Igneous petrogenesis and tectonic setting of the Elkahatchee quartz diorite, Alabama Appalachians: implications for Penobscotian magmatism in the eastern Blue Ridge

Abstract

The Elkahatchee Quartz Diorite (EQD) is a pre-metamorphic (Penobscot age, 490-500 Ma) batholith and the largest intrusive complex (880 km2) exposed in the Blue Ridge province of the southern Appalachians. Slightly peraluminous to metaluminous, calc-alkaline I-type tonalite-granodiorite is the principal lithology of the batholithic complex, with subordinate cumulate hornblende-biotite gabbro-diorite and biotite-epidote schistose enclaves, quartz-biotite metadacite porphyry, and felsic granitoids (granite, trondhjemite, and quartz monzonite). It is suggested that the EQD represents continental margin magmatism associated with incipient subduction of an oceanic slab beneath Laurentia. This investigation has compiled numerous Penobscot age plutonic, tectonic (ophiolite emplacement), and metamorphic events distributed throughout the Appalachians, which are proximal to previously proposed Laurentian margins. The Penobscot age orogenesis may have spanned the length of the Appalachians and is, in part, represented by continental margin magmatism, such as the EQD. -from Authors