Gokul, V. S.Sreejith, K. M.Rao, G. SrinivasaRadhakrishna, M....
12页
查看更多>>摘要：The Indian Ocean Geoid Low (IOGL) in the Central Indian Ocean is the largest geoid depression on the globe. Spectral decomposition of geoid anomalies reveals that a significant fraction (up to similar to 90%) of the IOGL is due to mass anomalies lying within the lower mantle (similar to > 700 km). The crustal density structure and Moho depth variations obtained from 3-D gravity inversion along with the upper mantle density structure derived from SL2013sy tomographic model are used to compute the total geoid anomaly up to 700 km depth and compare it with degree-10 residual geoid anomaly map. Comparison of these two maps necessitated the presence of relatively shallow low- density sources within the upper mantle that were not resolved in the 3-D modelling. The presence of two anomalous sources: i) low S-wave velocities at the base of the LAB (4.4 km/s) and ii) an anomalous source of Vs = -1.0% at a depth of 320-400 km within the sub-lithospheric mantle observed in the tomographic model accounted for this difference. We model the geometry of these low-density anomalous bodies using 2-D joint gravity-geoid modelling, which reveals the total contribution of density structure up to the upper mantle depths (700 km) accounts for only 10% of the IOGL whereas the remaining part is primarily caused by mass anomalies in the lower mantle probably related to high-density subducted slabs or plume sources at the core-mantle boundary as proposed by earlier studies.
查看更多>>摘要：The NE-trending Liaodong Bay Subbasin (LDBS), a subunit of the Bohai Bay Basin (BBB), developed along the Tan-Lu Fault Zone (TLFZ) in eastern China. The LDBS is controlled by both extensional and dextral strike-slip fault systems and has an episodic evolutionary history, leading to a poor understanding of its tectonic origin. In this paper, through interpretations of seismic data and other geological and geophysical data, four best-fit finite element models were generated to reveal the tectonic development of the LDBS and the whole BBB. The deformation features predicted by the modelling results are consistent with the geological evidence. The modelling results revealed that the extension directions of the LDBS changed from WNW-ESE during the Paleocene-early Eocene, to NW-SE during the middle-late Eocene and then to NWN-SES or nearly N-S in the Oligocene and Miocene. The changes in the extension direction resulted in a strike-slip transition of the TLFZ in approximately the middle-late Eocene, from normal to dextral transtensional, and transformed the LDBS and the whole BBB from an extensional basin into a dextral transtensional basin. This transformation was likely triggered by the kinematic adjustment of the Pacific Plate from NNW to WNW in the middle-late Eocene, but was maintained and enhanced by the Indian-Asian collision during the rest of the Cenozoic.
查看更多>>摘要：Southern Africa is an amalgamation of a distinct Archean core, several Proterozoic mobile belts, and large igneous provinces, making it an ideal natural laboratory for studying Precambrian crustal evolution and deformation. Here we present a new radially anisotropic shear-velocity model of the crust and uppermost mantle beneath Southern Africa using Rayleigh- and Love-wave ambient noise tomography from multiple seismic networks. In the upper and middle crust, the distribution of the isotropic shear velocity correlates well with known surface geology. However, in the lower crust there is no systematic lateral variation of shear velocity between the Archean and Proterozoic terranes, which is likely due to the intensive modifications of Precambrian crust by several later thermo-tectonic events through processes such as lower crustal flow. The strong positive radial anisotropy (V-SH > V-SV) in the lower crust, when combined with weak azimuthal anisotropy imaged previously, suggests a complex flow pattern, the directions of which likely varied on local-scale due to inhomogeneous shortening or extension during the multiple post-cratonization thermo-tectonic events.
查看更多>>摘要：As an active intracontinental omgenic belt within the far field influence of the India-Eurasia collision, the Tien Shan is a natural laboratory to study the mechanisms of the large-scale mountain building. In this study, we image crustal seismic structures beneath the central Tien Shan using the H-kappa-c method with the harmonic corrections on Ps and its crustal multiples (PpPs, PpSs + PsPs) in P-wave receiver functions (RFs). The RFs are calculated from three-component seismograms recorded by 43 broadband stations located in central Tien Shan and surrounding areas. The robust and high-resolution images of the crustal thickness (H) and average Vp/Vs ratio (kappa) are finally obtained. From our observations, the crustal thickness beneath the central Tien Shan is larger (50- 65 km) than those beneath the Kazakh Shield (similar to 45 km) and Tarim Basin (similar to 42 km). The x image denotes a general distribution of kappa which is higher than 1.73 in most parts of the central Tien Shan, as well as the margins of the Kazakh Shield and Tarim Basin, while lower than 1.73 only in some sporadic areas of this orogenic belt. Our seismic results suggest the complex intracontinental collision with the inhomogeneous crustal thickening in the mountain building. Moreover, the kappa image implies the partial melting within the crust beneath the central Tien Shan. Combining with previous seismic studies, we infer that the magmatic intrusion of the hot upwelling mantle materials induces the partial melts within the crust, and also contributes to the rejuvenation of the Tien Shan orogenic belt.
