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231.
攀西裂谷带及其邻区的现代构造应力场特征 总被引:1,自引:0,他引:1
本文主要根据近30多年来,发生在攀西裂谷地区地震的断层面解,辅以其它手段的资料,讨论该地区的现代构造应力场。结果表明,攀西裂谷带的受力状态已由过去的拉张变为现今的压扭,是一条消亡的古裂谷带。 相似文献
232.
233.
本文对近年来在攀枝花-西昌(攀西)构造带所做的重力、地磁、航磁、古地磁、遥感、天然地震、大地电磁测深、地热和爆炸地震探测资料,进行了综合分析和研究,得出了该构造带的深部结构和地球物理场的特征。基于此,提出了攀西吉裂谷存在的地球物理标志,论述了该裂谷带与现代强烈活动的裂谷带和已消亡的古裂谷的差异与其“活化”的证据。本文最后提出,这是一个被动“活化”的古裂谷的论点。 相似文献
234.
A Landsat Thematic Mapper (TM) image acquired on 23 July 1991 recorded widespread activity associated with the Episode 48 of the Pu'u 'O'o-Kupaianaha eruption of Kilauea Volcano, Hawaii. The scene contains a very large number (>3500) of thermally elevated near infrared (0.8–2.35 m) pixels (each 900 m2), which enable the spatial distribution of volcanic activity to be identified. This activity includes a lava lake within Pu'u 'O'o cone, an active lava tube system (7.9 km in length) with skylights between the Kupaianaha lava shield and several ocean entry points, and extensive active surface flows (total area of 1.3 km2) within a much larger area of cooling flows (total16 km2). The production of an average flux density map from the TM data of the flow field, wherein the average flux density is defined in units of Wm-2, allows for the chronology of emplacement of active and cooling flows to be determined. The flux density map reveals that there were at least three breakouts (>5000 Wm-2) feeding active flows, but on the day that the data were collected the TM recorded a waning phase of surface activity in this area, based on the relatively large amount of intermediate power-emitting (cooling) flows compared to high power-emitting (active) flows. The production of a comparable flux density map for future eruptions would aid in the assessment of volcanic hazards if the data were available in near-real time. 相似文献
235.
The Rhine Graben begins to develop in the Upper Eocene. During the first paroxysmal stage a belt of sandstones and conglomerates, the so-called Conglomé-rats cotiers, is deposited on the rift border. In the graben an euryhaline lacustrine basin regulates the extension of fan-deltas which are developing along the boundary faults of the rift.Stromatolites preferentially colonize the littoral fringe of the lake where they find indurated substratums. So they appear to be excellent markers of the transgressive movements of the lake and its palaeomargins. The stromatolites also allow an excellent sequential subdivision to reconstruct the history of the basin. 相似文献
236.
237.
Active faults, seismicity and recent fracturing in the lithosphere of the Baikal rift system 总被引:1,自引:0,他引:1
A map of major active faults has been constructed for the Baikal rift system (BRS). Recent active faults are identified using seismological data. The BRS seismicity of the past 40 years is statistically analyzed. Areas of a “stable” concentration of epicenters are revealed. On this basis, a zone of recent fracturing of the lithosphere is identified and its relation to active and developing faults of the BRS is analyzed. The zone of the lithosphere fracturing is a major tectonic structure, which controls both the recent seismic process and the reactivation of ancient faults. It is demonstrated that the available seismological data can provide a basis for a detailed classification of faults by degree of their tectonic activity. Regularities in the distribution of strong earthquakes along the zone of the recent fracturing of the lithosphere are established, as well as regularities in the distribution of strong and weak seismic events relative to transform and other faults. The degree of the fault reactivation is determined by their spatial closeness to the axial zone of the recent rupturing of the lithosphere. 相似文献
238.
Somdev Bhattacharji Rajesh Sharma Nilanjan Chatterjee 《Journal of Earth System Science》2004,113(4):771-784
The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. Three-dimensional
gravity modeling of +70mgal Bouguer gravity highs extending in the north-south direction along the western continental margin
rift indicates the presence of a subsurface high density, mafic-ultramafic type, elongated, roughly ellipsoidal body. It is
approximately 12.0 ±1.2 km thick with its upper surface at an approximate depth of 6.0 ±0.6 km, and its average density is
{dy2935} kg/m3. Calculated dimension of the high density body in the upper crust is 300 ±30 km in length and 25 ±2.5 to 40 ±4 km in width.
Three-dimensional gravity modeling of +10mgal to -30mgal Bouguer gravity highs along the intraplate Narmada-Tapti rift indicates
the presence of eight small isolated high density mafic bodies with an average density of {dy2961} kg/m3. These mafic bodies are convex upward and their top surface is estimated at an average depth of 6.5 ±0.6 (between 6 and 8km).
