Arc magmas and the continental crust share many chemical features, but a major question remains as to whether these features are created by subduction or are recycled from subducting sediment. This question is explored here using Th/La, which is low in oceanic basalts (<0 2), elevated in the continents (>0 25) and varies in arc basalts and marine sediments (0 09–0 34). Volcanic arcs form linear...

ome of the consequences of the motion of Earth's tectonic plates are quite evident: various mountain chains for instance. Others, such as events occurring deep in subduction zones where one plate plunges beneath another, can be seen only indirectly through seismic imaging techniques. The approach allows the structure of Earth's interior to be reconstructed from observed seismograms, and it cont...

[1] The oxygen and hydrogen isotope compositions of vein minerals and dO values of 64 whole rocks from the deeper kilometer of the 1.5 km lower crustal section of ODP Hole 735B in the SW Indian Ocean were analyzed in order to investigate seawater penetration into and reaction with the lower oceanic crust. Vein amphiboles have dD values of 35 to 65%, indicating formation from seawater fluids and...

Introduction: An overarching geologic theory, GEOMARS, coherently explains many otherwise anomalous aspects of the geological history of Mars [1]. Premises for a theory of martian geologic evolution include: (1) Mars is a water-rich terrestrial planet, (2) terrestrial planets should evolve through progressive stages of dynamical history (accretion, differentiation, tectonism) and mantle convect...

Flat slab subduction has been attributed to various causes including mantle wedge dynamics, overriding by the upper plate, age of the subducting plate, and subduction of anomalously thick oceanic crust. One often favored explanation for flat slabs is the subduction of buoyant features on the oceanic plate in the form of an aseismic-ridge or oceanic plateau. We show through plate tectonic recons...