Geology and geochronology of Grenville-age rocks in the Van Horn and Franklin Mountains area, west Texas: Implications for the tectonic evolution of Laurentia during the Grenville

摘要

New U-Pb zircon and 40Ar/39Ar geochronological data for the Mesoproterozoic rocks at Van Horn, far west Texas, indicate that metarhyolite, quartzite, phyllite, and metabasalt of the Carrizo Mountain Group were formed ca. 1380–1330 Ma and are probably a southern part of the Southern Granite–Rhyolite province of W.R. Van Schmus and coworkers. These rocks were thrust over the ca. 1250 Ma carbonate-basalt-rhyolite sequence of the Allamoore and Tumbledown Formations and the younger Hazel Conglomerate (ca. 1035 Ma). The Castner Marble and Mundy Breccia of the Franklin Mountains near El Paso are coeval, and probably correlative, with the Allamoore-Tumbledown sequence. The ca. 1120 Ma granite and rhyolite boulders in the Hazel Formation are coeval with the Red Bluff Granite Suite and rhyolite of the Thunderbird Formation, both occurring in the Franklin Mountains, indicating that formation of granite and rhyolite was widespread in far west Texas at this time.