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The Milos, Christiana-Santorini-Kolumbo (CSK) and Kos-Yali-Nisyros (KYN) volcanic complexes of the Aegean Volcanic Arc have repeatedly produced highly explosive eruptions from at least ∼360 ka into historic times and still show recent unrest. We present the marine tephra record from an array of 50, up to 7.4 m long, sediment cores along the arc collected in 2017 during RV Poseidon cruise POS513, which complements earlier work on distal to ultra-distal eastern Mediterranean sediment cores. A unique set of glass-shard trace element (LA-ICPMS) compositions complements our major element (EMP) data on 220 primary ash layers and 40 terrestrial samples to support geochemical fingerprinting for correlations with 19 known tephras from all three volcanic complexes and with the 39 ka Campanian Ignimbrite from the Campi Flegrei, Italy. The correlations include eleven eruptions from CSK (Kameni, Kolumbo 1650, Minoan, Cape Riva, Cape Tripiti, Upper Scoriae 1 and 2, Middle Pumice, Cape Thera, Lower Pumice, Cape Therma 3). We identify a previously unknown widespread tephra from a plinian eruption on Milos (Firiplaka Tephra). Near the KYN we correlate marine tephras with the Kos Plateau Tuff, the Yali 1 and Yali 2 tephras, and the Upper and Lower Pumice on Nisyros. Between these two major tephras, we found two tephras from Nisyros not yet observed on land. The four Nisyros tephras form a systematic trend toward more evolved magma compositions. In the companion paper we use the tephrostratigraphic framework established here to constrain new eruption ages and magnitudes as a contribution to volcanic hazard assessment.

We use the tephrostratigraphic framework along the Aegean Volcanic Arc established in part 1 of this contribution to determine hemipelagic sedimentation rates, calculate new tephra ages, and constrain the minimum magnitudes of (sub)plinian eruptions of the last 200 kyrs. Hemipelagic sedimentation rates range from ∼0.5 cm/kyr up to ∼40 cm/kyr and vary laterally as well as over time. Interpolation between dated tephras yields an eruption age of ∼37 ka for the Firiplaka tephra, showing that explosive volcanism on Milos is ∼24 kyrs younger than previously thought. The four marine Nisyros tephras (N1 to N4) identified in part 1 (including the Upper (N1) and Lower (N4) Pumice) have ages of ∼57 ka, ∼63 ka, ∼69 ka, and ∼76 ka, respectively. Eruption ages for the Yali-1 and Yali-2 tephras are ∼55 ka and ∼34 ka, respectively. The Yali-2 tephra comprises two geochemically and laterally distinct marine facies. The southern facies is identical to the Yali-2 fall deposit on land but the western facies has slightly less evolved glass compositions. Overall, erupted plinian and co-ignimbrite fall tephra volumes range from <1 to 56 km3 (excluding possible caldera fillings and ignimbite volumes), and 80% of the eruptions had magnitude 5.5

The origins of many supergiant ore deposits remain unresolved because the factors responsible for such extreme metal enrichments are not understood. One factor of critical importance is the timing of mineralization. However, timing information is commonly confounded by the difficulty of dating ore minerals. The world's largest uranium resource at Olympic Dam, South Australia, is exceptional because the high abundance of U allows U-Pb dating of ore minerals. The Olympic Dam U(-Cu-Au-Ag) ore deposit is hosted in ca. 1.59 Ga rocks, and the consensus has been that the supergiant deposit formed at the same time. We argue that, in fact, two stages of mineralization were involved. Paired in situ U-Pb and trace element analyses of texturally distinct uraninite populations show that the supergiant size and highest-U-grade zones are the result of U addition at 0.7–0.5 Ga, at least one billion years after initial formation. This conclusion is supported by a remarkable clustering of thousands of radiogenic 207Pb/206Pb model ages of Cu sulfide grains at this time. Upgrading of the original ca. 1.59 Ga U deposit to its present size at 0.7–0.5 Ga may have resulted from perturbation of regional fluid flow triggered by global climatic (deglaciation) and tectonic (breakup of Rodinia) events.

The felsic-dominant Gawler Range Volcanics and cogenetic Hiltaba Suite granitoids constitute the ca. 1590 Ma Gawler silicic large igneous province in the Gawler Craton, South Australia. The province includes minor occurrences of olivine-phyric basalt at Kokatha and Mount Gunson. In this study, we describe additional olivine-phyric basalts and dykes intersected by drill holes at the Olympic Dam Iron Oxide Cu–U–Au–Ag deposit and the Wirrda Well Cu–Au prospect. Laser Ablation Inductively Coupled Plasma Mass Spectrometry U–Pb dating results (un-anchored) of apatite in the basalts and dykes at Mount Gunson (1576 ± 33 Ma), Wirrda Well (1596 ± 17 Ma), and Olympic Dam (1621 ± 20 Ma) confirm their effective temporal correlation with the ca. 1590 Ma Gawler silicic large igneous province. Compositions of Cr-spinel inclusions enclosed in former olivine phenocrysts (forsterite number >80) in basalts at Mount Gunson, Wirrda Well and Olympic Dam imply derivation from a heterogeneous mantle source that may have been modified by subduction. Least-altered olivine-phyric basalts at Mount Gunson and Kokatha are characterized by negative Nb and Ta anomalies, which are typical of arc basalts but are also common in back-arc basin basalts, in accordance with the result suggested by the Cr-spinel source indicator. The mafic components of the Gawler Range Volcanics generally have higher Zr contents and Zr/TiO2 ratios than those of high-Mg basalts and picrites produced in variable tectonic settings worldwide, possibly reflecting continental crustal components involved in their mantle source.High abundances (typically ~20 vol.%) of former olivine phenocrysts in the basalt at Olympic Dam imply high-Mg whole-rock compositions and a high temperature of the primary magma. This result is consistent with previous models in which the heat flux from mantle magmas caused large-scale partial melting of crustal rocks that subsequently gave rise to silicic magmas erupted and intruded to form the Gawler si

The >800-m-thick, Oligocene Ohanapecosh Formation records voluminous sedimentation of volcanic clasts in the Ancestral Cascades arc (Washington State, USA). Most volcaniclastic beds are dominated by angular pumice clasts and fiamme of andesitic composition, now entirely devitrified and altered. All beds are laterally continuous and have uniform thickness; fine sandstone and mudstone beds have features typical of deposits from low-density turbidity currents and suspension settling. Erosion surfaces, cross-beds, and evidence of bi-directional oscillatory currents (i.e., wave ripples and swaley and hummocky cross-stratification) are almost entirely absent. We infer that the setting was subaqueous and below wave base. The abundance of angular pumice clasts, crystals and dense volcanic clasts, and the extreme thickness of several facies, suggest they were derived from magmatic volatile-driven explosive eruptions. The extremely thick beds are ungraded or weakly graded, and lack evidence of hot emplacement, suggesting deposition from subaqueous, water-supported, high-concentration volcaniclastic density currents. Some of the thickest beds contain coarse, rounded, dense clasts at their base and are interbedded with accretionary lapilli–bearing mudstone; these beds are interpreted to be deposits from subaqueous density currents fed by subaerial pyroclastic flows that crossed the shoreline. Shallow basaltic intrusions and mafic volcanic breccia composed of scoria lapilli indicate the presence of intra-basinal scoria cones that may have been partly subaerial. The range in facies in the Ohanapecosh Formation is typical of below-wave-base, continental (lacustrine) basins that form in proximity to active volcanic arcs, and includes eruption-fed and resedimented facies. Extreme instantaneous aggradation rates are related directly to explosive eruptions, and sediment pathways reflect the locations of active volcanoes, in contrast to conventional sedimentation processes acting in no

