نتایج جستجو برای: rocks
تعداد نتایج: 22088 فیلتر نتایج به سال:
During Kand Si-metasomatism of deformed, relatively-mafic parent rocks to form more felsic, granitic rocks containing myrmekite, Ca, Mg, and Fe must leave the system as the modified rock is enriched in K, Na, and/or Si. When this kind of metasomatism occurs, the subtraction of Ca, Mg, and Fe would also be accompanied by losses of other metals present in the ferromagnesian silicates that were re...
Introduction: The aim of this abstract is to acquaint the reader with the major geochemical and geochronological properties of lunar rocks formed or affected by impact events, and thus how these rocks constrain lunar bombardment history, with particular emphasis on constraints upon the proposed Lunar Cataclysm or Late Heavy Bombardment [1]. To this end, the focus is on clast-poor impact melt ro...
Scientists from the U.S. Geological Survey are evaluating the potential for undiscovered sulfide deposits containing varying amounts of nickel, copper, platinumgroup metals, and cobalt in the Lake Superior region as part of an ongoing effort to assess the mineral potential of the United States. Similarities between rocks of the Midcontinent rift and rocks that host the Voisey Bay nickel-copper-...
Potassium-argon ages of eight volcanic rocks from some of the geologically oldest flows exposed in the Galápagos Archipelago indicate that the Galápagos Islands have a probable maximum age of 3 million years. Rocks from six islands were dated; the oldest are from Española (3.2 +/- 0.2), Sante Fe (2.7 +/- 0.1), and Plazas (4.2 +/- 1.8 million years). The new data suggest that the Galápagos Islan...
Global maps of thermal and fast neutron fluxes from the moon suggest three end-member compositional units. A high thermal and low fast neutron flux unit correlates with the lunar highlands and is consistent with feldspathic rocks. The South Pole-Aitken basin and a strip that surrounds the nearside maria have intermediate thermal and fast neutron flux levels, consistent with more mafic rocks. Th...
The Spirit landing site in Gusev Crater on Mars contains dark, fine-grained, vesicular rocks interpreted as lavas. Pancam and Mini-Thermal Emission Spectrometer (Mini-TES) spectra suggest that all of these rocks are similar but have variable coatings and dust mantles. Magnified images of brushed and abraded rock surfaces show alteration rinds and veins. Rock interiors contain </=25% megacrysts....
The rocks are formed through very complex processes and the complex behaviour of rock masses is dominated by the planes of weaknesses . Rock mass consists of intact rock and discontinuities. Many rocks show strain softening behaviour under loads. In this paper, the constitutive models for intact rocks and rock joints are presented. These form the basis for the development of constitutive models...
In the last two centuries, European fire suppression practices have produced increases in vegetation density and canopy cover in many landscapes. Potentially, increases in canopy cover could negatively affect small populations of nocturnal reptiles that use sun-exposed shelters for diurnal thermoregulation. We hypothesized that vegetation encroachment over rock outcrops might partly explain the...
The main reservoir in the Dixie Valley geothermal field of Nevada is hosted in fractured Jurassic rocks within the hanging wall of the Stillwater fault. Within the Jurassic sequence, at least four major stages of alteration related to the fault system can be identified. The paragenetic sequence from oldest to youngest consists of Stage I) biotite-potassium feldspar veins, and epidote-chlorite-c...
Absbvct New petrographic and chemical data of volcanic rocks from the Metales Belt, Rio de las Tunas area, in the Frontal Cordillera of Argentina are presented. The rocks display a broadly basaltic composition. ‘PNO varieties of basaltic dikes can be differentiated. One group, whose mineralogy comprise essentially tremolite-actinolite, plagioclase, pyroxene and limited amounts of olivine as the...
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