Summary of the Precambrian and Paleozoic geology of south-central Texas

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Authors:Freed, Robert L.
Author Affiliations:Primary:
Trinity Univ., Dep. Geol., San Antonio, TX, United States
Volume Title:Compass of Sigma Gamma Epsilon, 1915-84
Source:Compass of Sigma Gamma Epsilon, 1915-84, 63(4), p.130-144. Publisher: National Council of Sigma Gamma Epsilon, University of Oklahoma, Norman, OK, United States. ISSN: 0010-4213
Publication Date:1986
Note:In English. 60 refs.; illus. incl. 3 tables, sect., sketch maps
Summary:In the Llano region of south-central Texas, deposition of protolith for the Valley Spring and Lost Creek gneisses began >1200 m.y. ago. After these sediments were deposited, an island arc complex developed with land-derived sediments and volcaniclastics, protolith for the Packsaddle schist. Regional dynamothermal metamorphism reached a maximum 1167 m.y. ago, accompanied by syntectonic emplacement of tonalitic and granitic magmas. This metamorphism was terminated approx 1129 m.y. ago, with the closing of the back-arc basin. Uplift of 5-8 km was followed by intrusion of basalt-dacite-rhyolite dykes approx 1080 m.y. ago. Large, unfoliated granitic plutons were intruded approx 1056 m.y. ago marking the conclusion of island arc/continental collision and associated crustal thickening and uplift. Deposition of Palaeozoic sediments followed the removal of 6-9 km of Precambrian material. Middle Palaeozoic events are uncertain due to a highly fragmented geological record, but epeirogeny and erosion were important factors. Upper Palaeozoic rocks record the deposition of Pennsylvanian Marble Falls sediments followed by deposition of Smithwick prodeltaic sediments derived from the Pennsylvanian Ouachita foldbelt to the east. [O.C.K.]
Subjects:Arkose; Basalts; Cambrian; Carboniferous; Clastic rocks; Dacites; Diorites; Ellenburger Group; Granites; Igneous rocks; Lower Ordovician; Magmas; Marble Falls Group; Ordovician; Paleozoic; Pennsylvanian; Plutonic rocks; Precambrian; Regression; Rhyolites; Sea-level changes; Sedimentary rocks; Stratigraphy; Tonalite; Transgression; Uplifts; Upper Cambrian; Volcanic rocks; Volcaniclastics; Wilberns Formation; Llano County Texas; Llano Texas; Texas; United States; Loot Creek Gneiss; Marble Falls Formtion; Packsaddle Schist; Riley Formation; Smithwick Formation; South-central Texas; Valley Spring Gneiss
Abstract Numbers:87M/6677
Record ID:1987006799
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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