Quantifying the P–T–t conditions of north–south Lhasa terrane accretion: new insight into the pre‐Himalayan architecture of the Tibetan plateau          下载免费PDF全文

O. M. Weller  M. R. St‐Onge  M. P. Searle  D. J. Waters  N. Rayner  S. Chen  S.‐L. Chung  R. M. Palin 《Journal of Metamorphic Geology》2015,33(1):91-113

An integrated field, petrological and geochronological study of the Basong Tso region of south‐eastern Tibet has constrained the timing and P–T conditions of north–south Lhasa terrane accretion and provides new insight into the tectonothermal evolution of the Tibetan plateau. Two distinct high‐grade metamorphic belts are recognized in the region: a southern belt (the Basong Tso complex) that consists of sheared schist and orthogneiss; and a northern belt (the Zhala complex) that comprises paragneiss and granite. Combined pseudosection modelling and U–Pb geochronology of monazite and zircon indicates that the Basong Tso complex records peak metamorphic conditions of 9 ± 0.5 kbar and 690 ± 25 °C at c. 204–201 Ma, whereas the Zhala complex experienced peak metamorphic conditions of 5.0 ± 1.0 kbar and 740 ± 40 °C at c. 198–192 Ma. Microstructural analysis suggests that the two belts share a common early prograde history, after which the Basong Tso complex attained peak conditions following rapid burial, and the Zhala complex approached peak conditions along an isobaric path. Overall it is inferred that the Basong Tso and Zhala complexes represent the lower and upper structural levels of an evolving orogen that underwent Barrovian‐type metamorphism following collision (M1), followed by Buchan‐style overprinting at higher structural levels due to heat advection by syn‐tectonic granites (M2). Mylonitization (sensu lato) of the Basong Tso complex and juxtaposition of the two units occurred after attainment of peak conditions. The dominance of Mesozoic regional metamorphism across most of the Tibetan plateau indicates that Cenozoic crustal thickening processes, where present, are only manifested at depth.  相似文献   

Contaminant transport and biodegradation in saturated porous media: model development and simulation     

Song‐Bae Kim 《水文研究》2005,19(20):4069-4079

  相似文献   

Postglacial chironomid assemblage succession in northernmost Ungava Peninsula,Canada     

Émilie Saulnier‐Talbot  Reinhard Pienitz 《第四纪科学杂志》2010,25(2):203-213

Sediment cores spanning the postglacial period were recovered from two coastal freshwater basins located 300 km apart in northernmost Ungava (Nunavik, Canada). A basal date from the sequence recovered near Wakeham Bay suggests that the region was ice‐free by as early as 9600 cal. a BP. The initial development of both investigated lacustrine ecosystems was characterised by chironomid assemblages strongly dominated by the Subtribe Tanytarsina. These early postglacial assemblages showed greatly reduced diversity but much greater abundance than during subsequent periods of lake evolution. An abrupt and distinct turnover in sedimentary chironomid assemblage composition and productivity, marked by a switch to a dominance of Orthocladiinae, occurred around 6 ka BP. This turnover likely corresponds with a significant disturbance in the regional environment, which could be linked to the final disappearance of the last remnants of the Laurentide Ice Sheet. These findings, based on the first palaeolimnological investigations undertaken in northernmost Ungava, provide new insights into lateglacial and postglacial faunal recolonisation patterns in aquatic ecosystems of the eastern Canadian Arctic. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Evaluation of typhoon‐induced rainfall using nonparametric Monte Carlo simulation and locally weighted polynomial regression     

