Petrology and Geochemistry

A microscopic information system (MIS) for petrographic analysis

by Simone Tarquini

Tarquini S., Favalli M.
2010, Computers & Geosciences 36, 665-674

The database and visualization facilities of Geographic Information System (GIS) software are employed to support the... more The database and visualization facilities of Geographic Information System (GIS) software are employed to support the analysis of rock texture from thin section by image processing. A Microscopic Information System (MIS) is hence obtained. The method is applied to transmitted light images of 137 samples obtained from 8 granitoid rocks. A slide scanner and a mount for crossed polarization are used to acquire the input images. For each thin section 5 collimated RGB images are scanned: 4 under different directions of crossed polarization and 1 without polarization. A grain segmentation procedure, based on two region growing functions is applied. The output is converted to vector format and refined using editing tools in the MIS environment, which enables a straightforward match between the input imagery and the final vectorized texture. GIS software provides optimal management of the MIS database, allowing the cumulative measurement of more than 87,000 grains.

Power law olivine crystal size distributions in lithospheric mantle xenoliths

by Simone Tarquini

Armienti P. and Tarquini S.
2002, Lithos 65, 273-285.

Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing... more Olivine crystal size distributions (CSDs) have been measured in three suites of spinel- and garnet-bearing harzburgites and lherzolites found as xenoliths in alkaline basalts from Canary Islands, Africa; Victoria Land, Antarctica; and Pali Aike, South America. The xenoliths derive from lithospheric mantle, from depths ranging from 80 to 20 km. Their textures vary from coarse to porphyroclastic and mosaic–porphyroclastic up to cataclastic. Data have been collected by processing digital images acquired optically from standard petrographic thin sections. The acquisition method is based on a high-resolution colour scanner that allows image capturing of a whole thin section. Image processing was performed using the VISILOG 5.2 package, resolving crystals larger than about 150 Am and applying stereological corrections based on the Schwartz–Saltykov algorithm.
Taking account of truncation effects due to resolution limits and thin section size, all samples show scale invariance of crystal size distributions over almost three orders of magnitude (0.2–25 mm). Power law relations show fractal dimensions varying between 2.4 and 3.8, a range of values observed for distributions of fragment sizes in a variety of other geological contexts. A fragmentation model can reproduce the fractal dimensions around 2.6, which correspond to well-equilibrated granoblastic textures. Fractal dimensions >3 are typical of porphyroclastic and cataclastic samples. Slight bends in some linear arrays suggest selective tectonic crushing of crystals with size larger than 1 mm. The scale invariance shown by lithospheric mantle xenoliths in a variety of tectonic settings forms distant geographic regions, which indicate that this is a common characteristic of the upper mantle and should be taken into account in rheological models and evaluation of metasomatic models.

Palaeomagnetic and anisotropy of magnetic susceptibility data bearing on the emplacement of the Western Granite, Isle of Rum, NW Scotland

by Valentin Troll

Shallow-level processes at Anak Krakatau: Crystallisation and late stage crustal contamination

by Valentin Troll

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

by Valentin Troll

Sulfide oxidation as a process for the formation of copper-rich magmatic sulfides

by Raúl Fonseca

Wohlgemuth-Ueberwasser C. C., Fonseca R. O. C., Ballhaus C. and Berndt J. Mineralium Deposita in press DOI: 10.1007/s00126-012-0420-9 (2012)

Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic... more Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic Cu/Fe ratio of these sulfides is typically less than unity. However, there are rare magmatic sulfide occurrences that are dominated by Cu-rich sulfides (e.g., bornite, digenite, and chalcopyrite, sometimes coexisting with metallic Cu) with atomic Cu/Fe as high as 5. Typically, these types of sulfide assemblages occur in the upper parts of moderately to highly fractionated layered mafic–ultramafic intrusions, a well-known example being the Pd/Au reef in the Upper Middle Zone of the Skaergaard intrusion. Processes proposed to explain why these sulfides are so unusually rich in Cu include fractional crystallization of Fe/(Ni) monosulfide and infiltration of postmagmatic Cu-rich fluids. In this contribution, we explore and experimentally evaluate a third possibility: that Cu-rich magmatic sulfides may be the result of magmatic oxidation. FeS-dominated Ni/Cu-bearing sulfides were equilibrated at variable oxygen fugacities in both open and closed system. Our results show that the Cu/Fe ratio of the sulfide melt increases as a function of oxygen fugacity due to the preferential conversion of FeS into FeO and FeO1.5, and the resistance of Cu2S to being converted into an oxide component even at oxygen fugacities characteristic of the sulfide/sulfate transition (above FMQ + 1). This phenomenon will lead to an increase in the metal/S ratio of a sulfide liquid and will also depress its liquidus temperature. As such, any modeling of the sulfide liquid line of descent in magmatic sulfide complexes needs to address this issue.

