库鲁克塔格赛马山一带中元古界构造变形研究

通过构造解析的研究，确定赛马山地区中元古代所发生的阿尔金运动共有三幕变形，第一幕发生在长城纪早期，为EW向伸展机制下中部构造相的大规模顺层滑脱韧性变形，形成了赛马西山顺层滑脱韧性变形带，具超塑性流动变形特征和多层结构样式，第二幕发生在长城纪末，为主期变形，在NS向挤压机制下，在浅部构造相形成了EW向紧闭褶皱（局部倒转褶皱），并卷入早期的顺层滑脱韧性变形带，褶皱后期，由于应力的集聚，在浅表层次下，沿兴地塔格群内岩层软弱面发生剪切而形成了滑脱面，产生由南向北的逆冲，形成了具叠瓦扇结构的永红山飞来峰构，第三幕，蓟县纪末由于SN向强烈挤压后出现“松驰”引张而产生EW向挤压应力，形成NS向开阔褶皱，叠加于主期褶皱之上，形成了赛马西山－永红山穹盆构造。     

川渝湘鄂薄皮构造带多层拆离滑脱系的岩石力学性质及其对构造变形样式的控制

川渝湘鄂多层拆离推覆构造发育于秦岭-大别造山带、雪峰山厚皮构造带与四川盆地之间。这个薄皮构造带是在晚中生代沿一系列岩石薄弱层从南东向北西多层拆离滑脱构造作用下形成的,然而单纯的地表构造地质调查无法揭示各滑脱层是如何控制区内褶皱-断层关系的。因此,对拆离滑脱层进行识别是认识区内构造样式及其成因机制的关键。利用单轴岩石力学实验方法,对取自区内沿达县-大庸地质剖面不同岩性地层组合的样品进行岩石力学分析,并结合前人在区内已经获得的数据,结果表明区内至少发育5个可能的区域性拆离滑脱层。这些滑脱层主要由泥质岩、粉砂岩和泥质灰岩组成的,分别沿下寒武统牛碲塘组(Det I)、下志留统罗惹坪组和龙马溪组 (Det II)、下二叠统栖霞组(Det III)、下三叠统大冶组(Det IV)和中三叠统巴东组 (Det V)发育。野外调查表明,Det I控制了深部构造层次的断弯褶皱和叠瓦扇, Det II 可能控制了中部构造层次的断展褶皱和拆离褶皱,Det III则可能与Det IV和Det V一起,共同控制了上部构造层次的侏罗山式褶皱。     

Architecture,deformation style and petrophysical properties of growth fault systems: the Late Triassic deltaic succession of southern Edgeøya (East Svalbard)

The Late Triassic outcrops on southern Edgeøya, East Svalbard, allow a multiscale study of syn‐sedimentary listric growth faults located in the prodelta region of a regional prograding system. At least three hierarchical orders of growth faults have been recognized, each showing different deformation mechanisms, styles and stratigraphic locations of the associated detachment interval. The faults, characterized by mutually influencing deformation envelopes over space‐time, generally show SW‐ to SE‐dipping directions, indicating a counter‐regional trend with respect to the inferred W‐NW directed progradation of the associated delta system. The down‐dip movement is accommodated by polyphase deformation, with the different fault architectural elements recording a time‐dependent transition from fluidal‐hydroplastic to ductile‐brittle deformation, which is also conceptually scale‐dependent, from the smaller‐ (3rd order) to the larger‐scale (1st order) end‐member faults respectively. A shift from distributed strain to strain localization towards the fault cores is observed at the meso to microscale (<1 mm), and in the variation in petrophysical parameters of the litho‐structural facies across and along the fault envelope, with bulk porosity, density, pore size and microcrack intensity varying accordingly to deformation and reworking intensity of inherited structural fabrics. The second‐ and third‐order listric fault nucleation points appear to be located above blind fault tip‐related monoclines involving cemented organic shales. Close to planar, through‐going, first‐order faults cut across this boundary, eventually connecting with other favourable lower‐hierarchy fault to create seismic‐scale fault zones similar to those imaged in the nearby offshore areas. The inferred large‐scale driving mechanisms for the first‐order faults are related to the combined effect of tectonic reactivation of deeper Palaeozoic structures in a far field stress regime due to the Uralide orogeny, and differential compaction associated with increased sand sedimentary input in a fine‐grained, water‐saturated, low‐accommodation, prodeltaic depositional environment. In synergy to this large‐scale picture, small‐scale causative factors favouring second‐ and third‐order faulting seem to be related to mechanical‐rheological instabilities related to localized shallow diagenesis and liquidization fronts.     

