Dip variations of the North American and North Caribbean Plates dominate the tectonic activity of Puerto Rico–Virgin Islands and adjacent areas

The M 7.0 Haiti earthquake of 2010 in the Greater Antilles is a reminder that the northeastern Caribbean is at a high risk for seismic and tsunami hazards. The Greater Antilles consist of the Hispaniola microplate to the west and Puerto Rico–Virgin Islands to the east and are situated between two subduction zones with the Puerto Rico Trench to the north and the Muertos Trough to the south. Although there is no active volcanism on Puerto Rico, earthquake depths and previous seismic tomography results imply that the slabs of Caribbean and North American Plates exist at depth. However, how far the east Muertos Trough subduction of the North Caribbean Plate has extended has not been fully addressed. In addition, the Puerto Rico–Virgin Islands are bounded by extensional regimes to both the west (Mona Rift) and east (Anegada Passage). The cause of the extension is still under debate. In this paper, we use new 3D seismic tomography and gravity data to carry out an integrated study of the geometry of the subducting slabs of the North American and North Caribbean Plates in the Puerto Rico–Virgin Islands area. The results indicate that both slabs have an increase of dip westward, which is strongly controlled by the subduction rollback of the North American Plate. These variations affected the tectonic evolution of the Puerto Rico–Virgin Islands. Thus, the results of this research advance our understanding of the kinematic evolution of the Puerto Rico–Virgin Islands and associated natural hazards. Copyright © 2015 John Wiley & Sons, Ltd.     

The Alboran Sea (Western Mediterranean) revisited with a view from the Moroccan Margin

This paper presents a new depth to acoustic basement map based on a grid of seismic profiles. In the Western Alboran Basin the basement is more than 10 km deep. An examination of a seismic profile of this region suggests that Late Oligocene–Early Miocene 5 km thick synrift formation has been accumulated in this basin. This West Alboran basin has been formed in an extensional setting, but in a fore‐arc position, south of the Balearic Islands then westwards transported behind a subduction zone.     

关于敦化盆地下白垩统的讨论

前人根据敦化盆地的地层的地层,认为该盆地下白垩统为河流—湖泊相碎屑岩。通过对新钻的敦参1井岩屑录井资料的分析、对16条二维地震资料的层位标定与追踪,以及对敦化盆地早白垩世盆地演化阶段的分析,得到了以下主要结论:1)敦化盆地下白垩统可能有两种分布形态,在盆地的主体部位,以浅变质岩形态存在,而在其他部位则以正常沉积岩形态零星存在;2)敦化盆地白垩系的分布规模不大,夹持于一个北北东向的狭窄长槽内;3)敦化盆地早白垩世处于裂谷盆地发展的初始张裂阶段;4)敦化盆地下白垩统不宜作为勘探目的层。     

Characteristics of Meso-Cenozoic Igneous Complexes in the South Yellow Sea Basin, Lower Yangtze Craton of Eastern China and the Tectonic Setting

The South Yellow Sea Basin is partially surrounded by the East Asian continental Meso-Cenozoic widespread igneous rocks belt. Magnetic anomaly and multi-channel seismic data both reveal the prevalent occurrence of igneous rocks. We preliminarily defined the coupling relation between magnetic anomalies and igneous rock bodies. Some igneous complexes were also recognized by using multi-channel seismic and drilling data. We identified various intrusive and extrusive igneous rock bodies, such as stocks, sills, dikes, laccoliths and volcanic edifice relics through seismic facies analysis. We also forecasted the distribution characteristics of igneous complexes. More than fifty hypabyssal intrusions and volcanic relics were delineated based on the interpretation of magnetic anomaly and dense intersecting multi-channel seismic data. It is an important supplement to regional geology and basin evolution research. Spatial matching relations between igneous rock belts and fractures document that extensional N–E and N–NE-trending deep fractures may be effective pathways for magma intrusion. These fractures formed under the influence of regional extension during the Meso-Cenozoic after the Indosinian movement. Isotopic ages and crosscutting relations between igneous rock bodies and the surrounding bedded sedimentary strata both indicate that igneous activities might have initiated during the Late Jurassic, peaked in the Early Cretaceous, gradually weakened in the Late Cretaceous, and continued until the Miocene. Combined with previous studies, it is considered that the Meso-Cenozoic igneous activities, especially the intensive igneous activity of the Early Cretaceous, are closely associated with the subduction of the Paleo-Pacific Plate.     

