40Ar/39Ar geochronology of the Neogene-Quaternary Harrat Al-Madinah intercontinental volcanic field,Saudi Arabia: Implications for duration and migration of volcanic activity

New ⁴⁰Ar/³⁹Ar ages, based on incremental heating techniques for groundmass separates of 25 samples, are presented for the Harrat Al-Madinah volcanic field, part of Harrat Rahat in the north western part of the Arabian plate. This area is an active volcanic field characterized by the occurrence of two historical eruptions approximately in 641 and 1256 AD. Field investigations of the main volcanic landforms indicate dominantly monogenetic strombolian eruptions, in addition to local more explosive eruptions. The lavas consist mainly of olivine basalt and hawaiite flows with minor evolved rocks of mugearite, benmoreite, and trachyte that occur mainly as domes, tuff cones and occasionally as lava flows. Previous K/Ar dating shows that the Harrat Al-Madinah lava flows and associated domes comprise seven units spanning an age range of ca. 1.7 Ma–Recent. The new ⁴⁰Ar/³⁹Ar age determinations confirm, to a great extent, the previously obtained K/Ar ages in the sense that no major systematic biases were found in the general stratigraphy of the different flow units. However, the ⁴⁰Ar/³⁹Ar plateau ages show that volcanism in this area began in the Neogene (∼10 Ma) and continued to Recent, with the most voluminous eruptions occurring in the Quaternary. Neogene volcanism occurred in at least three pulses around 10, 5 and 2 Ma, whereas Quaternary volcanism produced at least seven units reflecting lava flow emplacement in the time period of 1.90 Ma–Recent. Thus, the whole duration of volcanic activity in the Harrat Al-Madinah (10 Ma–Recent) appears much longer than that previously identified. The longevity of volcanism in the same part of the moving Arabian plate and absence of evidence for uni-directional migration of volcanic activity indicate that there is no fixed plume beneath this region. The NNW-trending distribution of the volcanic vents is parallel to the Red Sea, and suggests their origin is related to periodic extensional episodes along the reactivated Red Sea fault system.     

Seismicity associated with active, new-born, and re-awakening basaltic volcanoes: case review and the possible scenarios for the Harraat volcanic provinces, Saudi Arabia

During April–June 2009, a swarm of more than 30,000 earthquakes struck the Harrat Lunayyir, situated in the north-western end of the Saudi Arabian Harraat, east of the Red Sea. This sharp increase in the seismic activity in the region of ancient basaltic volcanic centers indicated a likelihood of a future eruption. To check the situation, a short review of the best-documented seismic activity associated with active, new-born, and re-awakening basaltic volcanoes is presented in this article. Basing on the review, some regularity in the development of seismic activity associated with basaltic eruptions was formulated. Three stages in the development of seismic activity were identified: preliminary, preceding, and continuous. The duration of preceding stage varies from a few hours for active and re-awakened volcanoes to some weeks for new-born volcanoes and may serve as a criterion for discriminations of different types of basaltic eruptions. The duration of the seismic activity during the 2009 episode at Harrat Lunayyir was longer than any activity preceding the basaltic eruptions of different types. Therefore, the most probable scenario is the arrest of sub-surface intrusion without any eruption in the region of Harrat Lunayyir. The next probable scenario would be the dike injections along the rift zones. The re-awakening of the old Harrat Lunayyir volcano or the birth of a new volcano at Harrat Lunayyir is less probable.     

