Janet Hergt

Bougainville Island represents the northwestern extension of the Solomon Islands Arc. It is broadly a NW SE trending island initially formed as a response to SW subduction of the Pacific Plate. Subduction ceased upon collision with the abnormally thickened oceanic lithosphere of the Ontong Java Plateau during the Miocene [1]. Arc reversal occurred approximately 10 Myr BP, with subsequent subduction of the Solomon Sea Plate in a NE direction along the New Britain San Cristobal Trench. Subduction in this direction continues to the present day and is responsible for ongoing volcanism on Bougainville. Most elemental covariations, involving both the pre-and post-reversal volcanic rocks, appear to reflect simple fractional crystallisation processes (e.g., MgO vs SiO2); an observation ostensibly supported by relatively uniform 87Sr/86Sr vs 143Nd/144Nd and 176Hf/177Hf compositions. Yet at any particular silica content, magmatism on Bougainville shows significant variation in K2O (i.e., by a...

The composition of altered oceanic crust (AOC) revisited T.-Y. KUO, J. WOODHEAD, J. HERGT School of Earth Sciences, University of Melbourne, Victoria 3010, AUSTRALIA (*tzuyingk@student.unimelb.edu.au) 2 School of Earth Sciences, University of Melbourne, Victoria 3010, AUSTRALIA (jdwood@unimelb.edu.au) 3 School of Earth Sciences, University of Melbourne, Victoria 3010, AUSTRALIA (jhergt@unimelb.edu.au)

The Serra Norte Carajas banded iron-formation (BIF)-hosted iron ore deposits are located in the Carajas mineral province. The deposits are hosted in the ca. 2.7 Ga Grao Para Group, a metamorphosed volcanic-sedimentary sequence where jaspilites are under- and overlain by basalts, both at greenschist facies conditions. They represent one of the largest high-grade (>60 wt % Fe) BIF iron ore deposits and resources in the world, with hypogene iron mineralization considered to be Paleoproterozoic. Four main open pits have, to date, produced about 1.2 billion metric tons (Bt) of high-grade iron ore with additional resources of 10 Bt. Ore types at the Serra Norte deposits include soft and hard ore; the latter consists of banded, massive and/or brecciated ores and is mainly localized along the contact with the surrounding hydrothermally altered basalts. Distinct hydrothermal alteration zones consist of veins and breccias that surround the hard ores, including: (1) an early alteration zone (distal portion of orebodies), characterized by recrystallization of jasper, formation of magnetite (+/- martite), and the local introduction of quartz and carbonate-sulfide (+/- quartz) veins; (2) intermediate alteration, synchronous with the main iron ore-forming event, which is accompanied by widespread development of martite, quartz-hematite and hematite-quartz veins, and dissolution of carbonate; and (3) proximal alteration zone having various types of hard and hard-porous hematite ores containing naicroplaty, anhedral, euhedral, and tabular hematite species. Locally, high-grade breccia ores contain dolomite and kutnahorite matrices indicating carbonate introduction. High-grade ore zones contain quartz +/- carbonate-hematite veins and breccias. Combined microthermometry, iron chromatography, and in situ laser ablation ICP-MS analyses on fluid inclusion assemblages from five vein types reveal that (1) early alteration vein-breccia quartz-carbonate contains high-salinity (up to 30 equiv wt % NaCl) fluid inclusions, with Ca, besides Na, K, and Mg, which were trapped at temperatures of 220 degrees to 320 degrees C. The quartz-hosted fluid inclusions have a wide range of Cl/Br ratios, presence of Li, base metals Cu-Pb-Zn, and Fe; (2) intermediate alteration vein quartz contains both low-salinity (Na-Fe-Mg-rich) and high-salinity (Ca-Mg-Fe-rich) fluid inclusions, with trapping temperatures of 210 degrees to 290 degrees C; (3) advanced alteration vein and breccia quartz-carbonate has low- to high-salinity fluid inclusions and trapping temperatures between 240 degrees to 310 degrees C, with the low-salinity inclusions being much more abundant in quartz. There is a gradual dilution of the metals signature in fluid inclusions from early to late- and/or advanced-stage veins and breccias. The large amount of Ca in the fluid inclusions is compatible with extensive exchange of the hydrothermal fluids with the surrounding chloritized-hematitized metabasaltic wall rock. Oxygen isotope analyses on different oxide species reveal that the heaviest delta O-18(smow) values, up to 15.2 parts per thousand, are recorded for jaspilites, followed by magnetite, between 0.4 to +4.3 parts per thousand, and then by different hematite species such as microplaty, anhedral and tabular, which fall in the range of -9.5 to 2.4 parts per thousand. These results show a progressive depletion in delta O-18 values from the earliest introduced hydrothermal oxide magnetite toward the latest tabular hematite. The advanced alteration stage in high-grade ore displays the most depleted 180 values and represents the highest fluid/rock ratio during hydrothermal alteration. This depletion is interpreted to result from the progressive mixture of descending, heated meteoric water with ascending modified magmatic fluids. Sulfides from the distal zone of metabasaltic rocks have delta S-34 values close to 0 parts per thousand, consistent with a magmatic origin for the sulfur. Heavier delta S-34 values, of up to 10.8 parts per thousand, in vein sulfides hosted in jaspilite, may reflect interaction with meteoric waters or, alternatively, variations in fO(2) and pH conditions during evolution of the hydrothermal fluid. Calcite-kutnahorite delta C-13 and delta O-18 values from the distal alteration zones show a large delta C-13 range of -5.5 to -2.4%o and a relatively narrow delta O-18 range of 9.3 to 11.7 parts per thousand. However, dolomite matrix breccias from the advanced hydrothermal zone, i.e., ore, exhibit a wider delta O-18 range from 15.1 to 21.8 parts per thousand and a more restricted delta O-13 range from 5.0 to 3.9 parts per thousand. This latter range points to a single carbon source, of possible magmatic nature, whereas the larger delta O-18 range suggests multiple carbon and oxygen sources. The Sr-87/Sr-86 ratios for carbonates from the distal and advanced hydrothermal zones range between 0.7116 to 0.7460, suggesting incorporation of strontium from multiple crustal…

