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Tertiary volcanism (34.3 ± 1.2 Ma and 0.4 ± 0.7 Ma) in NW Turkey produced lead + zinc bearing trachyte, latite, dacite and rhyodacite tuffs, and agglomerates, as well as basaltic andesite, andesite, dacite, and rhyolite lavas. The primary objective of this study is to develop quantitative models for the evolution of magmas that produced these rocks and for the dissolution, transport, and deposition of disseminated ore as sphalerite and galena vein deposits. Our petrogenetic modelling using the MELTS algorithm (Ghiorso, M.S., and Sack, R.O., 1995, Chemical mass transfer in magmatic processes IV: a revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures: Contributions to Mineralogy and Petrology, v. 119, p. 197–212) indicates that the ore-bearing volcanic rocks reflect mixing of a basaltic andesite parental magma with a rhyolite magma. In addition, our aqueous geochemistry modelling us...

Rock samples recovered during the Australian–French AUSFAIR MD153 Survey in 2006 from the northern Lord Howe Rise and the Fairway Ridge provide new constraints on the tectonostratigraphic evolution of the region and represent significant new information from a region in which few rocks have been dated. SHRIMP U–Pb dating of zircon from rocks from the Lord Howe Rise indicates alkali volcanism in the area at 97 Ma (trachyte) and 74 Ma (latite). The older volcanic activity is probably related to the widespread Late Cretaceous magmatism along the eastern Gondwana margin, whereas the younger activity may be related to the opening of the Tasman Sea or rifting in the New Caledonia Basin. The pebbly clasts and shell fossils in some of the associated volcaniclastic rocks provide evidence for the existence of landmasses as a sediment source area in the northern Lord Howe Rise region, and the initial marine incursion into the area around Campanian time.

High-K volcanic rocks of the Stanislaus Group record magmatic events that occurred when the Sierra Nevada microplate began to calve off from the western edge of the Nevadaplano at 10–9 Ma. Despite the fact that these rocks have been studied in the Sierra Nevada for 120 years, their stratigraphy is not well known, because they were largely deposited in a complicated palaeocanyon network that drained the Nevadaplano and are preserved on high peaks in roadless areas. We present new 1:6000 scale mapping and a detailed measured section in the Bald Peak–Red Peak area of the Sonora Pass, in the upper reach of the ‘Cataract’ palaeocanyon, or palaeo-Stanislaus river. The Bald Peak–Red Peak area was proposed as the type section for the Stanislaus Group in 1953 but had not been mapped or measured in sufficient detail to demonstrate stratigraphic relations. Our work demonstrates the following stratigraphy (from base to top): (1) Table Mountain Latite (TML) trachyandesite (latite) and basaltic trachyandesite (shoshoni...

The Miocene Stanislaus Group (Stanislaus, Calaveras, Tuolomne, Alpine and Mono counties, CA), composed of intercalated latite and quartz-latite (trachyandesite and trachyte/trachydacite) lavas and ignimbrites, provides an important marker for reconstructing the elevation history and tectonic development of the Sierra Nevada and Walker Lane. We present new 40Ar/39Ar geochronology and magnetostratigraphy indicating that the Stanislaus Group was emplaced in two pulses: (1) major outpouring of latite lavas at ca. 10.4 Ma and (2) ignimbrite eruptions alternating with lesser lava flow eruptions during ca. 9.4–9.8 Ma. These two events filled the ancestral Stanislaus River drainage in the region of the present Sierra Nevada crest, whereas the ignimbrite eruptions formed the Little Walker Caldera. Our new and previous results date these topographic changes and yield improvements to the Stanislaus Group stratigraphy.

