Sedimentary and crustal structure of the US Gulf Coast revealed by Rayleigh wave and teleseismic P coda data with implications for continent rifting

Abstract

We have developed an S-wave model of the south-central US focusing on the Gulf Coast sedimentary basin and its crust to understand continental rifting and regional tectonics. The model was derived by a joint inversion of Rayleigh wave phase velocities, Z/H ratios and P-coda data. The surface- and body-wave measurements were made, respectively, from ambient noise and teleseismic earthquakes recorded by 215 USArray stations in a rectangular area of 100°–87° west and 28°–37° north. We employed a cross-convolution function and H-κ analysis to better constrain sedimentary and Moho structure. We find that the southern edge of the Ouachita fold-and-thrust belt (OFTB) appears as a boundary in measured phase velocities, Z/H ratios, sediment basement depths, Moho depths, average crustal Vs and Vp/Vs ratios. The model shows southeastward thickening of the sedimentary basin, accompanied by thinning of the crystalline crust. The Moho gradient suggests that early rifting between North America and the Yucatan block commenced in a SE direction and involved most of the Pangea crust south of the OFTB boundary (i.e., Gondwana crust). We believe that a high velocity feature in the lowermost crust and upper mantle parallel to the southeast Texas coast was emplaced as a mafic body and is the source of the Houston magnetic anomaly. The seismic structures of the crust and uppermost mantle observed beneath the Mississippi Embayment and the Mississippi Valley Graben are consistent with plume induced Cretaceous uplift of the Mississippi Embayment as North America passed over the Bermuda hotspot.