Electron petrography of shock-produced veins in the Tenham chondrite

Electron microscopy of the minerals in, and adjacent to the black veins of the Tenham meteorite reveals that the minerals have undergone varying degrees of shock. The orthopyroxenes of the bulk of the meteorite have been transformed to clinopyroxenes in areas adjacent to the veins, and to majorite in the black vein itself. The majorite, which occurs in both equant and dendritic habit, is associated with a glassy phase from which it crystallized, and with a microcrystalline clinopyroxene aggregate produced from the majorite upon the release of pressure. The olivines of the meteorite are also deformed, and some have been transformed to the high pressure spinel polymorph. The spinel has subsequently partially inverted to the -phase polymorph.     

Timescales of geological processes: Preface

正1. Introduction One of the major challenges in Geoscience is to understand how the formation and evolution of the Earth System are governed by timescales e that is, how the various geological processes that continue to contribute to its present-day structure and composition operated in the deep past. The traditional view of such processes refers to events that occur at immense spatial scales and over hundreds of millions of years, constrained in most cases by the ages of rocks determined using isotopic dating methods or the fossil record. However, the modern view of geological processes has increasingly acknowledged that their durations can be significantly shorter than previously thought possible, or indeed detectable