The Cauvery Shear Zone, Southern Granulite Terrain, India: A crustal-scale flower structure

The Cauvery Shear Zone (CSZ) is a crustal-scale shear system within the Southern Granulite Terrain along the southern margin of the Archaean Dharwar craton. Structural interpretation of satellite data and field observations reveal four major shear zones within the CSZ system. They show dextral shear kinematics synchronous with a major Neoproterozoic tectono-metamorphic event (D2) associated with intracrustal melting and migmatisation. The disposition, geometry and contemporaneity of shear fabrics of the CSZ system are modelled in terms of a crustal-scale flower structure akin to transpressional and collisional orogens. In the light of recent seismic evidence for a displaced Moho structure and a mid- to lower-crustal low velocity zone, the flower structure across the CSZ may extend to mantle depths.     

Mesofossil flora from the Late Cretaceous of New Zealand

This study presents the first report of mesofossils of flowers, fruits and seeds found in the Cretaceous of New Zealand. The specimens were recovered from the Late Cretaceous (Maastrichtian, ca. 70 Ma) at Kai Point Mine, South Island in a sequence of floodplain sediments sampled just below the Barclay Coal Seam. Angiosperm flowers, fruits and seeds occur in the sample. The most common form is an actinomorphic flower with two whorls of three tepals. Anther bases are preserved and the ovary develops into a drupe, all features that are consistent with placement in the Lauraceae. Reproductive structures including seeds of conifers are also described, with some allied to the Podocarpaceae. This contrasts with interpretations of the flora based on macrofossils that indicate abundant Araucariaceae and highlights the different perspectives that mesofossil floras give to any assemblage. The results of the present study support a Late Cretaceous flora at this site mainly dominated by conifers with affinities to Podocarpaceae but also including lauraceous angiosperms.     

Tectono-stratigraphic development of the Coastal Group of south-eastern Jamaica

The sedimentary succession of southeastern Jamaica preserves a depositional record of accommodation changes and tectonic events for the last 14 Ma. The depositional systems which occur in the area have been classified according to distinct tectono-stratigraphic packages based on the depositional environments, rapid facies changes, and or significant erosion surfaces. This paper places the sedimentology and geochemistry within a tectonic evolutionary framework for the northern margin of the Caribbean Plate over the last 14 Ma. This involves considering issues of changing accommodation; deformation episodes including folding and faulting and the subsequent cutting of unconformities. A model for the tectono-stratigraphic development of southeastern Jamaica is also proposed. The model incorporates critical surfaces, major faults, subsidence and uplift which later influence the depositional environments.     

Transpression and juxtaposition of middle crust over upper crust forming a crustal scale flower structure: Insight from structural,fabric, and kinematic studies from the Rengali Province,eastern India

Deformational, metamorphic, monazite age and fabric data from Rengali Province, eastern India converge towards a multi-scale transpressional deformational episode at ca. 498–521 Ma which is linked with the latest phase of tectonic processes operative at proto-India-Antarctica join. Detailed sector wise study on mutual overprinting relationships of macro-to microstructural elements suggest that deformation was regionally partitioned into fold-thrust dominated shortening zones alternating with zones of dominant transcurrent deformation bounded between the thrust sense Barkot Shear Zone in the north and the dextral Kerajang Fault Zone in the south. The strain partitioned zones are further restricted between two regional transverse shear zones, the sinistral Riamol Shear Zone in the west and the dextral Akul Fault Zone in the east which are interpreted as synthetic R and antithetic R' Riedel shear plane, respectively. The overall structural disposition has been interpreted as a positive flower structure bounded between the longitudinal and transverse faults with vertical extrusion and symmetric juxtaposition of mid-crustal amphibolite grade basement gneisses over low-grade upper crustal rocks emanating from the central axis of the transpressional belt.     

Detailed fault structure of the Tarutung Pull-Apart Basin in Sumatra,Indonesia, derived from local earthquake data

The Tarutung Basin is located at a right step-over in the northern central segment of the dextral strike-slip Sumatran Fault System (SFS). Details of the fault structure along the Tarutung Basin are derived from the relocations of seismicity as well as from focal mechanism and structural geology. The seismicity distribution derived by a 3D inversion for hypocenter relocation is clustered according to a fault-like seismicity distribution. The seismicity is relocated with a double-difference technique (HYPODD) involving the waveform cross-correlations. We used 46,904 and 3191 arrival differences obtained from catalogue data and cross-correlation analysis, respectively. Focal mechanisms of events were analyzed by applying a grid search method (HASH code). Although there is no significant shift of the hypocenters (10.8 m in average) and centroids (167 m in average), the application of the double difference relocation sharpens the earthquake distribution. The earthquake lineation reflects the fault system, the extensional duplex fault system, and the negative flower structure within the Tarutung Basin. The focal mechanisms of events at the edge of the basin are dominantly of strike-slip type representing the dextral strike-slip Sumatran Fault System. The almost north–south striking normal fault events along extensional zones beneath the basin correlate with the maximum principal stress direction which is the direction of the Indo-Australian plate motion. The extensional zones form an en-echelon pattern indicated by the presence of strike-slip faults striking NE–SW to NW–SE events. The detailed characteristics of the fault system derived from the seismological study are also corroborated by structural geology at the surface.     

