Martos, Federico E.Naipauer, MaximilianoFennell, Lucas M.Acevedo, Eliana...
19页
查看更多>>摘要：The Neogene Penitentes basin registers the earliest synorogenic infill in an inner region of the southern Central Andes, between Principal and Frontal cordilleras at 33 degrees S, which contrast with other Neogene basins that are distributed to the east, in the foreland area. In this work, we focused on the study of the first infill of the basin, the Penitentes Conglomerate, which crops out along the Aconcagua fold-and-thrust belt (Principal Cordillera). We carried out sedimentological, geochronological, and structural studies to better understand the genesis and evolution of these synorogenic deposits. We recognized the Penitentes Conglomerate at the Blanco river and the Potrero Escondido creek, located to the south of the previously established boundaries of the basin. We obtained a maximum depositional age of 15 +/- 1 Ma (weighted mean 206Pb/238 U age; n = 8; MSDWD = 4.5; error of 95% conf.) for the base of the Penitentes Conglomerate in the Potrero Escondido creek. Based on clast composition and U-Pb detrital zircon ages of the Penitentes Conglomerate base, the provenance analysis reflects the Aconcagua's fold-and-thrust belt exhumation to the west of the basin. The denudation processes that affected the Principal Cordillera generated an unroofing sequence within the Penitentes Conglomerate. In contrast, towards the top of the sequence, the Penitentes Conglomerate has sediment input derived from eastern sources, which indicates that the Frontal Cordillera was exhumed and acted as a sediment source area for the Penitentes basin by the Middle Miocene (similar to 14 Ma). In this sense, the chronology of the uplift of Principal and Frontal cordilleras agrees with the east-vergent orogenic model for the Andes. The structural analyses presented in this paper show a minimum shortening of 62% for the Aconcagua fold-and-thrust belt with an out-of-sequence deformational phase during the mid-late Miocene, after the uplift of the Frontal Cordillera.
Santos, Edgar do AmaralJelinek, Andrea RitterMachado, Joao PacificoStockli, Daniel...
18页
查看更多>>摘要：Passive margins form in response to rifting affecting a continental area. Rifting evolution is dependent on structural and rheological inheritance, generally controlling differential denudation, and deposition. The Brazilian continental margin developed over a complex basement, composed of the omgenic lithosphere of the Brasiliano-Pan-African orogenic belts (e.g., the Aracuai Orogen), and the cratonic lithosphere of the Sao Francisco Craton. In this work, we focus on the transitional zone between the warm and cold lithosphere of the northern segment of the Aracuai Orogen to the Sao Francisco Craton. This study provides the first suite of two low-temperature thermochronometers, i.e., zircon and apatite (U - Th)/He, for the region. Using this approach, we examine the main cooling events, the geodynamic forces acting upon the lithosphere, the denudation rates affecting this region since West Gondwana amalgamation, and the correlation between thermochronology and structural inheritance. Our results indicate that ZHe corrected ages range from 483.1 +/- 38.6 to 93.8 +/- 7.5 Ma and eU concentrations vary from 10.91 to 632.51 mg/g. AHe corrected ages span from 129.9 +/- 7.79 to 32.7 +/- 1.96 Ma and eU concentrations range from 5.6 to 62.8 mg/g. Both ZHe and AHe ages display a positive correlation with eU concentration. Based on this dataset, we identify three cooling episodes, constrained from Lower Devonian to Carboniferous, Triassic/Jurassic to the present day, and Late Cretaceous/Paleocene to the present day. Additionally, two reheating episodes are constrained from Middle Jurassic to Early Cretaceous and from Late Cretaceous to Paleocene. Furthermore, we analyzed lineament directions in the omgenic, cratonic, and Cenozoic sedimentary cover domains to understand how structural inheritance affects the thermochronological record. Our observations reveal that reactivation of the Brasiliano NW-SE inherited structures during continental breakup up until the Paleocene possibly kept the AHe system open, resulting in the youngest AHe ages of our data set.
