HR: 1330h
AN: V42D-0380    [PDF]
TI: Oxygen isotopic signature of mantle xenoliths from the Patagonia region, Argentina
AU: * Koester, E
EM: koester@vortex.ufrgs.br
AF: Laboratorio de Geologia Isotopica, CPGq, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, C.P. 15001, Porto Alegre, RS 91501970 Brazil
AU: Mallmann, G
EM: guilherme.mallmann@ufrgs.br
AF: PPGGeo, Bolsista CNPq, Universidade Federal do Rio Gramdo do Sul, Av. Bento Goncalves 9500, C.P. 15001, Porto Alegre, RS 91501970 Brazil
AU: Conceicao, R V
EM: rommulo.conceicao@ufrgs.br
AF: Laboratorio de Geologia Isotopica, CPGq, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, C.P. 15001, Porto Alegre, RS 91501970 Brazil
AU: Mariga, J
EM: jmariga@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East Tenth street, Bloominton, IN 47405 United States
AU: Bertotto, G W
EM: gwbertotto@yahoo.com.ar
AF: CONICET, Universidad Nacional de La Plata, Calle 1, 844, La Plata, 1900 Argentina
AU: Schilling, M
EM: mschilling@esfera.cl
AF: Universidad de Chile, Beauchef 850, Santiago, 6511265 Chile
AU: Chemale, F
EM: farid.chemale@ufrgs.br
AF: Laboratorio de Geologia Isotopica, CPGq, Universidade Federal do Rio Grande do Sul, Av. Bento Goncalves 9500, C.P. 15001, Porto Alegre, RS 91501970 Brazil
AU: Cingolani, C
EM: ccingola@cig.museo.unpl.edu.ar
AF: CONICET, Universidad Nacional de La Plata, Calle 1, 844, La Plata, 1900 Argentina
AB: In order to provide petrological information about the continental lithospheric mantle in the Patagonian region, a series of oxygen isotopic analyses were performed in mantle xenoliths. Hosted by Miocene-Pleistocene alkaline basalts erupted in the Andean back-arc setting, the studied mantle xenoliths are represented by anhydrous spinel-bearing lherzolites to harzburgites, and subordinately websterites and olivine websterites. Using a conventional vacuum extraction line employing BrF$_{5}$, oxygen isotopic analyses were conducted in whole-rock, olivine, clinopyroxene and orthopyroxene at the Department of Geological Sciences, Indiana University, Bloomington - USA. Isotopic ratios were measured on a Finnigan MAT 252 stable isotope mass spectrometer. Values of NBS-28 quartz are $\delta$ $^{18}$O = +9.6 $\pm$ 0.2 $\permil$. Errors obtained were better than $\pm$ 0.1 $\permil$ (2SD). Whole-rock data suggests a wide range of $\delta$ $^{18}$O from +5.5 to +10.1 $\permil$, whereas mantle rocks, in general, presented values ranging around 5.5 $\pm$ 0.2 $\permil$. Olivines showed two distinct isotopic ranges, with values of +5.0 to +5.9 $\permil$, similar to values for upper mantle olivines, but also low $\delta$ $^{18}$O values, around 3.2 $\permil$. Pyroxenes demonstrated a wide range of values, between +4.5 and +6.3 $\permil$ similar to upper mantle pyroxenes. The discrepancy of some whole-rock and olivine values in relation to mantle compositions could be interpreted as an inter-mineral disequilibrium, mineral zonation reflecting or not, metasomatic interaction, or even crust participation during subduction
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting