Basic Igneous Rocks Research Articles

Structural style and kinematics of the Taihang-Luliangshan fold belt, North China: Implications for the Yanshanian orogeny

AbstractThe Middle–Late Jurassic to earliest Cretaceous fold belts of the Yanshanian orogen in North China remain enigmatic with respect to their coeval deformation histories and possible relationship to the contemporaneous Cordilleran-style margin of eastern Asia. We present geological mapping, structural data, and a >400-km-long, strike-perpendicular balanced cross section for the Taihang-Luliangshan fold belt exposed in the late Cenozoic central Shanxi Rift. The northeast-southwest–trending Taihang-Luliangshan fold belt consists of long-wavelength folds (∼35–110 km) with ∼1–9 km of structural relief cored by Archean and Paleoproterozoic metamorphic and igneous basement rocks. The fold belt accommodated ≥11 km of northwest-southeast shortening between the Taihangshan fault, bounding the North China Plain, in the east and the Ordos Basin in the west. Geological mapping in the Xizhoushan, a northeast-southwest–oriented range within the larger Taihangshan mountain belt, reveals two major basement-cored folds: (1) the Xizhou syncline, with an axial trace that extends for ∼100 km and is characterized by a steep to overturned forelimb consistent with a southeast sense of vergence, and (2) the Hutuo River anticline, which exposes Archean–Paleoproterozoic rocks in its core that are unconformably overlain by shallowly dipping (<∼20°) Lower Paleozoic rocks. In the Luliangshan, Mesozoic structures include the Luliang anticline, the largest recognized anticline in the region, the Ningjing syncline, which preserves a complete section of Paleozoic to Upper Jurassic strata, and the Wuzhai anticline; together, these folds are characterized by a wavelength of ∼45–50 km. Shortening in the Taihang-Luliangshan fold belt is estimated to have occurred between ca. 160 Ma and 135 Ma, based on the age of the youngest deformed Upper Jurassic rocks in the Ningjing syncline, previously published low-temperature thermochronology, and regional correlations to better-studied Yanshanian fold belts. The timing of basement-involved deformation in the Taihang-Luliangshan fold belt, which formed >1000 km from the nearest plate margin, corresponds with the termination of arc magmatism along the eastern margin of Asia, implying a potential linkage to the kinematics of the westward-subducting Izanagi (paleo-Pacific) plate.

Early Messinian manganese deposition in NE Cyprus related to cyclical redox changes in a silled hemipelagic basin prior to the Mediterranean salinity crisis

Unusual bedded manganese deposits occur within hemipelagic carbonates, dated as early Messinian (<6.82 Ma but >5.97 Ma) based on calcareous nannofossils. These sediments accumulated during a time of increased isolation of the Mediterranean Sea from the Atlantic Ocean but prior to major sea-level fall and evaporite precipitation during the Messinian salinity crisis. The manganese deposits form six main laterally continuous beds (up to 70 cm thick). Compositionally, they are dominated by poorly crystalline manganese oxide (birnessite), with associated mild enrichment in some trace elements (e.g., Ba, Ni, Cu, Mo, As, U). Background minerals include magnesian carbonate, kaolinite, chlorite, mixed-layer clays and talc (serpentinite-derived). A tectonically controlled deep-water basin existed to the south of a topographic ridge (future Kyrenia Range) in which seawater alternated between oxidising and oxygen-depleted at depth. Orbital precession influenced the weathering of continental source areas that included basic igneous rocks and some pre-existing hydrothermal deposits. After entering the basin via land runoff, manganese was retained in solution below the chemocline during stagnant low-oxygen periods. Manganese oxide and associated trace elements (e.g., Mo, U) precipitated in response to cyclical seawater oxidation to form manganese-rich layers up to layers with up to with up to c. 30% MnO. To reach these very high concentrations, soluble manganese may have fluxed upwards from an anoxic environment represented by early Messinian sapropels. Manganese precipitation events diminished with time giving way to well-oxygenated hemipelagic marl accumulation with a shelly infauna. Gypsum appears abruptly upwards above the marls in adjacent sections. The Mn deposition mainly represents an interplay between tectonically-controlled basin formation, chemically favourable source climatic conditions, possible sea-level change effects and likely diagenetic manganese enrichment. The regional tectonic setting relates to early-stage collision of the African and Tauride (Eurasian) plates.

