The Interpretation of Igneous RocksKeith Gordon Cox Our aim in writing this book is to try to show how igneous rocks can be persuaded to reveal some ofthe secrets of their origins. The data of igneous rocks consist of field relations, texture, mineralogy, and geochemistry. Additionally, experimental petrology tells us how igneous systems might be expected to behave. Working on this material we attempt to show how hypotheses concerning the origins and evolution of magmas are proposed and tested, and thus illuminate the interesting and fundamental problems of petrogenesis. The book assumes a modest knowledge of basic petro graphy, mineralogy, classification, and regional igneous geology. It has a role complementary to various established texts, several of which are descriptively good and give wide coverage and evaluation of petrogenetic ideas in various degrees of detail. Existing texts do not on the whole, however, deal with methodology, though this is one of the more important aspects of the subject. At first sight it may appear that the current work is a guidebook for the prospective research worker and thus has little relevance for the non-specialist student of geology. We hope this will prove to be far from the case. The methodological approach has an inherent interest because it can provide the reader with problems he can solve for himself, and as an almost incidental consequence he will acquire a satisfying understanding. |
Contents
| 1 | |
| 3 | |
| 12 | |
Phase diagrams introduction | 42 |
Ternary systems I | 83 |
The interpretation of twoelement variation diagrams | 145 |
Petrographic aspects of volcanic rocks | 176 |
Quaternary systems | 197 |
Petrographic aspects of plutonic rocks | 283 |
The interpretation of data for plutonic rocks | 308 |
Trace elements in igneous processes | 332 |
The use of isotopes in petrology | 360 |
Nomenclature of igneous rocks 399 | 398 |
Norm calculations | 407 |
Calculation of plotting parameters for OHara 1968 polybaric phase | 415 |
| 432 | |
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Common terms and phrases
albite alkali feldspar amphibole analyses anorthite approximately assemblage basalts behaviour binary boundary curve bulk composition calculated chemical clinopyroxene components composition point contain cooling crystal fractionation crystal settling cumulus diopside discussed down-temperature end-member enstatite equilibrium crystallisation eruption eutectic example experimental exsolution Figure forsterite fractional crystallisation fractionation paths gabbro garnet granites groundmass hypersthene igneous rocks illustrated incompatible elements isothermal section isotope kbar L₁ lavas leucite liquid composition liquidus projection mantle minerals Na2O nepheline normative olivine orthopyroxene oxide parameters partial melting peridotite petrogenetic petrographic petrology phase diagram phase relations phenocrysts pigeonite plagioclase plot pressure primary phase field processes proportions pyroxene quartz quenching rare earth Rb/Sr ratios reaction relative represented residual liquid resorption sequence silica SiO2 Skaergaard solid phases solid solution solidus spinel stage sub-solidus ternary texture tholeiites TiO2 trace element triangle tridymite univariant variation diagrams volcanic rocks