Crustal Structure across the Northwestern Margin of South China Sea: Evidence for Magma‐poor Rifting from a Wide‐angle Seismic Profile

We present results from a 484 km wide-angle seismic profile acquired in the northwest part of the South China Sea (SCS) during OBS2006 cruise. The line that runs along a previously acquired multi-channel seismic line (SO49-18) crosses the continental slope of the northern margin, the Northwest Subbasin (NWSB) of the South China Sea, the Zhongsha Massif and partly the oceanic basin of the South China Sea. Seismic sections recorded on 13 ocean-bottom seismometers were used to identify refracted phases from the crustal layer and also reflected phases from the crust-mantle boundary (Moho). Inversion of the traveltimes using a simple start model reveals crustal images in the study area. The velocity model shows that crustal thickness below the continental slope is between 14 and 23 km. The continental part of the line is characterized by gentle landward mantle uplift and an abrupt oceanward one. The velocities in the lower crust do not exceed 6.9 km/s. With the new data we can exclude a high-velocity lower crustal body (velocities above 7.0 km/s) at the location of the line. We conclude that this part of the South China Sea margin developed by a magma-poor rifting. Both, the NWSB and the Southwest Sub-basin (SWSB) reveal velocities typical for oceanic crust with crustal thickness between 5 and 7 km. The Zhongsha Massif in between is extremely stretched with only 6–10 km continental crust left. Crustal velocity is below 6.5 km/s; possibly indicating the absence of the lower crust. Multi-channel seismic profile shows that the Yitongansha Uplift in the slope area and the Zhongsha Massif are only mildly deformed. We considered them as rigid continent blocks which acted as rift shoulders of the main rift subsequently resulting in the formation of the Northwest Sub-basin. The extension was mainly accommodated by a ductile lower crustal flows, which might have been extremely attenuated and flow into the oceanic basin during the spreading stage. We compared the crustal structures along the northern margin and found an east-west thicken trend of the crust below the continent slope. This might be contributed by the east-west sea-floor spreading along the continental margin.     

Investigation of the deep structure of the Sivas Basin (innereast Anatolia, Turkey) with geophysical methods

Sivas Basin is the easternmost and third largest basin of the Central Anatolian Basins. In this study, gravity, aeromagnetic and seismic data are used to investigate the deep structure of the Sivas Basin, together with the well seismic velocity data, geological observations from the surface and the borehole data of the Celalli-1 well. Basement depth is modeled three-dimensionally (3D) using the gravity anomalies, and 2D gravity and magnetic models were constructed along with a N–S trending profile. Densities of the rock samples were obtained from the distinct parts of the basin surface and in-situ susceptibilities were also measured and evaluated in comparison with the other geophysical and geological data. Additionally, seismic sections, in spite of their low resolution, were used to define the velocity variation in the basin in order to compare depth values and geological cross-section obtained from the modeling studies. Deepest parts of the basin (12–13 km), determined from the 3D model, are located below the settlement of Hafik and to the south of Zara towns. Geometry, extension and wideness of the basin, together with the thickness and lithologies of the sedimentary units are reasonably appropriate for further hydrocarbon exploration in the Sivas Basin that is still an unexplored area with the limited number of seismic lines and only one borehole.     

塔里木盆地中部航磁异常带新解译

横亘于塔里木盆地中部的纬向航磁高ΔTa异常带,一直是探讨盆地及深部基底的物质组成及结构构造的焦点。根据钻井及地震资料综合分析,发现满加尔坳陷中南部上奥陶统内发育大型地震反射异常体,平面上主要由8个地震反射异常体近东西向呈带状展布,与盆地中部航磁高ΔTa异常带相关。从地层发育及地震相特征分析,这些地震反射异常体应为辉绿岩-玄武岩等基性火成岩体,且与航磁ΔTa异常带上的磁力高相对应。异常体具有垂直向下的通道,与断裂及岩浆活动通道有关。盆地中部高航磁异常带为多期构造易活动带,反映了满加尔坳陷震旦纪与中晚奥陶世处于拉张的构造背景。     

