查看更多>>摘要：In foreland thrust systems, the complex structural geometry creates greater difficulties in constraining the seismotectonics of moderate magnitude earthquakes without pronounced surface ruptures and in assessing future seismic risk. The 2013 M 5.1 Urumqi earthquake was a moderate event that occurred in the Urumqi foreland thrust system. Based on surface investigations, geological mapping, and interpretations of deep seismic reflection profiles, we suggest that the Urumqi foreland thrust belt is a typical active wedge thrust system. Two connected fault segments of the gently south-dipping blind fault ramp and the north-dipping Xishan back-thrust fault merge at a depth of similar to 11 km and bound the wedge-shaped fault block. Analyses of the focal mechanism and aftershock distribution indicate that the seismogenic fault responsible for the M 5.1 Urumqi event is the south-dipping Xishan fault ramp with a dip angle of similar to 10-30 degrees, which highlights the potential seismic hazards of the unruptured north-dipping Xishan back-thrust ramp. The four fault branches on the hanging wall of the Xishan fault are interpreted as flexural-slip thrusts. Our results indicate that multiple surface ruptures over a 6 km-wide area may form if a large earthquake occurs along the Xishan fault system.
查看更多>>摘要：The motivation for this work was to model the crustal thickness, and the geometry of the Mohoroyieie (Moho) discontinuity, the crust-upper mantle boundary around the Japanese archipelago. The western Pacific Ocean is one of the most eminent subduction zones in the world. The subduction zone complexity is due to alteration within the geometry of the stagnant slab. We compiled a three-dimensional density distribution model for subduction plates around the Japan Islands, and estimated the depth to Moho using the constrained non-linear inversion of gravity data derived from the latest Gravity field and Ocean Circulation Explorer, or GOCE, model known as GOCO06s. The study had three steps, starting with the data corrections followed by the inversion, and ending with the modeling and comparing of the estimated results with previous models and studies. In this study, we used available receiver function results, seismic tomography models, global crustal thickness, and geological and tectonic information as constraints. The model estimated the crustal thickness, surface geometry of the Moho, and geometry of the stagnant slab in the Kuril Trench, Japan Trench, Nankai Trough, and Izu-Bonin Trough. In gravity inversion, we used 34 km and 600 kg m(-3) as the Moho depth reference and density contrast, respectively. Results showed that the crustal thickness ranged from 14 to 43 km with a - 0.78 mean misfit for Moho depths derived from seismic P-wave analysis. The calculated gravity data had a 0.16 mGal misfit with the observed data. The normalized analytical signal helped to sharply delineate the different plates and their edges. Three cross-sections were conducted to model the stagnant slab along the subduction zone of the Eastern Eurasian plate, western Pacific plate, Okhotsk plate, and Philippine Sea plate. The eastern area of the entire region (Pacific plate) had a low crust thickness and high density compared to the western area (Eurasian plate), which had a high crust thickness and low density.
查看更多>>摘要：We combine structural and microstructural data with stable and clumped isotopes of syntectonic calcite veins or slickenfibers of five thrust and four strike-slip faults to characterize the paleofluid circulation in the Jura foldand-thrust belt, eastern France. Syn-tectonic fluid circulation occurred along high permeability networks of breccias, foliated fault rocks, and discrete fault surfaces. At the regional scale, fluid circulation was dominated by cold meteoric fluids that infiltrated downward along both thrust and strike-slip faults, with various degrees of interaction with the carbonate host rocks. Fault-related mineralizations precipitated from fluids with delta O-18 values between -0.8%o and - 7.8 parts per thousand (V-SMOW) at temperatures between 8 degrees C and 54 degrees C. The delta O-18 values of the paleofluids partly overlap those of modern meteoric waters of the region. The calcite mineralizations yielding the highest calculated delta O-18 paleofluid values are also the warmest ones and those with the heaviest carbon isotope signal, indicating strong host rock buffering and fluid heating at depth. A contribution of deep fluids from PermoTriassic rocks cannot be excluded, but not likely. This could be related to the presence of Middle Jurassic Opalinus Clay Formation, which acted as a regional low-permeability barrier in the sedimentary succession. This can create two different fluid circulation systems characterized by warm and partly basement-derived fluids and by cold meteoric fluids, respectively, below and above the Middle Jurassic Opalinus Clay Formation. Results from this study can be used for modeling fluid circulation at the regional scale in carbonate-dominant foreland fold-and-thrust belts elsewhere in the world.
