Stratigraphy, facies architecture and tectonic implications of the Upper Devonian to Lower Carboniferous Campwyn Volcanics of the northern New England Fold Belt

Upper Devonian to Lower Carboniferous strata of the Campwyn Volcanics of east central Queensland preserve a substantial sequence of first-cycle volcaniclastic sedimentary and coeval volcanic rocks that record prolonged volcanic activity along the northern New England Fold Belt. The style and scale of volcanism varied with time, producing an Upper Devonian sequence of mafic volcano-sedimentary rocks overlain by a rhyolitic ignimbrite-dominated sequence that passes upward into a Lower Carboniferous limestone-bearing sedimentary sequence. We define two facies associations for the Campwyn Volcanics. A lower facies association is dominated by mafic volcanic-derived sedimentary breccias with subordinate primary mafic volcanic rocks comprising predominantly hyaloclastite and peperite. Sedimentary breccias record episodic and high energy, subaqueous depositional events with clastic material sourced from a mafic lava-dominated terrain. Some breccias contain a high proportion of attenuated dense, glassy mafic juvenile clasts, suggesting a syn-eruptive origin. The lower facies association coarsens upwards from a lithic sand-dominated sequence through a thick interval of pebble- to boulder-grade polymict volcaniclastic breccias, culminating in facies that demonstrate subaerial exposure. The silicic upper facies association marks a significant change in eruptive style, magma composition and the nature of eruptive sources, as well as the widespread development of subaerial depositional conditions. Crystal-rich, high-grade, low- to high-silica rhyolite ignimbrites dominate the base of this facies association. Biostratigraphic age controls indicate that the ignimbrite-bearing sequences are Famennian to lower-mid Tournaisian in age. The ignimbrites represent extra-caldera facies with individual units up to 40 m thick and mostly lacking coarse lithic breccias. Thick deposits of pyroclastic material interbedded with fine-grained siliceous sandstone and mudstone (locally radiolarian-bearing) were deposited from pyroclastic flows that crossed palaeoshorelines or represent syn-eruptive, resedimented pyroclastic material. Some block-bearing lithic-pumice-crystal breccias may also reflect more proximal subaqueous silicic explosive eruptions. Crystal-lithic sandstones interbedded with, and overlying the ignimbrites, contain abundant detrital volcanic quartz and feldspar derived from the pyroclastic deposits. Limestone is common in the upper part of the upper facies association, and several beds are oolitic (cf. Rockhampton Group of the Yarrol terrane). Overall, the upper facies association fines upward and is transgressive, recording a return to shallow-marine conditions. Palaeocurrent data from all stratigraphic levels in the Campwyn Volcanics indicate that the regional sediment-dispersal direction was to the northwest, and opposed to the generally accepted notion of easterly sediment dispersal from a volcanic arc source. The silicic upper facies association correlates in age and lithology to Early Carboniferous silicic volcanism in the Drummond (Cycle 1) and Burdekin Basins, Connors Arch, and in the Yarrol terranes of eastern Queensland. The widespread development of silicic volcanism in the Early Carboniferous indicates that silicic (rift-related) magmatism was not restricted to the Drummond Basin, but was part of a more substantial silicic igneous province.

Yarrol terrane of the northern New England Fold Belt: forearc or backarc?

The Upper Devonian to Lower Carboniferous volcanosedimentary rocks of the Yarrol terrane of the northern New England Fold Belt have previously been ascribed to a forearc basin setting. New data presented here, however, suggest that the Yarrol terrane developed as a backarc basin during the Middle to early Late Devonian. Based on field studies, we recognise four regionally applicable strati graphic units: (i) a basal, ?Middle to Upper Devonian submarine mafic volcanic suite (Monal volcanic facies association); (ii) the lower Frasnian Lochenbar beds that locally unconformably overlie the Monal volcanic facies association: (iii) the Three Moon Conglomerate (Upper Devonian - Lower Carboniferous): and (iv) the Lower Carboniferous Rockhampton Group characterised by the presence of oolitic limestone. Stratigraphic and compositional differences suggest the Monal volcanic facies association post-dates Middle Devonian silicic-dominated magmatism that was coeval with gold-copper mineralisation at Mt Morgan. The Lochenbar beds, Three Moon Conglomerate and Rockhampton Group represent a near-continuous sedimentary record of volcanism that changed in composition and style from mafic effusive (Late Devonian) to silicic explosive volcanism (Early Carboniferous). Palaeocurrent data from the Three Moon Conglomerate and Rockhampton Group indicate dispersal of sediment to the west and northwest, and are inconsistent with derivation from a volcanic-are source situated to the west (Connors-Auburn Arch). Geochemical data show that the Monal volcanic facies association ranges from tholeiitic subalkaline basalts to calc-alkaline basaltic andesite. Trace and rare-earth element abundances are distinctly MORE-like (e.g, light rare earth element depletion), with only moderate enrichment of the large-ion lithophile elements in some units, and negative Nb anomalies, suggesting a subduction-related signature. Basalts of the Monal volcanic facies association are best described as transitional between calc-alkali basalts and N-MORB. The elevated high field strength element contents (e.g. Zr, Y, Ti) are higher than modern island-are basalts, but comparable to basalts that floor modern backarc basins. This geochemical study, coupled with stratigraphic relationships, suggest that the eruption of backarc basin basalts followed widespread Middle Devonian, extension-related silicic magmatism (e.g. Retreat Batholith, Mt Morgan), and floored the Yarrol terrane. The Monal volcanic facies association thus shows similarities in its tectonic environment to the Lower Permian successions (e.g. Rookwood Volcanics) of the northern New England Fold Belt. These mafic volcanic sequences are interpreted to record two backarc basin-forming periods (Middle - Late Devonian and Late Carboniferous - Early Permian) during the Late Palaeozoic history of the New England Orogen. Silicic-dominated explosive volcanism, occurring extensively across the northern New England Fold Belt in the Early Carboniferous (Varrol terrane, Campwyn Volcanics, Drummond and Burdekin Basins), reflects another period of crustal melting and extension, most likely related to the opening of the Drummond Basin.

