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Sample records for lamprophyres

  1. Petrogenesis of lamprophyres from Chhota Udepur area, Narmada rift zone, and its relation to Deccan magmatism

    NASA Astrophysics Data System (ADS)

    Chalapathi Rao, N. V.; Dharma Rao, C. V.; Das, Sanjay

    2012-02-01

    Geological setting, petrology and geochemistry of a new find of lamprophyre dykes, intruding the Precambrian basement gneisses from the Chhota Udepur area, Narmada rift zone, Western India, are presented. Of the three lamprophyre dykes, two of them display E-W trend paralleling that of the Narmada rift, extend up to ˜2.5 km in length and constitute the longest yet recorded lamprophyre dykes from the Indian shield. The Chhota Udepur lamprophyres (CUL) show several overlapping mineralogical and geochemical characteristic features displayed by alkaline- and calc-alkaline lamprophyres and hence it is not straight forward to pigeon-hole them in existing lamprophyre classification schemes. They are porphyritic-panidiomorphic with euhedral to sub-hedral phenocrysts and microphenocrysts of olivine (Fo 78.33-78.42 Fa 21.24-21.37), diopsidic augite to titaniferous augite (Wo 54.83-59.03 En 36.75-41.36 Fs 0.1-5.66), biotite and amphibole (kaersutite). Feldspar (orthoclase perthite and plagioclase) is essentially confined to the groundmass along with accessory phases such as apatite and spinel (ti-magnetite). Rare carbonate ocelli are also present. In terms of major element geochemistry the CUL are nepeheline-normative and predominantly sodic (Na 2O > K 2O); yet their K 2O and SiO 2 contents are sufficiently high to signal traits of calc-alkaline lamprophyres. On the other hand, the CUL exclude negative spikes at Nb-Ta which are considered to be a characteristic of subduction-related (calc-alkaline) magmas, are highly evolved (Mg#: 27.82-55.45), enriched in incompatible trace elements (high La/Nb, Zr/Nb) and have fractionated REE distribution patterns (La/Yb N ratios: 35-44). Post-emplacement alteration and crustal contamination have had little influence on their geochemistry. Th/Yb, Ta/Yb, Nb/U and Ce/Pb ratios of the CUL imply an OIB type-enriched mantle source, similar to that displayed by other Deccan-related lamprophyres. A metasomatised (enriched) garnet lherzolite

  2. Multi-tests for pore structure characterization-A case study using lamprophyre

    NASA Astrophysics Data System (ADS)

    Li, Zhen; Feng, Guorui; Luo, Yi; Hu, Shengyong; Qi, Tingye; Jiang, Haina; Guo, Jun; Bai, Jinwen; Du, Xianjie; Kang, Lixun

    2017-08-01

    The pore structure plays an important role to understand methane adsorption, storage and flow behavior of geological materials. In this paper, the multi-tests including N2 adsorption, mercury intrusion porosimetry (MIP) and CT reconstruction have been proposed on Tashan lamprophyre samples. The main findings are listed: (1) The pore size distribution has a broad range ranging from 2-100000nm, among which the adsorption pores (<100nm) occupies the mainly specific surface areas and pore volume while the seepage pores (>100nm) only account for 34% of total pore volume. (2) The lamprophyre open pores are mainly slit-like/plate-like and ink-bottle-shaped pores on a two-dimensional level. The lamprophyre 3D pore structure shows more stochastic and anisotropic extension on the z axis to form a complex pore system on a three-dimensional level. (3) The closed pores (>647nm) occupy averaged 74.86% and 72.75% of total pores (>647nm) volume and specific surface area indicating a poor connectivity pore system. The revealed results provide basic information for understanding the abnormal methane emission reasons in similar geological conditions with lamprophyre invasions.

  3. Geochemistry of lamprophyres in Karakaya (İscehisar, Afyon), Western Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Dedeoglu, Deniz; Yılmaz, Kamil

    2016-10-01

    The geochemical characteristics of the volcanism, occured in the western Anatolia, display calc-alkaline (Oligocene-Lower Miocene) and alkaline (Upper Miocene-Pliocene) affinities. These two different volcanism have an important role to understand the geodynamic evolution of the western Anatolia during the Neogene time. The Karakaya lamprophyres, one of the products of these volcanism lying in the western Anatolia, comprises alkaline basaltic rocks extruded into the ignimbrites. Petrographically, they have mostly hyalopilitic, trachytic, intersertal, vitrophyric porphyritic, pilotaxitic and glomeroporphyritic texture. Olivine (mostly altered to iddingisite and resorbed by carbonate), clinopyroxene (diopside, augite) and phlogopite (partly transformed into Fe-Ti oxide) as phenocyrst phase, and apatite, quartz, garnet and opaque minerals as accessory phase defined. In some thin sections, quartz phenocrysts are surrounded by clinopyroxene needles that evulated as evidence of magma mixing. These lamprophyres are characterized by low concentrations of SiO2, TiO2 and total Fe2O3, high concentrations of Mg#, enriched in LREE and LILE but variably depleted in HFSE. In the total alkali silica diagram, Karakaya lamprophyres mainly plot in the fields of trachyandesite, basaltic trachyandesite. According to mineral chemistry results, olivines show normal zoning by increasing of CaO and decreasing of Fo contents from core to the rim. Pyroxenes are classified as diopside and augite compositions. The mica minerals are generally phlogopite The overall data about the petrograhic and mineral chemistry exhibit that these lamprophyres appear to derived by fractional crystallization of a magma mixing which formed by melting of the continental crust with effect of the uprising lithospheric mantle during in a extensional tectonic regime after the Middle Miocene.

  4. Crustal xenoliths in post-collisional Variscan lamprophyres: records of late Variscan collision and orogenic extension

    NASA Astrophysics Data System (ADS)

    Soder, Christian; Ludwig, Thomas; Schwarz, Winfried; Trieloff, Mario

    2017-04-01

    Crustal xenoliths entrained in post-collisional shoshonitic lamprophyres from the Variscan Odenwald (Mid-German Crystalline Zone, MGCZ) include felsic granulites (garnet, quartz, plagioclase, K-feldspar, biotite, omphacite, rutile) and basaltic eclogites (omphacite, garnet, quartz, kyanite, phengite, epidote, rutile). Classical thermobarometry, Zr-in-rutile thermometry and equilibrium phase diagrams reveal temperatures of 700-800°C and pressures of 1.7-1.8 GPa. Both lithologies record isothermal decompression resulting in partial melting at still elevated pressures (1.3-1.5 kbar) before entrainment into the magma. The development of diverse fine-grained microstructures is linked to the interaction with the rising melt. The eclogitic garnet preserves compositional sector zonation patterns, which indicate rapid crystal growth, shortly followed by overgrowth/recrystallization during decompression. The preservation of these zonation patterns indicates crystallization immediately before the lamprophyre magmatism. These findings are supported by SIMS U-Pb dating of zircon rims, which gave ages of 330±3 Ma for both lithologies, indistinguishable from the published age of lamprophyre emplacement. Therefore, the xenoliths are a unique document of the late Variscan collisional process with marked crustal thickening to 60 km and a subsequent decompression event. Magmatic protolith ages are 430 Ma for the basaltic eclogite and 2.1 Ga for the felsic granulite. Silurian magmatism is well established within the MGCZ while the Paleoproterozoic age represents a hitherto unknown magmatic event.

  5. Paleoproterozoic mantle enrichment beneath the Fennoscandian Shield: Isotopic insight from carbonatites and lamprophyres

    NASA Astrophysics Data System (ADS)

    Woodard, Jeremy; Huhma, Hannu

    2015-11-01

    The isotope geochemistry of carbonatite from Naantali, southwest Finland as well as lamprophyres from North Savo, eastern Finland and the NW Ladoga region, northwest Russia has been investigated. These Paleoproterozoic dykes represent melting of an enriched mantle source spread over a ~ 96,000 km2 area within the Fennoscandian Shield and intruded during post-collisional extension. The carbonatites have εNd(T) ranging from -0.8 to + 0.4, while lamprophyres have εNd(T) between -0.8 and + 0.3. 87Sr/86Sr ratios from the primary carbonatite samples from Naantali form a tight cluster between 0.70283 and 0.70303. For the lamprophyres, 87Sr/86Sr ratios range from 0.70327-0.70339 from NW Ladoga and 0.70316-0.70327 from North Savo. These characteristics are consistent with derivation from an enriched mantle showing an EMII trend, formed when sediments of mixed Archean and Proterozoic provenance were recycled back into the mantle via subduction during the preceding Svecofennian orogeny. Linear mixing of these subducted sediments and depleted mantle shows that a multistage process of enrichment is required to produce the observed isotope compositions. Batch melting of the subducted sediment first generated hydrous alkaline silicate melt, which crystallised as mica- and amphibole-rich veins in the mantle wedge. Continued melting of the subducted material under higher P-T conditions produced carbonatite melt, which infiltrated preferentially into this vein network. Assuming the silicate melt exerts greater influence on 87Sr/86Sr ratios while the carbonatite more greatly affects 143Nd/144Nd ratios, the model predicts significant regional variation in the silicate metasomatism with more consistent carbonatite metasomatism throughout the Fennoscandian subcontinental lithospheric mantle. The subducted sediments were likely also rich in organic matter, resulting in highly negative δ13C in mantle carbonates. The model predicts a higher content of organic carbon in the sediments in

  6. Paleogene post-collisional lamprophyres in western Yunnan, western Yangtze Craton: Mantle source and tectonic implications

    NASA Astrophysics Data System (ADS)

    Lu, Yong-Jun; Campbell McCuaig, T.; Li, Zheng-Xiang; Jourdan, Fred; Hart, Craig J. R.; Hou, Zeng-Qian; Tang, Suo-Han

    2015-09-01

    A suite of lamprophyres, spatially associated with mafic lavas and potassic felsic intrusive rocks, was emplaced between 36.5 ± 0.2 and 33.7 ± 0.5 Ma (based on phlogopite 40Ar/39Ar dating) on the eastern side of the Ailao Shan-Red River shear zone in the western Yangtze Craton. These shoshonitic and ultrapotassic intrusive rocks post-date the 60-55 Ma collisional event between the Indian and the Asian continents. They are characterized by: (1) enrichment in large-ion lithophile elements and light rare-earth elements with (La/Sm)n = 3.15-7.15; (2) strong positive Pb spikes; (3) depletion in high-field-strength elements (e.g. Nb/La = 0.08-0.98); (4) high initial 87Sr/86Sr (0.706-0.709) with negative εNd(t) values of - 10.5 to - 0.9; (5) old Nd model ages of 1542-945 Ma; and (6) radiogenic (207Pb/204Pb)i of 15.57-15.70 and (208Pb/204Pb)i (38.70-39.06). These features suggest that the mantle source was metasomatized by Proterozoic subduction beneath the Yangtze Craton. The lamprophyres have similar trace element patterns, and Sr-Nd-Pb isotope compositions, as coeval mafic lava, indicating a common source of metasomatized veined continental lithospheric mantle (CLM). Lower degree partial melting of metasomatic veins likely generated the lamprophyres, whereas the coeval mafic lava was likely derived from melting of phlogopite harzburgite. The lamprophyres and mafic lava have similar Sr-Nd isotope systematics as CLM-derived Neoproterozoic mafic rocks and Late Permian Emeishan low-Ti basalt in the region, indicating that they share the same Proterozoic source. We envisage that mantle plumes thermally eroded the Proterozoic metasomatized CLM beneath the western part of the Yangtze Craton during 825-750 Ma and 260-250 Ma, although residual metasomatized domains remained before being tapped by delamination after the India-Asia continental collision during the Paleogene period.

  7. Petrological and geochemical characteristics of Paleoproterozoic ultramafic lamprophyres and carbonatites from the Chitrangi region, Mahakoshal supracrustal belt, central India

    NASA Astrophysics Data System (ADS)

    Srivastava, Rajesh K.

    2013-06-01

    A number of ENE-WSW trending Paleoproterozoic dykes and plugs of mafic, ultramafic, alkaline and carbonatite rocks intrude Mahakoshal supracrustal belt (MSB), which is a part of the Central Indian Tectonic Zone (CITZ). Best exposures of these intrusions are found in the eastern parts of the MSB, particularly in and around Chitrangi area. Many of these intrusions have greenschist facies mineral composition and show sharp contact with supracrustal rocks. However, igneous textures, such as porphyritic/glomeroporphyritic, are still preserved in the form of partly pseudomorphed olivines, phlogopites and pyroxenes. Striking feature observed in some ultramafic samples is the presence of melanite garnet and rounded or elliptical carbonate ocelli. The petrographic characteristics suggest occurrence of carbonate-rich ultramafic lamprophyres; close to aillikite composition. Coarse-grained carbonatites show hypidiomorphic texture and mostly composed of calcite with appreciable amount of silicate minerals like clinopyroxene, phlogopite and olivine (often pseudomorphed by calcite, amphibole and chlorite). It is difficult to establish any direct genetic relationship between carbonatite and ultramafic lamprophyre samples on the basis of their chemistry; they were likely derived from distinct parental melts. High Mg# (up to ~78), and high Ni and Cr contents (up to ~1700 and ~1100, respectively) and low HREE concentration in few ultramafic lamprophyre samples apparently suggest their derivation from a near-primary mantle-derived melts originated at great depths. Geochemistry and presence of carbonate ocellae in ultramafic lamprophyre samples suggest genesis of these silicate rocks and associated carbonatites through liquid immiscibility, however possibility of their derivation through vein-plus-wall-rock melting model cannot be ignored. A multi-stage veined mantle melting model is suitable in the latter case. It is suggested that early stages of rifting in the Mahakoshal region due

  8. Petrogenesis of Archean lamprophyres in the southern Vermilion Granitic Complex, northeastern Minnesota, with implications for the nature of their mantle source

    NASA Astrophysics Data System (ADS)

    Wesley McCall, G.; Nabelek, Peter I.; Bauer, Robert L.; Glascock, Michael D.

    1990-07-01

    Petrogenetic modeling of major and trace element and isotopic data is used: 1. to define probable modes of petrogenesis of Archean spessartitic lamprophyric rocks in the southern portion of the Vermilion Granitic Complex (VGC) of northeastern Minnesota, and 2. to place constraints on the nature of the mantle source of these rocks. The lamprophyres range from olto qtz-normative and are associated with cumulate hornblendites and pyroxenites. The silica-rich lamprophyres are shown to be the result of low-pressure fractionation upon emplacement. On the other hand, the composition range of the ol-normative lamprophyres is explained by approximately 40% polybaric fractionation of elinopyroxene + olivine yielding ne-normative liquids. The fractionation explains low Cr, Ni and Sc concentrations compared to primary mantle-derived melts. Modeling of the lamprophyre MgO-FeO compositions using the olivine saturation surface (Hanson and Langmuir 1978) suggests that the 0.42 to 0.55 Mg/(Mg+Fe) ratios of most of the lamprophyres can be explained by the high-pressure fractionation. The model parent melt composition is similar to sanukitoid-type rocks found in Japan and elsewhere in the Superior Province. The lamprophyres have ɛ{/Nd 2700} values of +1.4 to +2.0, indicating derivation from a depleted mantle source. Growth curves on an ɛ Nd vs. age diagram are consistent with the extraction of the lamprophyres from a depleted source (Sm/Nd>chondrite) just prior to 2700 Ma, the accepted age of the VGC. The lamprophyres have fractionated REE patterns (Ce/Ybn=10 15) that indicate genesis by a) 1% to 3% fusion of a pristine garnet lherzolite or b) ˜10% fusion of an enriched mantle source. However, consideration of the pressure of melting and elemental plots of Al and Ti indicate that garnet was not a residual phase during lamprophyre genesis. Thus, the enrichment of the LREE (80 100 x chondrite), Sr (580 1400 ppm), and Ba (590 1600 ppm) indicate derivation from an enriched mantle

  9. Devonian ultramafic lamprophyre in the Irkineeva-Chadobets trough in the southwest of the Siberian Platform: Age, composition, and implications for diamond potential prediction

    NASA Astrophysics Data System (ADS)

    Kargin, A. V.; Nosova, A. A.; Postnikov, A. V.; Chugaev, A. V.; Postnikova, O. V.; Popova, L. P.; Poshibaev, V. V.; Sazonova, L. V.; Dokuchaev, A. Ya.; Smirnova, M. D.

    2016-09-01

    The results of geochronological, mineralogical, petrographical, and geochemical study of the Ilbokich ultramafic lamprophyre are reported. The specific features in the mineral and chemical compositions of the studied ultramafic lamprophyre indicate that it can be regarded as a variety similar to aillikite, while other differences dominated by K-feldspar can be referred to damtjernite. According to Rb-Sr analysis, ultramafic lamprophyre dikes intruded at the turn of the Early and Middle Devonian, about 392 Ma ago. This directly proves the existence of Early Paleozoic alkali-ultramafic magmatism in the northern part of the southwest Siberian Platform. A finding of Devonian alkali-ultramafic lamprophyre is of dual predictive importance. On the one hand, it is indicative of the low probability of finding large diamond-bearing deposits in close association with aillikite. On the other hand, it can be indicative of a possible large Devonian diamond province in the studied territory, where diamondiferous kimberlite is structurally separated from aillikite.

  10. Enigmatic diamonds in Archean calc-alkaline lamprophyres of Wawa, southern Ontario, Canada

    NASA Astrophysics Data System (ADS)

    de Stefano, Andrea; Lefebvre, Nathalie; Kopylova, Maya

    2006-02-01

    A suite of 80 macrodiamonds recovered from volcaniclastic breccia of Wawa (southern Ontario) was characterized on the basis of morphology, nitrogen content and aggregation, cathodoluminescence (CL), and mineral inclusions. The host calc-alkaline lamprophyric breccias were emplaced at 2.68-2.74 Ga, contemporaneously with voluminous bimodal volcanism of the Michipicoten greenstone belt. The studied suite of diamonds differs from the vast majority of diamond suites found worldwide. First, the suite is hosted by calc-alkaline lamprophyric volcanics rather than by kimberlite or lamproite. Second, the host volcanic rock is amongst the oldest known diamondiferous rocks on Earth, and has experienced regional metamorphism and deformation. Finally, most diamonds show yellow-orange-red CL and contain mineral inclusions not in equilibrium with each other or their host diamond. The majority of the diamonds in the Wawa suite are colorless, weakly resorbed, octahedral single crystals and aggregates. The diamonds contain 0-740 ppm N and show two modes of N aggregation at 0-30 and 60-95% B-centers suggesting mantle storage at 1,100-1,170°C. Cathodoluminescence and FTIR spectroscopy shows that emission peaks present in orange CL stones do not likely result from irradiation or single substitutional N, in contrast to other diamonds with red CL. The diamonds contain primary inclusions of olivine (Fo92 and Fo89), omphacite, orthopyroxene (En93), pentlandite, albite, and An-rich plagioclase. These peridotitic and eclogitic minerals are commonly found within single diamonds in a mixed paragenesis which also combines shallow and deep phases. This apparent disequilibrium can be explained by effective small-scale mixing of subducted oceanic crust and mantle rocks in fast “cold” plumes ascending from the top of the slabs in convergent margins. Alternatively, the diamonds could have formed in the pre-2.7-2.9 Ga cratonic mantle and experienced subsequent alteration of syngenetic inclusions

  11. Phenocrysts and megacrysts of olivines from ultramafic lamprophyres of the Chadobets and Il'bokich uplifts, Southwestern Siberia

    NASA Astrophysics Data System (ADS)

    Smirnova, Maria; Sazonova, Lyudmila; Nosova, Anna; Kargin, Alexey; Shcherbakov, Vasiliy

    2017-04-01

    The study of composition and zoning of olivines from ultramafic lamprophyres of the SW Siberian craton allowed us to distinguish their main types (phenocrysts and megacrysts) and to estimate the possible P-T conditions of phenocryst crystallization. The studied rocks occur as sills and dikes in the Chadobets and Il'bokich uplifts of the Irkeneeva-Chadobets trough. The ultramafic lamprophyres of these uplifts are spaced around 80 km apart and differ in age by more than 150 Ma. The rocks of the Il'bokich Uplift are dated at Devonian, while the age of the Chadobets Complex is restricted to the Triassic. The episodes of these complexes formation were separated by the large flood basalt event. According to classification (Tappe et al., 2005), the studied rocks are aillikite and damtjernite. Olivine phenocrysts from the rocks of the Il'bokich and Chadobets complexes are represented by sub- and euhedral grains. They are composed of core, transitional zone, and rim. Olivine cores in the aillikites of the Il'bokich Complex are characterized by Mg# 89; CaO - 0.13-0.14 wt %; TiO2 around 0.03 wt %, Al - 200-380 ppm, and Cr - 130-340 ppm. The cores of phenocrysts from the Chadobets lamprophyres have Mg# 85-87, CaO varying within 0.1-0.2 wt %, and TiO2 - 0.02-0.05 wt %. The megacrysts differ from the phenocrysts of these rocks in the lower Mg# 83-84 and CaO - 0.08-0.14 wt % at higher TiO2 - 0.04-0.05 wt %. Al - 100-700 ppm, Cr - 20-65 ppm. The most striking difference between olivines of the two complexes is observed between their Mg#-Ni relations. The cores of olivine phenocrysts from the Il'bokich lamprophyres are characterized by the high Mg number (Mg# = 89) and Ni content (2800-3000 ppm), whereas olivine cores of the Chadobets aillikites have higher contents of Ni (3000-3500 ppm) at lowered (Mg# = 86-88). These characteristics reflect the compositions of their protolith. The temperature was estimated using monomineral olivine thermometer based on the contents of Cr and Al

  12. PGE and Re-Os geochemistry of lamprophyres in the Zhenyuan gold deposit in Yunnan Province, China: Petrogenetic implications and mantle evolution

    NASA Astrophysics Data System (ADS)

    Gan, Ting; Huang, Zhilong

    2017-04-01

    Lamprophyres are generally thought to be formed from mantle-derived magmas and can provide significant insight into the continental lithospheric mantle (CLM) composition and its metasomatic history. Cenozoic lamprophyres are widespread along the Ailaoshan tectonic belt in the Sanjiang region, SW China, where there are also many important gold deposits, especially the Zhenyuan gold deposit. In this gold deposit, lamprophyres are closely associated in space-time to the gold ore bodies. However, the evolution of the lamprophyres during magmatic differentiation, and the mantle enrichment mechanism remain controversial. Thus, we have carried out a geochemical investigation of the lamprophyres in terms of platinum-group elements (PGEs) and Os isotopes. The Zhenyuan lamprophyres are calc-alkaline with SiO2 of 41.4 to 50.1 wt%, and total alkalis (Na2O+K2O) of 1.17 to 7.56 wt%. Consistant with previous studies of calc-alkaline lamprophyres, they are strongly light-rare-earth elements enriched, with enrichment of large ion lithophile elements and depletion of high field strength elements, indicating they came from an enriched lithospheric mantle metasomatized by subduction slab fluids. The Zhenyuan lamprophyres can be divided into high-Os (> 0.05 ppb Os) and low-Os (< 0.05 ppb Os) ones. The isotopic ratio of 187Os/188Os corrected for in situ growth in the lamprophyre is highly variable, ranging from typical mantle values to 1.13. These lamprophyres seem to represent some of the most radiogenic Os from mantle-derived rocks. The highly radiogenic Os isotopic signatures are interpreted to be due to long-time integration of elevated Re/Os in the lithospheric mantle, possibly due to subduction-related metasomatism. The slab-derived fluids may include sulfide liquid or oxidized and Cl-rich aqueous fluid to transfer palladium-group PGEs (PPGEs) and Re (relative to iridium-group PGEs (IPGEs)) from the subducted slab to the overriding mantle wedge. The highly variable 187Os/188Os

  13. Structural evolution of lamprophyric dikes in Lailai, northeastern coast of Taiwan, deduced from mesoscopic structures in dikes and country rocks

    NASA Astrophysics Data System (ADS)

    You, Cian-Siang; Huang, Wen-Jeng; Lo, Wei; Wang, Tzu-Bin; Chen, Chien-Chih

    2015-04-01

    Lamprophyric dikes are standing in right-stepping en echelon up to 2.3 meters high within the Oligocene Tatungshan formation on the Lai-Lai wave-cut platform in the northeastern coast of Taiwan. The marine platform composed mainly of argillite is the extension of Hsuehshan range, which has the tallest peak of 3,886 m high in Taiwan. The dikes formed at depth in the late Miocene of 9±1.1 Ma ago are exposed on the marine platform nowadays due to the exhumation and Penglai orogeny resulting from the collision of Eurasian plate and Philippine Sea plate, which began in Pleistocene of 5-6 Ma ago. In consequence, folds, faults, joints and other structures are associated with them. In this study, the distribution of the dikes and fractures were mapped by conducting accurate surveys with a total station theodolite and orthorectifying aerial images taken by an unmanned aerial vehicle in different elevations. Electrical resistivity exploration was performed to decipher the arrangement of the dikes underground and the characteristics of the faults. The associated mesoscopic structures were delineated by mapping at a scale of 1: 40 in the field. We infer that the dikes was formed at depth of approximately 2.4 kilometers according to the thickness of overlaying sedimentary rocks formed from late Oligocene to late Miocene. Thus, it excludes the possibility that fractures existed before the lamprophyric magma intruded into the country rocks. Our observations help restore the original status of the current 19 dike segments. We conclude that the lamprophyric magma forcedly and vertically intruded into the Oligocene rocks and the direction change of maximum principle stress at depth of 2.4 kilometers resulted in three or more right-stepping en-echelon dikes.