南海南部礼乐盆地结构演化及其对区域地质背景的响应

运用丰富的二维地震资料,通过构造结构与地层结构的分析,对礼乐盆地的盆地结构演化与转型过程及其对南海地区复杂动力学背景的响应特征进行研究。结果表明:受控于NNE、NEE、NW和近EW向的断裂体系,礼乐盆地现今构造格局表现为"两坳一隆"的结构特征;两个关键的区域角度不整合T70和T50将礼乐盆地新生界自下而上划分为三层结构:陆缘裂陷层、漂移裂陷层和前陆-拗陷层;响应于太平洋板块俯冲、印度-欧亚板块碰撞、新南海扩张、古南海消亡和菲律宾海板块楔入等一系列周缘板块重组事件,礼乐盆地的盆地结构演化及转型经历了三个阶段:陆缘多幕裂陷阶段,盆地结构受控于NNE和NEE向断裂体系,南北坳陷连通;漂移裂陷阶段,NNE和NW向共轭断裂体系控制盆地格局,中部隆起形成,分隔南、北坳陷;前陆-拗陷阶段,前陆盆地结构形成,随后盆地因热沉降进入拗陷沉积阶段。     

Petrology of Mantle Xenoliths from Harrat al Kishb: The Mantle beneath Western Saudi Arabia

Tertiary to Recent continental rifting and sea floor spreadingformed the Red Sea. Mantle xenoliths from the Saudi ArabianRed Sea margin provide an opportunity to study the mantle beneaththe flanks of this young ocean basin. The Harrat al Kishb mantlexenolith suite consists of Cr-diopside group spinel harzburgiteand lherzolite mantle wall rock, and a variety of pyroxenitesproduced by crystallization from mafic magmas within the mantle.The pyroxenites include two texturally distinct varieties ofCr-diopside group spinel websterites, and Al-augite group spinelpyroxenite, garnet-spinel websterite, and garnet-bearing spinelclinopyroxenite. All Harrat al Kishb xenoliths are deformedto some degree and many are recrystallized. Mineral exsolutionand zoning textures indicate reequilibration to decreasing temperatureconditions. Several xenoliths provide evidence for metasomaticprocesses in the mantle beneath western Saudi Arabia. Estimates of peridotite temperatures are 900–980?C withpressure bracketed between 13 and 19 kb. Al-augite spinel pyroxenitesyield temperatures of 1050–1070?C. Garnet-spinel websteritesyield temperatures and pressures in the range 1000–1030?C,13.8–16.5 kb. These P-T estimates show that mantle temperatures are elevatedwell above those predicted by low surface heat flow measurements.Mantle heating associated with rifting is young enough thatsurface heat flow has not yet equilibrated. The xenolith dataare consistent with a model of asthenosphere upwelling beneaththe Red Sea rift. Comparison of xenolith data with existingseismic refraction data reveals a coherent picture of the compositionof the western Saudi Arabian lithosphere.     

Petrogenesis of granitic rocks of the Jabal Sabir area,South Taiz City,Yemen Republic

The Tertiary granitic intrusive body(～21 Ma) of the Jabal Sabir area was emplaced during the early stages of the Red Sea opening.This intrusive body occupies the southern sector of Taiz City.It is triangular in shape,affected by two major faults,one of which is in parallel to the Gulf of Aden,and the other is in parallel to the eastern margin of the Red Sea coast.The petrogenesis of such a type of intrusion provides additional information on the origin of the Oligo-Miocene magmatic activity in relation to the rifting tectonics and evolution of this part of the Arabian Shield.The granitic body of Jabal Sabir belongs to the alkaline or peralkaline suite of A-type granites.It is enriched in the REE.The tight bundle plot of its REE pattern reflects neither tectonism nor metamorphism.This granite body is characterized by high alkali(8.7%-10.13%),high-field strength elements(HFSE),but low Sr and Ba and high Zn contents.The abundance of xenoliths from the neighboring country rocks and prophyritic texture of the Jabal Sabir granite body indicate shallow depths of intrusion.The major and trace elements data revealed a fractional crystallization origin,probably with small amounts of crustal contamination.It is interpreted that the Jabal Sabir intrusion represents an anorogenic granite pertaining to the A-type,formed in a within-plate environment under an extensional tectonic setting pertaining to rift-related granites.     