Geochemical assessment of claystone deposits from the Patti Formation, Southern Bida Basin, Nigeria

Abstract Geochemical studies of claystone deposits from the Patti Formation in the southern Bida Basin, north-Central Nigeria, were carried out on representative samples to determine the basin’s depositional conditions, provenance and tectonic setting. The localities within the study area included Gegu, Ahoko, Ahoko-Etigi, Omu and Idu. Semi-quantitative phase analysis using the Rietveld method and X-ray powder diffraction data revealed that the claystone samples had prominent kaolinite with other constituents such as quartz, illite–muscovite, K-feldspar, pyrite, marcasite, anatase, rutile and gorceixite. Enrichment of Al2O3, Ba, Th, Sr, Cr and La suggests that these elements are primarily controlled by the dominant clay minerals. Geochemical parameters such as U, U/Th, Ni/Co, V/Cr and Cu/Zn ratios strongly implied that these claystones were deposited in an oxidising environment. Provenance deducing ratios for felsic, mafic and basic igneous rocks were compared. Al2O3/TiO2 ratio suggested intermediate to felsic rocks as the probable source rocks for the claystone samples; however, Y/Ni, Cr/V, La/Sc and Th/Sc ratios suggested a felsic progenitor. The tectonic discrimination diagram showed that the samples’ plot was within the region specified for passive margin-type tectonic setting.

Tectonothermal Records in Migmatite-Like Rocks of the Guandi Complex in Zhoukoudian, Beijing: Implications for Late Neoarchean to Proterozoic Tectonics of the North China Craton

Migmatite-like rocks transformed from strongly metamorphosed and deformed enclave-bearing felsic plutons usually make people confuse with the true migmatites and mistake in interpretation of their petrogenesis and tectonic implications. Here we report a suite of rocks that have long been called as migmatites from the Guandi complex in Zhoukoudian region, southwest of Beijing. The rocks are dominated by felsic gneisses with garnet-free amphibolites. Field occurrence, petrography and geochemistry indicate that the felsic gneisses and amphibolites were metamorphosed from protoliths of intermediate-acid and basic igneous rocks, respectively. New LA-ICP-MS zircon U-Pb dating and geothermobarometry study further reveal that precursor magmas of the two types of rocks were emplaced at 2.54-2.56 Ga and the rocks subsequently underwent medium P / T -type metamorphism with upper amphibolite facies conditions of 0.55-0.90 GPa and 670-730℃ at~2.48-2.50 Ga. Geochemically, precursor magmas of the amphibolites were suggested to be derived from an enriched lithospheric mantle source in continental arc setting, and those of the felsic gneisses are characterized by tonalitic to trondhjemitic magmas that are usually considered to be generated by partial melting of hydrated, thickened metamorphosed mafic crust with garnet as residues, suggesting that the rock associations are not of true migmatites but migmatite-like rocks. Our study reveal that protoliths of the migmatite-like rocks from the Guandi complex, were likely formed via magmatism in a continental arc setting, followed by accretion and collision of the continental arc as well as the intro-oceanic arc terranes to the Eastern Block of the North China Craton in the transition from the Late Neoarchean to Early Paleoproterozoic.

On Electrical Conductivity at Depth in the Shanuch Copper–Nickel and the Aginskoe Gold-Ore Fields, Kamchatka

This paper is concerned with the method of interpretation and with the results of magnetotelluric sounding (MTS) along the line connecting the Shanuch copper–nickel and the Aginskoe gold ore deposit. The interpretation revealed that the upper section divides into two blocks according to the electrical resistivity. The western block has a high resistivity, which is due to the metamorphic and igneous basement rocks that are exposed at the ground surface. The eastern block has a low resistivity, which is due to the presence of a conductive sedimentary–volcanogenic cover involving a wide network of discontinuities. A low resistivity layer was identified at depths of 30–60 km. The deep-seated faults that have been identified by interpretation in the eastern block penetrate through the lithosphere as far as the conductive layer; fluids can move along these faults upward into the upper crust where at lower temperatures they release minerals whose accumulations make up ore deposits of nonferrous and noble metals.