  14. Origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in Beiya area, western Yunnan, China

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang; Zhang, Bao-Lin; Qin, Ke-Zhang; Mao, Qian; Cai, Xin-Ping

    2007-12-01

    Lamprophyres consisting mainly of diopside, phlogopite and K-feldspar formed in the early Tertiary around 60 Ma in the Beiya area and are characterized by low SiO 2 ± 46-50 wt.%), Rb (31-45 ppm) and Sr (225-262 ppm), high Al 2O 3, (11.2-13.1 wt.%), CaO (8.0-8.7 wt.%), MgO (11.5-12.1 wt.%), K 2O(4.9-5.5 wt.%), TiO 2 (2.9-3.3 wt.%) and REE (174-177 ppm), and compatible elements (e.g. Sc, Cr and Ni) and HSF elements (e.g. Th, U, Zr, Nb, Ta, Ti and Y), and low 143Nd/ 144Nd 0.512372-0.512536, middle 87Sr/ 86Sr 0.707322-0.707395, middle 206Pb/ 204Pb 18.50-18.59, 207Pb/ 204Pb 15.60-15.65 and 208Pb/ 204Pb 38.75-38.8. These rocks developed peculiar quartz megacrysts with poly-layer reaction zones, melt inclusions, and partial melted K-feldspar and plagioclase inclusions, and plastic shapes. Important features of these rocks include: (1) hybrid composition of elements, (2) abrupt increase of SiO 2 content of the melt, recorded by zoned diopside, (3) development of sanidine and aegirine-augite reaction zones, (4) alkaline melt and partial melted K-feldspar and plagioclase inclusions, (5) deformed quartz inclusions associated with quartz megacrysts, (6) the presence of quartz megacrysts in plastic shape with their parent melts, (7) the occurrence of olivine, high-MgO ilmenite and spinel inclusions within earlier formed diopside, phlogopite and magnetite. Median 87Sr/ 86Sr values between Tertiary alkaline porphyries in the Beiya area and the western Yunnan and Tertiary basalt in the western Yunnan indicate that the Beiya lamprophyre melts were derivative and resulted from the mixing between basic melts that were related to the partial melting of phenocrysts of spinel iherzolite from a mantle source. The alkaline melts originated from partial melting along the Jinshajiang subduction ductile shear zone at the contact between the buried Palaeo-Tethyan oceanic lithosphere and the upper mantle lithosphere. The alkaline melts are composed of 65% sanidine (Or 70Ab 28An 2) and 35% Si

  15. Partial Melting of Subducted Sediments Produced Early Mesozoic Calc-alkaline Lamprophyres from Northern Guangxi Province, South China.

    PubMed

    Su, Hui-Min; Jiang, Shao-Yong; Zhang, Dong-Yang; Wu, Xiang-Ke

    2017-07-07

    There is growing agreement that subducted sediments recycled into the deep mantle could make a significant contribution to the generation of various mantle-derived rocks. However, solid evidence and examples to support this view are few, and whether or not the subducted sediments can act as the dominating material source for the magma is unclear. Here, we report a comprehensive geochemical study that demonstrates that the newly identified Early Mesozoic calc-alkaline lamprophyres in the northern Guangxi Province, southeastern Yangtze Block in South China were likely derived in large part from the partial melting of the subducted terrigenous sediments in the deep mantle. The investigated lamprophyres are SiO2-rich minettes, characterized by moderate TFeO and MgO and high Mg(#) (>70). The multi-element pattern shows a typical crustal-like signature, such as enrichments in large-ion lithophile elements (LILE) and light rare earth elements (LREE) with troughs in Nb-Ta, Ti and Eu and peaks in Th-U and Pb. These rocks also show sediment-like ratios of Nb/U, Nb/Th and Ce/Pb, together with extremely radiogenic (87)Sr/(86)Sr (0.71499-0.71919), unradiogenic (143)Nd/(144)Nd (0.51188-0.51195) and radiogenic (207)Pb/(204)Pb (15.701-15.718) isotopic compositions.

  16. Mid-Tertiary (25-21 Ma) lamprophyres in NW Mexico derived from subduction-modified subcontinental lithospheric mantle in an extensional backarc environment following steepening of the Benioff zone

    NASA Astrophysics Data System (ADS)

    Orozco-Garza, Alberto; Dostal, Jaroslav; Keppie, J. Duncan; Paz-Moreno, Francisco A.

    2013-04-01

    The mid-Tertiary lamprophyre dike swarm (~ 8 km × 2.5 km in size) from Hermosillo (Sonora, NW Mexico) has calc-alkaline characteristics and includes NNW-striking, amphibole-phyric spessartite (~ 85% of the swarm) and NNE-striking, phlogopite-phyric kersantite. The 40Ar/39Ar geochronology of amphibole and phlogopite gives overlapping plateau ages ranging from 25 to 21 Ma. Although all the lamprophyres are enriched in incompatible elements and display negative Nb-Ta and Ti anomalies on the primitive mantle-normalized plots, kersantite has higher K/Na, La/Yb, P, Ti and incompatible trace elements (e.g., Zr) compared to spessartite. The lamprophyres have radiogenic Sr and Nd isotopic signatures (87Sr/86Sr ~ 0.7057-0.7065 and ɛNd ~- 1 to - 2.3) suggesting derivation from the subcontinental lithospheric mantle that was previously modified by subduction-related fluids. This mantle is similar to that beneath the southern Grenvillian orogen, which has younger TDM ages than the 1.6-1.7 Ga TDM ages of the Caborca block. The lamprophyric magmas were generated at various mantle depths at the southwestern edge of North America. Intrusion of the lamprophyres was synchronous with extension that produced normal faults and core complexes with WSW-vergence. Extension occurred immediately following steepening of the Benioff zone, during which the magmatic arc migrated from east to west of Hermosillo, and the lamprophyres were intruded just behind the contemporaneous arc.

  17. Kimberlite, lamproite, ultramafic lamprophyre, and carbonatite relationships on the Dharwar Craton, India; an example from the Khaderpet pipe, a diamondiferous ultramafic with associated carbonatite intrusion

    NASA Astrophysics Data System (ADS)

    Smith, C. B.; Haggerty, S. E.; Chatterjee, B.; Beard, A.; Townend, R.

    2013-12-01

    Are kimberlites, lamproites, ultramafic lamprophyres and carbonatites genetically associated or not? There are strong opinions for and against any relationship. The 20 Ha Khaderpet pipe, discovered by Rio Tinto Exploration, is an unusual diamondiferous carbonatite-kimberlite clan rock (KCR) association in the Anumpalle Cluster of the Wajrakarur Kimberlite Field in the Dharwar Craton of Peninsular Indian. The Khaderpet pipe has a discrete sovite phase intrusive into KCR breccia, not noticed elsewhere in the Wajrakarur kimberlite field. Petrographically, the KCR is a clast-supported lithic breccia and crystal lithic tuff, with occasional pelletal lapilli. Clasts show a weak horizontal imbrication. The overall appearance of the tuffs and breccias is suggestive of terminal-blocked, vent accumulations that formed by under pressure, with spallation of country rock causing an abundance of granitoid debris. The sovite phase has up to 95% calcite, occasionally showing flow textured polycrystalline laths set in a minor saponite matrix. There are mineralogical gradations from an olivine-rich ultramafic to a calcite-dominant rock resembling pure carbonatite. Rare REE mineral phases in the carbonatite include allanite and other REE-rich unidentified mineral phases. Xenocrystic high pressure phases in both ultramafic and carbonatite include mantle-derived diamonds, lherzolitic-, eclogitic- and subcalcic-pyrope, Ti-poor andradite, chrome diopside, picrochromite and picroilmenite. Extensive metasomatism in the form of reddening of country rock feldspars by hematite, introduction of green chlorite, and saponitic alteration of breccia clasts and the ultramafic phase is common. The chemistry of the Khaderpet ultramafic component, suggests that the KCR is transitional between kimberlite and ultramafic lamprophyres, like certain other pipes in the Wajrakarur Kimberlite Field, with strong enrichment in LREE, CaO and CO2. However, low MgO (~ 13%) and high CaO (~ 10%) values are more

  18. Carbonatite-silicate immiscible melt inclusion in lamprophyre from Kutch, western India: Implication for plume-lithosphere interaction and initiation of Deccan Trap magmatism

    NASA Astrophysics Data System (ADS)

    Ray, Arijit; Paul, Dalim Kumar; Sen, Gautam; Biswas, Sanjib Kumar

    2014-05-01

    Kutch province of western India has undergone repeated rifting and marine transgression events from late Triassic to the late Cretaceous. Magmatic rocks occur in profusion in Kutch Basin. The southern part is characterized by occurrences of thick flows of tholeiitic basalt of Deccan Trap affinity, central part of Kutch Basin has numerous volcanic plugs of alkali basalt which is also considered as member of Deccan Trap, contain thin, discoidal mantle xenoliths of spinel lherzolite and wehrlite composition. Northern Kutch is dominated by suite of alkaline magmatic rocks similar to magmatic rocks of continental rift zone. The alkaline suite contains alkali pyroxenite, theralite, teschenite, basanite, nepheline syenite and kaersutite bearing lamprophyre (Ray et al., 2006, Das et al., 2007, Paul et al., 2008). The newly discovered east-west trending lamprophyre dyke swarm of northern Kutch (Pachham Island) is camptonite in composition and contains kaersutite phenocrysts in large proportion. These kaersutite phencrysts contain immscible melt/glass phases as melt inclusions. The lamprophyre yields an age of ca. 67 Ma.by Ar-Ar method (Sen et al., 2014 in press) synchronous with alkali basalt of central Kutch. The melt inclusions are fundamentally of two types - calciocarbonatite and alkaline silicate melts. We found sphene within carbonatitic melt and the rare mineral rhonite in silicate melt. Petrographic evidence indicates that carbonatite melt always occurs within alkali silicate melt as immiscible fraction. These carbonatite melts are extremely rich in CaCO3 (upto 95%) which contradicts the experimental results of carbonate melt composition (upto 80% CaCO3) in silicate-carbonate immiscible melt pair by Lee and Wyllie. The abundance of wehrlite xenoliths over lherzolite in alkali basalt, petrographic evidence of orthopyroxene to clinopyroxene transformation in wehrlite xenoliths, occurrence of calcite vein in mantle xenoliths indicate carbonatite metasomatism of spinel

  19. Petrogenesis of late-Variscan high-K alkali-calcic granitoids and calc-alkalic lamprophyres: The Aber-Ildut/North-Ouessant complex, Armorican Massif, France

    NASA Astrophysics Data System (ADS)

    Caroff, Martial; Labry, Cyrill; Le Gall, Bernard; Authemayou, Christine; Grosjean, Denise Bussien; Guillong, Marcel

    2015-12-01

    The Aber-Ildut/North-Ouessant Variscan granitoid complex in the Armorican Massif is an example of high-K alkali-calcic zoned pluton, c. 304 Ma in age. A first magmatic batch intruded through a northern EW-trending sinistral transcurrent shear zone, before injecting southwards as a huge horizontal zoned sill, with moderately peraluminous muscovite-free granitoids in the north and strongly peraluminous muscovite-bearing leucogranites to the south. The second magmatic stage resulted in the intrusion of a large two-mica leucogranitic body from a root zone along the same shear zone, prior to the end of crystallization of the first injection. Finally, ultrapotassic dykes, including calc-alkalic lamprophyres (leucominettes), intrude the complex. The strongly peraluminous granites are interpreted as pure melting products of crustal clay-rich pelitic material. All the other petrographic types, including leucominettes, are thought to result from mixing of crustal melts and mantle-derived mafic liquids. Highly silicic tourmaline-bearing leucogranites are significantly affected by a tetrad effect, in relation with REE complexing behavior. Aber-Ildut/North-Ouessant granitoids probably formed during the Variscan late-orogenic stage associated with exhumation and lithospheric thinning, at low pressure and by advective heating of a ≤ 50 km-thick crust from hot metasomatized asthenosphere.

  20. Interaction of extended mantle plume head with ancient lithosphere: evidence from deep-seated xenoliths in basalts and lamprophyre diatremes in Western Syria

    NASA Astrophysics Data System (ADS)

    Sharkov, Evgenii

    2016-04-01

    The Middle Cretaceous lamprophyric diatremes of the Jabel Ansaria Ridge contain xenoliths of ancient lower crustal rocks mainly represented by the suite of partly altered garnet granulite and eclogite-like rocks, which were formed at the expense of ferrogabbros and ferroclinopyroxenites most likely in the course of underplating of Fe-Ti basalt. Garnet (Alm26Grs11Py63) megacrysts and coarse-granular garnet-clinopyroxene intergrowths are most likely the varieties of rocks of this series. Garnet megacrysts are represented by large (up to 10 cm in diameter) round "nodules," often molten from the surface. Garnet is usually fractured, and the kelyphite material similar to that in rocks of the eclogite-granulite series occurs in fractures. In addition, we found several intergrowths of garnet with large (up to 3-5 cm in length) crystals of high-Al augite with the low of Ti and Na contents like in rocks of the eclogite-granulite suite. Coarse-grained garnet-clinopyroxene-hornblende rocks with spinel, as well as megacrysts of Al-Ti augite with kaersutite, form the second group in prevalence. This group is close to mantle xenoliths of the "black series" in alkali Fe-Ti basalt worldwide. Kaersutite in these rocks contains gaseous cavities, which provides evidence for the origin of rocks at the expense of a strongly fluidized melt/fluid. In contrast to rocks of the eclogite-granulite series, these rocks did not undergo alteration. Garnet Alm19-26Grs12-13.5Py59-67.5 usually associates with dark opaque spinel. In contrast, the Late Cenozoic plateaubasalts of the region practically do not contain lower crustal xenoliths, whereas xenoliths of mantle spinel lherzolite (fragments of the upper cooled rim of the plume head) are widely abundant. According to data of mineralogical thermobarometry, rocks of the eclogite-granulite suite were formed at 13.5-15.4 kbar (depths of 45-54 km) and 965-1115°C. Rocks of this suite are typical representatives of the continental lower crust

  1. Between carbonatite and lamproite—Diamondiferous Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of cratonic MARID-type metasomes

    NASA Astrophysics Data System (ADS)

    Tappe, Sebastian; Foley, Stephen F.; Kjarsgaard, Bruce A.; Romer, Rolf L.; Heaman, Larry M.; Stracke, Andreas; Jenner, George A.

    2008-07-01

    New U-Pb perovskite ages reveal that diamondiferous ultramafic lamprophyre magmas erupted through the Archean crust of northern Labrador and Quebec (eastern Canada) between ca. 610 and 565 Ma, a period of strong rifting activity throughout contiguous Laurentia and Baltica. The observed Torngat carbonate-rich aillikite/carbonatite and carbonate-poor mela-aillikite dyke varieties show a large spread in Sr-Nd-Hf-Pb isotope ratios with pronounced correlations between isotope systems. An isotopically depleted component is identified solely within aillikites ( 87Sr/ 86Sr i = 0.70323-0.70377; ɛNd i = +1.2-+1.8; ɛHf i = +1.4-+3.5; 206Pb/ 204Pb i = 18.2-18.5), whereas some aillikites and all mela-aillikites range to more enriched isotope signatures ( 87Sr/ 86Sr i = 0.70388-0.70523; ɛNd i = -0.5 to -3.9; ɛHf i = -0.6 to -6.0; 206Pb/ 204Pb i = 17.8-18.2). These contrasting isotopic characteristics of aillikites/carbonatites and mela-aillikites, along with subtle differences in their modal carbonate, SiO 2, Al 2O 3, Na 2O, Cs-Rb, and Zr-Hf contents, are consistent with two distinctive metasomatic assemblages of different age in the mantle magma source region. Integration of petrologic, geochemical, and isotopic information leads us to propose that the isotopically enriched component originated from a reduced phlogopite-richterite-Ti-oxide dominated source assemblage that is reminiscent of MARID suite xenoliths. In contrast, the isotopically depleted component was derived from a more oxidized phlogopite-carbonate dominated source assemblage. We argue that low-degree CO 2-rich potassic silicate melts from the convective upper mantle were preferentially channelled into an older, pre-existing MARID-type vein network at the base of the North Atlantic craton lithosphere, where they froze to form new phlogopite-carbonate dominated veins. Continued stretching and thinning of the cratonic lithosphere during the Late Neoproterozoic remobilized the carbonate-rich vein material and

  2. Geochemistry, Sr-Nd-Pb isotopes and geochronology of amphibole- and mica-bearing lamprophyres in northwestern Iran: Implications for mantle wedge heterogeneity in a palaeo-subduction zone

    NASA Astrophysics Data System (ADS)

    Aghazadeh, Mehraj; Prelević, Dejan; Badrzadeh, Zahra; Braschi, Eleonora; van den Bogaard, Paul; Conticelli, Sandro

    2015-02-01

    Lamprophyres of different age showing distinctive mineralogy, geochemistry and isotopic ratios are exposed in northwestern Iran. They can be divided into Late Cretaceous sannaite, Late Oligocene-Early Miocene camptonite (amphibole-bearing) and Late Miocene minette (mica-bearing) and spessartite (amphibole-bearing) lamprophyres. Sannaites have high-Ti amphibole along with high-Ti and Al clinopyroxene, and they are characterised by homogeneous enrichment in incompatible trace elements with troughs at Pb. Spessartites have hornblende and low-Al and Ti clinopyroxene, and they are characterised by enriched incompatible trace element pattern with depletions of Nb, Ta, Pb, and Ti with respect to large ion lithophile elements. Minettes have high-Ti and Al brown mica and low-Al and Ti clinopyroxene, and similar to spessartite, are characterised by fractionation of high field strength elements with respect to large ion lithophile elements, with troughs at Nb, Ta, and Ti and a peak at Pb. Minettes show high initial 87Sr/86Sr values up to 0.70760 and low initial 143Nd/144Nd down to 0.512463 with a negative correlation, consistent with the trace element distribution related with an enriched mantle source modified after sediment recycling during subduction and continental collision. Cretaceous sannaites and Early Miocene spessartites show low initial 87Sr/86Sr approaching 0.70447 and high 143Nd/144Nd values up to 0.512667, which are consistent with a depleted within-plate mantle source. Minette and spessartite lamprophyres show high initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values, whereas sannaites have lower, but variable, initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values with respect to those of calc-alkaline lamprophyres. Minettes originated by partial melting of a metasomatised lithospheric mantle following siliciclastic sediment recycling by subduction. In contrast, sannaites were generated from the partial melting of a similar lithospheric mantle that was

  3. Unravelling the influence of antecryst settling on the composition of a lamprophyre sill: results from geochemical modelling and principal component analysis

    NASA Astrophysics Data System (ADS)

    Ubide, T.; Arranz, E.; Lago, M.; Galé, C.; Larrea, P.; Tierz, P.

    2012-04-01

    Small igneous intrusions can be regarded as scale models of the behaviour of large magma chambers. We have carried out a detailed petrological and geochemical study across a thin (< 0.5 m) mafic sill located in the Catalonian Coastal Ranges, in the vicinity of Calella de Palafrugell (NE Spain). It is a late-Cretaceous sub-horizontal alkaline lamprophyre, classified as a camptonite. The sill is visibly zoned, showing well developed chilled margins, several levels of vesicles and accumulation of large mafic crystals towards the bottom. According to their composition, these crystals are inherited antecrysts. The whole-rock composition varies across the sill, indicating that the sill is compositionally zoned. However, the mineral compositions are constant, suggesting that the magma emplaced in a single pulse. The whole-rock compositional variations reveal that the chilled margins are more evolved than the centre of the sill; this is especially clear for the lower chilled margin, which defines a marginal reversal. Therefore, the compositional zoning of the sill does not correlate with a normal fractionation trend inwards. Instead, it agrees with the variable proportions of antecrysts across the sill: the higher the proportion of antecrysts, the more primitive the whole-rock composition. In order to verify that the presence of antecrysts controls the whole-rock variations, a trace element model has been developed. Given that the sill displays a porphyritic texture defined by large antecrysts set in a fine-grained groundmass, the geochemical model quantifies the relative contributions of the antecrysts and the groundmass to the whole-rock compositions. Because the antecryst and whole-rock compositions were analysed for the different samples collected across the sill, the groundmass composition could be calculated for each sample. The obtained groundmass compositions are constant and more evolved than whole-rock compositions, supporting that the whole-rock variations are

  4. Clinopyroxene and amphibole crystal populations in a lamprophyre sill from the Catalonian Coastal Ranges (NE Spain): A record of magma history and a window to mineral-melt partitioning

    NASA Astrophysics Data System (ADS)

    Ubide, Teresa; Galé, Carlos; Arranz, Enrique; Lago, Marceliano; Larrea, Patricia

    2014-01-01

    A Cretaceous sill of alkaline lamprophyre (camptonite) cropping out in the northern Catalonian Coastal Ranges includes macrocrysts and microcrysts of clinopyroxene and amphibole with complex zoning patterns. The in-depth petrographic, compositional and barometric study of the different crystal populations, including statistical evaluation of the compositional dataset by principal component analysis, provides insights into the magmatic plumbing system. Macrocryst cores are inherited antecrysts crystallised in a deep (500-800 MPa) magma chamber or conduit. Their reverse zoning patterns reveal repeated injection and mixing of batches of a more primitive and water-rich magma with the resident magma in the magma chamber. Macrocryst rims and microcrysts, in contrast, crystallised during the ascent and shallow emplacement of the magma below 50 MPa pressure. They define normal zoning patterns that can be related to progressive fractionation of the magma. This study shows that an apparently simple porphyritic rock can actually contain a significant amount of recycled crystals, reflecting an open-system magmatic behaviour. Only the groundmass of the sill represents a closed-system, where microphenocryst cores are in chemical equilibrium with the bulk composition of the groundmass. Using trace element compositions obtained by LA-ICP-MS and geochemical modelling, a complete and consistent partition coefficient dataset is obtained for the first time for clinopyroxene and amphibole in camptonite melts. Both minerals show a similar partitioning behaviour for most trace elements. Clinopyroxene-melt and amphibole-melt partition coefficients are overall consistent with data from basic rocks, although clinopyroxene partition coefficients are generally higher than data from basalt and basanite melts. The results from this research support the use of naturally occurring mineral-melt equilibrium pairs for partitioning studies but emphasise the need for a detailed study of the phases

  5. Melt evolution beneath a rifted craton edge: 40Ar/39Ar geochronology and Sr-Nd-Hf-Pb isotope systematics of primitive alkaline basalts and lamprophyres from the SW Baltic Shield

    NASA Astrophysics Data System (ADS)

    Tappe, Sebastian; Smart, Katie A.; Stracke, Andreas; Romer, Rolf L.; Prelević, Dejan; van den Bogaard, Paul

    2016-01-01

    amphibole-rich metasomatic components. The metasomatic components were likely introduced to the lithospheric mantle beneath the southern Baltic Shield margin during extensive Permo-Carboniferous magmatic activity, a scenario that is supported by the geochemical and isotope compositions of ca. 286 Ma lamprophyres from Scania (87Sr/86Sri = 0.7040-0.7054; εNdi = +2.0 to +3.1; εHfi = +6.1 to +9.0; 206Pb/204Pbi = 17.8-18.2). Strong variations in lithosphere thickness and thermal structure across the southern Baltic Shield margin may have caused transient small-scale mantle convection. This resulted in relatively fast and focused upwellings and lateral flow beneath the thinned lithosphere, where mafic alkaline magmas formed by low degrees of decompression melting of sublithospheric mantle. Such a geodynamic scenario would allow for enriched recycled components with low melting points to be preferentially sampled from the more depleted and refractory convecting upper mantle when channeled along a destabilizing craton edge. Similar to the 'lid effect' in oceanic island volcanic provinces, lithospheric architecture may exert strong control on the mantle melting regime, and thus offer a simple explanation for the geochemical resemblance of continental and oceanic intraplate mafic alkaline magmas of high Na/K affinity.

  6. Mesozoic east North American alkaline magmatism: Part 1. Evolution of Monteregian lamprophyres, Québec, Canada

    NASA Astrophysics Data System (ADS)

    Bédard, Jean H.

    1994-01-01

    The Cretaceous Monteregian alkaline igneous province is composed of shallowly emplaced plutonic complexes, and cogenetic dykes and sills. The mafic dykes are principally camptonites, monchiquites and alnöites, and sample the magmas that fed the plutons. The three principal dyke suites have different incompatible trace element ratios ( Y/Ce, Zr/Nb), and are not interrelated by closed-system fractional crystallization. Zonation of pyroxene grains imply a polybaric crystallization history, indicating that magmas ascended as mafic crystal-charged mushes. Intrasuite chemical variations among monchiquites are broadly consistent with segregation of the suspended phenocrysts from interstitial "syenitic" melts. Partial resorption of suspended amphibole megacrysts, assimilation of syenitic material (5-8%) and exsolution of carbonatitic melt are required to explain the variations of Ba, Rb, K 2O, Th, La, and TiO 2. Chemical variations among mafic camptonites are acceptably modelled by fractionation of pyroxene and olivine only, implying that their amphibole-rich character is the result of postfractionation crystallization under volatile-rich conditions. High- Zr/Nb camptonites and Rb-rich (AC) monchiquites could not unequivocably be linked to the main lineages and may represent distinct sources or have been affected by crustal contaminants.

  7. Age and origin of the Cortlandt Complex, New York: Implications from Sm-Nd data

    USGS Publications Warehouse

    Domenick, M.A.; Basu, A.R.

