Geochemistry

Estudio paleoambiental a partir de precipitados químicos: espeleotemas de la Sala Roja (Cueva Goikoetxe, Busturia, Bizkaia)

by Virginia Martínez-Pillado

Paleoenvironmental study from chemical precipitates: Speleothems of the Sala Roja (Goikoetxe cave, Busturia, Bizkaia)

A 24 h investigation of the hydrogeochemistry of baseflow and stormwater in an urban area impacted by mining: Butte, Montana

by Christopher Shope

Magma-Carbonate Interaction Processes and Associated CO2 Release at Merapi Volcano, Indonesia: Insights from Experimental Petrology

by Valentin Troll

Pb-isotope evidence for contrasting crustal contamination of primitive to evolved magmas from Ardnamurchan and Rum: implications for the structure of the underlying crust

by Valentin Troll

Pb-isotope evidence for contrasting crustal contamination of primitive to evolved magmas from Ardnamurchan and Rum: implications for the structure of the underlying crust

by Valentin Troll

Marine-continental tephra correlations: Volcanic glass geochemistry from the Marsili Basin and the Aeolian Islands, Southern Tyrrhenian Sea, Italy

by Alessio Di Roberto

P.G. Albert, E.L. Tomlinson, V.C. Smith, A. Di Roberto, A. Todman,
M. Rosi, M. Marani, W. Muller, M.A. Menzies published in Journal of Volcanology and Geothermal Research

Major, minor and trace element analysis of volcanic glass in proximal and distal tephra (<2mm) deposits underpins... more Major, minor and trace element analysis of volcanic glass in proximal and distal tephra (<2mm) deposits underpins tephrochronology. This approach has been tested in the Aeolian Islands and the Tyrrhenian Sea using juvenile clasts in pyroclastic fall and flow deposits. Geochemical data are used to link marine tephras in the Marsili Basin (core TIR2000-C01) to explosive eruptions of (i) Lipari (Monte Pilato; 776 cal AD); (ii) Vulcano; (iii) Campi Flegrei (Soccavo 1; 11915-12721 cal yrs BP). Whether a polymictic coarse grained volcaniclastic turbidite in the Marsili Basin originated from collapse on Salina remains unresolved because multi-elemental analysis raises doubt about the published correlation to the Pollara region. It is evident that correlation of proximal continental and distal marine tephras, at a high level of confidence, requires a full complement of major, minor and trace element data. In conjunction with considerations of the mineralogy and morphology of juvenile deposits these data help define petrological lineages such that precise provenance can be established. Whilst a precise proximal-distal match must be based on identical major, minor and trace element concentrations it is clear that resurgent activity from a single volcano can produce magmas with identical compositions. In such cases stratigraphic relationships must complement any geochemical study. Occasionally proximal stratigraphies may be unrepresentative of the complete eruptive history because of a lack of exposure due to burial by more recent effusive and explosive activity, or sector collapse which can remove vital stratigraphy particularly on volcanic islands.

The Triassic-Jurassic boundary in the Danish Basin: implications on events of the end-Triassic mass extinction

by Sofie Lindström

Reference:
Lindström, S., Dybkjær, K., Pedersen, G.K., Nielsen, L.H., Erlström, M. & van de Schootbrugge, B. 2011: The Triassic-Jurassic boundary in the Danish Basin: implications on events of the end-Triassic mass extinction. FORCE Applications of biostratigraphy to the Norwegian Shelf. 8 December, 2011. Stavanger, Norway. Force/Norwegian Oil Directorate. Applications of biostratigraphy to the Norwegian Shelf, abstracts, 2-3.

The end-Triassic mass extinction event is estimated to have caused the disappearance of several marine families (23%)... more The end-Triassic mass extinction event is estimated to have caused the disappearance of several marine families (23%) and genera (50%) on a global scale (Hallam and Wignall, 1999; van de Schootbrugge et al. 2007). In the terrestrial realm regional to supraregional losses of vertebrate families (up to 42%) and plant species (up to 95%) have been recorded (McElwain et al, 1999, 2007; Olsen et al., 2002; Whiteside et al., 2007). The event is temporally linked to the flood basalt volcanism of the Central Atlantic Magmatic Province (CAMP)(Schoene et al. 2010) and major perturbations in the carbon cycle recorded in stable carbon isotope records globally are generally attributed to the effects of outgassing of 12C-enriched CO2 from this large igneous province (Hesselbo et al., 2002). However, recently injection of methane was put forward as a more likely cause for the most prominent C-isotope excursion, and thus also as a trigger of the end-Triassic mass extinction (Ruhl and Kürschner, 2011; Ruhl et al, 2011).