查看更多>>摘要：This paper reports new whole-rock major- and trace-element and zircon U-Pb and Hf-O isotopic data for Early Cretaceous granitic rocks on Liaodong Peninsula, NE China, with the aim of constraining continental reworking in the northeastern North China Craton. On the basis of SiO2, MgO, and Sr contents and Sr/Y values, the rocks can be divided into three groups. The low-Mg adakitic rocks show zircon U-Pb ages of (134-120 Ma), and high SiO2 (67.11-71.14 wt%) and low MgO (0.53-0.62 wt%) contents, and high Sr (531-1108 ppm) contents, Sr/Y (29.3-132) ratios, with enriched Sr-Nd-Hf-O isotopic compositions, indicating an origin of thickened lower mafic crust. The high-Mg adakitic rocks show ages of (126-114 Ma) and are characterized by low SiO2 (53.11-63.88 wt%) and high MgO (2.07-8.93 wt%) contents, and high Sr (391-1041 ppm) contents, Sr/Y (23.9-64.1) ratios, with relatively depleted Sr-Nd-Hf-O isotopic compositions, suggesting that they were derived from partial melting of delaminated lower mafic crust. The normal granitic rocks show ages of (127-121 Ma) and high SiO2 (71.65-77.22 wt%) and low MgO (0.10-0.51 wt%) and Sr (12.1-309 ppm) contents, Sr/Y (0.89-24.5) ratios, with relatively depleted Sr-Nd-Hf-O isotopic compositions, suggesting an origin from lower mafic crust with normal crustal thickness. These constraints, combined with the regional occurrence of A-type granites, bimodal igneous rocks, and metamorphic core complexes, as well as the regional distribution of Mesozoic granitic rocks displaying a younging trend from southeast to northwest for the Jurassic rocks but a reverse trend for the Cretaceous rocks, recorded the roll-back of the Paleo-Pacific plate towards the Eurasian continental margin.
查看更多>>摘要：The Balearic Promontory (Spain) is of key importance to understand the tectonic kinematics of the westernmost Mediterranean, because its continued marine sedimentation has recorded the contrasting effects expected from competing geodynamic models proposed for the region. Near the center of this promontory, between the islands of Mallorca and Ibiza, the Miocene to Pleistocene stratigraphy of the Central Mallorca Depression presents an ideal record of the tectonic deformation that has received only limited attention. We use a widespread dataset of 2D seismic reflection profiles to identify, interpret and map the main prominent reflectors and extrapolate the thickness of the pre-Messinian and Pliocene-Quaternary sedimentary units. We then quantify the timing and style of deformation related to the various fault systems. Our results reveal for the first time a series of aligned small depressions bounded by extensional and strike-slip faults and filled with Plio-Quaternary sediment, perfectly aligned with the sub-basins of the onshore Mallorca Graben. A subsidence analysis confirms this correlation. We identify non-cylindrical deformation within the Plio-Quaternary unit that is remarkably similar to that observed onshore, suggesting continuous fault zones from the Central Mallorca Depression to Mallorca Island. We interpret an intra-PQ unconformity as the marker of a transition from extensional to strike-slip tectonic regime. The strikeslip stage is represented by both transpressional and transtensional structures, interpreted as restraining/releasing bends respectively and step overs along the faults. We show that these offshore faults in the Central Mallorca Depression overlap well with seismic epicenters and suggest major active strike-slip corridors that have an onshore continuity both until eastern Mallorca and in the southwestern Ibiza margin. The role of previous tectonic inherited structures (rifting, Betic thrusts, post-omgenic collapse) on the deformation reported here is discussed and we propose a tentative sketch that integrates our results in a Miocene to Present-day evolution at regional scale.
NSTL
Elsevier