The Gawler Range Volcanics (GRV) and the Hiltaba Suite (HS) of South Australia form a silicic-dominated large igneous province (the Gawler SLIP) emplaced in an intracontinental setting during the Mesoproterozoic. Emplacement of the GRV lasted for a short period of time (~2 Ma), and can be separated into two main phases. The first phase (lower GRV) is composed of thick (≤3 km) sequences erupted from distinct centres, and includes small to moderate volume (up to >150 km3) felsic lavas, ignimbrites, and minor mafic and intermediate lavas. The upper GRV include extensive felsic lavas that are up to >1000 of km3 in volume and >200 km across. Using well preserved, quartz-hosted melt inclusions, we investigated the composition of the lower GRV, including major, trace, and volatile elements. The results indicate high concentrations of K2O (≤7–8 wt.%), rare earth and high field strength elements, and low concentrations of Ca, Mg, Ni, Cr, Sr and Ba in comparison with felsic continental crust. Overall, melt inclusion compositions match whole-rock geochemical characteristics. We demonstrate that the GRV magma was F-rich (≤1.3 wt.%), and had high temperature for a silicic magma. High F concentrations and high temperature would have resulted in lower than usual polymerisation of the melt and relatively low viscosity. These characteristics help explain how very voluminous felsic magma was erupted effusively and emplaced as lavas. Other intracontinental SLIP contain extensive felsic lavas and ignimbrites which appear to share similar geochemical characteristics. We also show that selective alteration caused depletion of whole-rock compositions in some trace elements, namely Pb, U, and Sn.

Silicic-dominated large igneous provinces (SLIP) represent vast amounts of magma (≥ 105 km3) erupted onto the Earth's surface or injected into the crust over short time spans, and are important components of the continental crust. The conditions of formation and evolution of these large magmatic provinces and their magma chambers are still poorly constrained. In this contribution, we examine cathodoluminescence textures and trace element (Al, Ti, Fe) zoning of quartz in a Mesoproterozoic SLIP, the Gawler Range Volcanics (GRV), South Australia. We describe intra-granular textures such as truncation of growth textures and reverse zoning (rimwards increase of Ti content). These characteristics of quartz, together with remelting of already crystallised portions of the magma chamber (felsic enclaves), suggest a complex history of crystallisation and resorption, and fluctuating magma temperature. Titanium-in-quartz geothermometry indicates that adjacent quartz zones record temperature variations (ΔT) up to 70 °C in volcanic units. We also report contrasting (non-correlatable) zoning patterns amongst quartz crystals, each indicating different crystallisation conditions. The juxtaposition of quartz crystals with contrasting zoning patterns is consistent with a dynamic regime (convection, stirring, overturning) of the GRV magma chamber. These results point to pulsating magmatic conditions, compatible with a non-linear evolution of the GRV magma chamber. Heat, necessary to explain both intra-granular and infra-granular textural variations, may have been provided in different pulses by underplating of mafic magma.

Olympic Dam is a supergiant Fe oxide Cu-U-Au-Ag ore deposit (~9 × 109 t) that is also enriched in rare earth elements (REEs) and fluorine (F). The immediate host to the ore is hydrothermal breccia within granite and volcanic rocks of a Mesoproterozoic silicic large igneous province. Analyses of melt inclusions in quartz phenocrysts in rhyolite show that the silicic magmas of this province were unusually rich in F (up to 1.3 wt%). Fluorite and other F-rich minerals that crystallized from these magmas provided a gigantic reservoir of F. As a result, the Olympic Dam ore-forming fluid was F-rich and had exceptional capacity to transport diverse elements. Further, we infer that hydrofluoric acid, the most corrosive acid known, contributed to hydrothermal breccia formation by dissolution that in turn increased permeability and accelerated the rate of fluid-rock interaction. It is no accident that the world's largest hydrothermal ore deposit occurs in an F-rich silicic large igneous province.

Rhyolites of the Mesoproterozoic Gawler Range Volcanics (GRV) of South Australia are characterised by high concentrations of some trace elements (REE, Y, HFSE, Rb and F, in particular). Whole rock geochemical data suggest that these elements were incompatible during magma crystallisation. Accessory minerals (fluorite, zircon, REE-F-carbonate, Ti oxide, apatite, and titanite) can account for most of the trace element content of the rocks. These minerals occur in vesicles, micromiaroles, lithophysal vugs and in interstices between major mineral phases (quartz and feldspar as both phenocrysts and groundmass). Such textural evidence indicates that accessory minerals crystallised late in the history of the magma and that they were deposited from a volatile-rich (fluid) phase. These features are explained by the following sequence of events: 1) F dissolved in the magma lowered the crystallisation temperature of accessory minerals, causing trace elements (REE, Y, and HFSE) to behave as incompatible elements. 2) Protracted crystallisation of major mineral phases (quartz, feldspar, and oxides) formed a volatile- and trace element-enriched residual liquid. 3) A volatile element (H2O, F, and CO2)-rich phase (late-stage magmatic fluid) evolved from the magma. High concentration of fluorine and other complexing agents in this phase allowed trace elements to be transported in solution. 4) Accessory minerals crystallised from such a phase in vesicles, micromiaroles and interstices between the major mineral phases. © 2010 Elsevier B.V.

Lihir Gold mines the Ladolam gold deposit on Lihir Island, Papua New Guinea. With an average grade of 2.42 g/tonne, the deposit contains 40 000 000 oz gold. The gold is associated with epithermal-style alteration and mineralisation, and is mainly contained in refractory pyrite. The deposit is made up of four ore bodies; the Minifie, Leinetz, Coastal and Kapit. The results of an ongoing research project into the first two are discussed, highlighting the differences in geology and the paragenetic history., Lihir Gold mines the Ladolam gold deposit on Lihir Island, Papua New Guinea. With an average grade of 2.42 g/tonne, the deposit contains 40 000 000 oz gold. The gold is associated with epithermal-style alteration and mineralisation, and is mainly contained in refractory pyrite. The deposit is made up of four ore bodies; the Minifie, Leinetz, Coastal and Kapit. The results of an ongoing research project into the first two are discussed, highlighting the differences in geology and the paragenetic history.

The Chatree epithermal silver-gold deposit is located in Thailand in the central part of the Leoi Fold Belt. Current total resource at Chatree is 74 600 000 tonnes at 1.6 g/t gold and 13 g/t silver. The mineralisation occurs as veins/veinlets and stockworks in minor breccia in volcaniclastic and volcano-sedimentary rocks of andesitic to basaltic andesite composition and Permo-Triassic age. An initial oxygen isotope study on vein quartz showed that the values increased outwards from the centre of the main ore zones, and this could be used as a vector to ore., The Chatree epithermal silver-gold deposit is located in Thailand in the central part of the Leoi Fold Belt. Current total resource at Chatree is 74 600 000 tonnes at 1.6 g/t gold and 13 g/t silver. The mineralisation occurs as veins/veinlets and stockworks in minor breccia in volcaniclastic and volcano-sedimentary rocks of andesitic to basaltic andesite composition and Permo-Triassic age. An initial oxygen isotope study on vein quartz showed that the values increased outwards from the centre of the main ore zones, and this could be used as a vector to ore.

