Hasil untuk "Petrology"

Guolai Li, Zeina Naim, Luis Gibert et al.

Abstract This study examines the climatic controls on dolomite precipitation through a multiproxy investigation of a carbonate‐rich sediment core from Salinas Lake, a hypersaline playa in Alicante, south‐eastern Iberia. The ~120,000 year record captures depositional cycles and palaeoenvironmental changes driven by late Pleistocene to Holocene climate variability. Integrated analyses of sedimentology, lithology, geochemistry (elemental concentrations, total organic carbon, stable carbon and oxygen isotopes), scanning electron microscopy, microbial community characterisation and palynology reconstruct lake hydrology and its influence on carbonate mineralogy. The sediment succession is marked by alternating calcite‐ and dolomite‐rich intervals, with dolomite crystals displaying morphological evolution from spherical to rhombohedral forms with depth. Stable isotope signatures (δ13C: −6.5‰ to −2.4‰ VPDB; δ18O: −2.3‰ to +4.9‰ VPDB), alongside microbial structures such as extracellular polymeric substances (EPS) and internal crystal voids, suggest a biologically mediated precipitation mechanism. These mineralogical shifts closely correspond to rapid hydrological changes driven by Dansgaard–Oeschger climate oscillations, with dolomite formation favoured under arid, evaporative conditions that concentrate Mg and Ca ions and promote microbial mat development. Halophilic microbial communities, capable of catalysing carbonate precipitation, probably enhance dolomite nucleation and growth through EPS production and geochemical modulation. This work underscores the complex interplay between climate, hydrology, microbial activity and sedimentary mineral formation, providing new insights into the longstanding ‘dolomite problem’ within sedimentary environments.

Zilong Wang, Wei Tian, Wei-RZ Wang et al.

Abstract There is ongoing debate about whether lunar magnesian suite (Mg-suite) magmatism was a global, nearly synchronous event with a genetic link to potassium, rare-earth element and phosphorus components (KREEP). Arguin 002, the first whole-rock meteorite classified as a lunar norite, offers a unique opportunity to explore the genesis and timing of Mg-suite rocks. Here we investigated the petrology, mineralogy, geochemistry, and chronology of Arguin 002, revealing it to be an evolved, KREEP-free Mg-suite rock with chemical similarities to atypical Apollo-15 Fe-norites. It likely formed through plutonic magmatism originating from low-degree partial melting of a deep, KREEP-free mantle source and has a 207Pb/206Pb age of 4341.5  ± 9.3 Ma. The potential source of Arguin 002 is within the South Pole-Aitken basin, near the Chang’e-6 landing site. These findings indicate that Mg-suite magmatism was a global and nearly synchronous event, potentially driven by rapid global mantle overturn.

Hichem Horra, Ahmed Hadjadj, Elfakeur Abidi Saad et al.

Abstract This study aims to investigate the limitations of geostatistical prediction models outside the observed data range for estimating rock strength in nonreservoir formations in large geological fields with limited wireline data. To address this gap, this method explores alternative approaches to estimate rock strength using minimum data. A novel 3D rock strength prediction model that integrates geostatistic with deep learning algorithms is proposed. Initially, the deep learning model is trained using the available dataset to capture the complex nonlinear relationships within the data. The developed model is used to increase the dataset size by focusing on nearby data points to mitigate geological variability. geostatistic methods are then applied to establish spatial correlations of rock strength across an extended range compared with those of the actual dataset. The results reveal marked improvements in both the prediction range and spatial resolution of rock strength through the proposed methodology. The developed deep learning models achieved coefficient of determination values ranging from 0.9 to 0.99, demonstrating excellent predictive capability. Cross-validation confirms the model effectively captures local variations. The prediction range in the field expanded by 250% compared to the initial dataset, successfully addressing areas that previously exhibited flat readings when the model was applied to the initial data. This study advances petroleum industry knowledge by integrating deep learning and geostatistical methods to overcome rock strength prediction limitations in nonreservoir formations. The novel 3D model enhances the prediction range and spatial resolution, addresses data gaps and enables better decision-making for areas with limited wireline data.

Vesta O. Davydova, Anton A. Nuzhdaev, Ilya E. Bolshakov et al.