Opaque Mineralogy as a Tracer of Magmatic History of Volcanic Rocks:an Example from the Neogene-Quaternary Harrat Rahat Intercontinental Volcanic Field, North Western Saudi Arabia

The Neogene-Quaternary Harrat Rahat volcanic field is part of the major intercontinental Harrat fields in western Saudi Arabia.It comprises lava flows of olivine basalt and hawaiite,in addition to mugearite,benmorite,and trachyte that occur mainly as domes,tuff cones and lava flows.Based on opaque mineralogy and mineral chemistry,the Harrat Rahat volcanic varieties are distinguished into Group I(olivine basalt and hawaiite) and Group II(mugearite,benmorite and trachyte).The maximum forsterite content(~85) is encountered in zoned forsteritic olivine of Group I,whereas olivine of Group II is characterized by intermediate(Fo=50),fayalitic(Fo=25) and pure fayalite in the mugearite,benmorite and trachyte,respectively.The more evolved varieties of Group II contain minerals that show enrichment of Fe2+,Mn2+and Na+that indicates normal fractional crystallization.The common occurrence of coarse apatite with titanomagnetite in the benmorite indicates that P5+becomes saturated in this rock variety and drops again in trachyte.Cr-spinel is recorded in Group I varieties only and the Cr#(0.5) suggests lherzolite as a possible restite of the Harrat Rahat volcanics.The plots of Cr# vs.the forsterite content(Fo) suggest two distinct trends,which are typical of mixing of two basaltic magmas of different sources and different degrees of partial melting.The bimodality of Harrat Rahat Cr-spinel suggests possible derivation from recycled MORB slab in the mantle as indicated by the presence of high-Al spinel.It is believed that the subcontinental lithospheric mantle was modified by pervious subduction process and played the leading role in the genesis of the Harrat Rahat intraplate volcanics.The trachytes of the Harrat Rahat volcanic field were formed most probably by melting of a lower crust at the mantle-crust boundary.The increase in fO2 causes a decrease in Cr2 O3,and Al2 O3,and a strong increase in the proportion of Fe3+and Mg# of spinel crystallizing from the basaltic melt at T ~1200°C.The olivine-pyroxene and olivine-spinel geothermometers yielded equilibrium temperature in the range of 935-1025°C,whereas the range of <500-850°C from single-pyroxene thermometry indicates either post crystallization reequilibrium of the clinopyroxene,or the mineral is xenocrystic and re-equilibrated in a cooling basaltic magma.     

Seismic characteristics and kinematic models of Makkah and central Red Sea regions

Makkah and central Red Sea regions have been re-evaluated from recent earthquake data analysis. Epicenters of recent seismic activity are concentrated in three local seismic zones. These are Ad Damm fault (NE), Nu’man–Makkah–Fatima (NW), and Jeddah-Red Sea (NW) seismic zones. Moreover, an extended seismic zone along the central part of Red Sea is observed. Most of these epicenters are distributed along tectonic faults, as indicated from the subsurface structure analysis of the aeromagnetic anomaly map. Some epicenters of small magnitudes are inaccurately located. The study indicates the existence of large active structural basin south of Makkah region, which traverse Ad Damm fault zone with the Red Sea transform faults. Slip vector analyses were carried out for 50 available earthquake focal mechanisms around Makkah region. In Nu’man, Makkah, and Fatima structural zones, the slip vectors generally trend NW and NNW. However, in the southern part at the Ad Dam structure zone, the slip vector trends NE–SW. These may result from the current complicated drifting motion of Arabian plate away from African plate combined with the opening of the Red Sea rift.     

渤海西部海域新生代构造与演化及对油气聚集的控制

渤海西部处于渤海湾盆地黄骅坳陷中北区,东与渤中坳陷衔接,周临多个新生代富(含)烃洼陷,该区具有较大的油气勘探潜力。本文利用区内现有的大量勘探资料对其基本构造特征、演化史及其对油气聚集的控制作用进行了详细的研究与探讨。认为研究区整体构造格架受近东西向、北东向、北西向3组基底断裂控制,近东西向和北西向断层控制古近纪断陷及区内整体构造格局,而北东向与北西向断层在新近纪发生较强烈的走滑活动; 研究区新生代经历了多阶段演化过程,同时又整体表现出具隆拗过渡、整体隆升的演化背景; 复杂多阶段的演化过程使得区内油气多层位复式成藏; 另外,新近纪晚期构造活跃使得区内油气多在新近系浅层晚期成藏,并沿北西向与北东向断层优势成藏展布。     