The Ordovician volcanic and intrusive rocks of the Cadia – Neville region, in the southern Molong Volcanic Belt section of the Macquarie Arc in central-western New South Wales, display a temporal progression from shoshonitic basaltic volcanism (e.g. Mt Pleasant Basalt Member) in the late Darriwilian to Gisbornian (ca 460 – 453 Ma) to small-volume dacitic medium-K calc-alkaline magmatism (e.g. Copper Hill-type dacite) in the late Eastonian to early Bolindian (ca 450 – 445 Ma) to large-volume, high-K calc-alkaline to shoshonitic, mafic to highly evolved magmatism (e.g. Nullawonga Latite Member and Cadia Intrusive Complex) at about 445 – 440 Ma. The two episodes of shoshonitic magmatism are separated by at least 15 (but up to ∼20) million years, during which time limestones, associated with regional uplift, were deposited broadly coincident with emplacement of the medium-K calc-alkaline dacitic intrusions. Despite this, the lavas and intrusions associated with both episodes of shoshonitic magmatism have stri...

Miocene volcanism of the Oglakci region (Sivrihisar, Eskisehir) in northwestern Central Anatolia, Turkey, is represented by basaltic and trachytic groups of rocks. Samples of both groups have been investigated using mineral-chemical data together with whole-rock major-, trace-element, and radiogenic Sr-Nd isotopic data. The basaltic volcanic rocks consist of mugearites and shoshonites, whereas the trachytic rocks include trachytes, latite, and rhyolite. Both groups are of alkaline character. The basaltic rocks contain plagioclase (An29-63), alkali feldspar (Or12-74), olivine, orthopyroxene (En64-67), clinopyroxene (Wo43-48), biotite (Mg#82-88), and Fe-Ti oxide phenocrysts, whereas the trachytic rocks contain plagioclase (An21-64), alkali feldspar (Or10-53), clinopyroxene (Wo41-49), amphibole (Mg#64-83), biotite (Mg#79-85), Fe-Ti oxide, titanite, apatite, and quartz phenocrysts. The measured 87Sr/86Sr ratios of basaltic samples range from 0.7045 to 0.7048, and those of trachytic samples from 0.7054 to 0.70...

The Broughton Formation, the basal part of the lower Upper Permian (ca 264–263 Ma) Gerringong Volcanics of the Kiama area of the southern Sydney Basin, comprises intercalated shoshonitic lava flows and shallow‐marine, predominantly volcaniclastic, sediments emplaced under periglacial climatic conditions at high palaeolatitude. Four lower members of the Gerringong Volcanics (the Westley Park Sandstone, Blow Hole Latite, Kiama Sandstone and Bumbo Latite Members) were examined to elucidate the lava‐flow directions and coeval palaeophysiography. Field evidence indicates that the individual flows that comprise the compound‐flow‐units of the Blow Hole and Bumbo Latites advanced toward the north‐northwest and north, respectively, from an emergent island volcano or volcanic archipelago that developed offshore of the present‐day coastline, some tens of kilometres south‐southeast of Kiama. The field evidence incorporates descriptions and interpretations of features including vesicles and amygdales, lava tubes, pill...

Upper Permian shallow marine siltstone and sandstone units of the Broughton Formation are intercalated with basaltic and basaltic andesite sheets at Kiama, New South Wales. Parts of the two sheets examined in this study display peperite texture. The lower example (Blow Hole Latite Member) can be divided into two units with peperitic contacts suggesting their intrusion into wet unconsolidated sediments of the overlying Kiama Sandstone Member. The Bumbo Latite Member overlies the Kiama Sandstone Member and has been interpreted by previous workers as a lava. Well‐developed columnar joints cut the interior of the sheets. Along contacts with sedimentary facies and peperitic dykes which penetrate the sheets, columnar joints merge into a several metre‐wide zone of blocky jointing, pseudo‐pillows and hyaloclastite. In peperitic facies, sandstone or siltstone fills joints and fractures that define pseudo‐pillows, polyhedral joint blocks and columns (closely packed fabric) or sediment matrix‐rich breccia contains f...

