Metamorphic re-equilibration and metasomatism of highly chromian,garnet-rich peridotitic xenoliths from South African kimberlites     

Tim?J.?IvanicEmail author  Ben?Harte  John?J.?Gurney 《Contributions to Mineralogy and Petrology》2012,164(3):505-520

A history of decompression and metasomatism is preserved in a suite of highly chromian, garnet-rich peridotitic xenoliths from the diamondiferous Newlands and Bobbejaan kimberlites, South Africa. A high proportion of the garnets and chromites in these rocks plot in the diamond-facies fields on Cr₂O₃–CaO and Cr₂O₃–MgO wt% plots, and Cr-rich compositions are found in both the harzburgitic and lherzolitic fields. Petrographic evidence suggests that the earliest known mineralogies were those of olivine-bearing, garnet-rich rocks. These were modified by a decompression event that caused recrystallization of garnets and led to orientated spinel and pyroxene inclusions in garnet. Chemical zonation within garnet is divided into (1) external re-equilibration between garnet and matrix; (2) internal re-equilibration between garnet and its inclusions; and (3) metasomatically induced zoning between garnet core and a metasomatic rim. The compositional trajectories associated with zonations (1) and (2) in Ca–Cr plots may be closely modelled by means of sliding, garnet–spinel transition reactions whose slopes vary with bulk Ca composition; at intermediate Ca compositions, the trajectories closely match the slope of the lherzolite line or harzburgite/lherzolite boundary. The decreasing Cr/(Cr + Al) of the garnet in these zonations is in agreement with the evidence for decompression given by the petrographic recrystallization features, and overall decompression of probably 10–20 kb is indicated. We speculate on the age of these events, and consider the possibility of their association with major orogenic events documented by South African crustal rocks at 2.9–2.7 Ga, and events evidenced by peridotite-xenolith Re–Os model ages at 2.8–2.7 Ga.  相似文献   

Mathematical modeling of earths dynamical systems: a primer,by Rudy Slingerland & Lee Kump. Princeton University Press,Princeton & Oxford, 2011. No of pages: 231.Price: US$30.95. ISBN 978‐0‐691‐14514‐3 (paperback).     

Tim Davies 《Geological Journal》2014,49(3):327-327

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An oil sand pseudo-elastic model for determining ground deformation under large mobile mining equipment     

Ardeshir Dehmoobed Sharif-abadi  Tim Grain Joseph 《Geotechnical and Geological Engineering》2010,28(4):471-481

Strain softening of oil sand under dynamic loading from large mining equipment inhibits the ability of the equipment to function at optimal design performance. This paper looks at the findings of dynamic plate load tests, which effectively mimick the loading and unloading action of a shovel track pad. A pseudo-elastic model was proposed based on the results of the dynamic plate load testing to predict the deformation of oil sand under cyclic loading. Both field and laboratory cyclic plate load tests were performed on oil sand materials. The field tests were performed with different plate sizes, or footprints. The load was normalized based on the pressure stiffness concept in units of pressure per unit deformation. FLAC was used to model the field plate load test deformation with the elastic concept. The laboratory tests were performed at room temperature with more control on the load, loading rate, and cycles than possible during the field testing. Tests were conducted using a circular plate of 14.9 cm diameter, at stress magnitudes of 200, 400, 500 and 600 kPa. The plate load tests were conducted for varying loads, holding, and relaxation times of 0, 2, 5 and 10 min respectively for each magnitude of stress. The outcome of laboratory plate load tests show that after frequent cycles, the pressure stiffness (ratio of stress to deformation) converges on a plateau value of 8 kPa/mm. The proposed approach can be used to evaluate oil sands ground performance, enhancing the prediction process for ground deformation under the operation of ultra-class mining equipment.  相似文献   

西南太平洋汤加岛弧的海底火山和高温热液喷发     

Peter stoffers  周立君 《海洋地质前沿》2007,23(2):22-23

西太平洋中大多数已知的高温热液喷发都出现在洋内弧后环境中,如劳海盆、北斐济海盆和马里亚纳海沟.在弧前的海底火山上已经发现了热液喷发和相应的矿床,其中许多火山还在排气,并有释放到海底的岩浆挥发物的证据,但是只在水深超过1 km的最深的塌陷火山口发现了黑烟喷口、典型深洋中脊和弧后扩张中心.本文描述了汤加岛弧浅海底火山上首次发现的高温热液喷发和大面积的硫化物-硫酸盐烟道.  相似文献   

Graptolites; Writing in the Rocks. Fossils Illustrated Volume 1 edited by Douglas Palmer and Barrie Rickards,The Boydell Press, 1991. No. of pages: 182 (plus 138 plates). Price: £39.50 (hardback). ISBN 0–85115–262–7     

Tim Young 《Geological Journal》1992,27(1):98-99

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