南沙西南海域新生代构造活动特征与盆地演化

南沙海域处于已俯冲消亡的古南海和海底扩张形成的新南海洋盆之间, 其研究对于了解中生代末期以来南海北部陆缘张裂、新南海海底扩张和古南海向南俯冲消亡等构造过程具有重要意义.通过利用平衡剖面反演对该区新生代以来的构造活动和盆地演化进行研究.结果发现, 该区新生代以来的构造活动具有显著的分区性特征, 表现为以区内深大断裂为界, 所分隔的3个块体其构造活动的主导因素和活动阶段性存在差异.南沙块体构造活动的主导因素为NW向应力, 构造活动以中—晚中新世为界前张后压, 具有明显的阶段性; 万安盆地构造活动受万安断裂控制, 构造活动阶段性不明显; 曾母块体构造活动特征与南沙块体类似, 具有明显的阶段性, 但具体表现不同.在此基础上, 将该区主要盆地的演化划分为4个阶段, 即裂陷阶段、同沉积阶段、挤压阶段和区域沉降阶段.其表现又因盆地成因类型而有所不同: 北康盆地裂陷和挤压阶段突出, 沉降阶段缺失; 南薇西盆地裂陷阶段南弱北强; 万安盆地缺少挤压阶段; 曾母盆地则4个阶段均非常明显.      

3D analogue modeling of the South China Sea: A discussion on breakup pattern

The opening of the South China Sea is one of the most important Cenozoic events in SE Asia. In order to investigate its tectonic evolution, three analogue modeling experiments were compared. The modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial rheological stratification. Affected by the ductile flow of silicone (lower crust) and honey (asthenosphere), the faults became flattened, especially close to the breakup area. We conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension, which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope. In the experiments, breakup developed first at isolated points, which grew and coalesced to become a single spreading area. The conjugate boundaries were either all concave or all convex. Where a rigid massif was located at the divergent boundary, stretching history was different. In this case, the northern and southern areas thinned rapidly and developed into two deep troughs, which may finally evolve into spreading centers. The shape of the massif controls the orientation and boundary shape of the spreading area. It is interpreted that crustal breakup was more viscous in style, and the NW sub sea basin developed along the northern trough of the Zhongsha-Xisha massif (Macclesfield Bank).     

琼东南盆地新生代发育机制的模拟研究

琼东南盆地是南海西北陆缘上一个北东走向的伸展裂陷带,向西与北西走向的莺歌海盆地相接,因此其构造演化包含了较多红河断裂走滑活动的信息。综合地质分析与物理模拟实验,我们发现琼东南盆地的发育既受控于南海北部陆缘的南东向—南南东向伸展作用,而且受到红河断裂左行走滑作用的控制和影响。其中,中央坳陷带主要受控于南东至南南东向的伸展作用;南部坳陷带的发育主要受控于琼东南盆地的伸展及其沿北北西向边界断裂右行走滑作用的构造叠加;而北部坳陷带的发育主要受控于北西向断裂左行走滑作用。红河断裂左行走滑作用可能开始于晚始新世,晚于琼东南盆地的伸展裂陷作用,且早期走滑速率应小于琼东南盆地的伸展速率,早渐新世(T70)以后红河断裂左行走滑速率大于琼东南盆地伸展速率,导致琼盆西段的褶皱反转,以及一组北西—北北西走向张剪断裂的发育。     

