Mesoproterozoic geology of northeastern Llano Uplift, southwest Council Creek quadrangle, Burnet County, central Texas.

摘要

The Llano Uplift provides a unique structural-erosional window into the Texas basement that formed during the Mesoproterozoic assembling of the megacontinent Rodinia. Metamorphites and magmatites document the Grenvillian Llano mobile belt development between about 1.366-1.03 Ga ago. It is characterized by tectonic transport and stacking of rock units, continental marginal Valley Spring domain (VSD), marine basinal Packsaddle domain (PD), and island-arc Coal Creek domain (CCD). In the northeastern Llano Uplift, a 52 km2 exposure is characterized by lithotectonic packages (PD, VSD) and magmatic intrusions revealing a ∼5 km thick, attenuated section of heterogeneous mapping units dominated by felsic gneisses. Multiple stacking (D1), shearing (D3), and polydeformational fabric features are the result of five Mesoproterozoic deformational events (D1-D5). The series of metamorphic mineral assemblages (Me, Mt, Ma3, Ma4 and Ma5) implies post-eclogite facies retrogression under declining crustal P-T conditions along a clockwise P-T-t path during a protracted regional dynamothermal metamorphic event. Rotational fabric features indicate tectonic domain (PD, VSD) transport with top to the NW. Also, orientation of PD/VSD lithotectonic section segments strongly suggests structural overturning. Granitic magmatism is syn- to post-deformational while late stage basalt represents the youngest Mesoproterozoic rock forming event of the mobile belt as exposed in the Llano Uplift.