Cabrita, Dina I. G.Faleiros, Frederico M.Ribeiro, Bruno, VMenegon, Luca...
16页
查看更多>>摘要：Crustal-scale shear zones are key structures in orogenic belts linked to the assembly of West Gondwana. The Cubatao Shear Zone (CSZ) represents a significant segment of a crustal-scale transcurrent shear zone system that cuts Paleoproterozoic to Neoproterozoic units in the Ribeira Belt (SE Brazil). Despite its tectonic importance, the relationship between transcurrent deformation and orogenesis is still controversial. This work aims to understand this relationship by integrating the transcurrent deformation history of the CSZ with regional orogenic processes through structural analyses, phase-equilibria modelling, and zircon and apatite U-Pb-REE analyses. The results indicate that the CSZ developed within a transpressional setting with a dominant subhorizontal stretching lineation at medium-temperature conditions of 460-520 degrees C and 4.5-9.5 kbar, consistent with quartz recrystallisation microstructures indicative of subgrain rotation recrystallisation. Igneous-type apatite from the mylonites of the CSZ record ages of ca. 610-570 Ma, which are interpreted as reset ages due to ductile deformation at medium-temperature conditions. Zircon U-Pb geochronology indicates that mylonites are sourced from the Juquin Granite and the Atuba Complex. The CSZ activity is coeval with the main period of activity of other ductile shear zones from the Ribeira Belt, as indicated by available geochronological data. This age interval coincides with the main period of other regional shear zones activity, voluminous granitic magmatism, regional metamorphism and convergence of the cratons surrounding the Ribeira Belt, indicating active participation of the transcurrent shear zones in the orogenic processes that built up West Gondwana.
查看更多>>摘要：Most rifts and rifted margins around the world developed on former omgens. This implies that the pre-rift lithospheric configuration is heterogeneous in most cases. Here we investigate how collision inheritance in the form of inherited weak thrusts, long-term thermal weakening, compositional changes, and orogenic collapse, could have played into the spatio-temporal evolution and final architecture of rifted margins. We present interpretations of dynamic numerical experiments, including constraints representative of the North Atlantic Mid-Norwegian rift system phases of continental collision, omgenic collapse, and extension, and compare these to interpretations of seismic reflection profiles. The experiments form rifted margins characterized by basement structures and sedimentary geometries very similar to the More and Wring rifted margins - with onshore collapse-related basins, extensively deformed continental crust with detachments, shear zones, core complexes, rotated thrusts and an offshore succession of distinct structural domains (proximal, necking, hyperextension, exhumation, and outer). Although extensional models developed on homogeneous lithosphere are a good approximation of rifted margin architecture, our results suggest that models that consider pre-rift orogenic inheritance tend to reproduce more accurately the geometries observed in our natural example.
Sueoka, ShigeruKobayashi, YumiFukuda, ShomaKohn, Barry P....
17页
查看更多>>摘要：The South Fossa Magna region, central Japan, has been an active collision zone between the Honshu Arc and the Izu-Bonin Arc since the middle Miocene and provides an excellent setting for reconstructing the earliest stages of continent formation. Multi-system geo-thermochronometry was applied to different domains of the South Fossa Magna region, together with some previously published data, to reveal mountain formation processes, i.e., vertical crustal movements. Nine granitic samples yielded zircon U-Pb ages of 10.2-5.8 Ma (n = 2), apatite (U-Th)/He (AHe) ages of 42.8-2.6 Ma (n = 7), and apatite fission-track (AFT) ages of 44.1-3.0 Ma (n = 9). Thermal history inversion modeling based on the AHe and AFT data suggests rapid cooling events confined within the study region at similar to 6-2 Ma. The Kanto Mountains may have undergone a domal uplift in association with their collision with the Tanzawa Block at similar to 5 Ma. However, this uplift may have slowed down following the southward migration of the plate boundary and late Pliocene termination of the Tanzawa collision against Honshu Island. The Minobu Mountains and adjacent mountains may have been uplifted when motion of the Philippine Sea plate changed from northward to northwestward at similar to 3 Ma. Therefore, mountain formation in the South Fossa Magna region was mainly controlled by collisions of the Tanzawa and Izu Blocks and motional change of the Philippine Sea plate. Earlier collisions of the Kushigatayama Block at similar to 13 Ma and Misaka Block at similar to 10 Ma appear to have had little effect on mountain formation. Together with a clockwise rotation of the Kanto Mountains at 12-6 Ma, these observations suggest that horizontal deformation predominated during the earlier stage of arc-arc collision, and vertical movements due to buoyancy of the accreted crust resulting from crustal shortening and thickening developed at a later stage.
