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991.
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994.
New in situ data based on hydraulic fracturing and overcoring have been compiled for eastern Australia, increasing from 23 to 110 the number of in situ stress analyses available for the area between and including the Bowen and Sydney Basins. The Bowen Basin displays a consistent north‐northeast maximum horizontal stress (σH) orientation over some 500 km. Stress orientations in the Sydney Basin are more variable than in the Bowen Basin, with areas of the Sydney Basin exhibiting north‐northeast, northeast, east‐west and bimodal σH orientations. Most new data indicate that the overburden stress (σV) is the minimum principal stress in both the Bowen and Sydney Basins. The Sydney Basin is relatively seismically active, whereas the Bowen Basin is relatively aseismic. Despite the fact that in situ stress measurements sample the stress field at shallower depth than the seismogenic zone, there is a correlation between the stress measurements and seismicity in the two areas. Mohr‐Coulomb analysis of the propensity for failure in the Sydney Basin suggests 41% of the new in situ stress data are indicative of failure, as opposed to 13% in the Bowen Basin. The multiple pre‐existing structural grains in the Sydney Basin further emphasise the difference between propensity for failure in the two areas. Previous modelling of intraplate stresses due to plate boundary forces has been less successful at predicting stress orientations in eastern than in western and central Australia. Nonetheless, stress orientation in the Bowen Basin is consistent with that predicted by modelling of stresses due to plate boundary forces. Variable stress orientations in the Sydney Basin suggest that more local sources of stress, such as those associated with the continental margin and with local structure, significantly influence stress orientation. The effect of local sources of stress may be relatively pronounced because stresses due to plate boundary forces result in low horizontal stress anisotropy in the Sydney Basin. 相似文献
995.
996.
Josep Mas‐Pla Agustí Rodríguez‐Florit Manel Zamorano Carles Roqué Anna Menció David Brusi 《水文研究》2013,27(16):2352-2366
Intensive pumping in urban coastal areas is a common threat to water resource quality due to seawater intrusion. In those areas where subsurface water resources are not usually used for human consumption or irrigation, intensive pumping is associated with other activities like the lowering of the water table necessary to support underground structures and building foundations. This activity also increases the likelihood of soil settlement that affects building stability and the corrosion of concrete structures due to groundwater salinity. Under these circumstances, the awareness of a certain municipality (Calonge, NE Spain) of the potential effects of groundwater withdrawal upon foundations has led to an integrated approach to anticipate seawater intrusion related to urban development. Geological mapping and correlation of borehole logs, electrical resistivity tomography, and hydrochemical data provide comprehensive knowledge of the geology and hydrogeology of the area and act as screening tools necessary to discern the influence of hydrological processes in coastal areas. Developing Strack's analytical solution, new comprehensive, dimensionless expressions are herein derived to determine the critical pumping rate necessary to prevent seawater intrusion, as well as to reproduce the evolution of the wedge toe and the water table stagnation point under different withdrawal rates. Furthermore, the Dupuit–Forchheimer well discharge formula allows the estimation of the effects of the water table lowering due to such critical pumping in the surrounding building foundations. Field data from the Calonge coastal plain illustrate this approach and provide assessment criteria for future urban development and planning. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
997.
