Break Up of Australia-India-Madagascar Block, Opening of the Indian Ocean and Continental Accretion in Southeast Asia With Special Reference to the Characteristics of the Peri-Indian Collision Zones

Linear belts of Gondwana basins developed in the Indian continent since Late Palaeozoic along favoured sites of Precambrian weak zones like cratonic sutures and reactivated mobile belts. The Tibetan and Sibumasu - West Yunnan continental blocks, that were located adjacent to proto-Himalayan part of the Indian continent, rifted and drifted from the northern margin of the East Gondwanic Indo-Australian continent, during Late Palaeozoic, when the said northern margin was under glacial or cool climatic condition and rift-drift tectonic setting. The Indo-Burma-Andaman (IBA), Sikule, Lolotoi blocks were also rifted and drifted from the same northern margin during Late Jurassic. This was followed by the break-up of the Australia-India-Madagascar continental block during the Cretaceous. The activity was associated with hot spot related volcanism and opening up of the Indian Ocean. The Late Cretaceous and Tertiary phases of opening of the Arabian Sea succeeded the Early Cretaceous phase of opening of the Bay of Bengal, part of the Indian Ocean. The Palaeo- and Neo-Tethyan sutures in Tibet, Yunnan, Laos, Thailand and Vietnam reveal the complex opening and closing history of the Tethys. The IBA block rotated clockwise from its initial E-W orientation because of 90°E and adjacent dextral transcurrent fault movements caused due to faster northward movement of the Indian plate relative to that of Australia. The India-Tibet terminal collision during Early-Middle Eocene initiated Himalayan orogenesis and contemporaneously there was foreland basin development that was accompanied with sporadic but laterally extensive continental-flood-basalt (CFB) type and related volcanism. The Paleogene rocks of the Himalayan foreland basin are involved in tectonism and are mostly concealed under older rocks.

The Mesozoic-Early Eocene ophiolite terrane on IBA does not represent the eastern suture of the Indian plate but occurs as klippe on IBA, caused due to oblique collision between Sibumasu and IBA during Late Oligocene. Post-collisional indentation of Y-shaped Indian continent into the Asian collage produced Himalayan syntaxes, clockwise rotation of the Sibumasu block which was then sutured to the Tibetan and SE Asian blocks, and tectonic extrusion of the Indochina block along the Ailao Shan Red River (ASRR) shear zone. Highly potassic magmatic rocks were emplaced during Late Palaeogene at the oroclinally flexed marginal parts of the South China continental lithosphere. These magmatic bodies were dislocated by the ASRR left lateral shear zone soon afterwards. Petrogenetic and tectonic processes that generated the Eocene CFB volcanics at the Himalayan foreland basin may have also produced Late Palaeogene magmatism from outer parts of the Namche-Barwa Syntaxis. Their site-specific location and time sequence suggest them to be genetically related to the India-Asia collision process and Indian continent's indentation-induced syntaxial buckling. Deep mantle-reaching fractures were apparently produced during India-Asia terminal collision at the strongly flexed leading brittle edge of the Indian continental lithosphere, and possibly later in time at the outer oroclinally bent marginal parts of the rigid South China continental lithosphere, generating typical magma.

The subduction zone that developed along the western margin of IBA due to oblique convergence between the IBA and the Indian plate is still active. The northern end of IBA ultimately collided with the NE prolongation of the Indian continent and was accreted to it during Mio-Pliocene. The Shillong massif was uplifted and overthrust over the Bengal Basin located over its passive margin to the south, whereas, the Eocene distal shelf sediments of IBA were overthrust over the Tertiary shelf of the Indian continent.     

新疆哈图早二叠世富镁闪长岩的时代、地球化学特征和可能的成因机制

西准噶尔别鲁阿嘎希地区广泛发育富镁闪长质小岩体和岩墙。对岩墙全岩样品的Ar-Ar测年获得了292±3Ma的坪年龄,显示其主要形成于早二叠世。这些小岩体和岩墙均为钙碱性系列岩石,具有宽的SiO₂(51.9%～62.6%)、高的MgO(Mg^#>60)、Cr(45.8×10^-6～539×10^-6)、Ni(17.2×10^-6～197×10^-6)含量,富集大离子亲石元素(LILE)(如 K、Rb、Ba、Th和U)、亏损高强场元素(如Nb、Ta、Ti),富集LREE,亏损HREE。这些特征类似于日本中新世Setouchi火山岩带中的赞岐岩。这些岩体/岩墙很可能是在俯冲过程中,经洋壳板片的脱水形成流体与地幔橄榄岩相互作用而成。这表明,西准噶尔别鲁阿嘎希地区早二叠世为岛弧环境。而富镁闪长岩的形成过程也有利于铜-金矿床的形成,显示该区有良好的成矿远景。     

