Petrology and geochronology of 1.48 to 1.45 Ga igneous rocks in the St. Francois Mountains terrane, southeast Missouri

First posted February 19, 2021 For additional information, contact: Director, Geology, Geophysics, and Geochemistry Science CenterU.S. Geological SurveyBox 25046, MS-973Denver, CO 80225-0046 The igneous geology of the St. Francois Mountains terrane in southeast Missouri is dominated by products 1.48 to 1.45 billion year old volcanic plutonic magmatism but also includes volumetrically minor, compositionally bimodal contributions added during plutonism between 1.34 1.27 years ago. rocks are bimodally distributed dominant felsic minor with mafic intermediate compositions. All these ferroan, which like most their trace element abundances, suggests a genesis associated farfield intraplate extensional tectonism decompression-related magmatism. diversity compositions among probably reflects mixtures mantle-derived inputs low-degree partial melting more evolved crustal protoliths. Newly determined ages define essentially continuous 30-million-year period this coeval, whether intrusive or extrusive having mafic, intermediate, In addition, iron oxide-apatite (for example, Pea Ridge) likely oxide-copper gold (Boss) deposits have coincident magmatic episode. Spatial temporal relations mineral they host suggest mineralization processes genetically related.Geochemical, petrographic, geochronologic, terrane-wide physical characteristics consistent an origin involving extension well inboard from margin Laurentian craton, mantle upwelling, lower response thermal inputs, mixing mantle- juvenile crustal-derived melts. Significant major compositional dispersion reflect midcrustal magma reservoir fractionation principal rock-forming minerals. resultant magmas constitute series variably hybridized reservoirs, emplaced at upper levels crust, that form eruptive products.