    1982-01-01

    Sm-Nd systematics for nine whole-rock samples of hornblende norites, pyroxenites and a lamprophyre from various parts of the Cortlandt Complex were analyzed. Six of these samples from the central and eastern parts of the complex give an isochron age of 430??34 (2 ??) Ma with an e{open}Nd value of -2.9??0.5, and the other three samples from the western part, including the lamprophyre, define a similar age of 394??33 (2 ??) Ma but with a distinctly different e{open}Nd value of -1.4??0.4. The two different initial 143Nd/144Nd ratios corresponding to these e{open}-values are interpreted to reflect continental crustal contamination of the lamprophyric parental liquid prior to final emplacement and crystal fractionation to produce the different rock types of the complex. The intrusion age of 430 Ma for the complex clearly post-dates the major metamorphic event of the Taconic orogeny. The Nd-isotopic data also suggest a relationship between the Cortlandt Complex and a belt of lamprophyric dike rocks to the west, known as the Beemerville trend, which cuts across the metamorphic trends of the Taconic (Ratcliffe 1981). ?? 1982 Springer-Verlag.

  8. Apparent polar wander paths and the close of late Archean crustal transpression, northern Ontario

    NASA Astrophysics Data System (ADS)

    Borradaile, G. J.; Lemmetty, T. J.; Werner, T.

    2003-08-01

    Lamprophyre dikes of the southern Superior Province of the Canadian Shield crosscut Archean structures, including a late Archean unconformity and its overlying younger Archean Timiskaming sedimentary and volcanic rocks. The dikes also cut the single schistosity that formed in these rocks. Nevertheless, the lamprophyre dikes show a weak internal tectonic fabric that is approximately parallel to the schistosity in the bedrock and oblique to dike walls. The consistent orientation of this internal tectonic fabric has been recognized in every lamprophyre dike using anisotropy of magnetic susceptibility (AMS). Thus the lamprophyre dikes provide a useful chronological marker, trapping the last pulse of Archean tectonism. Unfortunately, our previous attempts to compare the lamprophyre paleopoles with those of the age-calibrated apparent polar wander path (APWP) failed because it was not possible to isolate separate young and old components of magnetization. That failure occurred due to the overlap of blocking temperatures or coercivities for the different characteristic vector components [, 1994a]. Using new cores from the same specimens, here we distinguish successfully between consistently oriented vector components by using low-temperature demagnetization (LTD) before thermal demagnetization. Although the paleopoles appear well defined, comparisons with published APWPs for the Superior Province from late Archean [, 1979; , 1983; , 1994] to early Proterozoic [, 2000] are difficult. Moreover, the earlier parts of the paths are progressively less precise and complete. Nevertheless, A component remanences for the dikes give a paleopole near the path at ˜2650 Ma. For a Timiskaming volcanic breccia with a U-Pb age of 2696 Ma the A component paleopole may lie between 2600 and 2650 Ma. B component remanences yield paleopoles in the NW Pacific region, incompatible with any proposed Archean path but perhaps representing some much younger Proterozoic remagnetization event (e

  9. Enigma of lamprohyres

    NASA Astrophysics Data System (ADS)

    Vasyukova, Elena

    2013-04-01

    Till now lamprophyres are 'the camera obscure' in petrology. There is no the complete agreement about the origin, classification, genetic links and their role in the ore formation processes yet. Traditionally ca-alkaline lamprophyres associated with the diorites, syenites and granitoids. But modern studies show the geochronological, geochemical and isotopic evidences of the genetic links between lamprophyres and carbonatites (Woodard, 2010;.Coulson et al., 2003) and as a consequence the formation of REE-ore deposits. These authors explain the origin of lamprophyres and carbonatites by the different melting degrees of the metasomatised mantle. In this work we found another mechanism of their generation - the liquation of carbonate-silica melt. Within the area of Chuya complex (South-East Altai-North-West Mongolia) the lamphrophyric dykes are distributed irregularly and create the belts or series of bodies located next to the faults of different order. We studied about 30 dykes from three different areas (South Chuya, Yustyd, Aktash) and related rocks from the Tarakhata intrusion. Very similar rock and mineral composition, close time-space characteristics allow us to suggest their comagmatic nature. In the lamprophyres of South-Chuya area there are strong petrography evidences of liquation of carbonate-silicate melt during their evolution. The ocellar structures with the ocelli composed by the silicate mineral and inter globule material represented by carbonates with ore and other nonmetallic minerals. One of them is Ba-celestine which compiles the intergranular space, veinlets and pseudomorphoses after the silicates. It associates with the apatites, quartz, chlorite, carbonates (calcite and dolomite) and oxides (magnetite, goethite, chromite etc). The multi-element and rare-earth diagrams of all investigated rocks are equal in the form, at the position of HFSE minima, high La/Yb and Gd/Yb relations, except the Ba and Sr anomalies. In the graphs of the south

  10. Chief Joseph Dam, Columbia River, Washington, Additional Units and Structural Modification Foundation Report

    DTIC Science & Technology

    1988-01-01

    that include granodiorite , granodiorite gneiss, dark schistose granodiorite , hornblende granodiorite , and lamprophyre. These various rock types...exhibit different characteristics of soundness as described in the paragraphs below: a. Granodiorite is the predominant rock type. It is hard, medium to...4 f22 b. Granodiorite gneiss is a hard, medium to coarse grained, light gray to gray colored rock which exhibits a banded structure with mineral

  11. Mantle evolution in the Variscides of SW England: Geochemical and isotopic constraints from mafic rocks

    NASA Astrophysics Data System (ADS)

    Dupuis, Nicolle E.; Murphy, J. Brendan; Braid, James A.; Shail, Robin K.; Nance, R. Damian

    2016-06-01

    The geology of SW England has long been interpreted to reflect Variscan collisional processes associated with the closure of the Rhenohercynian Ocean and the formation of Pangea. The Cornish peninsula is composed largely of Early Devonian to Late Carboniferous volcanosedimentary successions that were deposited in pre- and syn-collisional basins and were subsequently metamorphosed and deformed during the Variscan orogeny. Voluminous Early Permian granitic magmatism (Cornubian Batholith) is broadly coeval with the emplacement of ca. 280-295 Ma lamprophyric dykes and flows. Although these lamprophyres are well mapped and documented, the processes responsible for their genesis and their relationship with regional Variscan tectonic events are less understood. Pre- to syn-collisional basalts have intra-continental alkalic affinities, and have REE profiles consistent with derivation from the spinel-garnet lherzolite boundary. εNd values for the basalts range from + 0.37 to + 5.2 and TDM ages from 595 Ma to 705 Ma. The lamprophyres are extremely enriched in light rare earth elements, large iron lithophile elements, and are depleted in heavy rare earth elements, suggesting a deep, garnet lherzolite source that was previously metasomatised. They display εNd values ranging from - 1.4 to + 1.4, initial Sr values of ca. 0.706, and TDM ages from 671 Ma to 1031 Ma, suggesting that metasomatism occurred in the Neoproterozoic. Lamprophyres and coeval granite batholiths of similar chemistry to those in Cornwall occur in other regions of the Variscan orogen, including Iberia and Bohemia. By using new geochemical and isotopic data to constrain the evolution of the mantle beneath SW England and the processes associated with the formation of these post-collisional rocks, we may be able to gain a more complete understanding of mantle processes during the waning stages of supercontinent formation.

  12. Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif.

    PubMed

    Nardi, Lauro V S; Plá-Cid, Jorge; Bitencourt, Maria de Fátima; Stabel, Larissa Z

    2008-06-01

    The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism.

  13. Chronology of Late Cretaceous igneous and hydrothermal events at the Golden Sunlight gold-silver breccia pipe, southwestern Montana

    USGS Publications Warehouse

    DeWitt, Ed; Foord, Eugene E.; Zartman, Robert E.; Pearson, Robert C.; Foster, Fess

    1996-01-01

    Gold mineralization at the Golden Sunlight breccia pipe, southwestern Montana, is related to emplacement of Late Cretaceous alkali-calcic rhyolite and subsequent collapse of the Belt Supergroup wallrock and rhyolite in the pipe. The pipe is inferred to grade downward into an alkalic porphyry molybdenum system. The pipe is cut by alkalic to sub-alkalic lamprophyre dikes and sills, which locally contain high-grade gold where emplaced along late shear zones and vein systems. Determination of the emplacement age of the rhyolite is hampered by inherited lead or inherited Late Archean zircon from the source region of the rhyolite. An emplacement age of about 80 Ma for the rhyolite can be inferred if a basement age of 2,600 Ma is assumed. This Late Archean age is in agreement with basement ages determined in many parts of southwestern Montana. A 206 Pb- 238 U whole-rock date of 84 ? 18 Ma from altered and mineralized Belt Supergroup strata and rhyolite in the breccia pipe indicates hydrothermal alteration related to gold mineralization in Late Cretaceous time. Although sericite is a relatively widespread hydrothermal mineral, attempts to date the very fine grained material by the 40 Ar- 39 Ar method did not provide a spectra that could be interpreted unambiguously. A 40 Ar- 39 Ar plateau date of 76.9 ? 0.5 Ma from biotite phenocrysts in the lamprophyre indciates intrusion of mafic magma and attendant CO 2 metasomatism in the Late Cretaceous. Fission-track data from zircon in the rhyolite are permissive of slow uplift of the Belt Supergroup strata, 1U.S. Geological Survey, Box 25046, Denver Federal Center, Denver, CO 80225. 2Golden Sunlight Mines, Inc., 453 MT Highway 2 East, Whitehall, MT 59759. rhyolite, and lamprophyre between 55 and 50 Ma, but the data are not definitive. Rhyolitic welded tuff in the informally named units 7, 9, and 11 of the Elkhorn Mountains Volcanics is most similar in chemistry and age to the rhyolite at the Golden Sunlight mine. Trachybasalt in

  14. The Kimberlites and related rocks of the Kuruman Kimberlite Province, Kaapvaal Craton, South Africa

    NASA Astrophysics Data System (ADS)

    Donnelly, Cara L.; Griffin, William L.; O'Reilly, Suzanne Y.; Pearson, Norman J.; Shee, Simon R.

    2011-03-01

    The Kuruman Kimberlite Province is comprised of 16 small pipes and dikes and contains some of the oldest known kimberlites (>1.6 Ga). In this study, 12 intrusions are subdivided into three groups with distinct petrology, age, and geochemical and isotopic compositions: (1) kimberlites with groundmass perovskites defining a Pb-Pb isochron age of 1787 ± 69 Ma, (2) orangeite with a U-Pb perovskite age of 124 ± 16 Ma, and (3) ultramafic lamprophyres (aillikite and mela-aillikite) with a zircon U-Pb age of 1642 ± 46 Ma. The magma type varies across the Province, with kimberlites in the east, lamprophyres in the west and orangeite and ultramafic lamprophyres to the south. Differences in the age and petrogenesis of the X007 orangeite and Clarksdale and Aalwynkop aillikites suggest that these intrusions are probably unrelated to the Kuruman Province. Kimberlite and orangeite whole-rock major and trace element compositions are similar to other South African localities. Compositionally, the aillikites typically lie off kimberlite and orangeite trends. Groundmass mineral chemistry of the kimberlites has some features more typical of orangeites. Kimberlite whole-rock Sr and Nd isotopes show zoning across the Province. When the kimberlites erupted at ~1.8 Ga, they sampled a core volume (ca 50 km across) of relatively depleted SCLM that was partially surrounded by a rim of more metasomatized mantle. This zonation may have been related to the development of the adjacent Kheis Belt (oldest rocks ~2.0 Ga), as weaker zones surrounding the more resistant core section of SCLM were more extensively metasomatized.

  15. The volcanic-subvolcanic rocks of the fernando de noronha archipelago, southern atlantic ocean: Mineral chemistry

    NASA Astrophysics Data System (ADS)

    Lopes, Rosana Peporine; Ulbrich, Mabel N. Costas; Ulbrich, Horstpeter

    2014-12-01

    Fernando de Noronha archipelago presents an older Remédios Formation with subvolcanic intrusions, belonging to two different alkaline series, the sodic (undersaturated: basanites, tephrites, essexites, tephriphonolites, phonolites), and potassic ones (mildly undersaturated to silicic, with alkali basalts, basaltic trachyandesites, trachyandesites, trachytes), and lamprophyres. The upper Quixaba Formation presents nephelinite flows and basanites. A third minor unit, São José, is constituted by basanites carrying mantle xenoliths. Magnesian olivines occur in the Remédios basanites and alkali basalts, and in nephelinites. Melilites are present as groundmass grains in melilite melanephelinites (MEM). Clinopyroxenes (cpx) are mostly salites to titaniferous salites (Remédios sodic series), grading into aegirines in the differentiated aphyric phonolites. Cpx in the lamprophyres show disequilibrium textures. In the Quixaba flows, cpx are salites, enriched in Mg (especially in MEM). Amphiboles, remarkably, are common in tephriphonolites and phonolites and in basaltic trachyandesites, sometimes with disequilibrum zoning textures, and a conspicuous phase in lamprophyres. Dark micas are present as groundmass plates in MEM, OLM and PYM (olivine and pyroxene melanephelinites), with compositional variety (enriched in Ti, Ba, Sr) depending on the composition of the parent rock; BaO can be as high as 16-19%. Feldspars crystallize as calcic plagioclases, sanidines and anorthoclases, depending on the rock types, as phenocrysts and in groundmass, both in Quixaba and Remédios rocks; they are absent in nephelinites. Nephelines are found in Remédios sodic series types and Quixaba rocks. Haüyne and noseane are rarely observed in Remédios rocks.

  16. Evidence for alkaline igneous activity and associated metasomatism in the Reelfoot rift, south-central Midcontinent, U. S. A

    SciTech Connect

    Goldhaber, M.B.; Diehl, S.F.; Sutley, S.J. ); Flohr, M.J.K. )

    1993-03-01

    Alkaline igneous magmatism is commonly associated with intracontinental rifts such as the Reelfoot rift (RR). Direct evidence for alkaline magmatism in the area of the RR occurs as lamprophyre and syenite encountered in deep wells. The authors' new studies of lamprophyres and sedimentary rocks from wells in the region provide additional examples of alkaline magmatism and emphasize the effects of related metasomatism. Sedimentary rocks in the Dow Chemical No. 1 Garrigan well, which is not known to contain lamprophyre dikes, probably also were metasomatically altered, as they contain authigenic fluorapatite, Ce-phosphates, and other REE-rich minerals. Enrichments of incompatible and large ion lithophile elements commonly associated with alkaline magmatism occur in the New Madrid test well, near the crest of the Pascola Arch. The carbonate-free fraction of Paleozoic rocks in this well is highly enriched in Nb (500 ppm), Ba (> 5,000 ppm), La (500 ppm), Th (1,000 ppm), and F (2,400 ppm). Abundant inclusion-rich potassium-feldspar cement in a nearby well may also be the result of alkaline metasomatism. Fluorite and elevated F concentrations are found in several wells in the RR, and contrast with stratigraphically correlative platform carbonates of the Ozark uplift, which lack F enrichment. Well and spring water samples above the RR are enriched in fluorine (as much as 5,000 ppb) compared to samples away from the rift which typically have concentrations two orders of magnitude smaller. The data and observations are consistent with relatively widespread alkaline metasomatism, which was associated with the intrusion of alkaline magmas in the RR.

  17. Complete Analytical Data for Samples of Jurassic Igneous Rocks in the Bald Mountain Mining District, Nevada

    USGS Publications Warehouse

    du Bray, Edward A.

    2009-01-01

    This report presents all petrographic, major oxide, and trace element data for a set of 109 samples collected during an investigation of Jurassic igneous rocks in the Bald Mountain mining district, Nevada. Igneous rocks in the district include the Bald Mountain stock, quartz-feldspar porphyry dikes, basaltic andesite dikes, aplite sills, and rare lamprophyre dikes. These rocks, although variably altered near intrusion-related mineral deposits, are fresh in many parts of the district. Igneous rocks in the district are hosted by Paleozoic sedimentary rocks.

  18. Uranium and other element analyses of igneous rocks of Arkansas

    SciTech Connect

    Steele, K.F.

    1982-05-01

    Seventy-six samples of igneous rocks representing a variety of rock types and locations in Arkansas were analyzed by neutron activation analysis for the elements U, Th, Na, Al, Sc, Ti, V, Mn, Fe, La, Ce, Sm, Eu, Dy, Yb, Lu, and Hf. Samples were collected from the major igneous intrusions at Granite Mountain, Bauxite, Magnet Cove, Potash Sulfur Springs, and Murfreesboro, representing various syenites, lamprophyres, carbonatite, kimberlite, and periodotite. To make the data available for public use without further delay, this report is being issued without the normal technical and copy editing.

  19. Tectonic implications of Early Miocene OIB magmatism in a near-trench setting: The Outer Zone of SW Japan and the northernmost Ryukyu Islands

    NASA Astrophysics Data System (ADS)

    Kiminami, Kazuo; Imaoka, Teruyoshi; Ogura, Kazuki; Kawabata, Hiroshi; Ishizuka, Hideo; Mori, Yasushi

    2017-03-01

    The Outer Zone of the SW Japan and northernmost Ryukyu arcs was affected by intense igneous activity during the Miocene, characterized by MORB-like basalts, alkaline basalts, and S-type (with subordinate I-type) felsic to intermediate volcano-plutonic complexes. These igneous rocks are inferred to be the products of near-trench magmatism. Early Miocene (∼18 Ma) alkaline basalt dikes from the Shingu-Otoyo area in central northern Shikoku, and an alkaline lamprophyre dike from Tanegashima, one of the northernmost Ryukyu Islands, pre-date the Middle Miocene felsic to intermediate igneous rocks. The basalts and lamprophyre have compositions of basanite, basalt, trachybasalt and phonotephrite. They are characterized by elevated large-ion lithophile elements (LILEs; e.g., Sr, Ba, and Th) and high concentrations of high-field strength elements (HFSEs; e.g., TiO2, Nb, and Zr). The geochemical signatures of the basalts and lamprophyre suggest an ocean island basalt-type (OIB-type) mantle source. The occurrence of alkaline basalts and lamprophyre with OIB-type, intraplate geochemical signatures in a near-trench setting is unusual with regard to plate tectonic processes. We propose that trench-ward motion of the overriding plate during the period around the Early Miocene resulted in a shallowly dipping slab, and interplate coupling between the subducting Philippine Sea Plate (PSP) and the overlying crust beneath most of the Outer Zone in the western part of SW Japan and the northernmost Ryukyu Islands. The OIB-type magmatism in the near-trench environment is most plausibly explained by the upwelling of asthenospheric material from beneath the subducting slab, which migrated through fractures and/or tears in the slab. We envisage two possible scenarios for the formation of these fractures or tears: (1) the shallowing dip angle of the subducted PSP resulted in concave-upwards flexure of the slab, generating fractures in the flexed region; and (2) differential motion within

  20. Evidence for Differential Unroofing in the Adirondack Mountains, New York State, Determined by Apatite Fission-Track Thermochronology.

    PubMed

    Roden-Tice; Tice; Schofield

    2000-03-01

    Apatite fission-track ages of 168-83 Ma for 39 samples of Proterozoic crystalline rocks, three samples of Cambrian Potsdam sandstone, and one Cretaceous lamprophyre dike from the Adirondack Mountains in New York State indicate that unroofing in this region occurred from Late Jurassic through Early Cretaceous. Samples from the High Peaks section of the Adirondack massif yielded the oldest apatite fission-track ages (168-135 Ma), indicating that it was exhumed first. Unroofing along the northern, northwestern, and southwestern margins of the Adirondacks began slightly later, as shown by younger apatite fission-track ages (146-114 Ma) determined for these rocks. This delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the High Peaks. Apatite fission-track ages for samples from the southeastern Adirondacks are distinctly younger (112-83 Ma) than those determined for the rest of the Adirondack region. These younger apatite fission-track ages are from a section of the Adirondacks dissected by shear zones and post-Ordovician north-northeast-trending normal faults. Differential unroofing may have been accommodated by reactivation of the faults in a reverse sense of motion with maximum compressive stress, sigma1, oriented west-northwest. A change in the orientation of the post-Early Cretaceous paleostress field is supported by a change in the trend of Cretaceous lamprophyre dikes from east-west to west-northwest.

  1. The Late Cretaceous Alkaline Igneous Province in the Iberian Peninsula, and its tectonic significance

    NASA Astrophysics Data System (ADS)

    Rock, N. M. S.

    1982-04-01

    The Iberian Province consists of the following: the three subvolcanic, syenitic, major intrusive complexes of Monchique, Sines and Sintra in W. and SW Portugal, together with their basanitic/lamprophyric minor intrusive suites; basanitic volcanic complexes around Lisbon; at least some of a widespread suite of basanitic to theralitic minor intrusives in west central Portugal; about 80 small basanitic/lamprophyric to nepheline syenitic intrusions scattered through the Pyrenees, NE Spain, the French Corbières, and off the coast of NW Spain; and the Ormonde Seamount of the Gorringe Bank off the SW coast of Portugal. Most of these occurrences have been dated isotopically or from field evidence as Late Cretaceous. Geological and petrological details of the various occurrences are compiled and reviewed. Primary basanitic magmas were probably parental to the entire Province, and generated syenitic magmas by differentiation processes; oversaturated rocks were produced by alkali loss and perhaps also by crustal involvement. The Iberian Province is related to the opening of the N. Atlantic, specifically that of the Bay of Biscay.

  2. Early Jurassic mafic dykes from the Xiazhuang ore district (South China): Implications for tectonic evolution and uranium metallogenesis

    NASA Astrophysics Data System (ADS)

    Wang, Lian-Xun; Ma, Chang-Qian; Lai, Zhong-Xin; Marks, Michael A. W.; Zhang, Chao; Zhong, Yu-Fang

    2015-12-01

    A comprehensive study on zircon U-Pb age dating, whole-rock geochemistry and Sr-Nd isotope data has been conducted on the mafic rocks of the Xiazhuang uranium ore district and adjacent regions in South China. Based on field work and petrographic features, three rock types (the Kuzhukeng gabbro, the WNW-trending dolerite dykes and the NNE-trending lamprophyre dykes) are distinguished. Early Jurassic SHRIMP and LA-ICPMS ages of zircon for the Kuzhukeng gabbro (198 ± 1 Ma) and WNW-trending dolerite dykes (193 ± 4 Ma) have been obtained, which are 50 Ma older than previously thought (being Cretaceous). These geochronologic data provide new evidence for the rarely identified Early Jurassic magmatisms in South China. Whole-rock geochemical data for the Kuzhukeng gabbro and WNW-trending dolerite dykes are similar, both of which being higher in FeO and TiO2 but lower in SiO2 and K2O than the NNE-trending lamprophyre dykes. Trace element characteristics and Sr-Nd isotope data indicate arc-like signatures similar to the Cretaceous southeast coast basalts of China for the lamprophyre dykes, but an OIB-like geochemical affinity for the high-TiO2 mafic rocks similar to the Permo/Triassic Emeishan flood basalts and the Middle Jurassic Ningyuan alkaline basalts. We propose that the lamprophyre dykes formed in an arc volcanic system driven by the subduction of the paleo-Pacific plate. In contrast, the Kuzhukeng gabbro and associated dolerite dykes record the post-orogenic (Indosinian) extension event in the Tethyan tectonic regime. This further implies that the Indosinian extension may have lasted until the Early Jurassic, and therefore, the subduction of the paleo-Pacific plate in south China was probably later than this period. Most U deposits of the Xiazhuang area are located at the intersection between the WNW-trending dolerite dykes and the NNE-trending faults within the Triassic granites of eastern Guidong complex, South China. Previous metallogenesis studies assumed that

  3. Late-Variscan rare metal ore deposition and plume-related magmatism in the eastern European Variscides (D, CZ)

    NASA Astrophysics Data System (ADS)

    Seifert, Thomas

    2014-05-01

    Located at the northwestern border of the Bohemian Massif in the eastern part of the European Variscides, the Erzgebirge-Krušné hory is one of the most important metallogenic provinces in Europe with a 800-year history of mining. The following rare metal resources are associated with late-Variscan (315 - 280 Ma), postmagmatic mineralization pulses in the Erzgebirge-Krušné hory and surrounded areas: 900 kt Sn, 230 kt W, 10 kt Mo, 1 kt Ta, 300 kt Li, 200 kt Rb, 2 kt Cs, 1.5 kt In, 230 t Ge, 320 t Sc, 14 kt Sb, 10 kt Bi, and 3 kt Ag. At the end of the Variscan Orogeny the regional tectonic regime in Central Europe changed, indicating the beginning of the break-up of the supercontinent. The Late Carboniferous-Early Permian in Europe was a period of widespread basin formation that was associated in many areas with mantle-derived magmatic activity. 300 Ma-old dike swarms in NE England and the Scottish Midland Valley, the Oslo Graben and Scania, radiate from a triple junction in the northernmost part of Jutland. This triple junction marked the axis of a deep-mantle plume centered in this area. In this context it is important to note that the mantle plume center is surrounded by significant lamprophyre intrusions which show in some districts spatial-time relationships to Sn-W-polymetallic, Ag-base metal, and U mineralization. During the Late Carboniferous and Early Permian an extensive magmatic province developed within the present northern and central Europe, intimately with extensional tectonics, in an area stretching from southern Scandinavia, through the North Sea, into Northern Germany. Peak magmatic activity was concentrated in a narrow time-span from 300 to 280 Ma. Simultaneously in Stephanian-Early Permian an intensive bimodal magmatism associated with intra-continental extensional setting occurs in the European Variscides. Permo-Carboniferous volcanism in the Spanish Central System, Iberian Ranges, Cantabrian Chain, Pyrenees and the French Massif Central

  4. Ar-Ar ages, Sr-Nd isotope geochemistry, and implications for the origin of the silicate rocks of the Jacupiranga ultramafic-alkaline complex (Brazil)

    NASA Astrophysics Data System (ADS)

    Chmyz, Luanna; Arnaud, Nicolas; Biondi, João Carlos; Azzone, Rogério Guitarrari; Bosch, Delphine; Ruberti, Excelso

    2017-08-01

    The Jacupiranga Complex is one of several Meso-Cenozoic alkaline intrusive complexes along the margins of the intracratonic Paraná Basin in southern Brazil. The complex encompasses a wide range of rock-types, including dunites, wehrlites, clinopyroxenites, melteigites-ijolites, feldspar-bearing rocks (diorites, syenites, and monzonites), lamprophyres and apatite-rich carbonatites. While carbonatites have been extensively investigated over the last decades, little attention has been paid to the silicate rocks. This study presents new geochonological and geochemical data on the Jacupiranga Complex, with particular emphasis on the silicate lithotypes. 40Ar/39Ar ages for different lithotypes range from 133.7 ± 0.5 Ma to 131.4 ± 0.5 Ma, while monzonite zircon analyzed by SHRIMP yields a U-Pb concordia age of 134.9 ± 1.3 Ma. These ages indicate a narrow time frame for the Jacupiranga Complex emplacement, contemporaneous with the Paraná Magmatic Province. Most of the Jacupiranga rocks are SiO2-undersaturated, except for a quartz-normative monzonite. Based on geochemical compositions, the Jacupiranga silicate lithotypes may be separated into two magma-evolution trends: (1) a strongly silica-undersaturated series, comprising part of the clinopyroxenites and the ijolitic rocks, probably related to nephelinite melts and (2) a mildly silica-undersaturated series, related to basanite parental magmas and comprising the feldspar-bearing rocks, phonolites, lamprophyres, and part of the clinopyroxenites. Dunites and wehrlites are characterized by olivine compositionally restricted to the Fo83-84 interval and concentrations of CaO (0.13-0.54 wt%) and NiO (0.19-0.33 wt%) consistent with derivation by fractional crystallization, although it is not clear whether these rocks belong to the nephelinite or basanite series. Lamprophyre dikes within the complex are considered as good representatives of the basanite parental magma. Compositions of calculated melts in equilibrium with

  5. Petrogenetic constraints for the genesis of Archaean sanukitoid suites: geochemistry and isotopic evidence from Karelia, Baltic Shield

    NASA Astrophysics Data System (ADS)

    Kovalenko, A.; Clemens, J. D.; Savatenkov, V.

