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851.
The principle of lithostatic pressure is habitually used in metamorphic geology to calculate burial/exhumation depth from pressure given by geobarometry. However, pressure deviation from lithostatic, i.e. tectonic overpressure/underpressure due to deviatoric stress and deformation, is an intrinsic property of flow and fracture in all materials, including rocks under geological conditions. In order to investigate the influences of tectonic overpressure on metamorphic P–T paths, 2D numerical simulations of continental subduction/collision zones were conducted with variable brittle and ductile rheologies of the crust and mantle. The experiments suggest that several regions of significant tectonic overpressure and underpressure may develop inside the slab, in the subduction channel and within the overriding plate during continental collision. The main overpressure region that may influence the P–T paths of HP–UHP rocks is located in the bottom corner of the wedge‐like confined channel with the characteristic magnitude of pressure deviation on the order of ~0.3 GPa and 10–20% from the lithostatic values. The degree of confinement of the subduction channel is the key factor controlling this magnitude. Our models also suggest that subducted crustal rocks, which may not necessarily be exhumed, can be classified into three different groups: (i) UHP‐rocks subjected to significant (≥0.3 GPa) overpressure at intermediate subduction depth (50–70 km, P = 1.5–2.5 GPa) then underpressured at depth ≥100 km (P ≥ 3 GPa); (ii) HP‐rocks subjected to ≥0.3 GPa overpressure at peak P–T conditions reached at 50–70 km depth in the bottom corner of the wedge‐like confined subduction channel (P = 1.5–2.5 GPa); (iii) lower‐pressure rocks formed at shallower depths (≤40 km depth, P ≤ 1 GPa), which are not subjected to significant overpressure and/or underpressure. 相似文献
852.
H. Omrani M. Moazzen R. Oberhänsli T. Tsujimori R. Bousquet M. Moayyed 《Journal of Metamorphic Geology》2013,31(8):791-812
The Shanderman eclogites and related metamorphosed oceanic rocks mark the site of closure of the Palaeotethys ocean in northern Iran. The protolith of the eclogites was an oceanic tholeiitic basalt with MORB composition. Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation. Minerals formed during the prograde stages are preserved as inclusions in peak metamorphic garnet and omphacite. The rocks experienced blueschist facies metamorphism on their prograde path and were metamorphosed in eclogite facies at the peak of metamorphism. The peak metamorphic mineral paragenesis of the rocks is omphacite, garnet (pyrope‐rich), glaucophane, paragonite, zoisite and rutile. Based on textural relations, post‐peak stages can be divided into amphibolite and greenschist facies. Pressure and temperature estimates for eclogite facies minerals (peak of metamorphism) indicate 15–20 kbar at ~600 °C. The pre‐peak blueschist facies assemblage yields <11 kbar and 400–460 °C. The average pressure and temperature of the post‐peak amphibolite stage was 5–6 kbar, ~470 °C. The Shanderman eclogites were formed by subduction of Palaeotethys oceanic crust to a depth of no more than 75 km. Subduction was followed by collision between the Central Iran and Turan blocks, and then exhumation of the high pressure rocks in northern Iran. 相似文献
853.
《水文科学杂志》2013,58(3)
Abstract Abstract Accurate estimates of water losses from mature Sitka spruce (Picea sitchensis) plantations in the UK uplands are required to assess the sustainability of water supply in the event of land-use change. Many investigations have demonstrated that afforestation increases water losses from temperate upland catchments, to up to 40% of annual site rainfall. In a 0.86 km2 upland water supply catchment in southwest Scotland, interception loss in a Sitka spruce-dominated 37-year old plantation, was 52% of annual precipitation (2912 mm), considerably higher than reported in previous studies of similar catchments. From direct measurements of rainfall, cloudwater, discharge and soil evaporation, the catchment water balance was 96–117% complete, within the limits of measurement error. The most probable explanation for the higher forest interception loss reported here is the inclusion of cloudwater measurements. 相似文献
854.
R. D. Staples H. D. Gibson R. G. Berman J. J. Ryan M. Colpron 《Journal of Metamorphic Geology》2013,31(7):729-753
Amphibolite facies metasedimentary schists within the Yukon‐Tanana terrane in the northern Canadian Cordillera reveal a two‐stage, polymetamorphic garnet growth history. In situ U‐Th‐Pb Sensitive High Resolution Ion Microprobe dating of monazite provide timing constraints for the late stages of garnet growth, deformation and subsequent decompression. Distinct textural and chemical growth zoning domains, separated by a large chemical discontinuity, reveal two stages of garnet growth characterized in part by: (i) a syn‐kinematic, inclusion‐rich stage‐1 garnet core; and (ii) an inclusion‐poor, stage‐2 garnet rim that crystallized with syn‐ to post‐kinematic staurolite and kyanite. Phase equilibria modelling of garnet molar and compositional isopleths suggest stage‐1 garnet growth initiated at ~600 °C, 8 kbar along a clockwise P–T path. Growth of the compositionally distinct, grossular‐rich, pyrope‐poor inner portion of the stage‐2 overgrowth is interpreted to have initiated at higher pressure and/or lower temperature than the stage‐1 core along a separate P–T loop, culminating at peak P–T conditions of ~650–680 °C and 9 kbar. Stage‐2 metamorphism and the waning development of a composite transposition foliation (ST) are dated at c. 118 Ma from monazite aligned parallel to ST, and inclusions in syn‐ to post‐ST staurolite and kyanite. Slightly younger ages (c. 112 Ma) are obtained from Y‐rich monazite that occurs within resorbed areas of both stage‐1 and stage‐2 garnet, together with retrograde staurolite and plagioclase. The younger ages obtained from these texturally and chemically distinct grains are interpreted, with the aid of phase equilibria calculations, to date the growth of monazite from the breakdown of garnet during decompression at c. 112 Ma. Evidence for continued near‐isothermal decompression is provided by the presence of retrograde sillimanite, and cordierite after staurolite, which indicates decompression below ~4–5 kbar prior to cooling below ~550 °C. As most other parts of the Yukon‐Tanana terrane were exhumed to upper crustal levels in the Early Jurassic, these data suggest this domain represents a tectonic window revealing a much younger, high‐grade tectono‐metamorphic core (infrastructure) within the northern Cordilleran orogen. This window may be akin to extensional core complexes identified in east‐central Alaska and in the southeastern Canadian Cordillera. 相似文献
855.
地下水流系统理论与研究方法的发展 总被引:6,自引:0,他引:6
地下水流系统理论的提出,推动了现代水文地质学的发展。以Tóth经典地下水流系统理论建立方法为基础,综述了基于Tóth方法的地下水流系统的模拟成果,分析了Tóth方法得出的水流模式与控制因素的关系,以及地下水流系统理论从概念到实际应用的发展。同时,对中国地质大学(武汉)提出的地下水流系统通量上边界模拟方法也进行了系统论述,在物理模拟实验与数值模拟基础上,认为通量上边界分析方法是对Tóth方法的改进与完善,有利于对地下水流系统发育的物理机制理解;该方法能够更全面认识地下水流系统模式及其转化,定量出各影响因素对地下水流模式的控制关系。最后指出地下水流系统理论是当代水文地质学的核心概念框架,应该重视地下水流系统理论物理机制和数学模拟方法的研究,加强新技术方法的引入,拓宽其应用领域的研究等。 相似文献
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860.
C. LÁZARO A. GARCÍA-CASCO Y. ROJAS AGRAMONTE A. KRÖNER F. NEUBAUER M. ITURRALDE-VINENT 《Journal of Metamorphic Geology》2009,27(1):19-40
Petrological and geochronological data of six representative samples of exotic blocks of amphibolite and associated tonalite-trondhjemite from the serpentinitic mélange of the Sierra del Convento (eastern Cuba) indicate counterclockwise P–T paths typical of material subducted in hot and young subduction zones. Peak conditions attained were ∼750 °C and 15 kbar, consistent with the generation of tonalitic partial melts observed in amphibolite. A tonalite boulder provides a U-Pb zircon crystallization age of 112.8 ± 1.1 Ma, and Ar/Ar amphibole dating yielded two groups of cooling ages of 106–97 Ma (interpreted as cooling of metamorphic/magmatic pargasite) and 87–83 Ma (interpreted as growth/cooling of retrograde overprints). These geochronological data, in combination with other published data, allow the following history of subduction and exhumation to be established in the region: (i) a stage of hot subduction 120–115 Ma, developed upon onset of subduction; (ii) relatively fast near-isobaric cooling (25 °C Myr−1 ) 115–107 Ma, after accretion of the blocks to the upper plate lithospheric mantle; (iii) slow syn-subduction cooling (4 °C Myr−1 ) and exhumation (0.7 km Myr−1 ) in the subduction channel 107–70 Ma; and (iv) fast syn-collision cooling (74 °C Myr−1 ) and exhumation (5 km Myr−1 ) 70–60 Ma. 相似文献