HR: 1340h
AN: V13D-1592    [Abstracts]
TI: Trace Element Geochemical Signature of Basalts and Diabases from the Bay of Islands Ophiolite in Western Newfoundland
AU: * Huang, J
EM: jian.huang@mail.uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Sciences and Research Building 1, R312, Houston, TX 77204, United States
AU: Casey, J F
EM: jfcasey@uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Sciences and Research Building 1, R312, Houston, TX 77204, United States
AU: Gao, Y
EM: yongjungao@uh.edu
AF: Geosciences Department, University of Houston, 4800 Calhoun Rd. Sciences and Research Building 1, R312, Houston, TX 77204, United States
AB: The Bay of Islands Ophiolite in western Newfoundland lies along the Appalachian Orogenic Belt and records the generation and destruction of the Proto-Atlantic Ocean from the Late-Precambrian to the middle Ordovician Taconic Orogeny. In previous geochemical studies, Jenner et al. (1991) analyzed mainly andesites and trondhjemites dominantly from Coastal Complex, which is not considered part of the Bay of Islands Ophiolite proper. He showed that these fractionated rocks mainly contained negative Nb anomalies on multi-element variations diagrams and attributed the petrogenesis of the Coastal Complex and by extension the Bay of Islands Complex to formation within arc or supra-subduction zone environment. Likewise Elthon's (1991) analyses of diabase from the North Arm Mountain Massif of the Bay of Islands Complex showed similar, but more moderately negative Ta anomalies. In this study, 50 diabases and basalts from the \label{OLE_LINK1}North Arm Mountain and Blow Me Down Mountain massifs in the Bay of Islands Ophiolite Complex (proper)were analyzed for trace elements via ICP-MS. When our existing XRF major and trace element geochemical data were supplemented by a more complete ICP-MS trace element data set from the Bay of Islands Complex (proper), it is quite clear that the Blow Me Down samples appear more MORB-like with very small negative Nb-Ta anomalies when compared to the North Arm samples, which have somewhat more negative Nb and Ta anomalies, relative to La and Th. The mafic assemblages from the ophiolite most likely include a mixture of what are referred to as MORB-like and arc-like (or suprasubduction zone) signatures. However, the North Arm and Blow Me Down Massif basalts and diabases signatures may be similar to some MORB with arc-like signatures. We review the ambiguities created by the use of Nb-Ta anomalies in interpreting tectonic setting and classifying ophiolites. We also review the validity of using Nb-Ta anomalies in highly fractionated andesites and plagiogranites as descriminators of tectonic environment.
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting