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Abstract. 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, coarse-grained, 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 evidence of shear in the lower part. The upper part was transported downcurrent above a zone of shear failure. Internal heterogeneities in physical properties resulted in variable strain rates causing some domains to be pervasively mixed while others remained intact. Intact large unconsolidated domains at the top were transported mostly above the zone of shearing.

At Menninnie Dam, South Australia, a drilling program has revealed a complete section through the subsurface feeder system and erupted products of a small, hydroexplosive, rhyolitic centre within the Mesoproterozoic Gawler Range Volcanics. Porphyritic rhyolite intruded near-vertical faults in the Palaeoproterozoic basement and at less than a few hundred metres depth, interacted with fault-hosted (hot?) groundwater. Hydrofracturing of the wall rock occurred in advance of and at the margins of the rhyolitic intrusions. The rhyolitic intrusions have peperitic margins and grade into discordant lithic-rich PB facies. The advancing fragmentation front intersected the palaeosurface, triggering phreatic eruptions that deposited a poorly sorted, lithic-rich explosion breccia. Rhyolite then rose to the surface through the intrusive breccias and shallow-seated magma–water interaction occurred in the conduit within <50m of the surface. As the magma discharge rate increased, “dry” explosive activity prevailed. A fall deposit, the top of which is welded, was deposited close to the vent, and in more distal locations (>800m from the inferred source), the products include muddy sandstone and pumice breccia. At the end of the eruption, rhyolitic lava was extruded in the form of a small dome. The presence of contemporaneous Pb–Zn–Ag mineralisation in the wall rocks suggests that an active hydrothermal system may have been involved in the formation of the Menninnie Dam hydroexplosive volcanic centre.

Summary: ¶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 (72–76.4 wt %) and higher Al2O3 (13.2–15.6 wt%) and Na2O (2.5–4.2 wt%) 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 lithofaci es (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 phenocryst s 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.

Abstract:  Lithic megablocks ranging from <1 to 50 m in diameter occur in the Yardea Dacite, a widespread (12,000 km2), thick (>200 m) felsic volcanic unit in the Mesoproterozoic Gawler Range Volcanic Province (GRV) of South Australia. Throughout its vast extent, the Yardea Dacite shows typical lava-like features, in that it is massive, columnar jointed and evenly porphyritic with 30–40% crystals in a spherulitic and granophyric groundmass. In addition, flow banding is present at many locations. The megablocks are abundant at two sites 50 km apart, but isolated megablocks and smaller (<6 cm) lithic clasts are also scattered throughout the unit. At both sites the megablocks are matrix supported, non-graded, randomly oriented and show no evidence of being confined to a particular stratigraphic level in the dacite. The most abundant and largest megablocks are granitoids derived from older basement and from early-crystallised plutons of the Hiltaba Suite, which is broadly coeval and comagmatic with the GRV. The granitoid megablocks have been partially melted, most likely prior to eruption when resident in the thermal aureole of the Yardea Dacite magma chamber. The lithic megablock occurrences are unlike coarse pyroclastic breccias but are similar in distribution and abundance to xenoliths in lavas, consistent with the lava-like character of the host dacite. Using reasonable estimates of megablock density, magma density and magma viscosity, we show that the rise rate of the dacitic magma exceeded the settling velocity of the megablocks, implying that they could have been entrained and erupted effusively. All but the largest and least-melted megablocks would have remained suspended or else settled very slowly in the dacitic lava during outflow. The rapid rate of magma withdrawal required to produce such an extensive felsic sheet could have also triggered disintegration of the thermally stressed wallrock surrounding the magma chamber, dislodging megablocks that were later entrained and effusively erupted.

A case of extrahepatic biliary obstruction is presented in a patient with a previously unrecognized condition of the bile ducts. Five other cases with similar histological features in the bile ducts are also presented. The possible relationship between this condition and other causes of biliary obstruction is discussed and its characteristic features are described. The problems of diagnosis and management are discussed. Because of clinical, radiological and pathological similarities to cholecystitis glandularis proliferans it is proposed that the condition be called proliferative cholangitis (cholangitis glandularis proliferans).