南海西部海域新生代构造古地理演化及其对油气勘探的意义

南海西部海域构造复杂,主要发育有北东—北东东向、北西向和近南北向3组深大断裂。其中,北西向断裂与板块汇聚、碰撞有关,多具走滑性质;北东—北东东向断裂具有与中国东部裂谷盆地相似的发育特点,呈张扭性质;近南北向断裂可能是南海在扩张活动期间于洋、陆壳过渡部位形成的走滑调节断裂,是洋盆扩张的西部边界。新生代里,南海经历了4次成盆事件与3期扩张活动,盆地经历了古新世—中始新世陆缘断陷、渐新世—早中新世扩展与中中新世以来的热沉降3个演化阶段。陆缘断陷阶段的充填系列主要是北东—北东东向与北西向的河流—冲积扇、湖泊沼泽等陆相沉积及火山岩等;盆地扩展阶段表现为中-小型断陷、断-坳陷逐渐复合与联合为大-中型坳陷,古地理格局逐渐由河流与湖沼陆相环境演变为滨海至浅海相的沉积环境;热沉降阶段的成盆活动逐渐减弱以至停止,地层表现超覆,盆地出现联合迹象。结合以往勘探与油气资源调查成果分析,认为南海西部海域陆架陆坡区发育的大-中型沉积盆地石油地质条件良好,蕴藏着丰富的油气资源,勘探潜力巨大。     

Exploring the association between the occurrence of earthquakes and the geologic-tectonic variables in the Red Sea using logistic regression and GIS

Al-Ahmadi et al. (Arab J Geosci doi:10.1007/s12517-013-0974-6, 2013) applied spatial pattern analysis techniques to a seismic data catalogue of earthquakes beneath the Red Sea in order to explore and detect global and local spatial patterns in the occurrence of earthquakes over the years from 1900 to 2009 using a geographical information system (GIS). They found that the techniques of spatial pattern analysis that they applied could detect global and local clusters and broader spatial patterns in the occurrence of earthquakes and concluded that earthquakes with higher magnitudes were notably concentrated beneath the central and southern areas of the Red Sea, while earthquakes with low and moderate magnitudes were concentrated beneath the northern area of the Red Sea. The aim of this paper is to report on the application of logistic regression models to explore the associations between the likelihood of the occurrence of an earthquake beneath the Red Sea and four selected variables, namely: (1) proximity to the boundary of the African–Arabian plates, (2) proximity to transform faults, (3) proximity to the mid-Red Sea ridge and (4) the stage of rift evolution. The study was undertaken to evaluate the potential of logistic regression modelling for research exploring potential associations between earthquakes and geological and tectonic variables. The results revealed that none of the assumptions underpinning the logistic regression models had been violated for the three logistic regression models that were used in this research. The authors inferred that the occurrence of the earthquakes beneath the Red Sea was statistically significantly associated with the proximity to the African–Arabian plate boundary. We concluded that earthquakes of moderate magnitudes occurred in the zone which represents the late evolutionary stage of the Red Sea rift, including the transition zone beneath the central area and the late-stage continental rift zone beneath the northern area of the Red Sea. In contrast, earthquakes with high magnitudes tended to occur in close proximity to the mid-ridges of the Red Sea.     

Plate tectonic control on the formation and tectonic migration of Cenozoic basins in northern margin of the South China Sea

