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In this study, the correlation of the Balkayası travertine formations with the Salanda Fault Zone (SFZ) located within the Central Anatolian Volcanic Province (CAVP) was investigated. Additionally, source and paleoclimatic significance were researched with age dates for the travertine formations obtained with the U-series dating method, stable isotope data, and major oxide, trace, and rare earth element (REE) analyses. The ages of the travertines outcropping in the study area were determined to vary from 9 to 55 ka according to U-series age analysis data. In the stress analysis taking into account the trending's of Balkayası travertines deposited in SFZ, it was found that the main compression and extension directions in the region were NNW-SSE and ENE-WSW, respectively. The δ13CPDB values varied from 11.36 to 13.16 and δ18OPDB values were from − 10.41 to − 8.66. ∑REE were in the interval 1.08–22.97 ppm. Negative Eu and Ce anomalies were determined. Travertine formations outcropping in the region were classified according to morphology as fissure ridge, range front, and eroded sheet travertines. Age dates obtained from the travertines reveal they formed in MIS 3 (marine isotope layer) representing very cold (dry) periods and MIS2 and the initial period of MIS 1. The extensional direction is consistent with the Tuz Gölü Fault Zone (TGFZ), one of the important structures in the region. Linked to the age data from the travertine formations, the strike-slip transition on the SFZ is interpreted to have extended to the Late Pleistocene. In conclusion, according to stable isotope data and geochemical data, the Balkayası travertines have epigenic character; however, they were affected by the hypogenic environment, precipitated in fresh water, and were fed by high pH and hydrothermal waters. [ABSTRACT FROM AUTHOR]

Volcanological studies coupled with detailed geochemistry can reveal important aspects regarding the melting and ascent processes of a magmatic body. The explosive part of the eruption giving rise to scoria and tephra deposits can hold a wealth of information which can complement chemical analyses of lava flows, however, it is often poorly exposed. A well-exposed scoria deposit and lava flow at the small eruptive center (SEC) San Jorge near Pucón in the Southern Volcanic Zone (SVZ), Chile, provides an opportunity to examine melting and storage processes in a primitive magma body almost in 'real time' through sampling up the stratigraphy of the deposit. This dataset comprises whole rock major and trace element chemistry, Sr–Nd and U-Th–Ra isotopes, in addition to mineral data through the eruption sequence. San Jorge whole rock compositions are unique in the area (MgO 10–12 wt%, SiO2 50–52 wt%, Cr 600–900 ppm) and the studied tephras extend to the highest uranium- and radium-excesses yet measured in the SVZ. The unusual composition of the volcanic material displays similarities to rocks from the arc-front stratovolcano Villarrica but is distinct from other stratovolcanoes in the area, which exhibit greater influence from sediment input to the source, crustal assimilation and prolonged storage. We model the San Jorge magmas as a mixture of melts originating from highly fluid-fluxed, depleted mantle and fractionated basalt from the same source, with increasing amounts of the latter component with progression of eruption. This suggests that San Jorge-like magmas were the main feeder of the longer lived system building Villarrica. Abrupt major element variations up-sequence additionally show a rapid switch to more fractionated compositions, indicating that storage and evolution through crystallization may have taken place once the initially wet melts 'dried out'. [ABSTRACT FROM AUTHOR]

Uranium and thorium isotopic composition of kasolite [Pb(UO)SiO-(HO)] from Jabal Sayid area was determined by thermal ionization mass spectrometry. Secondary electron imaging, back-scattered electron imaging, and energy dispersive spectral scans were used to investigate the mineralogical characteristics of this uranyl mineral phase. Distinct crystal faces and crystal growth of kasolite from the study area confirm mineral precipitation near the surface from the circulating groundwater. The obtained data were used to interpret the mechanism of uranium mobility in Jabal Sayid weathering profile and to construct a tentative model to explain the isotopic evolution of uranium and thorium. This model indicates that (1) uranium was leached at depth, (2) uranyl mineralization was precipitated along fractures and cavities in the host rocks during humid conditions and pluvial periods, (3) preferential leaching of U from uranyl mineralization by recoil processes was continuous indicative of a weakly circulating groundwater, and (4) U-deficiency resulted in isotopic signatures characterized by low U/U and high Th/U ratios. The modification pattern of these activity ratios suggests that uranyl mineralization of Jabal Sayid, most probably, has been precipitated during the same Late Quaternary pluvial periods responsible for the formation of the corresponding mineralizations in the Eastern Desert of Egypt. [ABSTRACT FROM AUTHOR]

