查看更多>>摘要：The geoid over the north Indian Ocean has a significantly large negative amplitude, even if the excess flattening of the Earth beyond its equilibrium shape is considered. The various mechanisms proposed for this geoid anomaly vary and acceptable geoid predictions are obtained for specific tomographic models only. In this study, we identified model-independent features in the mantle beneath the Indian Ocean and Ross Sea region by analyzing eight recent global tomographic models. We standardized each of the models and applied cluster analysis to regionalize geophysically significant features in various depth ranges. These regionalizations are compared grid-by-grid to construct vote-maps. They highlight the anomalous features consistent across models and their approximate dimensions. Low velocity anomalies of dV(S) similar to-1.1% in the similar to 400-680 km depth range are consistent in almost all the models beneath the Indian Ocean and Ross Sea. High velocity anomalies of dV(S) >= 1% at depths below 1600 km, incoherent in dimension and orientation, are also observed. High velocity anomalies are most likely subducted slabs while low velocity anomalies could be partial melts generated by hydration of mantle. Additionally, a consistent low velocity structure is seen throughout the mantle beneath the southwestern Indian Ocean and east Africa. It is mostly likely a plume rising from the African LLSVP. It connects to the probable partial melts beneath the Indian Ocean via a remnant trail. Forward modelling of the geoid using votemaps reveals that the E-W extent of the Indian Ocean Geoid Low is precisely reproduced by the consistent low velocity anomalies in the upper mantle. However, the N-S extent, most likely dependent on lower mantle anomalies, is not expressed since the dimension, orientation and dV(S) characteristics of high velocity structures are inconsistent in different models. The inter-model agreement is insufficient to identify structure(s) seen across models that can explain the geoid low over the Ross Sea.
查看更多>>摘要：An unexpectedly large uplift of 91 mm was detected by geodetic observations during the rupture of 2016 Mw 6.4 Meinong earthquake, Taiwan, which has been attributed as either a triggered anelastic and hydrologic related deformation from a proposed duplex/mud diapir or a triggered aseismic slip on a proposed backthrust. Here, using both high-rate GNSS and free-field strong motion data, we first estimated the coseismic source model. The locations of high PGV were inferred to explain the unexpected distribution of damaged buildings approximately 25-30 km west of the epicenter. Then, the aseismic surface displacements during the earthquake was differentiated using the coseismic source model. The aseismic extension of 3.8 mu strain is inferred at the unexpectedly large uplift region. Combining with local geology, residual gravity anomaly, seismic tomography, interseismic leveling vertical velocities, coseismic leveling uplifts and proposed Coulomb stress changes, the accelerated mud diapirism during the earthquake triggered by slip on the deep seismogenic fault was identified as the cause of unexpectedly large coseismic uplift.
查看更多>>摘要：We analyzed a set of 11 slow slip events occurred during the 2006-2016 period and affecting the GNSS (Global Navigation Satellite System) stations of the unstable flank of Mt. Etna volcano. Observed surface deformation for most of the detected slow slip events, concentrates on the south-eastern edge of the unstable flank while the slow slip events involving the north-eastern edge are less frequent. Such a pattern highlights the existence of two distinct families of events, involving two contiguous sectors of the unstable flank, which occasionally slip together in large slow slip events. The modelled slips also highlight that both contiguous sectors extend similar to 10-12 km offshore, on areas where active tectonic lineaments such as the ESE (northward of Catania Canyon) and the N102 degrees (along the southern slope of the Riposto Ridge) ones have been recently discovered. Equivalent seismic moments of slow slip events occurred in the last ten years (corresponding to magnitudes in the range 5.4-5.9) are larger than those associated to seismic events observed in the last 200 years, suggesting that most of the deformation affecting the eastern flank occurs aseismically.
