Crustal velocity inhomogeneities along the Hirapur–Mandla profile, central India and its tectonic implications

Wide-angle seismic and gravity data across the Narmada-Son lineament (NSL) in central India are analyzed to determine crustal structure, velocity inhomogeneities and hence constrain the tectonics of the lineament. We present the 2-D crustal velocity structure from deep wide-angle reflection data by using a ray-trace inverse approach. The main result of the study is the delineation of fault-bounded horst raised to a subsurface depth (1.5 km) and the Moho upwarp beneath the NSL. The crust below the basement consists of three layers with velocities of 6.45–6.7, 6.2–6.5 and 6.7–6.95 km/s and interface depths of about 5.5–8.7, 14–17 and 18–23 km along the profile. The low-velocity (6.2–6.5 km/s) layer goes up to a depth of 5 km and becomes the thickest part (13 km), while the overlying high-velocity (6.45–6.7 km/s) layer becomes the thinnest (3 km) and upper boundary lies at a depth of 1.5 km beneath the NSL. The overall uncertainties of various velocity and boundary nodes are of the order of ±0.12 km/s and ±1.40 km, respectively. The up-lifted crustal block and the up-warping Moho beneath the NSL indicate that the north and south faults bounding the NSL are deeply penetrated through which mafic materials from upper mantle have been intruded into the upper crust. Gravity modeling was also undertaken to assess the seismically derived crustal features and to fill the seismic data gap. The lateral and vertical heterogeneous nature of the structure and velocity inhomogeneities in the crust cause instability to the crustal blocks and played an important role in reactivation of the Narmada south fault during the 1997 Jabalpur earthquake.     

Conflicting drainage patterns in the Matera Horst Area,southern Italy

The Matera Horst (“Murgia materana”) is included in the Apulian plateau, basically formed by Mesozoic shallow-water carbonates. The zone is located in a present-day temperate belt and form a flat-topped morphostructural large element inside the foreland area of the southern Apennines. This horst is bordered by high-angle faults and surrounded by downthrown blocks covered by Plio-Quaternary marine and alluvial sediments. The structural high experienced several morphological cycles from Miocene to Quaternary. In particular, three evolutionary stages can be recognized at least. The first stage is currently represented by relics of a flat erosional landscape at the top of the relieves. The second one is testified by gentle slopes with wide glacis at the foothills, locally covered by coarse waste deposits. During the third stage a series of marine terraces formed and a drainage system developed creating both bland valleys and well-defined channels and gorges. The latter streams deeply carve the Cretaceous limestone of the Matera Horst for they represent the morphological response to the tectonic uplift of the area and clearly post-date the former features. Since the fluvial net took place on Pleistocene covers, later widely eroded, it is possible to conclude that the major part of the Matera Horst drainage system represents a good example of superimposition. However, low order streams and segments of major rivers appear to be structurally controlled, as suggested by comparison with the fracture system. Further, also open synclines and gently steeped flexures may locally exert a driving control on minor streams. These apparently conflicting genetic hypotheses can be explained by the role of exhumation of inherited structures of the bedrock in add to a constant interplay between tectonics, erosion and drainage evolution during Quaternary times.     

罗北凹地液体钾盐矿远景区“同源不同期”成矿模式分析

罗北凹地液体钾矿床位于新疆罗布泊地区北部,是一个大型的综合性盐类矿床。对矿区两处"成矿远景区"进行专门研究,从其与相邻地带的地层接触关系、水文地质和氢氧同位素条件分析,指出此区具备与罗北凹地相似的液体钾矿成矿条件,仅地层时代不同期,与矿体边界及周边湖岸阶地形成一种地垒模式,为指导在本地区或其它类似地区寻找新的不同时期、相同成矿条件的成矿带提出一种成矿模式。