Chemical Composition Of Rock-forming Minerals Research Articles

METAMORPHIC TRANSFORMATIONS OF ROCKS IN THE CENTRAL PART OF THE PRIMORSKY FAULT. WESTERN BAIKALIA

In this paper we compare metamorphic transformations in acid and mafic rocks in a zone of intense tectonic movements. The object of study is the exhumed part of damage zone of Primorsky fault – main collision suture, which connects the Siberian Craton and the Olkhon Terrane. The studied area is located near the Khorga River. Collected metamorphic rock samples are represented by both acid (plagiogranitegneiss) and mafic (amphibole-biotite plagiogneisses) rocks. The samples present two different parent rocks contacting each other but differ in chemical composition. The formation of identical metamorphic minerals belonging to the groups of garnet and epidote is noted in both types of rocks. Mineral formation was associated with high-pressure regional metamorphism and possibly with later collision. Studying chemical composition of rock-forming minerals has allowed to determine the P-T condition of metamorphism in these rocks via the method of multimineral thermobarometry. It was established that conditions of early metamorphism retain in amphibole-biotite plagiogneiss. Early metamorphism is characterized by high-pressure amphibolite facies of medium temperature next to eclogite facies. In plagiogranitegneisses were found conditions of later metamorphism that formed rocks at the same pressure but at a lower temperature in the paragonite-kyanite-zoisite subfacies of the eclogite facies next to the greenschist facies. Minerals formed in the early metamorphism are poorly preserved.

Обобщенный опыт изучения и диагностики конвергентных пород на примере карбонатизированных флюидоэксплозивных ультрамафитов дайкового комплекса Среднего Тимана

Fluid-explosive rocks of the dike complex are identified in the Middle Timan. The rocks have convergent properties due to a combination of explosive and metasomatic processes. The study of the petrographic features of the rocks revealed their explosive nature. Further study of the chemical composition of rock-forming minerals established the source of the mantle material and the paragenetic relationship with carbonatite magmatism. The fluid-explosive rocks of the dyke complex have a long-term multistage formation history. The fluids caused fenitization of the host strata and its disintegration. Solid-gas material of the mantle-crustal compound fills the cracks. At the last stage of formation of fluid-explosive rocks, the rare-metal, rare-earth, and sulfide mineralization took place.

X-RAY SPECTRAL MICROANALYSIS OF ROCK-FORMING MINERALS AND IMPURITIES ON AN INCA ENERGY+ SYSTEM INTEGRATED WITH A JSM-6490LV SCANNING ELECTRON MICROSCOPE

The chemical composition and morphology of rock-forming minerals have been studied. The metrological characteristics are evaluated and the results of the electron probe analysis of the chemical composition of rock-forming minerals and impurities in them during the registration of X-ray radiation by spectrometry methods with wave (WDS) and energy (EDS) dispersion are compared. The measurements were performed on an INCA ENERGY + microprobe analysis system (Oxford instruments), consisting of an Inca Energy 450 EDS spectrometer and an Inca Wawe 500 wave dispersion spectrometer installed on a JSM-6490LV (Jeol) scanning electron microscope. The object of the study was a sample prepared from phosphorite nodule (the Kolky formation of the Mohyliv-Podilskyi series of the Upper Vendian of Volyn). It was found that in the range of the content of the main components of minerals (C > 10%), the coefficient of variation characterizing the convergence of a single determination is about 2% when registering radiation by the WDS method and about 2.5% for the EDS method. Accordingly, in the region of the content of minor components (1 < C < 10%), the coefficient of variation is 8 and 10 %, and in the region of component impurities (0.3 < C < 1%), 15 and 25%. With an even lower content, EDS analysis is practically impossible. The study shows that when determining the main and secondary components of rock-forming minerals, the registration methods using EDS and WDS are comparable in accuracy. When determining impurity components, the EDS method is noticeably inferior to the WDS method, and at even lower concentrations it is generally not applicable. The EDS method is easier to implement, works in parallel mode, i.e. analyzes at the same time the analytical lines of all the elements and is able to produce results in a short time after turning on the device. The WDS method requires a significant investment of time in the preparation and implementation of the analysis protocol, but it is capable of conducting analysis with high accuracy and resolution, including when the content of the element being determined is below 1%. The technique described in this work is a generalization of part of the studies conducted by the author on the complex of electron probe analysis equipment at the Institute of Geological Sciences of the National Academy of Sciences of Ukraine.

