Basalt is the most voluminous of all the igneous rocks. Extensive field, experimental, petrographic and geochemical studies of basalt have provided us with a considerable understanding of igneous petrogenesis, plate tectonics, and crust-mantle interaction and exchange. One important aspect of geology that has developed over the last few decades is the study of oceanic basalts. The ocean basins cover about two thirds of the earth's surface and are floored by a basement of oceanic basalt that is continuously undergoing generation at spreading centres and destruction at subduction zones, a process which throughout geological time is recognized as the principal means of generating new crust. The study of oceanic basalts enables us to understand better the generation and recycling of crustal materials (including the continental crust), and the exchange between oceanic crust and seawater via hydrothermal activity. Compositional variations displayed by oceanic basalts provide windows into the mantle, and the identification of isotopically-distinct mantle reservoirs demonstrates that the source of oceanic basalts is heterogeneous and is controlled by convection and reservoir interactions within the mantle.

This volume illustrates some of the significant aspects of magmatic activity from Devonian (408 million years ago) to early Permian (270 million years ago) times in SW England. This period covers the progressive development of the Variscan mountain-building episode, from initial basin formation to final deformation and the subsequent development of a fold mountain belt - the Variscan Orogen. Both extrusive (volcanic) and intrusive (plutonic) rocks are found in the orogen, and chart the various stages of its magmatic development. The sites described in this volume are key localities selected for conservation because they are representative of the magmatic history of the orogen from initiation to stabilization. Some of the earliest volcanic activity in the Devonian is represented by submarine basaltic and rhyolitic lavas developed in subsiding basins, caused by the attenuation of the existing continental crust. In some cases, extensive rifting and attendant magmatism produced narrow zones of true oceanic crust, whereas elsewhere basaltic volcanism is related to fractures in the continental crust at the margins of the basins. After the filling of the sedimentary basins, and their deformation caused by crustal shortening (late Carboniferous Period), further activity is manifested by the emplacement of the Cornubian granites and later minor basaltic volcanism in the early Permian. Accounts of the constituent parts of this history have enriched geological literature from the nineteenth century onwards, and have contributed to the advancement and understanding of magmatic and tectonic processes.

Oceanic basalts are the most abundant rock type found at the earth's surface, and as such they have been the subject of considerable research, particularly since the concept of sea-floor spreading became widely accepted. This book provides a review of these rocks, first dicussing how we sample the ocean floor and what we know about the structure of the oceanic crust, followed by an overview of the various regional settings (Pacific crust, Atlantic crust, marginal basins, seamounts and islands) and finally examines the main processes (and their interactions) which prevail during the generation and emplacement of oceanic basalt magmas. This is a volume for geologists, geochemists and geophysicists and a source of reference for advanced undergraduate students and postgraduates in these disciplines.

Oceanic basalts are the most abundant rock type found at the earth's surface, and as such they have been the subject of considerable research, particularly since the concept of sea-floor spreading became widely accepted. This book provides a review of these rocks, first dicussing how we sample the ocean floor and what we know about the structure of the oceanic crust, followed by an overview of the various regional settings (Pacific crust, Atlantic crust, marginal basins, seamounts and islands) and finally examines the main processes (and their interactions) which prevail during the generation and emplacement of oceanic basalt magmas. This is a volume for geologists, geochemists and geophysicists and a source of reference for advanced undergraduate students and postgraduates in these disciplines.

Oceanic basalts are the most abundant rock type found at the earth's surface, and as such they have been the subject of considerable research, particularly since the concept of sea-floor spreading became widely accepted. This book provides a review of these rocks, first dicussing how we sample the ocean floor and what we know about the structure of the oceanic crust, followed by an overview of the various regional settings (Pacific crust, Atlantic crust, marginal basins, seamounts and islands) and finally examines the main processes (and their interactions) which prevail during the generation and emplacement of oceanic basalt magmas. This is a volume for geologists, geochemists and geophysicists and a source of reference for advanced undergraduate students and postgraduates in these disciplines.