    2005-01-01

    New Sm-Nd isotope data are presented for late Archaean sanukitoid suites of the Karelian granite-greenstone terrane of the Baltic Shield. Within the terrane, there are regional variations in the Nd isotope compositions of the sanukitoids. Sanukitoids in the youngest Central Karelian domain have Nd isotope characteristics similar to depleted mantle, whereas those from the older West Karelian and Vodlozero domains have lower initial ɛNd values. The isotopic heterogeneity of the sanukitoids is interpreted to result from variations in the time interval between mantle source enrichment and the partial melting that produced the sanukitoid magmas. We therefore suggest a two-stage model of the generation of sanukitoid magmas. During first stage, the mantle was metasomatised by fluids and/or melts generated during subduction or tectonic underplating. Later, between 2.74 and 2.70 Ga, a tectonothermal anomaly generated the sanukitoid magmas by melting of the previously metasomatised mantle. Most of the sanukitoid intrusions are cut by calc-alkaline lamprophyre dykes that have the similar geochemical signatures to their sanukitoid wall rocks. New Sm-Nd isotope data for these lamprophyres suggest a genetic kinship between the sanukitoids and the lamprophyres. Comparison between chemical signatures of sanukitoids and modern, subduction-related magmas shows that Archaean sanukitoids actually have no modern analogues. Sanukitoid melts can be modelled as partial melts of mantle that had been metasomatised a short time previously. The melts could have been in equilibrium with residues containing Ol, Cpx plus minor Phl and Grt, at a pressure of about 2.5 GPa and a temperature of 1150-1230 °C. The small percentage of residual phlogopite would retain Rb in the mantle and explain the peculiar signature of low-Rb and high Ba and Sr, characteristic of the sanukitoids. We envisage a temporal evolution of the composition of the mantle in this region. This pattern of evolution controlled

  6. The Lost Gardar Intrusion: Critical Metal Exploration at the Paatusoq Syenite Complex, South East Greenland

    NASA Astrophysics Data System (ADS)

    Stacey, Mark; Finch, Adrian; Hughes, Josh; Christiansen, Ole

    2014-05-01

    Regional mapping by GEUS (Garde, 1998) of the Paatusoq region, South-East Greenland, defined two intrusive centres, the Paatusoq Gabbro (~23km2) and the Paatusoq Syenite (~240km2). These intruded the lithospherically weak boundary between Ketilidian meta-sedimentary rock to the East and to the West the Pelite-Psammite zone sediments unconformably overlying the Julianehåb batholith. Following the discovery of high rare earth element (REE=La-Yb+Y) anomalies in stream sediments (Steenfeldt, 2012) in the Paatusoq region, Paatusoq was the target of exploration by Nuna Minerals A/S in June 2013. The objective was to provide an assessment of the critical metal potential of the region. Exploration involved helicopter reconnaissance and sampling. The Paatusoq syenite (1144±1 Ma) was recognised by Garde (2002) as part of the Gardar Alkaline Igneous Province (1300-1140 Ma). Gardar centres are predominantly found on the South-Western coast and represent products of magmatism associated with repeated Mesoproterozoic rifting. Globally significant critical metal deposits are associated with the province including Motzfeldt (Ta-Nb) and Ilímaussaq (REE-Zr-Nb). Gardar intrusions with significant critical metal mineralisation often record interaction with late-stage fluorine-bearing fluids.Analysis integrated petrography and geochemistry, supplemented by two indicators of fluid interaction with the syenite; the cathodoluminescence textures of feldspars and the halogen content of biotite. The Paatusoq Gabbro showed heterogeneous primary layering and pegmatite schlieren to the West against the syenite. A Gardar Lamprophyre dyke cuts the Gabbro. Petrology showed; subhedral olivine, labradorite, biotite and quartz. Incompatible element geochemistry showed the gabbro has a Zr/Nb ratio >15 consistent with a Ketilidian affinity and the lamprophyre has a Zr/Nb ratio ~5, comparable with other Gardar lamprophyres. The Paatusoq syenite showed lithological variation from quartz

  7. Subduction-related High- to Ultrahigh-Potassic Rocks of the Ankara-Erzincan Suture Belt of Turkey: a geochemical and isotopic approach to source and petrogenesis

    NASA Astrophysics Data System (ADS)

    Genc, S. Can; Gulmez, Fatma; Karacik, Zekiye; Tuysuz, Okan; Prelevic, Dejan; Roden, Michael F.; Hames, Willis E.; Zeki Billor, M.

    2014-05-01

    A Late Cretaceous Volcano-sedimantary Succession (LCVS) trends parallel to Neo-Tethyan Suture in North Central Anatolia. Volcanic members of the LCVS consist mainy of coeval leucite phonolite/tephrites, trachytes, lamprophyres and andesitic rocks. Obtained Ar-Ar ages reveal that the volcanic activity occurred between 73.6±0.18 and 76.78±0.19 Ma, contemporaneous with the subduction of the Neo-Tethyan ocean beneath the Pontides. The volcanic rocks of LCVS are classified as alkaline, High- to ultrahigh-K, and silica-saturated and silica-unsaturated, geochemically. Rare calc-alkaline andesitic lavas are also occur within the volcanic sucession. Except the calc-alkaline samples, magmatic members of LCVS have similar major and trace element concentrations similar to the plagioleucitites or ultrapotassic rocks of the active orogenic zones (i.e. the Roman Province ultrapotassic series, Peccerillo, 2005). The multi element patterns on N-MORB- and Chondrite-normalized spider diagrams are characterized by significant LILE and LREE enrichments relative to HFSE and HREE, and display apparent Nb and Ta depletions, implying the subduction-related magmas. 87Sr/86Sr(i) (0.704493-0.706090) and 143Nd/144Nd(i) (0.512523-0.512680) isotope ratios are close to the mantle array, and are also in between the Aeolian Islands CA-Potassic rocks (Peccerillo, 2005), BSE and the circum-Mediterranean anorogenic Cenozoic igneous province (CiMACI, Lustrino&Wilson, 2007). Variable Mg# (33-60) evidences that these rocks are the products of evolved melts. The lead isotope values display a trend between EMI and DM, suggesting that the crustal involvement is more effective process during the generation of some lamprophyres relative to the other ultrapotassic rocks of LCVS. The results of clinopyroxene thermobarometry calculations reveal significant differences in depth of crystallization for the rock suites. Some trace element abundances and inter elemental ratios together with their co-variations show

  8. Metaconglomerate preserves evidence for kimberlite, diamondiferous root and medium grade terrane of a pre-2.7 Ga Southern Superior protocraton

    NASA Astrophysics Data System (ADS)

    Kopylova, M. G.; Afanasiev, V. P.; Bruce, L. F.; Thurston, P. C.; Ryder, J.

    2011-12-01

    We studied heavy minerals extracted from a diamondiferous metaconglomerate that formed 2697-2701 Ma in a successor basin within the Michipicoten Greenstone Belt (MGB) of the Wawa-Abitibi Terrane (Southern Superior Craton). The conglomerate is metamorphosed in the greenschist facies and contains mainly locally derived igneous mafic to felsic detritus, but also very minor components of medium grade metamorphic minerals, diamonds and paragenetic diamond indicator minerals. Comparison of the size distribution, resorbtion and N aggregation of diamonds in nearby Wawa lamprophyres and the metaconglomerate diamonds confirms that the latter were not derived from the proximal lamprophyric source. The heavy minerals in the metaconglomerate include diopside, olivine, corundum, chromite, almandine, pyrope with kelyphitic rims, picroilmenite, amphibole and anorthite. Low abundances of the heavy minerals (several grains per 4-70 tons of the metaconglomerate) are, in part, explained by their complete or partial replacement by the greenschist mineral assemblage. Detrital almandine and amphibole are inferred to originate in amphibolite facies rocks. Cr-diopside, olivine, chromite and anorthite were sourced from mafic-ultramafic anorthosite- and chromitite-bearing layered complexes mapped in the MGB. The presence of pyrope with more than 6 wt.% Cr 2O 3 suggests derivation from a cratonic root. Picroilmenite has compositions typical of kimberlite and unlike that of ultramafic lamprophyres and other unconventional diamondiferous volcanics. The Wawa metaconglomerate, therefore, should be considered analogous to the Witwatersrand successor basin conglomerate in recording indirect evidence for Archean kimberlites. The tight localization of the diamondiferous conglomerate in time and space was controlled by a quick (~ 3 Ma) erosion of the source kimberlite body. The location of the kimberlite-bearing > 2.7 Ga Superior protocraton was inferred from the provenance of the metaconglomerate

  9. The petrogenesis of oceanic kimberlites and included mantle megacrysts: The Malaitan alnoite

    NASA Technical Reports Server (NTRS)

    Neal, Clive R.

    1988-01-01

    The study of unambiguous suboceanic mantle was facilitated by the occurrence of anomalous kimberlite-type intrusives on Malaita in the Solomon Islands. The pseudo-kimberlites were termed alnoites, and are basically mica lamprophyres with melilite in the ground mass. Alnoitic magmas were explosively intruded into the Ontong Java Plateau (OJP) 34 Ma ago. The OJP is a vastly overthickened portion of the Pacific plate which now abuts the Indo-Australian plate. Malaita is considered to be the obducted leading edge of the OJP. Initial diapiric upwelling beneath the OJP produced the proto-alnoite magma. After impingement on the rigid lithosphere, megacrysts fractionation occurred, with augites precipitating first, representing the parental magma. Sea water-altered oceanic crust, which underplated the OJP, was assimilated by the proto-alnoite magma during megacrysts fractionation (AFC).

  10. Alkaline igneous rocks

    SciTech Connect

    Fitton, J.G.; Upton, B.G.J.

    1987-01-01

    In this volume, an international team of scientists provides an up-to-date overview of the nature, origin, and evolution of alkaline magmas. Particular attention is paid to carbonatites, lamprophyres, and lamproites which are rock suites of current interest not recently reviewed elsewhere. Recent work on the classical alkaline provinces of East Africa, South Greenland, and the Kola Peninsula is included together with reviews of other areas of alkaline magmatism in North and South America, East Greenland, Europe, West Africa, and the ocean basins. Other papers discuss the impact of experimental isotopic and geochemical studies of the petrogenesis of alkaline rocks. This book will be of interest to petrologists and geochemists studying alkaline igneous rocks, and to other earth scientists as a reference on the rapidly expanding field of igneous petrology.

  11. The Magnet Cove Rutile Company mine, Hot Spring County, Arkansas

    USGS Publications Warehouse

    Kinney, Douglas M.

    1949-01-01

    The Magnet Cove Rutile Company mine was mapped by the U.S. Geological Survey in November 1944. The pits are on the northern edge of Magnet Cove and have been excavated in the oxidized zone of highly weathered and altered volcanic agglomerate. The agglomerate is composed of altered mafic igneous rocks in a matrix of white to gray clay, a highly altered tuff. The agglomerate appears layered and is composed of tuffaceous clay material below and igneous blocks above. The agglomerate is cut by aplite and lamprophyre dikes. Alkalic syenite dikes crop out on the ridge north of the pits. At the present stage of mine development the rutile seems to be concentrated in a narrow zone beneath the igneous blocks of the agglomerate. Rutile, associated with calcite and pyrite, occurs as disseminated acicular crystals and discontinuous vein-like masses in the altered tuff. Thin veins of rutile locally penetrate the mafic igneous blocks of the agglomerate.

  12. The structural history and mineralization controls of the world-class Geita Hill gold deposit, Geita Greenstone Belt, Tanzania

    NASA Astrophysics Data System (ADS)

    Sanislav, I. V.; Brayshaw, M.; Kolling, S. L.; Dirks, P. H. G. M.; Cook, Y. A.; Blenkinsop, T. G.

    2016-05-01

    The Geita Hill gold deposit is located in the Archean Geita Greenstone Belt and is one of the largest gold deposits in East Africa. The Geita Greenstone Belt experienced a complex deformation and intrusive history that is well illustrated and preserved in and around the Geita Hill gold deposit. Deformation involved early stages of ductile shearing and folding (D1 to D5), during which episodic emplacement of large diorite intrusive complexes, sills, and dykes occurred. These ductile deformation phases were followed by the development of brittle-ductile shear zones and faults (D6 to D8). The last stages of deformation were accompanied by voluminous felsic magmatism involving the intrusion of felsic porphyry dykes, within the greenstone belt, and the emplacement of large granitic bodies now forming the margins of the greenstone belt. Early, folded lamprophyre dykes, and later lamprophyre dykes, crosscutting the folded sequence are common, although volumetrically insignificant. The gold deposit formed late during the tectonic history of the greenstone belt, post-dating ductile deformation and synchronous with the development of brittle-ductile shear zones that overprinted earlier structural elements. The main mineralizing process involved sulfide replacement of magnetite-rich layers in ironstone and locally the replacement of ferromagnesian phases and magnetite in the diorite intrusions. The intersection between the brittle-ductile (D6) Geita Hill Shear Zone and different structural elements of ductile origin (e.g., fold hinges), and the contact between banded ironstone and folded diorite dykes and sills provided the optimal sites for gold mineralization.

  13. Processes accompanying of mantle plume emplacement into continental lithosphere: Evidence from NW Arabian plate, Western Syria

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.

    2015-12-01

    Lower crustal xenoliths occurred in the Middle Cretaceous lamprophyre diatremes in Jabel Ansaria (Western Syria) (Sharkov et al., 1992). They are represented mainly garnet granulites and eclogite-like rocks, which underwent by deformations and retrograde metamorphism, and younger fresh pegmatoid garnet-kaersutite-clinopyroxene (Al-Ti augite) rocks; mantle peridotites are absent in these populations. According to mineralogical geothermobarometers, forming of garnet-granulite suite rocks occurred under pressure 13.5-15.4 kbar (depths 45-54 kn) and temperature 965-1115oC. At the same time, among populations of mantle xenoliths in the Late Cenozoic platobasalts of the region, quite the contrary, lower crustal xenoliths are absent, however, predominated spinel lherzolites (fragments of upper cooled rim of a plume head), derived from the close depths (30-40 km: Sharkov, Bogatikov, 2015). From this follows that ancient continental crust was existed here even in the Middle Cretaceous, but in the Late Cenozoic was removed by extended mantle plume head; at that upper sialic crust was not involved in geomechanic processes, because Precambrian metamorphic rocks survived as a basement for Cambrian to Cenozoic sedimentary cover of Arabian platform. In other words, though cardinal rebuilding of deep-seated structure of the region occurred in the Late Cenozoic but it did not affect on the upper shell of the ancient lithosphere. Because composition of mantle xenolithis in basalts is practically similar worldwide, we suggest that deep-seated processes are analogous also. As emplacement of the mantle plume heads accompanied by powerful basaltic magmatism, very likely that range of lower (mafic) continental crust existence is very convenient for extension of plume heads and their adiabatic melting. If such level, because of whatever reasons, was not reached, melting was limited but appeared excess of volatile matters which led to forming of lamprophyre or even kimberlite.

  14. Late Archean mafic volcanism in the Rainy Lake area, Minnesota

    SciTech Connect

    Day, W.C.

    1985-01-01

    The Late Archean greenstone-granite terrane of the Rainy Lake area of Minnesota contains a bimodal suite of mafic and felsic volcanic and coeval intrusive rocks. New geochemical data show that the mafic rocks occur in three distinct suites: (1) low-Ti olivine- and quartz-tholeiite, (2) high-Ti quartz-tholeiite and basaltic andesite, and (3) calc-alkaline lamprophyric monzodiorite and quartz diorite. The low-Ti tholeiites have only slightly evolved Mg-numbers from 53-63, Ni=125-300 ppm, and MORB-like REE. In contrast, the high-Ti tholeiites are more evolved, with Mg*=26-48, Ni=43-135 ppm, and higher total REE. Compared to the tholeiitic suites, the monzodiorite suite has more primitive Mg-numbers, with Mg*=70-78, Ni<410 ppm, and anomalously high LREE. The two tholeiitic suites cannot be genetically related by simple fractionation from a single parent magma; however, lower degrees of partial melting (<8 percent) of a mantle source (spinel periodotite) with REE=2-4 times chondrites could have produced the high-Ti tholeiites, and higher degrees of melting (20-30 percent) of a similar source could have generated the low-Ti tholeiites. In contrast, the monzodiorite suite must have been generated from either a LREE-rich or (and) a garnet-bearing source (garnet periodotite). The authors conclude that shallow melting (<40-50 km) within the Archean mantle in the Rainy Lake area produced the tholeiitic rocks, and that deep melting (>40-50 km) generated the lamprophyric monzodiorites.

  15. The structural history and mineralization controls of the world-class Geita Hill gold deposit, Geita Greenstone Belt, Tanzania

    NASA Astrophysics Data System (ADS)

    Sanislav, I. V.; Brayshaw, M.; Kolling, S. L.; Dirks, P. H. G. M.; Cook, Y. A.; Blenkinsop, T. G.

    2017-02-01

    The Geita Hill gold deposit is located in the Archean Geita Greenstone Belt and is one of the largest gold deposits in East Africa. The Geita Greenstone Belt experienced a complex deformation and intrusive history that is well illustrated and preserved in and around the Geita Hill gold deposit. Deformation involved early stages of ductile shearing and folding (D1 to D5), during which episodic emplacement of large diorite intrusive complexes, sills, and dykes occurred. These ductile deformation phases were followed by the development of brittle-ductile shear zones and faults (D6 to D8). The last stages of deformation were accompanied by voluminous felsic magmatism involving the intrusion of felsic porphyry dykes, within the greenstone belt, and the emplacement of large granitic bodies now forming the margins of the greenstone belt. Early, folded lamprophyre dykes, and later lamprophyre dykes, crosscutting the folded sequence are common, although volumetrically insignificant. The gold deposit formed late during the tectonic history of the greenstone belt, post-dating ductile deformation and synchronous with the development of brittle-ductile shear zones that overprinted earlier structural elements. The main mineralizing process involved sulfide replacement of magnetite-rich layers in ironstone and locally the replacement of ferromagnesian phases and magnetite in the diorite intrusions. The intersection between the brittle-ductile (D6) Geita Hill Shear Zone and different structural elements of ductile origin (e.g., fold hinges), and the contact between banded ironstone and folded diorite dykes and sills provided the optimal sites for gold mineralization.

  16. Dyke swarms and their role in the genesis of world-class gold deposits: Insights from the Jiaodong peninsula, China

    NASA Astrophysics Data System (ADS)

    Li, Lin; Li, Sheng-Rong; Santosh, M.; Li, Qing; Gu, Yue; Lü, Wen-Jie; Zhang, Hua-Feng; Shen, Jun-Feng; Zhao, Guo-Chun

    2016-11-01

    Jiaodong peninsula, located at the southeastern margin of the North China Craton, is well known for its rich endowment of super-large gold deposits. This region is also characterized by hundreds of intermediate - mafic dykes that cluster into several dyke swarms. In this study, we present zircon U-Pb ages which show that the timing of dyke emplacement as ca. 120 Ma, which followed the crystallization of the (quartz-) diorite porphyry at ca. 130 Ma. These ages coincide with the peak ages reported for magmatism and metallogeny in the central North China Craton. The various ages (2450-2570 and 154 Ma) from the inherited zircon crystals in these rocks suggest that substantial lower to middle crustal basement rocks and Jurassic granitoids were involved during dyke emplacement. The dyke swarms, varying between alkaline and subalkaline, are compositionally low-Si low-Ti lamprophyre and low-Si high-Ti dolerite porphyry in the western of the Jiaodong peninsula, whereas those in the eastern part are composed of both high-Si low-Ti and low-Si high-Ti lamprophyres. These features imply multiple sources for the dykes from convective asthenospheric mantle to ancient enriched lithospheric mantle with magma generation at different depths involving mixture of slab-derived hydrous fluids. The source magmas of the dykes were hydrous and enriched in volatiles as well as ore components, and their evolution occurred under high oxygen fugacity conditions. The relatively rapid emplacement and cooling of the dyke systems enabled the migration of fluids into ore-controlling faults or fractures. We envisage that the dyke swarms played an important role in generating the world-class gold mineralization of Jiaodong.

  17. Shoshonitic and ultrapotassic post-collisional dykes from northern Karakorum (Sinkiang, China)

    NASA Astrophysics Data System (ADS)

    Pognante, Ugo

    1991-01-01

    High-K calc-alkaline, shoshonitic and ultrapotassic post-collisional dykes of Neogene age have been found in the remote and little known region of northern Karakorum located around the Shaksgam valley, north of the K2-Gasherbrum range (China). The dykes derive from more or less comparable basic magma(s) and display rather unusual petrographic and geochemical characters with respect to the other K-rich rocks. The geochemical data are consistent with derivation of the basic magma(s) from small degrees of partial melting of garnet-lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the Indian plate beneath Karakorum. The spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene, phlogopite, plagioclase, garnet±amphibole followed by the precipitation of abundant alkali feldspar, amphibole±apatite±quartz. Additionally, assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz ( ± plagioclase) xenocrysts and by the occasional presence of granitic xenoliths. An apparent connection exists between magmatism and tectonism in the complex Karakorum Fault Zone (KFZ). It is suggested that, during the Neogene, the strike-slip KFZ and some adjacent post-metamorphic faults transiently behaved as extensional fault systems down to deep levels, triggering ascent and emplacement of the K-rich magma. The subsequent (re)activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper Baltoro Glacier and K2-Gasherbrum range, relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the Shaksgam valley area.

  18. Mineralogical and stable isotope studies of gold-arsenic mineralisation in the Sams Creek peralkaline porphyritic granite, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Faure, Kevin; Brathwaite, Robert L.

