ABSTRACT Classic models proposed that continental rifting begins at hotspots—domal uplifts with associated magmatism—from which three rift arms extend. Rift arms from different hotspots link up to form new plate boundaries, along which the continent breaks up, generating a new ocean basin and leaving failed arms, termed aulacogens, within the continent. In subsequent studies, hotspots became increasingly viewed as manifestations of deeper upwellings or plumes, which were the primary cause of continental rifting. We revisited this conceptual model and found that it remains useful, though some aspects require updates based on subsequent results. First, the rift arms are often parts of boundaries of transient microplates accommodating motion between the major plates. The microplates form as continents break up, and they are ultimately incorporated into one of the major plates, leaving identifiable fossil features on land and/or offshore. Second, much of the magmatism associated with rifting is preserved either at depth, in underplated layers, or offshore. Third, many structures formed during rifting survive at the resulting passive continental margins, so study of one can yield insight into the other. Fourth, hotspots play at most a secondary role in continental breakup, because most of the associated volcanism reflects plate divergence, so three-arm junction points may not reflect localized upwelling of a deep mantle plume.

ABSTRACT We interpret that the thick Cunapo conglomerate blanket overlying a significant forebulge(?) unconformity on the floor of the Northern Basin, Trinidad, represents part of a relict foreland basin that was filled in with syncontractile or syntranspressional sediments, chiefly in the Miocene–Pliocene. These deposits were subsequently modified (tilted, bent, faulted) and buried by late postcontractile transform tectonics and related sedimentation. We studied five outcrops of distal Northern Basin Oligocene–Pliocene Cunapo conglomerate from upturned Nariva, Tamana (Guaracara Limestone), and Manzanilla formations outcrops along the north flank of the Central Range. We measured pebble clast size (range = 12–46 mm), roundness (sub-angular to rounded), projected sphericity (average = 0.7), clast shape (~equant), and used sedimentologic, map, and well control to determine that the Cunapo clasts were derived from a proximal provenance north of the outcrop belt. The clasts lithotypes are predominantly similar to the unmetamorphosed Mesozoic–Paleogene precontractile stratal succession, exposed today in central Trinidad that include brittlely deformed black chert and white argillite of the Naparima Formation or a lithically similar unit, black coarse- to fine-grained sandstone that may have been derived from Cretaceous Cuche or Gautier formations, and white-brown sandstones similar to the Eocene sandstones of the Pointe-a-Pierre and Chaudiere formations. The magnitude of brittle strain recorded in quartz veins in the pebbles (17%–48%, average = 26%) indicates significant strain in the clasts’ provenance area. We interpret that the clasts were eroded off a mostly now-missing, brittlely deformed, upper crustal “lid” of the proto-Northern Range.