Post-collisional granitoids from the Dabie orogen in China: Zircon U–Pb age, element and O isotope evidence for recycling of subducted continental crust

While recycling of subducted oceanic crust is widely proposed to be associated with oceanic island, island arc, and subduction-related adakite magmatism, it is less clear whether recycling of subducted continental crust takes place in continental collision belts. A combined study of zircon U–Pb dating, major and minor element geochemistry, and O isotopes in Early Cretaceous post-collisional granitoids from the Dabie orogen in China demonstrates that they may have been generated by partial melting of subducted continental crust. The post-collisional granitoids from the Dabie orogen comprise hornblende-bearing intermediate rocks and hornblende-free granitic rocks. These granitoids are characterized by fractionated REE patterns with low HREE contents and negative HFSE anomalies (Nb, Ta and Ti). Although zircon U–Pb dating gives consistent ages of 120 to 130 Ma for magma crystallization, occurrence of inherited cores is identified by CL imaging and SHRIMP U–Pb dating; some zircon grains yield ages of 739 to 749 Ma and 214 to 249 Ma, in agreement with Neoproterozoic protolith ages of UHP metaigneous rocks and a Triassic tectono-metamorphic event in the Dabie–Sulu orogenic belt, respectively. The granitoids have relatively homogeneous zircon δ¹⁸O values from 4.14‰ to 6.11‰ with an average of 5.10‰ ± 0.42‰ (n = 28) similar to normal mantle zircon. Systematically low zircon δ¹⁸O values for most of the coeval mafic–ultramafic rocks and intruded country rocks preclude an AFC process of mafic magma or mixing between mafic and felsic magma as potential mechanisms for the petrogenesis of the granitoids. Along with zircon U–Pb ages and element results, it is inferred that the granitic rocks were probably derived from partial melting of intermediate lower crust and the intermediate rocks were generated by amphibole-dehydration melting of mafic rocks in the thickened lower crust, coupled with fractional crystallization during magma emplacement. The post-collisional granitoids in the Dabie orogen are interpreted to originate from recycling of the subducted Yangtze continental crust that was thickened by the Triassic continent–continent collision. Partial melting of orogenic lithospheric keel is suggested to have generated the bimodal igneous rocks with the similar crustal heritage. Crustal thinning by post-collisional detachment postdated the onset of bimodal magmatism that was initiated by a thermal pulse related to mantle superwelling in Early Cretaceous.     

Seismic study on oceanic core complexes in the Parece Vela back-arc basin

Abstract   In the present study the seismic structure of oceanic core complexes (OCC) in the Parece Vela Basin, Philippine Sea have been imaged. Together with recent work on the Atlantis Massif OCC on the Mid-Atlantic Ridge, including deep drilling, this work provides an unprecedented opportunity to advance our understanding of OCC internal structure. A continuous, strong and relatively smooth reflection that was ca 0.15 s (two way time) below the sea floor of an OCC in the Chaotic Terrain of the Parece Vela Basin was identified. This reflection, termed the D-reflector, is similar to that observed beneath Atlantis Massif. A faster P-wave velocity (>6 km/s) is observed very shallow beneath the Chaotic Terrain OCC, suggesting that the core of these OCC is dominantly gabbroic. The D-reflector might be common beneath OCC, owing to localized alteration along fractured zones within gabbro. We further observed a series of three detachment events in the Chaotic Terrain. The first and second detachments exhumed shallow basaltic crust to deeper gabbroic core, whereas the last one only exhumed shallow basaltic crust.     

STUDY ON THE DYNAMIC PROCESS OF RILL EROSION OF LOESS SLOPE SURFACE

1 mTRODUCTIONAs a woridwide concem, excessive water erosion induces land degradation, causes losses of plantnutrients, and Ieads to off site enVironmental problems such as sedimentahon streams and reservoirs. mllerosion, which results from concentraed flow in a lindted and confined space, plays imPortant roles inthe erosion systCm on uPland areas. Data listed in Table l show its contribution and imPoftance to thetOtal slope soil losses. In the last decades, stodies on the physical mecha…     