Transpressive duplex and flower structure: Dent Fault System, NW England

Revised mapping along the Dent Fault (northwest England) has improved the resolution of folds and faults formed during Variscan (late Carboniferous) sinistral transpression. A NNE-trending east-down monocline, comprising the Fell End Syncline and Taythes Anticline, was forced in Carboniferous cover above a reactivated precursor to the Dent Fault within the Lower Palaeozoic basement. The Taythes Anticline is periclinal due to interference with earlier Acadian folds. The steep limb of the monocline was eventually cut by the west-dipping Dent Fault. The hangingwall of the Dent Fault was dissected by sub-vertical or east dipping faults, together forming a positive flower structure in cross-section and a contractional duplex in plan view. The footwall to the Dent Fault preserves evidence of mostly dip-slip displacements, whereas strike-slip was preferentially partitioned into the hangingwall faults. This pattern of displacement partitioning may be typical of transpressive structures in general. The faults of the Taythes duplex formed in a restraining overlap zone between the Dent Fault and the Rawthey Fault to the west. The orientations of the duplex faults were a response to kinematic boundary conditions rather than to the regional stress field directly. Kinematic constraints provided by the Dent and neighbouring Variscan faults yield a NNW–SSE regional shortening direction in this part of the Variscan foreland.     

航天飞机成像雷达数据在库车冲断带前缘构造分析中的应用

通过新疆库车县北航天飞机TM和SIR-C/X-SAR图像的处理,利用多参数雷达图像对浅覆盖物下隐伏构造的探测能力,从雷达图像上提取研究区低序次的构造信息,以此分析左行走滑活动相关变形产生的正、负花状构造的地面特征。采用分数维分析方法,研究不同冲积物图像表面的粗糙度特征,确定了库车冲断带前缘在库车县北向西端延伸的位置。显示出多波段多极化成像雷达对新构造的识别能力,从而确定库车冲断带前缘的构造特征。     

阿尔金断裂双层花状构造的厘定

阿尔金断裂带主要经历了两阶段的构造演化,形成不同层次且具有不同特点的典型花状构造型式。宏观断层构造组合、断层擦痕产状的变化以及节理组合充分反映出晚期阶段浅部层次花状构造的存在,早期阶段中部层次花状构造由反映区域应变型式的糜棱状岩石中其它应变标志性组合的存在表现出来。结合ArAr记年与矿物对测温结果,表明前者形成于距今46Ma,是一次规模最强烈的变形叠加事件;后者由距今91～89Ma的韧性走滑运动形成,并伴有断层带内的低级变质作用(温度270～500℃,压力0.05～0.45GPa)。两阶段双层花状构造并存充分说明区域性走滑作用过程及其调节作用的多阶段性与继承性,其出现部分地调节了由印度板块和欧亚板块陆—陆碰撞过程中区域性地壳物质的向东蠕散和隆升过程。     

Differences in production and mortality of reproductive structures in two Prosopis L. (Mimosaceae) shrub species from Patagonia, Argentina

Prosopis L. pods have been proposed as a source of gum (galactomannans), with potential applications as a thickening agent in the food industry. The objective of this work was to compare, under field conditions, the production and mortality of reproductive structures in two sympatric shrub species of Prosopis: P. alpataco Phillipi and P. denudans Bentham. Our results indicate that fruit production in Prosopis denudans and P. alpataco is very low and erratic in non-irrigated lands. Although large quantities of flowers (15,000–25,000 flowers*0.40 m⁻²) can be found in one flowering season, 70–80% are shed before they reach anthesis and 20–28% are aborted between anthesis and fruit set. We conclude that the utilization of native populations of Prosopis denudans and P. alpataco for fruit production in Patagonian steppe, could not guarantee a consistent supply for the food industry.     

The Neogene Fohnsdorf Basin: basin formation and basin inversion during lateral extrusion in the Eastern Alps (Austria)

The evolution of the early/middle Miocene Fohnsdorf Basin has been studied using borehole data, reflection seismic lines, and vitrinite reflectance. The basin is located along the sinistral Mur-Mürz fault system and probably formed as an asymmetric pull-apart basin, which was subsequently modified by halfgraben tectonics, as a consequence of eastward lateral extrusion. Sedimentation started with the deposition of fluvio-deltaic sediments. Thick coal accumulated in the northwestern basin. Thereafter subsidence rates increased dramatically with the formation of a lake several hundred meters deep. The lake was filled mainly from the north with more than 1500?m of sediments showing a coarsening-upward trend due to southward prograding deltaic lobes. A sequence of more than 1000?m of boulder gravels (Blockschotter) in the southeastern part of the basin are interpreted as the upper part of a coarse-grained fan delta succession, which accumulated along a normal fault along the southern basin margin. Fan deltas reached the central basin only during the early stages of sedimentation and during the late stages of basin formation. Miocene heat flow was approximately 65–70?mW/m², which is significantly lower than in other basins along the Mur-Mürz fault system. The present-day southwestern basin margin is a recent feature, which is related to transpression along the dextral Pöls-Lavanttal fault system. It is formed by reverse faults constituting the northeastern part of a flower structure. Miocene sediments in the Feeberg valley are preserved along its southwestern part. Uplift of the central part of the flower structure was at least 2.4?km. North–south compression resulted in the deformation of the basin fill, uplift of the E/W-trending basement ridge separating the Fohnsdorf and Seckau basins, and in the erosion of 1750?m of sediments along the northern basin margin.