查看更多>>摘要：Deformation in oblique convergent margins, especially non-plane deformation in de??collement belts within such a margin, is not fully understood. The northern Zhangbaling tectonic belt represents an oblique convergent margin to the east of the NNE???SSW-striking Tan???Lu Fault Zone that separates the Yangtze Block to the east from the North China Craton to the west, and it provides a good opportunity to understand deformation in the margin. The tectonic belt consists of a fold-and-thrust belt in the east and a low-angle ductile de??collement belt in the west. The fold-and-thrust belt in the marginal cover rocks indicates a pure shear-dominated deformation, and the fold axes rotated with the long axis of the horizontal finite strain ellipse. The underlying de??collement belt was involved in a non-plane deformation owing to the superposition of wrenching along the Tan???Lu Fault Zone and horizontal de??collement shearing. The horizontal de??collement shearing dominated in the development of the flat-lying foliation, whereas the wrenching mostly dominated in the development of stretching lineations. Top-to-theSSW sense of shear dominates in the central to southern parts of the de??collement belt, whereas top-to-the-SSE sense of shear is widely present in the northern part of the belt and locally in other parts. Partitioning of the non-plane deformation is shown by kinematic partitioning within the originally flat-lying de??collement belt, and it is different from the strain partitioning in a transpressional zone involved in plane deformation. The structural and geochronological data for the oblique convergent margin are consistent with sinistral faulting of the initial Tan???Lu Fault Zone during the Triassic.
查看更多>>摘要：The Daiyunshan volcanic field is one of the largest volcanic fields in the volcanic-plutonic complex belt along the coast of SE China, which records a long volcanic activity history from the Late Jurassic to the Late Cretaceous. In this paper, we conduct comprehensive petrological, geochemical, isotopic and zircon trace element analyses for two representative calderas (Shiniushan and Yunshan) to reveal the crystal-melt segregation and magma recharge processes of the Daiyunshan volcanic field. Systematic LA-ICP-MS zircon U-Pb dating and isotope analyses reveal that the porphyritic quartz monzonite, porphyritic granite and rhyolite of the Shiniushan caldera have identical crystallization ages (97???94 Ma) and consistent Nd-Hf isotope compositions [??Nd(t) = -3.6 to -2.8; zircon ??Hf(t) = -2.7 to 1.8], which are consistent with those of the porphyritic quartz monzonite and rhyolites in the nearby Yunshan caldera, indicating that the magmas of the two calderas were derived from a common magma source region. Volcanic-plutonic rocks from two calderas display metaluminous to peraluminous features and have low MgO, FeOT, Ni and Cr contents. We thus suggest that their parental magmas were derived by remelting of pre-existing crust with contributions of juvenile components. The Shiniushan porphyritic granite and rhyolite and the Yunshan rhyolites are characterized by distinctly negative Eu anomalies and depletions of Ba, Sr, P and Ti, while the porphyritic quartz monzonites from both calderas show complementary geochemical signatures, such as positive Ba anomalies and neglectable Eu anomalies. The back-scattered electron (BSE) images and energy-dispersive X-ray spectrometry (EDS) phase mapping of the Shiniushan porphyritic quartz monzonite reveal textural indicators of crystal accumulation, such as imbrication and synneusis of plagioclase phenocrysts. Their interstitial assemblages of K-feldspar, quartz and plagioclase commonly resemble the phenocryst assemblages of porphyritic granite. We believe that the Shiniushan porphyritic granite and rhyolite and Yunshan rhyolites represent extracted melts from the mush reservoir, while porphyritic quartz monzonites in both calderas are inherent cumulates that have lost interstitial melts. Therefore, our study shows that the Late Cretaceous volcanic-plutonic rocks in the Daiyunshan volcanic field should be connected by crystal-melt segregation processes. Furthermore, a typical zigzag variation in zircon ??Hf(t) values is shown by the Late Jurassic to Late Cretaceous volcanic-plutonic rocks from the Daiyunshan volcanic field, indicating variable contributions of asthenospheric mantle-derived melts and the multistage slab rollback of the subducting paleoPacific plate beneath SE China.
Serck, Christopher SaeboBraathen, AlvarHassaan, MuhammadFaleide, Jan Inge...