    2006-03-01

    At Sams Creek, a gold-bearing, peralkaline granite porphyry dyke, which has a 7 km strike length and is up to 60 m in thickness, intrudes camptonite lamprophyre dykes and lower greenschist facies metapelites and quartzites of the Late Ordovician Wangapeka formation. The lamprophyre dykes occur as thin (< 3 m) slivers along the contacts of the granite dyke. δ18Omagma values (+5 to +8‰, VSMOW) of the A-type granite suggest derivation from a primitive source, with an insignificant mature crustal contribution. Hydrothermal gold-sulphide mineralisation is confined to the granite and adjacent lamprophyre; metapelite country rocks have only weak hydrothermal alteration. Three stages of hydrothermal alteration have been identified in the granite: Stage I alteration (high fO2) consisting of magnetite-siderite±biotite; Stage II consisting of thin quartz-pyrite veinlets; and Stage III (low fO2) consisting of sulphides, quartz and siderite veins, and pervasive silicification. The lamprophyre is altered to an ankerite-chlorite-sericite assemblage. Stage III sulphide veins are composed of arsenopyrite + pyrite ± galena ± sphalerite ± gold ± chalcopyrite ± pyrrhotite ± rutile ± graphite. Three phases of deformation have affected the area, and the mineralised veins and the granite and lamprophyre dykes have been deformed by two phases of folding, the youngest of which is Early Cretaceous. Locally preserved early-formed fluid inclusions are either carbonic, showing two- or three-phases at room temperature (liquid CO2-CH4 + liquid H2O ± CO2 vapour) or two-phase liquid-rich aqueous inclusions, some of which contain clathrates. Salinities of the aqueous inclusions are in the range of 1.4 to 7.6 wt% NaCl equiv. Final homogenisation temperatures (Th) of the carbonic inclusions indicate minimum trapping temperatures of 320 to 355°C, which are not too different from vein formation temperatures of 340-380°C estimated from quartz-albite stable isotope thermometry. δ18O values

  19. Diamonds in an Archean greenstone belt: Diamond suites in unconventional rocks of Wawa, Northern Ontario (Canada)

    NASA Astrophysics Data System (ADS)

    Kopylova, Maya; Bruce, Loryn; Ryder, John

    2010-05-01

    Diamonds typically are found on Archean cratons entrained by younger Phanerozoic kimberlites. In contrast, Wawa diamonds are hosted in "unconventional", non-kimberlitic rocks that formed contemporaneously with the mafic and sedimentary rocks of the Archean Michipicoten Greenstone Belt (MGB). We studied two diamond suites that occur within the 2.9-2.7 Ga greenschist facies rocks of MGB located in the southwest portion of the Superior Craton (E. Canada). The first diamond suite henceforth referred to as the Wawa breccia diamonds (384 stones), are hosted in the 2618-2744 Ma calc-alkaline lamprophyres and volcaniclastic breccias, contemporaneous with pillow basalts and felsic volcanics of MGB. The second suite, the Wawa conglomerate diamonds (80 crystals), are hosted in the 2697-2700 Ma poorly sorted sedimentary polymictic conglomerate which is interpreted as a proximal alluvial fan debris flow in a fan-delta environment. The majority of the diamonds was found within the matrix of the conglomerate. The diamondiferous breccia occurs 20 km north of the town of Wawa, whereas the conglomerate is found 12 km northeast of Wawa. Diamonds from the 2 occurrences were characterized and described for provenance studies. Both the breccia and conglomerate diamonds show similar crystal habits, with the predominance of octahedral single crystals and ~ 10% of cubes. The conglomerate diamonds are significantly less resorbed (no resorbtion in 43% of the stones) than the breccia diamonds (8% non-resorbed stones). In both suites, only 21-24% show high degrees of resorption. The majority of crystals in both suites are colourless, with some yellow, brown and grey stones. Conglomerate diamonds had a wider variety of colours that were not seen in the breccia diamonds, including green and pink. The breccia diamonds contain 0-740 ppm N and show two modes of N aggregation at 0-30 and 60-95%. Among the breccia diamonds, Type IaA stones comprise 17%, whereas IaAB stones make up 49% of the

  20. Jurassic-Paleogene intra-oceanic magmatic evolution of the Ankara Mélange, North-Central Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Sarifakioglu, E.; Dilek, Y.; Sevin, M.

    2013-11-01

    Oceanic rocks in the Ankara Mélange along the Izmir-Ankara-Erzincan suture zone (IAESZ) in North-Central Anatolia include locally coherent ophiolite complexes (~179 Ma and ~80 Ma), seamount or oceanic plateau volcanic units with pelagic and reefal limestones (96.6 ± 1.8 Ma), metamorphic rocks with ages of 187.4 ± 3.7 Ma, 158.4 ± 4.2 Ma, and 83.5 ± 1.2 Ma, and subalkaline to alkaline volcanic and plutonic rocks of an island arc origin (~67-63 Ma). All but the arc rocks occur in a shaly-graywacke and/or serpentinite matrix, and are deformed by south-vergent thrust faults and folds that developed in the Middle to Late Eocene due to continental collisions in the region. Ophiolitic volcanic rocks have mid-ocean ridge (MORB) and island arc tholeiite (IAT) affinities showing moderate to significant LILE enrichment and depletion in Nb, Hf, Ti, Y and Yb, which indicate the influence of subduction-derived fluids in their melt evolution. Seamount/oceanic plateau basalts show ocean island basalt (OIB) affinities. The arc-related volcanic rocks, lamprophyric dikes and syeno-dioritic plutons exhibit high-K shoshonitic to medium-to high-K calc-alkaline compositions with strong enrichment in LILE, REE and Pb, and initial ϵNd values between +1.3 and +1.7. Subalkaline arc volcanic units occur in the northern part of the mélange, whereas the younger alkaline volcanic rocks and intrusions (lamprophyre dikes and syeno-dioritic plutons) in the southern part. The Early to Late Jurassic and Late Cretaceous epidote-actinolite, epidote-chlorite and epidote-glaucophane schists represent the metamorphic units formed in a subduction channel in the Northern Neotethys. The Middle to Upper Triassic neritic limestones spatially associated with the seamount volcanic rocks indicate that the Northern Neotethys was an open ocean with its MORB-type oceanic lithosphere by the Early Triassic. The Latest Cretaceous-Early Paleocene island arc volcanic, dike and plutonic rocks with

  1. Jurassic-Paleogene intraoceanic magmatic evolution of the Ankara Mélange, north-central Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Sarifakioglu, E.; Dilek, Y.; Sevin, M.

    2014-02-01

    Oceanic rocks in the Ankara Mélange along the Izmir-Ankara-Erzincan suture zone (IAESZ) in north-central Anatolia include locally coherent ophiolite complexes (∼ 179 Ma and ∼ 80 Ma), seamount or oceanic plateau volcanic units with pelagic and reefal limestones (96.6 ± 1.8 Ma), metamorphic rocks with ages of 256.9 ± 8.0 Ma, 187.4 ± 3.7 Ma, 158.4 ± 4.2 Ma, and 83.5 ± 1.2 Ma indicating northern Tethys during the late Paleozoic through Cretaceous, and subalkaline to alkaline volcanic and plutonic rocks of an island arc origin (∼ 67-63 Ma). All but the arc rocks occur in a shale-graywacke and/or serpentinite matrix, and are deformed by south-vergent thrust faults and folds that developed in the middle to late Eocene due to continental collisions in the region. Ophiolitic volcanic rocks have mid-ocean ridge (MORB) and island arc tholeiite (IAT) affinities showing moderate to significant large ion lithophile elements (LILE) enrichment and depletion in Nb, Hf, Ti, Y and Yb, which indicate the influence of subduction-derived fluids in their melt evolution. Seamount/oceanic plateau basalts show ocean island basalt (OIB) affinities. The arc-related volcanic rocks, lamprophyric dikes and syenodioritic plutons exhibit high-K shoshonitic to medium- to high-K calc-alkaline compositions with strong enrichment in LILE, rare earth elements (REE) and Pb, and initial ɛNd values between +1.3 and +1.7. Subalkaline arc volcanic units occur in the northern part of the mélange, whereas the younger alkaline volcanic rocks and intrusions (lamprophyre dikes and syenodioritic plutons) in the southern part. The late Permian, Early to Late Jurassic, and Late Cretaceous amphibole-epidote schist, epidote-actinolite, epidote-chlorite and epidote-glaucophane schists represent the metamorphic units formed in a subduction channel in the northern Neotethys. The Middle to Upper Triassic neritic limestones spatially associated with the seamount volcanic rocks indicate that the northern

  2. Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple Magma Types During Orogenic Collapse

    NASA Astrophysics Data System (ADS)

    Freeman, M.; Owen, J. P.; Hoskin, P. W.

    2009-05-01

    Eocene dyke swarms in southeastern British Columbia provide an important record of the tectonic and magmatic history of the Cordillera following orogenic collapse. New field mapping, petrographic, and geochemical data is presented for a swarm of more than thirty dykes located near the mining town of Trail, B.C. Detailed field mapping revealed that individual dykes are highly diverse, both in composition and morphology. As a group, the dykes trend northwest (average strike of 338 degrees) and dip steeply to the southwest. Their average thickness is approximately 1.5m, with a range from 4.5m to less than 1cm. Three sub-parallel dykes were mapped for a length of 2km, and exhibit irregularities in their form such as branching and offshoots that follow fractures in the country rock. Thin-section analysis shows a wide variety of rock types within the swarm, including: micro-quartz syenite, micro-syenite, micro-monzonite, latite, basalt, basaltic andesite, and lamprophyre. Texturally, these samples are consistently porphyritic and partially altered to chlorite and sericite. This alteration commonly occurs in concentric rims around phenocrysts. The samples are typically intergranular, although some display trachytic texture. Whole-rock geochemistry shows that the dykes have a wide range in composition, with SiO2 between 76.45 wt.% and 45.15 wt.% and MgO between 0.13 wt.% and 13.16 wt.%. The results also revealed that one dyke has very high values of Ni (430 ppm), Cr (1420 ppm), and Co (50 ppm), giving it a fairly primitive composition. Harker diagrams and trace element plots show three distinct groups: mafic calc-alkaline dykes, felsic calc- alkaline dykes, and minette lamprophyres. The felsic dykes are characterized by negative Eu and Sr anomalies suggesting fractionation of plagioclase feldspar, as well as pronounced negative P and Ti anomalies. The minettes are enriched in LILE and depleted in HSFE relative to the mafic dykes. The three groups do not appear to be

  3. Postorogenic Dike Complexes and Implications for Metallogenesis

    NASA Astrophysics Data System (ADS)

    Luo, Zhaohua; Lu, Xinxiang; Wang, Bingzhang; Chen, Bihe; Huang, Fan; Yang, Zongfeng; Wang, Yang

    Large scale granitic magmatism is commonly followed by emplacement of postorogenic dike swarms. These dikes swarms are characterized by a wide compositional spectrum and are volumetrically minor with respect to the associated granitic intrusions. Observations in the Taihangshan, Yanshan, Eastern Kunlun and Tianshan orogenic belts, show that dikes can be divided into five groups: lamprophyric, basaltic, dioritic (andesitic), granodioritic (dacitic) and granitic (rhyolitic). Most researchers have paid attention only on the basaltic or lamprophyric dikes and often confused them with the dike swarms related to the continental breakup. Combined with recent works on studies of magmatic processes, it can be inferred that these dikes are the products of primary or near-primary magmas. Based on the analysis of thermal regimes and regional lithospheric petrological structures, the authors suggest that conditions for the production of these magmas require lithospheric delamination of an orogen with a thickened mafic lower crust. Therefore, the dikes should be formed at the stage of transition of the regional structural stress field from compression to extension and can be used to mark the ending of an orogenic cycle. In this case, the dike swarm can be considered as postorogenic dike complexes. Furthermore, we suggest that such dike complexes are widespread worldwide. Thus, there are three types of dike swarms: (1) dikes related to continental breakup, (2) dikes related to batholiths, and (3) dikes associated with large igneous provinces. The emplacement of a postorogenic dike complex should be also accompanied by the large scale hydrothermal activity, when the rate of the heat transfer is considered. As the concentration of the ore-forming elements in the deep fluids depends on pressure, a new petrogenetic model implies that metallogenesis accompanies the postorogenic dike swarm. Field examinations suggest that the observations of outcrops can be used to recognize the paths

  4. Phlogopite- and clinopyroxene-dominated fractional crystallization of an alkaline primitive melt: petrology and mineral chemistry of the Dariv Igneous Complex, Western Mongolia

    NASA Astrophysics Data System (ADS)

    Bucholz, Claire E.; Jagoutz, Oliver; Schmidt, Max W.; Sambuu, Oyungerel

    2014-04-01

    We present field relationships, petrography, and mineral major and trace element data for the Neoproterozoic Dariv Igneous Complex of the Altaids of Western Mongolia. This unique complex of high-K plutonic rocks is composed of well-exposed, km-scale igneous intrusions of wehrlites, phlogopite wehrlites, apatite-bearing phlogopite clinopyroxenites, monzogabbros, monzodiorites, and clinopyroxene-bearing monzonites, all of which are intruded by late stage lamprophyric and aplitic dikes. The biotite-dominated igneous complex intrudes depleted harzburgitic serpentinite. The observed lithological variability and petrographic observations suggest that the plutonic rocks can be ascribed to a fractionation sequence defined by olivine + clinopyroxene ± Fe-Ti oxides → phlogopite + apatite → K-feldspar + plagioclase → amphibole + quartz. Notably, phlogopite is the dominant hydrous mafic mineral. Petrogenesis of the observed lithologies through a common fractionation sequence is supported by a gradual decrease in the Mg# [molar Mg/(Fetotal + Mg) × 100] of mafic minerals. Crystallization conditions are derived from experimental phase petrology and mineral chemistry. The most primitive ultramafic cumulates crystallized at ≤0.5 GPa and 1,210-1,100 °C and oxygen fugacity ( fO2) of +2-3 ∆FMQ (log units above the fayalite-quartz-magnetite buffer). Trace element modeling using clinopyroxene and apatite rare earth element compositions indicates that the dominant mechanism of differentiation was fractional crystallization. The trace element composition of a parental melt was calculated from primitive clinopyroxene compositions and compares favorably with the compositions of syn-magmatic lamprophyres that crosscut the fractionation sequence. The parental melt composition is highly enriched in Th, U, large ion lithophile elements, and light rare earth elements and has a pronounced negative Nb-Ta depletion, suggestive of an alkaline primitive melt originating from a subduction

  5. Heteromorphism and crystallization paths of katungites, Navajo volcanic field, Arizona, USA

    SciTech Connect

    Laughlin, A.W.; Charles, R.W.; Aldrich, M.J. Jr.

    1986-01-01

    A swarm of thin, isochemical but heteromorphic dikes crops out in the valley of Hasbidito Creek in NE Arizona. The swarm is part of the dominantly potassic, mid-Tertiary Navajo volcanic field of the Colorado Plateau. Whole-rock chemical analyses of five samples from four of the dikes indicate that they are chemically identical to the katungites of Uganda. These dikes show the characteristic seriate-porphyritic texture of lamprophyres. Samples of an olivine-melilitite dike from the same swarm lack this texture and the chemical analysis, while similar to those of the other dikes, shows effects from the incorporation of xenocrystic olivine. Over 20 mineral phases have been identified in the Arizona samples and as many as 18 phases may occur in a single sample. The major phases are phlogopite, olivine, perovskite, opaque oxides, +- melilite and +- clinopyroxene. Based upon the modal mineralogies and textures of ten dike samples, we recognize five general non-equilibrium assemblages. Comparison of these assemblages with recent experimental results shows that they represent various combinations of complete and incomplete reactions. Reaction relations were determined by entering melt and phase compositions into the computer program GENMIX to obtain balanced reactions. By combining petrographic observations with mineral chemical data, balanced reactions from GENMIX, and the recently determined phase diagrams we are able to trace crystallization paths for the katungite magma.

  6. Cortlandt-Beemerville magmatic belt: A probable late Taconian alkalic cross trend in the central Appalachians

    NASA Astrophysics Data System (ADS)

    Ratcliffe, Nicholas M.

    1981-07-01

    A belt of alkalic to alkalic-calcic pipes, lamprophyres, and intrusive complexes of probable Late Ordovician age extends from the Peach Lake Croton Falls area of Westchester County, New York, about 100 km S80°W to Beemerville, New Jersey. The rocks are intruded across a Taconic dynamothermal belt ranging from sillimanite grade on the east to chlorite grade on the west. Foliated Middle Ordovician and older rocks containing slaty cleavage or coarser grained metamorphic fabrics are crosscut by dikes that are posttectonic to late syntectonic relative to the Taconian dynamothermal events. Analysis of thrust faults and fold structures within this belt suggests that this cross-grain belt of alkalic to weakly alkalic rocks intruded steeply dipping brittle fractures trending N40° to 50°W, N35° to 60°E, and N70° to 80°E and along more ductile zones trending N20° to N70°E. This plutonic activity was restricted to a discrete east-west belt. The clear posttectonic to syntectonic nature of the dikes and the spatial and temporal association with Ordovician tectonism suggest that magmatic activity may be related to fracturing of mantle rock at the junction of two salients of Taconic age that intersect in the New York recess. The tectonic setting of the intrusive belt is unusual because it is associated in space and time with compressional tectonics of the Taconic orogeny, rather than with extensional rifting.

  7. Endogenous and nonimpact origin of the Arkenu circular structures (al-Kufrah basin—SE Libya)

    NASA Astrophysics Data System (ADS)

    Cigolini, Corrado; di Martino, Mario; Laiolo, Marco; Coppola, Diego; Rossetti, Piergiorgio; Morelli, Marco

    2012-11-01

    The twin Arkenu circular structures (ACS), located in the al-Kufrah basin in southeastern Libya, were previously considered as double impact craters (the "Arkenu craters"). The ACS consist of a NE (Arkenu 1) and a SW structure (Arkenu 2), with approximate diameters of about 10 km. They are characterized by two shallow depressions surrounded by concentric circular ridges and silica-impregnated sedimentary dikes cut by local faults. Our field, petrographic, and textural observations exclude that the ACS have an impact origin. In fact, we did not observe any evidence of shock metamorphism, such as planar deformation features in the quartz grains of the collected samples, and the previously reported "shatter cones" are wind-erosion features in sandstones (ventifacts). Conversely, the ACS should be regarded as a "paired" intrusion of porphyritic stocks of syenitic composition that inject the Nubia Formation and form a rather simple and eroded ring dike complex. Stock emplacement was followed by hydrothermal activity that involved the deposition of massive magnetite-hematite horizons (typical of iron oxide copper-gold deposits). Their origin was nearly coeval with the development of silicified dikes in the surroundings. Plugs of tephritic-phonolitic rocks and lamprophyres (monchiquites) inject the Nubian sandstone along conjugate fracture zones, trending NNW-SSE and NE-SW, that crosscut the structural axis of the basin.

  8. Mineralogical evolution and REE mobility during crystallisation of ancylite-bearing ferrocarbonatite, Haast River, New Zealand

    NASA Astrophysics Data System (ADS)

    Cooper, Alan F.; Collins, Alice K.; Palin, J. Michael; Spratt, John

    2015-02-01

    Ferrocarbonatites from the lamprophyric Alpine Dyke Swarm, south Westland, New Zealand are composed of dolomite-calcite-albite-hematite and contain interstitial patches dominated by calcite-ancylite-barite-monazite-thorite-albite-aeschynite-analcime, interpreted as modified late-stage segregations. The dominant carbonate in the ferrocarbonatite is a ferroan dolomite that contains vermicular and blocky patches of calcite and a more Fe-rich ankerite. The calcite is interpreted as the product of exsolution or the by-product, with dolomite and hematite, of the oxidation of primary ankerite during interaction with hydrothermal fluids. Late stage ancylite-rich segregations have elevated 87Sr/86Sr compositions relative to host carbonatite suggesting they have crystallised from fluids that have equilibrated with host schist, but with the REE derived from fractionation of ferrocarbonatite. Mineral veining indicates this stage of crystallisation post-dated the ankerite to dolomite replacement. The carbonatites, as inferred from mineral associations, textures and carbonate geothermometry, have a complex history of recrystallisation from late stage, low temperature carbo-hydrothermal fluids. All carbonatitic phases have convex-upward chondrite normalised REE patterns enriched in Nd, and are relatively depleted in lighter LREE and in HREE. Depletion in La and Ce is attributed to either complementary enrichment in felsic magmas during initial separation of carbonatite, or more likely, to subsequent preferentially enhanced mobility of La- and Ce-Cl- complexes in low-temperature aqueous fluids.

  9. Devonian to Early Carboniferous magmatic alkaline activity in the Tafilalt Province, Eastearn Morocco: An Eovariscan episode in the Gondwana margin, north of the West African Craton

    NASA Astrophysics Data System (ADS)

    Pouclet, André; El Hadi, Hassan; Bardintzeff, Jacques-Marie; Benharref, Mohammed; Fekkak, Abdelilah

    2017-05-01

    To the eastern edge of the Moroccan Anti-Atlas, the Tafilalt Province is the repository of a Lower Palaeozoic platform and basin sedimentation constrained by a W-E and NW-SE fault network. During the mid-late Devonian, an extensional tectonic activity, demonstrated by sharp changes in sediment thickness and development of syn-sedimentary faults, was contemporaneous with a significant magmatic activity. A great number of doleritic dykes, sills, and laccoliths intruded sedimentary Silurian to Lower Visean strata. The intrusions were linked to sub-water volcanic activities with spilitic lava flows and pyroclastites during two main pulses in the Famennian-Tournaisian and in the Early Visean. The rocks consist of basaltic dolerites, lamprophyric dolerites and analcite-bearing camptonites, sharing a sodic alkaline magma composition. The magma derived from low partial melting degree of the metasome layer of the lithospheric subcontinental mantle, below the spinel-garnet transition zone. This Tafilalt tectono-magmatic activity was coeval with the Eovariscan phase in the Moroccan Meseta, which was responsible for the opening of Western Meseta basins and their transitional to alkaline volcanic activities in the Late Devonian to Early Carboniferous time.

  10. New paleomagnetic data from 1.80-1.75 Ga mafic intrusions of Fennoscandia and Sarmatia: implications for the late Paleoproterozoic paleogeography of Baltica and Laurentia

    NASA Astrophysics Data System (ADS)

    Pisarevsky, Sergei; Lubnina, Natalia; Sokolov, Svetoslav; Bogdanova, Svetlana

    2016-04-01

    A series of recently dated 1.78-1.75 Ga lamprophyre and shoshonite intrusions are exposed north of Ladoga Lake in southern Karelia (Fennoscandia). We carried out a paleomagnetic study of these intrusions and an additional study of the coeval gabbro-dolerite Ropruchey sill near the Onega Lake. All studied rocks carry a stable primary remanence supported by positive contact tests. We also studied 14 mafic dykes and 1 mafic sill from Ukrainian shield (Sarmatia). Most of these intrusions have been dated or re-dated recently by U-Pb (baddeleyite) method at 1.80-1.75 Ga. Ukrainian dykes also carry a consistent stable bipolar remanence. Two positive contact tests suggest that this remanence is primary. A comparison of new and previously published paleomagnetic data shows a significant difference between Fennoscandian and Sarmatian 1.80-1.75 Ga paleopoles. This implies that the final assemble of Baltica by docking of Volgo-Sarmatia and Fennoscandia occurred after 1.75 Ga. Consequently these two parts of Baltica should be considered as independent blocks in pre-1.75 Ga paleogeographic reconstructions. Using late Paleoproterozoic paleomagnetic data from Laurentia together with geological constraints we have built a new kinematic paleogeographic model for Laurentia and Baltica in the Statherian.

  11. Chemistry and petrography of calcite in the KTB pilot borehole, Bavarian Oberpfalz, Germany

    USGS Publications Warehouse

    Komor, S.C.

    1995-01-01

    The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of calcite in the drilled section: 1) metamorphic calcite in calc-silicate and marble; 2) crack-filling calcite in all lithologies; and 3) replacement calcite in altered minerals. Crack-filling and replacement calcite postdate metamorphic calcite. Multiple calcite generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include calcite originally formed at temperatures of 150-350??C. Presently, crack-filling calcite is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling calcite to lower temperatures means that calcite chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author

  12. The Permian mafic dyke swarm of the Panticosa pluton (Pyrenean Axial Zone, Spain): simultaneous emplacement with the late-Variscan extension

    NASA Astrophysics Data System (ADS)

    Gil-Imaz, Andrés; Lago-San José, Marceliano; Galé, Carlos; Pueyo-Anchuela, Óscar; Ubide, Teresa; Tierz, Pablo; Oliva-Urcia, Belén

    2012-09-01

    The Panticosa dyke swarm was emplaced into the late Carboniferous (301 ± 7 Ma) Panticosa pluton. It consists of diabase and lamprophyre dykes. According to their composition, two lithotypes are differentiated: (i) an early system of calc-alkaline affinity and N-S average trend and (ii) a late system of alkaline affinity and E-W average trend. The fracture pattern distribution with respect to both dyke systems suggests that all dykes occupied pre-existing fractures. The magnetic fabric analysis and petrological data indicate that the emplacement model differed for each dyke system. For the calc-alkaline dykes, magma flow and tectonic stress conditions influenced emplacement. The emplacement of alkaline dykes, on the other hand, was mainly controlled by tectonic stress. The combined interpretation of structural and magnetic fabric data suggests an emplacement history for all late-Variscan dykes during a constant regional N-S trending extension. This study emphasizes the role of pure extension in the late-Variscan evolution of the Pyrenean Axial Zone.

  13. The low-grade Canal de las Montañas Shear Zone and its role in the tectonic emplacement of the Sarmiento Ophiolitic Complex and Late Cretaceous Patagonian Andes orogeny, Chile

    NASA Astrophysics Data System (ADS)

    Calderón, M.; Fosdick, J. C.; Warren, C.; Massonne, H.-J.; Fanning, C. M.; Cury, L. Fadel; Schwanethal, J.; Fonseca, P. E.; Galaz, G.; Gaytán, D.; Hervé, F.

    2012-02-01

    The Canal de las Montañas Shear Zone (CMSZ), southern Patagonian Andes (51-52°S), is a low-grade mylonite belt generated from felsic ignimbritic, pelitic and basaltic protoliths of the Late Jurassic-Early Cretaceous Rocas Verdes basin. The different types of rock fabrics across the CMSZ are thought to be associated with relatively intermediate and high strain conditions, characterized by the development of a narrow western belt of S-Ć-type mylonites and phyllonites interpreted as the metamorphic sole thrust of the Sarmiento Ophiolitic Complex. Highly strained rocks of the CMSZ display a reverse, continent-ward tectonic transport, with a minor dextral component of shearing. Transitional pumpellyite-actinolite and upper greenschist facies metamorphic conditions at ca. 5-6 kbar and 230-260 °C indicate that the primary shearing event occurred in a subduction zone setting. In-situ 40Ar/39Ar laserprobe chronology yielded ages of ca. 85 Ma on syntectonic phengite which are interpreted as representing cooling synchronous with mica crystallization during the main compressive deformational event. The 78-81 Ma U-Pb zircon crystallization ages of cross-cutting plutonic and hypabyssal rocks and 40Ar/39Ar amphibole age of ca.79 Ma from lamprophyric dikes within the fold-thrust belt constrain an upper age limit of the ophiolite tectonic emplacement deformation.