The tectonic evolution history of the South China Sea(SCS) is important for understanding the interaction between the Pacific Tectonic Domain and the Tethyan Tectonic Domain,as well as the regional tectonics and geodynamics during the multi-plate convergence in the Cenozoic.Several Cenozoic basins formed in the northern margin of the SCS,which preserve the sedimentary tectonic records of the opening of the SCS.Due to the spatial non-uniformity among different basins,a systematic study on the various basins in the northern margin of the SCS constituting the Northern Cenozoic Basin Group(NCBG) is essential.Here we present results from a detailed evaluation of the spatial-temporal migration of the boundary faults and primary unconformities to unravel the mechanism of formation of the NCBG.The NCBG is composed of the Beibu Gulf Basin(BBGB),Qiongdongnan Basin(QDNB),Pearl River Mouth Basin(PRMB) and Taixinan Basin(TXNB).Based on seismic profiles and gravity-magnetic anomalies,we confirm that the NE-striking onshore boundary faults propagated into the northern margin of the SCS.Combining the fault slip rate,fault combination and a comparison of the unconformities in different basins,we identify NE-striking rift composed of two-stage rifting events in the NCBG:an early-stage rifting(from the Paleocene to the Early Oligocene) and a late-stage rifting(from the Late Eocene to the beginning of the Miocene).Spatially only the late-stage faults occurs in the western part of the NCBG(the BBGB,the QDNB and the western PRMB),but the early-stage rifting is distributed in the whole NCBG.Temporally,the early-stage rifting can be subdivided into three phases which show an eastward migration,resulting in the same trend of the primary unconformities and peak faulting within the NCBG.The late-stage rifting is subdivided into two phases,which took place simultaneously in different basins.The first and second phase of the early-stage rifting is related to back-arc extension of the Pacific subduction retreat system.The third phase of the earlystage rifting resulted from the joint effect of slab-pull force due to southward subduction of the proto-SCS and the back-arc extension of the Pacific subduction retreat system.In addition,the first phase of the late-stage faulting corresponds with the combined effect of the post-collision extension along the Red River Fault and slab-pull force of the proto-SCS subduction.The second phase of the late-stage faulting fits well with the sinistral faulting of the Red River Fault in response to the Indochina Block escape tectonics and the slab-pull force of the proto-SCS.     

Remnants of Miocene fluvial sediments in the Negev Desert,Israel, and the Jordanian Plateau: Evidence for an extensive subsiding basin in the northwestern margins of the Arabian plate

Relics of a thick, widely spread, fluvial sequence of Early Miocene age are scattered throughout southern Israel, eastern Sinai, the Dead Sea Rift Valley and the western margins of the Jordanian Plateau. These relics are mainly preserved in structural lows, karstic systems, and abandoned stream valleys. The paleogeography of this fluvial system was reconstructed based on the relations between the sequence remnants and the main structural and morphological features of the southeastern Levant region.Three sedimentary associations were identified in the Miocene sequence: a lower part dominated by locally derived clastic sediments; a thicker middle part, composed mostly of far-field allochthonous clastic sediments; and an upper part composed of local as well as allochthonous sediments. The two lower parts are regionally distributed whereas the upper part is syn-tectonic and confined to the Dead Sea basin and the Karkom graben in the central Negev. The composition of the far-field allochthonous sediments points to a provenance of Precambrian crystalline rocks of the Arabo-Nubian massif that were exposed along the uplifted shoulders of the Red Sea Rift as the upper drainage basin of the fluvial system. The diverse mammal remains found in this fluvial sequence suggest a complex of savanna, forests and fluvial habitats similar to those of present East Africa, with monsoon-type rains, which were the dominant water source of the rivers.The thickness of the Miocene sequence in the central Negev is at least 1700 m, similar to that of the subsurface sequence encountered in the Dead Sea basin. This similarity suggests that both were parts of an extensive subsiding sedimentary basin that developed between the Neo-Tethys and the uplifted margins of the Red Sea.The relations between the reconstructed pre-depositional landscape of southern Israel during the Early Miocene and the overlying fluvial sequence indicate that the entire area was buried under several hundred meters of fluvial sediments, reflecting a subsidence of the northern margins of the African continent (Arabian plate) before its breakup and the splitting of the Sinai–Israel subplate by the Dead Sea Transform.During the early Middle Miocene the subsidence was inversed as the mountainous backbone of Israel was uplifted. The uplift triggered a large scale denudation that removed the thick Early Miocene fluvial sequence from the Negev and transported the eroded sediments northwestward toward the eastern Mediterranean basin. Additional uplift during the late-Middle Miocene was associated with entrenchment of the Be’er Sheva Valley between the Judea Mountains in the north and the Negev Highlands in the south. This valley was flooded by the sea during the Late Miocene.We suggest that the formation of the Early Miocene subsiding basin at the northern edge of the Arabian sub-plate predated the breakup of the Arabian plate by the DST. The inversion of the subsiding regime, which led to the establishment of the Negev Highlands seems to be intimately related to the detachment of the Sinai–Israel sub-plate from the Arabian plate during the Middle Miocene.     