It is widely acknowledged that olivine-hosted melt inclusions retain compositional information unavailable from the study of bulk-rock samples alone. Whether or not the compositions of melt inclusions are truly representative of geologically significant melt bodies has, however, been called into question; isotopic data are critical to resolving this debate but the rare existing data are contradictory. Previous studies of Pb

Speleothems are widely used archives of palaeoclimate variation and have yielded some remarkable insights into climatic conditions during the late Quaternary. Compared to other proxy methods, they offer the possibility of furnishing palaeoprecipitation as well as palaeotemperature records and are eminently suited to dating by U-series analysis, a technique which is highly robust for materials up to~ 500 ka in age. Unfortunately, beyond this time their value has been limited by a lack of appropriate chronometers. Expanding ...

Despite intense interest in the Earth's climate since the last glacial termination, there remain large uncertainties regarding the exact causes, timing and spatial extent of the key events of this period. Many of the millennial scale climatic fluctuations characterising the last deglaciation are well established in records from the Northern Hemisphere, and to some extent from the high latitudes of the Southern Hemisphere. However, deciphering the global response to these events has been hampered by the coverage of existing proxy records ...

Despite their economic and scientific significance, the tectonic drivers that lead to the genesis of kimberlites and related rocks remain enigmatic. The presence of any spatio-temporal relationship(s) between the rift, drift and collision history of continents and the emplacement of kimberlites can only be elucidated with accurate geochronological constraints. In this study, we evaluated the three most common radiogenic dating methods used to determine the emplacement ages of kimberlites and related rocks - Rb Sr phlogopite, U/Pb perovskite and 40Ar/39Ar phlogopite. We selected minimally altered samples from the Kaavi-Kuopio kimberlites, ultramafic lamprophyres and kimberlites from Kuusamo, and olivine lamproites from the Lentiira-Kuhmo-Kostomuksha cluster, all located in Finland. Our 33 new age determinations indicate that the olivine lamproites and ultramafic lamprophyres were emplaced on the Karelian craton during the interval between ~1180–1210 Ma, the Kuusamo kimberlites betwee...