  14. A fully coupled three-dimensional THM analysis of the FEBEX in situ test with the ROCMAS Code: Prediction of THM behavior in a bentonite barrier

    SciTech Connect

    Rutqvist, J.; Tsang, C-F.

    2003-09-01

    This paper presents a fully coupled thermal-hydrological-mechanical analysis of FEBEX--a large underground heater test conducted in a bentonite and fractured rock system. System responses predicted by the numerical analysis--including temperature, moisture content, and bentonite-swelling stress--were compared to field measurements at sensors located in the bentonite. An overall good agreement between predicted and measured system responses shows that coupled thermal-hydrological-mechanical processes in a bentonite barrier are well represented by the numerical model. The most challenging aspect of this particular analysis was modeling of the bentonite's mechanical behavior, which at FEBEX turned out to be affected by gaps between prefabricated bentonite blocks. At FEBEX, the swelling pressure did not develop until a few months into the experiment when moisture swelling of bentonite blocks had closed the gaps completely. Moreover, the wetting of the bentonite took place uniformly from the rock and was not impacted by the permeability difference between the Lamprophyres dykes and surrounding rock.

  15. A petrogenetic study of anorogenic felsic magmatism in the Cretaceous Paresis ring complex, Namibia: evidence for mixing of crust and mantle-derived components

    NASA Astrophysics Data System (ADS)

    Mingram, B.; Trumbull, R. B.; Littman, S.; Gerstenberger, H.

    2000-10-01

    Paresis is one of a group of Cretaceous ring complexes extending from the coast some 350 km NE across the Damara Belt. It consists of over 90% rhyolites and comendites, with subordinate intrusions of quartz syenite and alkali-feldspar syenite. These felsic units are accompanied by very minor amounts of silica-undersaturated basalt, phonolite and lamprophyre. Located near the edge of the Congo Craton, Paresis is the farthest inland of any felsic complex in the Cretaceous ring complex group. The other ring complexes in the vicinity consist of carbonatites and undersaturated alkaline rocks (e.g., Okorusu, Kalkfeld, Etaneno, Ondurakorume). Geochemical and isotopic data provide evidence for both mantle and crustal components in the sources of the Paresis magmas. The alkaline basalts, phonolite and lamprophyre have overlapping Sr and Nd isotopic initial ratios which plot within the mantle array close to bulk-earth values ( ɛNd=-0.9 to -2.8 and 87Sr/ 86Sr(i)=0.7042-0.7054) and may indicate a mantle plume component. The rhyolite units comprise metaluminous feldspar rhyolites and peraluminous, more differentiated quartz-feldspar rhyolites. Both units show prominent negative Nb and Ta anomalies on mantle-normalized multielement diagrams and have extremely nonradiogenic Nd ratios ( ɛNd=-21) and Sr initial ratios of 0.7117-0.7138. These isotopic values suggest a crustal origin from pre-Damara (Early Precambrian) gneisses and granitoids, which are exposed in the Congo craton and related inliers in northern Namibia. The comendites are peralkaline, highly differentiated rocks. In contrast to the rhyolites, comendites lack mantle-normalized Nb and Ta anomalies, have higher HFSE and LREE contents, extreme negative Eu anomalies and ɛNd values of -11. Like the comendites, alkali-feldspar syenites are peralkaline, lack Nb and Ta anomalies, have negative Eu anomalies and high HFSE concentrations. Their ɛNd values are -6.5 to -8. The quartz syenites overlap with the peralkaline

  16. Variable sources for Cretaceous to recent HIMU and HIMU-like intraplate magmatism in New Zealand

    NASA Astrophysics Data System (ADS)

    van der Meer, Q. H. A.; Waight, T. E.; Scott, J. M.; Münker, C.

    2017-07-01

    Continental intraplate magmas with isotopic affinities similar to HIMU are identified worldwide. Involvement of an asthenospheric HIMU or HIMU-like source is contested because the characteristic radiogenic Pb compositions coupled with unradiogenic Sr and intermediate Nd and Hf compositions can also result from in-situ ingrowth in metasomatised lithospheric mantle. Sr-Nd-Pb-Hf isotopic compositions of late Cretaceous lamprophyre dikes from Westland, New Zealand, provide new insights into the formation of a HIMU-like alkaline intraplate magmatic province under the Zealandia continent. The oldest (102-100 Ma) calc-alkaline lamprophyres are compositionally similar to the preceding arc-magmatism (206Pb/204Pb(i) = 18.6, 207Pb/204Pb(i) = 15.62, 208Pb/204Pb(i) = 38.6, 87Sr/86Sr(i) = 0.7063-0.7074, εNd(i) = -2.1 - +0.1 and εHf(i) = -0.2 - +2.3) and are interpreted as melts originating from subduction-modified lithosphere. Alkaline dikes erupted on the inboard Gondwana margin shortly after cessation of subduction (92-84 Ma) have heterogeneous isotopic properties: 206Pb/204Pb(i) = 18.7 to 19.4, 207Pb/204Pb(i) = 15.60 to 15.65, 208Pb/204Pb(i) = 38.6 to 39.4, 87Sr/86Sr(i) = 0.7031 to 0.7068, εNd(i) = +4.5 to +8.0 and εHf(i) = +5.1 to +8.0. Melt compositions point to an amphibole-bearing spinel facies lithospheric mantle source enriched by metasomatism that introduced, amongst many elements, U + Th which lead to rapid ingrowth to HIMU-like compositions. Importantly, this HIMU-like source enrichment appears to have completely originated from the complex local subduction history. A coeval episode of alkaline magmatism (mainly 98-82 Ma) occurred outboard of Gondwana's former active margin and on the Hikurangi oceanic plateau (accreted to Zealandia in the Early Cretaceous) with compositions closer to true HIMU (206Pb/204Pb(i) ≈ 20.5, 207Pb/204Pb(i) ≈ 15.7, 208Pb/204Pb(i) ≈ 40.0, εNd(i) ≈ 4.5 and εHf(i) ≈ 4.0). In contrast to the inboard HIMU-like magmas, the

  17. The Eruptive History of the Talpa-Mascota-San Sebastian Volcanic Field in Western Mexico.

    NASA Astrophysics Data System (ADS)

    Ownby, S.; Lange, R.; Carmichael, I. S.; Hall, C.

    2004-12-01

    The eruptive history of the Talpa-Mascota-San Sebastian (TMSS) volcanic field in the Jalisco Block (JB) of western Mexico is presented. The JB is bounded by the Tepic-Zacoalco and Colima grabens, as well as the Middle America Trench where the Rivera plate subducts beneath North America. The TMSS volcanic field spans ˜2030 km2 and contains ˜123 small cones and flows of minette, absarokite, basic hornblende lamprophyre, basaltic andesite, and andesite. The petrology of these lavas is described in Lange and Carmichael (1990, 1991) and Carmichael et al. (1996). Of the ˜123 distinguishable eruptive units within this volcanic field, 26 samples have been dated by the 40Ar/39Ar method, and are combined with 10 dates from a previous abstract and nine dates from the literature (for a total of 45). The oldest lavas (2.35 to 0.5 Ma) are found in the Talpa region, whereas the youngest lavas (predominantly < 0.5 Ma) are found in the Mascota and San Sebastain regions to the north. There is thus a clear trend of volcanism becoming younger to the north, away from the trench. On the basis of these ages, field mapping, and the use of ortho airphotos and DEMs, it is estimated that a combined volume of < 12 km3 erupted in the last 1 Myr. The dominant lava type is basaltic andesite ( ˜44 %), followed by minette ( ˜20 %), basic, hornblende lamprophyre ( ˜17 %), andesite ( ˜13 %), and absarokite ( ˜6 %). Thus more than half of the eruptive material (57 %) is andesite and basaltic andesite, which erupted in close spatial and temporal association with the highly potassic lavas. There is no time progression to the type of magma erupted. The volumes of the potassic lava types are dwarfed by the amount of intermediate, calc-alkaline magma ( ˜360 km3) that has erupted over the same time period (< 1 Ma) within the Tepic-Zacoalco graben in western Mexico. These age results confirm that the potassic lavas of Mascota (not unlike those erupted 3-4 Myr ago in the Sierra Nevada batholith

  18. Mantle xenocrysts of Chompolo field of the alkaline volcanics, Aldan shield, South Yakutia.

    NASA Astrophysics Data System (ADS)

    Nikolenko, Evgeny; Tychkov, Nikolay; Afanasiev, Valentin

    2015-04-01

    New mineralogical and chemical constraints for 10 dikes, veins (360-800m) and pipes (60-110 m) of Chompolo field discovered in 1957-1958 are discussed. Feld is located within Central Aldan Archean and Paleoproterozoic granulite-orthogneiss superterrane of Aldan-Stanovoy Shield, with peak of metamorphism - 2.1-1.9 Ga (Smelov, Timofeev, 2007). Originally (Shilina and Zeitlin 1959) and later (Kostrovitsky and Garanin 1992, Ashchepkov, Vladykin et al. 2001) these rocks were classified as kimberlites by mineralogy including pyrope, Cr spinel, and Cr diopside. Panina and Vladykin (1994), Davies et al, (2006) identified them as lamprophyres and lamproites. The age of Chompolo rocks is pre-Jurassic (Vladimirov et. al., 1989) dated by 40Ar/39Ar as 164.7±1 Ma (233.7±2.2 next plato)(unpublished Ashchepkov). The Rb-Sr isochron for lamprophyre "intrusions 104" indicate later age of 131±4 Ma (Zaitsev, Smelov, 2010). Magmatic bodies (Aldanskaya, Sputnik, Gornaya, Ogonek, Perevalnaya, Kilier-E) were studied during 2012-2013 fieldworks. Most of igneous rocks occur as inequigranular volcanic breccias with micro- or crypto-crystalline groundmass of K feldspar (up to 16.3 wt.% K2O, up to 3.2 wt.% FeO), chlorite, opaque minerals, melanocratic xenocrysts and phenocrysts (garnet, pyroxene, amphibole, Cr spinel, apatite, zircon, mica), and abundant xenogenic fragments of wallrock and crystalline basement. Garnet chemistry records the presence of mantle and crustal material. Mantle garnets lack the common megacryst, wehrlite, and high-temperature lherzolite varieties. Mantle mineralization prevails in the Aldan dike and the Sputnik, Gornaya, and Ogonek pipes, while crustal and elcogitic material is in the Perevalnaya and Kilier-E pipes. The Cr spinel consists of (in wt%) 3.5 to 50.9 Al2O3, 18.6-63.5 wt% Cr2O3, 6.1 to 19.1 MgO, and 0 to 1.61 TiO2. Al and Cr in spinels are in inverse proportion. The Chompolo alkaline volcanic rocks are most similar to the Central Aldan lamproites in trace

  19. Basement reservoir in Zeit Bay oil field, Gulf of Suez

    SciTech Connect

    Zahran, I.; Askary, S.

    1988-01-01

    Fractured basement, one of the most important reservoirs of Zeit Bay field, contains nearly one-third of oil in place of the field. The flow rates per well vary from 700 to 9,000 BOPD. Due to its well-established production potential, 60% of the wells for the development of the field were drilled down to basement. The Zeit Bay basement consist of granitic rocks of pegmatitic to coarse porphyritic texture and has equal proportions of alkali feldspars. Dykes of various compositions are present, traversing the granite at different intervals. Dykes include aplite, microsyenite, diabase and lamprophyre. The last two pertain to the post-granitic dykes of later Proterozoic age. The main granitic luton is related to one of the final stages of the tectonic-magmatic cycle of the Arabo-Nubian sheild. The Zeit Bay area was a significant paleohigh until the Miocene, hence its structural picture is very complicated due to the impact of different tectonic movements from the late Precambrian to Cenozoic. The resulting structural elements were carefully investigated and statistically analyzed to decipher the influence of various tectonic events. The presence of high porosity in some intervals and low porosity in others could be tied to the presence of new fractures and the nature of cementing minerals. The relation of mineralized fractures and their depths lead to zonation of porous layers in the granitic pluton. Diagenetic processes on the granitic body and the alternation/resedimentation of the diagenetic products controlled the magnitude and amplitude of the porosity layers.

  20. Basement reservoir in Zeit Bay oil field, Gulf of Suez

    SciTech Connect

    Zahran, I.; Askary, S.

    1988-02-01

    Fractured basement, one of the most important reservoirs of Zeit Bay field, contains nearly one-third of oil in place of the field. The flow rates per well vary from 700 to 9,000 BOPD. Due to its well-established production potential, 60% of the wells for the development of the field were drilled down to basement. The Zeit Bay basement consists of granitic rocks of pegmatitic to coarse porphyritic texture and has equal proportions of alkali feldspars. Dykes of various compositions are present, traversing the granite at different intervals. Dykes include aplite, microsyenite, diabase and lamprophyre. The last two pertain to the post-granitic dykes of late Proterozoic age. The main granitic pluton is related to one of the final stages of the tectonic-magmatic cycle of the Arabo-Nubian shield. The Zeit Bay area was a significant paleohigh until the Miocene, hence its structural picture is very complicated due to the impact of different tectonic movements from the late Precambrian to Cenozoic. The resulting structural elements were carefully investigated and statistically analyzed to decipher the influence of various tectonic events. The presence of high porosity in some intervals and low porosity in others could be tied to the presence of new fractures and the nature of cementing minerals. The relation of mineralized fractures and their depths lead to zonation of porous layers in the granitic pluton. Diagenetic processes on the granitic body and the alteration/resedimentation of the diagenetic products controlled the magnitude and amplitude of the porosity layers. A model has been constructed to illustrate the changes in the primary rock texture and structure with sequential diagenetic processes, taking into consideration the fracture distribution and their opening affinities as related to their depths.

  1. Contrasting methods of fracture trend characterization in crystalline metamorphic and igneous rocks of the Windham quadrangle, New Hampshire

    USGS Publications Warehouse

    Walsh, G.J.; Clark, S.F.

    2000-01-01

    The bedrock of the Windham quadrangle in southeastern New Hampshire consists of deformed early Palaeozoic crystalline metamorphic and intrusive igneous rocks intruded by Mesozoic igneous dikes. Generally, less common northeast striking, steeply dipping fractures developed sub-parallel to the pre-existing tectonic foliation in the Palaeozoic rocks. Mesozoic lamprophyre and diabase dikes intruded along the northeast trending fractures, utilizing the pre-existing anisotropy in the crystalline rocks. Northwest striking, steeply dipping systematic joints and joint sets are the most prominent fractures in the area and, at least in part, post-date the Mesozoic dikes. Sub-horizontal sheeting joints occur in all rock types. Locally, the coincidence of the sub-horizontal fractures with a sub-horizontal Paleozoic cleavage suggests that some of the sheeting fractures utilized the pre-existing ductile anisotropy during unloading. Generally, the metasedimentary rocks show a less complex pattern of fracturing than the intrusive rocks suggesting that rock type is a controlling factor. Metasedimentary rocks in the biotite zone and well-foliated igneous rocks show a greater tendency to fracture along pre-existing bedding and foliation surfaces than metasedimentary rocks in the garnet zone and poorly foliated igneous rocks. A comparison of mapped fracture data and station fracture data indicates that either mapped data or station data can be used to identify regional fracture trends. Local fracture trends can not be identified by limited measurements at a few fracture stations, however, because they do not address spatial variability. Some fracture trends may be scale-dependant because they may be either unique to a local area or present only at regional scales.

  2. U-Pb ages, geochemistry, C-O-Nd-Sr-Hf isotopes and petrogenesis of the Catalão II carbonatitic complex (Alto Paranaíba Igneous Province, Brazil): implications for regional-scale heterogeneities in the Brazilian carbonatite associations

    NASA Astrophysics Data System (ADS)

    Guarino, Vincenza; Wu, Fu-Yuan; Melluso, Leone; de Barros Gomes, Celso; Tassinari, Colombo Celso Gaeta; Ruberti, Excelso; Brilli, Mauro

    2016-09-01

    The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex. Drill-hole sampling and detailed mineralogical and geochemical study point out the existence of ultramafic lamprophyres (phlogopite-picrites), calciocarbonatites, ferrocarbonatites, magnetitites, apatitites, phlogopitites and fenites, most of them of cumulitic origin. U-Pb data have constrained the age of Catalão I carbonatitic complex between 78 ± 1 and 81 ± 4 Ma. The initial strontium, neodymium and hafnium isotopic data of Catalão II (87Sr/86Sri = 0.70503-0.70599; ɛNdi = -6.8 to -4.7; 176Hf/177Hf = 0.28248-0.28249; ɛHfi = -10.33 to -10.8) are similar to the isotopic composition of the Catalão I complex and fall within the field of APIP kimberlites, kamafugites and phlogopite-picrites, indicating the provenance from an old lithospheric mantle source. Carbon isotopic data for Catalão II carbonatites (δ13C = -6.35 to -5.68 ‰) confirm the mantle origin of the carbon for these rocks. The origin of Catalão II cumulitic rocks is thought to be caused by differential settling of the heavy phases (magnetite, apatite, pyrochlore and sulphides) in a magma chamber repeatedly filled by carbonatitic/ferrocarbonatitic liquids (s.l.). The Sr-Nd isotopic composition of the Catalão II rocks matches those of APIP rocks and is markedly different from the isotopic features of alkaline-carbonatitic complexes in the southernmost Brazil. The differences are also observed in the lithologies and the magmatic affinity of the igneous rocks found in the two areas, thus demonstrating the existence of regional-scale heterogeneity in the mantle sources underneath the Brazilian platform.

  3. Cretaceous potassic intrusives with affinities to aillikites from Jharia area: Magmatic expression of metasomatically veined and thinned lithospheric mantle beneath Singhbhum Craton, Eastern India

    NASA Astrophysics Data System (ADS)

    Srivastava, Rajesh K.; Chalapathi Rao, N. V.; Sinha, Anup K.

    2009-11-01

    Cretaceous potassic dykes and sills at the Jharia area intrude the Permo-carboniferous coal-bearing Gondwana sediments of the Eastern Damodar Valley, Singhbhum craton. These intrusives are widely regarded as a part of the Mesozoic alkaline and Rajmahal flood basalt magmatism in the Eastern Indian shield. Jharia intrusives display a wide petrographic diversity; olivine, phlogopite and carbonate are the predominant phases whereas apatite and rutile constitute important accessories. Impoverishment in sodium, silica and alumina and enrichment in potassium, titanium and phosphorous are the hallmark of these rocks and in this aspect they are strikingly similar to the rift-related aillikites (ultramafic lamprophyres) of Aillik Bay, Labrador. Crustal contamination of the Jharia magmas is minimal and the incompatible trace element ratios demonstrate (i) their generation by greater degrees of partial melting of a sub-continental lithospheric mantle (SCLM) source similar to that of the kimberlites of Dharwar craton, southern India, and (ii) retention of long-term memories of ancient (Archaean) subduction experienced by their source regions. We infer that a metasomatically veined and thinned lithosphere located at the margin of the Singhbhum craton and the inheritance of an ancient (Archaean) subducted component has played a significant role in deciding the diverging petrological and geochemical characters displayed by the Jharia potassic intrusives: those of kimberlites (orangeites) and lamproites (cratonic signature) and those of aillikites (rift-related signature). A substantial melt component of Jharia potassic intrusives was derived from the SCLM and the melt contribution of the Kerguelen plume is inferred to be minimal.

  4. U-Pb Geochronology of Devonian Granites in the Meguma Terrane of Nova Scotia, Canada: Evidence for Hotspot Melting of a Neoproterozoic Source.

    PubMed

    Keppie; Krogh

    1999-09-01

    U-Pb isotopic analyses of monazite and zircon from six granitic plutons in the Meguma Terrane yield nearly concordant ages of 373+/-3 Ma, interpreted as the time of intrusion. U-Pb analyses of euhedral zircons with thick rims overgrowing cores, which were abraded to remove all or most of the rim, plot on chords between 370+/-3 and 628+/-33 Ma (Larrys River and Halfway Cove plutons), 372+/-3 and approximately 660 Ma (Shelburne pluton), and 373+/-2 and approximately 732 Ma (Barrington Passage pluton). The upper intercepts are interpreted as the age of magma source, correlatives of which are present in the Avalon Composite Terrane to the north. This basement may be either in depositional or tectonic contact with the overlying Cambro-Ordovician Meguma Group. Other zircons in the granites are generally irregular-euhedral with thin rims, and most U-Pb isotopic analyses fall between two chords from 373-2040 and 373-2300 Ma, with a few lying outside this field. These zircons are probably derived from the country rock (Goldenville Formation), which a previous study has shown contains detrital zircons with concordant U-Pb ages of 3000, 2000, and 600 Ma, and numerous intermediate discordant ages. These new ages, along with published data, document a relatively short (5-10 m.yr.) but voluminous period of magmatism. This age is approximately synchronous with intrusion of mafic rocks and lamprophyre dikes and regional low-pressure metamorphism and was followed by rapid denudation of 5-12 km. These observations may be interpreted in terms of shallowly dipping subduction and overriding of a mantle plume that eventually penetrates through the subducting plate to melt the overriding continental plate. Subsequent northward migration of the plume could explain both the approximately 360 Ma magmatism in the Cobequid Highlands (Avalon Composite Terrane) and the mid-Carboniferous plume-related intrusions around the Magdalen Basin.

  5. Numerical simulation of ground-water flow through glacial deposits and crystalline bedrock in the Mirror Lake area, Grafton County, New Hampshire

    SciTech Connect

    Tiedeman, C.R.; Goode, D.J.; Hsieh, P.A.

    1997-12-31

    This report documents the development of a computer model to simulate steady-state (long-term average) flow of ground water in the vicinity of Mirror Lake, which lies at the eastern end of the Hubbard Brook valley in central New Hampshire. The 10-km{sup 2} study area includes Mirror Lake, the three streams that flow into Mirror Lake, Leeman`s Brook, Paradise Brook, and parts of Hubbard Brook and the Pemigewasset River. The topography of the area is characterized by steep hillsides and relatively flat valleys. Major hydrogeologic units include glacial deposits, composed of till containing pockets of sand and gravel, and fractured crystal-line bedrock, composed of schist intruded by granite, pegmatite, and lamprophyre. Ground water occurs in both the glacial deposits and bedrock. Precipitation and snowmelt infiltrate to the water table on the hillsides, flow downslope through the saturated glacial deposits and fractured bedrock, and discharge to streams and to Mirror Lake. The model domain includes the glacial deposits, the uppermost 150 m of bedrock, Mirror Lake, the layer of organic sediments on the lake bottom, and streams and rivers within the study area. A streamflow routing package was included in the model to simulate baseflow in streams and interaction between streams and ground water. Recharge from precipitation is assumed to be areally uniform, and riparian evapotranspiration along stream banks is assumed negligible. The spatial distribution of hydraulic conductivity is represented by dividing the model domain into several zones, each having uniform hydraulic properties. Local variations in recharge and hydraulic conductivities are ignored; therefore, the simulation results characterize the general ground-water system, not local details of groundwater movement. 47 refs., 25 figs., 10 tabs.

  6. Miscellaneous investigations series: Bedrock geologic map of the Lone Mountain pluton area, Esmeralda County, Nevada

    SciTech Connect

    Maldonado, F.

    1984-12-31

    The joint attitudes were measured in the field and plotted on aerial photos at a scale of 1:24,000. The pluton is intensely jointed, primarily as a result of cooling and movement of the magma within a northwest-trending stress field. Foliation, in general, is poorly developed, and quality varies from area to area, but it is best developed close to the contacts with the metasedimentary rocks. A prominent northwest foliation direction was observed that parallels the northwest elongation of the exposed pluton. Faults in the pluton are difficult to identify because of the homogeneity of the rock. Several faults were mapped in the northern part of the area where they have a northeast trend and intersect the northwest-trending lamprophyre dikes with little apparent displacement. A major fault that bounds the northern part of the pluton is downthrown to the north and strikes northeast. This fault offsets the alluvium, the metasedimentary rocks, and the pluton and forms fault scraps as high as 10 m. Aeromagnetic data (US Geological Survey, 1979) suggest the following: (1) the local magnetic highs in the central part of the Lone Mountain pluton are probably related to topographic highs (peaks) where the flight lines are closer to the pluton; (2) a magnetic low in the northeastern part of Lone Mountain coincides with the pluton-country rock contact, which may be very steep; (3) the contours for the southwestern part of the mapped area indicate that the pluton-country rock contact is not as steep as that in the northeastern part and that the pluton probably coalesces at depth with the Weepah pluton, a pluton exposed south of the mapped area; and (4) the contours for the area of the Lone Mountain pluton express a northwest-trending gradient that parallels the northwest elongation of the Lone Mountain pluton and the northwest-trending stress field. 10 refs.

  7. Garnet granulite xenoliths from the Northern Baltic shield- The underplated lower crust of a palaeoproterozoic large igneous province

    USGS Publications Warehouse

    Kempton, P.D.; Downes, H.; Neymark, L.A.; Wartho, J.A.; Zartman, R.E.; Sharkov, E.V.

