Page 8 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Subaqueous syn-volcanic sills and dykes ........................................................................................................ 64
Volcaniclastic deposits associated with silicic lava dome eruptions in shallow water .................................... 65
Case Study: Partly extrusive, submarine, dacite cryptodome, Sock Creek South, western Tasmania ........... 66
Subaerial silicic lava flows and domes ........................................................................................................................... 66
Subaerial basaltic lava flows ........................................................................................................................................... 69
Andesitic lavas ................................................................................................................................................................. 71

Part 4. Pyroclastic, resedimented volcaniclastic and volcanogenic sedimentary deposits

Genetic classification of volcaniclastic deposits ............................................................................................................. 94
Explosive eruptions and pyroclastic deposits ................................................................................................... 95
Explosive magmatic eruptions ................................................................................................................. 95
Phreatomagmatic eruptions ..................................................................................................................... 96
Phreatic or steam eruptions ..................................................................................................................... 96
Resedimented syn-eruptive volcaniclastic deposits ......................................................................................... 96
Volcanogenic sedimentary deposits ................................................................................................................. 97
Transport and deposition of volcaniclastic particles ..................................................................................................... 97
Mass movement and mass-flow deposits ........................................................................................................................ 98
Primary pyroclastic flow deposits............................................................................................................................ 99
Definition and genesis ..................................................................................................................................... 99
Transport and depositional processes .............................................................................................................. 99
Characteristics of pyroclastic flow deposits ................................................................................................. 100
Components .......................................................................................................................................... 100
Types of deposits ................................................................................................................................... 100
Textures and internal organisation of depositional units ..................................................................... 102
Grade ..................................................................................................................................................... 104
Geometry and aspect ratio ................................................................................................................... 104
Dimensions of pyroclastic flow deposits .............................................................................................. 105
Proximal to distal textural variations ................................................................................................... 105
Compositional zonation ........................................................................................................................ 105
Significance of pyroclastic flow deposits ...................................................................................................... 105
Subaqueously-emplaced pyroclast-rich mass-flow deposits ................................................................................. 106
Transgression of shorelines by pyroclastic flows ................................................................ s ...................................... 106
Welded ignimbrite interbedded with submarine sedimentary sequences .................................................... 106
Non-welded, pyroclast-rich, submarine mass-flow deposits ........................................................................ 107
Significance ................................................................................................................................................... 108
Water-supported and gravity-driven volcaniclastic mass flows and their deposits ............................................. 109
Turbidites ....................................................................................................................................................... Ill
Low-density turbidity currents ............................................................................................................. Il l
High-density turbidity currents ............................................................................................................ I l l
Volcaniclastic turbidites ......................................................................................................................... 112
Significance ............................................................................................................................................ 112
Cohesive debris flows, volcaniclastic debris flows and their deposits .......................................................... 112
Lahars ............................................................................................................................................................ 113
Volcaniclastic grain-flow deposits ................................................................................................................. 114
Volcanic slides, volcanic debris avalanches and their deposits ..................................................................... 114
Massive sulfide clast-bearing submarine volcaniclastic mass-flow deposits ................................................. 116
Traction transport and volcaniclastic traction current deposits .................................................................................. 117
Tractional sedimentary structures ......................................................................................................... 117
Characteristics ....................................................................................................................................... 117
Significance ............................................................................................................................................ 118
Pyroclastic surges and their deposits ............................................................................................................ 118