High resolution palynological and bulk organic C-isotope data from Triassic–Jurassic (T/J) successions in Denmark and Sweden provide evidence of major and partly coeval shifts in the marine and terrestrial palynofloras. The demise of typical Rhaetian dinoflagellate cysts and the temporary disappearance of these phytoplankton appear to coincide with an interval indicating terrestrial deforestation marked by a major decline in pollen from conifers, cycads and ginkgos. Instead high abundances of fern spores, the enigmatic pollen Ricciisporites tuberculatus and sphaeromorphs totally dominate the assemblages. Additional significant features of this interval within the basin, include increased erosion and reworking, changes in fluvial style and temporary loss of peat-forming vegetation.

Correlation between the organic C-isotope record and the terrestrial and marine biotic changes in the Danish Basin show that the major environmental perturbations took place prior to the most prominent negative C-isotope excursion. The subsequent reorganisation and recovery of the terrestrial ecosystem already commenced during this peak, hence negating injection of methane as a major cause of the end-Triassic mass extinction event. Instead we favour a scenario in which repeated episodic CO2 and SO2 release from the CAMP played a prominent role (van de Schootbrugge et al., 2009). Many of the changes recorded in the T/J-boundary succession of the Danish Basin can be attributed to outgassing of SO2 from the CAMP, and subsequent acid rain and acid deposition, and subsequent feedback effects.

References
Hallam, A. and Wignall, P.B. (1999). Mass extinctions and sea-level changes. Earth Sci. Rev., 48, 217-250.
Hesselbo, S.P., Robinson, S.A., Surlyk, F. and Piasecki, S. (2002). Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbations: A link to initiation of massive volcanism? Geology 30, 251-254.
McElwain, J.C., Beerling, D.J. and Woodward, F.I. (1999). Fossil plants and global warming at the Triassic-Jurassic boundary. Science 285, 1386-1390.
McElwain, J.C., Popa, M.E., Hesselbo, S.P., Haworth, M. and Surlyk, F. (2007). Macroecological responses of terrestrial vegetation to climate and atmospheric change across the Triassic/Jurassic boundary in East Greenland. Paleobiology 33, 547-573.
Olsen, P.E., Kent, D.V., Sues, H.D., Koeberl, C., Huberm H., Montanari, A., Rainforth, E.C., Fowell, S.J., Szajna, M.J. and Hartline, B.W. (2002). Ascent of dinosaurs linked to Ir anomaly at Triassic–Jurassic boundary. Science 296, 1305-1307.
Ruhl, M. and Kürschner, W.M., 2011, Multiple phases of carbon cycle disturbance from large igneous province formation at the Triassic-Jurassic transition: Geology, 39, p. 431-434.
Ruhl, M., Bonis, N.R., Reichart, G.-J., Sinninghe Damsté, J.S., and Kürschner, W.M., 2011, Atmospheric carbon injection linked to end-Triassic mass extinction: Science, v. 333, p. 430-434.
Schoene, B., Guex, J., Bartolini, A., Schaltegger, U. and Blackburn, T.J. (2010). Correlating the end-Triassic mass extinction and flood basalt volcanism at the 100 ka level. Geology 38, 387-390.
van de Schootbrugge, B., Tremolada, F., Bailey, T.R., Rosenthal, Y., Feist-Burkhardt, S., Brinkhuis, H., Pross, J., Kent, D.V. and Falkowski, P.G. (2007). End-Triassic calcification crisis and blooms of organic-walled disaster species. Palaeogeogr. Palaeoclimatol. Palaeoecol. 244, 126-141.
van de Schootbrugge, B., Quan, T.M., Lindström, S., Püttmann, W., Heunisch, C., Pross, J., Fiebig, J., Petschik, R., Röhling, H.-G., Richoz, S., Rosenthal, Y. and Falkowski, P.G. (2009). Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism. Nature Geoscience 2, 589-594.
Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J. and Et-Touhami, M. (2007). Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event? Palaeogeogr. Palaeoclimatol. Palaeoecol., 244, 345-367.