The presence of peperite, formed by dynamic mixing of magma with wet, unconsolidated sediment, is important in distinguishing sills from lavas or post-volcanic intrusions into solid rock. At the Onedin prospect in the Koongie Park Formation, Western Australia, high-grade massive sulphide is hosted in a carbonate lens up to 10 m below an extensive aphyric sill with peperitic upper and lower margins. The sill may have been an important heat source and also provided a cap to fluid flow. The remains of pumice-rich textures, largely destroyed during alteration and compaction, are also associated with carbonate alteration at the prospect, while relic perlite occurs at the margins of aphyric rhyolite sills. The high porosity, permeability and reactivity of the glassy pumice and intensely fractured glass of perlite may have focused hydrothermal flow, while the same properties will have promoted early alteration and loss of porosity., The presence of peperite, formed by dynamic mixing of magma with wet, unconsolidated sediment, is important in distinguishing sills from lavas or post-volcanic intrusions into solid rock. At the Onedin prospect in the Koongie Park Formation, Western Australia, high-grade massive sulphide is hosted in a carbonate lens up to 10 m below an extensive aphyric sill with peperitic upper and lower margins. The sill may have been an important heat source and also provided a cap to fluid flow. The remains of pumice-rich textures, largely destroyed during alteration and compaction, are also associated with carbonate alteration at the prospect, while relic perlite occurs at the margins of aphyric rhyolite sills. The high porosity, permeability and reactivity of the glassy pumice and intensely fractured glass of perlite may have focused hydrothermal flow, while the same properties will have promoted early alteration and loss of porosity.

Three volcanic sequences occur: the Cambro-Ordovician Mt Windsor Volcanics comprising rhyolitic lava and minor feldspathic to quartzose sandstone; Upper Devonian-Lower Carboniferous volcanics of the Drummond Basin sequence comprising andestic and rhyolitic lavas and dacitic ignimbrites; and late Carboniferous diverse ignimbrites, lavas and conglomerates overlain by less deformed rhyolitic ignimbrite sheets. All three sequences are considered to be prospective for precious and base metal mineralisation. Polymetallic massive sulphide deposits occur in the Mt Windsor Volcanics further west and many epithermal gold prospects and mines are hosted by volcanics at the base of the Drummond Basin., Three volcanic sequences occur: the Cambro-Ordovician Mt Windsor Volcanics comprising rhyolitic lava and minor feldspathic to quartzose sandstone; Upper Devonian-Lower Carboniferous volcanics of the Drummond Basin sequence comprising andestic and rhyolitic lavas and dacitic ignimbrites; and late Carboniferous diverse ignimbrites, lavas and conglomerates overlain by less deformed rhyolitic ignimbrite sheets. All three sequences are considered to be prospective for precious and base metal mineralisation. Polymetallic massive sulphide deposits occur in the Mt Windsor Volcanics further west and many epithermal gold prospects and mines are hosted by volcanics at the base of the Drummond Basin.

The spectrum of Cu-Au, Zn-rich and Au-only deposits in the Mount Read Volcanics, Tasmania, and the Mount Windsor sub-province, Queensland, is interpreted to represent a continuum from classic sea-floor VHMS deposits to those with features more akin to porphyry Cu-Au and epithermal Au-Ag deposits. This spectrum relates to the interplay between several factors: proportions of volcaniclastic, lava and subvolcanic intrusive facies; depth of sea water; permeability and porosity of volcanic host rocks; balance between magmatic and sea-water components in the ore fluid; and temperature and acidity of the ore fluid. Mineralogical, lithogeochemical and isotopic studies have revealed a range of alteration vectors useful in exploration for both Zn-rich and VHMS deposits: carbonate and white mica variations, Tl and Sb haloes, and O and S isotopes as important vectors towards the centre of the hydrothermal system., The spectrum of Cu-Au, Zn-rich and Au-only deposits in the Mount Read Volcanics, Tasmania, and the Mount Windsor sub-province, Queensland, is interpreted to represent a continuum from classic sea-floor VHMS deposits to those with features more akin to porphyry Cu-Au and epithermal Au-Ag deposits. This spectrum relates to the interplay between several factors: proportions of volcaniclastic, lava and subvolcanic intrusive facies; depth of sea water; permeability and porosity of volcanic host rocks; balance between magmatic and sea-water components in the ore fluid; and temperature and acidity of the ore fluid. Mineralogical, lithogeochemical and isotopic studies have revealed a range of alteration vectors useful in exploration for both Zn-rich and VHMS deposits: carbonate and white mica variations, Tl and Sb haloes, and O and S isotopes as important vectors towards the centre of the hydrothermal system.

The Cu-Pb-Zn orebody overlies a 1 000 m thick, westward-thinning volcanic succession. This represents an elevated rhyolitic volcanic centre constructed by the products of effusive eruptions in a subaqueous environment below the storm-wave base, similar to the setting of the Pacmanus hydrothermal field today. Phenocryst logging has distinguished several types of rhyolite in the footwall and dacite in the hangingwall, even though primary textures have been modified by hydrothermal alteration. Careful observation of texture has also allowed genuine clastic facies to be distinguished from false in the strongly altered footwall lavas and intrusions, and potentially prospective units emplaced by mass flow on the sea floor to be recognised. The mineralising hydrothermal system was active during rhyolitic volcanism but ceased before the final stages of rhyolite emplacement. Volcaniclastic facies rich in coarse quartz crystals are not restricted to the mineralised horizon or the mine area. Well-defined hydrothermal alteration zones cut across emplacement units and facies in the footwall., The Cu-Pb-Zn orebody overlies a 1 000 m thick, westward-thinning volcanic succession. This represents an elevated rhyolitic volcanic centre constructed by the products of effusive eruptions in a subaqueous environment below the storm-wave base, similar to the setting of the Pacmanus hydrothermal field today. Phenocryst logging has distinguished several types of rhyolite in the footwall and dacite in the hangingwall, even though primary textures have been modified by hydrothermal alteration. Careful observation of texture has also allowed genuine clastic facies to be distinguished from false in the strongly altered footwall lavas and intrusions, and potentially prospective units emplaced by mass flow on the sea floor to be recognised. The mineralising hydrothermal system was active during rhyolitic volcanism but ceased before the final stages of rhyolite emplacement. Volcaniclastic facies rich in coarse quartz crystals are not restricted to the mineralised horizon or the mine area. Well-defined hydrothermal alteration zones cut across emplacement units and facies in the footwall.

The Olympic Dam iron oxide copper-gold (IOCG)-uranium-silver deposit is hosted in the large Olympic Dam breccia complex within the ca. 1.59 Ga Roxby Downs Granite. This breccia complex formed through multiple stages of hydrothermal activity and texturally destructive brecciation that affected the granite. The deepest diamond drill hole to date intersected weakly altered, in situ brecciated granite (370-2 329 m) and a quartz-phyric felsic unit (2 010-2 265 m). These two rock units host coarse-grained hydrothermal minerals, from ca. 2 150 m to the end of the drill hole (2 329 m). The main minerals in this assemblage are magnetite (± haematite), pyrite, fluorapatite, and quartz, with minor disseminated chalcopyrite, sericite, chlorite, rare earth element (REE)-fluorcarbonates, monazite, uraninite, thorite, galena, sphalerite, anhydrite, schorl, rutile, and pyrrhotite. The assemblage is cut by abundant multiphase veinlets and calcite (± fluorite ± barite) veins. A zircon U-Pb age for the felsic unit (1 591 ± 11 Ma) implies that this unit is broadly coeval with the granite, whereas U-Pb ages for hydrothermal uraninite (1 593.5 ± 5.1 Ma), fluorapatite (1 583.3 ± 6.5 Ma), and haematite (1 592 ± 15 Ma) indicate that deposition of the U-REE-rich hydrothermal magnetite-fluorapatite-pyrite-quartz assemblage and replacement of magnetite by haematite occurred soon after emplacement of the granitic host rocks. Sm-Nd dating of ubiquitous calcite veins suggests formation at ca. 1.54 Ga., The Olympic Dam iron oxide copper-gold (IOCG)-uranium-silver deposit is hosted in the large Olympic Dam breccia complex within the ca. 1.59 Ga Roxby Downs Granite. This breccia complex formed through multiple stages of hydrothermal activity and texturally destructive brecciation that affected the granite. The deepest diamond drill hole to date intersected weakly altered, in situ brecciated granite (370-2 329 m) and a quartz-phyric felsic unit (2 010-2 265 m). These two rock units host coarse-grained hydrothermal minerals, from ca. 2 150 m to the end of the drill hole (2 329 m). The main minerals in this assemblage are magnetite (± haematite), pyrite, fluorapatite, and quartz, with minor disseminated chalcopyrite, sericite, chlorite, rare earth element (REE)-fluorcarbonates, monazite, uraninite, thorite, galena, sphalerite, anhydrite, schorl, rutile, and pyrrhotite. The assemblage is cut by abundant multiphase veinlets and calcite (± fluorite ± barite) veins. A zircon U-Pb age for the felsic unit (1 591 ± 11 Ma) implies that this unit is broadly coeval with the granite, whereas U-Pb ages for hydrothermal uraninite (1 593.5 ± 5.1 Ma), fluorapatite (1 583.3 ± 6.5 Ma), and haematite (1 592 ± 15 Ma) indicate that deposition of the U-REE-rich hydrothermal magnetite-fluorapatite-pyrite-quartz assemblage and replacement of magnetite by haematite occurred soon after emplacement of the granitic host rocks. Sm-Nd dating of ubiquitous calcite veins suggests formation at ca. 1.54 Ga.

