2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 8
Presentation Time: 10:05 AM


WEBER, John, Department of Geology, Grand Valley State University, 1 Campus Drive, 125 Padnos, Allendale, MI 49401-9403, weberj@gvsu.edu

Young orogenic belts in actively deforming plate boundary zones typically contain a complex assemblage of structures related to the full history of modern and earlier fossil plate motions that drive the deformation. We are using high-precision (geodetic) GPS (the Global Positioning System) to accurately quantify modern far-field plate and microplate motions, and near-field motions across active structures, in the Caribbean-South American (Trinidad/Tobago and Venezuela) wrench zone, and on and around the Adria microplate (Slovenia, Croatia, Italy) in the Eurasia-Nubia (Africa) collision zone. In both regions, GPS-determined plate and microplate motions has led to a better and more accurate understanding of the geology and tectonics, and helped to demonstrate that both of these plate boundaries have undergone geologically recently and significant plate kinematic changes.

GPS data show that near Trinidad and Venezuela the Caribbean plate currently moves ~eastward at ~20 mm/yr (SAωCA=57.6°N, 69.3°W, 0.233°/m.y.). Fossil Cenozoic foreland fold-thrust belt structures are overprinted by active right-stepping transforms that are connected by well-developed pull-apart basins (Gulf of Paria, Gulf of Cariaco). Trinidad contains a major transpressive restraining transform segment, the Central Range Fault, that is oblique (N75°E) to plate motion, currently aseismic, and probably elastically locked. Geology indicates that Caribbean-South American relative plate motion probably changed from oblique collision to transform at about 10Ma.

GPS data show that lithosphere in the northern Adriatic now moves as an independent, rigid microplate (Adria), currently rotating slowly ccw relative to Eurasia about a pole (pivot point) in northern Italy (EUωAD=46.2°N, 11.5°E, 0.680°/m.y.). Rates of motion and seismic moment release are lowest near the pole (e.g., Slovenia, northern Italy) and increase systematically southward away from it (Croatia, central Italy). Earlier in the Cenozoic, Adriatic lithosphere was subducting as an African (Nubian) promontory that was largely swallowed up beneath the Alps, Apennines, and Dinarides. The Adriatic microplate was probably torn off of Africa via slab break-off beneath the Apennines and born within just the past ~1 m.y.