Reinterpretation of adcoh and cocorp seismic reflection data with constraints from detailed forward modeling of potential field data — Implications for Laurentia-Peri-Gondwana suture

• Published in: Tectonophysics Vol. 712-713; pp. 426 - 437
• Main Authors: Duff, Patrick D., Kellogg, James N.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 21-08-2017; Elsevier BV
• Subjects: Alleghanian orogeny; Basement rock; Blue Ridge; Carolina terrane; Central Piedmont suture; Constraint modelling; Crustal thickness; Crystallization; Footwalls; Geology; Gravitation; Gravitational fields; Gravity; Gravity anomalies; Inner Piedmont; Metamorphism; Modelling; Paleozoic; Potential fields; Reflectors; Rock; Rocks; Rotation; Seismic activity; Seismic data; Seismic surveys; Seismological data; Structures; Studies; Thrust; Thrust faults; Two dimensional models; Uplift; Gondwana; Central Piedmont suture; Blue Ridge; Potential fields; Inner Piedmont; Alleghanian orogeny; Carolina terrane
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2017.06.002

To better constrain the structure of the Laurentian – Peri-Gondwana suture zone, maps and a 2-dimensional regional cross-section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields. The Central Piedmont Suture (CPS), the boundary between the Laurentian Inner Piedmont and the Peri-Gondwanan Carolina terrane is a low-angle thrust fault (~30°) ramping up from an Alleghanian mid-crustal detachment at depths of about 12km. ADCOH and COCORP seismic data image anticlinal structures in the footwalls of the Hayesville thrust and the CPS, above the Alleghanian decollement. The footwall rocks have previously been interpreted as Paleozoic shelf strata on the basis of sub-horizontal seismic reflectors; however, the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of Grenvillian basement. The Appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the Carolina Terrane toward the Appalachian core. A change in lower crustal density is not required, so that Grenville basement rocks may extend farther to the southeast than previously thought. The 5 to 10km of Alleghanian uplift and exhumation predicted by P-T crystallization data compiled in this paper can be easily accommodated by thrusting on four major low-angle thrust systems: Great Smoky Mountain Thrust (GSMT), Hayesville, Brevard, and CPS. Unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation. Alleghanian collision along the southeastern Appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter-clockwise rotation of Gondwanan West Africa, creating head-on collision in the southern Appalachians and at least 370km of shortening.
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•Reinterpretation of COCORP and ADCOH seismic incorporating constraints from forward models; first magnetic Euler deconvolution results.•The Central Piedmont Suture is a low-angle thrust fault decapitated by the mid-crustal Appalachian Decollement.•Footwall reflectors beneath the Blue Ridge thrust, previously interpreted as sediments, are reinterpreted as basement duplex structures.•5 to 10 km of Alleghanian uplift and exhumation predicted by P-T crystallization data can be accommodated by thrusting on 4 thrust fault systems.