The 46 000 000 oz Ladolam gold deposit, the largest alkalic epithermal gold deposit in the world in terms of contained gold, is composed of four ore zones: Minifie, Lienetz, Kapit, and Coastal. A detailed lithofacies study of the Minifie ore zone recognises three evolutionary stages: volcanosedimentary strata (part of an alkalic composite volcanic island); a porphyry-style breccia dyke; and epithermal-style breccias. Overprinting the volcanosedimentary stratigraphy are three hydrothermally cemented breccia facies, one deposited in the porphyry environment and two deposited in the epithermal environment. Porphyry-style alteration assemblages, focused around the central Minifie shear fault, are overprinted by shallow-level and deeper-level (below the present mining surface, more than 140 m below sea level) epithermal-style features composed of quartz-calcite-adularia-anhydrite-cemented breccias and shallowly northward-dipping to near-horizontal veins that have gold grades of 1 to more than 60 g/t Au. Shallow-level epithermal facies (adularia-quartz-pyrite-cemented breccias, veins and associated alteration) host the bulk-mineable gold ore, typically yielding more than 4 g/t Au over 12 m blast-hole samples., The 46 000 000 oz Ladolam gold deposit, the largest alkalic epithermal gold deposit in the world in terms of contained gold, is composed of four ore zones: Minifie, Lienetz, Kapit, and Coastal. A detailed lithofacies study of the Minifie ore zone recognises three evolutionary stages: volcanosedimentary strata (part of an alkalic composite volcanic island); a porphyry-style breccia dyke; and epithermal-style breccias. Overprinting the volcanosedimentary stratigraphy are three hydrothermally cemented breccia facies, one deposited in the porphyry environment and two deposited in the epithermal environment. Porphyry-style alteration assemblages, focused around the central Minifie shear fault, are overprinted by shallow-level and deeper-level (below the present mining surface, more than 140 m below sea level) epithermal-style features composed of quartz-calcite-adularia-anhydrite-cemented breccias and shallowly northward-dipping to near-horizontal veins that have gold grades of 1 to more than 60 g/t Au. Shallow-level epithermal facies (adularia-quartz-pyrite-cemented breccias, veins and associated alteration) host the bulk-mineable gold ore, typically yielding more than 4 g/t Au over 12 m blast-hole samples.

In the North Pole Dome the world's most ancient biogenic structures, 3.47-Ga-old algal mats and stromatolites, are closely associated with bedding-conformable and discordant laminar quartz, chalcedony, and barite, while barite-rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the biogenic structures. With the exception of the large volume of barite, these bedding-conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration typical of epithermal deposits formed from near-neutral pH fluids. The findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geological time, their present-day distribution being mainly the result of preservation, not process., In the North Pole Dome the world's most ancient biogenic structures, 3.47-Ga-old algal mats and stromatolites, are closely associated with bedding-conformable and discordant laminar quartz, chalcedony, and barite, while barite-rich quartz hydrothermal veins with similar mineralogy occur throughout the stratigraphy below the biogenic structures. With the exception of the large volume of barite, these bedding-conformable and discordant laminar quartz veins exhibit textures and associated hydrothermal alteration typical of epithermal deposits formed from near-neutral pH fluids. The findings support previous studies that demonstrate that the processes that form epithermal deposits have been active throughout geological time, their present-day distribution being mainly the result of preservation, not process.

24 volcanic and 16 intrusive rock samples from the basin area were analysed for delta 18 oxygen values. The results confirmed earlier suggestions that regional oxygen 18 depletion patterns in areas of predominantly silicic magmatism coincide with epithermal districts and indicate their value as an exploration tool., 24 volcanic and 16 intrusive rock samples from the basin area were analysed for delta 18 oxygen values. The results confirmed earlier suggestions that regional oxygen 18 depletion patterns in areas of predominantly silicic magmatism coincide with epithermal districts and indicate their value as an exploration tool.

The Cambrian Mount Read Volcanics comprise compositionally and texturally diverse lavas and volcaniclastic rocks, most of which were emplaced in submarine environments below wave base. The facies architecture reflects the contrasting character and geometry of primary volcanic and volcaniclastic facies which are strongly controlled by eruption style and emplacement processes. Studying the emplacement processes of diverse volcanic facies present in the northern Mount Read Volcanics has helped clarify the basic outline of the facies architecture. The predicted facies geometry of the principal volcanic facies has led to an approach to correlation in the Mount Read Volcanics. Mass-flow-emplaced pumiceous volcaniclastic facies provide the best framework for correlation because these are produced in large volumes, erupted infrequently, rapidly emplaced and are widely distributed. Distinctive units of this type that occur near Hellyer and 40km south at White Spur-Howards Road could each be part of the same regionally extensive volcaniclastic facies association. A similar volcaniclastic facies association hosts the Hercules and Rosebery masssive sulphide deposits and clearly demonstrates that such associations are prospective for this style of mineralisation., The Cambrian Mount Read Volcanics comprise compositionally and texturally diverse lavas and volcaniclastic rocks, most of which were emplaced in submarine environments below wave base. The facies architecture reflects the contrasting character and geometry of primary volcanic and volcaniclastic facies which are strongly controlled by eruption style and emplacement processes. Studying the emplacement processes of diverse volcanic facies present in the northern Mount Read Volcanics has helped clarify the basic outline of the facies architecture. The predicted facies geometry of the principal volcanic facies has led to an approach to correlation in the Mount Read Volcanics. Mass-flow-emplaced pumiceous volcaniclastic facies provide the best framework for correlation because these are produced in large volumes, erupted infrequently, rapidly emplaced and are widely distributed. Distinctive units of this type that occur near Hellyer and 40km south at White Spur-Howards Road could each be part of the same regionally extensive volcaniclastic facies association. A similar volcaniclastic facies association hosts the Hercules and Rosebery masssive sulphide deposits and clearly demonstrates that such associations are prospective for this style of mineralisation.

