Numerous important Miocene and early Pliocene epithermal Au-Ag deposits are present in the northern Great Basin. Most deposits are spatially and temporally related to two magmatic assemblages: bimodal basaltrhyolite and western andesite. These magmatic assemblages are petrogenetic suites that reflect variations in tectonic environment of magma generation. The bimodal assemblage is a K-rich thol...

[1] Spectral interpretation that silicic rocks are widespread on Mars implies that Earth’s differentiated crust is not unique. Evaluation of observations bearing on the composition of the Martian crust (Martian meteorite petrology and a possible crustal assimilant, analysis of Mars Pathfinder rocks, composition of Martian fines, interpretation of spacecraft thermal emission spectra, and inferre...

A remarkable record of early arc volcanism in the Izu–Bonin–Mariana (IBM) arc is exposed in and around the Bonin Islands, an uplifted segment of the IBM forearc. New Ar/Ar dating results imply that the boninitic volcanism on Chichijima Island occurred in a brief period during Eocene time, between 46–48 Ma. A slightly younger volcanic succession is identified along the Bonin Ridge, including 44....

Pyroxenes are among the most common minerals in the solar system and are ideally suited for remote geochemical analysis because of the sensitivity of their distinctive spectra to mineral composition. Fe is responsible for the dominant pyroxene absorptions in the visible and near-infrared, but substitutions of other cations such as Ca change the crystal structure and site geometries and thus the...

Introduction: Traditionally, the diogenite meteorites have been viewed as orthopyroxenite cumulates with small amounts of olivine [1]. Several olivine-rich, harzburgite diogenites have recently been recognized and may provide insight into the occurrence of olivine on Vesta and in the HED meteorite suite [2,3]. In both the harzburgite and orthopyroxenite diogenites, olivine has been interpreted ...

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...

Precise Fe/Mn ratios and MnO contents have been determined for basalts from the Hawaiian shields of Ko’olau and Kilauea by inductively coupled plasma mass spectrometry. It is well known that the youngest Ko’olau (Makapu’u-stage) shield lavas define a geochemical endmember for Hawaiian lavas in terms of CaO and SiO2 contents and isotopic ratios of O, Sr, Nd, Hf, Pb, and Os. We find that their Mn...

High precision oxygen three-isotope ratios were measured for four mineral phases (olivine, low-Ca and high-Ca pyroxene, and plagioclase) in equilibrated ordinary chondrites (EOC) using a secondary ion mass spectrometer. Eleven EOCs were studied that cover all groups (H, L, LL) and petrologic types (4, 5, 6), including S1-S4 shock stages, as well as unbrecciated and brecciated meteorites. SIMS a...