Hasil untuk "Petrology"

Javad Ghanei Ardakani, Maryam Ahankoub

IntroductionMineral chemistry has a significant role in determining the stages of magma evolution. Amphiboles, Biotite, plagioclase, and chlorite are minerals whose chemical composition show the temperature and pressure conditions of magma. These minerals are often used for the petrogenesis of granitoid bodies and record the characteristics and geochemical features as well as tectonic conditions of the producing magma (Abdel-Rahman, 1994; Nachit et al., 2005). The granitoid bodies of west Yazd have wide outcrops with different compositions. These rocks are part of the volcano-plutonic belt of Central Iran (Aftabi and Atapour, 2000) with calc-alkaline nature, meta luminous, and mostly of I-type (Hassanzade et al., 2002). The Hamaneh monzogranite bodies, with light color and dark enclaves, are located in 45 km at E53°48ˊ to E53°58ˊ longitude and N31°50ˊ to N31°56ˊ latitude. This area is part of the Shirkuh Mountain in Yazd with a northeast-southwest trend. Hamaneh monzogranite belongs to the Oligocene magmatic activity. In the present research, the mineral chemistry of amphibole, biotite, plagioclase, and chlorite has been investigated to determine the origin and stages of formation and evolution of the magma.Regional GeologyThe studied area geologically located in the middle part of the Urmia-Dokhtar magmatic zonewith a wide collection of Cenozoic magmatic rocks and is characterized by a length of about 2000 km, and a width of approximately 50 to 150 km, parallel to the metamorphosed zones of Sanandaj-Sirjan and Zagros, has a wide collection of Cenozoic magmatic rocks. This area has witnessed extensive magmatic activity in the Cenozoic, especially in the Eocene, which during the Oligocene-Miocene hosted numerous intrusive masses with different ages and compositions (Hassanzadeh et al., 2002). The oldest formation in the region is the green siltstone shale and sandstone of the Kahar Formation. The dolomitic rocks of the Soltanieh Formation are unconformably on the Kaher Formation with purple and cream-colored sand shale layers. The Permian sediments (Jamal Formation) composed of limestone and dolomite layers and the Mesozoic sediments started with a dark unit of volcanic laterite rocks with the Lower Triassic followed by dolomitic rocks belonging to the Otri Formation. The shale and sandstone of the Shemshak Formation are upper Triassic sediments. Cretaceous sediments are exposed in the form of destructive rocks. Upper Triassic (Sangestan Formation) has a variety of conglomerate and conglomerate sandstones with round to semi-round pieces of sandstone and Shirkuh granite. The Paleogene begins with the Kerman Formation conglomerate. Then, there are alluvial cones, alluvial plains, and alluviums of young rivers.Analytical methodsFor the lithology and chemistry of minerals in Hamaneh monzogranite, 20 thin-section samples were selected for chemical analysis of amphibole, plagioclase, biotite, and chlorite minerals and sent to Oklahoma City University laboratory. Microprobe analyses were performed with the Cameca model SX100 device with an accelerating voltage of 15 KV and current intensity of 15 nA. The results of