Estimating engineering properties of igneous rocks using semi-automatic petrographic analysis

An experimental study that contributes to the understanding of the relationships between petrographic features and engineering properties of igneous rocks is conducted. To this end, a wide range of igneous rocks were tested for their engineering properties including abrasivity (Cerchar abrasivity index), mechanical (point load strength index Is(50)), basic physical (dry density and porosity) and dynamic (P-wave velocity) characteristics. Moreover, a semi-automatic method has been developed to analyze petrographic data that relies on digital image acquisition from representative parts of representative thin sections of samples, semi-automatic image segmentation and image analysis. The method quantifies 18 petrographic features including size descriptors (area, perimeter, equivalent circular diameter, minimum Feret’s diameter, maximum Feret’s diameter), shape descriptors (elongation, orientation, eccentricity, compactness, rectangularity, solidity, convexity), rock fabric coefficients (index of interlocking, index of grain size homogeneity, texture coefficient) and mineralogical indices (saturation index, feldspathic index, colouration index). The Pearson’s correlation coefficient and multivariate regression analysis are employed to analyze the relationships between extracted petrographic features and engineering properties. In general, fine-grained and basic igneous rocks compared to the acidic and coarse-grained ones possess higher engineering quality and lower abrasiveness potential. The results imply that mineralogical composition tends to be more important than rock fabric characteristics in determining the engineering properties of igneous rocks. Furthermore, among rock fabric characteristics, size descriptors have significant influence on the engineering properties. Overall, it was found that mineralogical composition and rock fabric characteristics provide a suitable complement to reliably predict engineering properties of igneous rocks.

Provenance and Palaeoweathering Attributes of Proterozoic Rock Formations from the Son Valley, Central India

The characteristics of source rocks and weathering of Palaeoproterozoic phyllitic rock of Mahakoshal Group and Mesoproterozoic shales and siliciclastics of Vindhyan Supergroup exposed in Son Valley, Central India have been investigated by analyzing their chemical compositions. The investigations pertaining to the relationship between major-elements were carried out along Parshoi, Chitrangi, and Markundi areas of Son valley, Central, India. The studied rock strata have been classified into three categories namely phyllitic rocks, shales and sandstone. The A-CN-K ternary diagram, CIW, CIA, MIA, and ICV values indicate about the similar provenance or source rocks subjected to severe chemical weathering, under dry and hot-humid climates in a basic and acidic environment with changing lower to higher PCO2 of continental flora. Various geochemical discriminantts diagrams, elemental ratios suggest that rocks are derived from post-Archaean-Proterozoic igneous source. The igneous source was mainly granite with a minor contribution of granodioritic rock, in a passive margin setting. The sediments responsible for formation of shale and sandstones were most likely deposited in the interglacial period in between the Mesoproterozoic and Neoproterozoic glacial times. Compositionally the sandstones is distinctive of cratonic environments with their passive continental margin setting. However, the phyllities of Mahakoshal Group suggests their formation under lower weathering conditions in dry climatic conditions which were operating on more intermediate to basic igneous rocks with abundance of mafic minerals.

Geochemistry of heavy minerals and U–Pb detrital zircon geochronology in the Manantiales Basin: Implications for Frontal Cordillera uplift and foreland basin connectivity in the Andes of central Argentina

