The Missing Rheic Suture in the Central Atlantic and the Role of Structural Inheritance During Breakup

Abstract

The Rheic Ocean opened Late Cambrian – Ordovician as elongate terranes rifted from Gondwana and closed in the Late Paleozoic to form Pangea. Despite the significant role of the Rheic Ocean, many questions remain, especially in the Central Atlantic region where the suture is not exposed. In this region, Rheic closure was associated with the Alleghanian Orogeny. Although this event is well documented, there is little evidence of the suture zone, oceanic crust, intra-oceanic terranes or continental arcs on either side of the Central Atlantic. In the southeast US, the Rheic suture occurs between the Suwanee terrane and the collage of Appalachian terranes, but it is buried beneath younger sediments and continues to the northeast undercover and then offshore. Most published interpretations are based on outcrop and have not integrated offshore datasets (e.g. potential field, seismic reflection and refraction data). However, integrated interpretation of these datasets allows for extrapolation of basement terranes and structures, and modelling of crustal architecture. Several features of the offshore Central Atlantic margin are relevant to the interpretation of the history of the Rheic Ocean including: 1) the East Coast Magnetic Anomaly (ECMA; a high amplitude ~2000 km curvilinear positive anomaly) generally associated with a positive gravity anomaly, 2) high velocity lower crustal layer, 3) 15–20 km thick sediments, poorly imaged at depth, and 4) Brunswick Magnetic Anomaly (BMA; high amplitude negative anomaly). Effective evaluation of a passive margin requires assessment of the collisional history and the resulting geological units and fabric, as well as the extensional processes, especially on a margin such as the Central Atlantic where Pangea break up initiated only 20 myr after the end of the Alleghanian Orogeny. Interpretation and modelling of gravity and magnetic data, in combination with reflection and refraction data, has been used to assess crustal architecture and the location of the Rheic suture along the Central Atlantic Margin. The suture zone is defined by several geological units including an accretionary wedge (BMA and lower gravity), ophiolites, and a curvilinear accreted arc terrane (+/− obducted oceanic crust) which is represented by the ECMA and positive gravity anomaly. We propose that the opening of the Central Atlantic was initiated by reactivation of the Rheic suture.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015