Chemical composition of the rock-forming minerals in the Onnagawa Formation from Ayukawa oil and gas field, Akita Prefecture, Japan

Chemical compositions of rock-forming minerals in the pelitic rock, the siliceous rock, the felsic tuff, and the dolerite intrusions from the Onnagawa Formation in Ayukawa oil and gas field were compiled, based on their SEM-EDS analysis as basic data. They have been used for geochemical simulations to evaluate the precipitation and the dissolution of mineral in the water-rock interaction systems. The analyzed mineral groups were feldspar, zeolite, carbonate mineral and clay mineral. They seem to have relatively wide variation of their chemistry or to be important minerals in the simulation. This examination also revealed that the mineral described as talc in the former article （Okubo, et al.,1996） is pyrophyllite. Therefore its occurrence and chemical composition is also reported.

Chemical composition of rock-forming minerals and crystallization physicochemical conditions of the Middle Eocene I-type Haji Abad pluton, SW Buin-Zahra, Iran

The Haji Abad intrusion is a well-exposed Middle Eocene I-type granodioritc pluton in the Urumieh–Dokhtar magmatic assemblage (UDMA). The major constituents of the investigated rocks are K-feldspar, quartz, plagioclase, pyroxene, and minor Fe–Ti oxide and hornblende. The plagioclase compositions fall in the labradorite, andesine, and oligoclase fields. The amphiboles range in composition from magnesio-hornblende to tremolite–hornblende of the calcic-amphibole group. Most pyroxenes principally plot in the field of diopside. The calculated average pressure of emplacement is 1.9 kbar for the granodioritic rocks, crystallizing at depths of about 6.7 km. The highest pressure estimated from clinopyroxene geobarometry (5 kbar) reflects initial pyroxene crystallization pressure, indicating initial crystallization depth (17.5 km) in the Haji Abad granodiorite. The estimated temperatures using two-feldspar thermometry give an average 724 °C. The calculated average temperature for clinopyroxene crystallization is 1090 °C. The pyroxene temperatures are higher than the estimated temperature by feldspar thermometry, indicating that the pyroxene and feldspar temperatures represent the first and late stages of magmatic crystallization of Haji Abad granodiorite, respectively. Most pyroxenes plot above the line of Fe3+ = 0, indicating they crystallized under relatively high oxygen fugacity or oxidized conditions. Furthermore, the results show that the Middle Eocene granitoids crystallized from magmas with H2O content about 3.2 wt%. The relatively high water content is consistent with the generation environment of HAG rocks in an active continental margin and has allowed the magma to reach shallower crustal levels. The MMEs with ellipsoidal and spherical shapes show igneous microgranular textures and chilled margins, probably indicating the presence of magma mixing. Besides, core to rim compositional oscillations (An and FeO) for the plagioclase crystals serve as robust evidence to support magma mixing. The studied amphiboles and pyroxenes are grouped in the subalkaline fields that are consistent with crystallization from I-type calc-alkaine magma in the subduction environment related to active continental margin. Mineral chemistry data indicate that Haji Abad granodiorites were generated in an orogenic belt related to the volcanic arc setting consistent with the subduction of Neo-Tethyan oceanic crust beneath the central Iranian microcontinent.

Exotic Olivine-Mica Rocks from the Udachnaya-East Pipe (Yakutia): Features of the Chemical Composition and Origin

The chemical composition of rock-forming minerals from unusual olivine-mica rocks from the Udachnaya-East kimberlite pipe (Yakutia) was studied. It is shown that all these rocks were formed as a result of the influence of deep metasomatic fluids. Two ilmenite-bearing rocks show the similarity to polymict breccia genetically representing analogs of protokimberlite melts, which did not reach the Earth’s surface. Two other rocks (one with K-bearing amphibole, another with clinopyroxene) are most likely rocks from the zones of high permeability, which were formed upon consolidation of the Siberian Craton and were subjected to the influence of aggressive fluids from the early portions of the protokimberlite melt.

МИНЕРАЛОГИЯ ЩЕЛОЧНЫХ ПИКРОБАЗАЛЬТОВ ХРЕБТА ХЭНТЕЙ (ЮЖНОЕ ЗАБАЙКАЛЬЕ)

The purpose of the paper is to determine the crystallization order of rocks based on the study of the mineralogical and petrographic composition of the Khentei Range Cenozoic basaltoids. Methods. A microprobe X-ray spectral analysis by means of the JXA-8200 tool (JEOL Ltd., Japan) has been used in the study. Results. The research results in the determination of chemical compositions of rock-forming minerals and the sequence of minerals formation. Conclusions. Melt movement to the surface was accompanied with the capturing of mantle xenoliths. Olivine and pyroxene of the first generation were formed first, then, olivine and pyroxene of the second generation were formed, as well as oxide bearing minerals. Plagioclase, potassium feldspar, nepheline and leucite were crystallized last from the interstices. The presence of residual glass has also been noticed in the interstices.

