Marie and intermediate granulite xenoliths, collected from Cenozoic alkali basalts, provide samples of the lower crust in western Saudi Arabia. The xenoliths are metaigneous two-pyroxene and garnet granulites. Mineral and whole rock compositions are inconsistent with origin from Red Sea rift-reIated basalts, and are compatible with origin from island arc calc-alkatine and low-potassium tholeiit...

keybarkuh area is located 70 km southwest of khaf, khorasan razavi province. the study area is situated in northeastern lut block. the rock units in the area are paleozoic metamorphic rocks and cretaceous to tertiary subvolcanic intrusions intruded as dike, stock and batholith; their composition varies from granite to diorite. based on magnetic susceptibility, the intrusive rocks are divided in...

S U M M A R Y We argue that subduction may be initiated at passive continental margins without shortening the lithosphere. Overcoming the lithosphere’s high compressive strength requires special circumstances, and these make it difficult to explain the nearly complete recycling of old sea-floor. Instead, we present a model that predicts tensile decoupling of the continental and oceanic lithosph...

The results of a laser ablation microprobe–inductively coupled by the more widely used samarium–neodymium system (e.g. Dickin, 1995). As a tracer of petrogenetic processes, plasma mass spectrometry Lu–Hf isotope study of zircons in however, Lu–Hf has one important advantage over Sm– 0·93–1·67 Ga rocks from south Norway indicate that early Nd: zircons retain a robust memory of their initial Hf P...

The Demerara Plateau (offshore Suriname and French Guiana) is located at the junction of Jurassic Central Atlantic Cretaceous Equatorial Oceans. study its crustal structure fundamental to understanding tectonic history, relationship with adjacent oceanic domains enlightening formation Transform Marginal Plateaus (TMPs). This presents two wide-angle seismic velocity models from MARGATS cruise ex...

[1] Two of the most popular mechanisms for thickening the crust beneath the Tibetan Plateau are (1) pure shear with faulting and folding in the upper crust and horizontal shortening below and (2) flow of lower or middle crust without significant shortening of the upper crust. To help discriminate between the relative contributions of these two mechanisms, well-constrained estimates of upper cru...

The straightforward but unexpected relationship presented here relates crustal thickness to magma type in the Izu-Ogasawara (Bonin) and Aleutian oceanic arcs. Volcanoes along the southern segment of the Izu-Ogasawara arc and the western Aleutian arc (west of Adak) are underlain by thin crust (10-20 km). In contrast those along the northern segment of the Izu-Ogasawara arc and eastern Aleutian a...