INCIPIENT METAMORPHIC CORE COMPLEXES IN NORTHERN LOUISIANA?

Mickus et al. (2009) model the margin of the Gulf of Mexico along the Texas coast as a volcanic rifted margin. They specifically point out that a critical magnetic anomaly terminates near Lafayette, Louisiana. They further state "...the Texas volcanic rifted margin...gradationally changes to a nonvolcanic but still extensional boundary to the east along the Louisiana coast."

I propose that the transition in margin type is more abrupt than they imply and that the eastern (northeastern) limit of the volcanic rifted margin lies along a northwesterly trending line segment which parallels and connects the "five islands salt dome trend" in southern Louisiana (generally considered to lie along a basement discontinuity) to the termination of the magnetic anomaly near Lafayette, continues into Texas passing near Angelina County and, perhaps, extends as far as the Ouachita Orogenic Front.

To the northeast of this line I suggest that southeasterly directed extension has proceeded by low angle detachment (decollement) which has produced, in order from northwest to southeast: 1) a rifted basin (the Eagle Mills Late Triassic rift basin), 2) uplift (the Sabine and Monroe Uplifts), 3) a steep ramp (the Angelina County Texas to Caldwell Parish Louisiana flexure) and 4) a broad zone of basement faulting (the broad continent-ocean boundary of the eastern Gulf Coast). These features are analogous to the features associated with Metamorphic Core Complexes (MCC) in the American Cordillera except for the fact that the Sabine and Monroe Uplifts have yet to breach their sedimentary covers.

This MCC rifting model should be considered as data from the USArray are being interpreted. As well, I suggest denser seismometer arrays (such as those of the "flexible array") and magnetotelluric experments be deployed to achieve resolution of features within the crust and shallow mantle sufficient to test the validity of this incipient MCC proposal.