Evaluation of Phosphate Analysis and the Brongers Method of Detecting Decomposed Wood, Human Tissue and Organic Goods in a Bell Beaker Grave at Těšetice-Kyjovice, Czech Republic

by Klara Sabatova

Hlavica, M. - Petřík, J. - Prokeš, L. - Šabatová, K. 2011: Evaluation of Phosphate Analysis and the Brongers Method of Detecting Decomposed Wood, Human Tissue and Organic Goods in a Bell Beaker Grave at Těšetice-Kyjovice, Czech Republic. Interdisciplinaria Archaeologica – Natural Sciences in Archaeology (IANSA), 85-94, ISSN 1804-848X.

New constraints on the genesis and long-term stability of Os-rich alloys in the Earth’s mantle

by Raúl Fonseca

Raúl O.C. Fonseca, Vera Laurenz, Guilherme Mallmann, Ambre Luguet, Nadine Hoehne, and Klaus Peter Jochum. Geochimica et Cosmochimica Acta 87, 227-242 (2012)

A variety of seemingly unrelated processes, such as core-mantle interaction, desulfurization, and direct precipitation... more A variety of seemingly unrelated processes, such as core-mantle interaction, desulfurization, and direct precipitation from a silicate melt have been proposed to explain the formation of Ru-Os-Ir alloys (here referred to as osmiridiums) found in terrestrial mantle rocks. However, no consensus has yet been reached on how these important micrometer-sized phases form. In this paper we report the results of an experimental study on the solubilities of Ru, Os and Ir in sulfide melts (or mattes) as a function of alloy composition at 1300°C. Considering the low solubilities of Ru, Os, and Ir in silicate melts, coupled with their high matte/silicate-melt partition coefficients, our results indicate that these elements concentrate initially at the ppm level in a matte phase in the mantle source region. During partial melting, the extraction of sulfur into silicate melt leads to a decrease in fS2 that triggers the exsolution of osmiridiums from the refractory matte in the residue. The newly formed osmiridiums may persist in the terrestrial mantle for periods exceeding billions of years.

Oceanic plateaus

by Andrew Kerr

In press, Oceanic Plateaus review chapter for the second edition of the Treatise on Geochemistry

Ceramic technology and the materiality of Celtic graphitic pottery

by Attila Kreiter

Kreiter A. – Bajnóczi B. – Havancsák I. – Tóth M. – Szakmány, Gy. – Szöllősi Sz. 2012 (in press). Ceramic technology and the materiality of Celtic graphitic pottery. In Sabatini, S. – Alberti, M. E. (Eds.) Exchange networks and local transformations: interactions and local changes in Europe and the Mediterranean between Bronze and Iron Age. Oxford: Oxbow.

The Celtic “graphitic ware” is a widespread, distinctive type of pottery, found in most parts of the Central European... more The Celtic “graphitic ware” is a widespread, distinctive type of pottery, found in most parts of the Central European Celtic world. In Celtic research the term “graphitic ware” is commonly used for a special typological group of ceramics, the most characteristic of which are the situla-like pots or beakers that have a wide mouth, an inverted or swollen rim, accentuated shoulder and a wide, flat bottom. They are typically decorated with vertically incised bundles of lines.
This paper examines the technological aspects of Celtic ceramics obtained from a settlement at Dunaszentgyörgy (Hungary). They were examined by using polarising microscopy, X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) and electron microprobe analysis (EMPA). In this paper we will concentrate on the well-known, yet little-understood graphite-tempered situla-like pots of the Celts. The possible similarities and differences of graphitic and non-graphitic wares are also examined in terms of raw material compositions.
Multidisciplinary research has the potential to provide valuable insights into social aspects of prehistoric graphite procurement and the reasons behind manufacturing such pottery. It should be emphasised that we need to move beyond mere functionalist interpretations of pottery technology and raw materials because these practices divorce past human interactions with minerals from wider cognitive, symbolic, phenomenological and social contexts. Within pre-industrial societies minerals are frequently interwoven into not just economic and material, but also social, cosmological, mythical, spiritual and philosophical aspects of life.

