GPS-derived deformation rates in northwestern Himalaya and Ladakh   总被引：1，自引：0，他引：1  

Sridevi Jade  H. J. Raghavendra Rao  M. S. M. Vijayan  V. K. Gaur  B. C. Bhatt  Kireet Kumar  Saigeetha Jaganathan  M. B. Ananda  P. Dileep Kumar 《International Journal of Earth Sciences》2011,100(6):1293-1301

Deformation rates derived from GPS measurements made at two continuously operating stations at Leh (34.1°N, 77.6°E) and Hanle (32.7°N, 78.9°E), and eight campaign sites in the trans-Himalayan Ladakh spanning 11 years (1997–2008), provide a clear picture of the kinematics of this region as well as the convergence rate across northwestern Himalaya. All the Ladakh sites move 32–34 mm/year NE in the ITRF2005 reference frame, and their relative velocities are 13–16 mm/year SW in the Indian reference frame and ~19 mm/year W with reference to the Lhasa IGS station in southeastern Tibet. The results indicate that there is no statistically significant deformation in the 200-km stretch between the continuous sites Leh and Hanle as well as between Leh and Nubra valley sites along the Karakoram fault, whereas the sites in and around the splayed Karakoram fault region indicate surface deformation of 2.5 mm/year. Campaign sites along the Karakoram fault zone indicate a fault parallel surface motion of 1.4–2.5 mm/year in the Tangste and western Panamik segment of the Karakoram fault, which quantifies the best possible GPS-derived dextral slip rate of 3 mm/year along this fault during this 11-year period. Baselines of Ladakh sites show convergence rates of 15–18 mm/year with respect to south India and 12–15 mm/year with respect to Delhi in north India and Almora in the Himalaya ~400 km north-northeast of Delhi. These constitute an arc normal convergence of 12–15 mm/year across the western Himalaya, which is consistent with arc normal convergence all along the Himalayan arc from west to east. Baseline extension rates of 14–16 mm/year between Lhasa and Ladakh sites are consistent with the east–west extension rate of Tibetan Plateau.  相似文献   

Aliphatic biomarkers and their signal from two hydrogeochemically differing sedimentary environments of the Tertiary Krepoljin Coal Basin (Serbia)     

Gordana J. Dević  Zoran Popovic 《International Journal of Earth Sciences》2011,100(6):1391-1399

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HP–UHP metamorphism as an indicator of slab dip variations in the Alpine arc     

Nicolas Carry  Fredéric Gueydan  Didier Marquer  Jean Pierre Brun 《International Journal of Earth Sciences》2011,100(5):1087-1094

HP/UHP and LT metamorphic units that commonly occur in the inner parts of mountain belts result from the subduction of continental and oceanic material, most often exhumed prior to continental collision. The prograde pressure–temperature history of HP–UHP rocks strongly depends on the convergence rate and on the subduction zone geometry. The maximum pressure recorded provides a proxy for the depth of shearing off and stacking of HP metamorphic nappes. A 2-D thermal model of continental subduction at lithospheric scale is used to compute the length and pressure peak of detached HP metamorphic units as a function of the slab dip angle and the convergence rate. Model results are applied to the metamorphic nappe pile of the inner Alps. A mean convergence rate of 1 cm/year during the subduction of the Briançonnais terrane is indicated by the paleogeographic reconstructions between 46 and 38 Ma. On this basis, the available petrological data and lengths of metamorphic units are used to compute the variations of the slab dip angle. The slab dip angle is shown to increase, from the northeast to the southwest, along the Alpine arc with estimated values of 20° for Suretta, 30–45° for Monte Rosa and Gran Paradiso, and 60° for Dora Maira. From Eocene to Oligocene times, the increase in slab dip angle is controlled by changes of buoyancy, due to the spatial configuration of the Valaisan trough and the incoming of crustal material within the subduction zone.  相似文献   

The last erosional stage of the Molasse Basin and the Alps     

Fritz Schlunegger  Jon Mosar 《International Journal of Earth Sciences》2011,100(5):1147-1162