Mineral composition of alkaline lamprophyres of the Tomtor massif as reflection of their genesis

The influence of parental melts on the chemical composition of rock-forming minerals of alkaline lamprophyres (monchiquites) referred to as the volcanic series of porphyritic potassic alkaline-ultrabasic rocks was studied in the Tomtor alkaline-ultrabasic carbonatite massif (Yakutia) hosting a unique deposit of Sc-REE-Y-Nb ores. Previous fluid-melt inclusion study showed that these rocks formed from two mixing alkaline-basic melts of different alkalinity. A detailed study of the chemical composition of minerals revealed a repeated irregular zoning in most of phenocrysts, which reflects the influence of different parental magmas and their mixing. It was established that the cores of diopside phenocrysts (Di I) with inclusions of Na-Fe-rich silicate melts have a low Mg-number and low contents of Ti, Al, and Ca and high contents of Na and Mn. The intermediate zones of phenocrysts (Di II) containing inclusions of K-Mg-rich silicate melts show a high Mg-number and are rich in Ti and Al and poor in Mn and Na. Groundmass grains and rims (and, sometimes, intermediate zones) of diopside phenocrysts often have a mixed Di I-Di II composition with slightly elevated contents of Mg, Ti, and Al. Amphibole phenocrysts, like the diopside ones, have both zones with low Mg contents and high Na/K ratios and Mn contents and zones with high Mg contents, low Na/K ratios, and low Mn and elevated Ti contents. Phlogopites are also of two varieties: highly magnesian, with high contents of Si and K and low content of Mn, and lowly magnesian, with low contents of Si and K and high content of Mn. Ilmenite, titanomagnetite, and fine grains of femic minerals are mostly of mixed varying composition. The chemical composition of rock-forming minerals, especially zoned phenocrysts, evidences that they crystallized with the participation of two alkaline-basic melts: Na-Fe-rich silicate melt enriched in Mn and K-Mg-rich silicate melt enriched in Ti but depleted in Mn.

Chemical composition of rock-forming minerals in granitoids associated with Au–Bi–Cu, Cu–Mo, and Au–Ag mineralization at the Freegold Mountain, Yukon, Canada: magmatic and hydrothermal fluid chemistry and petrogenetic implications

The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au–Bi–Cu–As deposit, Revenue Au ± Cu and Stoddart Cu–Mo ± W mineral occurrences, and Laforma Au–Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4–91% Or), whereas plagioclase spans a wide range (4.4–70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu–Mo ± W, Laforma Au–Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au–Bi–Cu–As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10–13 and 10–11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8–7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6–2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520–780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu–Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au–Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.

Neoproterozoic mafic-ultramafic layered intrusion in Quruqtagh of northeastern Tarim Block, NW China: Two phases of mafic igneous activity with different mantle sources

In this paper we report zircon U–Pb age, chemical compositions of rock-forming minerals, and whole-rock elemental and Sr–Nd isotopic data for the No. II mafic-ultramafic intrusive complex (N2MC) in the Quruqtagh area at the northeastern margin of the Tarim Block, northwestern China to evaluate its petrogenesis and tectonic significance. The N2MC with an exposure area of ca. 12 km 2 has a funnel-shaped cross-section and intruded the Paleoproterozoic basement. U–Pb zircon dating gives a crystallization age of 760 ± 6 Ma. Rock types of the N2MC include lherzolite, pyroxenite, gabbro and minor diorite. Major elements geochemistry of these rocks exhibits a tholeiitic trend with a wide range of SiO 2 contents (38.8–60 wt.%). On the other hand, they are systematically enriched in LILE, LREE and depleted in HFSE and HREE, thus leading to low HFSE/LREE ratios (e.g., Nb/La ≈ 0.3). Isotopically, the studied rocks are characterized by negative whole-rock εNd( t) values (− 7.6 to − 2.8) and variable high ( 87Sr/ 86Sr) i (0.7095–0.7059). These features, together with chemical compositions of the rock-forming minerals and the presence of the primary phlogopite and hornblende, suggest that N2MC was likely formed via crystal fractionation/cumulation (with negligible crustal contamination) of a tholeiitic magma derived from a metasomatized subcontinental lithosphere mantle (SCLM) in an extensional environment. The enrichment of the mantle source could be ascribed to the metasomatism by subducted-slab-released fluids before partial melting. Overall, reported Neoproterozoic igneous rocks throughout the Tarim Block constitute two major phases of Neoproterozoic igneous activities, i.e., ca. 825–800 Ma and ca. 780–745 Ma, respectively. Similar to that of many other Rodinian continents, this feature is interpreted to be related to the two phases of Neoproterozoic mantle plume activity under the Rodinia. Furthermore, there exist two types of mafic-ultramafic complex at Quruqtagh, i.e. , the ca. 820 Ma carbonatite-bearing and the ca. 760 Ma tholeiitic, which could reflect the presence of two different mantle sources.