查看更多>>摘要：We applied the modified centroid method with a fractal magnetization model on a new magnetic anomaly grid for the Circum-Arctic area (CAMP) to obtain the first high-resolution Arctic Curie-point model and to infer geothermal structure. The shallowest Curie-point depths, found in the oceanic domain, reveal the cooling pattern of oceanic lithosphere and asymmetric mantle thermal activities across spreading ridges. The Cretaceous High Arctic large igneous province (HALIP), the most prominent magmatic feature in the Arctic, shows slightly lower heat flow and higher thermal conductivities than the surrounding area, indicating a complete cooling of the HALIP, but HALIP also has shallow Curie-point depths. We attribute this contradiction to the high titanium content of HALIP that lowers the Curie temperature. Therefore, Curie-point depths constrain well the boundary of the HALIP. On the Arctic continental shelves, the largest Curie-point depths are found in deep sedimentary basins, where lower crust eclogitization was previously interpreted. Furthermore, we found that this positive correlation between large Curie-point depths and large sediment thickness is prevalent for global continental margin sedimentary basins.
Yildirim, CengizAksoy, M. ErsenOzcan, OrkanIsiler, Mehmet...
18页
查看更多>>摘要：The Gulf of Gokova is one of the earthquake-prone areas in the Aegean Sea and southwestern Turkey. The paleoseismology of the region is not well known because of the lack of robust field data. In this study, we focused on marine tidal notches as geomorphic markers of modern and paleoseismic deformations. Our geomorphic surveys suggest that the 20 July 2017 Bodrum-Kos Earthquake coseismically uplifted the Karaada Islet at the Turkish coast. We also provide new observations for the entire coastal area of the Gulf of Gokova. The six well preserved uplifted notch levels up to 1.5 m a.s.l. at the east of Oren town are geomorphic markers of offshore earthquakes along the northern shores. Radiocarbon dating C-14 results suggest that the last 0.5 m of this uplift occurred in the last 2314 +/- 32 years. The four well-preserved marine tidal notches up to 1.2 m a.s.l. indicate the earthquake-related uplift along the southern shores. There are also submerged shorelines along the southern shores at 1 m and 3-4 m below sea level as geomorphic markers of relative sea-level change. The evidence of a longer-term deformation is the presence of an uplifted wave-cut marine terrace on the southern shore. We do not have age data, but the inner edge elevation of the terrace is 238 m above modern sea level. In this study, we reveal that the shores of the Gulf of Gokova have been uplifting since the Pleistocene and Holocene, with a high probability of large magnitude offshore earthquakes occurring on normal faults very close to the modern shoreline.
查看更多>>摘要：SKS wave splitting measurements revealed strong and complex seismic anisotropy in the upper mantle beneath the southeastern Tibetan Plateau. To better understand lithospheric deformation and upper mantle anisotropy observed in this region, we performed studies on microstructures, seismic anisotropy and chemical compositions of the mantle peridotite xenoliths collected from Maguan, Yunnan Province, in the SE Tibetan Plateau. The mantle xenoliths show two types of olivine crystal preferred orientation (CPO), AG-type and A-type. AG-type fabric is characterized by a concentration of [010]-axis normal to the foliation and a large circle girdle of the [100] and [001] axes in foliation. A-type fabric shows point concentrations of [100] and [010] axes subparallel to lineation and subnormal to foliation, respectively. Orthopyroxene and clinopyroxene align their [001]-axis sub-parallel to the [100]-axis of olivine. Seismic anisotropy calculated from the fabric of xenoliths displays moderate to strong polarization anisotropy (AV(s)) ranging from 3.1% to 7.0%, with 4.6% on average. Based on the seismic properties of xenoliths, we propose that, in SE Tibetan Plateau (south of 26 degrees N), the SKS wave splitting is attributed to melt-enhanced anisotropy with a vertical structural frame lithosphere. Under this structural configuration, the large delay time could be expected with the fast wave polarization direction (FPD) in E-W direction. Our study also supports the model of double anisotmpic layers in this area. The fast orientation of lower layer caused by lithospheric mantle anisotropy is in E-W direction, while the upper one with the NNW-SSE FPD is related to the frozen anisotropy in the middle-lower crust.