The Ural Volcanics are a early Devonian, submarine, felsic lava-sill complex, exposed in the western central Lachlan Orogen, New South Wales. The Ural Volcanics and underlying Upper Silurian, deepwater, basin-fill sedimentary rocks make up the Rast Group. The Ural Range study area, centrally located in the Cargelligo 1:100 000 map sheet area, was mapped at 1:10 000 scale. Seventeen principal volcanic facies were identified in the study area, dominated by felsic coherent facies (rhyolite and dacite) and associated monomictic breccia and siltstone-matrix monomictic breccia facies. Subordinate volcaniclastic facies include the pumice-rich breccia facies association, rhyolite - dacite -siltstone breccia facies and fiamme-siltstone breccia facies. The sedimentary facies association includes mixed-provenance and non-volcanic sandstone to conglomerate, black mudstone, micaceous quartz sandstone and foliated mudstone. The succession was derived from at least two intrabasinal volcanic centres. One, in the north, was largely effusive and intrusive, building a lava - sill complex. Another, in the south, was effusive, intrusive and explosive, generating lavas and moderate- volume (*3 km3) pyroclastic facies. The presence of turbidites, marine fossils, very thick massive to graded volcaniclastic units and black mudstone, and the lack of large-scale cross-beds and erosional scours, provide evidence for deposition in a submarine environment below storm wave-base. The Ural Volcanics have potential for seafloor or sub-seafloor replacement massive sulfide deposits, although no massive sulfide prospects or related altered zones have yet been defined. Sparse, disseminated sulfides occur in sericite-altered, steeply dipping shear zones.

Pumiceous peperite is associated with a rhyolitic sill that intruded wet, unconsolidated, submarine stratified pumice breccia in the Cambrian Mount Read Volcanics, Australia. Other examples of pumiceous peperite described in this paper occur at the pumiceous base of a rhyolitic lava and the margins of a rhyolitic cryptodome complex in the Miocene Green Tuff Belt, Japan. Intervals of pumiceous peperite are thin (less than 15 m), laterally discontinuous, massive, poorly sorted and the clast-to-matrix ratio varies significantly over short distances. They are composed of feldsparphyric tube pumice clasts and domains of clastic sediment that include stratified pumice breccia, pumiceous siltstone and bioturbated mudstone. The sediment domains may be massive or may display relic depositional structures. Sediment adjacent to pumice clasts is silicified, possibly reflecting induration on contact with hot pumice. Pumiceous peperite has gradational contacts with in situ and clast-rotated pumiceous hyaloclastite and coherent pumiceous rhyolite. Gradational relationships between pumiceous peperite and coherent pumiceous rhyolite, pumice clasts with chilled margins and curviplanar surfaces, and abundant jigsaw-fit texture imply that quench fragmentation and autobrecciation were the dominant mechanisms of clast formation. The formation of pumiceous peperite is favoured by a combination of low confining pressure and delayed quenching allowing vesiculation. Pumiceous peperite may easily be misinterpreted or overlooked as it resembles other pumice-rich facies that are common in submarine volcanic successions. The correct identification of pumiceous peperite can provide evidence to constrain the timing of intrusive episodes in volcanic successions.

Fiamme and eutaxitic texture are common in ancient non-welded, pumice breccias. The fiamme are phyllosilicate-rich lenses that define a bedding-parallel foliation resembling eutaxitic texture in welded ignimbrites. Pumice breccias in the Cambrian Mount Read Volcanics (Australia) are composed of tube pumice clasts, bubble-wall shards, plagioclase crystal fragments and volcanic lithic clasts, and contain dark green fiamme and stylolites. These sericite or chlorite+sericite fiamme are aligned roughly parallel to regional bedding, and are enclosed in pale pink feldspar+quartz-altered domains of uncompacted, randomly oriented, tube pumice clasts and bubble-wall shards. Similarly, pumice breccias in the Miocene Green Tuff Belt in the Hokuroku Basin (Japan) comprise tube pumice clasts, fiamme, bubble-wall shards, crystal fragments and non-vesicular volcanic clasts. The dark green, wispy smectite or chlorite fiamme are aligned parallel to bedding, and are enclosed in domains of variably clay-, zeolite- and sericite-altered, uncompacted pumice clasts and shards. The fiamme in these examples vary in length (0.5 mm to 1 m), length to height ratio (3:1 to 40:1), shape (e.g. flame-like, feathery, branching, bow tie, wedge), and internal texture (porphyritic, massive, vesicular or stylolitic). The fiamme define an anastomosing bedding-parallel, pre-tectonic eutaxitic texture. Delicate feathery terminations and locally preserved vesicles indicate that the fiamme are altered compacted pumice clasts. The presence of bedding-parallel stylolites and solution seams, undeformed shards and pumice clasts adjacent to the fiamme, and the overprinting of fiamme by the regional cleavage suggest that the fiamme formed during diagenesis, prior to tectonic deformation, and that compaction did not involve welding. Fiamme and eutaxitic texture in these examples resulted from the alteration, dissolution and mechanical compaction of cold tube pumice clasts during diagenesis and lithification.

The volcanic island of Milos, Greece, comprises an Upper Pliocene-Pleistocene, thick (up to 700 m), compositionally and texturally diverse succession of calcalkaline, volcanic, and sedimentary rocks that record a transition from a relatively shallow but dominantly belowwave-base submarine setting to a subaerial one. The volcanic activity began at 2.66 plus-minus 0.07 Ma and has been more or less continuous since then. Subaerial emergence probably occurred at 1.44 plus-minus 0.08 Ma, in response to a combination of volcanic constructional processes and faultcontrolled volcano-tectonic uplift. The architecture of the dominantly felsic-intermediate volcanic succession reflects contrasts in eruption style, proximity to source, depositional environment and emplacement processes. The juxtaposition of submarine and subaerial facies indicates that for part of the volcanic history, below-wave base to abovewave base, and shoaling to subaerial depositional environments coexisted in most areas. The volcanic facies architecture comprises interfingering proximal (near vent), medial and distal facies associations related to five main volcano types: (1) submarine felsic cryptodome-pumice cone volcanoes; (2) submarine dacitic and andesitic lava domes; (3) submarine-to-subaerial scoria cones; (4) submarine-tosubaerial dacitic and andesitic lava domes and (5) subaerial lava-pumice cone volcanoes. The volcanic facies areinterbedded with a sedimentary facies association comprising sandstone and/or fossiliferous mudstone mainly derived from erosion of pre-existing volcanic deposits. The main facies associations are interpreted to have conformable, disconformable,and interfingering contacts, and there are no mappable angular unconformities or disconformities within the volcanic succession.

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

Part of the Mesoproterozoic (1.6 Ga) Gawler Range Volcanics in South Australia is composed of mingled feldspar- quartz- phyric dacite, rhyodacite and rhyolite lavas. Field relationships suggest that dacite erupted first, locally grading into rhyodacite, followed by mingled dacite and rhyolite or rhyodacite and rhyolite, and finally in some areas rhyolite, and imply that the three lithofacies co-existed in a compositionally stratified magma chamber. Data on the bulk rock, groundmass and melt inclusion compositions suggest that post-eruption alteration has had very little effect on the original rock compositions. Melt inclusions in quartz from rhyolite and rhyodacite-dacite, respectively, belong to two compositional populations. Inclusions in the rhyolitic quartz have less evolved compositions with lower SiO2 (72-76.4wt%) and higher Al2O3 (13.2-15.6wt%) and Na2O (2.5-4.2wt%) abundances. In contrast, melt inclusions in quartz from the rhyodacite-dacite are more "evolved" (i.e., 75.5-78.3 wt% SiO2, 11.2-12.7 wt% Al2O3 and 1.7-2.2 wt% Na2O). The two melt populations define a single compositional trend towards groundmass compositions, which are essentially similar in all three lithofacies (77.8-80.5 wt% SiO2, 9.9-11.1 wt% Al2O3 and 2.2-2.4 wt% Na2O). This trend is consistent with the derivation of the groundmass melt from a single precursor melt of rhyolitic composition by means of crystallisation of dominant plagioclase, K-feldspar and minor quartz. Plagioclase-enriched dacite-rhyodacite magma comprises a mixture of the residual melt and plagioclase phenocrysts that accumulated in the upper part of the magma chamber and erupted first. Similar residual melt containing quartz and K-feldspar phenocrysts was present deeper in the magma chamber and erupted later to form quartz-, K-feldspar-phyric rhyolite.

