中国的板块构造区划

20世纪60年代板块构造学说传入中国,为广大地学工作者所接受并应用于相关的地质工作中。在新一代地质志的研究中,以板块学说为主导,已经成为共识。从板块构造来认识,板块的组成包括其核心及边缘。其核心为克拉通,由稳定的陆块组成;边缘包含了不同的活动大陆边缘和被动大陆边缘。边缘在后期板块汇聚的过程中,常由汇聚或碰撞等不同方式而成为不同的造山带。板块之间具有不同形式的汇聚带,其中主要是地壳对接消减带。在地球发展历史的过程中,不同时期的板块构造格局常有很大的变化。因此,本文以古生代的构造格架为主,探讨对中国大陆进行板块构造区划中的一些相关问题,并对全国的区划提出了一个初步方案。此方案将全国划分为7个I级单元(板块),30个II级单元(克拉通和造山带)以及103个III级单元。     

“承德逆掩片”之商榷——来自燕山地区中元古代长城系的沉积地质证据

外来岩片不但在构造变形上应具有显著的特征标志,而且在其卷入的各类地质体中也应该表现出与原地系统之间具有明显的差异.近年来,承德地区两条断裂之间所夹地质体,被部分学者认为是晚侏罗世时期从该地区南部向北推覆而来的"逆掩片",水平位移量超过40km.本文对比研究了"逆掩片"内部和"根带区"中元古代长城系原始沉积特征和相带展布以及其他证据,发现承德地区长城系各相带原始展布和格局与周边同期沉积并无显著差别,这表明晚侏罗世期间发生自南向北大规模水平位移(＞40km)的可能性很小,研究结果不支持"外来岩片"的认识.     

古太平洋岩石圈消减与中国东南部晚中生代火成岩成因——岩石圈消减与玄武岩底侵相结合模式的补充证据

本文根据中国东南部 140个晚中生代火成岩 Rb- Sr等时线年龄匹配的 Isr值 ,勾画了 Isr等值线图。该图与 TDM等值线图有好的对应 ,都在浙闽沿海地区、南岭东段和武夷山北段出现低值区或低值带 ,反映中国东南地壳在晚中生代时期 ,有广泛的地幔物质的加入 ,它们以底侵的形式底垫在中 -下地壳。沿海地区 Isr、TDM的低值区、带受地壳厚度的控制 ,内陆的低值区、带可能与局部应力场导致的拉张减薄有关。浙闽沿海晚中生代火成岩岩石地球化学显示大离子亲石元素 Rb、Sr、Ba、Th和 Ce富集 ,高场强元素 Nb、Ta、Zr、Hf和重稀土 Y、Yb亏损 ,具有明显的消减带岩浆作用的特征。西太平洋地震层析成像显示 ,西太平洋板块俯冲是连续的。在大约 2 0 0 0～ 12 0 0 km深度 ,地幔中正在下沉的古俯冲洋壳明显偏西 ,可能反映那时为低角度俯冲。中国东南部广泛发育的NE- NNE褶皱和断裂构造 ,与古太平洋板块向欧亚大陆之下的俯冲作用有关。大规模晚中生代岩浆活动之前的陆相沉积 ( T3- J2 )是造山磨拉石建造。上述地质证据均支持消减作用和底侵作用相结合的模式     

东昆仑山南缘大型转换挤压构造带和斜向俯冲作用

东昆仑地体和巴颜喀拉－－松潘甘孜地体之间的会聚边界是一条位于东昆仑南缘的大型转换挤压构造带。研究表明该带的东段（阿尼玛卿段）和西段（东－西大滩段）构造特征不同,阿尼玛卿段的构造以印支期具往南西造山极性的逆冲叠覆岩片和新生代脆性左行走滑构造为特征,东－西大滩段是由220Ma形成的EW向韧性左行走滑剪切带及两则伴生的挤压褶皱断裂带组成,韧性变形持续至20Ma,之后表现为脆性左行走滑构造再活动。因此,东昆仑南缘大型会聚带是一条由东段的“收缩挤压”为主向西段的“转换挤压”逐渐过度的特殊复杂的构造带,它的形成与巴颜喀拉－－松潘甘孜地体往NE方向斜向俯冲于东昆仑地体之下有关。     

