Petrogenesis of Adjacent Calc-Alkaline and Tholeiitic       Volcanoes on Umnak Island in the Aleutian Arc
{'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}
Okmok and Recheshnoi are adjacent volcanos on the volcanic front                of the Aleutian arc.  Although separated by only forty kilometers               on the island of Umnak, the two volcanos exhibit most of the                    range of compositional variability in the Aleutian.  Okmok is a                 type example of an Aleutian "tholeiitic" volcano, while                         Recheshnoi has all the characteristics of an Aleutian "calc-                    alkaline" volcano.  Almost three hundred samples from theses                    volcanos with substantial stratigraphic control from two major                  and one minor field expedition allow the study of two problems of               major importance to petrogenesis.  They are (1) the origins of                  the diversity of the major element compositions of lavas at                     convergent margins; and (2) the fractionation processes that                    occur in crustal magma chambers.  The chemical differences                      between the two volcanos have similar systematics to the global                 array of variability of convergent margin volcanics.  It is                     proposed that this global array is caused by different extents of               melting of the mantle wedge, controlled primarily by the                        thickness of the overlying crust.  But there are two other                      prominent hypotheses (Kay and Marsh) to explain the variability                 observed in Aleutian volcanos.  All three hypotheses can be                     tested by detailed study of adjacent, end-member volcanos.  The                 question of fractionation processes has been the subject of much                theoretical speculation.  Important constraints derive from time-               series evaluation of volcano evolution.  Okmok volcano allows                   such a time-series because of well-exposed pre-and post-caldera                 lavas, and a large well-preserved ash flow.  Plutonic inclusions                from both volcanos allow a comparison of plutonic and volcanic                  levels of the system.  This will be a multi-faceted approach to                 these problems, which includes additional field work unusually                  comprehensive analytical work, careful petrographic work with                   major and trace element studies of mineral zoning laboratory                    experiments, and quantitative modeling of both melting and                      crystallization processes.
{'FirstName': 'Charles', 'LastName': 'Langmuir', 'PI_MID_INIT': 'H', 'PI_SUFX_NAME': None, 'PI_FULL_NAME': 'Charles H Langmuir', 'EmailAddress': 'langmuir@eps.harvard.edu', 'NSF_ID': '000448846', 'StartDate': '07/01/1989', 'EndDate': None, 'RoleCode': 'Principal Investigator'}
{'Name': 'Columbia University Lamont Doherty Earth Observatory', 'CityName': 'Palisades', 'ZipCode': '10964', 'PhoneNumber': '9143592900', 'StreetAddress': 'Rt 9W', 'StreetAddress2': None, 'CountryName': 'United States', 'StateName': 'New York', 'StateCode': 'NY', 'CONGRESSDISTRICT': '17', 'CONGRESS_DISTRICT_ORG': 'NY17', 'ORG_UEI_NUM': None, 'ORG_LGL_BUS_NAME': None, 'ORG_PRNT_UEI_NUM': None}
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{'Code': '1557', 'Text': 'VOLCANOLOGY & MANTLE GEOCHEMIS'}
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