The Geology And Mapping Of Granite Batholiths

This book is mainly about the field geology of granites at all scales from that of a single outcrop to plutons and batholiths. All field geologists work initially at the scale of the outcrop, consequently most of the phenomena treated herein are those which are visible at outcrop scale. However, granites typically occur as plutons and batholiths, some of which are so large as to apparently defy any effort at systematic treatment. Having had the opportunity of mapping two very large and very different batholiths, namely the Coastal Batholith of Peru and the tin granites of Southeast Asia, I have found that it is possible to map large batholiths within a relatively short time, so that the geology of the batholith as a whole can be appreciated. Moreover batholiths are one of the most common modes of granite occurrence, so it makes sense to study them at their natural scale. During my working life I have worked with many geologists from underdevel oped countries and this book is mainly to help them in unravelling the geology of their native batholiths. I have been lucky with my friends and colleagues of many nationalities, and I particularly thank Wallace Pitcher, who took me on as an untried apprentice in Peru, and who, by his kindness and example, showed me how to look at granites properly.

This book is for undergraduates, postgraduates and research workers who wish to gain an insight into present ideas and speculations on the origin of granite batholiths. It is a summary of the proceedings of a one-day meeting of the Geochemistry Group of the Mineralogical Society held at the University of liverpool on the 2nd May 1979, entitled The Origin of Granite Batholiths: Geochemical Evidence. It was felt that relevant new geochemical and isotopic data with associated field and petrological observations would be helpful in clarifying the main issues connected with the origin of granitic rocks. The speakers who participated contri buted a wealth of data and ideas to the problem, based on many years' experience of granitic rocks in various parts of the world. The popularity of the meeting indicated that a summary of the talks might be welcomed by a wider audience; hence this book. For reasons of length and cost, authors have been limited to presenting only the essential results necessary to develop their arguments and ideas. The comprehensive reference list will, however, assist those who wish to pursue specific aspects in greater detail. Inevitably, the cost and speed of publication may have resulted in some errors and inconsistencies which would not have occurred in a book produced over a longer time-span, but the editors hope that the rapid and up-to-date publication will offset this. The controversy over the origin of granite is as old as the science of geology.

Proceedings of a meeting of the Geochemistry Group held May 2, 1979, University of Liverpool.

Granites (sensu lato) represent the dominant rock-type forming the upper–middle continental crust but their origin remains a matter of long-standing controversy. The granites may result from fractionation of mantle-derived basaltic magmas, or partial melting of different crustal protoliths at contrasting P–T conditions, either water-fluxed or fluid-absent. Consequently, many different mechanisms have been proposed to explain the compositional variability of granites ranging from whole igneous suites down to mineral scale. This book presents an overview of the state of the art, and envisages future avenues towards a better understanding of granite petrogenesis. Particular emphasis of this Volume is on the following topics: Compositional variability of granitic rocks generated in contrasting geodynamic settings during Proterozoic to Phanerozoic Periods, Main permissible mechanisms producing subduction-related granites, Crustal anatexis of different protoliths, and the role of water in granite petrogenesis, New theoretical and analytical tools available for modelling whole-rock geochemistry, in order to decipher the sources and evolution of granitic suites.

In this Special Paper, Hildebrand and Whalen present a big-picture, paradigm-busting synthesis that examines the tectonic setting, temporal relations, and geochemistry of many plutons within Cretaceous batholithic terranes of the North American Cordillera. In addition to their compelling tectonic synthesis, they argue that most of the batholiths are not products of arc magmatism as commonly believed, but instead were formed by slab failure during and after collision. They show that slab window and Precambrian TTG suites share many geochemical similarities with Cretaceous slab failure rocks. Geochemical and isotopic data indicate that the slab failure magmas were derived dominantly from the mantle and thus have been one of the largest contributors to growth of continental crust. The authors also note that slab failure plutons emplaced into the epizone are commonly associated with Cu-Au porphyries, as well as Li-Cs-Ta pegmatites.