chemical data of amphibole, biotite, feldspar, and chlorite minerals are given in Tables 1 to 4.Petrography and Minerals ChemistryIt is often fine to medium grain texture, granophyric and perthitic texture. The main minerals are orthoclase, plagioclase, and quartz. Orthoclase with an abundance of 25 to 32% is amorphous to semi-amorphous, and plagioclase is a frequency of 24 to 44% that was often as shaped to semi-shaped with zoning. The quartzes are often amorphous and intergranular, and some have wave extinction and fractures with a frequency of 19 to 31. The minor minerals were amphibole, biotite, sphene, zircon, and opaque minerals. Amphibole is green with an abundance of 2.5 to 4.5%, shaped to semi-shaped with a simple twinning. Biotite crystals with an abundance of 2 to 4%. Mineral chemistry of amphiboles was shown as calcic magmatic amphiboles, ranging from magneiso-hornblende and actinolite. Which formed at 530-890℃ and up to 4.3 kbars. That was shown depth 3 to 5.40 km and fO2 (0.5). <Fe#, which corresponds to the calc-alkaline nature in a subduction environment (Anderson, 1996; Rieder et al., 1998). The Hamaneh amphiboles were formed in active continental margins related to subduction. Mineral chemistry of biotites point to a primary biotites that are magmatic and emplaced between annite and phlogopite in the Mg-biotite range. The Hamaneh biotites are I-type indicating the tectonic setting of the calc-alkaline granitoid magmatic series in the subduction zone. Biotites under study were formed at 650-730°C and a pressure of 10-11 to 10-14 kbar. Also, feldspar are (An21 to An32) (Or45 to Or59) orthoclase. The feldspars are of the oligoclase-andesine type, as well as in the feldspar thermometry diagram (Elkins and Grove, 1990; Deer et al., 1991) that was formed in 700 to 800ºC. Based on mineral chemistry, the chlorites are ripidolite and pycnochlorite in composition. Regarding the relatively high iron amount, they have formed at 330 and 360 ºC by alteration of biotite and amphiboles.Discussion and Conclusion The Hamaneh monzogranite, with the main minerals of quartz, orthoclase, plagioclase, amphibole, biotite and secondary minerals of sphene, zircon, and apatite lies in the west of Yazd. The main textures are medium-fine-grained, granophyric, and myrmekite. This body is calc-alkaline and type I. Based on mineral chemistry data, the crystallization of minerals was according to the Bowen series. The calcic amphiboles of magnesio-hornblende to actinolite nature crystallized at 890-530 ℃. Simultaneously with this mineral, oligoclase-type plagioclase to andesine crystallized at 700-800 ℃ and magnesium biotites at 730-650 ℃. Finally, due to secondary alteration, chlorite was formed from the biotite and amphibole developed at a temperature of 330 to 360 ℃ All these minerals point to the mantle nature of the parent magma produced these mineral and have suffered crustal contamination during the ascent. This magma originated at a depth of 3 to 5.5 kilometers, pressure of 0.5 to 4.5 kbars, temperature of 530 to 890 ℃ and at oxidizing conditions. The parent magma of the rocks under study belongs to the subduction structural ground position related to the active continental margin.

