Computer Science
Scientific paper
Aug 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.3131s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 15, pp.3131-3154
Computer Science
17
Scientific paper
Subaqueously-erupted basalts that occur in kilometre-scale allochthons within the 1.9 Ga Flin Flon Belt, Canada, appear to have been generated at oceanic ridges and possibly oceanic plateaus, remote from Archean cratons. The ocean-floor basalts fall into two categories: (1) N-type, resembling N-MORBs and Mariana-type back-arc basin basalts (depleted to flat REE patterns, high Zr/Nb, variable Th/Nb, and initial Nd = +3.3 to +5.4); (2) E-type, resembling transitional and plume MORBs (slightly enriched REE patterns, lower Zr/Nb, initial Nd = +3.1 to +4.5). In the largest and best-studied allochthon, the Elbow-Athapapuskow `assemblage,' mixing between depleted (N-MORB) and enriched (OIB) sources or melts, coupled with variable addition of a subduction LILE component, can explain the chemical variations in the basalts. Zircon U-Pb dates of 1904 ± 4 Ma for a syn-volcanic diabase sill and 1901 Ma for a gabbro-peridotite cumulate complex demonstrate that crystallization of the `ocean-floor' basalts overlapped with, in part, eruption of the tectonically juxtaposed 1.90-1.88 Ga arc volcanic rocks. The Elbow-Athapapuskow allochthon is interpreted as back-arc basin crust that developed simultaneously with Flin Flon arc magmatism. Subaerially erupted basalts that chemically resemble tholeiitic OIBs (8-14% MgO, relative HREE depletion, initial Nd = +2.2 to +3.4) occur in tectonic contact with the Elbow-Athapapuskow assemblage. The OIBs may have been generated by deeper (garnet residue) melting of enriched mantle tapped during extension in the Elbow-Athapapuskow back-arc basin, and were possibly erupted onto a remnant arc. Deeper mantle melting is also indicated by the presence of the LREE-enriched oceanic plateau-like basalts of the Sandy Bay assemblage. The back-arc, OIB, and plateau volcanic assemblages were juxtaposed against ca. 1.9 Ga arc assemblages in a Philippines-like intraoceanic accretionary complex by 1.87 Ga.
Lucas Stephen B.
Stern Richard A.
Syme Eric C.
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