We obtained U-Th disequilibrium age data on zircons from each of the four rhyolite eruptions that built Tarawera volcano in the last 22 ka within the Okataina Volcanic Center (OVC), caldera, New Zealand. Secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near-eruption age to ~100 ka prior to eruption. Age-depth profiling of crystals reveals long periods of continuous (~34 ka) and discontinuous growth (~90 ka). Growth hiatuses of up to ~40 ka duration occur, but do not all relate to obvious resorption surfaces. Age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts. These features are best explained by periodic, complete, or partial, sub-solidus storage and/or inclusion in larger crystal phases, followed by rapid liberation prior to eruption. This is supported by high abundances of U and Th (~500 − >2,000 ppm) in some zircons consistent with periods of high crystallinity (>70%) in the magmatic system, based on crystal/melt partitioning. Contemporaneous but contrasting rim-ward trends of these elements within crystals, even in the same lava hand sample, require synchronous growth in separate melt bodies and little connectivity within the system, but also significant crystal transport and mixing prior to eruption. Many crystals record continuity of growth through the preceding ~60 ka OVC caldera-collapse and subsequent eruptions from Tarawera. This demonstrates a decoupling between eruption triggers, such as shallow crustal extension and mafic intrusion, and the crystallization state of the OVC silicic magmatic system. The data highlights the need to distinguish between the time for accumulation of eruptible magma and the long-term magma residence time based on the age of crystals with high closure temperatures, when assessing the potential for catastrophic eruptions. [ABSTRACT FROM AUTHOR]

The Auckland volcanic field is a Quaternary monogenetic basaltic field of 50 volcanoes. Rangitoto is the most recent of these at ~500 year BP and may mark a change in the behaviour of the field as it is the largest by an order of magnitude and is unusual in that it erupted magmas of alkalic then subalkalic basaltic composition in discrete events separated by ≤50 years. Major and trace element geochemistry together with Sr-Nd and U-Th-Ra isotopes provides the basis for modelling the melting conditions that brought about the eruption of two chemically different lavas with very little spatial or temporal change. Sr-Nd isotopes suggest that the source for both eruptions is similar with a slight degree of heterogeneity. The basalts show high Th-excess compared with comparable continental volcanic fields. We show that the alkalic basalts give evidence for lower degrees of partial melting, higher amounts of residual garnet, a longer melting column and lower melting and upwelling rates compared with the subalkalic basalts. The low upwelling rates (0.1-1.5 cm/year) modelled for both magmas do not suggest a plume or major upwelling in the mantle region beneath Auckland; therefore, we suggest localised convection due to relict movement from the active subduction system situated 400 km to the southeast. A higher porosity for the initial alkalic basalt is based on Ra-excesses, suggesting movement of melt by two different porosities: the initial melt travelling in fast high porosity channels from greater depths preserving a high Th-excess and the subsequent subalkalic magma travelling from a shallower depth through lower porosity diffuse channels preserving a high Ra-excess; this creates a negative array in (Ra/Th) versus (Th/U) space previously only seen in mid ocean ridge Basalt data. This mechanism suggests the Auckland volcanic field may operate by the presence of discrete melt batches that are able to move at different depths and speeds giving the field its erratic spatial and temporal pattern of eruptions, a type of behaviour that may have implications for the evolution of other continental volcanic fields worldwide. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

This study reveals the age, setting, and geochemistry of fissure ridge travertines outcropping in Yaprakhisar (Güzelyurt-Aksaray) that is located in the Central Anatolian Volcanic Province (CAVP) and investigates their relationship with main tectonic structures. Dating studies with the U-series analysis method identified that travertine formations were deposited from 3 to 147 ka BP. The travertines in the study area were divided into two groups based on the age and extension direction. The first group consists of fissure ridge travertines with 70° NE and deposited in the range of 126-147 ka BP. The second group has 10° NW strike and are fissure ridge travertines dated to 3-47 ka BP. The association between the travertine groups and the significant fault zones in the region was investigated, and three different formation models are presented. The relationship between the fissure ridge travertines and faults deforming the CAVP was determined using paleo-discontinuities. The Yaprakhisar travertines were determined to have Ce and Eu anomalies, along with low Ba and relatively low Sr values. When the trace element and REE content of the Yaprakhisar travertines are considered together, the travertines are concluded to have been deposited under oxic conditions from limestone-evaporite-dolomite-sourced hypogene water with low acidity and relatively low temperature. [ABSTRACT FROM AUTHOR]