Gatot Yuliyanto, Muhammad Irham Nurwidyanto

A microtremor survey based on ground surface data acquisition was used to identify and characterize the karst area of Cerme Cave, Yogyakarta, Indonesia, from the entrance to the exit of the cave. The entrance and exit of the cave are used as tie-in points because the characteristics of the two locations can be directly observed. Parameters used in this study include ground vibration amplification, shear wave velocity, and Poisson’s ratio. The presence of cavities can be characterized by a relatively strong contrast between these physical parameters and their surroundings. The exit of the cave, which can be considered as a sinkhole, has a dominant frequency of 3.2 to 4.6 Hz, which is relatively higher than that of the surrounding area. At the entrance of Cerme Cave, which has a large cavity, a small ground vibration amplification was detected, less than 0.1. The entrance and exit of the cave also exhibit a low shear wave propagation velocity of less than 350 m/s. The presence of a subsurface fluvial channel in Cerme Cave can be characterized by a high Poisson’s ratio of 0.4–0.5, a gain value of less than 0.1, and a shear wave velocity of less than 350 m/s.

Ahmed Farid Ibrahim, Sulaiman A. Alarifi, Salaheldin Elkatatny

Abstract This study proposes the use of different machine learning techniques to predict the estimated ultimate recovery (EUR) as a function of the hydraulic fracturing design. A set of data includes 200 well production data, and completion designs were collected from oil production wells in the Niobrara shale formation. The completion design parameters include the lateral length, the number of stages, the total injected proppant and slurry volumes, and the maximum treating pressure measured during the fracturing operations. The data set was randomly split into training and testing with a ratio of 75:25. Different machine learning methods were to predict EUR from the completion design including linear regression, random forest (RF), and decision tree (DT) in addition to gradient boosting regression (GBR). EUR prediction from the completion data showed a low accuracy. As result, an intermediate step of estimating the well IP30 (the initial well production rate for the first month) from the completion data was carried out; then, the IP30 and the completion design were used as input parameters to predict the EUR. The linear regression showed some linear relationship between the output and the inputs, where the EUR can be predicted with a linear relationship with an R-value of 0.84. In addition, a linear correlation was developed based on the linear regression model. Moreover, the other ML tools including RF, DT, and GBR presented high accuracy of EUR prediction with correlation coefficient (R) values between actual and predicted EUR from the ML model higher than 0.9. This study provides ML application with an empirical correlation to predict the EUR from the completion design parameters at an early time without the need for complex numerical simulation analysis. Unlike the available empirical DCA models that require several months of production to build a sound prediction of EUR, the main advantage of the developed models in this study is that it requires only an initial flow rate along with the completion design to predict EUR with high certainty.

Kazuto Mikuni, Naoto Hirano, Norikatsu Akizawa et al.

Abstract The lithospheric mantle, formed at the mid-ocean ridge as a residue of crustal production, comprises theoretically depleted peridotite, but more fertile components (e.g., lherzolite and pyroxenite) have been reported, creating an enigmatic picture of the lithosphere. The oceanic lithosphere has also been found to be locally modified by intraplate magmatism as proposed from geochemistry of mantle xenolith. Petit-spot xenoliths are particularly notable as direct evidence of old lithospheric mantle and expected to retain essential information about oceanic lithosphere prior to its subduction. In this study, we report on the lithological structure of Pacific lithosphere aged at 160 Ma, just subducting into Mariana Trench, based on petrology and chemistry of ultramafic xenoliths from a petit-spot knoll, and then, we suggest the occurrence of petit-spot melt infiltration resulting in mantle metasomatism and formation of pyroxene-rich vein. Our petit-spot ultramafic xenoliths can be divided into three main types: a depleted peridotite as a residue of crust production, an enriched peridotite, and fertile pyroxenites as the product of melt–rock interactions prior to entrapment. Geothermobarometry also suggests that the depleted peridotite was derived from the uppermost lithospheric mantle, whereas the enriched peridotite and Al-augite pyroxenites were obtained from deeper layers of the lithosphere. Moreover, thermal gradient of the lithosphere estimated from these data is considerably hotter than pristine geotherm estimated on the basis of plate age. Hence, we could illustrate that the oldest portion of the Pacific lithosphere (160 Ma), which was not observed before, was locally fertilized and heated by prior multiple petit-spot magmatic events, and pyroxene-rich metasomatic veins penetrated from the base to the middle/upper lithosphere. Such local lithospheric fertilization is plausible at the plate-bending field, and the nature of Pacific Plate subducting into Mariana Trench may be partly different from what has been assumed so far.

Olga A. Nikitenko , Valery V. Ershov

The paper discusses the directions of hydrogeochemical researches used to solve actual problems of the oil and gas industry: assessment of the oil and gas potential of territories, localization of oil and gas trap, prediction of the phase composition of hydrocarbon fields, control the development process of hydrocarbon fields, etc. Based on the literature data, the analysis and systematization of the main hydrogeochemical indicators of groundwater with oil and gas prospecting significance, as well as used already at the stage of development of oil and gas fields, have been carried out. The most efficiency of the application of hydrogeochemical researches in oilfield practice is achieved with the integrated use of various indicators. On the example of researches of the oil and gas potential of Sakhalin Island, it is shown that the hydrogeochemical data of the middle of the 20th century, obtained by outdated chemical analytical methods, cannot always be considered reliable. In this regard, additional researches are required to update the relevant hydrogeochemical data in this region.

Yixiong QIAN, Chenglin CHU, Yuejun LI et al.