柴达木盆地大柴旦地区盆地中新生代演化机制电性特征分析

柴达木盆地位于青海省西北部,是在昆仑山、阿尔金山和祁连山控制形成的山间断陷盆地,由于盆地中生代沉积了大范围的侏罗系地层,因此盆地内含有丰富的油气资源,众多学者对柴达木盆地的构造演化做了大量的研究,受限于盆地的山盆耦合模式,地形、地质条件复杂,山前地带大多是地震的空白区,仅在局部获得了地震勘探资料,但资料品质较差。由于缺乏详细资料,关于该区域构造演化的研究没能深入开展,盆地内部构造演化的研究主要在构造背景和构造格架上,对于构造的细节没有得到解析。本文通过音频大地电磁法探测大柴旦地区盆地地质特征,基于三维非线性共轭梯度(3D NLCG)反演算法,获得研究区三维电性模型,结合区域地质、地球物理资料研究盆地构造演化,结果表明：三维电性模型揭示了柴北缘地区盆地中生代以拉张为主形成一系列断陷盆地,新生代以喜山构造活动为主产生一系列挤压为主的冲断构造,造成早侏罗系-晚白垩系地层的局部缺失等地质活动的盆地演化动力学电性特征。     

The tectonic evolution of the Qiongdongnan Basin in the northern margin of the South China Sea

Qiongdongnan Basin is a Cenozoic rift basin located on the northern passive continental margin of the South China Sea. Due to a lack of geologic observations, its evolution was not clear in the past. However, recently acquired 2-D seismic reflection data provide an opportunity to investigate its tectonic evolution. It shows that the Qiongdongnan Basin comprises a main rift zone which is 50–100 km wide and more than 400 km long. The main rift zone is arcuate in map view and its orientation changes from ENE–WSW in the west to nearly E–W in the east. It can be divided into three major segments. The generally linear fault trace shown by many border faults in map view implies that the eastern and middle segments were controlled by faults reactivated from NE to ENE trending and nearly E–W trending pre-existing fabrics, respectively. The western segment was controlled by a left-lateral strike-slip fault. The fault patterns shown by the central and eastern segments indicate that the extension direction for the opening of the rift basin was dominantly NW–SE. A semi-quantitative analysis of the fault cut-offs identifies three stages of rifting evolution: (1) 40.4–33.9 Ma, sparsely distributed NE-trending faults formed mainly in the western and the central part of the study area; (2) 33.9–28.4 Ma, the main rift zone formed and the area influenced by faulting was extended into the eastern part of the study area and (3) 28.4–20.4 Ma, the subsidence area was further enlarged but mainly extended into the flanking area of the main rift zone. In addition, Estimates of extensional strain along NW–SE-trending seismic profiles, which cross the main rift zone, vary between 15 and 39 km, which are generally comparable to the sinistral displacement on the Red River Fault Zone offshore, implying that this fault zone, in terms of sinistral motion, terminated at a location near the southern end of the Yinggehai Basin. Finally, these observations let us to favour a hybrid model for the opening of the South China Sea and probably the Qiongdongnan Basin.     

Tectonic Evolution of the Wanan Basin,Southwestern South China Sea

Quantitative studies on the extension and subsidence of the Wanan Basin were carried out based on available seismic and borehole data together with regional geological data.Using balanced cross-section and backstripping techniques,we reconstructed the stratigraphic deposition and tectonic evolution histories of the basin.The basin formed from the Eocene and was generally in an extensional/transtensional state except for the Late Miocene local compressoin.The major basin extension ocurred in the Oligocene and Early Miocene(before ~16.3 Ma) and thereafter uniform stretch in a smaller rate.The northern and middle basin extended intensely earlier during 38.6–23.3 Ma,while the southern basin was mainly stretched during 23.3–16.3 Ma.The basin formation and development are related to alternating sinistral to dextral strike-slip motions along the Wanan Fault Zone.The dominant dynamics may be caused by the seafloor spreading of the South China Sea and the its peripheral plate interaction.The basin tectonic evolution is divided into five phases:initial rifting,main rifting,rift-drift transition,structural inversion,and thermal subsidence.     

南海北部陆坡深水沉积体系研究

陆源碎屑物质是深水地质研究的重要内容,在全球“从源到汇”研究计划中占有重要地位。海底峡谷-水道搬运沉积体系和块体搬运沉积体系（海底滑坡）是大陆坡最重要的两种搬运沉积过程。根据高分辨率2D、3D多道反射地震资料、多波束测深法、旁扫声纳、重力与活塞取样等资料研究发现,在南海北部陆坡地层中,广泛发育大型深水块体搬运体系和相应深水水道沉积体系。针对白云凹陷和琼东南盆地深水陆坡区的实例研究,揭示了典型深水块体搬运的平面形态、内部结构和变形过程,进而深入认识这一地质体的形成演化过程。采用2D/3D地震资料和多种数值模拟新方法发现了第四系深水高弯曲水道及其沉积相特征、上新世琼东南盆地中央水道及中新世古珠江深水水道体系。深水沉积体系对研究我国深水油气资源的成因机理和分布规律,以及深水工程的地质灾害预测和防护具有十分重要的意义。     