SummaryRegionally mappable, silicic, outflow ignimbrite sheets are interbedded with fluvial volcanogenic conglomerates and sandstones of the Late Carboniferous Currabubula Formation of north-eastern N.S.W. Four of the most widespread of these ignimbrites are described and defined as members. The oldest member is comprised of many thin, originally non-welded flow units. Interbedded accretionary lapilli horizons may indicate phreatomagmatic activity at vent during the eruption in addition to local rain-flushing of co-ignimbrite ash clouds. Of the three other members, two are multiple flow-unit sheets, 160?180 m in aggregate thickness. Substantial portions of these sheets were originally welded. The remaining member is a simple welded ignimbrite characterized by abundant spherulites and lithophysae. Irregular pre-eruption topography and contemporaneous erosion were responsible for thickness variations of the ignimbrite sheets. Some palaeovalleys, now delineated by the ignimbrites, persisted in spite of repeated pyroclastic influxes. Relic pumice, shards and crystal fragments are ubiquitous components of the sedimentary facies of the Currabubula Formation, and were probably derived from originally poorly consolidated pyroclastic deposits such as airfall ash layers and non-welded ignimbrites. No surface trace of the sources of these ignimbrites exists. However, internal facies, thickness variations and volumes of the ignimbrites indicate that they periodically emanated from a multiple-caldera terrain which was continuously active during the Late Carboniferous, and located several kilometres to the west of present exposures.

Isolated outcrops of coarse- and medium-grained, quartz-feldspar porphyry occur for some 60 km from Nobles Nob to near Warrego in the Early Proterozoic Tennant Creek Block of the central Northern Territory. The outcrops appear to be part of an approximately conformable sheet of variable thickness (several tens to a few hundred metres), enclosed by sedimentary rocks of the Warramunga Group. The porphyry is characterized by euhedral, complete, evenly distributed crystals up to 2 cm across, in a microcrystalline groundmass. In some samples the groundmass shows relict perlitic cracks and was formerly coherent glass. In detail, upper and lower contacts of the porphyry sheet are highly irregular: porphyry contains wisps, blocks and large rafts of sandstone, and sandstone encloses single euhedral crystals and blebs, tongues and lobes of porphyry. Clasts of each rock type commonly have fluidal shapes. Sedimentary rocks at both the upper and the lower contacts are indurated and silicified. Close to the contacts, bedding is not easily identified, or else is disturbed. The quartz-feldspar porphyry is interpreted to have cooled and solidified from phenocryst-rich magma that intruded approximately parallel to bedding in the enclosing sedimentary sequence. The peperite margins of the sill suggest that the porphyritic magma invaded relatively weak, poorly consolidated, wet sediments rather than solid sedimentary rock. Rapid expansion and movement of heated pore fluid would have temporarily disrupted particle packing in the sediments at the contacts, and allowed intricate penetration of magma accompanied by quenching and fragmentation. In addition to relatively short-term and local effects on the pore fluid chemical and physical properties, the intrusion was probably responsible for premature and permanent dewatering of the adjacent sediments. The sill together with its bordering zone of peperite and indurated sedimentary rocks may have constituted a significant physical barrier to any subsequent fluid transport in the enclosing sedimentary sequence.

AbstractThe Coombadjha Volcanic Complex is the remnant of a Late Permian cauldron. It is part of an extensive sequence of silicic calc-alkaline volcanics that covers the southeastern portion of the New England Orogen in NSW. The Complex is elliptical, measuring 15 ? 24 km, and is outlined by a ring pluton and an arcuate fault. Bedding in the volcanic units of the Complex defines a structural basin, with steep inward dips at the monoclinal rim and gentle to horizontal orientations near the centre. An older group of outflow ignimbrites, lavas, breccias and volcaniclastic rocks at least 1500 m thick, is conformably overlain by more than 500 m of texturally homogeneous, crystal-rich, dacitic ignimbrite. Ignimbrites of the older group are the products of several discrete eruptions from separate vents, all of which were situated outside the Coombadjha area. Silicic lava domes with volcaniclastic aprons, and a tuff ring, mark the positions of local vents active on a small scale during intervals between the emplacement of the outflow ignimbrites. No significant subsidence occurred, nor did a caldera exist at this stage. Cauldron subsidence occurred in response to the large magnitude eruption that produced the crystal-rich ignimbrite. The central cauldron block was lowered at least 2000 m by downwarping and fault displacement, and remained largely intact. There is no evidence for resurgent doming of the cauldron after subsidence, although igneous activity continued with intrusion of an adamellite ring pluton along much of the cauldron margin. The crystal-rich ignimbrite and the ring pluton are similar in composition and may have been successive products of a common magma source that sustained this simple, single cauldron cycle.

