Page 7 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Contents

Acknowledgements ........................................................................................................................... ix

Part 1. Interpreting textures: terminology and techniques

The imprint of genetic processes on textures in volcanic deposits .................................................................. 1
Emphasis and organisation ............................................................................................................................... 1
An approach to the genetic interpretation of textures in volcanic deposits ....................................................3
Two textural categories: coherent volcanic and volcaniclastic ..........................................................................3
Descriptive nomenclature for coherent volcanic and volcaniclastic deposits ...................................................7
Graphic logging technique ..................................................................................................,.......................... 12
Important textures and structures .................................................................................................................. 15
A summary of the essential features of the seafloor massive sulfide environment ........................................ 15
Introduction to the Mount Read Volcanics ... ..15

Part 2. Common components, textures and structures in volcanic deposits
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Phenocrysts and porphyritic texture .............................................................................................................. 21
Crystals and crystal fragments ........................................................................................................................ 22
Vesicles ............................................................................................................................................................. 22
Volcanic glass ................................................................................................................................................... 23
Devitrification ................................................................................................................................................. 24
Spherulites ....................................... .' ....................................................................................................... 24
Lithophysae .............................................................................................................................................. 25
Micropoikilitic texture ............................................................................................................................. 25
Perlite ............................................................................................................................................................... 25
Pumice and scoria ........................................................................................................................................... 27
Achneliths, bombs and blocky juvenile clasts ................................................................................................ 27
Glass shards...................................................................................................................................................... 28
Lithic fragments .............................................................................................................................................. 29
Accretionary lapilli .......................................................................................................................................... 29
Fiamme and pseudofiamme ............................................................................................................................ 30
Flow foliations ................................................................................................................................................. 30
Joints ................................................................................................................................................................ 31
Part 3. Lavas, syn-volcanic intrusions and related volcaniclastic deposits

Autobreccia ...................................................................................................................................................... 54
Talus ................................................................................................................................................................. 54
Hyaloclastite .................................................................................................................................................... 54
Peperite ............................................................................................................................................................ 57
Pillow lavas ...................................................................................................................................................... 58
Subaqueous basaltic lava flows ....................................................................................................................................... 60
Subaqueous silicic lava flows, domes and syn-volcanic intrusions ............................................................................... 61
Subaqueous silicic lava flows and extrusive domes ........................................................................................ 61
Subaqueous partly extrusive cryptodomes ...................................................................................................... 64