Tae‐Suk Oh  Young‐Il Moon  Hyun‐Han Kwon 《水文研究》2011,25(11):1765-1777

Typhoons in Korea are the major causes of natural disasters in the Korean peninsula. In this study, rainfall generated by typhoons was quantitatively analysed using various statistical methods. First, the frequency analysis of rainfall induced by typhoons was carried out to calculate the design rainfall. Second, the frequency analysis of simulated rainfall derived by nonparametric Monte Carlo simulation (NMCS) was performed to evaluate the uncertainty of rainfall caused by typhoons. Third, the regression relationship between the physical characteristic factors of typhoons and rainfall was established by locally weighted polynomial regression (LWPR), and the characteristic factors of typhoons were simulated. The simulated characteristic factors were then used to estimate rainfall and to calculate the design rainfall by typhoons. Comparative analyses of design rainfalls as estimated using various statistical methods were performed. The LWPR showed good performance in terms of reproducing typhoon characteristics. Therefore, the combined NMCS and LWPR method suggested in this study can be used as a supplementary technique for assessing extreme rainfall with climate change and reflected variability. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The stability of sapphirine + quartz: calculated phase equilibria in FeO–MgO–Al2O3–SiO2–TiO2–O     

K. TAYLOR‐JONES  R. POWELL 《Journal of Metamorphic Geology》2010,28(6):615-633

The presence in rocks of coexisting sapphirine + quartz has been widely used to diagnose conditions of ultra‐high‐temperature (UHT) metamorphism (>900 °C), an inference based on the restriction of this assemblage to temperatures >980 °C in the conventionally considered FeO–MgO–Al₂O₃–SiO₂ (FMAS) chemical system. With a new thermodynamic model for sapphirine that includes Fe₂O₃, phase equilibra modelling using thermocalc software has been undertaken in the FeO–MgO–Al₂O₃–SiO₂–O (FMASO) and FeO–MgO–Al₂O₃–SiO₂– TiO₂–O (FMASTO) chemical systems. Using a variety of calculated phase diagrams for quartz‐saturated systems, the effects of Fe₂O₃ and TiO₂ on FMAS phase relations are shown to be considerable. Importantly, the stability field of sapphirine + quartz assemblages extends down temperature to 850 °C in oxidized systems and thus out of the UHT range.  相似文献   

Intertidal gastropod assemblages shaped by key environmental variables across the northern Persian Gulf and the Gulf of Omanss     

Fatemeh Amini‐Yekta  Mohammad Reza Shokri  Abdolvahab Maghsoudlou  Hassan Rajabi‐Maham 《Marine Ecology》2019,40(3)

Variations in environmental factors can alter the species distribution pattern in intertidal rocky shores. The Persian Gulf (PG) and the Gulf of Oman (GO) vary substantially with respect to environmental and oceanographic conditions. The abundance and biodiversity of intertidal rocky gastropods in five locations across the northern PG and the GO were compared, and the environmental variables underlying the distribution pattern of these organisms were investigated. A total of 67 gastropod species were identified. The largest average density (294 ind./m²) and diversity (N = 43) for gastropods occurred in the Hotel Lipar station (LIP) located in Chabahar Bay in the GO. Clypeomorus bifasciata (107.43 ind./m²) followed by Cerithium caeruleum (94.67 ind./m²) were the most abundant species. Planaxis sulcatus and Siphonaria spp. occurred in all locations during both sampling occasions. Species richness and abundance of gastropods showed significant differences between LIP and remaining locations. A significant difference was found in assemblage structure across locations. In general, the species richness and density in the locations at GO were significantly larger than those locations in the PG, suggesting that the harsh environmental condition in the PG might be the forcing factor for this diminish. Distinct grouping was observed in both assemblage structure and species composition between locations in the PG and the GO. The spatial and temporal distribution patterns of gastropods assemblages were significantly correlated with variation in salinity and substrate rugosity.  相似文献   

A new probabilistic approach to estimating marine gastropod densities from baited traps          下载免费PDF全文

Jennifer Coston‐Guarini  Jean‐Marc Guarini  Frederike Ricarda Boehm  Thomas R. H. Kerkhove  Frances C. Rivera  Karim Erzini  François Charles  Tim Deprez  Laurent Chauvaud 《Marine Ecology》2018,39(3)

