Structural style in a young flexure-induced oblique extensional system,north-western Bonaparte Basin,Australia

In the north-western Bonaparte Basin (North West Shelf of Australia) Neogene to Recent flexure-induced extension superimposed obliquely over the Mesozoic rift structures. Thus, the area offers a good opportunity to investigate the dynamics and architecture of oblique extension fault systems. Analysis of basin-scale 2D and 3D seismic data along the Vulcan sub-basin shows that Neogene deformation produced a new set of extensional, en échelon faults, at places accompanied by the reactivation of the Mesozoic faults. The pre-existing Mesozoic structures strongly control the distribution of the Neogene-Recent deformation, both at regional and local scales. Main controls on the Neogene-Recent fault style, density and segmentation/linkage include: (1) the orientation of the underlying Mesozoic structures, (2) the obliqueness of the younger extension relative to the rift-inherited faults, and (3) the proximity to the Timor Trough. Three types of vertical relationships have been observed between Mesozoic and Neogene-Recent faults. Hard linkages seems to develop when both fault systems trend parallel, therefore increasing risks for trap integrity. It is suggested that the orientation of maximum horizontal stress (S_Hmax) relative to the Mesozoic faults, forming hydrocarbon traps, is critical for their potential seal/leak behaviour. Stratigraphic growth across the faults indicates that main fault activity occurred during the Plio-Pleistocene, which corresponds to the timing of tectonic loading on Timor Island and the development of lithospheric flexure. Synchronism of normal faulting with flexural bending suggests that extensional deformation on the descending Australian margin accompanied the formation of the Timor Trough.     

甘肃古浪、景泰活断层上的树木地震学研究

在树木地震学测年技术研究的基础上，沿古浪活断层西段鉴定和评价了数百棵树。对树木生长速率及年轮比率低值偏离的３种类型进行了有效的识别。结果表明：断崖上被破坏的青海云杉中，记录的结构和生长速率异常，可以归因于１９２７年５月２３日古浪８级大地震的影响。从而为古浪地震断层的判定提供了准确的年代证据。并将前人认为的古浪地震断层位置向冷龙岭北麓南移了３０余公里。用该方法在老虎山活断层上对１８８８年１１月２日景秦６１／４级地震破裂带定年，再次获得成效     

Geomorphic Evidence for and Rate of Sinistral Strike-slip Movement Along Northwest-trending Faults in Chaoshan Plain

Two sets of active faults,northwest-and northeast-trending faults,are developed in the Chao-shan Plain of East Guangdong.After detailed interpretation of aerophotos,we have found outthat there is the clear phenomenon of sinistral dislocation of drainage system on the Huang-gang-shui fault and part of Fengshun-Shantou fault.Field investigation confirmed that the geo-morphic bodies along the two faults have undergone displacement.Large-scale topographicmapping was made at three displaced sites and samples for age dating were collected from thegeomorphic booies.Calculation indicates that the average rate of sinistral strike-slip movementin the Holocene time amounts to 1.11±0.09～2.69±0.24mm/a along the Huanggangshuifault and 3.26±0.26mm/a along the Fengshun-Shantou fault.These two more active NW-trending faults extend into sea area,where they intersect the NE-trending strongly active Nius-han Island-Xiongdi Isle-Nanpeng Isles fault at a depth of 40～50m in water.The intersection isa location favorable fo     

Geochemistry of the Pliocene basalts erupted along the Malatya-Ovacik fault zone (MOFZ), eastern Anatolia, Turkey: Implications for source characteristics and partial melting processes