The Hianana Volcanics consist of bedded tuff and dacitic lava that form a locally mappable unit within the extensive, Late Permian silicic volcanic sequence of northeastern New South Wales. Principal components of the bedded tuff are crystal and volcanic lithic fragments ranging from coarse ash to lapilli, accompanied by variable amounts of fine ash matrix. Well denned plane parallel thin bedding is characteristic. Sandwave bed forms, including low-angle cross-beds and wavy beds, are confined to an area of 2-3 km2 coinciding with the thickest sections (70 m) of bedded tuff. A high-aspect ratio flow of porphyritic dacitic lava overlies the bedded tuff in the same area. The setting, lithofacies, extent and geometry of the bedded tuffs of the Hianana Volcanics are comparable with modern tuff rings which are composed of the deposits from base surges generated by explosive phreatomagmatic eruptions at primary volcanic vents. Many of these have also discharged lava late in their activity. Proximal parts of the Hianana tuff ring were buried by the porphyritic lava after the phreatomagmatic eruptions had ceased. In more distal sections, the bedded tuff is less than 10 m thick and dominantly comprises fine grained, plane parallel, very thin beds and laminae; these features suggest an origin by fallout from ash clouds that accompanied the phreatomagmatic eruptions. The distal ash was covered and preserved from erosion by a layer of welded ignimbrite, the source of which is unknown.

At Rakiraki in northeastern Viti Levu, the Pliocene Ba Volcanic Group comprises gently dipping, pyroxene-phyric basaltic lavas, including pillow lava, and texturally diverse volcanic breccia interbedded with conglomerate and sandstone. Three main facies associations have been identified: (1) The primary volcanic facies association includes massive basalt (flows and sills), pillow lava and related in-situ breccia (pillow-fragment breccia, autobreccia, in-situ hyaloclastite, peperite). (2) The resedimented volcaniclastic facies association consists of bedded, monomict volcanic breccia and scoria lapilli-rich breccia. (3) The volcanogenic sedimentary facies association is composed of bedded, polymict conglomerate and breccia, together with volcanic sandstone and siltstone-mudstone facies. Pillow lava and coarse hyaloclastite breccia indicate a submarine depositional setting for most of the sequence. Thick, massive to graded beds of polymict breccia and conglomerate are interpreted as volcaniclastic mass-flow deposits emplaced below wave base. Well-rounded clasts in conglomerate were reworked during subaerial transport and/or temporary storage in shoreline or shallow water environments prior to redeposition. Red, oxidised lava and scoria clasts in bedded breccia and conglomerate also imply that the source was partly subaerial. The facies assemblage is consistent with a setting on the submerged flanks of a shoaling basaltic seamount. The coarse grade and large volume of conglomerate and breccia reflect the high supply rate of clasts, and the propensity for collapse and redeposition on steep palaeoslopes. The clast supply may have been boosted by vigorous fragmentation processes accompanying transition of lava from subaerial to submarine settings. The greater proportion of primary volcanic facies compared with resedimented volcaniclastic and volcanogenic sedimentary facies in central and northwestern exposures (near Rakiraki) indicates they are more proximal than those in the southeast (towards Viti Levu Bay). The proximal area coincides with one of two zones where NW-SE-trending mafic dykes are especially abundant, and it is close to several, small, dome-like intrusions of intermediate and felsic igneous rocks. The original surface morphology of the volcano is no longer preserved, though the partial fan of bedding dip azimuths in the south and east and the wide diameter (exceeding 20 km) are consistent with a broad shield.