The Ordovician to Lower Silurian Forest Reefs Volcanics in the Cadia – Neville region, northeastern Lachlan Orogen, represent the product of at least two shoshonitic volcanic centres intercalated with a volcaniclastic apron. The two episodes of shoshonitic volcanism in the Forest Reefs Volcanics are separated by between 15 and 20 million years. The Forest Reefs Volcanics are informally divided into lower and upper parts, separated by an inferred unconformity that broadly coincides in age with a limestone-forming hiatus in volcanism (449 – 447 Ma) and emplacement nearby of medium-K calcalkaline dacitic intrusions (448 – 445 Ma). The lower part includes shoshonitic basaltic andesite, feldsparrich sandstone, volcanic lithic breccia and lesser black mudstone; polymictic volcanic conglomerate with sandstone matrix and calcareous sandstone are important near the top. The basaltic facies association occurs near the base of the lower Forest Reefs Volcanics and could represent a submarine basaltic volcano at least 12 km in diameter. A major change in provenance for the upper Forest Reefs Volcanics is reflected in the increased abundance of ferromagnesian crystals and coarse mafic volcanic fragments, particularly in the mafic volcanic sandstone, polymictic volcanic conglomerate with coarse volcanic matrix and polymictic hornblende andesite breccia. The trachyandesite facies association records another episode of shoshonitic volcanism that probably occurred late in the accumulation of the upper Forest Reefs Volcanics and could represent an intrusive complex or the initial, largely shallow intrusive stages of a cone volcano. Highly porphyritic basalt to basaltic andesite intrusions were emplaced as sills before the volcaniclastic succession was lithified. The final magmatic activity generated coarsely equigranular, mafic to intermediate intrusions. The trachyandesite facies association, the highly porphyritic basalt to basaltic andesite intrusions and the coarsely equigranular

Miocene submarine basanite pillows, lava lobes, megapillows and sheet lavas in the Stanley Peninsula, northwestern Tasmania, Australia, are well-preserved in three dimensions. The pillows have ropy wrinkles, transverse wrinkles, symmetrical wrinkles, contraction cracks and three types of spreading cracks on their surfaces, and concentric and radial joints in the interior. The lava lobes have ropy wrinkles and contraction cracks on their surfaces. The megapillows are cylindrical with a smoothly curved upper surface and steep sides, and are characterized by distinct radial columnar joints in the interior. They are connected to pillows that propagate radially from its basal margin. The sheet lavas are tabular and have vertical columnar joints in the interior. The largest sheet lava shows a remarkable gradation from a lower 5-m-thick pillow facies to an upper massive facies. The pillows, lava lobes, megapillows and sheet lavas are inferred to have been emplaced completely below sea level but in a shallow marine environment. Their morphological features suggest that the pillows grew by episodic rupture of a near-solid crust and emergence of hot lava, whereas the lava lobes propagated by continuous stretching of the outer skin at the flow front. The megapillows and sheet lavas were master feeder channels by which molten lava was conveyed to the advancing pillows. The sheet lavas propagated by repeated processes of pillow formation and overriding by an upper massive part. Alternating pillow and massive facies commonly found in ocean-floor drill cores and exposed in cross-section in many subaqueous volcanic successions may have formed by propagation of pillows from the basal margins of advancing sheet lavas.

Fiamme and eutaxitic texture are common in ancient non-welded, pumice breccias. The fiamme are phyllosilicate-rich lenses that define a bedding-parallel foliation resembling eutaxitic texture in welded ignimbrites. Pumice breccias in the Cambrian Mount Read Volcanics (Australia) are composed of tube pumice clasts, bubble-wall shards, plagioclase crystal fragments and volcanic lithic clasts, and contain dark green fiamme and stylolites. These sericite or chlorite+sericite fiamme are aligned roughly parallel to regional bedding, and are enclosed in pale pink feldspar+quartz-altered domains of uncompacted, randomly oriented, tube pumice clasts and bubble-wall shards. Similarly, pumice breccias in the Miocene Green Tuff Belt in the Hokuroku Basin (Japan) comprise tube pumice clasts, fiamme, bubble-wall shards, crystal fragments and non-vesicular volcanic clasts. The dark green, wispy smectite or chlorite fiamme are aligned parallel to bedding, and are enclosed in domains of variably clay-, zeolite- and sericite-altered, uncompacted pumice clasts and shards. The fiamme in these examples vary in length (0.5 mm to 1 m), length to height ratio (3:1 to 40:1), shape (e.g. flame-like, feathery, branching, bow tie, wedge), and internal texture (porphyritic, massive, vesicular or stylolitic). The fiamme define an anastomosing bedding-parallel, pre-tectonic eutaxitic texture. Delicate feathery terminations and locally preserved vesicles indicate that the fiamme are altered compacted pumice clasts. The presence of bedding-parallel stylolites and solution seams, undeformed shards and pumice clasts adjacent to the fiamme, and the overprinting of fiamme by the regional cleavage suggest that the fiamme formed during diagenesis, prior to tectonic deformation, and that compaction did not involve welding. Fiamme and eutaxitic texture in these examples resulted from the alteration, dissolution and mechanical compaction of cold tube pumice clasts during diagenesis and lithification.

Peperite involving basalt and polymictic volcanic conglomerate occurs in the Pliocene Ba Volcanic Group at Yaqara in northern Viti Levu, Fiji. Because the host sediment is coarse-grained and dominated by basalt clasts, the peperite could be easily overlooked and mistaken for another coarse volcaniclastic facies. However, the presence of groups of basalt clasts that show jigsaw-fit texture, fluidally shaped basalt clasts with complete glassy margins, gradational contacts with adjacent sedimentary facies and the absence of stratification indicate that molten basalt mingled with unconsolidated gravel. Using these criteria, we show that other superficially similar, coarse, polymictic facies with fluidal basalt clasts are not peperite. Both blocky and fluidal basalt clasts occur together in the peperite. The amoeboid basalt clasts in the fluidal peperite result from dismembering of ductile, low-viscosity, relatively hot magma. At this stage, propagating magma lobes were probably insulated from direct contact with the wet sediment by a vapour film. The angular, polyhedral basalt clasts in the blocky peperite indicate brittle disintegration of somewhat cooler, higher-viscosity magma. The presence of jigsaw-fit texture and polyhedral clasts with glassy margins suggest that quench fragmentation of the basalt was important in the formation of the blocky peperite. Although there is no positive evidence for steam explosivity, the presence of steam could be recorded by small quartz-filled cavities that occur within the host sediment. The co-existence of fluidal and blocky basalt clasts is interpreted to reflect successive ductile then brittle fragmentation of intruding magma. The change from fluidal to blocky peperite might have resulted from progressive cooling of the magma during intrusion, and also from the breakdown of fluidisation when the limited supply of fine sediment in the host gravel was exhausted.