Krenitsyn Peak is one of the two active volcanoes on Onekotan Island (Greater Kuril Ridge). The inaccessibility of the island, along with the volcano being situated within a sizeable (7 km in diameter) and cold (3.7 °C) caldera lake, has led to minimal research on the area. We present the first detailed characterization of the rocks from the only historical eruption of Krenitsyn Peak (November 1952) and a brief description of the ancient lava and pyroclastic density current (PDC) deposits that make up the building of the volcano. The 1952 eruptive products are represented by two-pyroxene andesites (59.2–63.3 wt.% SiO₂), and the older lava and pyroclastic flow rocks consist of two-pyroxene andesites and dacites (62–67.6 wt.% SiO₂). Almost all samples belong to the calc-alkaline, medium-K, and medium-Fe series, and the pumiceous lapilli from the 1952 eruption fall into the low-Fe series. The minerals exhibit signs of magma mingling, including relic high-Ca (up to An₉₂) plagioclase cores with signs of dissolution and recrystallization, and oscillatory-zoned pyroxene.

Veronika Szilágyi, Kata Furholt, Zoltán Kovács et al.

‘Whitestone’ is a characteristic raw material in the Late Neolithic (Tisza and Lengyel culture) polished stone tool (chisel, adze, macehead) archaeological record in Southern Hungary. However, the lithology—the technical term not reflecting a petrographic definition—needs detailed petrographic-analytical investigations (by optical microscopy, PGAA, and SEM-EDS) to determine the exact rock types and to connect them to specific geological sources. This article identifies the main types of ‘whitestone’ and, furthermore, focuses on the predominant ‘silicified magnesite’ type and the secondary ‘silicified limestone/dolomite’ type. Based on our results, both types originated from the alteration of serpentinized ultramafic assemblages, most probably from the closest magnesitic alteration zones of serpentinite outcrops in Serbia. Thus, the most possible provenance of the Late Neolithic ‘whitestone’ polished stone tools is the Serbian magnesite. These lithologies are in the territory of the Late Neolithic Vinča culture, which was engaged in mass production of ‘whitestone’ tools. This fact indicates the strong relationship of that population with the Tisza and Lengyel communities.

Pierre Lanari, Mahyra Tedeschi

Chemical mapping using electron beam or laser instruments is an important analytical technique that allows the study of the compositional variability of materials in two dimensions. While quantitative compositional mapping of minerals has received considerable attention over the last two decades, pixel misclassification in commonly used software solutions remains a fundamental limitation affecting several applications. Calibration of intensity maps to fully quantitative compositional maps requires accurate classification, for example when a calibration curve is applied to a group of pixels that are assumed to have the same matrix behavior under the electron beam or the laser. This paper compares seven automated supervised machine learning classification algorithms implemented in the open source XMapTools software along with various tools for manual classification, for selecting training data and assessing the quality of a classification result. This new implementation aims to provide the research and industry communities with a free software tool for fast and robust classification of chemical maps. A standardized color scheme with reference colors for minerals and mineral groups is proposed to improve the readability of the classified maps in petrological studies. The performance of each algorithm varies depending on the data set, especially when minerals exhibit strong compositional zoning or when different minerals have similar compositions for a given element. The random forest algorithm based on bootstrap aggregation provides satisfactory results in most situations and is recommended for general use in XMapTools.

Anant Aishwarya Dubey, Pelina Toprak, Allan Pring et al.

Abstract Bacterial mineralisation of calcium carbonates (CaCO3) has become a focal point of interest in the scientific community owing to their versatile applications as biomaterials. However, despite extensive research, the knowledge on factors influencing biogenic CaCO3 polymorph (calcite, vaterite or aragonite) selection in nature remains obscure. Bacterial mineralisation happens in nature on diverse substrates by different pathways, often in the presence of organic matter such as biofilm and extracellular polymeric substances (EPS) secreted with the regular metabolic activities of microbes. This study examines the bacterial CaCO3 mineralisation process by two distinct pathways on different natural substrates with advanced analytical techniques, including Time of Flight- Secondary Ions Mass Spectrometry (ToF-SIMS). A high EPS-producing microbe (Bacillus subtilis, BS) was compared with the standard ureolytic strain (Sporosarcina pasteurii, SP). Natural geological minerals, including apatite, calcite and quartz, were selected as substrates. This study demonstrates that SP favours the precipitation of rhombohedral calcite crystals (2 to 40 μm in size), regardless of the mineral substrate. In contrast, the EPS-producing BS culture induced the formation of significantly larger vaterite structures (20 to 100 μm in size) in spheroid and hexagonal shapes. The mineralogy of precipitates was confirmed with Raman spectroscopy. ToF-SIMS enabled the spatial tracking of organic macromolecules and the adsorption of calcium ions on them. The functional groups of the EPS involved in these interactions were characterised by Fourier Transform Infrared Spectroscopy (FTIR). This study reveals that microbial activity dominates over substrate mineralogy in selecting the phase and shaping the morphology of biogenic CaCO3, with EPS playing a crucial role in promoting the aggregation of small nanocrystals into large vaterite structures and their stabilisation.

Mingming Zhang, Jinglin Wen, Zhiming Xu et al.

Abstract Borehole instability in igneous rock formation has attracted more and more attention in recent ten years. In order to understand the mechanism of wellbore instability in igneous formation, a borehole stability model is established by applying the thermal, seepage and stress coupling model combined with a true triaxial rock strength criterion, which can reveal evolution of borehole collapse pressure with time. The effect of drilling cycle on borehole collapse pressure considering the coupling effects of temperature, seepage, and stress is quantitatively analyzed. Results show that, compared with only considering the effect of stress, wellbore collapse pressure increases with the coupling effect of temperature, seepage, and stress. Meanwhile, the stability of wellbore can be enhanced by reducing drilling fluid temperature; with the increase of formation porosity, the borehole collapse pressure increases rapidly, and then remains unchanged or decreases; while with the increase of formation permeability, borehole collapse pressure decreases rapidly, i.e. the shear failure of wellbore is mitigated. Besides, compared with vertical well, the horizontal well is more sensitive to the change of rock permeability. The investigation of drilling cycle shows that, the borehole collapse pressure increased sharply when the formation was drilled instantaneously. However, the subsequent growth trend slows down, which suggests that during the early stages of drilling operation, it is advisable to appropriately increase the mud weight to enhance the wellbore’s support capability by the bottomhole pressure. The research findings can enhance the understanding of the instability mechanism of igneous rock formations and reduce the risk of wellbore instability in igneous rock formations.

Mudiaga Chukunedum Onojake, Nsikan Edet Nkanta, Joseph Onyekwelu Osakwe et al.

Abstract Geochemical and biomarker characteristics of representative crude oil samples from selected fields in southern Nigeria were evaluated to determine the organic matter input, origin of biological material, depositional environment, thermal maturity, and genetic relationship between the oils. Four crude oil samples were obtained from various oil producing fields from Delta, Bayelsa and Abia state in southern Nigeria and labeled Kwale (KW), Kolo creek (KLC), Owaza (OWA1 and OWA2). The crude oil samples were fractionated into saturates, aromatic hydrocarbons and polar compounds using column chromatography on silica gel thereafter, analyzed using Gas chromatography-mass spectrometry (GC–MS). The calculated ratios of normal alkanes, acyclic isoprenoids, carbon preference index (CPI), hopanes, and steranes showed the following results: Pr/Ph (0.34 to 0.89); C29/C27 (0.78 to 1.25); 20S/(20S + 20R)C29sterane (0.28 to 0.66); 22S/(22S + 22R)C32 homohopane (0.17 to 0.23); CPI (0.96 to 0.98); Ts/Ts + Tm (0.46 to 0.50); and sterane/hopane (0.16 to 0.87). The results obtained were used to correlate the crude oils with respect to depositional environment, thermal maturity, and organic matter source. The Pr/Ph ratios of KW and KLC were less than one, and the cross-plot of Pr/nC17 versus Ph/nC18 of KW and KLC suggested that the oils were deposited under anoxic environments, whereas OWA1 and OWA2 indicated oxic conditions with no biodegradation. From the calculated ratios of 22S (22S + 22R)C32 homohopane and CPI, the oils were mature and had entered the generating window. Sample OWA1 is the most mature, while KLC is the least mature. The calculated ratios also showed that the four oil samples were from a shale source rock with both terrestrial and marine inputs.

Soultana Kyriaki Kovaiou, Anastasia Kokkari, George Floros et al.

