Giri, YellalacheruvuRadhakrishna, MunukutlaBetts, Peter GrahamBiswal, Tapas Kumar...
17页
查看更多>>摘要：We present a joint interpretation of the aeromagnetic and gravity anomaly datasets of the Precambrian Eastern Ghats Mobile Belt, eastern India, to delineate the detailed crustal architecture, identify faults and shear zones, as well as boundaries of different terranes throughout this belt. We use geological constrained analysis of the distinct aeromagnetic anomaly signatures to re-interpret the extent of the Jeypore, Krishna, Eastern Ghats, and Rengali Provinces. Forward modelling of paired gravity anomalies and an increase in magnetic response along the craton-mobile belt boundary reveal that it is dominated by high-density and highly magnetic granulite facies rocks that overthrust the low-density and low magnetic older cratonic gneissic rocks along the deep crustal faults, suggesting the Eastern Ghats Mobile Belt terranes are allochthonous in nature. Two high magnetic anomaly belts in the Krishna and Eastern Ghats Provinces define a terrane-scale fold (orocline). The younger normal faults of Godavari Basin overprint the charnockitic belt in the southern part of the Eastern Ghats Province, suggesting that these high magnetic belts pre-date the Pan-African Orogeny. The boundary between the Eastern Ghats Province and Krishna Province is identified by the change in anomalies in magnetic and gravity maps. The Sileru Shear Zone and Kerajung Shear Zone separates the Eastern Ghats Province-Jeypore Province and Eastern Ghats Province-Rengali Province respectively, are characterized by a sharp change in magnetic anomalies. The intraprovince Nagavali-Vamsadhara Shear Zone and Mahanadi Shear Zone are characterized by subdued magnetic anomalies. Inversion of the regional gravity anomalies revealed that the Moho is slightly shallower (similar to 5 km) beneath the Eastern Ghats Mobile Belt compared to the neighbouring Cratons.
查看更多>>摘要：We review in this paper the major late Mesozoic contractional deformation in North and NE China and establish the tempo-spatial distribution pattern of Jurassic-Cretaceous magmatism, with the aim at clarifying its link with evolving multi-plate convergent geodynamics in NE Asia. We recognize two major changes in tectonic regime, one occurring at-170 Ma, which marks the tectonic switch from extensional to compressional regimes, while another at-135 Ma which manifests the change from compressional to extensional settings. Accordingly, Jurassic-Cretaceous magmatism migrated from the marginal zones in-200-170 Ma to the continental interior in 170-135 Ma and then was followed by Mid-Cretaceous (135-120 Ma) magmatic flare-up in the continental interior, which migrated progressively eastward since-120 Ma. Based on these observations, we make a division of three tectonic stages and discuss their plate geodynamic setting. (1) The early stage in 200-170 Ma was dominantly under extensional setting with A-type granitoids and bi-modal volcanism occurring along the eastern and northern marginal zones. (2) The middle stage in 170-135 Ma was manifested by significant multidirectional crustal shortening and rejuvenation of the ancient orogenic belts, as distant response to multi-plate convergence along the East Asia continental margins. (3) The late stage was manifested first by a thermal surge in 135-120 Ma with the formation of extensional structures and rift basins in the continental interior, then followed by alternation of tectonic compression and extension, related to the effect of paleo-Pacific slab subduction. We propose that the thickening acquired during the middle tectonic stage and subsequent lithospheric thinning in the late stage triggered large-scale crustal melting, episodic magmatism and associated metallogenic outbreak in North and NE China.
查看更多>>摘要：To understand the stress controls on the occurrence of a multi-fault rupture, we estimated the crustal stress between April 2013 to December 2018, i.e., before and after the Mw7.8 Kaiko??ura earthquake that occurred in New Zealand on 13 November 2016. We used both the focal mechanism solutions from the temporary seismic networks and the GeoNet moment tensor solutions and selected the solutions that differed significantly from the mainshock fault planes and rakes. Then, we performed stress tensor inversions for the selected focal mechanism solutions. Using the stress tensor inversion results, we also calculated the slip tendency. Prior to the Kaiko??ura earthquake, the stress regime was the strike-slip type, and the maximum eigenvalue of the stress tensor (??1) was oriented WNW???ESE. The stress field orientation did not change significantly after the earthquake. This suggests that the stress change during the Kaiko??ura earthquake was too small to alter the stress orientations, implying that there may have been large differential stress prior to the Kaiko??ura earthquake. However, the average stress ratio in different clusters changed in two different patterns after the earthquake, suggesting possible changes in the magnitude of different components of the stress tensor, or of pore pressure in different regions. A high slip tendency was observed at the hypocentre, while a low slip tendency was observed at the northern end of the Kaiko??ura earthquake faults. This may suggest that the stress orientation and the stress ratio controlled the initiation and the end of the multi-fault rupture. These results corroborate previous fault propagation models.
查看更多>>摘要：The Mongolian Plateau, as an important geological unit of the Central Asian Orogenic Belt, has experienced extensive deformations in multiple periods since the Proterozoic. In this study, we measured SKS splitting from 114 portable stations to reveal the complicated deformation of the upper mantle under western Mongolia. The predominant NW-SE-oriented fast polarization directions (FPDs) are consistent with lithospheric deformation and asthenospheric flow to the first order. However, the FPDs of the stations close to the Siberian Craton are more parallel to the cratonic margin than those departing from the craton. It indicates that the shape of the rigid Siberian Craton may determine the extent of the present lithospheric deformation and cause the deflection of the asthenospheric flow. Large SKS splitting delay times are distributed in the Hovsgol rift and Gobi-Altai range, implying superimposed past and present lithospheric anisotropy, and the asthenospheric anisotropy as well under the Hovsgol rift. Small delay times in the Hangai Dome indicate the asthenospheric upwelling which causes the uplift of the dome.
NSTL
Elsevier