Early Palaeozoic subduction in the southeastern Lachlan Fold Belt,Batemans Bay,New South Wales     

E. I. Prendergast 《Australian Journal of Earth Sciences》2013,60(4):481-501

The southeastern Lachlan Fold Belt at Batemans Bay on the New South Wales south coast is an accretionary complex with a prolonged deformation history. Early features include synsedimentary folds, mélange, disaggregated bedding and faults. Fabrics within the clast-in-matrix mélange and mudstone match those found in cores from the lower slopes of modern accretionary prisms. At the toe of the accretionary prism, the contact between the craton-derived Adaminaby Group and ocean floor deposits of the Wagonga Group is conformable. As subduction continued, the early structures were overprinted by (D₁) deformation that produced meridional north – south-trending, tight to isoclinal folds (F₁) and associated axial-plane cleavage (S₁). This west-dipping subduction occurred in the Late Ordovician/Early Silurian but probably began much earlier. A younger regional deformation (D₂) resulted in north – south-trending, open to tight folds (F₂), slightly oblique to F₁, and an axial-surface cleavage (S₂).  相似文献   

Synorogenic alluvial-fan – fan-delta deposition in the Papuan foreland basin: Plio-Pleistocene Era Formation,Papua New Guinea     

R. D. Winn Jr  P. Pousai 《Australian Journal of Earth Sciences》2013,60(5):507-523

The Pliocene to possibly Pleistocene uppermost Orubadi and Era Formations, southwest margin of the Papuan Peninsula, are interpreted as having been deposited in alluvial-fan, fan-delta and shallow-marine environments. The alluvial-fan facies consists primarily of lenticular, coarse-grained conglomerate (up to 2 m boulders) and cross-bedded and horizontally laminated sandstone. Conglomerate and sandstone were deposited in shallow fluvial channels and by overbank sheetfloods. The facies also contains thick mudflow diamictite and minor tuff and terrestrial mudstone. The shallow-marine and fan-delta facies, in contrast, consists of heterogeneously interbedded marine and terrestrial mudstone, sandstone, diamictite, conglomerate and limestone. Marine mudstone is calcareous, sandy, bioturbated, and contains marine shells. Limestone is mostly packstone that has a varied, open-marine fauna. Rare coral boundstone is also present. Marine sandstone is burrowed to bioturbated and is hummocky cross-stratified in places. Some marine mudstone contains sandstone pillows formed by loading of unconsolidated sand by storm waves. Other sandstone in the fan-delta facies is cross-bedded, lacks shells and was probably deposited by fluvial processes. Several conglomerate beds in the fan-delta facies are well sorted and imbricated and were also deposited by stream floods. The synorogenic Orubadi and Era Formations were deposited in a foreland basin formed from loading of the Papuan–Aure Fold and Thrust Belt on the edge of the Australian craton. Deformation in the fold and thrust belt was probably related to docking and compression of the Finisterre Terrane–Bismarck Arc against the New Guinea Orogen. The Era Formation interfingers with the reefal Wedge Hill Limestone in which reef facies likely grew on a deforming anticline. Era Formation siliciclastics were sourced from volcanic, metamorphic and sedimentary rocks that were uplifted in the orogen to the northeast. Volcanic sediment was derived mostly from a then-active volcanic arc likely related to southward subduction at the Trobriand Trough.  相似文献   

青藏高原东北缘基底结构研究——玛多—共和—雅布赖剖面上地壳地震折射探测          下载免费PDF全文

郭文斌  嘉世旭  段永红  王夫运 《地球物理学报》2016,59(10):3627-3636

利用青藏高原东北缘玛多-共和-雅布赖人工地震测深剖面的沉积盖层及上地壳折射波Psed、Pg走时,使用正则化方法反演该剖面基底速度结构,并通过射线数分布、分辨率分析等手段分析反演结果的可靠程度,得到了沿剖面850km近地表沉积盖层及结晶基底结构性质及构造变化特征,揭示了巴颜喀拉块体中段、东昆仑—西秦岭褶皱带、祁连褶皱带东侧及阿拉善块体等四个一级地质构造单元以及各块体内部若干次级构造沉积盖层介质岩性及厚度,结晶基底性质及被改造特征,在此基础上分析了(沿测线)青藏高原东北缘与外围阿拉善块体、高原内部块体间上部地壳构造耦合以及与地表构造形态关系.  相似文献   