In recent years, the number of available chemical pesticides has been dramatically reduced, urging the need for the discovery of alternatives to chemical pesticide products such as, among others, natural zeolites (zeolitic rocks). We determined the mineralogical and chemical composition of a specific and continuous layer of zeolitic rock sample (ZeotP) from Petrota, Evros, Greece, and evaluated its oviposition-deterrent effect on the olive fruit fly <i>Bactrocera oleae</i> Gmelin (Diptera: Terphritidae). The tested natural zeolite contained 70 wt. % clinoptilolite, 18 wt. % amorphous material, 7 wt. % feldspars, 4 wt. % cristobalite, and 1 wt. % quartz. We tested the oviposition-deterrent effect of ZeotP mixed or not with an emulsifier adjuvant, NU-FILM-P^®, in water and applied it to the surface of olive fruits. The ZeotP oviposition-deterrent effect on the olive fly was very high under a series of tested temperatures (17 °C, 20 °C, 25 °C, and 30 °C) and RHs (23%, 33%, 55%, 75%, and 94%). In addition, the ZeotP residual deterrent effect after equable water spraying was high, like the respective effect of the pyrethroid insecticide Decis^® (deltamethrin). Our results may contribute to the effective control of the olive fruit fly using an alternative to chemical pesticides: natural zeolite (zeolitic rocks) products.

Matija Perne

For proper cave surveying using DistoX, the device needs to be calibrated with adequate accuracy. Calibrating does not require any tools; but, tools to make calibration easier have been developed. Theoretical consideration shows that the use of certain tools enables one to introduce a type of calibration error that goes undetected by the calibration software. In this study, the existence of such errors is experimentally confirmed and their magnitude is estimated. It is demonstrated to be crucial that the DistoX is calibrated and that the calibration is valid, that is, that the device has not changed since it was last calibrated. No part of the DistoX must have moved or changed its magnetization since calibration, not even the battery. The calibration method used and the quality of the resulting calibration are important too. It is highly recommended that the DistoX be checked immediately before surveying a cave and thus avoid the possibility of using an uncalibrated, not validly calibrated, or poorly calibrated device. To complete the check, a few survey shots are measured multiple times with the device at different roll angles, and the back shot of one of the shots is measured. If the device is properly calibrated, the measurements will agree with each other within the acceptable measurement error. This is not the case for a device that is not properly calibrated.

Alireza Noohnejad, Kaveh Ahangari, Kamran Goshtasbi

Abstract Use of vital geomechanical parameters for determination of safe mud pressure window is generally associated with high level of uncertainty primarily because of absence of sufficient calibration data including laboratory and field test information. The traditional deterministic wellbore stability analysis methodologies usually overlooked the uncertainty of these key parameters. This paper exhibits implementing a quantitative risk assessment technique on the basis of Monte-Carlo modeling to consider uncertainty from input data so as to make it possible to survey not just the likelihood of accomplishing a desired level of wellbore stability at a particular mud weight, but also the impacts of the uncertainty in each single parameter on the wellbore stability. This methodology was implemented to a case study. The most important parameters have been recognized using a sensitivity analysis approach in which the outcome of this QRA procedure suggests the mud weight window with likelihood of well drilling success which can elude the wellbore collapse and lost circulation events. This sort of stochastic approach to deal with anticipated safe mud weight window can guarantee stable wellbore with considerable cost viability associated with drilling success. The technique built up in this paper can give the scientific foundation for assessment of wellbore stability under complicated geological circumstances. It was likewise noted that based on sensitivity analysis, uniaxial compressive strength and maximum horizontal stress are the most effective parameter in estimation of mud weight window. This accentuates the significance of trustworthy determinations of these two parameters for safe drilling of the future wells in the field.

Yousef Kazemzadeh, Behnam Dehdari, Zahra Etemadan et al.

Abstract Nanofluids because of their surface characteristics improve the oil production from reservoirs by enabling different enhanced recovery mechanisms such as wettability alteration, interfacial tension (IFT) reduction, oil viscosity reduction, formation and stabilization of colloidal systems and the decrease in the asphaltene precipitation. To the best of the authors’ knowledge, the synthesis of a new nanocomposite has been studied in this paper for the first time. It consists of nanoparticles of both SiO2 and Fe3O4. Each nanoparticle has its individual surface property and has its distinct effect on the oil production of reservoirs. According to the previous studies, Fe3O4 has been used in the prevention or reduction of asphaltene precipitation and SiO2 has been considered for wettability alteration and/or reducing IFTs in enhanced oil recovery. According to the experimental results, the novel synthesized nanoparticles have increased the oil recovery by the synergistic effects of the formed particles markedly by activating the various mechanisms relative to the use of each of the nanoparticles in the micromodel individually. According to the results obtained for the use of this nanocomposite, understanding reservoir conditions plays an important role in the ultimate goal of enhancing oil recovery and the formation of stable emulsions plays an important role in oil recovery using this method.

Ahmadreza Ejraei Bakyani, Ameneh Taghizadeh, Amir Nematollahi Sarvestani et al.