Temporal and spatial patterns of Cenozoic deformation across the Qaidam Basin,Northern Tibetan Plateau

We conducted a systematic analysis of the temporal and spatial patterns of Cenozoic deformation of the northeastern (NE) and southwestern (SW) parts of the Qaidam Basin, the largest and thickest Cenozoic sedimentary basin within the Tibetan Plateau, by constructing balanced cross‐sections traversing the whole basin using high‐resolution seismic‐reflection data. We found that that these two parts deformed synchronously with similar temporal patterns involving nearly constant NE–SW contraction before c. 2.5 Ma and much more intense shortening, possibly enhanced by fierce wind erosion, since then. However, the spatial deformation patterns of these two areas differ markedly: an eastward weakening trend in the SW part is not observed in the NE part. We believe that this difference is due to their different boundary conditions. This result places new constraints on the formation mechanisms of the northern Tibetan Plateau.     

4D modelling of fault reactivation using complete paleostress tensors from the Cooper–Eromanga Basin,Australia

Determining fault activity through time has typically utilised high-resolution seismic data to identify stratigraphic thickness changes or displacement vs distance plots; however, this approach is not possible in regions with low-resolution seismic data. We present a new approach for determining fault reactivation (tensile and shear) through time by integrating three-dimensional seismic data, geomechanical modelling and complete paleostress tensors from calcite twin stress inversion. The Cooper–Eromanga Basin is used as a case study to model the stress conditions present during six tectonic events that have affected the basin and, in doing so, constrain the effective paleostress magnitudes through time. Results show that the likelihood of dilation and shear reactivation of individual fault sets varies through time, with N–S- and E–W-striking faults likely to have been open to fluid flow after the critical moment in the hydrocarbon system. These results have substantial implications for hydrocarbon migration pathway models and structural and stratigraphic models for the Cooper–Eromanga Basin. This approach would benefit other provinces with low-resolution seismic data preventing fault growth analysis, or in regions where hydrocarbon migration pathways are poorly defined.     

The Minorca Basin: a buffer zone between the Valencia and Liguro‐Provençal Basins (NW Mediterranean Sea)

Detailed analyses of seismic profiles and boreholes in the Valencia Basin (VB) reveal a differentiated basin, the Minorca Basin (MB), lying between the old Mesozoic Valencia Basin sensu strico (VBss) and the young Oligocene Liguro‐Provençal Basin (LPB). The relationship between these basins is shown through the correlation of four Miocene‐to‐present‐day megasequences. The Central and North Balearic Fracture Zones (CFZ and NBFZ) that border the MB represent two morphological and geodynamical thresholds that created an accommodation in steps between the three domains. Little to no horizontal Neogene movements are found for the Ibiza and Majorca Islands. In contrast, the counterclockwise movement of the Corso‐Sardinian blocks induced a counterclockwise movement of the Minorca block towards the SE along the CFZ and NBFZ, during the exhumation of lower continental crust in the LPB. This new understanding implies pure Neogene vertical subsidence in the VBss and places the AlKaPeCa northeastward of the present‐day Alboran Area.     

Late Neogene–Quaternary evolution of the intermontane Clusone Basin (Southern Alps,Italy): integration of seismic and geological data

In the Clusone Basin (a large intermontane basin filled by thick late Neogene–Quaternary sediments in the Middle Val Seriana, Southern Alps), two high‐resolution seismic profiles have been acquired in order to reconstruct the geometries of the sediments that fill the depression, with a maximum thickness of more than 200 m as documented by available well data, and to define their relationships with the bedrock, consisting of Late Triassic carbonates. In addition to standard seismic reflection processing, a seismic refraction inversion technique has been applied. The integration of geological (both surface and well data) and seismic data indicates a complex history of the drainage patterns of the Clusone Basin, documenting a shift of the Serio River from a palaeodrainage toward the southeast (Val Borlezza) to the present situation, toward the south (Val Seriana): between the older and the present‐day drainages an important depositional stage occurred, as documented by the thick sediments that fill the Clusone Basin, controlling the capture of the Serio River along the Val Seriana. Copyright © 2004 John Wiley & Sons, Ltd.     