The Neoproterozoic Binggounan Formation mud shale in the Hongliugou Ⅰ section on the northwestern margin of the Altyn Tagh fault was deposited in a passive continental margin. They are shelf sediments about 60 m thick, interbedded with siliceous rocks, undergone a low temperature thermodynamic metamorphism, and had hydrocarbon generation potential. The tectonic background, provenance, weathering and sedimentary environment of the mud shale were discussed with regard to stratigraphic sections, mineralogy and geochemical analyses. The mud shale was mainly composed of silica-rich clay rock and mud-rich siliceous shale, followed by mud-silica mixed shale. They have simila-rities in Si, Mg, K, P, Sc, Y, Hf, Th Sc contents compared with the Post Archaean Australian shale (PAAS). The Ti, Mn, Fe, Ta contents and δEun, δCen, ΣREE values are higher, while the Al, Ca, Na, Nb and Zr contents are lower. The primitive sediment sources of the Binggounan mud shale were recycled sedimentary clasts, intermediate mafic and acid intrusive rocks, similar to a normal shale and arenites argillites and ensialic of continental upper crust in composition. The shale has undergone moderate chemical weathering in warm and humid conditions. The formation was divided into three sedimentary cycles from bottom to top, mainly anaerobic and anoxic, and occasionally oxidized. Hydrothermal alteration also occured in the lower section. The mud shale with a clay content of about 40% is rich in trace elements (REE) and organic matter, which was deposited in a suboxic to anoxic section on the shelf, showing a high productivity and hydrocarbon-generation potential.

Hans-Peter Hubrich, Stephan Kempe

The Harz Mountains in Germany are a south-tilting block of variscan-folded Devonian and Carboniferous rocks thrust over Mesozoic sediment along its northern border. Along the South Harz the overlying, unfolded upper-most Carboniferous, Permian and Buntsandstein (lower Triassic) series are exposed in a wide belt. They include a thick series of Upper Permian (“Zechstein”) evaporitic rocks, dipping with about 10° S to SW, representing a nearly continuous sulfate and carbonate karst area about 90 km long, covering 338 km². In his dissertation, the first author compiled a new geological map for the Zechstein at a scale of 1:10,000 and deduced a tectonic model to advance our understanding of the karstic features. Karstification determines the morphology of the South Harz including over 180 registered caves, thousands of sinkholes, uvalas, sinking creeks and large karstic springs. Specifically, lines of sinkholes appear to follow faults. By detailed mapping of the three lowermost Zechstein cycles, a dense matrix of faults is revealed. 85° to 125° striking faults reoccur every few 500 m, formed during the Harz-lifting compressional phase during the Upper Cretaceous. Many of these faults are reverse with a Nward thrust. This leads to repetitive exposure of the strata, causing the broadening of the Zechstein outcrop beyond what would be caused by the dip of the series alone. In other areas, horstand graben-structures are present, resulting in kilometer-long Lower Buntsandstein ridges. Below ground, the groundwater flowing southward along the dip is diverted into the direction of diachronicalthe strike, thus causing strike-parallel depressions, valleys and sinkhole rows. In the final extension phase, faults striking 150° to 180° have caused graben-structures, allowing groundwater and surface rivers to flow southward, breaking through the escarpment of the overlying Lower Buntsandstein. Therefore, the tectonic structure of the South Harz determines its hydrology and the karst features apparent at the surface. The tectonic situation of the three largest karstic springs, the Salza Spring at Förste, the Rhume Spring, and the Salza Spring at Nordhausen is discussed along with more shallow karstic settings of the Hainholz/Beierstein, the Trogstein and the area of Hainrode.

Jia Jia Leam, Cheng Seong Khor, Sarat C. Dass

Abstract Saybolt color determination is one of the techniques used to evaluate the quality of petroleum products as an indicator of the degree of refinement. As color is a property readily observed by operators, conventional procedures require operators to determine Saybolt color either through direct visual observation or through Saybolt chromometers. These methods are subjective due to the variability in perception of colors across different observers and may be influenced by external factors such as the level of illuminance. Digital oil color analyzers, on the other hand, cost almost four times as much as Saybolt chromometers. An alternative approach to color measurement is to develop a correlation model between Saybolt color with the physical and chemical properties of condensates and light crude oils from Malaysian oil and gas fields. This work applies several multiple linear regression techniques (such as stepwise regression) performed both manually and using the R software (version 3.6.1) to obtain statistically significant results. The step, regsubsets and glmulti functions from R are explored to develop the correlation model which predicts Saybolt color using only identified key properties, overcoming the possible drawbacks associated with conventional laboratory analysis. The models developed through these different techniques are analyzed and compared based on criteria indicated through the coefficient of multiple determination, R 2 and F-tests to infer on suitable regression approaches. Results obtained from these regression methods for models with and without interaction terms report deviations of less than 5% for 75% of the samples used for validation.