Two igneous rock units were recovered at Site 841. More than 200 m of island-arc rhyolites, rhyolitic tuffs, lapilli tuffs, and pumice breccias, divided into five units, compose the basement at the site. These rhyolitic volcanics are late middle Eocene or older and ...

Energetics of catabolic reactions in diffuse hydrothermal fluids – Clues to subseafloor microbial metabolism M. HENTSCHER*, W. BACH, M. PERNER, A. KOSCHINSKY, D. GARBE-SCHÖNBERG AND J.P. AMEND University of Bremen, D-28359 Bremen, Germany (*correspondence: hentscher@uni-bremen.de) University of Hamburg, D-22609 Hamburg, Germany Jacobs University Bremen, D-28753 Bremen, Germany University of Kiel, D-24098 Kiel, Germany Washington University, St. Louis, MO 63130, USA

Naturalistic depictions of animals are a common subject for the world’s oldest dated rock art, including wild bovids in Indonesia and lions in France’s Chauvet Cave. The oldest known Australian Aboriginal figurative rock paintings also commonly depict naturalistic animals but, until now, quantitative dating was lacking. Here, we present 27 radiocarbon dates on mud wasp nests that constrain the ages of 16 motifs from this earliest known phase of rock painting in the Australian Kimberley region. These initial results suggest that paintings in this style proliferated between 17,000 and 13,000 years ago. Notably, one painting of a kangaroo is securely dated to between 17,500 and 17,100 years on the basis of the ages of three overlying and three underlying wasp nests. This is the oldest radiometrically dated in situ rock painting so far reported in Australia.

<p>As clinopyroxene is the main host of most lithophile elements in the lithospheric mantle, the trace element and radiogenic isotope systematics of this mineral have frequently been used to characterise mantle metasomatic processes. To further our understanding of mantle metasomatism, both solution-mode Sr-Nd-Hf-Pb and in situ trace element and Sr isotopic data have been acquired for clinopyroxene grains from a suite of peridotite (lherzolites and wehrlites), MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside), and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks from the Kimberley kimberlites (South Africa). The studied mantle samples can be divided into two groups on the basis of their clinopyroxene trace element compositions, and this subdivision is reinforced by their isotopic ratios. Type 1 clinopyroxene, which comprises PIC, wehrlite, and some sheared lherzolite samples, is characterised by low Sr (~100–200 ppm) and LREE concentrations, moderate HFSE contents (e.g., ~40–75 ppm Zr; La/Zr < 0.04), and restricted isotopic compositions (e.g., <sup>87</sup>Sr/<sup>86</sup>Sr<sub>i</sub> = 0.70369–0.70383; εNd<sub>i</sub> = +3.1 to +3.6) resembling those of their host kimberlite magmas. Available trace element partition coefficients can be used to show that Type 1 clinopyroxenes are close to equilibrium with kimberlite melt compositions, supporting a genetic link between kimberlites and these metasomatised lithologies. Thermobarometric estimates for Type 1 samples indicate equilibration depths of 135–155 km within the lithosphere, thus showing that kimberlite melt metasomatism is prevalent in the deeper part of the lithosphere beneath Kimberley. In contrast, Type 2 clinopyroxenes occur in MARID rocks and coarse granular lherzolites, which derive from shallower depths (<130 km), and have higher Sr (~350–1000 ppm) and LREE contents, corresponding to higher La/Zr of >~0.05. The isotopic compositions of Type 2 clinopyroxenes are more variable and extend from compositions resembling the “enriched mantle” towards those of Type 1 rocks (e.g.,…

The Kimberley region in Western Australia hosts one of the world’s most substantial bodies of indigenous rock art thought to extend in a series of stylistic or iconographic phases from the present day back into the Pleistocene. As with other rock art worldwide, the older styles have proven notoriously difficult to date quantitatively, requiring new scientific approaches. Here, we present the radiocarbon ages of 24 mud wasp nests that were either over or under pigment from 21 anthropomorphic motifs of the Gwion style (previously referred to as “Bradshaws”) from the middle of the relative stylistic sequence. We demonstrate that while one date suggests a minimum age of c. 17 ka for one motif, most of the dates support a hypothesis that these Gwion paintings were produced in a relatively narrow period around 12,000 years ago.