Deciphering the presence of axial-planar veins in tectonites     

《地学前缘(英文版)》2019,10(6):2101-2115

Veins and dikes are often oriented subparallel to the axial surfaces of folds in the adjacent layered or foliated rocks.This implies an awkward situation,since veins would lay in planes close-to-parallel to the maximum stretching axis.A series of geometric models have been conceived in order to gain insight into the possible mechanisms for their formation.The models are based on the analysis of a varied selection of field structures and on the review of similar structures in the existing literature.A first categorization consists on distinguishing between axial-planar veins achieved by either progressive or polyphase deformation.Five models of axial-planar veins resulting from progressive deformation are described and discussed:(1) fold-related veins associated with the standard folding mechanisms,(2) fracture arrays localized along the short limbs of folds(asymmetric fold-related veins),(3) folds associated with rotation of extension veins(vein-related folds),(4) high strain and transposition of early veins,and(5) high strain and late veins parallel to axial planar foliations(axial planar foliation-related veins).The axial planar geometry is achieved through variable amounts of progressive rotational strain,except in model 5,in which the co-planarity is acquired at the time of vein intrusion.The possibility for axial-planar veins to have developed in two distinct phases in the context of polyphase or polyorogenic tectonics has also been explored and discussed.This study contributes to a better understanding of the intriguing interplays between deformation,metamorphic and magmatic processes in orogenic belts.  相似文献   

华北克拉通东部地块和大别—苏鲁造山带印支期褶皱-逆冲构造与动力学背景   总被引：8，自引：6，他引：2  

李三忠  刘鑫  索艳慧  刘丽萍  钱存超  刘晓春  张国伟  赵国春 《岩石学报》2009,25(9):2031-2049

大别-苏鲁造山带不同岩片(块)经历了不同的褶皱变形.榴辉岩块(或透镜体)和硬玉石英岩片经历了高压-超高压背景下的两幕褶皱变形之后,在区域性第一幕变形期间主要发生透镜化为主,后期与围岩共同经历紧闭同斜第二幕褶皱.而其它岩片主要经历了现今野外可见的区域性三幕褶皱,其中区域性第一幕褶皱为片内残留褶皱,在斜长角闪岩透镜体中多见,宏观规律不明.区域性第二幕褶皱在露头尺度多见,轴面为折劈理,局部强烈置换成片理化带(复合片理或第二期片理),恢复第三幕褶皱改造作用后,揭示出各种岩片中的各级尺度的第二幕褶皱都为轴面北西倾南东倒、轴迹走向为NNE向的紧闭不对称褶皱,不对称性一致反映其指向与各种岩片向南东的逆冲运动有关.第三幕褶皱为以片理或折劈理为变形面的宽缓褶皱,轴迹走向NWW,枢纽向西倾伏.韧性剪切带为非透入性构造,分早晚两期,早期为韧性逆冲,新县穹隆以南,运动学标志指示向北逆冲,错切第二幕褶皱,结合新县穹隆北部向南的逆冲特征,反映这些韧性逆冲断层多数为第二幕大型褶皱翼部的次级逆冲断层;晚期为韧性滑脱带,其发育局限于几个岩性差异较大的接触带,带内伸展型折劈理发育,并对挤压构造样式有重要的改造作用.华北克拉通东部地块是华北克拉通的重要组成,其盖层古生界和三叠系在印支运动期间经历了一幕宽缓褶皱作用,其轴迹方向主体也为NWW向.这一褶皱构造明显在变形时间、变形样式和展布方向上都和大别-苏鲁造山带中的第三幕褶皱非常一致,说明它们具有动力学上的必然联系.同时,研究表明在华北克拉通东部地块中没有经历大别-苏鲁造山带中区域性第一、第二幕褶皱变形的记录,故本文认为印支期这两幕变形主要发生在华北板块东南缘的边界上,并没有波及到板内,而且从东向西高压-超高压岩石剥露具有穿时性.只有当华北板块和华南板块在第二幕变形之后构成了统一块体后,第三幕变形才波及华北板内.  相似文献   

局部构造环境演化差异性对于成矿的控制作用——以辽西地区东五家子金矿与排山楼金矿为例     

张璟  邵军  赵东芳  周永恒  王宏博 《地质与资源》2015,24(6):545-553

辽西地区东五家子金矿与排山楼金矿空间位置相距较近,同属华北陆块北缘东段,且均产于新太古代变质表壳岩-深成岩组合岩系中.然而,东五家子金矿作为石英脉型金矿的代表,与以排山楼金矿为代表的韧性剪切带蚀变岩型金矿在成矿机制、成矿时代及成矿特征等方面均存在较大差别.通过对比分析上述2个金矿的矿床特征,认为局部构造环境演化差异性造成了二者成矿的不同.与此同时,内蒙地轴宝国老隆起石英脉型金矿密集分布的格局与燕山褶皱带北镇隆起韧性剪切带蚀变岩型金矿稀疏分布的格局,这一鲜明反差现象也依据“波的传导”理论得到了较好的解释.与宝国老隆起具有相似局部构造环境的旧庙隆起已发现金矿点稀少,且存在明显Au化探异常,因而有望在该区域发现“东五家子式”金矿.  相似文献   