The Manantiales Foreland Basin, located at ~32°15′S in the Frontal Cordillera, Argentina, contains the sedimentary record of erosion of igneous basement and Miocene volcanic rocks exhumed during the Andean orogeny. U–Pb ages of detrital zircons from the basin fill succession (Chinches Formation) constrain the onset of deposition to ca. 22Ma (early Miocene). We present the first geochronological control (ca. 22Ma) from the lower part of the Manantiales Foreland Basin (Areniscas Chocolate member) on the basis of U–Pb ages of detrital zircons, shedding light about an older initiation of this foreland basin. The main heavy mineral association in the sedimentary basin, clinopyroxene+amphibole, indicates two events of volcanic supply, probably corresponding to the Farellones Formation in the Principal Cordillera, and the La Ramada Volcanic Complex and subvolcanic rocks similar to the La Laguna body in the Argentinean Frontal Cordillera. Detrital zircon geochronology indicates dominant sourcing from upper Paleozoic–lower Triassic Choiyoi Magmatic Province rocks. Initial sediment supply at ca. 22–19Ma was from the Cenozoic volcanic arc of the Principal Cordillera. At ca. 19Ma, exhumation of the Frontal Cordillera was registered by supply from the Choiyoi Magmatic Province, related to tectonic uplift of a western block (La Ramada–El Espinacito ranges) through a thrust of the La Ramada fold-and-thrust belt. At ca. 16Ma, supply from the Cenozoic volcanic arc recommenced, providing evidence for capture and erosion of the Principal Cordillera, which could be related to thrusting in normal sequence of the La Ramada fold-and-thrust belt. At ca. 10Ma, the La Ramada Volcanic Complex and rocks similar to the La Laguna subvolcanic body became a local source of sediment for the basin. The Manantiales Foreland Basin was linked to Neogene sedimentary basins in the Precordillera at its first part in its history, between ca. 22 and 19Ma and probably until ca. 12Ma, when the eastern Frontal Cordillera (Cordillera del Tigre) and Precordillera were uplifted, and the foreland basin was broken. Thus, the Frontal Cordillera was uplifted through two diachronous thick-skinned blocks from west (La Ramada–El Espinacito ranges) to east (Cordillera del Tigre). This result can explain the diverse ages for uplift deduced for the Frontal Cordillera in previous studies, where it has been considered rather as a singular N-S block. The source of late Mesoproterozoic detrital zircons registered in the Manantiales Basin is uncertain, but we infer recycling from Mesozoic sedimentary rocks of the Principal Cordillera.

Study of aeromagnetic anomalies of Idah and Angba areas, north central Nigeria, using high resolution aeromagnetic data

Aeromagnetic data of Idah and Angba environs, north central Nigeria, has been interpreted by applying spectral analysis and forward and inverse modeling methods. Quantitatively, spectral analysis and forward and inverse modeling techniques were employed in interpretation with the aim of determining depth/thickness of the sedimentary Basin and magnetic susceptibilities that give clue on the type of mineralization prevalent in the area. The result from spectral analysis revealed two main magnetic anomaly source depths; deep magnetic anomaly source and the shallow magnetic anomaly source. The deep magnetic anomaly source varies between 2.194 and 6.764 km with an average depth value of 5.014 km which represents the depth to sedimentary thickness. The shallow anomaly source varies from 0.597 to 1.592 km with an average depth value of 1.093 km and these were observed within the basement region. Forward and inverse modeling estimated depths for profiles 1–5 were 526, 461, 4347, 1751, and 6847 m, respectively, with respective susceptibility values of 0.0003, 0.0879, 0.0800, 0.0004 and 0.0700 which indicate intermediate and basic igneous rocks (diorite, andesite and gabbro or basalts) and basic sedimentary rocks (sandstone and limestone). The maximum depths obtained from these two applied methods show sufficiently thick sediments suitable for hydrocarbon generation and accumulation.

The formation of the giant Bayan Obo REE-Nb-Fe deposit, North China, Mesoproterozoic carbonatite and overprinted Paleozoic dolomitization

The Bayan Obo ore deposit in Inner Mongolia, North China, the largest-known rare earth element (REE) deposit in the world, is closely associated with carbonatite dykes. Scarce zircon grains, with a wide range of ages and diverse origins, have been extracted from the Wu dyke, a REE-enriched calcitic carbonatite dyke 2 km from the East Ore Body of the Bayan Obo deposit. Three zircon populations were identified based on ages and trace element compositions: 1) Captured zircons with Paleoproterozoic and Archean ages. These zircons have REE patterns and moderate Th/U ratios similar to zircon with silicate inclusions from basement igneous rocks, which have been recognized as contaminants from wall rocks. 2) Carbonatite magmatic zircons with Mesoproterozoic ages. These zircons have high to extremely high Th/U ratios (13–1600), a characteristic signature of the Bayan Obo deposit. Two zircon grains yielded concordant 206Pb/238U ages (1.27 ± 0.11 Ga ∼ 1.42 ± 0.18 Ga) and 208Pb/232Th age (1.26 ± 0.20 Ga) with calcite inclusions, indicating that the Wu dyke was emplaced at ca. 1.34 Ga, which coincides with a worldwide generation of Mesoproterozoic kimberlites, lamprophyres, carbonatites, and anorogenic magmatism. 3) Hydrothermal zircons with Caledonian and Triassic ages. The Caledonian zircon has 206Pb/238U age of 381 ± 4 Ma and 208Pb/232Th age of 367 ± 14 Ma with dolomite inclusion. These evidences are consistent with multiple stages of mineralization, Mesoproterozoic calcite carbonatite magmatism interacted by protracted fluxing of subduction-released Caledonian fluids during the closure of the Palaeo-Asian Ocean, coupled with interaction with the mantle wedge and metasomatism of overlying sedimentary carbonate.

First evidence of prehistoric eclogite quarrying for polished tools and their circulation on the Iberian Peninsula

AbstractThis research provides the first evidence of prehistoric quarrying of eclogitic rocks on the Iberian peninsula. Such metamorphosed basic igneous rocks are known to have been used in southern Spain and Portugal during late prehistory as a raw material for the making of polished lithic tools (axes, adzes, chisels, and hammers). These rocks were widely used primarily because of their tolerance to blow and friction due to their mineralogical and textural characteristics. We have identified two quarries within the Sierra de Baza Natural Park (Granada), in the Betic Cordillera of southern Spain: Rambla del Agua and Cerro de San Cristóbal. The bedrock geology of these quarries forms part of the Mulhacen Complex Ophiolite Unit (Nevado‐Filábride Domain), which discontinuously outcrops along a 250‐km belt in southeastern Spain. Petrographic and geochemical analyses were conducted on raw materials from quarries in the Sierra de Baza and compared with archaeological materials from different sites in southern Iberia. These analyses allow us to specify the Nevado‐Filábride‐derived lithic source and define exchange networks. Archaeological sites around the studied quarries chronologically date their use between the early Neolithic and Bronze Age (∼5500–1500 B.C.).

Lead and sulfur isotope composition of trace occurrences of Mississippi Valley-type mineralization in the U.S. midcontinent

Mississippi Valley-type (MVT) Zn-Pb mineralization in the U.S. mid-continent has formed in numerous widely dispersed trace occurrences and in a few large ore deposits that have been mined. Based on similarly high fluid inclusion salinities and high homogenization temperatures relative to inferred burial depth, the trace MVT occurrences and MVT ore deposits may be genetically related by having precipitated from the same regional groundwater flow system mobilized by Pennsylvanian-Permian tectonism. The purpose of the present study was to test the robustness of this inferred genetic relationship by characterizing the Pb and S isotope composition of trace MVT occurrences in light of the much more thoroughly studied MVT ore deposits.Lead and sulfur isotope compositions have been obtained for trace MVT occurrences from three broad regions of the U.S. mid-continent: the Forest City basin (FCB), the Illinois basin (ILB), and the Greater Upper Mississippi Valley (GUMV) region. Lead isotope compositions of trace MVT occurrences from each of these three areas define discrete linear trends that are similarly oriented but not strictly collinear with one another or with the Pb isotope trends of MVT ore deposits, suggesting that trace MVT occurrences in each of these three regions derived their Pb from separate pairs of end-member Pb sources. An exception is the GUMV trace MVT occurrences and the Upper Mississippi (UMV) district ores, which appear to have collinear Pb isotope trends and thus may be the most closely related genetically with respect to sources of Pb. All of the trace MVT occurrences have radiogenic Pb suggesting derivation from Precambrian igneous basement rocks and not from the formations that host trace MVT mineralization. Trace MVT occurrences tend to have less radiogenic Pb than the MVT ore deposits, although trace MVT occurrences from the GUMV region are the most heterogeneous and can have Pb that is as radiogenic as the MVT ore deposits. Regionally, Pb isotope compositions of trace MVT occurrences tend to become less radiogenic southwestward and southward, but do not correlate with host rock age, and by proxy, distance from the Precambrian basement.The sulfur isotope compositions of sphalerite and galena from the trace MVT occurrences are light compared to the MVT ore deposits and likely reflect incomplete reduction of marine sulfate reservoirs or derivation from organic matter. The Pb and S isotope compositions of the trace MVT occurrences do not correlate well, suggesting that Pb and S were not transported together in the same fluid.