We present a synoptic overview of the Miocene-present development of the northern Alpine foreland basin (Molasse Basin), with special attention to the pattern of surface erosion and sediment discharge in the Alps. Erosion of the Molasse Basin started at the same time that the rivers originating in the Central Alps were deflected toward the Bresse Graben, which formed part of the European Cenozoic rift system. This change in the drainage direction decreased the distance to the marine base level by approximately 1,000 km, which in turn decreased the average topographic elevation in the Molasse Basin by at least 200 m. Isostatic adjustment to erosional unloading required ca. 1,000 m of erosion to account for this inferred topographic lowering. A further inference is that the resulting increase in the sediment discharge at the Miocene–Pliocene boundary reflects the recycling of Molasse units. We consider that erosion of the Molasse Basin occurred in response to a shift in the drainage direction rather than because of a change in paleoclimate. Climate left an imprint on the Alpine landscape, but presumably not before the beginning of glaciation at the Pliocene–Pleistocene boundary. Similar to the northern Alpine foreland, we do not see a strong climatic fingerprint on the pattern or rates of exhumation of the External Massifs. In particular, the initiation and acceleration of imbrication and antiformal stacking of the foreland crust can be considered solely as a response to the convergence of Adria and Europe, irrespective of erosion rates. However, the recycling of the Molasse deposits since 5 Ma and the associated reduction of the loads in the foreland could have activated basement thrusts beneath the Molasse Basin in order to restore a critical wedge. In conclusion, we see the need for a more careful consideration of both tectonic and climatic forcing on the development of the Alps and the adjacent Molasse Basin.  相似文献   

Polyphase thrusting and dyke emplacement in the central Southern Alps (Northern Italy)     

Paolo D’Adda  Andrea Zanchi  Maria Bergomi  Fabrizio Berra  Marco G. Malusà  Annalisa Tunesi  Stefano Zanchetta 《International Journal of Earth Sciences》2011,100(5):1095-1113

The Triassic succession of the central Southern Alps (Italy) is stacked into several units bounded by south-verging low-angle thrust faults, which are related to two successive steps of crustal shortening. The thrust surfaces are cut by high-angle extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts motions. Intrusion ages based on SHRIMP U–Pb zircon dating span between 42 ± 1 and 39 ± 1 Ma, suggesting close time relationships with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in the Southern Alps. Fission-track ages of magmatic apatites are indistinguishable from U–Pb crystallization ages of zircons, suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2–4 km). These data indicate that the central Southern Alps were already structured and largely exhumed in the Middle Eocene. Although we describe minor faults affecting magmatic bodies and local reactivations of older structures, no major internal deformations have occurred in the area after the Bartonian. Neogene deformations were instead concentrated farther south, along the frontal part of the belt.  相似文献   

Geochemical characterization of a Quaternary monogenetic volcano in Erciyes Volcanic Complex: Cora Maar (Central Anatolian Volcanic Province,Turkey)     

Gonca Gencalioglu-Kuscu 《International Journal of Earth Sciences》2011,100(8):1967-1985

Central Anatolian Volcanic Province (CAVP) is a fine example of Neogene-Quaternary post-collisional volcanism in the Alpine-Mediterranean region. Volcanism in the Alpine-Mediterranean region comprises tholeiitic, transitional, calc-alkaline, and shoshonitic types with an “orogenic” fingerprint. Following the orogenic volcanism, subordinate, within-plate alkali basalts (sl) showing little or no orogenic signature are generally reported in the region. CAVP is mainly characterized by widespread calc-alkaline andesitic-dacitic volcanism with orogenic trace element signature, reflecting enrichment of their source regions by subduction-related fluids. Cora Maar (CM) located within the Erciyes pull-apart basin, is an example to numerous Quaternary monogenetic volcanoes of the CAVP, generally considered to be alkaline. Major and trace element geochemical and geochronological data for the CM are presented in comparison with other CAVP monogenetic volcanoes. CM scoria is basaltic andesitic, transitional-calc-alkaline in nature, and characterized by negative Nb–Ta, Ba, P and Ti anomalies in mantle-normalized patterns. Unlike the “alkaline” basalts of the Mediterranean region, other late-stage basalts from the CAVP monogenetic volcanoes are classified as tholeiitic, transitional and mildly alkaline. They display the same negative anomalies and incompatible element ratios as CM samples. In this respect, CM is comparable to other CAVP monogenetic basalts (sl), but different from the Meditterranean intraplate alkali basalts. Several lines of evidence suggest derivation of CM and other CAVP monogenetic basalts from shallow depths within the lithospheric mantle, that is from a garnet-free source. In a wider regional context, CAVP basalts (sl) are comparable to Apuseni (Romania) and Big Pine (Western Great Basin, USA) volcanics, except the former have depleted Ba contents. This is a common feature for the CAVP volcanics and might be related to crustal contamination or source characteristics. Indeed, HFS and other incompatible element ratios suggest the role of crustal contamination in the genesis of the CAVP monogenetic basalts.  相似文献   