K. A. CUTTS P. D. KINNY R. A. STRACHAN M. HAND D. E. KELSEY M. EMERY C. R. L. FRIEND A. G. LESLIE 《Journal of Metamorphic Geology》2010,28(3):249-267
In situ LA‐ICP‐MS monazite geochronology from a garnet‐bearing diatexite within the Moine Supergroup (Glenfinnan Group) NW Scotland records three temporally distinct metamorphic events within a single garnet porphyroblast. The initial growth of garnet occurred in the interval c. 825–780 Ma, as recorded by monazite inclusions located in the garnet core. Modelled P–T conditions based on the preserved garnet core composition indicate an initially comparatively high geothermal gradient regime and peak conditions of ~650 °C and 7 kbar. Monazite within a compositionally distinct second shell of garnet has an age of 724 ± 6 Ma. This is indistinguishable from a SIMS age of 725 ± 4 Ma obtained from metamorphic zircon in the sample, which is interpreted to record the timing of migmatization. This second stage of garnet growth occurred on a P–T path from ~6 kbar and 650 °C rising to ~9 kbar and 700 °C, with the peak conditions associated with partial melting. A third garnet zone which forms the rim contains monazite with an age of 464 ± 3 Ma. Monazite in the surrounding matrix has an age of 462 ± 2 Ma. This corresponds well with a U–Pb SIMS zircon age of 463 ± 4 Ma obtained from a deformed pegmatite that was emplaced during widespread folding and reworking of the migmatite fabric. The P–T conditions associated with the final phase of garnet growth were ~7 kbar and 650 °C. The monazite ages coupled with the phase relations modelled from this multistage garnet indicate that it records two Neoproterozoic tectonothermal events as well as the widespread Ordovician Grampian event associated with Caledonian orogenesis. Thus, this single garnet records much of the Neoproterozoic to Ordovician thermal history in NW Scotland, and highlights the long history of porphyroblast growth that can be revealed by in situ isotopic dating and associated P–T modelling. This approach has the potential to reveal much of the thermal architecture of Neoproterozoic events within the Moine Supergroup, despite intense Caledonian reworking, if suitable textural and mineralogical relationships can be indentified elsewhere. 相似文献
998.
The use of in situ geochronological techniques allows for direct age constraints to be placed on fabric development and the metamorphic evolution of polydeformed and reworked terranes. The Shoal Point region of the southern Gawler Craton consists of a series of reworked granulite facies metapelitic and metaigneous units which belong to the Late Archean Sleaford Complex. Structural evidence indicates three phases of fabric development with D1 retained within boudins, D2 consisting of a series of upright open to isoclinal folds producing an axial planar fabric and D3 composed of a highly planar vertical high‐strain fabric which overprints the D2 fabric. Th–U–total Pb EPMA monazite and garnet Sm–Nd geochronology constrain the D1 event to the c. 2450 Ma Sleaford Orogeny, whereas the D2 and D3 events are constrained to the 1730–1690 Ma Kimban Orogeny. P–T pseudosections constrain the metamorphic conditions for the Sleafordian Orogeny to between 4.5 and 6 kbar and between 750 and 780 °C. Subsequent Kimban‐aged reworking reached peak metamorphic conditions of 8–9 kbar at 820–850 °C during the D2 event, followed by high‐temperature decompression to metamorphic conditions <6 kbar and 790–850 °C associated with the development of the D3 high‐strain fabric. The P–T–t evolution of the Shoal Point rocks reflects the transpressional exhumation of lower crustal rocks during the Kimban Orogeny and the development of a regional ‘flower structure’. 相似文献
999.
辽东草河群由北向南,可以分出比较完整的中压型巴罗式变质带、变质带的分界线或等变质度线和面基本上与地槽褶皱的构造方向一致,显示出带型区域变质作用和复合变质作用的特点。区域变质相带的矿物共生组合、斜长石号码、岩石类型、矿物的物理化学性质都具独自的特征。变质相带的变泥质岩石中的石榴石均属铁铝榴石,随变质度的增高,石榴石成分中的Al2O3、MgO、FeO Fe2O3含量增加,CaO、MnO含量降低。 相似文献
1000.
最近十年来中国地理科学的进展 总被引:10,自引:0,他引:10
最近十年来中国地理科学的最重要进展有:自然地理学与人文地理学的平衡发展,人口、资源、环境的研究,遥感的应用与地理信息系统的建立,自然地理定位观测,青藏高原隆起对自然环境的影响,城市与城市规划,中国历史地理研究等。最近,并已开始研究气候变化与海平面上升对中国的影响,使我国地理科学研究紧紧跟上世界发展的步伐。 相似文献