Relationship between density, compressive strength, tensile strength and aggregate properties of andesites from Hungary

Aggregate properties and strength parameters of four andesites from two operating Hungarian quarries of Nogradkovesd (one lithotype) and Gyongyossolymos (three lithotypes) are presented in this paper. Air-dry, water-saturated and freeze–thaw subjected specimens were tested on core-drilled cylindrical specimens, and the aggregate properties were also determined from the remaining part of the drilled rock blocks. Tensile strength values rapidly decreased from air-dry to water-saturated and finally to freeze–thaw subjected specimens. Linear relationships between air-dry and water-saturated bulk densities and between UCS and modulus of elasticity were found. Micro-fabric influences strength and aggregate parameters of studied andesites; fine porphyritic andesite has the highest UCS and tensile strength and the best micro-Deval results, while coarser porphyritic andesite has lower strength and aggregate parameters. Test results were compared with previously published rock mechanical data of intermediate and basic igneous rocks. A good exponential correlation was found between micro-Deval and UCS values of this paper and previously published data sets, but there was no indication that micro-Deval values correlate well with Los Angeles values.

Ancient magma sources revealed

The composition of Earth's oldest crust is uncertain. Comparison of the most ancient mineral grains with more recent analogues suggests that formation of the earliest crust was heavily influenced by re-melting of igneous basement rocks.

Geochemical effect of the rock chemistry and the anthropogenic activities on groundwater: The case study of NW Euboea, Greece

A geochemical study of NW Euboea island ground waters was undertaken, in order to examine the possible effect of the chemical composition of the country rocks of the area as well as of the anthropogenic activities, to the concentration of environmentally important elements and chemical compounds in the groundwaters. NW Euboea consists of a great variety of rock types showing a wide range in mineralogical and chemical composition. The main groups of rocks occurring in NW Euboea are: i) various types of sedimentary rocks e.g. shale and chert formations, carbonate and clastic rocks, ii) ophiolitic rocks including peridotite, gabbro, serpentinite etc, and iii) epizonally metamorphosed basic igneous rocks, with schist and phyllite intercalations. A number of hot springs also occur in the area. The main anthropogenic activity in the area is the agricultural land use, as any significant industrial activity is absent. For that purpose, 45 water samples were collected and analyzed by Spectrophotometry for the main anions and by FP and AAS for major and a number of trace elements. On the basis of those analyses, a number of the water samples were selected and analyzed by ICP-AES and ICP-MS for a large group of mainly metallic trace elements. The interpretation of the analytical data showed clearly that the content of the groundwater for a significant group of trace elements (e.g. Cr, Ni, Zn) was considerably influenced by the chemical composition of the surrounding rocks, especially the ophiolitic and metamorphic rocks. The anthropogenic activities also affect the groundwater quality, near areas where the use of fertilizers and pesticides for agricultural purposes is extensive, resulting to the increase of various anion concentrations (NO3 -, SO4 -2, PO4 -3).

Manganilmenite in the Magnetite Ore Body from Pokphur Area of Nagaland, North East India and the Possibility of Microdiamonds in the Ophiolites of Indo-Myanmar Ranges

Manganilmenite is found to be associated with the magnetite ore body of Pokphur area in the Nagaland ophiolites, North East India. There is perhaps no earlier description of the mineral from the Indian subcontinent. It occurs as an accessory mineral with magnetite and Fe-chlorite (chamosite). Electron probe micro-analytical data reveal that the mineral contains 5.6-8.5 wt% MnO and traces of MgO, ZnO and Cr2O3, while the TiO2 content remains within narrow limits of 50-53 wt%. The calculated pyrophanite end-member varies from 13% to 18%. Although the magnetite body of Pokphur has been reasonably proved to be a hydrothermally altered product of basic and ultrabasic igneous rocks, and most of the minerals in the magnetite body are supergene in nature, different end-member compositions of mangan ilmenite indicate that it has originally crystallized with the basic suite of rocks and has survived the alteration process with only marginal effects. Since manganilmenite has been considered as a diamond indicator mineral and ophiolites are a newly documented host of microdiamonds elsewhere in the world, the presence of manganilmenite in the Pokphur magnetite hints towards occurrence of microdiamonds in the ophiolite suite of rocks of the Indo-Myanmar ranges.

