The syn-orogenic sedimentary record of the Grenville Orogeny in southwest Laurentia

Abstract

Late Mesoproterozoic sedimentary sequences in southwest Laurentia range in age from 1340 to 1035Ma and record regionally extensive intracratonic sedimentation before and during the Grenville Orogeny in southern Laurentia. This paper examines the specific links between intracratonic sedimentation and orogenesis and develops a new tectonic model for basin formation throughout southwest Laurentia during the Late Mesoproterozoic. New detrital zircon, muscovite, and biotite ages refine the provenance, depositional age, and regional correlations of Late Mesoproterozoic strata throughout southwest Laurentia. These data provide a new view of the Grenville orogen in southern Laurentia as it evolved from a continental margin arc to a continent-continent collision based on the record of inboard sedimentation. Deposition of all Late Mesoproterozoic sequences in southwest Laurentia was facilitated by far-traveled, continental-scale rivers that flowed north off the developing Grenville orogen. Sediment accumulation took place during four discrete basin forming events that can be directly linked to changes in the style of convergence and collision along the southern margin of Laurentia. The oldest basin system (lower Apache and Pahrump Groups) records distal back arc basin sedimentation at 1340–1320Ma, synchronous with widespread magmatism along the southern margin of Laurentia. Unconformably overlying shallow marine carbonate-bearing sequences (lower Unkar Group and correlatives) were deposited between 1255 and 1230Ma in a regionally extensive retroarc basin with clastic sediment sourced in part from an active continental arc along the southern margin of Laurentia. Shallow marine and terrestrial siliciclastic sequences (upper Unkar Group and correlatives) were deposited at 1140–1100Ma and were sourced from unroofing thrust nappes in the orogen to the south in an extensive foreland basin system during continent-continent collision. Finally, coarse-grained siliciclastic deposits of the 1060–1035Ma Hazel Formation represent a proximal foreland basin recording the final stages of the Grenville Orogeny in southern Laurentia.