Fracture modes in the Silurian Qusaiba Shale Play,Northern Saudi Arabia and their geomechanical implications

Fracture and in-situ stress studies were conducted for unconventional prospect evaluation in the Silurian Qusaiba Shale, northern Saudi Arabia. Borehole image logs, oriented cores, seismic, and drilling observations were used in the studies. The fractures include natural fractures and induced fractures. The induced fractures were studied to assess the stress regime in terms of directions and magnitudes. The present day maximum horizontal in-situ stress trend varies from NNW-SSE to NNE-SSW, and shows a regional pattern dominated by Arabian plate tectonics. The relative magnitudes of the current day stresses are characteristic of an extensional to strike-slip regime. Natural fractures of microscopic (microfractures) to macroscopic (macrofractures) scales include extension fractures (joints/veins), and faults manifested as shear and hybrid (extensional-shear and compressional-shear) fractures. Joints clustering into zones are rare, unless when associated with fault zones. Over half of the faults (56%) show clustering into fault zones with their widths (thickness) varying by up to 5 orders of magnitude, and lengths and displacements varying by up to 4 orders of magnitudes respectively. The study identified five distinctive, regional, fracture sets: one gently dipping (bedding-parallel or at low angle to bedding) and up to four moderately to steeply dipping fracture sets: an easterly striking set is the oldest, followed by three younger major sets striking NNW-SSE, N-S, and NNE-SSW. The younger fractures are nearly parallel to the present day maximum horizontal in-situ stress. Crack-seal mechanism (natural hydrofracturing) dominates initial fracture growth, some with several phases of partial to complete mineralization or coating, dominated by calcite, quartz, and dolomite. Aqueous and hydrocarbon gaseous and fluid inclusions are common in the fractures' mineral filling. The regional nature of in-situ stresses and natural fractures means their occurrence, orientation, relative dominance, and relative age and relative apertures are easier to predict and manipulate for well planning and completion, including hydrofracturing. Forward modeling shows that natural fracture network are not critically stressed under reservoir conditions but when subjected to massive hydrofracture stimulation they and the bedding discontinuities form the seeds for the growth of a complex hydrofracture network that potentially grows out of presumed stress-barriers. Lack of stress rotation around faults in wells supports the modeling results. Microseismic monitoring gives time-lapse (incremental) microseismic events of two types; random and linear patterns parallel to maximum horizontal in-situ stress and the predominant natural fracture trend. Bulk microseismic cloud has no unique link to fault trends mapped from high resolution borehole images. This finding challenges the usability of uncalibrated microseimic monitoring of massive hydrofracturing to map faults.     

Side-Scan Sonar Characteristics and Manganese Nodule Abundance in the Clarion—Clipperton Fracture Zones,NE Equatorial Pacific

The deep ocean floor between the Clarion and Clipperton fracture zones (NE equatorial Pacific) has the highest known manganese nodule abundance in the world oceans. A detailed analysis of MR1 (Mapping Researcher 1, 11–12?kHz) sonar images and free-fall grab data in the Korean manganese nodule field areas reveals a close relationship between side-scan sonar characteristics of the seafloor and manganese nodule abundance. Eight sonar facies are identified based on back-scattering intensity and distribution patterns. These sonar facies can be interpreted as (1) volcanic seamounts (facies I-1), (2) bounding faults of abyssal hills (facies I-2 and II-1), (3) lava flows or volcanoclastic mass-flow deposits around the volcanic seamounts (facies I-3 and II-2), (4) crests of abyssal hills (facies II-1), (5) abyssal troughs between abyssal hills (facies III-1), (6) relatively flat areas (facies II-3 and III-2). In the areas where facies II-1 (abyssal hill crests with thin sediment cover) and II-3 (relatively flat areas draped by thin sediments) are dominant, manganese nodules occur abundantly. In contrast, zones comprising facies III-1 (abyssal troughs with thick sediment cover) and III-2 (relatively flat areas covered by thick sediments) are characterized by low abundance of manganese nodules. This relationship between distribution of sonar facies and manganese nodule abundance implies that (1) the qualitative difference in acoustic reflectivity of long-range side-scan sonar with some ground truth data is useful for regional assessment of manganese nodule occurrence over wide areas in a reasonable time, and (2) seafloor topography and sediment thickness are important controlling factors for regional occurrences of manganese nodules.     