Rongda Zhang, Guanghui Yang, Kang Ma et al.

Abstract Worldwide, for older fields that are in the late stages of production period, production wells that lose production value due to high water cut are usually shut down. In this situation, the remaining oil in the reservoir will be re-enriched under the influence of gravity differentiation and capillary forces. Production practices find when the production well is closed for a long time and then opened for restarting production, the water cut drops dramatically and the output rise sharply. In order to anticipate the effects of enrichment of remaining oil in the reservoir, this paper analyzes 10 influencing factors respectively. Secondly, change of water cut before and after shut-in is used as the evaluation index of residual oil enrichment effect. Numerical simulation method is used to simulate the influence of different factors on the effect of external migrations of remaining oil at different levels. Grey correlation analysis is utilized to rank the correlation of 10 factors on residual oil enrichment and then we can get the main controlling factors affecting residual oil enrichment. Finally, the response surface analysis method is used to establish a 5-factor 3-level model, and the corresponding prediction results are obtained through numerical simulation experiments. The main control factors are fitted to obtain the prediction formula of the remaining oil enrichment effect. As a result, we can use the prediction formula to forecast the enrichment effect of remaining oil under different reservoir parameters.

Li Gang Zhang, G. R. Liu, Wei Li et al.

Abstract Steering control algorithm plays an important role in a rotary steerable system for horizontal well drilling, including the determination of the well trajectory, vibrations, stability, durability among other variables. This work develops a control algorithm for three static push-the-bit rotary steerable systems (RSSTSP) (TSP is the abbreviation of “three static push-the-bit”). Based on the structure, mechanism, and working process of the RSSTSP, mechanical and mathematical models are proposed to determine the required steering force (amplitude and direction) to move the drill bit from a point to another. Additional equations are constructed to overcome the non-uniqueness and then compute the optimal forces for the three pads to achieve the required steering force. Moreover, a new control algorithm of RSSTSP is developed, considering the steerability, stability, durability, favorable area, unfavorable area, maximum usable magnitude of steering force. The proposed control algorithm is also applied to a new RSSTSP and tested on a GU-693-P102 well for validation. It is found that each pad force changes smoothly, the drilling tool is stable, and the well trajectory is consistent with the design, demonstrating that our proposed control algorithm is robust and effective for RSSTSP for horizontal well drilling.

L. B. Freeman

Weiqiang Li, Longxin Mu, Taiju Yin et al.

Abstract As the Xingshugang Oilfield is in the late stage of development, a conventional geological model could not meet the needs of further enhancing oil recovery, and the establishment of a fine 3-D geological model, namely the 3-D reservoir architecture model, is urgently required. The 3-D reservoir architecture model has a strong advantage in the detailed characterization of the distribution of various architectural elements and flow baffles and barriers in 3-D space. Based on the abundant data from close well spacing, in combination with the understanding of sedimentary facies and reservoir architecture, this study builds the 3-D reservoir architecture model to show the spatial distribution of different architectural elements and intercalations (mud drapes) under the control of third-, fourth- and fifth-order bounding surfaces. The study then establishes the property model under the control of sedimentary facies (architectural elements). Subsequently, based on the fine 3-D geological model, the distribution of remaining oil is obtained after the numerical reservoir simulation. The remaining oil primarily lies in the port of channel bifurcation, the parts blocked by intercalations and abandoned channels, and the edges of different facies. This observation provides a theoretical basis for further development and adjustment.

