Geochemistry and tectonic setting of lower Proterozoic supracrustal rocks of the Pinal Schist, southeastern Arizona ( USA)

Two lithologic assemblages are identified in the early Proterozoic (approx 1700 Ma) supracrustal rocks of the Pinal Schist in SE Arizona. A W assemblage is composed largely of quartz wacke turbidites, and an E assemblage includes bimodal volcanics and variable amounts of sediment, chiefly feldspathic quartzite and conglomerate. Basalts from the E assemblage have incompatible-element distributions similar to those found in basalts from continental-margin arcs or evolved oceanic arcs, whereas those from the W assemblage have distributions similar to within-plate or back-arc basin basalts. The E assemblage may represent remnants of a major NE-trending continental-margin arc system, and the W assemblage may have been deposited in an intra-arc basin or a NW-trending aulacogen which opened on the southwest.-from Authors