Alleghanian amalgamation and Mesozoic breakup of western Equatorial Pangea, and a practical method for modelling Mesozoic syn-rift paleo-dynamic elevation and dissipation

I present an updated series of paleo-tectonic maps outlining the Alleghanian collision between Laurentia and Pangea that formed western Pangea 350–275 Ma, and the subsequent opening of the Central Atlantic, Gulf of Mexico, and Proto-Caribbean 230–125 Ma. The new maps enhance the Alleghanian model of Dewey (1982) and Pindell and Dewey (1982). Six reconstructions at 15 Myr intervals in the North American reference frame with accurate crustal block outlines provide a standardized framework for future integration of new data and mapping. The Alleghanian Orogeny involved dextral-oblique subduction of Rheic Ocean crust and east-to-west progressive collision. We show how the Sabine Block may have undergone a period of independent motion relative to either continent between 350–305 Ma, pulled into the Ouachita re-entrant by subduction roll back and intra-arc extension as a means of ensuring continuous suturing. I hypothesize that a Peru-Bolivia style compressive continental arc orogen developed along the Pacific margin, spanning the Laurentia and Gondwana suture, in Late Permian–Early Triassic time. In addition, the study provides a spatial and temporal framework for understanding the Penn-Perm interior sedimentary basins of North America associated with Alleghanian orogenesis.

 

Concerning Mesozoic breakup, the regional azimuth of Late Triassic (230–195 Ma) inter-continental extension appears best defined by the 165° trend of a short basement segment along the Guyana margin. This trend is more north–south than the established ~130° initial Atlantic opening vector. Hence, compression would be expected at this segment but is not observed, suggesting a distinct stage of 345° extension prior to the 195 Ma onset of Atlantic spreading (i.e., Late Triassic). This stage encompasses Eagle Mills and Newark deposition and created what we call the South Florida–Suriname Basin (SFB), which then became the site of the region’s best developed volcanic SDR sets in the Early to Middle Jurassic. I will propose, via global analogues, that the SDR accumulations within the SFB formed the center of a regional syn-rift dynamic high that affected predicted isostatic base levels for some 50 Myrs (200–150 Ma). I will also outline a practical method of incorporating syn-rift dynamic elevation into more traditional methods of isostasy-based basin analysis. Implications are significant, including creation of syn-rift basins 1–2 km higher than expected, often above global sea level, and seafloor spreading commencing at only ~1 km subsea which impacts paleogeographic mapping.