2012: Quantification of particle-induced inflammatory stress response: a novel approach for toxicity testing of earth materials

by Martin Schoonen

Andrea D Harrington, Stella E Tsirka and Martin A.A. Schoonen  Geochemical Transactions 2012, 13:4 doi:10.1186/1467-4866-13-4

Background

Reactive oxygen species (ROS) are vital regulators of many cellular functions in the body. The... more Background

Reactive oxygen species (ROS) are vital regulators of many cellular functions in the body. The intracellular ROS concentration is highly regulated by a balance between pro-oxidants and anti-oxidants. A chronic excess of pro-oxidants leads to elevated ROS concentrations and inflammation, possibly initiating or enhancing disease onset. Mineral-induced generation of ROS, the role of minerals in upregulating cellular ROS, and their role in the development of several occupational diseases are now widely recognized. However, there is no standard protocol to determine changes in ROS production in cells after exposure to mineral dust or earth materials in general. In this study, a new method for determining the degree of cellular toxicity (i.e., cytotoxicity) of particles is described that will help bridge the gap in knowledge.
Results

By measuring the production of ROS and the viability of cells, an inflammatory stress response (ISR) indicator is defined. This approach normalizes the ROS upregulation with respect to the number of viable cells at the time of measurement. We conducted experiments on a series of minerals and soils that represent materials that are inert (i.e., glass beads, anatase, and a soil with low trace element content), moderately reactive (i.e., soil with high trace element content), and highly reactive (i.e., pyrite). Inert materials generated the lowest ISR, averaging 350% compared to the control. Acid washed pyrite produced the highest ISR (1,100 fold higher than the control). The measurements conducted as a function of time showed a complex response. Most materials showed an increase in ISR with particle loading.
Conclusions

The amount of cellularly generated ROS and cell viability combined provide a better understanding of particle-induced oxidative stress. The results indicate that some earth materials may solicit an initial burst of ROS, followed by a second phase in which cell viability decreases and ROS production increases, leading to a high ISR value. Hence, measurements conducted over a range of particle loading combined with multiple data measurements up to 24 hours can provide new insights in the possible effect of exposure to earth materials on human health.

Ferromanganese nodules and micro-hardgrounds associated with the Cadiz Contourite Channel (NE Atlantic): palaeoenvironmental records of fluid venting and bottom currents

by F. Javier González Sanz

González, F. J., Somoza, L., León, R., Medialdea, T., Torres, T., Ortiz, J. E., Lunar, R., Martínez-Frías, J., Merinero, R. 2012. Ferromanganese nodules and micro-hardgrounds associated with the Cadiz Contourite Channel (NE Atlantic): palaeoenvironmental records of fluid venting and bottom currents. Chemical Geology (doi:10.1016/j.chemgeo.2012.03.030)

Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf... more Ferromanganese nodule fields and hardgrounds have recently been discovered in the Cadiz Contourite Channel in the Gulf of Cadiz (850–1000 m). This channel is part of a large contourite depositional system generated by the Mediterranean Outflow Water. Ferromanganese deposits linked to contourites are interesting tools for palaeoenviromental studies and show an increasing economic interest as potential mineral resources for base and strategic metals. We present a complete characterisation of these deposits based on submarine photographs and geophysical, petrographic, mineralogical and geochemical data. The genesis and growth of ferromanganese deposits, strongly enriched in Fe vs. Mn (av. 39% vs. 6%) in this
contourite depositional system result from the combination of hydrogenetic and diagenetic processes. The interaction of the Mediterranean OutflowWater with the continental margin has led to the formation of Late Pleistocene–Holocene ferromanganese mineral deposits, in parallel to the evolution of the contourite depositional system triggered by climatic and tectonic events. The diagenetic growth was fuelled by the anaerobic oxidation of thermogenic hydrocarbons (δ13CPDB=−20 to −37‰) and organic matter within the channel floor sediments, promoting the formation of Fe–Mn carbonate nodules. High 87Sr/86Sr isotopic values (up to 0.70993±0.00025) observed in the inner parts of nodules are related to the influence of radiogenic fluids fuelled by deep-seated fluid venting across the fault systems in the diapirs below the Cadiz Contourite Channel. Erosive action of the Mediterranean Outflow Water undercurrent could have exhumed the Fe–Mn carbonate nodules, especially in the glacial periods, when the lower core of the undercurrent was more active in the study area. The growth rate determined by 230Thexcess/232Th was 113±11 mm/Ma, supporting the hypothesis that the growth of the nodules records palaeoenvironmental changes during the last 70 ka. Ca-rich layers in the nodules could point to the interaction between the Mediterranean OutflowWater and the North Atlantic DeepWater during the Heinrich events. Siderite–rhodochrosite nodules exposed to the oxidising sea-bottom waters were replaced by Fe–Mn oxyhydroxides. Slow hydrogenetic growth of goethite from the seawaters is observed in the outermost parts of the exhumed nodules and hardgrounds, which show imprints of the Mediterranean Outflow Water with low 87Sr/86Sr isotopic values (down to 0.70693±0.00081). We propose a new genetic and evolutionary model for ferromanganese oxide nodules derived from ferromanganese carbonate nodules formed on continental margins above the carbonate compensation depth and dominated by hydrocarbon seepage structures and strong erosive action of bottom currents. We also compare and discuss the generation of ferromanganese deposits in the Cadiz Contourite Channel with that in other locations and suggest that our model can be applied to ferromanganiferous deposits in other contouritic systems affected by fluid venting.

