Metamorphism of the ordinary chondrites: A review |
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| Affiliation: | 1. Department of Geological Sciences, University of Oregon, Eugene, OR 97403, USA;2. Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA;1. Department of Geology, University of Maryland, College Park, MD 20740, United States;2. Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, United States;3. NIRVANA Labs, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, United States;4. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02540, United States;1. NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA;2. Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA;3. Department of Geological Sciences, University of Florida, Gainesville, FL 32611, USA;1. Department of Earth and Planetary Sciences, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA;2. Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia;3. Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA;1. Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, United States;2. Science and Technology Division, Corning Incorporated, Corning, NY 14831, United States;3. Dept. of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, United States;4. Dept. of Geophysical Sciences, University of Chicago, Chicago, IL 60637, United States |
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| Abstract: | Textural variations among the ordinary chondrites are paralleled by mineralogioal and chemical trends, most of which are consistent with the view that these chondrites have experienced various degrees of alteration in the solid state. On the basis of mineralogical and textural data, it is inferred that this alteration took place at temperatures of roughly 400 to greater than 820°C, under load pressures on the order of 1–2 kbar, in the absence of penetrative stress and under relatively dry, reducing conditions.The mineralogical data do not indicate whether alteration took place during reheating of cold material (progressive metamorphism) or during cooling of a hot agglomerate (autometamorphism). The former mechanism seems more likely, for the latter requires extremely rapid and deep burial, which would be difficult to achieve within existing models for the origin of chondritic material.Alternative models which attribute the textural, mineralogical and chemical variations among ordinary chondrites to crystal-liquid-vapor interactions prior to accumulation find little support in the chondrites and are regarded as less satisfactory than the metamorphic hypothesis. |
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