Zakharov, V. S.Lubnina, N., VStepanova, A., VGerya, T., V...
13页
查看更多>>摘要：Available data suggest that the breakup of the Neoarchean Kenorland supercontinent at 2.5-2.4 Ga was likely triggered by a large mantle plume upwelling that caused significant magmatism. Here, we present 2D high-resolution magmatic-thermomechanical numerical models of extension of the continental crust underplated by a hot mantle plume material. Using this model, it is demonstrated that mantle plume underplating generates a large amount of mafic melt by decompression melting. This melt penetrates into the extending continental crust along normal faults thereby forming multiple generations of mafic dyke-like intrusions along normal faults. In case of extension velocity of 0.2-1 cm/yr, lower crustal heating and hot mafic melt emplacement may cause partial melting of the continental crust that can generate significant volume of felsic melts. This in turn triggers emplacement of felsic intrusions that temporarily and spatially associate with the mafic dyke-like intrusions. The modeling results agree well with geological data from the Karelian Craton and provide possible explanation for the observed association of Paleoproterozoic mafic dykes and felsic intrusions which formed in a relatively short time interval (up to 20 Myrs) in the early stages of the supercontinent breakup.
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：We investigated the late Upper Pleistocene activity of the eight main faults that comprise the active, dip-slip Gran Sasso fault system (GSFS) in the Gran Sasso d' Italia Massif (central Italian Apennines; 2912 m a.s.l.). We carried out novel paleoseismological analyses at four sites of three different fault segments, and reviewed the data of the previous results for three other segments. We carried out several topographic profiles across the offset hillslopes, alluvial fans, glacial cirques, moraines, and valley floor. Through the dozen radiocarbon datings that were combined and cross-checked with many other ages published in previous studies, we have provided robust sliprates and reconstructed the Holocene seismic history of this fault system. Paleoseismic analyses revealed the presence of three consecutive earthquakes since the onset of the Late Holocene, which were separated by 3.3 ky and 2.2 ky, respectively. The last one occurred in the 13th-14th century CE, a time-span that fits with the catastrophic 1349 seismic sequence. Our review of the macroseismic intensity distribution of this sequence indicates the existence of two distinct mesoseismic areas; a southern one that was already related to the Aquae Iuliae fault rupture (Abruzzi-Campania-Molise borders), and a northern one that robustly matches the hanging-wall of the Gran Sasso fault system. Given the length of this fault system, we estimated Mw 7 for its entire rupture, which accounts for the total destruction of L'Aquila and the neighboring villages. This also accounts for the strong effects and severe damage suffered by several settlements in the para-Tyrrhenian far field, especially to buildings characterized by long fundamental resonance periods, as seen for the monuments of Rome. Although characterized by long recurrence times (2.8 +/- 0.5 ky), our results suggest that as for all of the main silent faults of the eastern set of active structures in the central Apennines, this fault system has one of the largest seismogenic potentials of the whole Apennine chain, with seismic risk implications extended even to its far-field.
查看更多>>摘要：The Qilian Shan on the northeastern edge of the Tibetan Plateau contains structural, sedimentary and tectonothermal records of plateau formation and growth in response to the Indian-Asian continental collision. In this study, we reveal the tectonic deformation evolution of the Qilian Shan by detrital apatite fission track (AFT) thermochronology and provenance analysis of a sedimentary section on the northern flank of the Qilian Shan based on paleocurrent measurements and detrital zircon UPb geochronology. The unannealed detrital AFT peak ages span similar to 154-10 Ma, and the zircon U-Pb ages range between similar to 3260 Ma and similar to 178 Ma. Detrital AFT ages showing that the initial exhumation occurs ca. 154-135 Ma and ca. 105-81 Ma and abundant ages of ca. 61-24 Ma indicate the prominent exhumation of the sedimentary provenance from the Qilian Shan at those times. Zircon U-Pb analysis suggests that the sediments were generally sourced from the Qilian Shan to the south, with moderate provenance changes at similar to 10 Ma and 5.1 Ma. These geochronological datasets imply that the Qilian Shan experienced multistage deformation during the Mesozoic-Cenozoic, i.e., late Jurassic-early Cretaceous (153.6-135.2 Ma), late Cretaceous (104.5-80.9 Ma), late Paleocene-Oligocene (61-43.1 Ma;38.2-24.6 Ma), mid-late Miocene (10 +/- 4 Ma) and Pliocene (5.1-3.6 Ma). During the Cenozoic, the deformation initiated in the late Paleocene reflects the synchronous far-field response of the northeastern Tibetan Plateau margin to the Indian-Asian plate collision.