Hydrothermal mineralization along submarine rift zones,Hawaii

This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe‐Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ‐MnO₂. The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn‐cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and permeability. Precipitation of Mn oxide below the seafloor is indicated by its occurrence as cement, growth textures that show mineralizing fluids were introduced from below, and pervasive replacement of original matrix of clastic rocks.     

基于基塘系统保护的国土空间治理策略——以顺德区为例

以佛山市顺德区作为实证研究案例,采用野外调研、访谈等研究方法,剖析基塘与国土空间的协同发展机制,提出基于多功能基塘的国土空间治理策略。结果表明：顺德国土空间治理面临空间破碎化和空间嵌套分布、灾害与生态风险加剧、岭南水乡文化特色日渐流失等问题;协调基塘与不同地域子系统之间的功能耦合关系,发挥基塘对地域系统功能的支撑与协同作用,是实现国土空间协同发展和可持续利用的基础;实施基塘功能分区治理,保护集中连片基塘,整合基塘文化资源,推进基塘与村级工业园、村边塘、村心塘协同治理等策略,发挥基塘的多功能作用,有助于实现国土空间的安全、高效与可持续利用。     

低植被覆盖区斑岩铜矿遥感找矿模型及其应用——以环巴尔喀什-西准噶尔成矿带为例

针对遥感找矿过程中所面临的干扰因素多、地表覆盖类型多样导致的遥感找矿困难的问题,提出了低植被覆盖区斑岩铜矿"小型侵入岩体异常+线性构造异常+蚀变矿物异常"的多尺度遥感找矿模型,并系统总结了该模型的基本原理和技术流程。以环巴尔喀什-西准噶尔成矿带为研究区,分析了研究区的成矿地质背景;在遥感找矿模型的指导下,依据遥感找矿技术流程提取了研究区的岩性、构造和蚀变矿物等控矿要素;结合野外地表验证情况,综合多源数据,圈定了5处重点远景区;结合大比例尺遥感蚀变矿物填图、地质、地球物理、地球化学和探槽取样的分析结果,圈定3处遥感找矿靶区。     

深部碳循环的环境气候效应SCIEI北大核心CSCD

地球表层温度主要由接收的太阳辐射能量及大气温室气体的保温能力共同控制。CO_(2)等温室气体通过对大气温度的调节影响着全球环境气候变化,工业革命以来全球CO_(2)排放量的增加被认为是全球变暖的重要原因,地质历史时期大气CO_(2)浓度的波动与温室和冰室气候的交替出现相对应。地球超过90%的碳赋存于深部,因此地球深部过程的些许波动便会影响到地表碳含量,进而深刻影响着地球的环境气候变化。以往的研究注重地表碳循环对环境气候的影响,对深部碳的贡献考虑不足。最近十余年全球开展了详细的深部碳循环研究,基于已经取得的重要成果,本文从大火成岩省、裂谷和俯冲带的视角对深部碳循环驱动的环境气候效应进行了系统回顾。认为未来的研究需要对地球深部碳循环通量和碳同位素组成进行更精确的定量,这是我们认识深部碳循环对地表环境气候影响的基础;除了碳元素本身我们还需要关注其他挥发性元素和有害金属元素的综合效应;俯冲带作为全球壳-幔相互作用和物质交换循环最重要的场所,应该是进行深部碳循环观察和环境气候效应研究的重点。     

大洋板块俯冲带地震波各向异性及剪切波分裂的成因机制

大洋板块俯冲带是许多重要地质作用(例如脱水、部分熔融、岩浆和地震活动)发生的场所.对位于俯冲带之上的地震台站所检测到的不同剪切波的数据解析,可以获得源于上覆板块、地幔楔、俯冲板块和板下地幔的地震波各向异性的关键信息.本文系统总结了世界各地大洋俯冲带的剪切波分裂样式,对目前国际上流行的大洋俯冲带的地震波各向异性的主要成因...     

中国干旱、半干旱区末次冰期以来气候变化规律

以临夏塬堡末次冰期中晚期黄土剖面为基础,选用我国干旱、半干旱区末次冰期以来同期异相或同期同相的气候记录与研究剖面进行对比分析后表明：位于西风气流控制的新疆地区全新世气候总体表现为偏干偏冷,晚期较为温暖的特点．其气候波动的幅度和频率较低。而位于季风环流控制的其它地区．全新世气候变化反映了同样的变化规律,即早全新世的升温波动期、中全新世的温暖稳定期和晚全新世的变冷期,其气候波动的幅度和频率较快。而无论是西风气流控制的新疆地区,还是季风环流影响的其它我国干旱、半干旱区,末次冰期气候变化均表现为早晚期的干冷期和中期的温湿期,尽管其干冷和温湿的程度不尽相同。