Digital modeling studies for evaluation of hydrogeological characteristics in Shadnagar granite basin,Andhra Pradesh,India

The use of digital models has increased significantly in recent years with the accessibility of fast computing machines. A variable dimensioned digital model was constructed for the Shadnagar granite basin using SPECTRUM-7 micro computer to integrate various hydrogeological characteristics and for their quantitative evaluation. The basin has an areal extent of 437 sq km and is demarcated with clear water divides in all directions. Transmissivity, recharge and discharge at each cell of the basin area were estimated by trial and error simulation of the hydrogeological phenomenon under steady state condition. Dynamic simulation at representative nodes facilitated the estimation of storage coefficient. The capability of the constructed model was established by the conformance of the simulated hydrographs with the actual behaviour of the ground water system. The entire studies ammended the earlier arrived estimates of various input/output hydrogeological parameters and evolved a methodology for efficient processing of aquifer simulation data     

元古宙蛇绿岩研究现状及其板块构造意义

在回顾元古宙蛇绿岩研究简史的基础上,对元古宙蛇绍岩的时空分布特征,岩石组合类型,变质作用程度,大地构造背景及源区地球化学制约等进行了系统总结,并就元古宙蛇绿岩的板块构造意义作了探讨。     

Crustal and upper mantle seismic structure of the Australian Plate, South Island, New Zealand

Seismic reflection and refraction data were collected west of New Zealand's South Island parallel to the Pacific–Australian Plate boundary. The obliquely convergent plate boundary is marked at the surface by the Alpine Fault, which juxtaposes continental crust of each plate. The data are used to study the crustal and uppermost mantle structure and provide a link between other seismic transects which cross the plate boundary. Arrival times of wide-angle reflected and refracted events from 13 recording stations are used to construct a 380-km long crustal velocity model. The model shows that, beneath a 2–4-km thick sedimentary veneer, the crust consists of two layers. The upper layer velocities increase from 5.4–5.9 km/s at the top of the layer to 6.3 km/s at the base of the layer. The base of the layer is mainly about 20 km deep but deepens to 25 km at its southern end. The lower layer velocities range from 6.3 to 7.1 km/s, and are commonly around 6.5 km/s at the top of the layer and 6.7 km/s at the base. Beneath the lower layer, the model has velocities of 8.2–8.5 km/s, typical of mantle material. The Mohorovicic discontinuity (Moho) therefore lies at the base of the second layer. It is at a depth of around 30 km but shallows over the south–central third of the profile to about 26 km, possibly associated with a southwest dipping detachment fault. The high, variable sub-Moho velocities of 8.2 km/s to 8.5 km/s are inferred to result from strong upper mantle anisotropy. Multichannel seismic reflection data cover about 220 km of the southern part of the modelled section. Beneath the well-layered Oligocene to recent sedimentary section, the crustal section is broadly divided into two zones, which correspond to the two layers of the velocity model. The upper layer (down to about 7–9 s two-way travel time) has few reflections. The lower layer (down to about 11 s two-way time) contains many strong, subparallel reflections. The base of this reflective zone is the Moho. Bi-vergent dipping reflective zones within this lower crustal layer are interpreted as interwedging structures common in areas of crustal shortening. These structures and the strong northeast dipping reflections beneath the Moho towards the north end of the (MCS) line are interpreted to be caused by Paleozoic north-dipping subduction and terrane collision at the margin of Gondwana. Deeper mantle reflections with variable dip are observed on the wide-angle gathers. Travel-time modelling of these events by ray-tracing through the established velocity model indicates depths of 50–110 km for these events. They show little coherence in dip and may be caused side-swipe from the adjacent crustal root under the Southern Alps or from the upper mantle density anomalies inferred from teleseismic data under the crustal root.     