Timing and chemistry of fluid-flow events in the Lawn Hill Platform, Northern Australia

Mudrocks and carbonates of the Isa superbasin in the Lawn Hill platform in northern Australia host major base metal sulfide mineralization, including the giant strata-bound Century Zn-Pb deposit. Mineral paragenesis, stable isotope, and K-Ar dating studies demonstrate that long-lived structures such as the Termite Range fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic in response to major tectonic events. Illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures (up to 300 degrees C) than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values provides further information oil the thermal regime in the basin and shows that clay formation was controlled not only by temperature increase with depth but also by high water/rock ratios along relatively permeable zones. K-Ar dating of illite, in combination with other data, may indicate three major thermal events in the central and northern Lawn Hill platform Lit 1500, 1440 to 1400, and 1250 to 1150 Ma. This study did not detect the earlier Century base metal mineralizing event at 1575 Ma. 1500 Ma ages are recorded only in the south and correspond to the age of the Late Isan orogeny and deposition of the Lower Roper superbasin. They may reflect exhumation of a provenance region. The 1440 to 1300 Ma ages are related to fault reactivation and a thermal pulse at similar to 1440 to 1400 Ma possibly accompanied by fluid flow, with subsequent enhanced cooling possibly due to thermal relaxation or further crustal exhumation. The youngest thermal and/or fluid-flow event at 1250 to 1150 Ma is recorded mainly to the cast of the Tern-lite Range fault and may be related to the assembly of the Rodinian supercontinent. Fluids in equilibrium with illite that formed over a range of temperatures, at different times in different parts of the platform. have relatively uniform oxygen isotope compositions and more variable hydrogen isotope compositions (delta O-18 = 3.5-9.7 parts per thousand V-SMOW; delta D = -94 to -36 parts per thousand V-SMOW). The extent of the 180 enrichment and the variably depleted hydrogen isotope compositions suggest the illite interacted with deep-basin hypersaline brines that were composed of evaporated seawater and/or highly evolved meteoric water. Siderite is the most abundant iron-rich gangue phase in the Century Zn-Pb deposit, which is surrounded by all extensive ferroan carbonate alteration halo. Modeling suggests that the ore siderite formed at temperatures of 120 degrees to 150 degrees C, whereas siderite and ankerite in the alteration halo formed at temperatures of 150 degrees to 180 degrees C. The calculated isotopic compositions of the fluids are consistent with O-18-rich basinal brines and mixed inorganic and organic carbon Sources (6180 = 3-10 parts per thousand V-SMOW, delta C-13 = -7 to -3 parts per thousand V-PDB). in the northeast Lawn Hill platform carbonate-rich rocks preserve marine to early diagenetic carbon and oxygen isotope compositions, whereas ferroan carbonate cements in siltstones and shales in the Desert Creek borehole are O-18 and C-13 depleted relative to the sedimentary carbonates. The good agreement between temperature estimates from illite crystallinity and organic reflectance (160 degrees-270 degrees C) and inverse correlation with carbonate delta O-18 values indicates that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with the 1250 to 1150 Ma fluids. The calculated isotopic compositions of the fluid are consistent with evolved basinal brine (delta O-18 = 5.1-9.4 parts per thousand V-SMOW; delta C-13 = -13.2 to -3.7 parts per thousand V-PDB) that contained a variable organic carbon component from the oxidation and/or hydrolysis of organic matter in the host sequence. The occurrence of extensive O-18- and C-13-depleted ankerite and siderite alteration in Desert Creek is related to the high temperature of the 1250 to 1150 Ma fluid-flow event in the northeast Lawn Hill platform, in contrast to the lower temperature fluids associated with the earlier Century Zn-Pb deposit in the central Lawn Hill platform.