http://www.sciencedirect.com/science/article/pii/S1674987113000546

In the eastern part of the Indian shield,late PaleozoiceMesozoic sedimentary rocks of the Talchir Basin lie precisely along a contact of Neoproterozoic age between granulites of the Eastern Ghats Mobile Belt(EGMB)and amphibolite facies rocks of the Rengali Province.At present,the northern part of the basin experiences periodic seismicity by reactivation of faults located both within the basin,and in the Rengali Province to the north.Detailed gravity data collected across the basin show that Bouguer anomalies decrease from the EGMB(wt15 mGal),through the basin(w 10 mGal),into the Rengali Province(w 15 mGal).The data are consistent with the reportedly uncompensated nature of the EGMB,and indicate that the crust below the Rengali Province has a cratonic gravity signature.The contact between the two domains with distinct sub-surface structure,inferred from gravity data,coincides with the North Orissa Boundary Fault(NOBF)that defnes the northern boundary of the Talchir Basin.Post-Gondwana faults are also localized along the northern margin of the basin,and present-day seismic tremors also have epicenters close to the NOBF.This indicates that the NOBF was formed by reactivation of a Neoproterozoic terrane boundary,and continues to be susceptible to seismic activity even at the present-day.     

从东海和南海北部盆地群演化探讨日本大陆板块的形成过程

日本列岛是位于欧亚东缘和西太平洋过渡带上的大陆板块,其来源和成因机制得到了广泛研究,传统上认为其成因是由太平洋俯冲形成的沟弧盆体系的一部分,但仍存在诸多争议。基于地形地貌、地震勘探剖面和盆地构造演化史恢复、古地磁测量和古生物等诸多证据,将南海北部的珠江口盆地、台西南盆地和东海盆地及冲绳海槽的构造迁移进行统一的系统分析,研究结果表明日本大陆板块在新生代由两个区域分别漂移而来。北海道来自赤道附近,而本州、四国和九州来自华南大陆边缘。其成因动力机制与欧亚板块从北大西洋的裂解东漂和印度与欧亚碰撞密切相关,在这个过程中,位于欧亚板块东缘的日本三岛首先发生了裂解,之后发生了漂移。新的大陆漂移模型合理地解释了沟弧盆体系的形成机制和过程,说明了弧状岛弧的成因机制,也给出了所形成的盆地内油气富集的规律。本研究为大陆漂移模式提供了一个新的动力机制。     

Field evidences from northern Dead Sea Fault Zone (South Turkey): New findings for the initiation age and slip rate

The left-lateral strike–slip Dead Sea Fault Zone (DSFZ) extends from the Red Sea in the south to the East Anatolian Fault Zone (EAFZ) in the north. This study examines the northern part of the DSFZ around Amik Basin and presents surface and subsurface geological evidence for the Quaternary activity and initiation age of the northernmost DSFZ. The DSFZ extends N–S in the south of the Amik Basin where clear geological and morphological evidence exists for faulting. Geological observations around Amik Basin, analyses of borehole data and electrical resistivity profiles within the Amik Basin indicate that the activity of the northern DSFZ started after Pliocene in the Amik Basin. Subsurface data in the basin suggest that the DSFZ offsets a pre-Quaternary basin sinistrally by about 7.9 km. The offset pre-Quaternary basin suggests at least 4.94 ± 0.13 mm/year slip rate for the northern part of the DSFZ. The Karasu Fault Zone (KFZ) extends in an en-echelon pattern along the western margin of the Karasu Valley and it transfers the significant amount of slip from DSFZ to the EAFZ.     

Geological structure of the sedimentary cover and evaluation of the oil and gas potential of the Deryugin Basin (Sea of Okhotsk)

Results of interpretation of the seismic refraction survey in the southern part of the Deryugin Basin are presented. A geological-geophysical model was developed, and a scheme of the sedimentary cover evolution of the basin (Late Cretaceous-Pleistocene) is suggested. The data obtained indicate a high hydrocarbon potential comparable with that of the adjacent oil and gas-bearing shelf of northeastern Sakhalin.     

东海陆架盆地新生代扩张率的估算

东海陆架盆地是位于中国大陆东部边缘大陆地壳之上的边缘海盆地。盆地新生代构造演化经历了断陷(初始沉降)和坳陷(热控沉降)两个阶段。本文利用钻井及地震反射剖面资料,通过钻井古地层剥蚀量和剥蚀时间的恢复,应用Mckenzie(1978)的均一拉伸模式和Sclater(1985)的双层拉伸模式对陆架盆地,主要是浙东坳陷的西湖凹陷进行了基底沉降和地壳岩石圈扩张率的定量估算。计算结果表明东海陆架盆地沉降速率早期较快,后期变慢。西湖凹陷新生代以来地壳岩石圈扩张率,在凹陷北部(D800测线)为40%-50%,中部(D688测线)为100%-140%,南部(G455测线)为60%-120%。