The study area is located on the middle sector of the Malatya-Ovacık Fault Zone (MOFZ) in the eastern Anatolia. Four basaltic flows from bottom to top, which are tholeiitic in character and intercalated with Pliocene sedimentary rocks, were erupted along this fault zone. Chemical compositions of these flows reveal some differences between the first flow and others in terms of high-field strength elements (HFSEs) (e.g. Ti, Zr, Nb). Limited variations in compositions within the first flow and upper flows suggest a limited fractionation range. Trace-element patterns exhibit that all the flows have similar and OIB-like patterns without positive peak at Pb and a trough at Nb—Ta, indicating minimal or no crustal contribution. Rare-earth element (REE) patterns indicate that the first flow has flat patterns with negative Eu anomaly, whereas the upper flows have variable enrichments in LREE and depletions in HREE. La/Sm_N, Dy/Yb_N and Zr/Y ratios exhibit that the degree of partial melting decreases from the first flow to upper flows. Higher values of La/Yb_N ratio for the upper flows and depletions at Y and Yb on the trace-element patterns suggest the presence of garnet as a residual phase, which imply that the depth of partial melting took place solely in the garnet-stability field. OIB-like trace-element patterns and trace-element ratios (e.g. La/Nb, Ce/Y and Zr/Nb) emphasize that the melts forming the Arguvan basalt were originated from the asthenospheric mantle rather than the lithospheric mantle.     

江汉盆地大型富锂卤水矿床成因与资源勘查进展:综述

古近纪时期,华南江汉盆地的潜江凹陷和江陵凹陷发育盐湖,沉积了巨厚的蒸发岩,并形成和储藏了富锂、钾、铷、铯、溴、碘等元素的卤水资源,这些元素含量达到工业品位或综合利用品位;富锂卤水属于深层地下卤水型锂矿资源,镁锂比值低,是非常优质的锂资源。本文总结了江汉盆地大地构造特征、火成岩及古气候背景,论述了古盐湖沉积岩相特征、富锂卤水水化学、分布及储层特征、卤水中锂的来源与富集机理、卤水型锂矿成矿模式以及富锂卤水勘查与开采技术进展,提出了卤水开发利用中存在的问题和解决途径。江汉盆地富锂卤水成因包括:古盐湖锂可能主要来自高温水岩反应产生的富锂热液流体的补给;在干旱的气候下,古湖水不断蒸发浓缩,导致卤水中锂浓缩富集;在盐湖演化末期,逐渐埋藏的盐类晶间富锂卤水被转移至裂隙、砂岩及玄武岩储层中储集;在较高的地热背景值下,埋藏卤水与储层岩石可能发生水岩反应,进一步促进了卤水中锂的富集。江汉盆地深层卤水初步勘查显示,氯化锂资源量已达到大型工业规模,展示了巨大的资源潜力。此外,卤水锂开采技术已基本形成,建议进一步加强富锂卤水的绿色开发技术研究,制定相关勘查开发规范。     

Geochemisty and tectonic setting of igneous rocks in the Glenrock Station area,N.S.W.

In the Upper Murray Valley, Victoria, Late Silurian, high‐Si igneous rocks, which are closely associated with alkalic, basaltic dykes, were emplaced at high crustal levels following the peak of the Benambran Orogeny, which deformed and metamorphosed the Wagga Zone in Late Ordovician‐Early Silurian times. These rocks, which are informally termed ‘the Upper Murray high‐Si magmatic suite’, include leucogranites, rhyolite dykes and flows, and ash‐flow tuffs characterised by the following features. They are transitional from mildly peraluminous to mildly metaluminous; they represent relatively anhydrous magmas, in which halides were important volatile constituents; they have high Si, total alkalies, Rb, Th, U, Nb, Sn and heavy rare earth elements; and they are relatively repleted in Mg, Ca, Sr, Eu, V, Cr and Ni. In these respects and in their post‐orogenic setting and close association with alkalic basalts, they resemble many post‐orogenic granitoids from elsewhere. Such granitoids appear to have formed as partial melts during crustal extension following major episodes of deformation and high‐Si magmatism. A residual granulitic crust, from which an earlier generation of granitoid magmas had been extracted, is argued to be the source rock‐type for these post‐orogenic magmas. Tectonic extension, affecting such a crust, was accompanied by deep fracturing and basaltic vol‐canism. Mantle‐derived, CO₂‐ and halide‐rich fluids moved into the residual crust, causing widespread metasomatism, and emplacement of basaltic magma caused temperatures to rise until melting took place and a second group of magmas was produced. This model explains most aspects of the trace and major element chemistry of post‐orogenic, high‐Si igneous rocks and, for the Upper Murray high‐Si suite it also provides an explanation for variations in trace elements and isotopic characteristics. Other processes, such as crystal fractionation, magma mixing, thermogravi‐tational diffusion, and separation and loss of a volatile phase, provide explanations for variations within individual units of the suite, but they do not explain overall variations or the highly fractionated nature of the suite.     