On the formation and distribution of ochreous minerals in northern Malawi

by Andrew Zipkin

Andrew M. Zipkin, Alison S. Brooks, John M. Hanchar, Jessica C. Thompson, and Elizabeth Gomani-Chindebvu

J. Desmond Clark’s Middle Stone Age excavation at Chaminade 1A, Karonga, Malawi during the 1960s yielded utilized... more J. Desmond Clark’s Middle Stone Age excavation at Chaminade 1A, Karonga, Malawi during the 1960s yielded utilized ochre artefacts suggestive of pigment production. Our 2011 survey of regional ochre deposits suggested that many potential sources are difficult-to-characterize, sedimentary rocks containing detrital minerals from diverse parent rocks. Here we report a new comparative study of three approaches to ochre provenance geochemistry. Instrumental Neutron Activation Analysis and two variants of Laser Ablation – Inductively Coupled Plasma Mass Spectrometry (1. Bulk Ochre “Paint Chip” Ablation and 2. Zircon Crystal Ablation) were applied to Malawian ochre source samples in order to test the Provenance Postulate and identify the minimum sample mass required for reliable characterization. While our results indicate that all three techniques are suitable for collecting trace element concentrations, “Paint Chip” Ablation data analyzed with multivariate statistics to highlight inter-group variation is the most effective method of distinguishing between ochre sources. A future sourcing study of the Chaminade 1A ochre assemblage using one or more of these techniques is warranted.

1985: Geochemical studies in the drainage basin of the Rio Vouga (Portugal): II. A model for the origin of hydrothermal water in the Vouzela region

by Martin Schoonen

Geochemical studies in the drainage basin of the Rio Vouga (Portugal): II. A model for the origin of hydrothermal water in the Vouzela region
Chemical Geology, Volume 51, Issues 3–4, 30 October 1985, Pages 225-238
H.Lo Ten Haven, Rudy Konings, Martin A.A. Schoonen, J.Ben H. Jansen, Simon P. Vriend, Cornelis H.Van Der Weijden, Jeanine Buitenkamp

The hydrothermal waters in the Vouzela region (Portugal) have a temperature of 68°C and are characterized by a high... more The hydrothermal waters in the Vouzela region (Portugal) have a temperature of 68°C and are characterized by a high content of F, Li, B, bicarbonate, sulphate and silica. Ninety-three water samples, including two hydrothermal waters, were analyzed for major and trace elements in order to investigate the genesis of the hydrothermal water.

In the Vouzela region two Older Hercynian Granites are exposed, the Abas Granite and the São Pedro do Sul Granite. The Abas Granite is intersected by the Ribama fault. Albitization is ubiquitous. Other alteration effects are tourmalinization, K-feldspathization and muscovitization. These processes and the associated Sn—W deposits were induced by the intrusion of the Younger Viseu Granite.

In the present situation rainwater penetrates into the Abas Granite especially via the Ribama fault and the greisenization zone. It becomes part of a hydrothermal system, leaches Li, F, B and silica, and rises via the Termas fault in the hydrothermal springs of Termas de São Pedro do Sul. Geothermal equilibrium calculations yield a temperature of 205 ± 10°C for the thermal reservoir. The percentage of mixing with cold groundwater near the surface in the circulation system is estimated at 73%. The circulation system is possibly maintained by the heat generated by the decay of U, Th, K and their daughter products, elements which are encountered in extremely high concentrations in the São Pedro do Sul Granite.

Preservation of fire-derived carbon compounds and sorptive stabilisation promote the accumulation of organic matter in black soils of the Southern Alps

by Eileen Eckmeier

Eckmeier, E., Egli, M., Schmidt, M.W.I., Schlumpf, N., Nötzli, M., Minikus-Stary, N. & Hagedorn, F. (2010): Preservation of fire-derived carbon compounds and sorptive stabilisation promote the accumulation of organic matter in black soils of the Southern Alps. Geoderma 159: 147-155.