3-D assessment of peak-metamorphic conditions by Raman spectroscopy of carbonaceous material: an example from the margin of the Lepontine dome (Swiss Central Alps)   总被引：2，自引：0，他引：2  

Michael Wiederkehr  Romain Bousquet  Martin A. Ziemann  Alfons Berger  Stefan M. Schmid 《International Journal of Earth Sciences》2011,100(5):1029-1063

This study monitors regional changes in the crystallinity of carbonaceous matter (CM) by applying Micro-Raman spectroscopy to a total of 214 metasediment samples (largely so-called Bündnerschiefer) dominantly metamorphosed under blueschist- to amphibolite-facies conditions. They were collected within the northeastern margin of the Lepontine dome and easterly adjacent areas of the Swiss Central Alps. Three-dimensional mapping of isotemperature contours in map and profile views shows that the isotemperature contours associated with the Miocene Barrow-type Lepontine metamorphic event cut across refolded nappe contacts, both along and across strike within the northeastern margin of the Lepontine dome and adjacent areas. Further to the northeast, the isotemperature contours reflect temperatures reached during the Late Eocene subduction-related blueschist-facies event and/or during subsequent near-isothermal decompression; these contours appear folded by younger, large-scale post-nappe-stacking folds. A substantial jump in the recorded maximum temperatures across the tectonic contact between the frontal Adula nappe complex and surrounding metasediments indicates that this contact accommodated differential tectonic movement of the Adula nappe with respect to the enveloping Bündnerschiefer after maximum temperatures were reached within the northern Adula nappe, i.e. after Late Eocene time.  相似文献   

Geology and geochronology of the Xilamulun molybdenum metallogenic belt in eastern Inner Mongolia,China   总被引：1，自引：0，他引：1  

Qingdong Zeng  Jianming Liu  Zuolun Zhang  Weijun Chen  Weiqing Zhang 《International Journal of Earth Sciences》2011,100(8):1791-1809

The Xilamulun molybdenum metallogenic belt, located in eastern Inner Mongolia, China, has great economic potential as a major producer of molybdenum. Four major types of Mo deposits have been recognized in the Xilamulun molybdenum metallogenic belt: porphyry, quartz vein, volcanic-hosted, and greisen. These Mesozoic Mo deposits are closely related to Si- and K-rich intrusives and are usually hosted by granite plutons or located at the endo- or exo-contact zones of the granite porphyry. SHRIMP zircon U–Pb dating gives the emplacement ages of the intrusions related to Mo mineralization as 245.1 ± 4.4, 152.4 ± 1.6, and 139.1 ± 2.3 Ma. Re–Os analysis of five molybdenite samples from the Chehugou porphyry Mo deposit yields an isochron age of 245 ± 5 Ma (2σ), indicating that the mineralization age of the porphyry Mo deposit is about 245 Ma. Re–Os analyses of six molybdenite samples from the Nianzigou quartz-vein-type Mo deposit yield an isochron age of 154.3 ± 3.6 Ma (2σ), constraining the mineralization age of the quartz-vein Mo deposit to 154 Ma. Our results suggest that the Mo mineralization in the Xilamulun belt formed during at least three stages, i.e., the Triassic, Late Jurassic, and Early Cretaceous, and is coeval with the granitic magmatism. The corresponding geodynamic background covers the syncollision between the North China and Siberian plates during the Early to Middle Triassic, a compression setting related to the subduction of the Paleo-Pacific plate during the Jurassic and lithospheric thinning during the Early Cretaceous in eastern China.  相似文献   