Abstract A significant percentage of hydrocarbon reservoirs around the world is fractured. Moreover, the major part of gas reservoirs in Iran is also fractured type, so the existence of an in-house software is necessary. In this study, an efficient, user-friendly, and indigenous simulation of a three-dimensional black oil fractured dry gas reservoir has been developed through IMPES method with the two-phase flow of gas and water. The presented simulator, which was written by C++ language and was known as fracture dry gas reservoir simulator, uses the implicit pressure and explicit saturation method for solving the equations. Also, effect of gravity pressure is neglected and effect of the capillary is considered in equations. By this simulator, we can investigate the dry gas reservoirs behavior with fractures. Darcy or non-Darcy fracture and matrix flow, Cartesian, cylindrical, and combination of Cartesian–cylindrical reservoir gridding, single porosity, dual porosity–single permeability, and dual porosity–dual permeability modeling are abilities of this simulator too. Additionally, this simulator is able to make outputs (such as pressure) at any given specific radius and time interval as numerical and/or graphical output in so little run time. Also, this simulator has PVT box and gridding box for doing the calculation of PVT and gridding. PVT box contains new correlations and EOS in comparison with another reservoir simulator. Gridding box makes us be able to simulate fractured dry gas reservoirs and hydraulically fractured well reservoirs too. Finally, the validity of this simulator was verified by comparing the simulation results with the other reservoir simulator (Eclipse) and showed a good compatibility between the developed software and Eclipse results in each time with different conditions such as various gridding conditions, various fluid data conditions and also various well configuration conditions.

Fengrui Sun, Yuedong Yao, Xiangfang Li et al.

Abstract Huge amount of works was done on modeling of gas transport in nanopores (both organic and inorganic) of shale formation. However, the study on oil transport behaviors is quite limited. Based on the study on water transport in carbon nanotubes, an analytical model is developed for oil transport in nanopores of shale formation. The new model takes the effect of oil–wall interaction on the oil viscosity in the adsorption region into consideration. Results show that: (1) the oil–wall interaction on oil viscosity in the adsorption region plays an important role in oil transport behaviors and cannot be neglected; (2) when the critical thickness is smaller than 1 nm, the volume flux increases slowly with increasing contact angle; (3) when the critical thickness increases to 2 nm, the volume flux increases rapidly to infinity when the contact angle is larger than 140°.

Manjeet Kumar, Manjeet Kumari, Mahabir Singh Barak

Abstract The present work deals with the reflection of plane seismic waves at the stress-free plane surface of double-porosity dual-permeability material. The incidence of two main waves (i.e., P 1 and SV) is considered. As a result of the incident waves, four reflected (three longitudinal and one shear) waves are found in the medium. The expressions of reflection coefficients for a given incident wave are obtained as a non-singular system of linear equations. The energy shares of reflected waves are obtained in the form of an energy matrix. A numerical example is considered to calculate the partition of incident energy for fully closed as well as perfectly open pores. Effect of incident direction on the partition of the incident energy is analyzed with the change in wave frequency, wave-induced fluid-flow, pore-fluid viscosity and double-porosity structure. It has been confirmed from the numerical interpretation that during the reflection process, conservation of incident energy is obtained at each angle of incidence.

Michal Šujan, Alexander Lačný, Régis Braucher et al.