最大有效力矩准则及相关地质构造

摩尔-库伦准则广泛用以说明断裂构造的形成,然而却不能解释自然界广泛分布的大变形。最近提出的岩石变形新理论--最大有效力矩准则,其数学表达式为Meff=0.5(σ1-σ3)L.sin2α.sinα。式中,σ1-σ3代表变形岩石的屈服强度,L为单位长度,α为σ1与变形带间的角度。该准则证明最大有效力矩出现在σ1轴左右54.7°方向,55°±10°区间力矩无显著变化,天然和实验的全部观测值全部位于该区间内。相关地质构造包括:膝褶带、伸展褶劈理、膏盐层中的屈服带、低角正断层、高角逆断层、结晶基底中的菱网状剪切带、地震反射剖面中的鳄鱼嘴构造和前陆盆地中的拆离褶皱等。据该准则可确定有关构造形成时的应力状态和运动学涡度,并扩展说明深俯冲超高压岩石的折返-出露机制。     

西南印度洋脊龙旂热液区蚀变岩岩石学特征及对热液流体循环的指示

慢速?超慢速扩张洋脊的海底热液活动区多出露类型多样的蚀变岩石，记录了地壳深部的流体与围岩的相互作用，为研究深部热液流体特征以及循环过程提供了样本。本研究选取了中国大洋第30、34和40航次在超慢速扩张西南印度洋脊龙旂热液区(A区、B区和C区)利用电视抓斗采集的蚀变玄武岩、蚀变辉长岩、蚀变辉石岩和蛇纹岩等蚀变岩样品，利用光学显微镜、电子探针开展了岩相学和矿物化学分析。岩相学结果表明，龙旂热液区蚀变岩石样品约95%发生了地壳浅部的脆性变形作用，靠近龙旂1号热液区(A区)约有5%的蚀变岩石混合发育了脆性变形及脆性?塑性变形特征。研究区岩石蚀变属于中?低温变质作用，变质相近似绿片岩相，变质矿物组合为绿泥石?绿帘石?钠长石?阳起石?榍石。其中，A区的蚀变岩中的绿泥石形成温度(201～341℃)以及蛇纹石、阳起石、绿泥石等蚀变矿物的Fe元素含量(17.5%～27.5%)都高于龙旂3号热液区(B区和C区)的绿泥石形成温度(239～303℃)和Fe元素含量(16.8%～26.5%)，这也与在该区观测到高温的热液喷口相符合。本研究认为龙旂热液区所在洋脊段发育的拆离断层为热液流体的向上运移提供了通道，洋壳扩张后期轴部的岩浆熔体在轴侧区域的岩浆侵入或喷发活动可能为热液循环提供了热源。     

Downslope soil detachment–transport on steep slopes via rain splash

This study developed a one‐dimensional model of downslope rain splash transport based on field experiments and previous studies. The developed model considers soil detachment processes, ground cover, probability densities, and the effect of overland run‐off in preventing detachment. Field monitoring was conducted to observe precipitation run‐off, ground cover, and sediment production on steep hillslopes. Field‐observed data were used to develop the splash detachment rate equation, probability densities for splash transport, and the maximum splash transport distance. Observed and estimated splash transport showed overall agreement, with some differences for small storm events or events with relatively low intensity, probably caused by variation of overland run‐off depth and connectivity as well as differences in soil surface cohesion at various degrees of wetness. Our model can provide insights on the interactions among rainfall intensity, soil surface condition, soil wetness, and splash transport on forested hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Impact of the Late Triassic Dashtak intermediate detachment horizon on anticline geometry in the Central Frontal Fars,SE Zagros fold belt,Iran

Integration of 2-D seismic lines, well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific Central Frontal Fars region in the SE Zagros fold belt. These variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level, located along the Late Triassic Dashtak Formation. Anticlines of short wavelength contain a significant over-thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m (from an original thickness of 550–800 m). Folds containing thick Dashtak evaporites show decoupling across the detachment level and, thus, a shift of the anticline crest in the underlying Permo-Triassic carbonates of the Dehram Group, which form the major gas reservoir in the Central Frontal Fars. Four main parameters control the extent and distribution of the decoupled anticlines in the study area: (a) original large thickness of the Late Triassic evaporitic basin; (b) coinciding larger amounts of anhydrites with increasing total thickness of formation; (c) parallel occurrences of abnormally high fluid pressures; and (d) shortening variations across, and along, the strike of specific folds. The present work relating the different parameters of the Dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth, which is applicable to oil and gas exploration in the SE Zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons.