The effect of transition regions between continental and oceanic structures on the propagation of L, waves from continental sources is examined. In particular, the attenuation due to variations in layer thickness in such transition regions is calculated and explained for a suite of simple models. The measured attenuation, due tq the geometry of the transition regions between the oceanic and con...

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...

We demonstrate that observed contrasts of upper crustal structures across large continental strike-slip faults are sufficient to produce artificial vertical Moho offsets of several kilometers in studies using laterally homogenous models. This can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust. An existing hypothesis that ...

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...

Continental crust rises higher than oceanic crust because it is less dense: It is rich in Si and poor in Mg. However, basalt, which is derived from magma, is denser and has a higher ratio of Mg to Si than the rock that makes up mature continental crust. Cin-Ty Lee et al. argue that chemical weathering alters the composition of continental crust as it ages and helps give it its more buoyant char...

Continental crust is too Si-rich and Mg-poor to derive directly from mantle melting, which generates basaltic rather than felsic magmas. Converting basalt to more felsic compositions requires a second step involving Mg loss, which is thought to be dominated by internal igneous differentiation. However, igneous differentiation alone may not be able to generate granites, the most silicic endmembe...

Continental crust rises higher than oceanic crust because it is less dense: It is rich in Si and poor in Mg. However, basalt, which is derived from magma, is denser and has a higher ratio of Mg to Si than the rock that makes up mature continental crust. Cin-Ty Lee et al. argue that chemical weathering alters the composition of continental crust as it ages and helps give it its more buoyant char...

Depletion of Nb relative to K and La is characteristic of lavas in subduction-related magmatic arcs, as distinct from mid-ocean ridge basalts. Nb depletion is also characteristic of the continental crust. This and other geochemical similarities between the continental crust and high-Mg# andesite magmas found in arcs suggests that the continental crust may have formed by accretion of andesites. ...

Rocks metamorphosed under high-pressure (HP) and ultra high-pressure (UHP) conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities. In the Mediterranean realm, their occurrence in several belts related to a single subduction event shows that the burial-exhumation cycle is a recurrent transient process. Using...

T study of the deep structure and evolution of passive continental margins is important for the understanding of rifting processes and the formation of associated sedimentary basins. Since the classical models of McKenzie (1978) and Wernicke (1985), understanding how passive continental margins form, that is to say mainly the way that continental lithosphere is thinned leading to subsidence, re...