Country‐rock structural fabrics as a guide to pluton emplacement depth: An example from the Hodgkinson Province,northeastern Australia

Country‐rock structures adjacent to plutons of the linear, northwest‐southeast‐trending Mt Alto Supersuite, Hodgkinson Province, northeastern Australia, are variably developed from north to south along the belt. S₃ and S₄ cleavages show close temporal relationships with pluton emplacement and are better and more widely developed around plutons in the north, whereas much weaker cleavages of the same generation are only sporadically developed to the south. Cleavage trend lines anastomose around less elongate plutons to the north but are generally truncated by more elongate plutons to the south. It is proposed that a major crustal dislocation, the Alto Fault Zone, comprises a set of subparallel structures that formed prior to granite intrusion and controlled emplacement of some plutons and their final shapes. The north‐south variation in structural relations is interpreted to reflect a corresponding variation in depth of emplacement from north to south, which resulted when post‐emplacement reactivation of the Alto Fault Zone uplifted and sinistrally displaced the northern end of the supersuite relative to the southern end. Reactivation of the fault zone after granite emplacement is supported by the truncation of some plutons.     

Polygonal deformation bands

We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1–5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.     

徐家围子断陷深层火石岭组致密火山岩储层地应力分布规律研究

徐家围子断陷位于松辽盆地北部,其深层中生代火石岭组为致密火山岩气藏,天然裂缝发育,地应力分布非均质性强。结合诱导裂缝法与井径崩落法进行单井现今地应力方向分析,利用声波测井法计算现今地应力大小的纵向分布。依据火石岭组构造顶底面图、火山岩相组及断层分布特征建立非均质三维地质模型;在动、静态岩石物理参数拟合校正的基础上,结合实验测试及已有研究成果,确定不同岩相组和断层岩石物理参数,建立三维力学模型;利用Ansys有限元数值模拟软件建立火石岭组三维数学模型并进行相关运算获得三维现今地应力分布模型。计算结果表明在火石岭组地层中,水平最大主应力方向主要为东西向,应力值范围在86~110 MPa;水平最小主应力方向主要为南北向,应力值范围在67~84 MPa。分析模拟结果可知火山岩相、断层和构造起伏三者对火石岭组现今地应力分布影响较大。其中水平主应力的方向主要受断层和近火山口相分布的影响,而水平主应力的大小则是受三者综合作用。在构造低部位,近火山口相组发育处,断层上盘及断层端部皆为主应力的集中区域。依据现今地应力研究成果可为徐家围子断陷下一步开发井网部署、压裂改造方案和水平井的设计以及注水管理提供重要指导。      

Field evidence for normal fault linkage and relay ramp evolution: the Kırkağaç Fault Zone,western Anatolia (Turkey)

Linking of normal faults forms at all scales as a relay ramp during growth stages and represents the most efficient way for faults to lengthen during their progressive formation. Here, I study the linking of normal faulting along the active K?rka?aç Fault Zone within the west Anatolian extensional system to reconstruct fault interaction in time and space using both field- and computer-based data. I find that (i) connecting of the relay zone/ramp occurred with two breaching faults of different generations and that (ii) the propagation was facilitated by the presence of pre-existing structures, inherited from the ?zmir-Bal?kesir transfer zone. Hence, the linkage cannot be compared directly to a simple fault growth model. Therefore, I propose a combined scenario of both hangingwall and footwall fault propagation mechanisms that explain the present-day geometry of the composite fault line. The computer-based analyses show that the approximate slip rate is 0.38 mm/year during the Quaternary, and a NE–SW-directed extension is mainly responsible for the recent faulting along the K?rka?aç Fault Zone. The proposed structural scenario also highlights the active fault termination and should be considered in future seismic hazard assessments for the region that includes densely populated settlements.