Archaeometric examination of Early and Middle Bronze Age ceramics from Százhalombatta-Földvár, Hungary

by Attila Kreiter

Kreiter, A. – Bajnóczi, B. – Sipos, P. – Szakmány, Gy. – Tóth, M. 2007. Archaeometric examination of Early and Middle Bronze Age ceramics from Százhalombatta-Földvár, Hungary. Archeometriai Műhely/Archaeometry Workshop, 2, 33-47

This paper examines the technological aspects of Early and Middle Bronze Age ceramics from a tell settlement at... more This paper examines the technological aspects of Early and Middle Bronze Age ceramics from a tell settlement at Százhalombatta (Hungary) by using polarising and cathodoluminescence microscopy, X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) analyses. Towards the end of the Middle Bronze Age, during
the Koszider period, ceramic production became more elaborate; and highly distinctive vessels appeared in terms of their decoration, surface treatment and firing conditions. For this analysis eight sherds belonging to fine and coarse wares were selected. In order to assess how potters may have altered their raw materials potential clay samples around the tell settlement were also examined by the same techniques. Results suggest that potters used locally available clays and even the most distinct vessels in terms of decoration (Rákospalota type wares) seem to be locally made. In spite of the similarities in clay compositions, however, there is a clear
distinction between how potters manipulated their clay and temper even within a similar vessel type. This practice resulted in the existence of intrasite technological traditions

Crystallization history of primitive Deccan basalt from Pavagadh hill, Gujarat, western India

by Hari K R

For reprint request, please send a mail to krharigeology@gmail.com

Mildly alkaline basalts from Pavagadh Hill, India: Deccan flood basalts with an asthenospheric origin

by Hari K R

For reprint request, please send a mail to krharigeology@gmail.com

Petrology, fluid inclusions and metamorphic history of Bhopalpatnam granulites, central India

by Hari K R

For reprint request, please send a mail to krharigeology@gmail.com

Petrology of the eclogites from western Tasmania: Insights to the Cambro-Ordovician evolution of the paleo-Pacific margin of Gondwana. Lithos

by Reia M. Chmielowski

Palmeri, R., Chmielowski, R. M., Sandroni, S., Talarico, F. and Ricci, C. A. in-press: Lithos (available on line as of July 2008)

Eclogite-facies rocks along the Paleozoic active margin of Gondwana are rare. They are limited to isolated segments of... more Eclogite-facies rocks along the Paleozoic active margin of Gondwana are rare. They are limited to isolated segments of northern Victoria Land (Antarctica), western Tasmania and south-eastern Australia. New petrological data for mafic rocks and their host garnet-kyanite schists from the Franklin Metamorphic Complex (western Tasmania) permit reconstruction of six main stages of mineral growth for the eclogite.  Stage I and II occurred at greenschist/amphibolite-facies conditions (ca. 500-600 °C; 0.55-0.7 GPa for stage II) before attaining high pressure conditions (at ≈600-650 °C; > 1.5 GPa - stage III). The following stages, IV and V, record the decompression from high pressure conditions to amphibolite facies (ca. 500-600 °C; 0.4-1.0 GPa). Finally, stage VI represents the late greenschist-facies retrogression. However, the pelitic schist, surrounding the eclogite, records only the medium-pressure amphibolite-facies stage. The P-T evolution over time outlines a clockwise path which is quite steep both in the prograde and retrograde segments. The latter shows a nearly isothermal decompression between the eclogite and the high pressure amphibolite-facies stage IV which was achieved at deep crustal levels (≈ 30 km), and a final decrease in both pressure and temperature from deep/intermediate to shallow crustal levels with a typical cooling-unloading path. The lack of a complete re-equilibration during the different stages and the high dP/dT for both the prograde and retrograde paths are indicative of a rapid burial and initially rapid exhumation. The similarity of the mafic whole rock chemical composition including N, T to E – MORB and of the peak metamorphic age (≈ 500 Ma) between the Tasmanian eclogites and the UHP rocks from northern Victoria Land supports the idea that they formed in the context of the same contractional event. However, the different P-T conditions and dP/dT point to different tectono-metamorphic settings for the two sectors of the paleo-Pacific margin of Gondwana during the Ross/Tyennan orogeny.