Fluid-mobile trace element constraints on the role of slab melting and implications for Archaean crustal growth models

We use published and new trace element data to identify element ratios which discriminate between arc magmas from the supra-subduction zone mantle wedge and those formed by direct melting of subducted crust (i.e. adakites). The clearest distinction is obtained with those element ratios which are strongly fractionated during refertilisation of the depleted mantle wedge, ultimately reflecting slab dehydration. Hence, adakites have significantly lower Pb/Nd and B/Be but higher Nb/Ta than typical arc magmas and continental crust as a whole. Although Li and Be are also overenriched in continental crust, behaviour of Li/Yb and Be/Nd is more complex and these ratios do not provide unique signatures of slab melting. Archaean tonalite-trondhjemite-granodiorites (TTGs) strongly resemble ordinary mantle wedge-derived arc magmas in terms of fluid-mobile trace element content, implying that they-did not form by slab melting but that they originated from mantle which was hydrated and enriched in elements lost from slabs during prograde dehydration. We suggest that Archaean TTGs formed by extensive fractional crystallisation from a mafic precursor. It is widely claimed that the time between the creation and subduction of oceanic lithosphere was significantly shorter in the Archaean (i.e. 20 Ma) than it is today. This difference was seen as an attractive explanation for the presumed preponderance of adakitic magmas during the first half of Earth's history. However, when we consider the effects of a higher potential mantle temperature on the thickness of oceanic crust, it follows that the mean age of oceanic lithosphere has remained virtually constant. Formation of adakites has therefore always depended on local plate geometry and not on potential mantle temperature.

Upper Devonian biostratigraphy of the Iberian Pyrite Belt, southwest Spain Part One: Miospores

The Iberian Pyrite Belt (IPB), which forms part of the Variscan orogenic massif, is renowned for the magnitude and extent of its massive sulfide mineralization. The stratigraphic record of the IPB consists of Upper Palaeozoic sedimentary and igneous rocks. In ascending order, these comprise the thick Phyllite-Quartzite Group attributed to the Middle and Upper Devonian and characterized by shales and quartzites with conglomeratic and carbonate intercalations towards the top; the appreciably thinner Volcano-Sedimentary Complex, a heterogeneous uppermost Devonian-Mississippian unit embodying diverse volcanic, subvolcanic, and sedimentary rocks that host the massive sulfide deposits; and the shaly and sandy, turbiditic Culm Group (Carboniferous). This entire succession was folded and faulted during the Asturian phase of the Variscan Orogeny that gave rise to a thin-skinned type structure. The present study constitutes a detailed blostratigraphic investigation of palynologically productive samples representative of the Phyllite-Quartzite Group and the basal (anoxic) portion of the Volcano-Sedimentary Complex. These were collected from surface and mine exposures variously located in the Spanish part of the IPB; out of 282 samples processed, 117 proved to be productive palynologically. The aim of this project is to provide comprehensive palynostratigraphic data applicable to precise dating and correlation of the IPB's stratigraphic succession (i.e., of the two sampled lithostratigraphic units), which has hitherto been investigated biostratigraphically on a relatively localized basis. The results are incorporated in two successive parts. The first of these, i. e., the present paper, focuses on the systematic analysis of the terrestrial (miospore) component of the palynological assemblages. The second part, devoted to the marine, organic-walled microphytoplankton (acritarchs and prasinophytes), will evaluate the stratigraphic significance of the IPB palynofloras and their application to elucidating the geological history of the region. In the systematic-descriptive section, which occupies the bulk of this paper, 55 species of trilete miospores are described and are allocated among 34 genera, two of which (Cristicavatispora and Epigruspora) are newly instituted herein. The majority of the species are either positively identifiable or closely affiliable with previously named species. The nine newly established species are as follows: Camptozonotriletes confertus, Indotriradites diversispinosus, Cristicavatispora dispersa (type species), Epigruspora regularis (type species), Ancyrospora? implicata, Endosporites tuberosus, Rugospora explicata, Spelaeotriletes plicatus, and Teichertospora iberica.

Eastern edge, General Purpose North 3, University of Queensland, St Lucia

As seen from informal courtyard; Duhig Tower beyond.

Protein fold recognition without Boltzmann statistics or explicit physical basis

We present a fast method for finding optimal parameters for a low-resolution (threading) force field intended to distinguish correct from incorrect folds for a given protein sequence. In contrast to other methods, the parameterization uses information from >10(7) misfolded structures as well as a set of native sequence-structure pairs. In addition to testing the resulting force field's performance on the protein sequence threading problem, results are shown that characterize the number of parameters necessary for effective structure recognition.

Outbreaks of pink wax scale, Ceroplastes rubens Maskell (Hemiptera : Coccidae), on umbrella trees in south-eastern Queensland: Patterns of parasitisation

The degree and distribution of parasitisation in relation to densities of pink wax scale, Ceroplastes rubens Maskell, on umbrella trees, Schefflera actinophylla (Endl.), in south-eastern Queensland were investigated to determine whether scale outbreaks could be attributed, in part, to low levels of parasitisation. Rates of parasitisation were independent of or inversely dependent on host density, and highly variable, especially at low densities. The absence of density dependent parasitisation may occur as a result of: (i) non-aggregation by parasitoids; (ii) aggregation by parasitoids where parasitisation is limited by intrinsic or extrinsic factors; and/or (iii) high rates of hyperparasitisation.