查看更多>>摘要：This paper presents a 230-km long refraction/wide-angle reflection profile that was acquired in the southern Baltic Sea across the Teisseyre-Tornquist Zone (TTZ), the boundary between the East European Craton (EEC) and the West European Platform (WEP). This profile is nearly parallel to the western Polish coast, halfway between Poland and the Danish island of Bornholm. The data acquisition was conducted with 15 ocean bottom seismometers (OBS) and 2 land stations. We applied the trial-and-error iterative ray-tracing technique using all identified seismic phases to derive crustal models by minimizing misfit between calculated and observed P-wave travel-times for individual layers. Final velocity model was further verified by forward potential field modelling, testing various P-wave velocity (V-p) to density relationships. The Moho boundary was inferred at 33-38 km depth, deepening towards the EEC, with the local similar to 3 km rise in a 40-km-wide zone north of the Caledonian Deformation Front, corresponding to the elevated middle-crust velocities V-p > 6.5 km/s. The lower and middle crust are mostly continuous along the BalTec profile with only minor perturbations between the EEC and WEP. Nevertheless, the thickness of these crustal layers is poorly constrained by seismic data along the SW section of the profile. In contrast, the upper crust and sedimentary cover can be subdivided into three domains, corresponding, from the NE to SW, to the EEC, TTZ and WEP, respectively. The EEC is characterised by the flat top of the basement, uniformly inclined towards the SW. The TTZ shows rapid thinning of cratonic upper crust and thickening of sedimentary layer. The WEP reveals, despite limited seismic coverage, a 13-km thick sedimentary overburden. The lateral changes of seismic structure within the upper crust and sedimentary cover along the BalTec profile can be attributed to protracted phases of late Palaeozoic-Mesozoic extension punctuated by the Carboniferous and Late Cretaceous inversion phases.
查看更多>>摘要：New petrostructural data are presented from the southeastern Quadrilatero Ferrifero, a distinct polyorogenic domain of the Sao Francisco Craton characterized by granite-gneiss domes and keel structures. The Minas Supergroup of Siderian age that hosts a huge volume of ferriferous sediments was deposited on the flat and eroded surface of the Archean basement. The domes of Archean gneisses and granites represent semi-rigid extrusions around which the Minas Supergroup accumulated in deep synclines with common triple junctions. This study focuses first on the petro-structural context of low-pressure thermal aureoles observed towards the dome margins. Pressure-temperature estimates on these mineral assemblages indicate nearly static burial to >= 10 km depths of the Minas Supergroup cover, followed by decompression and heating during the intrusion of pegmatites and granitoids of late Rhyacian age in basement and cover. The Archean basement and the thermal aureoles were severely overprinted by synkinematic greenschist facies metamorphism portrayed by chloritoid, chlorite, pyrophyllite, kyanite, phengitic mica and secondary biotite. This deep greenschist facies metamorphism (T ca. 420 degrees C and P = 0.4 to 0.45 GPa) is regionally observed in all units from the domes and the keels ranging in age from Archean to Ediacaran. It is concluded that this major tectono-metamorphic event relates to tectonic burial of the southern Quadrilatero Ferrifero below the west-verging nappes of the Aracuai belt during the Early Paleozoic, as documented by 40Ar/39Ar ages of 490-485 Ma obtained on syn-kinematic metamorphic micas [Chauvet et al., 2001]. It is proposed that building up of the dome and keel tectonic style is first a consequence of the high-density contrast estimated around 0.5 g/cm(3) between the crystalline basement and the Minas Supergroup, the final architecture being achieved during the Cambro-Ordovician stage of the E-W Late Neoproterozoic collision.
查看更多>>摘要：The NNW-SSE trending Sierra Palomera fault is characterized as an active, nearly pure extensional fault with mean transport direction towards N230 degrees E, consistent with the ENE-WSW extension trajectories of the recent to present-day regional stress field. Its macrostructure is described from surface geology and magnetometric and electromagnetic surveys, which have allowed identifying two subsidiary, nearly parallel normal faults (antithetic and synthetic, respectively). The structural contour map of an extensive planation surface, dated to 3.8 Ma, provides a maximum fault throw s.s. of 330 m for the main fault (480 m including bending), and a net slip rate of 0.09-0.10 mm/a (0.13-0.15 mm/a including bending). Trench study focussed on the subsidiary antithetic fault shows evidence of its activity during Middle-Late Pleistocene times, offsetting ca. 2.5 m the slope of a well-preserved alluvial fan. Detailed analysis and retrodeformation of the antithetic fault and other minor ruptures in the trench has allowed defining seven deformation events. The lack of a consistent age model for the involved sedimentary sequence makes them almost meaningless in terms of paleoseismic history. However, geometry and sequential development of meso-scale faults (intermediate between seismic-scale and analogue models) allows unravelling the extensional deformation history within the hanging-wall block of the Sierra Palomera fault. Progressive rupture patterns reveal shifting from dominantly synthetic to dominantly antithetic faulting, suggesting both kinematical control linked to rollover growth, and dynamical control by the regional stress field.
查看更多>>摘要：In this study, we present new two- and three-dimensional resistivity models of the Huya fault region in the east margin of the Tibetan Plateau, imaged with magnetotelluric (MT) method. According to those models, a high-angle low-resistivity anomaly beneath the Huya fault is revealed, which is interpreted as a crustal thrust fault. The Minshan Uplift is imaged as a two-layered resistivity structure. The Bikou Block exhibits relatively uniform high-resistivity characteristics in our models, with its basement connected to a high-resistivity body beneath the Longmenshan fault belt. Thus, we infer that the Bikou Block belongs to the Yangtze Block. The Longmenshan fault belt exhibits strips of alternating high- and low-resistivity anomalies in the upper crust, with its middle and lower crust being highly resistive. The middle and lower crust of the western study region shows low resistivity, with its geometry changed greatly as it extends southeastward and upward. This is interpreted as an eastward channel of escaping material of the Tibetan Plateau. However, this channel is imaged to be blocked horizontally by the Bikou Block near the Huya fault, causing part of mid-to-lower crustal material to be upwelling, resulting in the Minshan Uplift. Another part of the low resistivity anomaly extended southeastward and was blocked by the lithospheric high-resistivity body beneath the Longmenshan fault belt, and then extended to the northeast and the southwest.
NSTL
Elsevier