Testing the continuity of Lesser Antilles forearc provinces based on gravity modeling and a compilation of radiometric age dates

Abstract:

The largely submarine, Cretaceous-recent Lesser Antilles subduction system includes the Aves remnant arc (ARA), the Grenada back-arc basin (GBAB), the Lesser Antilles volcanic arc (LAVA), the Tobago forearc basin (TFAB), and the Barbados accretionary prism (BAP). Several previous models have been proposed that differ in their interpretation of how and when these different components of the Lesser Antilles subduction system evolved along the 850-km-long trend of the subduction system. We correlate three dip regional gravity transects and one strike transect with seismic reflection and refraction data and radiometric age dates to reconstruct the largely extensional history of this multi-component arc system. Dredged samples of plutonic rocks from the Aves ridge remnant arc have been dated as Campanian to Paleocene (78-57 Ma) and represent the earliest known volcanic arc magmatism of the Lesser Antilles. Rifting of the GBAB and TFB basins occurred during the early to middle Eocene with the formation of forearc, oceanic crust during the middle Eocene. Onlap of Oligocene clastic sediments against more steeply-dipping Oligocene clastic sediments record the intrusion and emergence of the LAVA and its partitioning of the GBAB and TFB during the Oligocene. The intrusion of the nascent LAVA entrained Middle Eocene oceanic crust now exposed in the Grenadine Islands. Gravity data reveals that the southern LAVA with age dates of latest Oligocene-early Miocene (24-20 Ma) bifurcates into two northern branches beginning at the island of Martinique and separating along the Miocene to recent Kallinago rift. The western, active branch (Inner Arc) shows a range of dates from Pliocene to Recent (4-0 Ma) while the extinct, outer arc capped by limestone shows dates ranging from late Eocene to early Miocene (35-20 Ma). The tectonic model that best fits the gravity profiles and dates include 1) eastward shift about 190 km of the volcanic arc from the late Cretaceous Aves Ridge to its present-day location of the LAVA during the Oligocene; this was likely a response to slab rollback; 2) westward shift from the inactive Limestone Caribbees to the active Inner Arc (10-5 Ma); this was likely a response to over thickened, fracture zones producing slab shallowing that pushed the volcanic axis westward.