Alkaline gabbroids of the Chirii outcrop (North Minusa depression): mineralogy and melt evolution

We studied the chemical composition of rock-forming minerals in gabbroids from the Chirii outcrop and the evolutionary features of parental basic melt during the crystallization of these rocks. Results were compared with data for basanites from pipes of the North Minusa depression. The mineralogical composition and thermobarogeochemical data of the gabbroids were examined in detail, and chemical analyses of rock-forming minerals (clinopyroxene, plagioclase, amphibole, biotite, titanomagnetite, and apatite) were carried out. Based on the homogenization temperatures of primary melt inclusions, we established the minimum temperatures and sequence of mineral crystallization in the gabbroids: clinopyroxene (>1160 °C), plagioclase, magnetite → amphibole (>950 °C) → biotite. The rock crystallization proceeded at shallow depths. Thermometric data are confirmed by results of modeling of equilibrium gabbroid crystallization. The crystallization of parental basic melt was accompanied by the accumulation of SiO 2, Al 2O 3, alkalies, and Cl and depletion in femic components. The melt evolved to granodiorite and alkali-syenite compositions. Compared with basanites from pipes, the parental melt had a longer evolution. The geochemical features of the gabbroids indicate that they, like basanites, crystallized from intraplate alkali-basaltoid magmas. But in petrochemistry and mineralogy the Chirii gabbroids differ considerably from the pipe basanites.

Chemical composition of rock-forming minerals in gold-related granitoid intrusions, southwestern New Brunswick, Canada: implications for crystallization conditions, volatile exsolution, and fluorine-chlorine activity

Chemical composition of rock-forming miner- als in Appalachian Siluro-Devonian granitoid intru- sions, southwestern New Brunswick, was systematically determined by electron microprobe. The mineral chem- ical data together with petrographic examination was used to test magmatic equilibration and to constrain crystallization conditions, volatile exsolution, and fluo- rine-chlorine activity of fluids associated with these intrusions. Mineralogical distinction between Late Silu- rian to Early Devonian granodioritic to monzogranitic series (GMS) and Late Devonian granitic series (GS) rocks is evident, although both are subsolvus I-type to evolved I-type granitoids. Oxidized to reduced GMS rocks consist of quartz, plagioclase (An>10), K-feld- spar, biotite, apatite, titanite, zircon, monazite, ± hornblende, ± pyroxene, ± magnetite, ± ilmenite, and ± sulfide. GS rocks comprise quartz, K-feldspar, pla- gioclase (An<10), mica group minerals, zircon, mon- azite, apatite, sulfide, ± ilmente, ± magnetite, ± topaz, ± columbite, and ± xenotime. Inter-intrusion and intra-intrusion variations in mineral chemistry are in- terpreted to reflect petrogenetic processes (e.g., assim- ilation and fractional crystallization) during granitoid evolution. Although magmatic equilibration among rock-forming minerals are disturbed by subsolidus hy- drothermal processes, GMS rocks appear to have higher magmatic temperatures, variable levels of emplacement, a range of fO2 (i.e., reduced intrusions 10 � 16.7 � 10 � 13.4 and oxidized intrusions 10 � 14.0 � 10 � 10.5 bars), and rela- tively low fHF/fHCl ratios (10 � 3.0 � 10 � 1.0 ) in exsolved fluids, compared to GS rocks. Reduced GMS intrusions bear higher gold potential and thus may be prospective targets for intrusion-related gold systems.

Hercynian granites and metamorphic rocks from the Mts. Papuk, Psunj, Krndija, and the surrounding basement of the Pannonian Basin in Slavonija (Northern Croatia, Yugoslavia)

Hercynian crystalline complex of the Slavonian Mountains and surrounding basement of the Pannonian Basin comprises the following units: (1) anchimetamorphic and very low-grade metamorphic rocks with metabasic igneous rocks, (2) Progressive metamorphic succession of greenschist and amphibolite facies, (3), migmatites, (4) S-type granitoids, and (5) I-type granitoids. In the paper is presented a petrological interpretation for each of the mentioned unit which is based on Chemical composition of rock-forming minerals, petrographical and geochemical data including major and trace element contents, REE, and O and Sr isotopic composition. Numerous geochemical and petrochemical diagrams are presented for all these rock groups as the basis for detailed genetic and geotectonic considerations.