skip to main content

Title: Petrology and geochemistry of lower crustal granulites from the Geronimo Volcanic Field, southeastern Arizona

Mafic to intermediate composition granulite xenoliths occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust. Low {sup 143}Nd/{sup 144}Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the meta-diorites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free granulites have more mafic compositions and their trace element characteristics are consistent with a cumulate origin. A negative correlation of {sup 208}Pb/{sup 204}Pb vs. {sup 206}Pb/{sup 204}Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range.
Authors:
;  [1] ;  [2] ;  [3]
  1. (The Open Univ., Milton Keynes (England))
  2. (NERC Isotope Geosciences Laboratory, Keyworth (England))
  3. (Department of Earth Sciences, Oxford (England))
Publication Date:
OSTI Identifier:
6053924
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta; (USA); Journal Volume: 54:12
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ARIZONA; GRANULITES; GEOCHEMISTRY; PETROGENESIS; PETROLOGY; CHEMICAL COMPOSITION; ISOTOPE RATIO; MINERALOGY; VOLCANIC REGIONS; CHEMISTRY; FEDERAL REGION IX; GEOLOGY; METAMORPHIC ROCKS; NORTH AMERICA; ROCKS; USA 580000* -- Geosciences