Late Permian (early Tatarian, 258 Ma) palaeosols exposed near Kiama and Dapto on the south coast of New South Wales can be recognised from their red colour, clayey and massive texture, and clay‐filled root traces. Harvey pedotype palaeosols are within the upper Jamberoo Sandstone Member of the Broughton Formation. Loveleigh pedotype palaeosols are within the basal Kiama Sandstone overlying columnar jointed flows of the Blow Hole Latite Member of the Broughton Formation. Both kinds of palaeosols are strongly ferruginised with little relict bedding, yet they are little weathered and have surprisingly high amounts of feldspar and pyroxene. Both also show deformation of subsurface layers comparable to the active layer of permafrosted soils. Root traces in these palaeosols are sparse and comparable to those of woody gymnosperms, not chambered like the known roots of Glossopteris. Plausible components of the taiga woodland represented by the palaeosols include Gangamopteris, cordaites, seed ferns, and equisetal...

Magmatic associations of the shoshonite-latite geochemical type are abundant in epi-Caledonian structures of Central Tien Shan. They are concentrated along long-lived abyssal faults and form a narrow, elongate zone located near a marginal intercontinental rift created during Hercynian tectonomagmatic activation synchronous with orogenic processes in the Southern Tien Shan geosynclinal zone. The rocks belong to a gabbromonzonite (syenite)-granite association, sometimes with shoshonite, latite, and potassic dacite proper. Evolution of the magmatic systems involved magmagenesis in deep-seated chambers by partial melting of metasomatized mantle, formation of sialic magmas in intermediate chambers at crustal levels, possible mixing of mantle and crustal melts, and final emplacement primarily under hypabyssal and subvolcanic conditions.

The southern part of the Sydney Basin of New South Wales is comprised mainly of Permian and Triassic marine to freshwater clastic sedimentary rocks. Within this sequence there are six latite extrusive units, several medium‐sized monzonite intrusions and a large number of small to medium‐sized basic to intermediate intrusions. Thin basaltic flows were extruded onto the Tertiary topographic surface. All of these rocks are relatively undeformed. Radiometric (K‐Ar) dating has previously been carried out on Mesozoic and Tertiary intrusions and flows of the southwestern portion of the Sydney Basin. However, relatively few Permian, and no post‐Permian, K‐Ar dates have been published for the southeastern portion of the basin. The present investigation provides nine K‐Ar dates from the latter area. Four extrusive and intrusive units have been confirmed as Permian in age (238 ± 6; 241 ± 4; 245 ± 6; and 251 ± 5 m.y.). Five post‐Permian (on stratigraphic criteria) intrusions yielded Tertiary ages (26.2 ± 3.0...

The IUGS Subcommission on the Systematics of Igneous Rocks recommends that volcanic rocks should be classified on a non‐genetic basis using the total alkali silica (TAS) diagram. This is divided into 14 fields, three of which contain two root names which are separated according to other chemical criteria, giving the following 17 root names: basalt, basaltic andesite, andesite, dacite, rhyolite, alkali rhyolite, trachybasalt, trachyandesite, trachyte, alkali trachyte, picrobasalt, basanite, tephrite, phonotephrite, tephriphonolite, phonolite and foidite. Using other simple parameters, trachybasalt may be further divided into the sub‐root names of hawaiite and potassic trachybasalt, and trachyandesite may be further divided into the sub‐root names of mugearite, shoshonite, benmoreite and latite.

Woodlark Island, the largest above‐sea portion of the Woodlark Rise, has an exposed basement of pre‐Miocene (?Cretaceous‐Eocene) low‐K tholeiitic basalt and dolerite, and minor sediments. The basement is unconformably overlain by Early Miocene limestone and volcaniclastic sediments and later Miocene high‐K volcanics and comagmatic intrusives. Pleistocene to Recent sediments partly blanket the Tertiary sequence. Basement low‐K tholeiites vary only slightly in composition and are interpreted as ocean floor or possible marginal basin material. The high‐K suite appears to be chemically similar to late Tertiary to Recent high‐K igneous rocks of mainland Papua New Guinea. It includes porphyritic hornblende‐, clinopyroxene‐, biotite‐ and magnetite‐bearing shoshonite, latite and toscanite, and intrusive equivalents that range from olivine normative to strongly quartz normative compositions (S1Q2 46% to 75%). Computer mixing models indicate that separation of the pheno‐crysts in the shoshonites, particula...