About the genesis of ovoidal K-feldspar porphyry and quartz in rapakivi granites and related rocks

A comparative study of structural peculiarities of ovoid K-feldspar porphyry and quartz of rapakivi granite of different arrays (Aland, Vyborg, Salmi batholith rapakivi of the Baltic shield and Bardiaush batholith rapakivi of the South Ural), and hybrid rocks of various genesis allowed us to clarify their role in the formation of rapakivi granite complexes. It was established, that the porphyritic quartz and ovoides of K-feldspar and their plagioclase shell was formed before the crystallization of the residual cotectic melt of rapakivi granite. In the composite hybrid magmatic rocks xenocryst K-spar have undergone a disintegration of solid solution with formation of a secondary cryptoperthite plagioclase. And xenocrystic quartz was subject to decrepitation by primary fluid inclusions and the formation of new secondary high-temperature inclusions. In a hybrid composite rocks formed as metamorphic and basic igneous rocks ovoid-like porphyroblast Kspar (including plagioclase shells) and quartz porphyry (including the ‘ocelly’) was crystallized from solution. In the crystals of quartz primary inclusions (negative crystals) of trigonal symmetry were present, typical for low-temperature α-modification. Refs 24. Figs 9. Tables 2.

Les Roches Basiques Du Bas-Limousin (Massif Central Français) : Geochimie Et Implications Geodynamiques

The upper unit gneisses represent most of the Bas - Limousin. It is characterized by the intercalation of basic igneous rocks (metagabbro- and metadolerite). These are affected by regional metamorphism but primary textures are preserved. The aim of this work is to present new geochemical data, which allow characterizing the geochemical nature of these rocks and discussing their geodynamic meaning. Chemical analyzes of the major and traces elements were carried out at “Service commun des sciences de la terre de l’ Université de Nancy I”, rare earths elements were analyzed at CRPG of Nancy. The results of this geochemical study show that these basic rocks are comparable to continental tholeiitic rocks.

Provenance of heavy minerals from recent sediments of Balakyan River, Kurdistan Region, Iraq

Heavy mineral assemblages of the sediments in Balakyan River have been studied to determine their concentrations and provenance. Twelve sediment samples were analyzed for heavy mineral assemblage determination. The unstable heavy minerals (pyroxene and amphibole) represent more than 50%. The mineral chemistry and petrographic studies refer to the predominant clinopyroxene mineral is diopside. Actinolite, tremolite, and magnesiohornblende are common calc-amphibole in the sediments. The ultrastable heavy minerals are present in trace amounts. According to the mineral chemistry the clinopyroxene is derived from basic igneous rocks crystallized at 1150-1220⁰C and low pressure. Amphibole and epidote crystallized under low temperature and/or formed under low grade metamorphism. The detrital chromian spinel is derived from basic and ultrabasic igneous rocks of Alpine type peridotite formed in fore-arc. The probable source of these assemblages is Ophiolite Complex to the north of the studied area (north Iraq) and igneous parts of Walash Series and Red Bed Series also the sedimentary rocks of Shiranish and Tanjero formations.

Geodynamics of the Barents–Kara margin in the Mesozoic inferred from paleomagnetic data on rocks from the Franz Josef Land Archipelago

New data on paleomagnetism and isotope geochronology of Jurassic and Early Cretaceous basic igneous rocks on Franz Josef Land Archipelago (FJL) represented by flows and dikes are discussed. The first paleomagnetic data obtained for these rocks offer the opportunity to suggest a model of spatial changes in the FJL block position during the Jurassic‒Cretaceous. In the Early Jurassic, the block occupied a different position relative to Europe from the modern one. It was displaced in the northeasterly direction by a distance of approximately 500 km and rotated clockwise by about 40° relative to its modern position. By the Early Cretaceous, the FJL block occupied a position close to the present-day one avoiding subsequent substantial relative displacements. The data obtained are of principal significance for reconstructing the geodynamic evolution of Arctic structures in the Mesozoic and contribute greatly to the base of paleomagnetic data for the Arctic region, development of which is now in progress.