18页
查看更多>>摘要：The Utsira High (North Sea) records rift faulting that culminates with Jurassic-Cretaceous crustal-scale rollover towards the Viking Graben. This deformation is superimposed on Paleozoic fault-bounded basins on a substrate of Caledonian nappes. The latter contains multilevel crustal-scale shear systems that domed under the Utsira High during the Devonian, as indicated by mapping and interpretation of a large long-offset 2D seismic reflection dataset. Restorations show that isostatically driven doming from excision of overthickened crust caused uplift and erosion of basins and the underlying nappe stack. Doming took place above a crustal rollback system as a symmetrical metamorphic core complex formed. The dome discloses vertical flattening kinematics below bidirectional shear systems, evident by opposite shear-fabric kinematics on opposite dome flanks. A major detachment marks the upper boundary of a transition between upper and lower plate strain regimes, coinciding with low-reflective granitic units above strongly reflective Caledonian nappes. This detachment hosts transportparallel corrugations that strike E-W to NE-SW. A series of deeply eroded half-grabens on top of the upper plate are bounded by pre-Permian faults exhibiting top-NE extensional kinematics. Faults sole out in the fundamental detachment level, locating the brittle-ductile transition, with all structures subsequently rotated during doming. A new localized detachment formed at a shallower level above the region of maximum crustal uplift, seen as upwards detachment migration driven by heating. Later faulting locates to the dome flanks, either rejuvenating rotated shear zones or cutting to deeper crustal levels while recording predominantly down-eastward transport. During Jurassic-Cretaceous rifting, deformation localized to the Viking Graben Boundary Fault, giving room for thick growth wedges in the Viking Graben and establishing the Utsira High as a crustal-scale rollover structure.
查看更多>>摘要：One major critical issue in seismic hazard analysis deals with the computation of the maximum earthquake magnitude expected for a given region. Its estimation is usually based on the analysis of past seismicity that is incomplete by definition, or derived from the dimension of faults through empirical relationships with the intrinsic uncertainty in source characterization. Here, we propose a workflow aimed at providing a timeindependent estimate for the maximum possible magnitude based on geological and geophysical evidence. Our estimate is also source unrelated as it is constrained by the seismic brittle volume of the crust that scales with the effective seismic energy. The seismic brittle volume is calculated considering fault kinematics and rock rheology (i.e., the brittle-ductile transition depth) over a grid that covers the entire study area. The maximum earthquake magnitude is calculated at each point of the grid based on a volume/magnitude empirical relationship. We apply this model to Italy for which we propose a map of the maximum possible magnitudes. Maximum predicted magnitudes are 7.3 ?? 0.25 for thrust faulting, 7.6 ?? 0.77 for normal faulting and 7.6 ?? 0.37 for strike-slip faulting (?? deviation from the mean value calculated at each node). These magnitudes are locally higher than the historical record. This could be due to an overestimation of the involved volumes; smaller volumes and lower magnitudes may occur where faults are detached at decollements shallower than the brittle ductile transition or where they behave aseismically. Alternatively, strong or major earthquakes could be possible, but they have longer recurrence time and they have never been recorded yet in Italy. Regardless these values are fully reliable or not, the recurrence of earthquakes with the predicted magnitude is related to current strain rates. We conclude that a large part of the Italian territory is prone to trigger Mw > 5 earthquakes.
查看更多>>摘要：Located in the western Northpatagonian region, Argentina, the Lower Jurassic Can??ad??on Chileno Complex (CCHC) provides a remarkable opportunity to assess the roles of pre-, syn-, and post-eruptive faulting in felsic diatremes complexes evolution. The structural analyses of fractures, dikes, and folds allow recognition of the occurrence of four different strain partitions (SP1-SP4) developed during the Lower to Middle Jurassic. Recognized strain configurations show equivalent temporal and structural relationships throughout the Jurassic backarc system of Patagonia and contemporary basins of southern South America. The stratigraphical criteria allow inferring an Upper Sinemurian to Lower Pliensbachian time interval for the initial strain configurations (SP1, SP2, and SP3). WNW, NNE, and NE-oriented extensional phases were defined and correlated with adjoining areas. Particularly, the third strain partition phase is characterized by a significant transpressive deformation. A NE contractional episode characterizes the post-eruptive deformation stage (SP4) during the Bajocian to Callovian interval. Tectonic interpretations were elaborated concerning subduction dynamics, continental drift, and rotation that controlled the regional and local stress configuration throughout the Jurassic Period of Patagonia and central Argentina.
NSTL
Elsevier