

The continental breakup which gave way to the formation of the oceanic South China Sea (SCS) basin began in the latest Cretaceous in the northeastern SCS and propagated in southern and western direction over a long period of time, possibly more than 40 m.y. The seafloor spreading history of the South China Sea has been interpreted in different ways in the past and the debate over the correct timing of the major tectonic events continues. We review the different models that have been published and present a revised interpretation of seafloor spreading anomalies based on three datasets with documented high quality which cover all of the SCS but the northernmost and southernmost parts. We can precisely date the onset of seafloor spreading in the central part of the SCS at 32 Ma. After a ridge jump at 25 Ma spreading also began in the southwestern sub-basin and spreading ended at 20.5 Ma in the entire basin, followed by a phase of magmatic seamount formation mainly along the abandoned spreading ridge. Spreading rates vary from 56 mm/yr in the early stages to 72 mm/yr after the ridge jump to 80 mm/yr in the southwestern sub-basin. We find indications for a stepwise propagation of the seafloor spreading from northeast to southwest in segments bounded by major fracture zones. Seafloor spreading ended abruptly probably because the subduction zone along the eastern and southern boundary of the SCS (of which today the Manila Trench remains) was blocked by collision with a continental fragment, possibly the northern part of Palawan or a part of the Dangerous Grounds.     

Microearthquakes along the back-arc spreading system in the eastern Bismarck Sea

OBS's were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges.     

Microearthquakes along the back-arc spreading system in the eastern Bismarck Sea

OBS’s were deployed for 26 to 29 days in the eastern Bismarck Sea to investigate the back-arc spreading. Hypocenters of 186 shallow earthquakes were determined using P- and S-waves from at least five stations. In the western survey area, a transform fault zone is marked by a linear micro-earthquake activity striking N65°W and less than 5 km wide. The predominant type of their focal mechanisms is strike-slip. In the eastern area, several intermittent zones of micro-earthquakes and their strike-slip type focal mechanisms suggest the location of short-length transform faults separating en-echelon spreading ridges.     

The western intersection of Oceanographer fracture zone with the mid-Atlantic ridge

A survey across the western intersection of the mid-Atlantic ridge with Oceanographer fracture zone near 35°N shows this intersection to be different in character from its more typical eastern counterpart. At the western junction the transform valley broadens into a parallelogram shaped deep some 46 by 24 km, which extends well across the trace of the active transform. Within 30 km south of the fracture zone the median valley becomes oblique forming a NE trending ridge which is the SE edge of the deep. Magnetic mapping shows the current spreading centre to be adjacent to this ridge.A sequence of evolution for this intersection over the past 0.7 Ma is proposed to explain the features mapped. We suggest that the oblique ridge crest trends extended across the transform trace to form the elongated graben-like deep with its associated faults and sediment slumps. Such complex patterns may occur as plate-wide changes in spreading direction become modified by localised shear stress fields at ridge crest-transform intersections, as have been observed in a number of other cases. The absence of significant tranverse ridges across from the spreading centre at this particular fracture zone intersection, may have temporarily allowed these stress patterns to propagate across the fracture zone.     

Morphology of the Blanco Transform Fault Zone-NE Pacific: Implications for its tectonic evolution

The right-lateral Blanco Transform Fault Zone (BTFZ) offsets the Gorda and the Juan de Fuca Ridges along a 350 km long complex zone of ridges and right-stepping depressions. The overall geometry of the BTFZ is similar to several other oceanic transform fault zones located along the East Pacific Rise (e.g., Siquieros) and to divergent wrench faults on continents; i.e., long strike-slip master faults offset by extensional basins. These depressions have formed over the past 5 Ma as the result of continual reorientation of the BTFZ in response to changes in plate motion. The central depression (Cascadia Depression) is flanked by symmetrically distributed, inward-facing back-tilted fault blocks. It is probably a short seafloor spreading center that has been operating since about 5 Ma, when a southward propagating rift failed to kill the last remnant of a ridge segment. The Gorda Depression on the eastern end of the BTFZ may have initially formed as the result of a similar occurrence involving a northward propagating rift on the Gorda ridge system. Several of the smaller basins (East Blanco, Surveyor and Gorda) morphologically appear to be oceanic analogues of continental pull-apart basins. This would imply diffuse extension rather than the discrete neovolcanic zone associated with a typical seafloor spreading center. The basins along the western half of the BTFZ have probably formed within the last few hundred thousands years, possibly as the result of a minor change in the Juan de Fuca/Pacific relative motion.     

琼东南盆地深水区主要构造因素与成盆机制分析-地震解释与物理模拟实验

Located at the northwest continental slope of the South China Sea, the Qiongdongnan Basin bears valley-shaped bathymetry deepening toward east. It is separated from the Yinggehai Basin through NW-trend...     

