Crustal structure of the Texas gulf coast

Abstract

The coastal region of Texas is a zone of transition from oceanic structure in the Gulf of Mexico to continental structure in central Texas. Knowledge of crustal structure in this region is necessary to understand the tectonic history of the coastal region of Texas, the Ouachita system, and the Gulf of Mexico.

Gravity measurements were made and combined with measurements from earlier studies to produce a gravity map of the coastal region of Texas. These data were interpreted by computer modeling, and analysis of the data suggests that the. crust thins and the sedimentary column thickens from central Texas toward the coast. The buried core of the Ouachita system has a distinct positive gravity signature, and gravity profiles suggest that the same general crustal structure exists through much of the Texas coastal region.

Two tripartite arrays of vertical long-period seismographs were deployed for study of Rayleigh wave propagation in the coastal region of Texas. Analysis of Rayleigh wave group-velocity dispersion in the Rio Grande Embayment area suggests that thick Paleozoic, as well as thick Mesozoic and Cenozoic, sediments are present. 7JDsence of a typical granitic layer is also suggested. The model proposed for this area is a crust 32 km thick composed of 12 km of basaltic material and 20 km of sedimentary rocks.

The second tripartite was deployed in the area of the central Texas Gulf Coast. The model proposed for this area is a crust 31.5 km thick composed of 13.5 km of basaltic material, 5 km of Mesozoic and Cenozoic sediments, and 9. km of Paleozoic rocks which are in part of igneous origin.

The combination of geological data, gravity data, previous seismic refraction studies, and Rayleigh wave dispersion data suggests a generalized crustal model which is valid all along the Texas Gulf Coast. The generalized model is b€:F:t explained by interpreting the Ouachita system. as a Paleozoic-Cordilleran type mountain belt and the Texas Gulf Coast as the site of the Paleozoic subduction zone.