    2001-01-01

    Garnet granulite facies xenoliths hosted in Devonian lamprophyres from the Kola Peninsula are interpreted to represent the high-grade metamorphic equivalents of continental flood tholeiites, emplaced into the Baltic Shield Archaean lower crust in early Proterozoic time. Geochronological data and similarities in major and trace element geochemistry suggest that the xenoliths formed during the same plume-related magmatic event that created a widespread Palaeoproterozoic large igneous province (LIP) at 2.4-2.5 Ga. They are, thus, the first samples of the lower crust of a Palaeo-proterozoic LIP to be studied in petrological detail. The suite includes mafic granulites (gar + cpx + rutile ?? plag ?? opx ?? phlog ?? amph), felsic granulites (plag + gar + cpx + rutile ?? qtz ?? Kspar ?? phlog ?? amph) and pyroxenites (?? phlog ?? amph), but mafic garnet granulites predominate. Although some samples are restites, there is no evidence for a predominance of magmatic cumulates, as is common for Phanerozoic lower-crustal xenolith suites. Metasediments are also absent. Phlogopite and/or amphibole occur in xenoliths of all types and are interpreted to be metasomatic in origin. The K-rich metasomatic event occurred at ?????0 Ga, and led to substantial enrichment in Rb, K, LREE/HREE, Th/U, Th/Pb and, to a lesser extent, Nb and Ti. The fluids responsible for this metasomatism were probably derived from a second plume that arrived beneath the region at this time. Evidence for partial melting of mafic crust exists in the presence of migmatitic granulites. The timing of migmatization overlaps that of metasomatism, and it is suggested that migmatization was facilitated by the metasomatism. The metamorphism, metasomatism and migmatization recorded in the Kola granulite xenoliths may be representative of the processes responsible for converting Archaean LIP-generated proto-continents into continental crust.

  8. Archaean lode gold deposits: the solute source problem

    SciTech Connect

    Kerrich, R.

    1985-01-01

    On a regional scale lode gold deposits typically occur throughout the entire spectrum of greenstone belt stratigraphy. In the Abitibi Belt lode deposits are sited at the base of the volcanic cycle (Noranda), at the boundary of two volcanic cycles (Timmins) and in the stratigraphically highest groups at Kirkland Lake and Bousquet. The gold deposits are preferentially disposed along major structures apparently demarking rift zones, where extension was accommodated by listric normal faults that subsequently acted as thrusts during compression. These major structures were also sites of emplacement of trondhjemite magmas, lamprophyres and potassic basalts. From previous work Abitibi Belt volcanism spans 2725 to 2703 Ma, batholith emplacement 2675 to 2685 Ma (U-Pb on zircons), and the terminal Matachewan dyke swarm which transects all major structures is 2690 +/- 93 Ma. The lode deposits have age corrected /sup 87/Sr//sup 86/Sr initials of 0.7015 to 0.7025, as well as more radiogenic Pb and higher ..mu.. relative to contemporaneous mantle Sr and Pb isotope ratios. Tourmaline, scheelite, piemontite and apatites separated from 14 deposits all possess /sup 87/Sr//sup 86/Sr 0.7015 to 0.7025. These more radiogenic values contra-indicate a direct mantle source for Sr and Pb, but rather indicate that all mineralizing fluids carry contributions from a felsic crustal source having a significant production of Rb, U and Th radiogenic daughter nuclides as well as from komatiites and tholeiites. Gold, along with an array of lithophile elements including K, Rb, Pb, Li, Sr and CO/sub 2/ were distilled from this mixed source.

  9. The newly discovered Jurassic Tikiusaaq carbonatite-aillikite occurrence, West Greenland, and some remarks on carbonatite-kimberlite relationships

    NASA Astrophysics Data System (ADS)

    Tappe, Sebastian; Steenfelt, Agnete; Heaman, Larry M.; Simonetti, Antonio

    2009-11-01

    We discuss mineral chemistry data and report ten high-precision U-Pb (zircon, baddeleyite, pyrochlore, and perovskite) and Rb-Sr phlogopite ages for the newly discovered Tikiusaaq carbonatite intrusion and associated ultramafic dykes from the North Atlantic craton, West Greenland. At Tikiusaaq, massive dolomite-calcite carbonatite sheets intruded an 2 × 3 km area along a ductile shear zone between ca. 158 and 155 Ma. The accompanying carbonatite and carbonate-rich ultramafic silicate dykes were emplaced between ca. 165 and 157 Ma in close proximity to this carbonatite centre utilizing pre-existing brittle fractures. The deep volatile-rich magmatism at Tikiusaaq forms part of a larger Jurassic alkaline province in southern West Greenland and represents the earliest manifestation of rifting processes related to the opening of the Mesozoic-Cenozoic Labrador Sea Basin. Although the ultramafic silicate dykes macroscopically resemble hypabyssal kimberlites, they are identified as kimzeyite-bearing monticellite aillikites (carbonate-rich ultramafic lamprophyres) using a modern mineralogical-genetic classification. The overlapping emplacement ages of the carbonatite sheets and aillikite dykes, along with the carbonate-rich nature of the latter, suggest a genetic relationship between these magma types. The aillikites carry garnet peridotite xenoliths and have mineralogical characteristics of primitive magmas such as highly forsteritic olivine (up to Fo 90 mol%) and Cr-rich spinel (up to 46 wt.% Cr 2O 3) microphenocrysts; whereas the carbonatite sheets reveal a higher degree of differentiation such as Fe-rich dolomite compositions (up to 9 wt.% FeO). The initial findings reported here from Tikiusaaq suggest that a link between these magma types by an increasing degree of partial melting of a common carbonated upper mantle peridotite source region, as commonly envisaged for the compositionally similar Sarfartoq complex, is untenable. Rather, proto-aillikite magma may be

  10. Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America

    USGS Publications Warehouse

    Dostal, Jaroslav; Karl, Susan M.; Keppie, J. Duncan; Kontak, Daniel J.; Shellnutt, J. Gregory

    2013-01-01

    The circular Bokan Mountain complex (BMC) on southern Prince of Wales Island, southernmost Alaska, is a Jurassic peralkaline granitic intrusion about 3 km in diameter that crosscuts igneous and metasedimentary rocks of the Alexander terrane. The BMC hosts significant rare metal (rare earth elements, Y, U, Th, Zr, and Nb) mineralization related to the last stage of BMC emplacement. U–Pb (zircon) and 40Ar/39Ar (amphibole and whole-rock) geochronology indicates the following sequence of intrusive activity: (i) a Paleozoic basement composed mainly of 469 ± 4 Ma granitic rocks; (ii) intrusion of the BMC at 177 ± 1 Ma followed by rapid cooling through ca. 550 °C at 176 ± 1 Ma that was synchronous with mineralization associated with vertical, WNW-trending pegmatites, felsic dikes, and aegirine–fluorite veins and late-stage, sinistral shear deformation; and (iii) intrusion of crosscutting lamprophyre dikes at >150 Ma and again at ca. 105 Ma. The peralkaline nature of the BMC and the WNW trend of associated dikes suggest intrusion during NE–SW rifting that was followed by NE–SW shortening during the waning stages of BMC emplacement. The 177 Ma BMC was synchronous with other magmatic centres in the Alexander terrane, such as (1) the Dora Bay peralkaline stock and (2) the bimodal Moffatt volcanic suite located ~30 km north and ~100 km SE of the BMC, respectively. This regional magmatism is interpreted to represent a regional extensional event that precedes deposition of the Late Jurassic – Cretaceous Gravina sequence that oversteps the Wrangellia and Alexander exotic accreted terranes and the Taku and Yukon–Tanana pericratonic terranes of the Canadian–Alaskan Cordillera.

  11. U-Pb ages, geochemistry, C-O-Nd-Sr-Hf isotopes and petrogenesis of the Catalão II carbonatitic complex (Alto Paranaíba Igneous Province, Brazil): implications for regional-scale heterogeneities in the Brazilian carbonatite associations

    NASA Astrophysics Data System (ADS)

    Guarino, Vincenza; Wu, Fu-Yuan; Melluso, Leone; de Barros Gomes, Celso; Tassinari, Colombo Celso Gaeta; Ruberti, Excelso; Brilli, Mauro

    2017-09-01

    The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex. Drill-hole sampling and detailed mineralogical and geochemical study point out the existence of ultramafic lamprophyres (phlogopite-picrites), calciocarbonatites, ferrocarbonatites, magnetitites, apatitites, phlogopitites and fenites, most of them of cumulitic origin. U-Pb data have constrained the age of Catalão I carbonatitic complex between 78 ± 1 and 81 ± 4 Ma. The initial strontium, neodymium and hafnium isotopic data of Catalão II (87Sr/86Sri = 0.70503-0.70599; ɛNdi = -6.8 to -4.7; 176Hf/177Hf = 0.28248-0.28249; ɛHfi = -10.33 to -10.8) are similar to the isotopic composition of the Catalão I complex and fall within the field of APIP kimberlites, kamafugites and phlogopite-picrites, indicating the provenance from an old lithospheric mantle source. Carbon isotopic data for Catalão II carbonatites (δ13C = -6.35 to -5.68 ‰) confirm the mantle origin of the carbon for these rocks. The origin of Catalão II cumulitic rocks is thought to be caused by differential settling of the heavy phases (magnetite, apatite, pyrochlore and sulphides) in a magma chamber repeatedly filled by carbonatitic/ferrocarbonatitic liquids ( s.l.). The Sr-Nd isotopic composition of the Catalão II rocks matches those of APIP rocks and is markedly different from the isotopic features of alkaline-carbonatitic complexes in the southernmost Brazil. The differences are also observed in the lithologies and the magmatic affinity of the igneous rocks found in the two areas, thus demonstrating the existence of regional-scale heterogeneity in the mantle sources underneath the Brazilian platform.

  12. Tectonic significance of mantle sources for mafic synextensional dikes in metamorphic core complexes, southern Arizona and northern Sonora

    SciTech Connect

    Wright, J.E. ); Haxel, G.B. ); Simmons, A.M.

    1992-01-01

    Synextensional microdiorite and lamprophyre dikes in the metamorphic core complexes (MCCs) of southern Arizona represent magmatism unambiguously associated with middle Tertiary crustal extension. These 24--20 Ma dikes are shoshonitic and primitive. Petrographic and geochemical data and AFC modeling suggest absence of an essential crustal source component. Dikes from individual MCCs have closely similar sr and Pb isotopic compositions that do not correlate with degree of fractionation, indicating little or no crustal assimilation. Minimal crustal interaction is consistent with emplacement of the dikes in a strongly extensional tectonic regime. Samples from the two MCC belts differ isotopically and chemically. Isotopic and trace element data indicate a minimum of three mantle sources, two lithospheric and one asthenospheric. The predominant lithospheric source for dikes in the northern belt was LILE-depleted Proterozoic lithosphere (EM1-like), whereas in the southern belt it was LILE-enriched lithosphere (trending toward EM2) strongly influenced by Proterozoic to Tertiary subduction. The asthenospheric source was available under both MCC belts but more widely or frequently tapped beneath the more highly extended northern belt. The presence of an asthenospheric component in some of the MCC dikes is the only known exception to the observation that asthenosphere-derived Cenozoic basalts first appeared in Arizona ca Ma. By the later stages of middle Tertiary crustal extension, the subduction zone beneath Arizona evidently had fragmented or became inactive, so that it did not form a barrier to ascent of asthenosphere-derived magmas. Continued study will evaluate the belief that these data support tectonic models for middle tertiary crustal extension in which the asthenospheric mantle is active rather than passive.

  13. Parental melts of melilitolite and origin of alkaline carbonatite: evidence from crystallised melt inclusions, Gardiner complex

    NASA Astrophysics Data System (ADS)

    Nielsen, T. F. D.; Solovova, I. P.; Veksler, I. V.

    1997-02-01

    Perovskite and melilite crystals from melilitolites of the ultramafic alkaline Gardiner complex (East Greenland) contain crystallised melt inclusions derived from: (1) melilitite; (2) low-alkali carbonatite; (3) natrocarbonatite. The melilitite inclusion (1) homogenisation temperature of 1060 °C is similar to liquidus temperatures of experimentally investigated natural melilitites. The compositions are peralkaline, low in MgO (ca.␣5 wt%), Ni and Cr, and they are low-pressure fractionates of more magnesian larnite-normative ultramafic lamprophyre-type melts of primary mantle origin. Low-alkali carbonatite compositions (2) homogenise at 1060-1030 °C and are compositionally similar to immiscible calcite carbonatite dykes derived from the melilitolite magma. Natrocarbonatite inclusions (3) homogenise between 1030 and 900 °C and are compositionally similar to natrocarbonatite lava from Oldoinyo Lengai. Nephelinitic to phonolitic dykes which are related to the calcite carbonatite dykes, are very Zr-rich and agpaitic (molecular Na2O + K2O/Al2O3 > 1.2) and resemble nephelinites of Oldoinyo Lengai. The petrographic, geochemical and temporal relationships indicate unmixing of carbonatite compositions (ca. 10% alkalies) from evolving melilitite melt and continued fractionation of melilitite to nephelinite. It is suggested that the natrocarbonatite compositions represent degassed supercritical high temperature fluid formed in a cooling body of strongly larnite-normative nephelinite or evolved melilitite. The Gardiner complex and similar melilitolite and carbonatite-bearing ultramafic alkaline complexes are believed to represent subvolcanic complexes formed beneath volcanoes comparable to Oldoinyo Lengai and that the suggested origin of natrocarbonatite may be applied to natrocarbonatites of Oldoinyo Lengai.

  14. Petrogenesis of coeval sodic and potassic alkaline magmas at Spanish Peaks, Colorado: Magmatism related to the opening of the Rio Grande rift

    NASA Astrophysics Data System (ADS)

    Lord, A. Brooke Hamil; McGregor, Heath; Roden, Michael F.; Salters, Vincent J. M.; Sarafian, Adam; Leahy, Rory

    2016-07-01

    Approximately coeval, relatively primitive (∼5-10% MgO with exception of a trachyandesite) alkaline mafic dikes and sills at or near Spanish Peaks, CO are divided into relatively sodic and potassic varieties on the basis of K2O/Na2O. Many of these dikes are true lamprophyres. In spite of variable alkali element ratios, the alkaline rocks share a number of geochemical similarities: high LIL element contents, high Ba and similar Sr, Nd and Hf isotope ratios near that of Bulk Earth. One important difference is that the potassic rocks are characterized by lower Al2O3 contents, typically less than 12 wt.%, than the sodic dikes/sills which typically have more than 13 wt.% Al2O3, and this difference is independent of MgO content. We attribute the distinct Al2O3 contents to varying pressure during melting: a mica-bearing, Al-poor vein assemblage for the potassic magmas melted at higher pressure than an aluminous amphibole-bearing vein assemblage for the sodic magmas. Remarkable isotopic and trace element similarities with approximately contemporaneous, nearby Rio Grande rift-related basalts in the San Luis Valley, indicate that the magmatism at Spanish Peaks was rift-related, and that lithosphere sources were shared between some rift magmas and those at Spanish Peaks. High Zn/Fe ratios in the Spanish Peaks mafic rocks point to a clinopyroxene- and garnet-rich source such as lithosphere veined by pyroxenite or eclogite. Lithospheric melting was possibly triggered by foundering of cool, dense lithosphere beneath the Rio Grande rift during the initiation of rifting with the potassic parent magmas generated by higher pressure melting of the foundered lithosphere than the sodic parent magmas. This process, caused by gravitational instability of the lithosphere (Elkins-Tanton, 2007) may be common beneath active continental rifts.

  15. Geochemistry of Mesozoic carbonatite complexes in the southwestern part of Greenland

    NASA Astrophysics Data System (ADS)

    Park, B.; Lee, J.; Lee, M.

    2013-12-01

    This is the results of geochemical analysis of carbonatite taken at the kimberlite and carbonatite complexes in Tikilusaag and Qaqarssuk located in the southwestern part of Greenland. These complexes have high grade of rare earth elements (REE), gold, olivine and diamond ore deposits. These kimberlite, lamprophyre and carbonatite are originated from complex carbonatitic and silicate magma. This kind of ultramafic alkaline complex is not common compared to other igneous bodies in the crust. Tikilusaag carbonatite complex in contains REE in calcite carbonatite. Carbonatite minerals are strontianite (SrCO3) and ancylite (SrCe(CO3)2(OH)H2O). Strontianite contains Ce and ancylite contains considerable amounts of La, Ce, Nd, respectively. Two minerals are the major components which have LREE in the complexes. Tikilussaaq carbonatite complex contain apatite which has maximum 200 micro meter in size and mostly euhedral. Most apatite crystals show compositional zoning under CL attached to SEM (JEOL, JSM-6610). This zoning reflects physiochemical condition of magma at the time of crystallization and the compositional difference of Ca, P, and F with the consideration of chemical composition of apatite. The apatite contain F instead of Cl, namely fluorine apatite. Compositional zoning reflect the difference of Ca and P according to CL image. Qaqarssuk carbonatite complex is consisted of several minerals containing Ba composition. Ba in calcite which is the major mineral of Ba carbonatite (Barytocalcite, CaBa(CO3)2) coexists with barite and Ba-Sr carbonatite. Fenitization near the complex is common process. Basic rocks formed during carbonatitization contain hornblendite predominantly, and high grade of fenitization produced albite-bearing granitic rocks in the area.

  16. Compositions and processes of lithospheric mantle beneath the west Cathaysia block, southeast China

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Zheng, Jianping; Pan, Shaokui; Lu, Jianggu; Li, Yihe; Xiang, Lu; Lin, Abing

    2017-08-01

    Knowledge about the nature and history of the lithospheric mantle beneath the west Cathaysia block (South China) is still sparse. The major- and trace-element compositions and H2O contents of minerals from peridotite xenoliths entrained in the Cenozoic lamprophyres of the Anyuan area (SE China), were conducted to investigate the nature and evolution of the lithospheric mantle, as well as the factors controlling the distribution of water. The xenoliths including spinel harzburgites and lherzolites are moderately refractory (Mg# Olivine = 90.2-91.2) with minor fertile lherzolites (Mg# Olivine = 89.1-89.9). Clinopyroxenes in lherzolites show variable REE patterns from LREE-depleted to LREE-enriched patterns, and commonly exhibit negative anomalies of U, Pb and Ti. The mantle represented by the xenoliths mostly experienced 1-10% partial melting and obvious subsequent silicate metasomatism. H2O contents of clinopyroxene, orthopyroxene, and olivine in the peridotites are 320-404 ppm, 138-200 ppm, and 11-33 ppm, respectively. The whole-rock H2O contents range from 63 to 120 ppm, similar to that estimated for the MORB source. The negative correlations of H2O contents with Mg# in olivine and lack of correlation correlations with (La/Yb)N in clinopyroxene suggest that the H2O contents are mainly controlled by the partial melting process rather than mantle metasomatism. The fertile and moderately refractory peridotite xenoliths have similar equilibrium temperatures, implying that the lithospheric mantle is not compositionally stratified. Integrated with published data, we suggest that the widespread fertile and moderately refractory lithospheric mantle beneath the studied area (west Cathaysia), even the whole South China, might be eroded or melt-rock reacted by upwelling asthenospheric materials. Finally, the cooling of the upwelled asthenospheric materials resulted in the formation of the accreted lithospheric mantle mixed with pre-existing moderately refractory volumes.

  17. Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska): evidence for Early Jurassic rifting prior to accretion with North America

    USGS Publications Warehouse

    Dostal, Jaroslav; Karl, Susan M.; Keppie, J. Duncan; Kontak, Daniel J.; Shellnutt, J. Gregory

    2013-01-01

    The circular Bokan Mountain complex (BMC) on southern Prince of Wales Island, southernmost Alaska, is a Jurassic peralkaline granitic intrusion about 3 km in diameter that crosscuts igneous and metasedimentary rocks of the Alexander terrane. The BMC hosts significant rare metal (rare earth elements, Y, U, Th, Zr, and Nb) mineralization related to the last stage of BMC emplacement. U–Pb (zircon) and 40Ar/39Ar (amphibole and whole-rock) geochronology indicates the following sequence of intrusive activity: (i) a Paleozoic basement composed mainly of 469 ± 4 Ma granitic rocks; (ii) intrusion of the BMC at 177 ± 1 Ma followed by rapid cooling through ca. 550 °C at 176 ± 1 Ma that was synchronous with mineralization associated with vertical, WNW-trending pegmatites, felsic dikes, and aegirine–fluorite veins and late-stage, sinistral shear deformation; and (iii) intrusion of crosscutting lamprophyre dikes at >150 Ma and again at ca. 105 Ma. The peralkaline nature of the BMC and the WNW trend of associated dikes suggest intrusion during NE–SW rifting that was followed by NE–SW shortening during the waning stages of BMC emplacement. The 177 Ma BMC was synchronous with other magmatic centres in the Alexander terrane, such as (1) the Dora Bay peralkaline stock and (2) the bimodal Moffatt volcanic suite located ∼30 km north and ∼100 km SE of the BMC, respectively. This regional magmatism is interpreted to represent a regional extensional event that precedes deposition of the Late Jurassic – Cretaceous Gravina sequence that oversteps the Wrangellia and Alexander exotic accreted terranes and the Taku and Yukon–Tanana pericratonic terranes of the Canadian–Alaskan Cordillera.

  18. Isotopic and geochemical studies of a Pliocene porphyry-Mo system, Rico, Colorado

    SciTech Connect

    Wareham, C.D.

    1991-01-01

    The historic mining district of Rico in southern Colorado Mineral Belt contains a Pliocene porphyry-Mo deposit and peripheral epithermal Pb-Zn-Ag deposits, and hot-springs. The porphyry-Mo mineralization is confined almost exclusively to Precambrian greenstone. The epithermal mineralization is hosted by a Paleozoic and Mesozoic sequence dominated by carbonates, but containing evaporites. The system is geologically complex and focused on a resurgent dome which is cored by a horst of Precambrian strata, and cut by reactivated Precambrian basement shears. The shears have controlled the emplacement of the Laramide and Pliocene granitoids in area. The mineralization is associated with more evolved members of the latter suite. Sr-Nd-Pb-O isotope and minor element data on the granitoid intrusions indicate that they are not simply differentiates of mantle magmas. However, Nd model ages indicate that they are not purely remelts of 1800Ma Precambrian crust. Realistically it is impossible to quantify the relative proportions of crust and mantle material involved in the genesis of the intrusions. Notwithstanding this, the Rico granitoids are isotopically distinct from those associated with Climax-type porphyry-Mo deposits in Colorado. Sd-Nd-Pb isotope and trace element data on a lamprophyre suite in the area suggest two episodes of mafic magmatism; a period whereby the source was predominantly, OIB-type, asthenospheric mantle. [sigma][sup 34]S data and ore deposit paragenesis indicate that the sulphide S has an igneous origin and that the sulphate S was derived by mobilization of Pennsylvanian evaporites. Modelling of the S isotopic data indicates a common S source for the epithermal and porphyry mineralization. The sulphate and sulphide S reservoirs remained essentially decoupled during mineralization. [sigma][sup 34]C data are compatible with the hydrothermal C having been derived by the dissolution and re-precipitation of host sequence carbonate.

  19. Petrographic and chemical characteristics of the Panda Hill carbonatite complex, Tanzania

    NASA Astrophysics Data System (ADS)

    Basu, Nitin Kumar; Mayila, Agnes

    The Panda Hill carbonatite complex, situated near the south-western flank of the Rukwa Trough in south-western Tanzania, comprises a carbonatite body, a fenite aureole and feldspathic agglomerate and breccia. Petrographic study, supported by some analyses of both rocks and minerals, indicates that the fenite zone and the agglomerate and breccia are very rich in potash. Fenites consist mainly of monomineralic orthoclase rock grading to basement gneiss away from the carbonate body. Fragments of agglomerates range from feldspathic fenites to altered basement gneiss with some fragments carbonatized. The central plug and most of the carbonatite body consist of sövite. Beforsite occurs as dyke-like bodies often cutting across flow-lines of sövite. Beforsite forms the outermost boundary of the carbonatite body on the south-east. Ferrocarbonatite forms the outermost boundary of the main body in the eastern foothills. A number of pseudo-phoscorite layers are associated with sövite often imparting a flow structure to the rock. Several mafic dykes intrude into the main carbonatite body. All these dykes are more or less carbonatized. Two types of mafic dykes are distinguished: carbonatized lamprophyre dykes; dolerite dykes. The primary magma from which the Panda Hill carbonatite and its associates originated appears to have had a potash-rich fraction. Explosiv eruption of alkali-rich magma and influx of alkali-rich solution led to extensive fenitization. The central plug indicates forceful injection of the body simultaneously with the explosive eruption. The distribution of tuffs and volcanic breccia around three hill-tops shows existence of volcanic vents. Intrusion of minor dykes of mafic and ultramafic rocks took place along with the intrusion of the carbonatite plug. During falling temperature, permeation of the country rocks surrounding the carbonatite body by carbonate fluids caused partial replacement of all the minerals by carbonates.

  20. The Krásná Hora, Milešov, and Příčovy Sb-Au ore deposits, Bohemian Massif: mineralogy, fluid inclusions, and stable isotope constraints on the deposit formation

    NASA Astrophysics Data System (ADS)

    Němec, Matěj; Zachariáš, Jiří

    2017-04-01

    The Krásná Hora-Milešov and Příčovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks. Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krásná Hora-Milešov) or are associated with local strike-slip faults (Příčovy). Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 °C and gold at 200 to 130 °C from low-salinity aqueous fluids. The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 °C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature ( 250 MPa, 400 °C). The estimated oxygen isotope composition of the ore-bearing fluid (4 ± 1‰ SMOW; based on post-ore calcite) suggests its metamorphic or mixed magmatic-metamorphic origin and excludes the involvement of meteoric water. Rapid cooling of warm hydrothermal fluids reacting with "cold" host rock was probably the most important factor in the formation of both stibnite and gold.

  1. Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania

    NASA Astrophysics Data System (ADS)

    Pál-Molnár, Elemér; Batki, Anikó; Almási, Enikő; Kiss, Balázs; Upton, Brian G. J.; Markl, Gregor; Odling, Nicholas; Harangi, Szabolcs

    2015-12-01

    Mafic-ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75-73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~ 1000-1050 °C and ~ 0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting.