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.     

珠江口盆地珠一坳陷新生代盆地结构与成因演化

运用丰富的三维地震资料,在断裂体系的静态描述基础上,通过断层活动速率计算和平衡剖面分析,并结合残留地 层展布特征,恢复了新生代盆地垂向演化与叠合过程,探讨盆地发育与转型的动力学机制。珠一坳陷新生代经历了裂陷早 期、裂陷晚期、裂后拗陷和构造活动期四大演化阶段。裂陷期（E2w-E2e）,印支地块旋转挤出和古南海俯冲,区域拉张应 力场由NW 向顺时针转变为近SN 向,导致了裂陷早期NE、NEE 向断裂控盆向裂陷晚期近EW 向、NWW 向断裂控盆转变, 岩石圈伸展作用由宽裂谷方式向窄裂谷方式转变,导致盆地格局由彼此孤立的半地堑或窄地堑系趋于相互扩展连通;裂后 拗陷期（E3z-N1z-N1h）,岩石圈伸展中心迁移至南海扩张中心,南海北部地区整体处于裂后热沉降阶段,构造活动微弱;构 造活化期（N1y-N2w-Q）,菲律宾海板块NWW 向仰冲-碰撞联合作用下产生NNE 向拉张,同时派生近EW 向和NW 向的共 轭剪切作用,导致了先存NWW 向和近EW 断裂的活化,以及隆起区NWW 向张性断裂和近EW 向、NW 向走滑断裂带的形 成。该研究所揭示的盆地发育演化过程不仅对该区油气勘探提供指导,也对被动大陆边缘演化的研究有着一定的借鉴意义。     

Groundwater potential zonation for basaltic watersheds using satellite remote sensing data and GIS techniques

This paper summarizes the findings of groundwater potential zonation mapping at the Bharangi River basin, Thane district, Maharastra, India, using Satty’s Analytical Hierarchal Process model with the aid of GIS tools and remote sensing data. To meet the objectives, remotely sensed data were used in extracting lineaments, faults and drainage pattern which influence the groundwater sources to the aquifer. The digitally processed satellite images were subsequently combined in a GIS with ancillary data such as topographical (slope, drainage), geological (litho types and lineaments), hydrogeomorphology and constructed into a spatial database using GIS and image processing tools. In this study, six thematic layers were used for groundwater potential analysis. Each thematic layer’s weight was determined, and groundwater potential indices were calculated using groundwater conditions. The present study has demonstrated the capabilities of remote sensing and GIS techniques in the demarcation of different groundwater potential zones for hard rock basaltic basin.     

Late Mesozoic and Cenozoic rifting and its dynamic setting in Eastern China and adjacent areas