Volcanological study of the middle Miocene Okiduse Volcanic Group,Woodlark Island (Muyuw), eastern Papua

Woodlark Island (Muyuw) is located in a tectonically complex region, one of the few places on Earth where continental breakup is occurring ahead of seafloor spreading. Rifting commenced in the late Miocene (8.8–6 Ma) and is associated with the westward-propagating Woodlark Basin Spreading Centre. The island comprises approximately 850 km² of raised Pleistocene coral reef and associated sediments with a central, moderately elevated range underlain by the middle Miocene calc-alkaline to shoshonitic Okiduse Volcanic Group (new name). It provides an exposure of upper Cenozoic geology in close proximity to the spreading centre. The Okiduse Volcanic Group is host to most of the island's historical gold and silver production and recently defined mineral resources totalling 1.75 Moz gold. This study uses facies analysis of pyroclastic deposits to develop a detailed geological map of the Okiduse Volcanic Group, with a revision and reinterpretation of the unit. Facies associations suggest that two major volcanic centres erupted synchronously during the middle Miocene (14–12 Ma), referred to as the Watou Mountain Eruptive Centre (new name) and the Uvarakoi Caldera (new name). The mafic–intermediate Watou Mountain Eruptive Centre formed during frequent small eruptions of widely varying style. Strombolian, subplinian, vulcanian and dome-related explosive eruptions occurred, alternating with extrusion of block and ash flow deposits and lava domes. Pyroclastic deposits were rapidly reworked from the steep cone, and were redeposited in a series of coalescing aprons surrounding the volcano. The felsic Uvarakoi Caldera formed during a series of violent explosive eruptions by rapid removal of magma from the underlying chamber, followed by collapse. Plinian and possibly phreatoplinian eruptions, as a result of magma–water mixing in the surface environment, resulted in widely dispersed, highly fragmented tuff deposits. The caldera was modified by widespread erosion following eruptions, resulting in fluvial, laharic and slope-wash deposits. This study highlights lithological controls (porosity and permeability) by various units within the Okiduse Volcanic Group on ore deposition.     

Role of the Kazerun fault system in active deformation of the Zagros fold-and-thrust belt (Iran)

Field structural and SPOT image analyses document the kinematic framework enhancing transfer of strike-slip partitioned motion from along the backstop to the interior of the Zagros fold-and-thrust belt in a context of plate convergence slight obliquity. Transfer occurs by slip on the north-trending right-lateral Kazerun Fault System (KFS) that connects to the Main Recent Fault, a major northwest-trending dextral fault partitioning oblique convergence at the rear of the belt. The KFS formed by three fault zones ended by bent orogen-parallel thrusts allows slip from along the Main Recent Fault to become distributed by transfer to longitudinal thrusts and folds. To cite this article: C. Authemayou et al., C. R. Geoscience 337 (2005).     

月球东海盆地综合解析与撞击初始条件的研究

东海是月球上最年轻的多环撞击盆地,关于其形成机制的研究很多,但成果大都基于正撞击的机制提出的,虽然有部分学者提出东海是斜撞击的,但缺乏具体撞击参数。本文通过多源数据融合,综合分析LRO影像数据、LOLA地形数据、M~3高光谱数据和IIM高光谱数据,对东海地区的地貌特征、物质成分进行了较为系统的解译,发现在东海中央熔融区存在一条与东海撞击方向垂直的中央隆起区域(中央隆起线),其也是中央熔融区粗糙部分与光滑部分的分界线,结合撞击坑成坑理论,认为其可能是撞击过程冲击波作用引起的堆叠作用形成的。同时利用GRAIL数据及对该地区的重力异常的成因进行了分析,认为异常是由于压强、温度及岩石粘度的改变引起局部莫霍面抬升和中央熔融物的形成而出现的,进而估算出熔融物占盆地内物质的25%,约为1.1×10~6km~3。同时,对GRAIL数据的剖面分析结果也支持了本文的斜撞击理论。最后,综合多方面的信息和撞击理论获取东海盆地构造分布图,并根据中央隆起线、溅射物及线性构造的分布特征等,提出东海盆地理论上是由一直径在50~100km的撞击体以10~30km/s的速度自东偏北约20°~30°方向以20°~30°的角度斜撞击月表而形成的。这可为研究更早期的月球撞击坑提供理论参考。