ALBERT

Beschreibung: Publication date: Available online 13 September 2013 Source: Geoscience Frontiers Author(s): K. Naganjaneyulu

Beschreibung: Publication date: Available online 9 June 2013 Source: Geoscience Frontiers Author(s): Yangfan Deng , Zhongjie Zhang , Weiming Fan , Marta Pérez-Gussinyé The effective elastic thickness (Te) represents the thickness of the elastic layer or the flexural rigidity of the lithosphere, the equivalent of which can be calculated from the spectral analysis of gravity and topographic data. Studies of Te have profound influence on intracontinental deformation, and coupling of the tectonic blocks. In this paper, we use the multitaper spectral estimation method to calculate the coherence between Bouguer gravity and topography data, and to obtain the Te map of South China. Through the process of correction, we discuss the relationships of Te versus heat flow, and Te versus seismicity. The results show that Te distribution of South China is affected by three factors: the original age, which controls the basic feature; the Mesozoic evolution, which affects the Te distribution; and the Neotectonic movement, which shaped the final distribution. The crust age has a positive correlation with the first-order Te distribution; thus the Yangtze Craton has a relatively higher Te (about 50 km) whereas the Te in Cathaysia block is only 10‒20km. By analysis and comparison among the tectonic models of South China, the Te distribution can be well explained using the flat-subduction model. As is typical with Neotectonics, the region with a higher heat flow is related with a lower Te. The seismicity does not have a clear relationship with Te, but the strong seismicity could cause a low Te. Seismogenic layer (Ts) has a similar trend as Te in the craton, whereas in other areas the relationship is complex. Graphical abstract

Beschreibung: Publication date: Available online 10 April 2013 Source: Geoscience Frontiers A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994–`95, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories: i) Growth related textures in the form of coarse/fine sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H 2 O or pressure or composition of the crystallizing melt; and ii) morphological texture , like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma (convection, turbulence, degassing, etc.). Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self-mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics. Graphical abstract

Beschreibung: Available online 30 March 2013 Publication year: 2013 Source: Geoscience Frontiers The Aravalli–Delhi and Satpura Mobile Belts (ADMBand SMB) and the Eastern Ghat Mobile Belt (EGMB) in India form major Proterozoic mobile belts with adjoining cratons and contemporary basins. The most convincing features of the ADMB and the SMB have been the crustal layers dipping from both sides in opposite directions, crustal thickening (∼45 km) and high density and high conductivity rocks in upper/lower crust associated with faults/thrusts. These observations indicate convergence while domal type reflectors in the lower crust suggest an extensional rifting phase. In case of the SMB, even the remnant of the subducting slab characterized by high conductive and low density slab in lithospheric mantle up to ∼120 km across the Purna–Godavari river faults has been traced which may be caused by fluids due to metamorphism. Subduction related intrusives of the SMB south of it and the ADMB west of it suggest N-S and E-W directed convergence and subduction during Meso‒Neoproterozoic convergence. The simultaneous E-W convergence between the Bundelkhand craton and Marwar craton (Western Rajasthan) across the ADMB and the N-S convergence between the Bundelkhand craton and the Bhandara and Dharwar cratons across the SMB suggest that the forces of convergence might have been in a NE-SW direction with E-W and N-S components in the two cases, respectively. This explains the arcuate shaped collision zone of the ADMB and the SMB which are connected in their western part. The Eastern Ghat Mobile Belt (EGMB) also shows signatures of E-W directed Meso‒Neoproterozoic convergence with East Antarctica similar to ADMB in north India. Foreland basins such as Vindhyan (ADMB–SMB), and Kurnool (EGMB) Supergroups of rocks were formed during this convergence. Older rocks such as Aravalli (ADMB), Mahakoshal–Bijawar (SMB), and Cuddapah (EGMB)) Supergroups of rocks with several basic/ultrabasic intrusives along these mobile belts, plausibly formed during an earlier episode of rifting during Paleo‒Mesoproterozoic period. They are highly disturbed and deformed due to subsequent Meso‒Neoproterozoic convergence. As these Paleoproterozoic basins are characterized by large scale basic/ultrabasic intrusives that are considerably wide spread, it is suggested that a plume/superplume might have existed under the Indian cratons at that time which was responsible for the breakup of these cratons. Further, the presence of older intrusives in these mobile belts suggests that there might have been some form of convergence also during Paleoproterozoic period. Graphical abstract

Beschreibung: Publication date: Available online 8 April 2013 Source: Geoscience Frontiers The Asmari Formation (a giant hydrocarbon reservoir) is a thick carbonate sequence of the Oligocene‒Miocene in the Zagros Basin, southwest of Iran. This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates. The age of the Asmari Formation in the study area is the late Oligocene (Chattian)‒early Miocene (Burdigalian). Ten microfacies are defined, characterizing a gradual shallowing upward trend; the related environments are as follows: open marine (MF 8‒10), restricted lagoon (MF 6‒7), shoal (MF 3‒5), lagoon (MF 2), and tidal flat (MF 1). Based on the environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 3‒7 are characterized by the occurrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp, influenced by wave and tidal processes. MF 8‒10, with large particles of coral and algae, represent a deeper fair weather wave base of a middle ramp setting. Graphical abstract

Beschreibung: Available online 3 April 2013 Publication year: 2013 Source: Geoscience Frontiers In this paper, we analyze lithospheric density distribution of China and surrounding regions on the basis of 30´ × 30´ gravity data and 1° × 1° P-wave velocity data. Firstly, we used the empirical equation between the density and the P-wave velocity difference as the base of the initial model of the Asian lithospheric density. Secondly, we calculated the gravity anomaly, caused by the Moho discontinuity and the sedimentary layer discontinuity, by the Parker formula. Thirdly, the gravity anomaly of the spherical harmonics with 2–40 order for the anomalous body below the lithosphere is calculated based on the model of EGM96. Finally, by using Algebra Reconstruction Techniques (ART), the inversion of 30´ × 30´ residual lithospheric Bouguer gravity anomaly caused by the lithosphere yields a rather detailed structural model. The results show that the lithospheric density distribution of China and surrounding regions has a certain connection with the tectonic structure. The density is relatively high in the Philippine Sea plate, Japan Sea, the Indian plate, the Kazakhstan shield and the Western Siberia plain, whereas the Tibetan plateau has low-density characteristics. The minimum value of density lies in the north of Philippines, in the Taiwan province and in the Ryukyu island arc. Graphical abstract