A new probabilistic approach is proposed to assess muricid species population abundances at scales relevant to both Ancient and Modern coastal fisheries. Motivated by the long‐term goal of reconstructing the dynamics of exploited murex populations during Antiquity, the objective was to estimate the population density of the banded dye‐murex, Hexaplex trunculus (Linnaeus, 1758) from successive captures with baited traps, using a method similar to the technique employed in the Mediterranean purple dye industry. The stochastic model developed simulates cumulative captures while accounting for high variability. It was calibrated with data acquired during a field trapping experiment (Crete Island, Greece). Traps’ catchability and Effective Area of Attraction (EAA) were estimated using the individual speed and behavioural response towards bait from laboratory experiments. Average density of H. trunculus was estimated as 2.2 ± 1.4 SE individuals per square metre, with no significant differences between seagrass and rocky habitats. The clearing time of successive capture experiments averaged 84 ± 6 SE hr. Clearing ca. 0.4 ha of subtidal area would be necessary to produce ca. 1.0 g of pure Tyrian purple pigment. The method described is generalizable to making population abundance estimates for similar groups, such as whelks, in modern fisheries.  相似文献   

Groundwater response to tidal fluctuations in a leaky confined coastal aquifer with a finite length     

Zhixue Zhao  Xiaoguang Wang  Yonghong Hao  Tongke Wang  Abderrahim Jardani  Herve Jourde  Tian‐Chyi Jim Yeh  Ming Zhang 《水文研究》2019,33(19):2551-2560

The study on the hydraulic properties of coastal aquifers has significant implications both in hydrological sciences and environmental engineering. Although many analytical solutions are available, most of them are based on the same basic assumption that assumes aquifers extend landward semi‐infinitely, which does not necessarily reflect the reality. In this study, the general solutions for a leaky confined coastal aquifer have been developed that consider both finitely landward constant‐head and no‐flow boundaries. The newly developed solutions were then used to examine theoretically the joint effects of leakage and aquifer length on hydraulic head fluctuations within the leaky confined aquifer, and the validity of using the simplified solution, which assumes the aquifer is semi‐infinite. The results illustrated that the use of the simplified solution may cause significant errors, depending on joint effects of leakage and aquifer length. A dimensionless characteristic parameter was then proposed as an index for judging the applicability of the simplified solution. In addition, practical application of the general solution for the constant‐head inland boundary was used to characterize the hydraulic properties of a leaky confined aquifer using the data collected from a field site at the Seine River estuary, France, and the versatility of the general solution was further justified.  相似文献   

Petrogenesis and shock metamorphism of the enriched lherzolitic shergottite Northwest Africa 7755          下载免费PDF全文

Shu‐Zhou Wang  Ai‐Cheng Zhang  Run‐Lian Pang  Jia‐Ni Chen  Li‐Xin Gu  Ru‐Cheng Wang 《Meteoritics & planetary science》2017,52(11):2437-2457

Northwest Africa (NWA) 7755 is a newly found enriched lherzolitic shergottite. Here, we report its detailed petrography and mineralogy. NWA 7755 contains both poikilitic and non‐poikilitic lithologies. Olivine has different compositional ranges in the poikilitic and non‐poikilitic lithologies, Fa_30–39 and Fa_37–40, respectively. Pyroxene in the non‐poikilitic lithology is systematically Fe‐richer than that in the poikilitic lithology. The chromite grains in non‐poikilitic lithology are highly Ti‐richer than those in the poikilitic lithology. The chemical variations of olivine, pyroxene, and chromite between the poikilitic and non‐poikilitic lithologies support a two‐stage formation model of lherzolitic shergottites. Besides planar fractures and strong mosaicism in olivine and pyroxene, shock‐induced melt veins and pockets are observed in NWA 7755. Olivine grains within and adjacent to melt veins and/or pockets have either transformed to ringwoodite, amorphous phase, or dissociated to bridgmanite plus magnesiowüstite. Merrillite in melt veins has completely transformed to tuite; however, apatite only has partially transformed to tuite, indicating a relatively sluggish transformation rate. The partial transformation from apatite to tuite resulted in fractional devolatilization of Cl and F in apatite. The fine‐grained mineral assemblage in melt veins consists mainly of bridgmanite, minor magnesiowüstite, Fe‐sulfide, Fe‐phosphide, and Ca‐phosphate minerals. The coexistence of bridgmanite and magnesiowüstite in these veins indicates a shock pressure of >~24 GPa and a temperature of 1800–2000 °C. Coesite and seifertite are probably present in NWA 7755. The presence of these high‐pressure minerals indicates that NWA 7755 has experienced a more intense shock metamorphism than other enriched lherzolitic shergottites.  相似文献   