Kimberlites are often closely associated, both in time and space, with a wide variety of alkaline ultramafic rock types; yet the question of a genetic relationship between these rock types remains uncertain. One locality where these relationships can be studied within the same cluster is the Karelian craton in Finland. In this study we present the first petrographic, mineral and whole-rock geochemical results for the most recently discovered kimberlite cluster on this craton, which represents an example of the close spatial overlap of kimberlites with ultramafic lamprophyres. The Kuusamo cluster incorporates seven bodies (Kasma 45, Kasma 45 south, Kasma 47, Kalettomanpuro (KP), Kattaisenvaara (KV), Dike 15 and Lampi) distributed along a 60 km NE-SW corridor. Hypabyssal samples from KV, KP, Kasma 45 and Kasma 47 consist of altered olivine macrocrysts and microcrysts and phlogopite phenocrysts in a groundmass of perovskite, apatite, spinel, ilmenite, serpentine, and calcite. These pet...

... More recently, Kyle et al. (1980) reviewed the available age determinations and, with the analysis of samples by the 4~ step-heating method, reduced the spread in ... 1972; Kyle 1980; Mens-ing et al. 1984; and numerous others). In the study of Faure et al. ...

Eclogite and peridotite xenoliths occur in early Cretaceous high-Mg adakites of the eastern North China craton (NCC). The primary mineral assemblage (garnet + omphacite + quartz + rutile pargasite), and garnet and quartz-rod exsolutions in clinopyroxene in the eclogite xenoliths constrains a minimum pressure of >1.5 GPa, while the estimated peak metamorphic temperatures range from 800 to 1060 °C (Xu

Our understanding of climatic conditions, and therefore forcing factors, in North America during the past two glacial cycles is limited in part by the scarcity of long, well-dated, continuous paleoclimate records. Here, we present the first, to our knowledge, continuous, millennial-resolution paleoclimate proxy record derived from millimeter-thick pedogenic carbonate clast coatings (pedothems), which are widely distributed in semiarid to arid regions worldwide. Our new multiisotope pedothem record from the Wind River Basin in Wyoming confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and U-Th dating by laser ablation inductively coupled plasma mass spectrometry. This pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the N...

Obsidian characterisation studies have been one of the most successful archaeometrical investigations in the Near East archaeology since 1960s, especially in shedding light on long distance exchange system. Most research, however, has focused on artefacts collected from settlements that are located in regions quite distant from the sources. Consequently, the precise nature of obsidian exploitation and procurement in the source areas remain unclear. This paper presents the results of analyses carried out on both artefacts from Eastern Anatolian settlements and samples collected from the sources themselves. The survey of obsidian sources in Eastern Anatolia is the most thorough conducted so far. Among the settlements, Sos Höyük features prominently in the analyses, with over one hundred samples from the late Chalcolithic levels to the Middle Bronze Age strata. The results revealed that even at Sos Höyük which is located in the vicinity of some obsidian sources, its inhabitants utilise...

ABSTRACT The Middledale Gabbroic Diorite (MGD) in New South Wales, Australia, is host to the internationally distributed TEMORA 2 zircon reference material and its prototype, TEMORA 1. The original characterisation of the source of the reference zircons revealed that the more altered TEMORA 2 host rock contains an order of magnitude more zircon than the TEMORA 1 host, despite similar bulk-rock Zr concentrations. Although TEMORA 1 and 2 preserve the same U–Pb age, they are variable in oxygen isotope composition.