The five major mass extinctions identified in 1982 by Raup and Sepkoski have expanded to six, with the suggestion that the Permian-Triassic extinction was a double event. Is there a general explanation for great mass extinctions, or can they result from different triggers, or even from internal system instabilities? The two most-discussed candidates for a general extinction mechanism are impact...

Introduction: Major ambiguities remain in our current understanding of the geochemical evolution of the moon. That situation arises partly because (a) our geochemical and isotopic data sets for mare basalts are overly influenced by samples from the Procellarum KREEP Terrain (PKT [1]), and (b) samples of the highland crust useful for isotopic studies are limited in both quantity and quality. Fut...

We report 230Th-238U disequilibrium data on mid-ocean ridge basalts recovered 5 to 40 kilometers off the ridge axis near 9 degrees 30'N of the East Pacific Rise. These data indicate near-symmetrical eruptions of normal mid-ocean ridge basalts (NMORBs) and incompatible element-enriched mid-ocean ridge basalts (EMORBs) as far as 20 kilometers off axis. Our results suggest large-scale subsurface l...

Some workers have held that mid-ocean ridge basalts are fractionated from high pressure (15-30 kbar) picritic primary magmas whereas others have favored primary magmas generated at about 10 kbar with compositions close to those of mid-ocean ridge basalts. Of critical significance are presumed differences in composition between experimentally determined primary magmas and the least fractionated ...

This chapter summarizes the oxygen isotope geochemistry of terrestrial basalts and their mantle sources, including the conceptual framework for interpreting such data and the phenomenology of known variations. In particular, the first section outlines the motivations for and first-order results of oxygen isotope studies of terrestrial and lunar basalts over the last 30 years; the second section...

This chapter summarizes the oxygen isotope geochemistry of terrestrial basalts and their mantle sources, including the conceptual framework for interpreting such data and the phenomenology of known variations. In particular, the first section outlines the motivations for and first-order results of oxygen isotope studies of terrestrial and lunar basalts over the last 30 years; the second section...

Lunar sample 15474,4 is a tiny fragment of olivine-augite vitrophyre that is a mare basalt. Although petrographically distinct from all other Apollo 15 samples, it has been ignored since its first brief description. Our new petrographic and mineral chemical data show that the olivines and pyroxenes are distinct from those in other basalts. The basalt cooled and solidified extremely rapidly; som...

The Nayband strike-slip fault forms the western margin of the micro-continental Lut block in Eastern Iran. Neogene and Quaternary mafic volcanic rocks collected near Tabas, along the northern part of the fault (NNF; 15 Ma), and further to the south, along the middle part of the fault (MNF; 2 Ma), are within-plate sodic-series alkali olivine basalts with high TiO2 and up to >16% normative nephel...

Introduction: The behavior of multivalent elements such as iron, chromium, vanadium, and euro-pium in magmatic systems reflects the f O2 of the environment. The oxidation state of these elements will influence the mineral assemblage, crystallization sequence , and element partitioning[1]. The effect of f O2 on the relative proportions of divalent and trivalent Eu has proven to be a useful tool ...

In this paper, we report analysis of various basaltic lunar samples including 14053 and 14072, KREEP basalt 15386, thirty basalt clasts from Apollo 14 breccia 14321, as well as impact-generated samples (matrix from breccia 14168, olivine vitrophyres 14321,1180 and 14321,1539, and impact melt 14310) using a combination of solution and laser ablation inductively coupled plasma mass spectrometry (...