Chemical Mohometry: Assessing Crustal Thickness of Ancient Orogens Using Geochemical and Isotopic Data.

Convergent plate boundaries are key sites for continental crustal formation and recycling. Quantifying the evolution of crustal thickness and paleoelevation along ancient convergent margins represents a major goal in orogenic system analyses. Chemical and in some cases isotopic compositions of igneous rocks formed in modern supra-subduction arcs and collisional belts are sensitive to Moho depths at the location of magmatism, implying that igneous suites from fossil orogens carry information about crustal thickness from the time they formed.

Copper systematics in arc magmas and implications for crust-mantle differentiation.

Arc magmas are important building blocks of the continental crust. Because many arc lavas are oxidized, continent formation is thought to be associated with oxidizing conditions. On the basis of copper's (Cu's) affinity for reduced sulfur phases, we tracked the redox state of arc magmas from mantle source to emplacement in the crust.

The redox state of arc mantle using Zn/Fe systematics.

Many arc lavas are more oxidized than mid-ocean-ridge basalts and subduction introduces oxidized components into the mantle. As a consequence, the sub-arc mantle wedge is widely believed to be oxidized. The Fe oxidation state of sub-arc mantle is, however, difficult to determine directly, and debate persists as to whether this oxidation is intrinsic to the mantle source.

Upside-down differentiation and generation of a 'primordial' lower mantle.

Except for the first 50-100 million years or so of the Earth's history, when most of the mantle may have been subjected to melting, the differentiation of Earth's silicate mantle has been controlled by solid-state convection. As the mantle upwells and decompresses across its solidus, it partially melts. These low-density melts rise to the surface and form the continental and oceanic crusts, driving the differentiation of the silicate part of the Earth.