These isolated mafic bodies have an average length of 23.8 ±2.4km and width of 15.9 ±1.5km. Estimated average thickness of
these mafic bodies is 12.4±1.2km. The difference in shape, length and width of these high density mafic bodies along the western
continental margin and the intraplate Narmada-Tapti rifts suggests that the migration and concentration of high density magma
in the upper lithosphere was much more dominant along the western continental margin rift. Based on the three-dimensional
gravity modeling, it is conjectured that the emplacement of large, ellipsoidal high density mafic bodies along the western
continental margin and small, isolated mafic bodies along the Narmada-Tapti rift are related to lineament-reactivation and
subsequent rifting due to interaction of hot mantle plume with the lithospheric weaknesses (lineaments) along the path of
Indian plate motion over the Réunion hotspot. Mafic bodies formed in the upper lithosphere as magma chambers along the western
continental margin and the intraplate Narmada-Tapti rifts at estimated depths between 6 and 8 km from the surface (consistent
with geological, petrological and geochemical models) appear to be the major reservoirs for Deccan flood basalt volcanism
at approximately 65 Ma. 相似文献
239.
Maria Sachpazi Mireille Laigle Nikos Roussos 《Earth and Planetary Science Letters》2003,216(3):243-257
Continental extension is forming the Gulf of Corinth across the strike of earlier Alpine evolution. Here, we present the first deep reflection sections with pre-stack depth-migration processing across the deep basin of the Corinth active rift, which image structures unpredicted by current models. Resolving the infill as a pile of layers that are broken by faults allows one to follow their subsidence and deformation history. Variation among the profiles suggests that southern normal faults control the rift in a time progression from the east towards its western tip. On the central, Derveni-Itea transect, a 3-km widening of the basin accrued since the initiation of this control that is marked by an unconformity between the two main sedimentary units. This is estimated to have occurred 0.5-0.6 Myr ago, assuming the glacio-eustatic sea-level changes have controlled the stratigraphy of sediments deposited as a succession of layers on the subsiding hangingwall, as they did on the southern footwall in forming the famous flight of marine terraces of Corinth. A roll-over anticline and crestal collapse graben are diagnostic of the control by a normal fault of dip varying with depth. The deeper low-angle part of this bi-planar fault is indeed imaged as a reflector in the basement. The occurrence of the collapse with a breakaway at the steep southern basin-bounding fault of the hangingwall slab can be estimated 0.12-0.2 Myr ago, with a marked increase in extension rate that brought it to its present fastest value over 10 mm/yr. The low-angle part of the active fault might also have controlled earlier evolution upslope and in the basin. When compared with inferences from earthquake studies, this low-angle active fault may not appear to be seismogenic but may participate to the seismic cycle, possibly in a conditionally stable regime. Active faults seen as sea-bottom scarps merely accommodate deformation of its subsiding hangingwall. The footwall of the low-angle faults, which current seismicity shows to be in extension, appears then as being pulled out from beneath the rift, in a motion towards the rolling-back slab that causes the Hellenic subduction retreat. 相似文献
240.
Yongbei Zhang Shihua Sun Chengyan Xu Hao Wang Chongsun Zhao Zhihua Zhu 《Resource Geology》2003,53(4):261-272
Abstract. The Kunyang rift on western margin of Yangtze Platform is a continental rift, and also a rare Precambrian Fe-Cu mineralization zone in China. The Wuding-Lufeng mineralization area in the middle section of the rift is an important part of the zone, and an elliptic-shaped volcanic collapsed basin, controlled by a ring fracture system with carbonatitic volcanic rocks mainly occurring along the northwestern edge of the basin. The Hetaoqing Fe-Cu ore deposit at the western side of the basin is hosted in carbonatitic volcanic rocks and pyroclastic sedimentary rocks. The original ore bodies occur as layers, bands and lenses conformable to the host carbonatitic rocks. The ores usually appear as massive, impregnated and granular in carbonatitic rocks, and as brecciform and sandy in pyroclastic sedimentary rocks. Ore-forming minerals are magnetite, hematite, chalcopy-rite, bornite, pyrite, carrollite, molybdenite, cobaltite and skinnerite, and secondary minerals limonite, chalcocite, azurite, malachite and tenorite. Gangue minerals are calcite, dolomite, ankerite, common hornblende, arfvedsonite, augite, aegirine-augite, albite, phlogopite, biotite, chlorite and apatite. Evidences of mineral chemistry, trace elements and isotopic ratios of ores, as well as geological features, suggest that the original ores are igneous in origin. Chemical features of magnetites in the deposit belong to carbonatite type, and are similar to those from the Bayan Obo carbonatites. The ores are rich in iron, titanium, rare earth elements, niobium, tantalum, gold, silver, phosphor and sulfur. These features indicate that the Fe-Cu deposit associated with volcanic activity in the Wuding-Lufeng basin is alkali-carbonatite volcanic type. 相似文献