Imposition of a Proterozoic salient on a Palaeozoic orogen at the eastern margin of Gondwana     

H.A. Williams  J.R. Stewart  P.G. Betts 《Gondwana Research》2009,16(3-4):669-686

Regional analysis of the distribution of metamorphic fabrics and shear zones in the Palaeo-Mesoproterozoic Curnamona Province has enabled the deconstruction of a Cambrian fold arc that defines part of the eastern margin of Gondwana. We suggest a tectonic model whereby the arc formed at ca. 500 Ma, during accretion of Phanerozoic terranes to the eastern margin of Precambrian Australia. The regional fold arc is interpreted to have formed along an irregular plate margin comprising a SE-convex rigid promontory of Precambrian basement during initial accretion of the Phanerozoic terranes during the Cambrian. An early phase of dextral oblique-slip along shear zones in the south and west of the province indicates an initial WNW transport direction. As the arc was folded, a slightly later phase of sinistral oblique-slip shearing was initiated along shear zones in the east, in response to deflection of the arc around the rigid promontory.  相似文献   

新平大红山铜矿二期基建探矿控矿构造特征   总被引：1，自引：0，他引：1  

李飞  王文辉  李正元  陈泽华 《云南地质》2009,28(2):179-184

二期基建揭露的断层按其产出方向分为四个组：NWW向的正断层,NNE向的平移正断层,NE～NEE向的正断层,NW向的矿区断层F3;按形成时间可分为早期断层和晚期断层,除边界断层F3外均为早期断层。早期断层又按其切错关系,可分为5个活动期次。断层构造将矿体沿走向切错成条块状,沿倾向切错成阶梯状排列,形成堑、垒式构造,对矿床开采产生较大的影响。  相似文献   

Formation of small scale folds and faults in northern Ohio     

L. De Chant 《Engineering Geology》1998,50(3-4):329-335

Folds and faults in the Devonian shales of the Berea area, Ohio have been analyzed on a small scale (several meters) to determine their method of formation. A simple elastic model has been developed to account for stress concentration due to lithostatic pressures induced by local relief. This analytical model is then coupled to the beam–column buckling stability theory. The possibility of failure due to faulting is also examined using the Coulomb criterion. Initial results indicate that local stresses due to topography are a probable cause of these structures, though the possible role of regional tectonic effects cannot be eliminated. The state of the local stress field and the possibility of seismic events have important implications for surface and subsurface design problems.  相似文献   

Geochemical characteristics of gold mineralization of the Huai Kham On deposit,Sukhothai Fold Belt,Northern Thailand     

Ladda Tangwattananukul  Daizo Ishiyama  Punya Charusiri 《Resource Geology》2020,70(4):362-377

The Huai Kham On gold deposit is located in the central part of the Sukhothai Fold Belt, northern Thailand. The Sukhothai Fold Belt represents an accretionary complex formed by subduction and collision between the Indochina and Sibumasu Terranes. There are many small gold deposits in the Sukhothai Fold Belt; however, the styles and formation environments of those gold deposits are not clear. The geology of the Huai Kham On deposit consists of volcanic and volcanosedimentary rocks, limestone, and low‐grade metamorphic rocks of Carboniferous to Triassic age. Gold‐bearing quartz veins are hosted by volcanic and volcanosedimentary rocks. The quartz veins can be divided into four stages. The mineral assemblage of the gold‐bearing quartz veins of Stages I and II comprises quartz, calcite, illite, pyrite, native gold, galena, chalcopyrite, and sphalerite. Quartz veins of Stage III consist of microcrystalline quartz, dolomite, calcite, pyrite, native gold, and chalcopyrite. Veins of Stage IV consist of calcite, dolomite, chlorite, and quartz. Fluid inclusions in quartz veins are classified into liquid‐rich two‐phase (Types I_A and I_B), carbonic‐aqueous (Type II), and carbonic (Type III) fluid inclusions. The homogenization temperatures of Types I_A and II fluid inclusions that are related to the gold‐bearing quartz veins from Stages I to III ranged from 240° to 280°C. The δ¹⁸O values of quartz veins of Stages I to III range from +12.9 to +13.4‰, suggesting the presence of a homogeneous hydrothermal solution without temperature variation such as a decrease of temperature during the formation of gold‐bearing quartz veins from Stages I to III in the Huai Kham On gold deposit. Based on the calculated formation temperature of 280°C, the δ¹⁸O values of the hydrothermal solution that formed the gold‐bearing quartz veins range from +3.2 to +3.7‰, which falls into the range of metamorphic waters. The gold‐bearing quartz veins of the Huai Kham On deposit are interpreted to be the products of metamorphic water.  相似文献