During the Late Mesozoic and Cenozoic, extension was widespread in Eastern China and adjacent areas. The first rifting stage spanned in the Late Jurassic–Early Cretaceous times and covered an area of more than 2 million km² of NE Asia from the Lake Baikal to the Sikhot-Alin in EW direction and from the Mongol–Okhotsk fold belt to North China in NS direction. This rifting was characterized by intracontinental rifts, volcanic eruptions and transform extension along large-scale strike–slip faults. Based on the magmatic activity, filling sequence of basins, tectonic framework and subsidence analysis of basins, the evolution of this area can be divided into three main developmental phases. The first phase, calc-alkaline volcanics erupted intensely along NNE-trending faults, forming Daxing'anling volcanic belt, NE China. The second phase, Basin and Range type fault basin system bearing coal and oil developed in NE Asia. During the third phase, which was marked by the change from synrifting to thermal subsidence, very thick postrift deposits developed in the Songliao basin (the largest oil basin in NE China).Following uplift and denudation, caused by compressional tectonism in the near end of Cretaceous, a Paleogene rifting stage produced widespread continental rift systems and continental margin basins in Eastern China. These rifted basins were usually filled with several kilometers of alluvial and lacustrine deposits and contain a large amount of fossil fuel resources. Integrated research in most of these rifting basins has shown that the basins are characterized by rapid subsidence, relative high paleo-geothermal history and thinned crust. It is now accepted that the formation of most of these basins was related to a lithospheric extensional regime or dextral transtensional regime. During Neogene time, early Tertiary basins in Eastern China entered a postrifting phase, forming regional downwarping. Basin fills formed in a thermal subsidence period onlapped the fault basin margins and were deposited in a broad downwarped lacustrine depression. At the same time, within plate rifting of the Lake Baikal and Shanxi graben climaxed and spreading of the Japan Sea and South China Sea occurred. Quaternary rifting was marked by basalt eruption and accelerated subsidence in the area of Tertiary rifting. The Okinawa Trough is an active rift involving back-arc extension.Continental rifting and marginal sea opening were clearly developed in various kind of tectonic settings. Three rifting styles, intracontinental rifting within fold belt, intracontinental rifting within craton and continental marginal rifting and spreading, are distinguished on the basis of nature of the basin basement, tectonic location of rifting and relations to large strike–slip faults.Changes of convergence rates of India–Eurasia and Pacific–Eurasia may have caused NW–SE-trending extensional stress field dominating the rifting. Asthenospheric upwelling may have well assisted the rifting process. In this paper, a combination model of interactions between plates and deep process of lithosphere has been proposed to explain the rifting process in East China and adjacent areas.The research on the Late Mesozoic and Cenozoic extensional tectonics of East China and adjacent areas is important because of its utility as an indicator of the dynamic setting and deformational mechanisms involved in stretching Lithosphere. The research also benefits the exploration and development of mineral and energy resources in this area.     

The role of aeromagnetic data analysis (using 3D Euler deconvolution) in delineating active subsurface structures in the west central Arabian shield and the central Red Sea,Saudi Arabia

In this paper, we present a case study of structural mapping by applying the 3D Euler method to the high-resolution aeromagnetic data that was collected in the west central Arabian Shield region and the coastal region of the central Red Sea in Saudi Arabia. We show the 3D Euler deconvolution algorithm and apply it to magnetic potential field data from the west Central Arabian Shield and the Central Red Sea. The solution obtained with 3D Euler deconvolution gives better-focused depth estimates, which are closer to the real position of sources; the results presented here can be used to constrain depth to active crustal structures (volcanisms) for the study area. The results indicated that the area was affected by sets of fault systems, which primarily trended in the NNW–SSE, NW–SE, EW, and NE–SW directions. Moreover, estimated Euler solution map from aeromagnetic data delineated also the boundaries of shallow, small, and confined magnetic bodies on the offshore section of the study area. These nearly exposed basement intrusions are most likely related to the Red Sea Rift and may be associated with structures higher up in the sedimentary section. These volcanic bodies are extended to the continental part (onshore) of the west central Arabian Shield, particularly beneath both sides of the Ad Damm fault zone. This extension verifies that the fault was largely contemporaneous with a major period during the extension of the Red Sea Basin. Moreover, according to the distribution of circular magmatic-source bodies (circular-shaped ring dikes) that resulted from this study, we can state that the clustering of most earthquakes along this fault may most likely be attributed to the active mantle upwelling (volcanic earthquakes), which are ultimately related to volcanic processes. Furthermore, the oceanic crustal structures near and in the Red Sea offshore regions were also estimated and discussed according to the ophiolite occurrences and further opening of the Red Sea. Our results are largely comparable with studies of previous crustal sections, which were performed along the Red Sea Rift and the Arabian Shield. As a result, the areas above these anomalies are highly recommended for further geothermal study. This example illustrates that high-resolution aeromagnetic surveys can greatly help delineating the subsurface active structures in the west central Arabian Shield and the middle coastal region of the Red Sea of Saudi Arabia.