Results 231 to 240 of about 4,943,633 (275)
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Electrical conductivity structure in the lower crust
Geophysical Surveys, 1982The subject is reviewed, notwithstanding the existence of a number of disagreeing and/or controversial results found in the literature. First, a brief critical reexamination of the methodology is presented. Second, it is attempted to put the results, or partial conclusions by different authors, using different methods and referring to different ...
Giovanni P. Gregori, Louis J. Lanzerotti
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Recycling of granulitic lower crust into the mantle
Lithos, 2020Abstract Foundering of eclogitic lower crust into the convecting mantle is a well-recognized process invoked to explain the relatively evolved chemical composition of Earth's continental crust. However, it remains unclear the extent to which the foundering could control the newly-made lowermost crust, and whether mafic granulite in a thickened ...
Jun-Bo Zhang +3 more
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Syntexis and the genesis of lower oceanic crust
2000We propose that the term "syntexis" be revived and expanded to encompass all of the processes, mechanical and chemical, by which magmas react with and assimilate their host rocks. Synkinematic sills (≤50 m thick) make upthe dominant proportion of the crust of the North Arm Mountain massif of the Bay of Islands ophiolite, Newfoundland.
Jean H. Bedard +3 more
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Dating the lower crust by ion microprobe
Earth and Planetary Science Letters, 1987Ion microprobe UThPb ages of zircons from granulite facies lower crustal xenoliths from north Queensland, Australia, correlate well with the ages of major orogenic episodes manifest at the earth's surface. About half of the xenoliths contain Proterozoic zircons which are similar in age to the episodes of high-grade metamorphism of the older surface ...
Roberta L. Rudnick, Ian S. Williams
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Creation and destruction of lower continental crust
Geologische Rundschau, 1991Bulk continental crustal composition results from the net mass exchange between crust and mantle. Crustal addition is mainly by the rise of mantle-derived melts into and through the crust at convergent plate margins and (at a lower rate) within plate interiors.
Kay, R. W., Mahlburg-Kay, S.
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Thermodynamics of folding in the middle to lower crust
Geology, 2007We show that dissipative processes involving thermal-mechanical coupling produce fold systems with characteristics observed in the middle to lower crust. These comprise folds in layers with little strength contrast, scale invariance, no strict periodicity, small wavelength/thickness ratios, nonconcentric fold shapes, and axial plane crenulations.
Bruce Hobbs +2 more
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Scouring of gold from the lower crust
Geology, 1989Quartz-carbonate lodes have produced a major part of the world9s gold. The source for the lodes, which were emplaced along shear zones in the upper crust, has been enigmatic. The Bamble belt of south Norway is depleted in gold by more than an order of magnitude relative to its crustal abundance; other elements present in gold deposits have also been ...
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Seismic Anisotropy in the Lower Oceanic Crust
Nature, 1972HESS1 suggested that upper mantle compressional wave velocities near the Mendocino and Molokai fracture zones of the Pacific vary with azimuth and this anisotropy is the result of preferred mineral orientation. Recent seismic refraction evidence indicates that in many regions the Earth's upper mantle is anisotropic2–4 and the observed Anisotropy in the
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