Regolith breccia Northwest Africa 7533: Mineralogy and petrology with implications for early Mars          下载免费PDF全文

Roger H. Hewins  Brigitte Zanda  Munir Humayun  Alexander Nemchin  Jean‐Pierre Lorand  Sylvain Pont  Damien Deldicque  Jeremy J. Bellucci  Pierre Beck  Hugues Leroux  Maya Marinova  Laurent Remusat  Christa Göpel  Eric Lewin  Marion Grange  Allen Kennedy  Martin J. Whitehouse 《Meteoritics & planetary science》2017,52(1):89-124

Northwest Africa 7533, a polymict Martian breccia, consists of fine‐grained clast‐laden melt particles and microcrystalline matrix. While both melt and matrix contain medium‐grained noritic‐monzonitic material and crystal clasts, the matrix also contains lithic clasts with zoned pigeonite and augite plus two feldspars, microbasaltic clasts, vitrophyric and microcrystalline spherules, and shards. The clast‐laden melt rocks contain clump‐like aggregates of orthopyroxene surrounded by aureoles of plagioclase. Some shards of vesicular melt rocks resemble the pyroxene‐plagioclase clump‐aureole structures. Submicron size matrix grains show some triple junctions, but most are irregular with high intergranular porosity. The noritic‐monzonitic rocks contain exsolved pyroxenes and perthitic intergrowths, and cooled more slowly than rocks with zoned‐pyroxene or fine grain size. Noritic material contains orthopyroxene or inverted pigeonite, augite, calcic to intermediate plagioclase, and chromite to Cr‐bearing magnetite; monzonitic clasts contain augite, sodic plagioclase, K feldspar, Ti‐bearing magnetite, ilmenite, chlorapatite, and zircon. These feldspathic rocks show similarities to some rocks at Gale Crater like Black Trout, Mara, and Jake M. The most magnesian orthopyroxene clasts are close to ALH 84001 orthopyroxene in composition. All these materials are enriched in siderophile elements, indicating impact melting and incorporation of a projectile component, except for Ni‐poor pyroxene clasts which are from pristine rocks. Clast‐laden melt rocks, spherules, shards, and siderophile element contents indicate formation of NWA 7533 as a regolith breccia. The zircons, mainly derived from monzonitic (melt) rocks, crystallized at 4.43 ± 0.03 Ga (Humayun et al. 2013 ) and a ¹⁴⁷Sm‐¹⁴³Nd isochron for NWA 7034 yielding 4.42 ± 0.07 Ga (Nyquist et al. 2016 ) defines the crystallization age of all its igneous portions. The zircon from the monzonitic rocks has a higher Δ¹⁷O than other Martian meteorites explained in part by assimilation of regolith materials enriched during surface alteration (Nemchin et al. 2014 ). This record of protolith interaction with atmosphere‐hydrosphere during regolith formation before melting demonstrates a thin atmosphere, a wet early surface environment on Mars, and an evolved crust likely to have contaminated younger extrusive rocks. The latest events recorded when the breccia was on Mars are resetting of apatite, much feldspar and some zircons at 1.35–1.4 Ga (Bellucci et al. 2015 ), and formation of Ni‐bearing pyrite veins during or shortly after this disturbance (Lorand et al. 2015 ).  相似文献