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：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.
查看更多>>摘要：The base of the Silvretta Nappe (Austroalpine Unit, Eastern Alps) has localized extensive deformation, including the occurrence of multiple generations of pseudotachylytes, alternating with (ultra)mylonites, in the host amphibolite and gneiss. Previous works attributed the formation of pseudotachylytes and associated ultra-mylonites to the Eoalpine deformation phase (mid. Cretaceous). In this work, we report the presence of a younger generation of pseudotachylytes, which overprints the previously characterized pseudotachylyte-ultramylonite association. A detailed petrographic study of selected samples from the Jamtal, Tyrol (Austria), provides further constraints on the possible tectonic evolution of the Silvretta Nappe. Contrary to the Eoalpine pseudotachylytes, the younger pseudotachylytes are not completely recrystallized, foliated, and epidotized, but rather preserve the typical features of frictional melts (e.g., micmlites, glassy gmundmass, evidence of melt immiscibility, etc.). This suggests formation in relatively shallow conditions, rather than under greenschist facies, as assumed for the Eoalpine pseudotachylytes. The "young" pseudotachylytes, commonly discordant to the foliation, thus likely formed during the final subduction of the Penninic Unit in the Paleogene. This occurrence lends further support to the localization of deformation at the base of the upper plate, in this case represented by the Silvretta Nappe, as observed in other portions of the Alps.
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：Mantle deformation processes leading to seafloor spreading are often difficult to infer due to the highly serpentinized and weathered state of most abyssal peridotites. We investigated the development of high-temperature crystal-plastic deformation and lower temperature mylonitization processes in relatively fresh (<50% modal serpentine) and ultra-fresh (<1% serpentine) mantle peridotites derived from the heterogeneous mantle in the sparsely magmatic zone of ultraslow-spreading Gakkel Ridge system by analyzing 12 peridotites from two dredge sites (<1 km apart). Microstructurally, these 12 peridotites consist of seven high-T deformed samples and five mylonites. Modally, the 12 samples include harzburgites, lherzolites, an olivine websterite, and a plagioclase-bearing lherzolite. Based on their mineral major and trace element compositions, the lherzolites, harzburgites, and olivine websterite are residual peridotites. The lherzolites containing clinopyroxenes with flat REE patterns likely underwent refertilization with a high influx of melt. The plagioclase-bearing lherzolites probably formed by subsolidus reaction after the partial melting process. Microstructural observations support that high-T crystal-plastic deformation (most likely at temperatures exceeding 1000 degrees C) was active in the peridotites of the high-T deformation group, accommodating mantle flow beneath the Gakkel Ridge. The identified melt refertilization process may have contributed to the formation of [0101-fiber olivine fabrics in these peridotites. Mylonitic microstructures, decreasing fabric strength and grain-size reduction of olivine suggest that mylonitization occurred under relatively low-temperature mantle conditions (-800 degrees C) and probably accommodated strain localization. Water did not greatly affect the peridotites during the development of the shear zones, although amphibole with "dusty" zones developed in one mylonitic peridotite after mylonitization, indicating that late-stage metasomatism occurred locally within the shear zone. This low-T mylonitization is likely to have affected mantle peridotites of this region independently of petrogenetic processes. The development of these deformation processes in Gakkel Ridge suggests a shift from flow in the uppermost mantle to shear zone formation in the rift valley walls.
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.
NSTL
Elsevier