Watheq J. Al-Mudhafar

Abstract In this paper, an integrated procedure was adopted to obtain accurate lithofacies classification to be incorporated with well log interpretations for a precise core permeability modeling. Probabilistic neural networks (PNNs) were employed to model lithofacies sequences as a function of well logging data in order to predict discrete lithofacies distribution at missing intervals. Then, the generalized boosted regression model (GBM) was used as to build a nonlinear relationship between core permeability, well logging data, and lithofacies. The well log interpretations that were considered for lithofacies classification and permeability modeling are neutron porosity, shale volume, and water saturation as a function of depth; however, the measured discrete lithofacies types are sand, shaly sand, and shale. Accurate lithofacies classification was achieved by the PNN as the total percent correct of the predicted discrete lithofacies was 95.81%. In GBM results, root-mean-square prediction error and adjusted R-square have incredible positive values, as there was an excellent matching between the measured and predicted core permeability. Additionally, the GBM model led to overcome the multicollinearity that was available between one pair of the predictors. The efficiency of boosted regression was demonstrated by the prediction matching of core permeability in comparison with the conventional multiple linear regression (MLR). GBM led to much more accurate permeability prediction than the MLR.

E. Stolper, H. McSween

Jose Manuel Gil-Márquez, Matías Mudarra, Bartolomé Andreo et al.

The Salinas-Los Hoyos karst system is a geological diapiric structure formed by materials of diverse nature (clays, sandstones, evaporites, volcanic rocks, dolostones, etc.) placed between Malaga and Granada provinces (S Spain). The abundance of evaporite rocks (gypsum, anhydrite and halite) and their high solubility contribute to the development of exokarstic features (dolines, uvalas, sinkholes). Grande and Chica lakes are dolines located in the western border of the diapir that are intersected by the piezometric level. Close to the first wetland is the Aguileras spring, which is the main discharge point of the west sector of the system. To assess the wetland-spring relation and the general functioning of the system, the geomorphologic framework has been analyzed and hydrogeological controls have been performed, consisting in limnimetric and discharge logging and in situ measurements of physico-chemical parameters (EC and water temperature). Furthermore, spring, wetland and rain water samples have been taken for subsequent chemical and isotopic analysis. Preliminary results show that wetland water level and spring discharge follow a similar trend, consistently with the inertia of the system. However, their hydrochemical evolution and isotopic values differ, thus wetland groundwater interaction has not been fully determined. Nevertheless, present research suggests that the hydrogeological connection would be more likely during wet periods, when the water table is at higher altitude. Key words: Evaporitic (karst) aquifer, Hydrological and hydrogeological behaviours, Natural responses, South Spain, Wetlands.

Ivan Gams

V času med eocenom in pliocenom so bile s temena krednega apnenčevega antiklinorija v osrednjem in zahodnem delu planote Kras in s kozinsko-podgrajske antiklinale erodirane flišne plasti, zaradi česar se je ob splošnem zniževanju okoliške ravnine ob pogojih zajezenega krasa razširjal in zniževal ravnik na razkritih apnencih. Največji del planote Krasa predstavlja najstarejši del kraškega ravnika. Na Krasu so se v pliocenu in kvartarju pasovi ravnika hitreje zniževali v smeri proti SZ, vmesno zastajajoče ali dvigujoče se površje pa je s tem dobilo obliko vzpetin na severozahodnem robu planote. Zaradi hitrejšega grezanja vipavske sinklinale so vodni tokovi prenehali teči preko planote Krasa še preden je bil fliš, ki jim je preprečeval pot proti jugu, odstranjen zaradi grezanja severnega dela Tržaškega zaliva. Zaradi tega na Krasu ni slepih dolin ali polj. Pač pa je veliko vrtač, površje je kamnito, zaradi česar je iz Krasa nastal splošni pojem kras. Obe značilnosti sta tipični za submediteranske dinarske kraške ravnike, gosto naseljene in obdelane ter zaradi tega brez gozdov Between Eocene and Pliocene, erosion of flysch strata on the top of Cretaceous limestone anticlinorium in the central and western part of the Kras plateau and the Kozina-Podgrad anticline uncovered and widened – and simultanously lowered - the karst plain in the conditions of dammed karst. The largest portion of Kras plateau is covered with karst plain, its oldest part. In Pliocene, the karst plain was fractured and subsided towards the NW regardless of older folded structure; during this process, several zones of elevations were formed through slower subsiding or uplifting. Due to faster lowering of the Vipava syncline, water streams stopped running over the Kras plateau before the flysch, damming the waters from the Kras plateau to the south was removed due to the subsiding in the northern Gulf of Trieste. Thus, no fossil blind valleys or poljes are found on the Kras plateau. However, there is considerable density of dolines and the surface is stony, giving the karst its original name. Both phenomena are typical of deforrested, densely populated and cultivated Submediterranean Dinaric karst plains.