Assessment of vertical movements of tectonically bounded blocks is crucial for determination of geohazards in densely inhabited zones, such as the border zone of western Slovakia and eastern Austria. The morphostructure of the Malé Karpaty Mts. divides the Vienna and Danube basins in the Western Carpathian – Eastern Alpine junction, and its neotectonic activity is of high importance. This study was focused on 26Al/10Be burial dating of fluvial sediment in the Stará Garda Cave, located in the central part of the mountains. The structural research revealed predisposition of forming of horizontal passages in low angle to subhorizontal bedrock stratification together with low-grade metamorphic foliation. Fluvial origin of the passages was inferred from mezoscale erosional features on the bedrock as well as from facies character of the well preserved sedimentary profile. Cave sediment was according to petrographic analysis derived from a watershed comparable to recent one of the Stupavský Potok Stream. Three analysed dating samples provided low values of isotopic concentrations, allowing us only to calculate the minimum burial age of the deposit of 1.72 Ma. Assuming the low position of the cave above recent surface streams, resulting maximum incision rate of 26 m/Ma indicates very low uplift of the mountains horst during the Quaternary. The slow incision of the river network  is in good agreement with a widespread preservation of the planation surface called "Mid-mountain level". In contrast are relatively high values of palaeodenudation rates inferred from isotopic concentrations. Generally, our results indicate that the Malé Karpaty Mts. horst underwent relatively intense but short uplift in the Early Pleistocene, followed by very moderate uplift up to the recent. Key words: Western Carpathians, Malé Karpaty Mts., fluvial cave sediment, burial dating, Early Pleistocene, neotectonics. Zgodnja pleistocenska starost fluvialnih sedimentov v jami Stará Garda, ki jo je dala 26Al/10Be datacija: uporabnost za geomorfni razvoj Nizkih Karpatov (Zahodni Karpati) Ocena vertikalnih premikov tektonsko omejenih blokov je ključna za določitev geohazardov v gosto naseljenih območjih. Morfostruktura Malih Karpatov deli Dunajski in Donavski bazen na stičišču Zahodnih Karpatov – Vzhodnih Alp in njegova neotektonska aktivnost je zelo pomembna. Študija se je posvetila 26Al/10Be dataciji fluvialnih sedimentov v jami Stará Garda v osrednjem delu gorovja. Strukturna raziskava je razkrila predispozicijo oblikovanja vodoravnih jamskih rovov pod nizkim kotom v odvisnosti od subhorozontalne stratifikacije kamnine ter tudi z nizko stopnjo metamorfne foliacije. Na fluvialno poreklo rovov smo sklepali iz srednje velikih erozijskih oblik na njihovih stenah kot tudi iz lastnosti faciesov dobro ohranjenega sedimentnega profila. Glede na petrografske analize jamski sediment izhaja iz povodja, ki je primerljiv z recentnim povodjem potoka Stupavský. Trije analizirani vzorci so nam dali nizke vrednosti koncentracij izotopov, ki so nam omogočile le izračun najnižje pokopne starosti sedimenta, ki je znašala 1,72 Ma. Če upoštevamo, da leži jama nizko nad recentnimi vodnimi tokovi, dobimo maksimalno hitrost vrezovanja dolin samo 26 m/Ma, kar kaže na zelo majhen tektonski dvig v času kvartarja. Počasno vrezovanje rečne mreže se dobro ujema s široko ohranjenim uravnanim površjem, imenovanim »Srednjegorska uravnava«. V nasprotju pa so sorazmerno visoke  vrednosti hitrosti paleodenudacije, ki izhajajo iz koncentracij izotopov. Na splošno naši rezultati kažejo, da je bil horst Nizkih Karpatov podvržen relativno močnemu, toda kratkemu dvigovanju v spodnjem pleistocenu, ki mu je sledil zmeren dvig do sedanjosti. Ključne besede: Zahodni Karpati, Nizki Karpati, fluvialni jamski sedimenti, pokopna datacija, starejši pleistocen, neotektonika.

S. Tumiati, C. Tiraboschi, D. A. Sverjensky et al.

Current estimates of dissolved CO2 in subduction-zone fluids based on thermodynamic models rely on a very sparse experimental data base. Here, the authors show that experimental graphite-saturated COH fluids interacting with silicates at 1–3 GPa and 800 °C display unpredictably high CO2 contents.

Somayeh Samiee, Mohammad Hassan Karimpour, Majid Ghaderi et al.

The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma). These rocks have initial 87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.

Janja Kogovšek, Mitja Prelovšek, Metka Petrič

Križna jama and Križna jama 2 are of important natural value. They have been known for more than hundred years from spe­leobiological, paleontological, geomorphological and touristic points of view. In 2007 the establishment of a water treatment plant on Bloke plateau raised important question: can partly cleaned water from the water treatment plant contaminate both caves and decrease their value? To answer this question a tracer test was carried out at the Bloke plateau. It showed gen­eral underground water flow from Farovščica ponor at Bloke plateau toward the Šteberščica spring at Cerknica polje. Mi­nority of recovered tracer appeared at Žerovniščica and Izvir v Podložu springs. The tracer was not detected at Studenec v Ložu and Zlatovec springs. Between ponor and springs three karst caves were observed. The highest concentration of tracer was detected in the cave Mrzla jama pri Bločicah and a much smaller concentration in the Križna jama and Križna jama 2. This shows that at middle water level the underground Farovščica stream does not flow directly through Križna jama and Križna jama 2 but near or below them. Since the tracer ap­peared in both caves only after the precipitation, underground water course can be significantly different at high water level. Tracing test also showed some characteristics of underground water flow through dolomite and characteristics of a composed aquifer with alogenic-autogenic recharge.