No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction

by Sofie Lindström

Reference:
Sofie Lindström, Bas van de Schootbrugge, Karen Dybkjær, Gunver Krarup Pedersen, Jens Fiebig, Lars Henrik Nielsen, and Sylvain Richoz, 2012: No causal link between terrestrial ecosystem change and methane release during the end-Triassic mass extinction. Geology 40 (6), 531-534, doi:10.1130/G32928.1.

Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated... more Profound changes in both marine and terrestrial biota during the end-Triassic mass extinction event and associated successive carbon cycle perturbations across the Triassic-Jurassic boundary (T-J, 201.3 Ma) have primarily been attributed to volcanic emissions from the Central Atlantic Magmatic Province and/or injection of methane. Here we present a new extended organic carbon isotope record from a cored T-J boundary succession in the Danish Basin, dated by high-resolution palynostratigraphy and supplemented by a marine faunal record. Correlated with reference C-isotope and biotic records from the UK, it provides new evidence that the major biotic changes, both on land and in the oceans, commenced prior to the most prominent negative C-isotope excursion. If massive methane release was involved, it did not trigger the end-Triassic mass extinction. Instead, this negative C-isotope excursion is contemporaneous with the onset of floral recovery on land, whereas marine ecosystems remained perturbed. The decoupling between ecosystem recovery on land and in the sea is more likely explained by long-term flood basalt volcanism releasing both SO2 and CO2 with short- and long-term effects, respectively.

Late Holocene Paleoclimate Reconstruction and Long-Term Human Response in the Region of Timbuktu, Mali (West Africa): Interdisciplinary collaboration in the study of Lake Faguibine and the drought-afflicted populations

by Douglas Park 

Co-Authored with R. McIntosh, R. Smith, P. Douglas, C. Warren and P. Coutros. Yale Climate and Energy Institute Multidisciplinary Grant for climate and archaeology research in Timbuktu. Granted 2009 - ongoing

This interdisciplinary project seeks to integrate climatological, remote sensing, geomorphological and archaeological... more This interdisciplinary project seeks to integrate climatological, remote sensing, geomorphological and archaeological research into a cohesive study of long-term climate change over the past 5000 years at the border between the Sahara and the Sahel at Timbuktu, which is part of the Middle Niger hydraulic system. Understanding how humans have responded to Late Holocene climates in this region, to their long-term trends and abrupt excursions, will provide insight into the types of social institutions employed by the local populations that sought effectively to deal with the unpredictability of their physical world.

Contrasting origins of serpentinites in a subduction complex, northern Dominican Republic

by Benoit Saumur

Published in GSA Bulletin; part of M.Sc. at U. Ottawa

Soilscapes and settlements: remote mapping of activity areas in unexcavated prehistoric farmsteads

by Roderick Salisbury

Salisbury, Roderick B. 2012. Soilscapes and Settlements: Remote Mapping of Activity Areas in Unexcavated Small Farmsteads. Antiquity 86(331):178-190.

Evaluating the use of clay mineralogy, Sr-Nd isotopes and zircon U-Pb ages in tracking dust provenance: An example from loess of the Carpathian Basin

by Gábor Újvári

Gábor Újvári, Andrea Varga, Frank C. Ramos, János Kovács, Tibor Németh, Thomas Stevens (2012)
Chemical Geology 304-305, 83-96, doi: 10.1016/j.chemgeo.2012.02.007

Multiple competing hypotheses have been proposed to explain the source of loess dust in the Carpathian Basin yet none... more Multiple competing hypotheses have been proposed to explain the source of loess dust in the Carpathian Basin yet none has been demonstrated. Here bulk and grain-size differentiated Nd and Sr isotopic and bulk and clay mineralogical compositions, together with detrital zircon ages and morphologies from loess along the Danube in the Carpathian Basin are used to demonstrate that no single method is capable of unequivocally isolating sources, yet combined, they allow for discriminating likely provenance. Zircon ages indicate multiple sources for Carpathian Basin loess, restricting the use of bulk or grain-size differentiation methods. Ambiguities are further highlighted by the fact that the Sr-Nd isotopic composition of Greenland dust is very similar to Carpathian loess. This match demonstrates that such methods are not always capable of unequivocally excluding unlikely potential source areas and implies that current hypotheses regarding the origin of Greenland dust require further evaluation. Sr isotopes are also limited by high dolomite contents of loess, while palygorskite is of questionable utility as a Saharan dust indicator due to its rapid weathering under typical Carpathian climates. In terms of specific Carpathian loess sources, alluvial fans of the Danube River likely contribute, but detrital zircon ages and morphologies suggest that a proportion directly originates from eroded uplands and local rocks throughout the basin, while detrital dolomite implies local, primary sources such as the Transdanubian Range. An upper limit of 5-10% is placed on the North African contribution to fine dust in loess of the mid-Carpathian Basin based on mineralogy and grain size. Overall, results suggest that the single grain (zircon) approach is likely the most diagnostic method to identify sources in loess studies, although to solve complex provenance issues, simultaneous consideration of the isotopic characteristics of more than one heavy (or light) mineral is required.