T. Irvine

J. Moore

Breiter Karel, Broska Igor, Uher Pavel

A unique case of low-temperature metamorphic (hydrothermal) overprint of peraluminous, highly evolved rare-metal S-type granite is described. The hidden Dlhá dolina granite pluton of Permian age (Western Carpathians, eastern Slovakia) is composed of barren biotite granite, mineralized Li-mica granite and albitite. Based on whole-rock chemical data and evaluation of compositional variations of rock-forming and accessory minerals (Rb-P-enriched K-feldspar and albite; biotite, zinnwaldite and di-octahedral micas; Hf-(Sc)-rich zircon, fluorapatite, topaz, schorlitic tourmaline), the following evolutionary scenario is proposed: (1) Intrusion of evolved peraluminous melt enriched in Li, B, P, F, Sn, Nb, Ta, and W took place followed by intrusion of a large body of biotite granites into Paleozoic metapelites and metarhyolite tuffs; (2) The highly evolved melt differentiated in situ forming tourmaline-bearing Li-biotite granite at the bottom, topaz-zinnwaldite granite in the middle, and quartz albitite to albitite at the top of the cupola. The main part of the Sn, Nb, and Ta crystallized from the melt as disseminated cassiterite and Nb-Ta oxide minerals within the albitite, while disseminated wolframite appears mainly within the topaz-zinnwaldite granite. The fluid separated from the last portion of crystallized magma caused small scale greisenization of the albitite; (3) Alpine (Cretaceous) thrusting strongly tectonized and mylonitized the upper part of the pluton. Hydrothermal low-temperature fluids enriched in Ca, Mg, and CO2 unfiltered mechanically damaged granite. This fluid-driven overprint caused formation of carbonate veinlets, alteration and release of phosphorus from crystal lattice of feldspars and Li from micas, precipitating secondary Sr-enriched apatite and Mg-rich micas. Consequently, all bulk-rock and mineral markers were reset and now represent the P-T conditions of the Alpine overprint.

Jordi Rius, Oriol Vallcorba, Carlos Frontera et al.

The synchrotron through-the-substrate X-ray microdiffraction technique (tts-μXRD) is extended to the structural study of microvolumes of crystals embedded in polished thin sections of compact materials [Rius, Labrador, Crespi, Frontera, Vallcorba & Melgarejo (2011). J.Synchrotron Rad. 18, 891–898]. The resulting tts-μXRD procedure includes some basic steps: (i) collection of a limited number of consecutive two-dimensional patterns (frames) for each randomly oriented crystal microvolume; (ii) refinement of the metric from the one-dimensional diffraction pattern which results from circularly averaging the sum of collected frames; (iii) determination of the reciprocal lattice orientation of each randomly oriented crystal microvolume which allows assigning the hkl indices to the spots and, consequently, merging the intensities of the different frames into a single-crystal data set (frame merging); and (iv) merging of the individual crystal data sets (multicrystal merging) to produce an extended data set suitable for structure refinement/solution. Its viability for crystal structure solution by Patterson function direct methods (δ recycling) and for accurate single-crystal least-squares refinements is demonstrated with some representative examples from petrology in which different glass substrate thicknesses have been employed. The section of the crystal microvolume must be at least of the same order of magnitude as the focus of the beam (15 × 15 µm in the provided examples). Thanks to its versatility and experimental simplicity, this methodology should be useful for disciplines as disparate as petrology, materials science and cultural heritage.