莺-琼盆地基底控制断裂样式的模拟探讨

莺歌海盆地与琼东南盆地(即莺一琼盆地)是南海西北部2个重要的含油气盆地。莺歌海盆地走向NW,发育在红河断裂带上;琼东南盆地走向NE,与莺歌海盆地近直角相交。根据物理模拟实验,认为莺歌海盆地的演化受到了NW与近S-N向基底断裂的控制,在印支地块顺时针挤出应力场下发育和演化;而琼东南盆地则受到NE向基底断裂的控制,在SSE向伸展应力场控制下发育,NW与NE向构造带相互影响,造成了琼东南盆地北侧边界断裂走向近E—W,向南呈台阶式下掉,南侧边界断裂走向NE,莺琼过渡区隆凹格局复杂。由于莺歌海盆地NW向构造活动早于琼东南盆地NE向裂陷作用,从而导致NW向构造控制地位的形成,NW向断裂和构造表现为对NE向断裂和构造的阻截。     

阳江-一统东断裂的新生代活动：从珠江口盆地西部构造特征与演化过程分析得到的启示

阳江-一统东断裂是珠江口盆地西部一条重要的NW向区域大断裂,是盆地东西分块的重要分界线。南海北部陆缘在新生代经历了大陆裂谷-裂离-海底扩张-热沉降的过程,阳江-一统东断裂在新生代的活动是这一复杂过程的一部分。对分处断裂两侧的从陆架延伸至洋陆边界的两条NNW向多道地震剖面进行了地质解释,研究了珠江口西部的构造和沉积特征。利用2D-Move软件及构造回剥法建立了平衡剖面模型,计算了断层活动速率,结合构造位置、构造演化史、标志构造和应力分析推断了阳江-一统东断裂在新生代的活动史。结果表明,阳江-一统东断裂可以中部坳陷带为界分为两段,从65Ma到32Ma,断裂整体表现为左旋活动,继承了断裂在中生代时期的先存左旋走滑,其中,在此时期断裂南段主要表现为伸展活动,伴随着轻微的左旋走滑,这种伸展活动控制了云开低凸起的形成和演化;从32Ma到23.8Ma,断裂北段的左旋走滑活动持续,而南段逐渐转为轻微的右旋走滑或左旋活动停止。在23.8Ma之后,断裂南段的右旋走滑活动持续,北段的左旋走滑逐渐停止,或转为轻微的右旋走滑。阳江-一统东断裂的这种走滑旋向的转变可能与在珠江口盆地南部洋陆过渡带区域的岩浆底侵作用有关。根据对盆地构造活动强度和裂谷格架的分析,认为阳江-一统东断裂的新生代活动在珠江口盆地裂谷伸展过程中起到了应力调节的作用。     

南海南部断裂的分形研究

分形几何作为定量描述自然界中复杂非线性现象的强有力工具被应用于南海南部断裂体系的研究中,通过数盒子法计算了断裂分布的分维值.研究结果表明这种方法是可行的,断裂分布的分维值能有效地描述断裂的空间分布特征.南海南部断裂体系在标度区间25~250km具有很好的统计自相似性,全部断裂的分维值为1.6601,北东向断裂的为1.3875,北西向断裂的为1.2693.根据断裂分维等值线,沿西南海盆扩张轴,两侧断裂呈对称展布;北东向的与北西向的在空间上有一定的互补性,这反映了两组断裂在发育过程中的相互制约性.结合南海的构造演化及南海南部油气盆地的分布,初步探讨了断裂分形特征与南海的构造演化及断裂分形特征与油气盆地分布之间的关系.     

The antipodes fracture zone,a major structure of the south‐west pacific

The steep Antipodes Scarp, along the eastern boundary of the Campbell Plateau south‐east of New Zealand, is attributed to dextral tear‐faulting within a NE‐SW belt, the Antipodes Fracture Zone, which also truncates the eastern end of the Chatham Rise. A complementary zone of sinistral movement, the Waipounamu Fracture, separates the Campbell Plateau and Chatham Rise from mainland New Zealand.

The origin of these fracture zones is linked with that of the parallel Alpine Fault of South Island, and is related to a phase of NE‐SW crustal compression that dominated the New Zealand region during the Mesozoic era. It is suggested that this compression resulted from the north‐eastward “drift” of the Australian craton and the simultaneous elevation of the Darwin Rise in the central Pacific.     

胶东—苏北构造带特征及动力学演化

提出胶东—苏北构造带以广泛出露榴辉岩和超基性岩、普遍发育韧性剪切带和糜棱岩带为特征,具混杂岩特点。它经历了早元古代大陆推覆构造事件(2000～2400Ma)、早元古代末低角闪岩相变质热事件(1800～2000Ma)和元古代末大陆推覆构造事件(6O0～800Ma)。该构造带是华北陆块与华南陆块之间的过渡带。     

俄罗斯大洋固体矿产资源调查研究进展

介绍了俄罗斯的海洋多金属结核、铁锰结壳、热液硫化物和磷钙土资源调查研究活动概况和发展趋势。     

南海南部断裂的分形研究

分形几何作为定量描述自然界中复杂非线性现象的强有力工具,将其应用于南海南部断裂体系的研究中,通过数盒子法计算了断裂分布的分维值。研究结果表明这种方法是可行的,断裂分布的分维值能有效地描述断裂的空间分布特征。南海南部断裂体系在标度区间25～250km内具有很好的统计自相似性,全部断裂的分维值为1．6601,北东向断裂的为1．3875,北西向断裂的为1．2693。根据断裂分维等值线,沿西南海盆扩张轴,两侧断裂呈对称展布;北东向的与北西向的在空间上有一定的互补性,这反映了两组断裂在发育过程中的相互制约性。结合南海的构造演化及南海南部油气盆地的分布,初步探讨了断裂分形特征与南海的构造演化及断裂分形特征与油气盆地分布之间的关系。     

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.