Metamorphic Record of High-pressure Dehydration of Antigorite Serpentinite to Chlorite Harzburgite in a Subduction Setting (Cerro del Almirez, Nevado–Filábride Complex, Southern Spain)

by José Alberto Padrón-Navarta

Published in 'Journal of Petrology', 2011

The antigorite dehydration front preserved in the Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera, SE... more The antigorite dehydration front preserved in the Cerro del Almirez (Nevado–Filábride Complex, Betic Cordillera, SE Spain) offers a unique opportunity to investigate the high-pressure prograde breakdown of antigorite serpentinite (Atg-serpentinite) to chlorite harzburgite (Chl-harzburgite; olivine + orthopyroxene + chlorite + tremolite) in a subduction setting. Our detailed mapping of the antigorite dehydration front shows that in the transition between Atg-serpentinite and prograde Chl-harzburgite a narrow band of transitional lithologies occurs that consists of chlorite–antigorite–olivine-serpentinite (Chl-serpentinite), grading through antigorite–chlorite–orthopyroxene–olivine (Atg–Chl–Opx–Ol) rocks and, subsequently, to Chl-harzburgite. Just beneath the reaction front, Chl-harzburgite shows everywhere a granofelsic texture; however, down section, it is interspersed in decameter-sized domains with spinifex-like Chl-harzburgite. Field and textural relationships, mineral compositions and chemographic phase relations indicate that the prograde breakdown of Atg-serpentinite to Chl-harzburgite occurred through a series of continuous metamorphic reactions forming transitional lithologies. Chl-harzburgites with granofelsic and spinifex-like textures were formed under similar P–T conditions (1·6 – 1·9 GPa and 680–710°C). We ascribe their differing textures to shifts in the growth rate of the products caused by temporal and spatial fluctuations in the affinity of the antigorite-breakdown reaction driven by cyclic variations of the fluid pressure. Crystallization at a low affinity of the antigorite-breakdown reaction, producing granofelsic Chl-harzburgite, was attained by a slow drain of fluids from the dehydrating system. With the advancement of the dehydration front overpressured domains were left behind, preserving serpentinite that was highly metastable under lithostatic pressure. Brittle failure of rocks surrounding these overpressured domains resulted in an increase in their permeability, a fast drop in fluid pressure towards hydrostatic pressure, and sudden stabilization of the prograde reaction products. This process resulted in the crystallization of the prograde assemblage under a high affinity of the antigorite-breakdown reaction, accounting for disequilibrium fast growth of spinifex-like Chl-harzburgite. Prograde textures in the Cerro del Almirez hence witness the feedback between the rate of metamorphic reactions and the cyclic dynamics of metamorphic fluid expulsion during high-pressure serpentinite dehydration in a subduction setting.

Distinguishing crustal recycling and juvenile additions at active continental margins: the Paleozoic to recent compositional evolution of the Chilean Pacific margin (36- …

by Christian Creixell

Kos Plateau Tuff (KPT) on Kalymnos Island, Aegean Volcanic Arc: A Geochemical Approach.

by Dimitrios Zouzias

D Zouzias, K St Seymour (2011) Journal of Volcanology and Seismology 5: 6. in press December

Abstract: Thirteen pumice samples from the D and E ignimbrite units of Kalymnos Tuff have been analyzed for their... more Abstract: Thirteen pumice samples from the D and E ignimbrite units of Kalymnos Tuff have been analyzed for their biotite and feldspar phenocryst mineral chemistry and for bulk major and 20 trace, including 14 Rare Earth elements, to define and compare their petrochemistry with the Kos Plateau Tuff (KPT). For the same purpose major element analyses were obtained from Kalymnos Tuff and KPT glasses. Both KPT and Kalymnos pumice lapilli are rhyolites characterized by a well-developed ‘silky’ texture and roundish quartz. Phenocrysts of biotite and feldspars (sanidine, oligoclase) from both tuffs display compositional overlap. Crystals are characterized by undulatory extinction (quartz), fractures (sanidine, oligoclase) and bent cleavages (biotite) due to the explosive origin of their host. Both tuffs show well-defined petrogenetic trends and extensive compositional overlaps on major and trace element variation diagrams suggesting that they are consanguineous. However, D ignimbrite samples are more evolved than those obtained from E ignimbrite as indicated from major elements, alkali earths (Ba, Rb, Sr), immobile (Zr, Y), compatible (V) and hygromagmatophile trace element (Th) distributions. This evidence indicates a stratified magma chamber under a ~16 Km caldera superstructure which is mostly submarine.

Chronology of pluton emplacement and regional deformation in the southern Sierra Nevada batholith, California

by Cathy Busby

Saleeby, J., Ducea, M.N., Busby, C., Nadin, E., and Whetmore, P.H., 2008, Chronology of pluton emplacement and regional deformation in the southern Sierra Nevada batholith, California: in, J. Wright and J. Shervais (eds), Ophiolites, Arcs and Batholiths: Geological Society of America Special Paper 438, p. 397 – 428.

A Detailed Geochemical Study of Island Arc Crust: the Talkeetna Arc Section, South-Central Alaska

by Peter Clift