Role of unbalanced slab resistive force in the 2004 off Sumatra mega-earthquake (<Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> > 9.0) event     

Prosanta Kumar Khan 《International Journal of Earth Sciences》2011,100(7):1749-1758

Present study addresses the role of major plate-driving forces, particularly the slab pull and slab resistive forces, for the generation of 26 December 2004 M _w > 9.0 off Sumatra megathrust earthquake. Major controls on the plate-driving forces are normally visualized through age, speed, and average dip of the slab during subduction. Wide variation in age, plate obliquity, stress obliquity, subduction rate, dip angle, and flexing depth of the subducting oceanic lithosphere between Andaman and Sumatra thus allowed us for quantitative evaluation of the slab pull (F _SP) and slab resistive (F _SR) forces in three well-defined sectors (I, II and III). Computed values of these forces in the three sectors: (1) F _SP = 1.29 × 10¹³ N/m, F _SR = 1.41 × 10¹³ N/m; sector I, (2) F _SP = 2.10 × 10¹³ N/m, F _SR = 1.13 × 10¹³ N/m; sector II, and (3) F _SP = 2.08 × 10¹³ N/m, F _SR = 2.72 × 10¹³ N/m; sector III clearly suggest a spatial variation of stress regime in the subducting oceanic lithosphere. Excess F _SR in sectors I and III are interpreted as the causative forces behind the triggering of major seismic energy bursts near Sumatra and Andaman on 26 December 2004. A gap of minimum seismic energy burst near Great Nicobar possibly was controlled by the excess of F _SP in sector II. This study further advocates that the cyclic stress, resulted from unbalanced component of slab resistive force, had a definite control on the occurrence of 2004 off Sumatra megathrust earthquake around the flexing zone of the subducting lithosphere.  相似文献   

Thermal and redox state of the subcontinental lithospheric mantle of NE Spain from thermobarometric data on mantle xenoliths     

Gumer Galán  V. Oliveras  B. A. Paterson 《International Journal of Earth Sciences》2011,100(1):81-106

Mantle xenoliths in within-plate Cenozoic alkaline mafic lavas from NE Spain are used to assess the local subcontinental lithospheric mantle geotherm and the influence of melting and metasomatism on its oxidation state. The xenoliths are mainly anhydrous spinel lherzolites and harzburgites and gradations between, with minor pyroxenites. Most types show protogranular textures, but transitional protogranular–porphyroclastic and equigranular lherzolites also exist. Different thermometers used in the estimates provide higher subsolidus equilibrium temperatures for harzburgites (1,062 ± 29°C) than for lherzolites (972 ± 89°C), although there is overlap; the lowest temperatures correspond to porphyroclastic lherzolites, whereas pyroxenites give the highest temperatures (up to 1,257°C). Maximum pressures for subsolidus equilibrium of peridotites are at 2.0–1.8 GPa. Later they followed adiabatic decompression and harzburgites registered lower pressures (1.02 ± 0.19 GPa) than lherzolites (1.41 ± 0.27 GPa). One pyroxenite gives values consistent with the spinel lherzolite field (1.08 GPa). The shallowest barometric data are in agreement with the highest local conductive geotherms, which implies that the lithosphere–asthenosphere boundary is at 70–60 km minimum depth. Higher equilibrium temperatures for the harzburgites could be explained by the existence of mafic magma bodies or dykes at the lower crust–mantle boundary. Paleo-fO₂ conditions during partial melting as inferred from the covariation between V and MgO concentrations are mainly between QFM−1 and QFM−2 in log units. However, most thermobarometric fO₂ estimates are between QFM−1 and QFM+1, suggesting oxidation caused by later metasomatism during uplift and cooling.  相似文献