查看更多>>摘要：A striking feature of the seismicity in the Ibero-Maghrebian region is a narrow band of intermediate-depth earthquakes (50 < h < 100 km) beneath the western part of the Alboran Sea, with epicenters following a NNE-SSW alignment. The origin and characteristics of this seismicity are debated, and an accurate analysis of this seismic scenario is provided despite the low to moderate magnitude of these earthquakes. In this study, we collect 20 years of seismic data from permanent and temporary installations and reprocess these data with the aid of advanced seismological techniques, including non-linear probabilistic relocation with a 3D-Earth velocity model and a probabilistic moment tensor inversion scheme, to shed new light on intermediate-depth seismicity in Southern Spain and the Alboran Sea. We relocated 238 intermediate-depth earthquakes (M >= 3) using a nonlinear probabilistic approach and a recent regional 3D tomography lithospheric velocity model for the Alboran-Betic Rif Zone. Maximum likelihood hypocenters confirm the NNE-SSW distribution in a depth range between 50 and 100 km, depicting three clusters of epicenters with a seismic gap that may be correlate to the boundary between the sunken slabs of the Iberian and African plates around Gibraltar. We simultaneously determined the focal mechanisms of 25 mb > 3.9 earthquakes using P-waves and moment tensors by fitting body-wave amplitude spectra and waveform cross-correlations. We performed an accurate resolution study by repeating the inversion using different 1-D velocity models. The results show predominant horizontal T axes with a rotation on the direction from NE-SW in southern Spain to E-W near the African coast. The distribution of intermediate-depth earthquakes and their source geometries provide new evidence of the seismotectonic complexity of the region, which is possibly controlled by the stopping or slowing down of subduction.
查看更多>>摘要：Comparable to San Andreas fault in western United States, the Tanlu fault zone (TLFZ) is a large-scale continental tectonic belt in eastern China and has played an important role controlling the regional tectonics and earthquake activity in eastern China. It is known there exists an earthquake gap in the southern segment around Suqian, Jiangsu province, where no earthquakes greater than M5.5 occurred. Fine fault zone structure could help to understand the fault activity and the potential earthquake hazards. However, only regional scale velocity model is available in this region, making it difficult to characterize detailed fault structures. In this study, we obtained local Vs model in the upper crust in this region by ambient noise tomography with a dense seismic array. For the Suqian segment, Cretaceous brittle normal faulting controlled the development of the eastern and western graben as well as the central horst between them. The graben-boundary faults are known simply as F1-F4 from east to west, and the NNE-striking fault F5 is between F1 and F2. The eastern boundary fault F1 and western boundary fault F4 separated by about 30 km are associated with intermittent high velocity anomalies in the shallow crust and are inactive. In comparison, faults F2, F5 and F3 are mainly associated with low velocity anomalies and are relatively active. These high velocity anomalies are very likely caused by the upwelling magma migrated along faults F1 and F4 in the crust, which on freezing could weld the fault zone and make it less active. Because faults F1 and F4 are hindered to move, the deformation could be transferred to nearby faults F2, F3 and F5. Our study sheds light on what controls fault activities along the TLFZ by obtaining local velocity structure in the Suqian segment.
Schiffer, ChristianJess, ScottRondenay, StephanePeace, Alexander L....
24页
查看更多>>摘要：The Labrador Sea and Baffin Bay form an extinct Palaeogene oceanic spreading system, divided by a major continental transform, the Davis Strait, with the whole region defined as the Northwest Atlantic. The Davis Strait hosts the Ungava Fault Zone and is the central structural element of the Davis Strait Large Igneous Province (DSIP) that formed broadly coeval with continental breakup to its north and south. While constraints on the crustal structure in this region primarily exist in the offshore, crustal models are limited onshore, which makes an interpretation of regional structures as well as the extent, and therefore origin of the DSIP extremely difficult to ascertain. Here, we have collected all available teleseismic data from the Northwest Atlantic margins and applied a receiver function inversion to retrieve station-wise velocity models of the crust and uppermost mantle. We integrate the outcomes with published controlled-source seismic data and regional crustal models to make inferences about the crustal structure and evolution of the Northwest Atlantic. In particular, we focused on constraining the spatial extent and origin of high velocity lower crust (HVLC), and determining whether it is generically related to the Davis Strait Igneous Province, syn-rift exhumed and serpentinised mantle, or preexisting lower crustal bodies such as metamorphosed lower crust or older serpentinised mantle rocks. The new results allow us to better spatially constrain the DSIP and show the possible spatial extent of igneous-type HVLC across Southwest Greenland, Northwest Greenland and Southeast Baffin Bay. Similarly, we are able to relate some HVLC bodies to possible fossil collision/subduction zones/terrane boundaries, and in some instances to exhumed and serpentinised mantle.
NSTL
Elsevier