Deposition of Late Carboniferous and Early Permian continental conglomeratic strata along the western edge of the New England Orogen was continuously accompanied by silicic volcanism. Disconformable relationships exist locally between the Early Permian Glossopteris-bearing rocks and the Late Carboniferous Rhacopteris-bearing rocks but have negligible stratigraphic significance since erosional surfaces are common within the older sequence and probably also occur in the younger sequence. The western volcanic terrain which had supplied ignimbrites, airfall deposits and volcanogenic detritus eastward during the Late Carboniferous still had some active centres in the Early Permian, though eruptions waned in scale and changed in style to include effusion of lavas. Proximal Early Permian volcanics comprised of lithic-rich ignimbrites and lavas at Boggabri are the remnants of one such centre. After eruptions had ceased, denudation of this and other remaining centres contributed volcanogenic detritus, including 'flint clay' clasts, to coal measure sediments (Greta equivalent) accumulating in the flanking low-lying areas of the incipient Gunnedah Basin. There is no evidence in support of easterly provenance for these Early Permian coal measures nor for movement on the Mooki Thrust at this time.

The Tyndall Group is a Cambrian, dominantly submarine, volcano-sedimentary succession that occurs in the upper part of the Mt Read Volcanics, western Tasmania. The internal stratigraphy of the Tyndall Group is relatively complex, comprising a wide variety of lithofacies including crystal- and lithic-rich volcaniclastic breccia, conglomerate and sandstone, welded ignimbrite, rhyolite, laminated mudstone and carbonate. Problems with the previously defined stratigraphic nomenclature have prompted development of a new stratigraphic scheme, based on detailed facies analysis of major Tyndall Group exposures in the central Mt Read Volcanics. The Tyndall Group is divided into two formations, the Comstock Formation and the overlying Zig Zag Hill Formation. The Comstock Formation is subdivided into the Lynchford Member and the overlying Mt Julia Member. This stratigraphic scheme is based on regional lithological variations, which largely reflect different provenance characteristics. In both formations, volcaniclastic lithofacies deposited by low- to high-density turbidity currents are abundant, and imply that the depositional setting was subaqueous and below storm wave base. However, in situ welded ignimbrite and a fossiliferous limestone unit suggest that part of the group was deposited in proximity to subaerial environments. Many of the volcaniclastic units in the Comstock Formation, in particular the crystal-rich volcaniclastic facies, were ultimately sourced from subaerial or shallow-marine explosive volcanic eruptions producing pyroclastic flows which fed into the sea. The pyroclastic flows interacted with water, transforming into water-supported mass flows. Allochthonous blocks and in situ occurrences of welded ignimbrite in the Comstock Formation represent relicts of primary deposits from pyroclastic flows that did not interact with water. Rhyolite lava dome complexes also built up on the sea floor at this stage. In contrast to the Comstock Formation, which is dominated by syn-eruptive volcaniclastic facies, the Zig Zag Hill Formation records post-eruptive erosion and reworking of the subaerial to shallow-marine source areas that resulted in the influx of well-rounded, polymict, epiclastic debris to the marine basin.

THE pharyngeal pituitary gland is a small embryological remnant constantly present in man in the submucosa of the nasopharynx1,2. In some patients it is formed of squamous or undifferentiated epithelial cells (“inactivated” type)3, in others there is adenohypophyseal differentiation (“activated” type)3and in a few the two patterns are mixed4. The “activated” type is usually described as having abundant chromophobic cells, occasional acidophil cells and very few basophil cells1,3, but McGrath4has reported that basophil cells can be the most conspicuous cells in some “activated” glands. It has been suggested that the pharyngeal pituitary gland is capable of playing a compensatory part in pituitary function3,5, since adenohypophyseal differentiation is said to be more prominent in the pharyngeal pituitary gland after sellar pituitary gland ablation3,5,6, but there is no evidence of hyperplasia of these pharyngeal pituitary glands7. We have now investigated the localization of human growth hormone (HGH) antigen in the pharyngeal pituitary gland with the indirect immunofluorescence (IF) technique.