Jom-Bolok Holocene volcanic field in the East Sayan Mts., Siberia, Russia: structure, style of eruptions, magma compositions, and radiocarbon dating

by Alexei Ivanov

Jom-Bolok volcanic field is located in the East
Sayan Mts. of Siberia (Russia), a portion of the Asianmore Jom-Bolok volcanic field is located in the East
Sayan Mts. of Siberia (Russia), a portion of the Asian
convergent zone. It is located at the boundary of the
Riphean Tuva-Mongolia massif, which was probably
reactivated because of the interplay between far-field
tectonic stress derived from the India–Asia collision zone
and extension in the south-western Baikal rift system. The
volcanic field comprises a number of hawaiitic lava flows,
of various lengths, which flowed down paleorivers. Flows
were fed by fissure eruptions and the largest lava flow field
was dated as 7,130±140 cal 14C years BP using a buried
organic sample found inside the associated cinder cone.
This lava flow field is about 70 km long, ∼100 km2 in area,
and 7.9 km3 in volume. The area and volume of this flow
field ranks this eruption highly in the global record of
fissure-fed effusive eruptions. This lava flow field makes
up 97% of the entire Jom-Bolok volcanic field, a fact which
raises a puzzling question: why and/or how did a relatively
small-volume volcanic field produce such a large-volume
individual eruption? A working hypothesis is that a pond of
sublithospheric melt accumulated over a relatively prolonged period. This was then rapidly drained in response of
tectonic changes triggered by unloading of ice in the Early
Holocene.

Geochemical and isotopic development of the Coromandel Volcanic Zone, northern New Zealand, since 18 Ma

by Mathijs Booden

M. A. Booden, I. E. M. Smith, P. M. Black, and J. L. Mauk / Journal of Volcanology and Geothermal Research Research 219 p. 15-32 / 2012

Cenozoic subduction-related volcanism in northern New Zealand developed from mainly basaltic and andesitic volcanisms... more Cenozoic subduction-related volcanism in northern New Zealand developed from mainly basaltic and andesitic volcanisms in the Early Miocene to mainly silicic volcanism in the present Taupo Volcanic Zone. The first explosive silicic eruptions occurred at 12 Ma and large silicic calderas formed from 8 Ma. This transition is recorded by the 18–1.9 Ma Coromandel Volcanic Zone (CVZ) succession, which provides an outstanding opportunity to investigate the origins of the modern North Island volcanism. New major and trace element data on a rock suite representing CVZ andesites, rhyolites and basalts indicate a consistent subduction-related origin for the entire succession. The CVZ andesites generally define a consistent medium-potassic differentiation trend, however, distinct andesites with relatively sodic compositions occur at the bases of two consecutive eruptive series at ~ 18 and ~ 10 Ma. The distinct andesites are geochemically similar to basalts that erupted sporadically near the oceanic margin of the CVZ. CVZ rhyolites are medium- to high-potassic, peraluminous rocks with initial 87Sr/86Sr values comparable to or somewhat more radiogenic than coeval andesites (≥ 0.7049). Their bulk rock composition suggests derivation from sources comparable to least-differentiated andesites or basalts. We interpret the consecutive andesitic successions to represent stages in CVZ development during which distinct arc segments developed consecutively. The early stage in each segment yielded mainly intermediate volcanism whereas in the later stage volcanism locally proceeded rapidly (within ~ 1 Myr of initial andesitic activity) to silicic activity. Taken together, the succession records the rapid development and migration of arc system in a dynamic plate boundary setting.

Archaeological geophysical prospection in peatland environments: Case studies and suggestions for future practice

by Kayt Armstrong

Extended Abstract of a paper presented at the International Society for Archaeological Prospection 8th Conference, Paris, September 2009

Joint authors Paul Cheetham & Tim Darvill