Three widespread felsic volcanic units, the Eucarro Rhyolite, Pondanna Dacite Member and Moonaree Dacite Member, have been distinguished in the Mesoproterozoic Gawler Range Volcanics. These three units are the largest in the Gawler Range Volcanics, each in excess of 500 km3. Each unit is ~ 300 m thick and includes a black, formerly glassy base, a granophyric columnar-jointed interior, and an amygdaloidal outer margin. The units are very gently dipping and locally separated by thin (<20 m) lenses of either ignimbrite (Mt Double Ignimbrite), tuffaceous sandstone or faults. The youngest unit, the Moonaree Dacite Member, covers a central area with a diameter greater than 80 km. The southern two units have east-west extents in the order of 180 km, but are much less extensive from south to north (5-60 km). All three units are dominated by euhedral phenocrysts and are relatively crystal rich. Both the Eucarro Rhyolite and Moonaree Dacite Member contain clasts of basement granitoid and other lithologies and are locally heterogeneous in texture and composition. Some granitoid clasts have disintegrated, liberating feldspar and quartz crystals into the surrounding host. These liberated crystals cause textural variations, but can be identified on the basis of shape (amoeboid or skeletal) and/or size (megacrysts). Textural and lithofacies characteristics are consistent with the interpretation that these units are lavas; the strongly elongate distribution and wide extent of the Eucarro Rhyolite and Pondanna Dacite Member could indicate that vents were aligned along an extensive east-west-trending fissure system. Stratigraphic nomenclature has been revised to better reflect the presence of the three emplacement units. The oldest unit, the Eucarro Rhyolite, is dominated by plagioclase-phyric rhyolite that locally includes granitoid clasts and megacrysts. Along the northern margin, the rhyolite is amygdaloidal and has mingled with a quartz-rich rhyolite (Paney Rhyolite Member). The

Pumiceous peperite is associated with a rhyolitic sill that intruded wet, unconsolidated, submarine stratified pumice breccia in the Cambrian Mount Read Volcanics, Australia. Other examples of pumiceous peperite described in this paper occur at the pumiceous base of a rhyolitic lava and the margins of a rhyolitic cryptodome complex in the Miocene Green Tuff Belt, Japan. Intervals of pumiceous peperite are thin (less than 15 m), laterally discontinuous, massive, poorly sorted and the clast-to-matrix ratio varies significantly over short distances. They are composed of feldsparphyric tube pumice clasts and domains of clastic sediment that include stratified pumice breccia, pumiceous siltstone and bioturbated mudstone. The sediment domains may be massive or may display relic depositional structures. Sediment adjacent to pumice clasts is silicified, possibly reflecting induration on contact with hot pumice. Pumiceous peperite has gradational contacts with in situ and clast-rotated pumiceous hyaloclastite and coherent pumiceous rhyolite. Gradational relationships between pumiceous peperite and coherent pumiceous rhyolite, pumice clasts with chilled margins and curviplanar surfaces, and abundant jigsaw-fit texture imply that quench fragmentation and autobrecciation were the dominant mechanisms of clast formation. The formation of pumiceous peperite is favoured by a combination of low confining pressure and delayed quenching allowing vesiculation. Pumiceous peperite may easily be misinterpreted or overlooked as it resembles other pumice-rich facies that are common in submarine volcanic successions. The correct identification of pumiceous peperite can provide evidence to constrain the timing of intrusive episodes in volcanic successions.

The Filakopi Pumice Breccia (FPB) is a very well exposed, Pliocene volcaniclastic unit on Milos, Greece, and has a minimum bulk volume of 1 km3. It consists of three main units: (A) basal lithic breccia (4– 8 m) mainly composed of angular to subangular, andesitic and dacitic clasts up to 2.6 m in diameter; (B) very thickly bedded, poorly sorted pumice breccia (16–17 m); and (C) very thick, reversely graded, grain-supported, coarse pumice breccia (6.5–20 m), at the top. The depositional setting is well constrained as shallow marine (up to a few hundred metres) by overlying fossiliferous and bioturbated mudstone. This large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because: (1) pumice clasts are the dominant component; (2) the coarse pumice clasts (>64 mm) have complete quenched margins; (3) very large (>1 m) pumice clasts are common; (4) overall, the formation shows good hydraulic sorting; and (5) a significant volume of ash was deposited together with the coarsest pyroclasts. The bed forms in units A and B suggest deposition from lithic-rich and pumiceous, respectively, submarine gravity currents. In unit C, the coarse (up to 6.5 m) pumice clasts are set in matrix that grades upwards from diffusely stratified, fine (1–2 cm) pumice clasts at the base to laminated shard rich mud at the top. The coarse pumice clasts in unit C were settled from suspension and the framework was progressively infilled by fine pumice clasts from waning traction currents and then by watersettled ash. The FPB displays important features of the products of submarine explosive eruptions that result from the ambient fluid being seawater, rather than volcanic gas or air. In particular, submarine pyroclastic deposits are characterised by the presence of very coarse juvenile pumice clasts, pumice clasts with complete quenched rims, and good hydraulic sorting.

The Efate Pumice Formation (EPF) is the record of a major explosive eruption that occurred in the Vanuatu arc, southwestern Pacific, at about 1 Ma. The EPF is the oldest stratigraphic unit of the Efate Island Group and consists of a succession of non-welded, trachydacitic pumice breccia and shard-rich sand and silt beds with a minimum thickness of ~500 m and a minimum bulk volume of approximately 85 km3. The lower part (Efate Pumice Breccias) of the EPF comprises very thick beds composed almost exclusively of glassy, trachydacitic, pumice fragments with ragged terminations. In contrast, the upper part (Rentabau Tuffs) consists of up to 70 m of well-bedded and well-sorted shard-rich sand and silt. The clast population of this upper part comprises >95 % glassy or formerly glassy shards, but fossil foraminifera are a ubiquitous and important non-volcanic component. Some glass shards have blocky, equant shapes and arcuate fracture surfaces, features typically associated with the influence of external water during fragmentation, but most are cuspate and platy bubble-wall shards. Pyroclast morphologies indicate that the Efate Pumice Breccias were largely generated by magmatic-volatile-driven (dry), explosive fragmentation processes, and lithofacies characteristics indicate deposition in below-storm-wave-base environments, from eruption-sourced, water-supported density currents of waterlogged pumice. The Rentabau Tuffs are interpreted to represent a change to hydromagmatic activity in response to waning discharge that allowed ingress of water (presumably seawater) to the vent(s).

The Upper Pliocene Kalogeros cryptodome is exposed on the northeastern part of Milos, Greece. The dacite cryptodome is 800-1300 m across and at least 120 m high. It is inferred to have intruded wet, unconsolidated pumiceous sediments in a shallow marine environment. The Kalogeros cryptodome includes five facies. The coherent dacite facies (80 vol%) consists of massive, non-vesicular dacite and is characterised by radial columnar joints 20-250 cm across. The banded dacite facies (15 vol%) encircles the coherent core and is up to 40 m thick. It comprises alternating bands (0.5-4 m thick) of pale grey and black dacite. The fractured dacite facies (less than 1 vol%) forms an irregular zone (1-3 m thick) at the outer margin of the cryptodome. The outermost massive dacite breccia facies ( less than 2 vol%) consists of blocky to polyhedral dacite clasts (1-40 cm in diameter) and is characterised by domains of jigsawfit and clast-rotated breccia. The stratified dacite breccia (2vol%) is clast-to-matrix supported, monomictic, poorly sorted and composed of dacite clasts up to several metres in diameter. The facies association collectively records endogenous growth of a cryptodome that involved a continuous magma supply during a single intrusive phase and simple expansion (inflation). During emplacement, the margins of the Kalogeros cryptodome were quench fragmented, forming an outer domain of intrusive hyaloclastite and intensely fractured dacite. The near-solid outer carapace insulated the hotter, less viscous interior. Laminar shear accompanied inflation, generating large-scale flow banding around the outer part of the core. Once stagnant, concentric isotherms were established within the cryptodome and controlled the orientation of columnar joints. Cryptodomes are characterised by a well-developed internal concentric distribution of distinctive textural domains, modest autoclastic breccia, and the absence of redeposited autoclastic facies.

