Origins of Continental Cratons: Evidence from Kaapvaal      Xenoliths
{'Code': '06030107', 'Directorate': {'Abbreviation': 'GEO', 'LongName': 'Directorate For Geosciences'}, 'Division': {'Abbreviation': 'EAR', 'LongName': 'Division Of Earth Sciences'}}
{'SignBlockName': 'John L. Snyder', 'PO_EMAI': None, 'PO_PHON': None}
Coarse garnet peridotites that are the principal rock type                      in the Kaapvaal craton, southern Africa, have bulk and modal                    compositions that differ from oceanic preidotites in being richer               in Mg and in enstatite.  This distinction is fundemental in that                it implies a difference in the igneous processes through which                  continental and oceanic lithospheres have formed.  Both                         continental and oceanic peridotites appear to be residues and the               difference is speculated to reflect a greater depth of formation                for the craton peridotites.  In contrast, the high-temperature                  peridotites underlying the Kaapvaal craton have compositions                    similar to oceanic lithosphere and may have been subducted.                     Heterogeneities in mineral distribution in the continental                      peridotites on a scale of several centimeters are common and are                believed to be caused by exsolution of diopside and garnet from                 primary enstatite or pigeonite.  Study of variations in bulk                    composition that are igneous in origin and that exclude these                   subsolidus features requires analytical specimens weighing 0.5-1                kg.  This sample size requirement has limited acquisition of                    desired data.  Collection of additional large xenoliths, however,               is practical. This project will extend these studies to                         investigations of the igneous origins of the spinel peridotites                 from the top of the lithosphere within the craton and of the the                low-Ca garnet harzburgites that form the root.  The high-                       temperature peridotites underlying the craton appear from                       preliminary data to be more fertile towards the north than are                  those (subducted?0 beneath the southern margin.  This possibility               will be investigated.  Bulk, modal and mineral analyses of                      xenoliths weighing at least several kg will be combined with                    isotopic studies at the Department of Terrestrial Magnetism.                    Determinations of the areal distribution and depths of origin of                Kaapvaal ecligites are planned.
{'FirstName': 'Francis', 'LastName': 'Boyd', 'PI_MID_INIT': 'R', 'PI_SUFX_NAME': None, 'PI_FULL_NAME': 'Francis R Boyd', 'EmailAddress': None, 'NSF_ID': '000104950', 'StartDate': '09/01/1987', 'EndDate': None, 'RoleCode': 'Principal Investigator'}
{'Name': 'Carnegie Institution of Washington', 'CityName': 'WASHINGTON', 'ZipCode': '200151305', 'PhoneNumber': '2023876400', 'StreetAddress': '5241 BROAD BRANCH RD NW', 'StreetAddress2': None, 'CountryName': 'United States', 'StateName': 'District of Columbia', 'StateCode': 'DC', 'CONGRESSDISTRICT': '00', 'CONGRESS_DISTRICT_ORG': 'DC00', 'ORG_UEI_NUM': 'ZQ12LY4L5H39', 'ORG_LGL_BUS_NAME': 'CARNEGIE INSTITUTION OF WASHINGTON', 'ORG_PRNT_UEI_NUM': None}
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{'Code': '1573', 'Text': 'Petrology and Geochemistry'}
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