Mediato, Jose F.Ramos, AdriaGarcia-Senz, JesusPedrera, Antonio...
21页
查看更多>>摘要：Underground gas storage is one of the solutions required for reducing CO2 emissions and ensure the transition to a renewable power supply. The Hontomin pilot-plant in N-Spain is a well-studied CO2 facility located in the Burgalesa Platform, a fold belt in the Southern Basque-Cantabrian Basin. Previous works agree that crustal extension and evaporite migration controlled the subsidence in the area. The discrepancies lie in the salt expulsion models proposed during syn-rift and post-rift stages and the basin deformation during Cenozoic contraction. The models range from thin-skinned tectonics, basement-involved thrusting, strike-slip faulting, and interference between thick- and thin-skinned thrusting with lateral extrusion. There is multiple working hypothesis often with contradictory predictions of the underground structure. Understanding these structural styles is critical for identify the main salt structures suitable for gas storage in the Burgalesa Platform. We integrate multidisciplinary data from 2D seismic to wellbore, gravity and field data, allowing us to construct three restored cross-sections that illustrate the process of progradational loading and salt expulsion towards the SW during the Early Cretaceous, which led to the development of the Hontomin and other trap structures within the salt overburden. Differential loading occurred diachronously along strike during the Cenozoic, younging to the SE by evacuation of the remaining salt, which caused diapirism and salt welding. We found that most of the structures in the cover were formed by salt migration, whereas Cenozoic shortening caused the rejuvenation of salt-structures and local diapir squeezing. Shortening in the basement is consumed in the frontal thrust that overrides the Duero foreland and in the partial reactivation of the former Mesozoic transfer faults as transpressional faults. The results of this work have implications for a further understanding of the tectonic evolution of the external area of rift structures, and as tectonic analogues in other salt-bearing basins.
查看更多>>摘要：The Gulf of Mexico is an economically important basin with more than a century-long history of hydrocarbon exploration. However, the opening of the basin remains debated for two reasons: 1) the quality of data does not allow for reliable interpretations of crustal features beneath thick and complex overburden, and 2) most industry well and geophysical data are proprietary. The last concerted effort by industry and academia to summarize the state of knowledge regarding the Gulf of Mexico's formation was three decades ago and resulted in publication of a major volume as part of the Decade of North American Geology (DNAG). This paper reviews the key, publicly available, recently published geophysical datasets and geological observations that constrain the basin's tectonic history. We compare and contrast published tectonic models and formulate remaining controversies about the basin. These relate to tectonic affiliation of Triassic redbeds (early syn-rift vs. precursor basin[s]), the timing of seafloor spreading vs. salt deposition, the nature of breakup (magma-rich vs. magma-poor), and remaining ambiguities in restoring crustal blocks to their pre-rift positions. We then speculate on the datasets that can help resolve these controversies. We conclude that continued collaborative industry and academia partnerships are crucial for advancing our understanding of how the Gulf of Mexico formed.
查看更多>>摘要：Geological observations have revealed a rapid evolution and obvious east-west differential evolution in the North Sulawesi subduction zone. The Celebes Sea plate has inserted itself under the north arm of Sulawesi Islands, which has simultaneously rotated clockwise. The rotation of the north arm of the Sulawesi Islands might be critical in facilitating tectonic processes, such as the slab subduction and rollback of the Celebes Sea plate. For the east-west differences along the North Sulawesi subduction zone, a numerical model with the convergence rate of the plates as the basic variable is established to quantitatively describe the evolution process of the North Sulawesi subduction zone. Our results reproduced the east-west differences of the subducting Celebes Sea plate, showing a shallow-deep-shallow subduction style. We propose that the variable velocity ratio of the overriding plate to the subducting slab could be the principal reason for the differential subduction along the strike of the North Sulawesi subduction zone. We conclude that the residual slab and the rate of the eastern continental plate limit the downward movement of the subducted slabs of the eastern Sulawesi. Furthermore, the reason for the shorter subducted slab at the extreme western Sulawesi is the fact that subduction occurs outside the rotation radius. Moreover, the widespread extension at the western Sulawesi has a limited correlation with the clockwise rotation.
NSTL
Elsevier