The study of peperite is important for understanding magma-water interaction and explosive hydrovolcanic hazards. This paper reviews the processes and products of peperite genesis. Peperite is common in arc-related and other volcano-sedimentary sequences, where it can be voluminous and dispersed widely from the parent intrusions. It also occurs in phreatomagmatic vent-filling deposits and along contacts between sediment and intrusions, lavas and hot volcaniclastic deposits in many environments. Peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal, but other shapes occur and mixtures of different clast shapes are also found. Magma is dominantly fragmented by quenching, hydromagmatic explosions, magma-sediment density contrasts, and mechanical stress as a consequence of inflation or movement of magma or lava. Magma fragmentation by fluid-fluid shearing and surface tension effects is probably also important in fluidal peperite. Fluidisation of host sediment, hydromagmatic explosions, forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed. Factors which could influence fragmentation and mingling processes include magma, host sediment and peperite rheologies, magma injection velocity, volatile content of magma, total volumes of magma and sediment involved, total volume of pore-water heated, presence or absence of shock waves, confining pressure and the nature of local and regional stress fields. Sediment rheology may be affected by dewatering, compaction, cementation, vesiculation, fracturing, fragmentation, fluidisation, liquefaction, shear liquification and melting during magma intrusion and peperite formation. The presence of peperite intraclasts within peperite and single juvenile clasts with both sub-planar and fluidal margins imply that peperite formation can be a multi-stage process that va

The climax of the Kos Plateau Tuff (KPT) eruption (eastern Aegean, Greece) generated a highly energetic, coarse-grained, lithic-rich, pyroclastic flow. In most places on Kos, the deposit from this event is an ignimbrite (ignimbrite El) that comprises a basal, coarsegrained, lithic breccia and overlying pumiceous part, above a planar, strongly erosional lower contact. However, along the northern coast of central Kos, “normal” ignimbrite El overlies a hummocky, 6-m-thick layer of chaotic breccia comprising mingled-to-pervasively mixed ignimbrite El and unconsolidated sediment. The surface morphology of the chaotic breccia and its internal texture resemble those of a debris-avalanche deposit, but the breccia is neither proximal nor downcurrent of steep topography. The lower part of the chaotic breccia comprises distinct domains of unconsolidated sediment or lower KPT units that are deformed and/or mingled with pumiceous ignimbrite. The upper part is dominated by a matrix of mingled-to-pervasively mixed ignimbrite and sediment that contains sediment domains as large as 2–10 m in diameter. Such large intact allochthonous domains are best preserved at the top of the chaotic breccia and form the hummocks. The chaotic breccia formed synchronously with the passage of a highly energetic pyroclastic flow where it traversed wet, unconsolidated sediment. Shear-induced liquification, together with possible ground shaking associated with the eruption, probably caused failure. Part of the unconsolidated substrate and basal part of ignimbrite El were dislodged and resedimented a short distance (tens to hundreds of metres)downcurrent. The lower part records deformation and disintegration of the substrate induced by the overriding, shearing flow. Mingling and deformation of the poorly consolidated material occurred as a result of within-flow lateral shear. Attenuated worm burrows within the sediment domains, and pinch-and-swell and flame structures within the mingled domains, preserve

The Ural Volcanics are a early Devonian, submarine, felsic lava-sill complex, exposed in the western central Lachlan Orogen, New South Wales. The Ural Volcanics and underlying Upper Silurian, deepwater, basin-fill sedimentary rocks make up the Rast Group. The Ural Range study area, centrally located in the Cargelligo 1:100 000 map sheet area, was mapped at 1:10 000 scale. Seventeen principal volcanic facies were identified in the study area, dominated by felsic coherent facies (rhyolite and dacite) and associated monomictic breccia and siltstone-matrix monomictic breccia facies. Subordinate volcaniclastic facies include the pumice-rich breccia facies association, rhyolite - dacite -siltstone breccia facies and fiamme-siltstone breccia facies. The sedimentary facies association includes mixed-provenance and non-volcanic sandstone to conglomerate, black mudstone, micaceous quartz sandstone and foliated mudstone. The succession was derived from at least two intrabasinal volcanic centres. One, in the north, was largely effusive and intrusive, building a lava - sill complex. Another, in the south, was effusive, intrusive and explosive, generating lavas and moderate- volume (*3 km3) pyroclastic facies. The presence of turbidites, marine fossils, very thick massive to graded volcaniclastic units and black mudstone, and the lack of large-scale cross-beds and erosional scours, provide evidence for deposition in a submarine environment below storm wave-base. The Ural Volcanics have potential for seafloor or sub-seafloor replacement massive sulfide deposits, although no massive sulfide prospects or related altered zones have yet been defined. Sparse, disseminated sulfides occur in sericite-altered, steeply dipping shear zones.

A distinctive monomictic breccia, composed of fluidal and blocky basaltic andesite clasts, occurs in a Cambro-Ordovician submarine volcanic succession in northern Queensland, Australia. Associated with this ftuvial-clast buccia facies are coherent facies and coarse and fine breccia facies of the same composition. The ftuidal-clast breccia facies is internally massive and >250 m thick, varying only in the ratio of fluidal clasts to blocky clasts. Fluidal clasts range in size from 2 cm to 170 cm, and have moderately to highly vesicular cores and thick (up to 1 cm), non-vesicular, formerly glassy rims. Blocky clasts are highly vesicular to non-vesicular, <2 cm, angular, dominantly equant or splintery in shape and identical in composition to the ftuidal clasts. The ftuidal clasts strongly resemble subaerial volcanic bombs and are interpreted to be the products of submarine fire fountaining of relatively low-viscosity lava. The blocky clasts were mainly derived from disintegration of the fluidal clasts, by means of quench fragmentation. Coherent basaltic andesite intercalated with the ftuidal-clast breccia represents co-genetic lavas, dykes and irregular shallow intrusions. The coarse and fine breccia facies is very thickly bedded, monomictic (basaltic andesite), poorly sorted and clast supported. This facies is interpreted to have been generated by periodic gravitational collapse of unstable accumulations of the fluidal-clast breccia facies. Subaqueous fire-fountain breccias are distinguished from subaerial fire-fountain breccias by thick glassy margins on ftuidal clasts, the lack of welding and agglutination, and the distinctive association of highly vesicular, f1uidal clasts with nonvesicular, angular, blocky clasts. Recognition of submarine fire-fountain breccias in volcanic successions constrains the eruption style, proximity (tens of metres) to source and environment of deposition.

The Trooper Creek Formation is a mineralised submarine volcano-sedimentary sequence in the Cambro-Ordovician Seventy Mile Range Group, Queensland. Most of the Trooper Creek Formation accumulated in a below-storm-wave-base setting. However, microbialites and fossiliferous quartz-hematite plus or minus magnetite lenses provide evidence for local shoaling to above fairweather wavebase (typically 5-15 m). The microbialites comprise biogenic (oncolites, stromatolites) and volcanogenic (pumice, shards, crystal fragments) components. Microstructural elements of the bioherms and biostromes include upwardly branching stromatolites, which suggest that photosynthetic microorganisms were important in constructing the microbialites. Because the microbialites are restricted to a thin stratigraphic interval in the Trooper Creek area, shallow-water environments are interpreted to have been spatially and temporarily restricted. The circumstances that led to local shoaling are recorded by the enclosing volcanic and sedimentary lithofacies. The microbialites are hosted by felsic syneruptive pumiceous turbidites and water-settled fall deposits generated by explosive eruptions. The microbialite host rocks overlie a thick association (less than or equal to 300 m) of andesitic lithofacies that includes four main facies: coherent andesite and associated autoclastic breccia and peperite; graded andesitic scoria breccia (scoriaceous sediment gravity-flow deposits); fluidal clast-rich andesitic breccia (water-settled fall and sediment gravity-flow deposits); and cross-stratified andesitic sandstone and breccia (traction-current deposits). The latter three facies consist of poorly vesicular blocky fragments, scoriaceous clasts (10-90%), and up to 10% fluidally shaped clasts. The fluidal clasts are interpreted as volcanic bombs. Clast shapes and textures in the andesitic volcaniclastic facies association imply that fragmentation occurred through a combination of fire fountaining and Strombolian