  2. The Elk Creek Carbonatite, Southeast Nebraska-An Overview

    SciTech Connect

    Carlson, M. P. Treves, S. B.

    2005-03-15

    A framework geophysical program in southeastern Nebraska during 1970 identified a near-circular feature having gravity relief of about 8 mgal and a magnetic anomaly of about 800 gammas. Analysis of the geophysical data provided a model of a cylindrical mass of indefinite length with a radius of 5500 ft (1676 m) and beveled at the basement surface at about 600 ft (183 m). At the approximate depth at which Precambrian rocks were expected, the initial test hole (2-B-71) encountered an iron-rich weathered zone overlying carbonate-rich rock. The carbonate rocks consist essentially of dolomite, calcite, and ankerite and lesser amounts of hematite, chlorite, phlogopite, barite, serpentine, pyrochlore, and quartz and contain barium, strontium, and rare earths. Total REE, P2O5, and 87Sr/86Sr ratios confirm the carbonatite identification. Texturally, the rocks range from fragmental to contorted to massive. Associated with the carbonatite are lesser amounts of basalt, lamprophyre, and syenite. Additional exploratory drilling has provided about 80,000 ft (24,384 m) of rock record and has penetrated about 3400 ft (1038 m) of carbonatite. The carbonatite is overlain by marine sediments of Pennsylvanian (Missourian) age. The surrounding Precambrian basement rocks are low-to medium-grade metamorphic gneiss and schist of island arc origin and granitic plutons. The Elk Creek carbonatite is located near the boundary between the Penokean orogen created at about 1.84 Ga (billion years) and the Dawes terrane (1.78 Ga) of the Central Plains orogen. This boundary strongly influenced the geometry of both the Midcontinent Rift System (1.1 Ga) and the Nemaha uplift (0.3 Ga). It is assumed that the emplacement of the Elk Creek carbonatite (0.5 Ga) was influenced similarly by the pre-existing tectonic sutures.

  3. Late Mesozoic crustal extension and rifting on the western edge of the Parana Basin, Paraguay

    SciTech Connect

    DeGraff, J.M.

    1985-01-01

    Geophysical and geological evidence indicates that the western edge of the Parana basin in Paraguay was a site of NE-SW directed crustal extension during late Mesozoic time. Major zones of normal faulting in south-eastern Paraguay trend northwesterly on average, and mafic dikes of probable late Mesozoic age have similar orientations. At least two NW-trending zones of tectonic subsidence, each over 200 km long, are now recognized in eastern Paraguay. Most alkalic rocks of south-eastern Paraguay are concentrated along this rift, and occur as simple to composite stocks and ring complexes composed of rocks ranging from foid-syenite to essexite. NW-trending, lamprophyric to phonolitic dikes are associated with some alkalic complexes. The southern zone, located about 125 km southwest, is a composite tectonic basin about 60 km wide and nearly devoid of alkalic rocks. The timing of crustal extension and rifting in eastern Paraguay is largely based on isotopic ages of associated alkalic rocks, which cluster between 150 and 100 Ma (latest Jurassic to mid-Cretaceous). Geologic evidence for the age of faulting and subsidence is consistent with this age range; tectonic depressions were being filled in late Cretaceous to early Cenozoic time. The age range of alkalic rocks in Paraguay contain that of the Serra Geral basalts and spans the time when South America Separated from Africa. This suggests that alkalic activity and crustal extension in eastern Paraguay are grossly related to the Serra Geral extrusive event, and were a manifestation of the breakup of South America and Africa far from the site of final separation.

  4. H2O contents and geochemistry of peridotite xenoliths from the Anyuan: Nature and evolution of lithospheric mantle beneath the west Cathaysia block SE China

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Zheng, J.; Lu, J.; Tang, Z.

    2015-12-01

    The major-, trace-elements and H2O contents of minerals from peridotite xenoliths hosted in the Mesozoic lamprophyres of Anyuan area (SE China) were analyzed by electron microprobe, LA-ICPMS and Fourier transform infrared spectroscopy, respectively. The xenoliths include spinel harzburgites, lherzolites with or without spinel. The harzburgites and lherzolites with spinels are moderately refractory (Mg#Ol=90.2-91.2), whereas lherzolites without spinels are fertile (Mg#Ol=89.1-89.9). The REE patterns of clinopyroxenes in these xenoliths vary from LREE-depleted, through flat, to LREE-enriched patterns, and commonly exhibit negative U, Pb and Ti anomalies. The results suggest that the xenoliths mostly experienced 1-10% partial melting and subsequently silicate metasomatism. Water contents of clinopyroxene (cpx), orthopyroxene (opx), and olivine (ol) range from 330 to 404 ppm, 126 to 279 ppm, and 11 to 33 ppm, respectively. No correlations between H2O content and melting index (i.e., YbN in cpx, Cr# in spinel) and metasomatic index ((La/Yb)N in cpx) show that extent of partial melting and mantle metasomatism did not modify the initial H2O contents. Most water contents of the mantle source are largely preserved in pyroxenes. The whole-rock water contents range from 67 to 124 ppm, similar to that of the MORB source. Therefore, we suggest that the Cenozoic lithospheric mantle of the Cathaysia block is accreted from the upwelled and cooled asthenospheric mantle. On the other hand, the widespread refractory lithospheric mantle ever existed in the western Cathaysia. The coexistence of fertile mantle and refractory-transitional mantle beneath the west Cathaysia block might be attributed to the refertilization of the lithospheric mantle by the upwelling asthenospheric materials and eventually replacement resulting from the cooling of the upwelled asthenosphere.

  5. A Geochemical Investigation of the Early Cretaceous Ultrapotassic Dykes in the Raniganj Coalfields in Damodar Valley, India

    NASA Astrophysics Data System (ADS)

    Jude, T. A.

    2015-12-01

    The early Cretaceous ultrapotassic dyke rocks intruding the Permocarboniferous coal bearing Gondwana sediments of the Eastern Damodar Valley, Singhbum craton, are known for their petrographic and geochemical diversity. They remain a 'Pandora's box of petrological confusion' with a variety of exotic, and potentially diamondiferous, rocks such as lamprophyre, lamproite, orangeite and kimberlite being continuously reported from them for over one century or more. Intra-plate volcanism of this type discloses hidden information about the interior of the Earth. Samples from two dykes intruding Raniganj coalfield is studied here. The samples from Dyke1 are characterized by fine grained texture and phlogopite+apatite+K-feldspar+rutile+ankerite+dolomite+ chromite+chlorite+quartz assemblage while the samples from Dyke2 are characterized by coarse grained texture and phlogopite+ pseudomorphosed-olivine+apatite+ clinopyroxene +dolomite+ankerite+calcite+norsethite+talc+rutile+quartz+Ca-Mg-Fe-Zr silicate+K-feldspar+monazite+ perovskite assemblage. Based on the TiO2-Al2O3-FeO trends observed in phlogopites, the dykes seem to be a lamproite-orangeite transitional variety. The phlogopites observed in Dyke2 show two stages of crystallization defined by Ti-poor overgrowths on Ti-rich cores indicating that Dyke2 consolidated from a melt that fractionated from a magma which was initially emplaced at a different depth while the Dyke 1 phlogopites do not show any such sudden drop in Ti concentration in their rims indicating single stage crystallization. Ti-in-Quartz Thermometry yields temperatures between 769°C to 1115°C for Dyke1 and 779°C to 1019°C for Dyke2 which must corresponds to the emplacement and crystallization of these dykes. Trace element and isotopic ratios can be used to constrain particular mantle source characteristics of the dykes. Rb-Sr method can be used to determine the emplacement ages of these dykes.

  6. Topomineralogy of the Siberian diamonds

    NASA Astrophysics Data System (ADS)

    Afanasyev, Valentin; Lobanov, Sergey; Vasiliy, Koptil; Bogdan, Pomazanskiy; Alexander, Gerasimchuk; Nikolay, Pokhilenko

    2010-05-01

    nearby Eastern Sayan (south-west of the Siberian craton). Parasteresis 3 (unknown host rock type) includes yellow-orange cuboids (II type according to Orlov's classification), which occur in kimberlites in small quantities, but most common in the north-east placers of the Siberian craton. Parasteresis 4 (unknown host rock type) includes diamonds of V and VII types according to Orlov, which are entirely absent in kimberlites. Parasteresis 5 involves the so called yacutites - microcrystalline substance with the add of lonsdaleite phase, typical for diamonds from impact craters. Comparison of yacutites with diamonds from Popigay astrobleme showed up their complete similarity. This fact is evident for the relation of yacutites to the Popigay astrobleme. Thus, in the placers of the Siberian craton there are at least three groups of diamonds with the unknown host rock type. The distribution of the discriminated types of diamonds among the craton is higly uneven. Diamonds of 2,3,4 and 5 parasteresis type (supposed to be from lamprophyres, unknown sources and yacutites) predominate in the north-eastern placers of the Siberian craton, whereas the part of the kimberlitic diamonds is less then a half, in some areas they are completely absent. Early- carboniferous deposits of the Kjutungdinskij graben is the only area where kimberlitic diamonds strongly predominate. That was the case to predict mid-paleozoic kimberlitic field there. In the central part of the province the major role goes to the kimberlitic diamonds associated with the mid-paleozoic kimberlites. Roundish diamonds of the second parasteresis type are in lead on the south of the Siberian craton, and may probably associate with the lamprophyres such as Ingash complex. Mapping of distribution of the distinguished diamond parasteresises among the Siberian craton reveals the tendency of diamonds hypothetically from lamprophyres and unknown sources to associate with the precambrian protrusions - Anabar shield, Olenek rise

  7. Temporal distribution of mantle-derived potassic rocks and carbonatites linked to stabilization of mantle lithosphere and redox states during subduction

    NASA Astrophysics Data System (ADS)

    Foley, S. F.

    2014-12-01

    Mantle-derived potassic igneous rocks and carbonatites first appear in the geological record in the late Archean, coinciding with major crust-forming events on most continents. The compositions of potassic rocks require sources including discrete ultramafic rocks with phlogopite and pyroxenes, whereas carbonatites and ultramafic lamprophyres (carbonate-rich potassic rocks) require oxidizing conditions in which carbonate is stable. The presence of these source rocks from this time is probably related to the stabilization of mantle lithosphere. If mantle lithosphere had not been stable for considerable periods of time, then melting would be restricted to peridotite, which is not a viable option for strongly potassic rocks. The phlogopite-rich source-rock assemblages that are necessary precursors for potassic melts could be introduced into the lithosphere by either subduction processes or by multiple stages of low-degree melting. Many modern examples involve subducted sedimentary material, which concentrates potassium by the stabilization of micas in subduction metamorphism. Subduction involves a great variety of redox states, but the bulk effect is the return of oxidized material from the surface into the mantle. However, we cannot apply uniformitarianism unthinkingly, because subduction processes at and before 2.7 Ga may have had different redox states. Before the Great Oxidation Event the distribution and abundances of geological formations such as banded iron formations, red beds, and uraninites indicate that geological reservoirs became gradually oxidized, preventing an earlier increase in atmospheric oxygen. This means that the function of the subduction process to oxidize the upper mantle by the return of oxidized rocks from the surface was much weaker in the early Earth. Early continental mantle lithosphere was, therefore, likely to accumulate carbon in reduced form, which would be more easily remobilized in melts through low-temperature redox melting much

  8. Polytopic Vector Analysis (PVA) modelling of whole-rock and apatite chemistry from the Karkonosze composite pluton (Poland, Czech Republic)

    NASA Astrophysics Data System (ADS)

    Lisowiec, Katarzyna; Słaby, Ewa; Förster, Hans-Jürgen

    2015-08-01

    This study presents a novel approach for analysing the magma evolution path in composite plutons, applying the so-termed Polytopic Vector Analysis (PVA) to whole-rock and apatite chemistry. As an example of a multiphase magmatic body the Karkonosze granitoid pluton was chosen, which formed by a combination of magma mixing and fractional crystallization of two distinct melts - granitic crust-derived and lamprophyric mantle-derived. The goal was to model end-member magma compositions recorded by apatite and to estimate to what extent these end-members interacted with each other. Although using single minerals as proxies to magma compositions is tricky, the studied apatite well reflects the compositional trends within the magma (e.g., decreasing LREE/Y ratios, varying halogen content, increasing Mn and Na concentrations). The results of PVA simulations for whole-rock geochemistry demonstrate a model similar to that constrained from previous studies. Apart from the main trend of mixing between a felsic (~ 80 wt.% SiO2) and a mafic (~ 53 wt.% SiO2) end-member (EM), an additional process has been recognized, representing most probably the continuous evolution of the mafic end-member, responsible for the compositional diversity of some rocks. One felsic (REE-poor, Mn-F-rich) and one mafic (Cl-Sr-Si-REE-rich) apatite end-members were recognized, whereas the third one represents most probably a fluid component (enriched in Si, Y, Ce and Nd), present at all magmatic stages, however, most prominent during the late stage. The widest range of EM proportions and the highest contribution of the mafic EM are displayed by apatites from the early stage. During the middle and late stages, the apatites present a narrow range of EM proportions, with almost all apatites bearing a felsic signature. This pattern reflects the progressive homogenization of the system. Although the PVA method applied to mineral chemistry poses some limitations, it may provide a more detailed image of the

  9. Mantle wedge involvement in the petrogenesis of Archaean grey gneisses in West Greenland

    NASA Astrophysics Data System (ADS)

    Steenfelt, Agnete; Garde, Adam A.; Moyen, Jean-François

    2005-01-01

    The Archaean crust in West Greenland is dominated by grey orthogneiss complexes formed in periods of crustal accretion at around 3.8, 3.6, 3.2, 3.0-2.9 and 2.8-2.7 Ga. The majority of the gneisses have tonalite-trondhjemite-granodiorite (TTG) compositions, while subordinate quartz-dioritic and dioritic gneisses have calc-alkaline compositions. The major and trace element chemistry of gneiss samples has been compiled from three large regions representing different terranes and ages in southern and central West Greenland, the Godthåbsfjord, Fiskefjord and Disko Bugt regions. The TTG gneisses are typical for their kind and show little variation, except marked Sr enrichment in the Fiskefjord area and slight Cr enrichment in a unit within the Disko Bugt region. Thus, while most of the crust has probably formed from magmas derived by slab melting, local involvement of mantle-derived components is suggested. Most of the diorites have geochemical signatures compatible with mantle-derived parental magmas, i.e., elevated Mg, Cr and flat chondrite-normalised REE patterns. A group of quartz-diorite and diorite samples from the Fiskefjord region exhibits marked enrichment in Sr, Ba, P, K and REE, combined with steep REE patterns. A similar but much more pronounced enrichment in the same elements characterises Palaeoproterozoic subduction-related monzodiorites within the Nagssugtoqidian orogen, as well as carbonatites and carbonatitic lamprophyres within the same part of West Greenland. We argue that the parental magmas of the enriched diorites are derived by partial melting from regions within the mantle that have been metasomatised by carbonatite-related material, e.g., in the form of carbonate-apatite-phlogopite veins. Alternatively, ascending slab melts may have reacted with carbonatite-metasomatised mantle. Carbonatitic carbonates have high Sr and Ba, and carbonatitic apatite has high P 2O 5 and very steep REE spectra. Adding such a component to a peridotite-derived magma

  10. Metasomatic enrichment of Proterozoic mantle south of the Kaapvaal Craton, South Africa: origin of sinusoidal REE patterns in clinopyroxene and garnet

    NASA Astrophysics Data System (ADS)

    le Roex, Anton; Class, Cornelia

    2016-02-01

    indicates regional metasomatism by melts of various compositions. The strong HREEN depletion is interpreted to reflect the effect of initial melt depletion in the early Proterozoic, with melting extending into the spinel stability field requiring an oceanic realm, and again later in the Mesoproterozoic (Namaqua Orogeny). The superimposed incompatible element enrichment indicates subsequent multiple enrichment events by rising alkaline melts similar in composition to kimberlite or ultramafic alkaline lamprophyre, possibly related to Mesozoic plume upwelling beneath the region, that reintroduced clinopyroxene into the depleted Proterozoic harzburgite protolith.

  11. Mesoproterozoic orangeites of Karelia (Kostomuksha-Lentiira): evidence for composition of mantle lithosphere

    NASA Astrophysics Data System (ADS)

    Kargin, Alexey; Nosova, Anna; Larionova, Yulia; Kononova, Voctoria; Borisovskiy, Sergey; Kovalchuk, Elena; Griboedova, Irina

    2014-05-01

    The 1.23-1.20 Ga old diamondiferous lamproites and orangeites (kimberlites of II group) of the Kostomuksha-Taloveys and the Lentiira-Kuhmo dyke fields intrude the Archaean crust of the Karelian craton, NE of the East European Platform. Mineral (a trend of compositional evolution of mica, presence of carbonate minerals in basis, composition of olivine) and geochemical (major elements, ratio of trace elements, primitive mantle normalized trace elements patterns) characteristics of these rocks suggest an orangeitic rather than lamproitic or lamprophyric nature. The composition of Phl-Ol orangeites suggests intensive processes of fractional crystallization for their melts. Cpx-Phl-Ol orangeites indicate higher intensity of lithospheric mantle assimilation then other orangeitic types. Phl-Carb orangeites of the Taloveys area and Cpx-Phl-Ol one of the Lentiira area are closest to primary melts. The Ol-Phl-Cpx orangeites of the Lentiira area contain three generations of unaltered olivine that vary in composition and origin: a) xenocryst derived from depleted mantle peridotite; b) orangeitic olivine phenocryst and c) and olivine like early stage crystallization of megacryst assemblage or a product of metasomatic interaction between mantle peridotite and protokimberlitic melt. Orangeites of Kostomuksha-Lentiira have low- and medium-radiogenic value of (87Sr/86Sr)1200 that range from 0.7038 to 0.7067. Phl-Carb orangeites of Taloveys have less radiogenic isotopic composition of Nd (eNd -11 ... -12) then Cpx-Phl-Ol and Phl-Ol orangeites of Kostomuksha (eNd -6.9 ... -9.4). The study of Sm-Nd and Rb-Sr isotopic systems suggests that an ancient metasomatic mantle source took part in origin of orangeites. We propose a two-steps model of origin of their source (Kargin et al., 2014): 1) The metasomatic component of mantle source (like as MARID-type veins) formed during Lapland-Kola and/or Svecofennian orogeny events (2.1-1.8 Ga ago). 2) The intrusion of orangeites is comparable by

  12. Origin of Ti-rich garnets in the groundmass of Wajrakarur field kimberlites, southern India: insights from EPMA and Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Dongre, Ashish N.; Viljoen, K. S.; Rao, N. V. Chalapathi; Gucsik, A.

    2016-04-01

    Although Ti-rich garnets are commonly encountered in the groundmass of many alkaline igneous rocks, they are comparatively rare in kimberlites. Here we report on the occurrence of Ti-rich garnets in the groundmass of the P-15 and KL-3 kimberlites from the diamondiferous Wajrakarur field in the Eastern Dharwar craton of southern India. These garnets contain considerable Ti (11.7-23.9 wt.% TiO2), Ca (31.3-35.8 wt.% CaO), Fe (6.8-15.5 wt.% FeOT) and Cr (0.04-9.7 wt.% Cr2O3), but have low Al (0.2-5.7 wt.% Al2O3). In the case of the P-15 kimberlite they display a range in compositions from andradite to schorlomite, with a low proportion of grossular (andradite(17.7-49.9)schorlomite(34.6-49.5)-grossular(3.7-22.8)-pyrope(1.9-10.4)). A few grains also contain significant chromium and represent a solid solution between schorlomite and uvarovite. The Ti-rich garnets in the KL-3 kimberlite, in contrast, are mostly schorlomitic (54.9-90.9 mol %) in composition. The Ti-rich garnets in the groundmass of these two kimberlites are intimately associated with chromian spinels, perhaps suggesting that the garnet formed through the replacement of spinel. From the textural evidence, it appears unlikely that the garnets could have originated through secondary alteration, but rather seem to have formed through a process in which early magmatic spinels have reacted with late circulating, residual fluids in the final stages of crystallization of the kimberlite magma. Raman spectroscopy provides evidence for low crystallinity in the spinels which is likely to be a result of their partial transformation into andradite during their reaction with a late-stage magmatic (kimberlitic) fluid. The close chemical association of these Ti-rich garnets in TiO2-FeO-CaO space with those reported from ultramafic lamprophyres (UML) is also consistent with results predicted by experimental studies, and possibly implies a genetic link between kimberlite and UML magmas. The occurrence of Ti-rich garnets of

  13. Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

    USGS Publications Warehouse

    Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

    2011-01-01

    The type examples for the class of deposits termed intrusion-related gold systems occur in the Tombstone-Tungsten belt of Alaska and Yukon, on the eastern side of the Tintina gold province. In this part of the northern Cordillera, extensive mid-Cretaceous postcollisional plutonism took place following the accretion of exotic terranes to the continental margin. The most cratonward of the resulting plutonic belts comprises small isolated intrusive centers, with compositionally diverse, dominantly potassic rocks, as exemplified at Scheelite Dome, located in central Yukon. Similar to other spatially and temporally related intrusive centers, the Scheelite Dome intrusions are genetically associated with intrusion-related gold deposits. Intrusions have exceptional variability, ranging from volumetrically dominant clinopyroxene-bearing monzogranites, to calc-alkaline minettes and spessartites, with an intervening range of intermediate to felsic stocks and dikes, including leucominettes, quartz monzonites, quartz monzodiorites, and granodiorites. All rock types are potassic, are strongly enriched in LILEs and LREEs, and feature high LILE/HFSE ratios. Clinopyroxene is common to all rock types and ranges from salite in felsic rocks to high Mg augite and Cr-rich diopside in lamprophyres. Less common, calcic amphibole ranges from actinolitic hornblende to pargasite. The rocks have strongly radiogenic Sr (initial 87Sr/86Sr from 0.711-0.714) and Pb isotope ratios (206Pb/204Pb from 19.2-19.7), and negative initial εNd values (-8.06 to -11.26). Whole-rock major and trace element, radiogenic isotope, and mineralogical data suggest that the felsic to intermediate rocks were derived from mafic potassic magmas sourced from the lithospheric mantle via fractional crystallization and minor assimilation of metasedimentary crust. Mainly unmodified minettes and spessartites represent the most primitive and final phases emplaced. Metasomatic enrichments in the underlying lithospheric mantle

  14. Petrogenesis and geodynamic implications of the early Paleozoic potassic and ultrapotassic rocks in the South China Block

    NASA Astrophysics Data System (ADS)

    Jia, Xiaohui; Wang, Xiaodi; Yang, Wenqiang

    2017-03-01

    In this paper, some potassic and ultrapotassic rocks in the South China Block (SCB) have been recognized, according to a set of new geochronological, geochemical and Sr-Nd isotopic data. Zircon U-Pb dating from six plutons yield consistent crystallization ages of 445-424 Ma. These potassic and ultrapotassic rocks can be geochemically subdivided into three groups. Group 1, represented by the Longchuan gabbro, longmu diabase, Tangshang and Danqian diorite (445-433 Ma), have low silica contents (SiO2 = 47.38-54.16 wt.%), and high MgO (4.21-9.51 wt.%) and total alkalis (Na2O + K2O = 3.08-5.57 wt.%), with K2O/Na2O ratios of 0.62-1.82. They are enriched in LREE and depleted in Ba, Sr and Ta-Nb-Ti, and exhibit relatively high initial 87Sr/86Sr ratios (0.70561-0.71128), low εNd(430 Ma) values (-8.4 to -3.2), suggesting that they were most plausibly generated by the partial metling of enriched mantle source (EMI). Group 2, from the Huwei diorite (424 Ma), have 45.68-52.87 wt.% of SiO2, 5.79-9.25 wt.% of MgO and 52-65 of mg-number. They have significantly higher Th (9.92 ppm), Ce (88.0-115 ppm) concentration and Ce/Yb (27.6-46.8), Th/Yb ratios (2.58-7.99), and relatively low initial 87Sr/86Sr ratios (0.70501-0.70599), and high εNd(430 Ma) values (-2.1 to -1.5). We propose that they originated from the partial melting of the depleted mantle source with subsequent contamination by crustal materials. Group 3, represented by the Daning lamprophyre (∼445 Ma), has SiO2 contents ranging from 41.73 wt.% to 45.22 wt.%, MgO from 13.74 wt.% to 15.16 wt.%, and mg-muber from 73 to 77, with high K2O/Na2O ratios (>2.0). They have 87Sr/86Sr ratios of 0.62912-0.70384 and εNd(t = 430 Ma) values of -6.4 to -6.3, indicating that the source components are close to the EMI source, with significant sediments involved. These Silurian potassic and ultrapotassic rocks in the SCB can be responsible for post-orogenic delamination and intra-plate extension. And the delamination had a small size and

  15. Protracted, coeval crust and mantle melting during Variscan late-orogenic evolution: U-Pb dating in the eastern French Massif Central

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Couzinié, Simon; Zeh, Armin; Vanderhaeghe, Olivier; Moyen, Jean-François; Villaros, Arnaud; Gardien, Véronique; Chelle-Michou, Cyril

    2017-01-01

    The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt, which makes it akin to "hot" orogens. These processes resulted in the development of large granite-migmatite complexes, the largest of which being the 305-300-Ma-old Velay dome in the eastern French Massif Central (FMC). This area also hosts a wide range of late-Variscan plutonic rocks that can be subdivided into four groups: (i) cordierite-bearing peraluminous granites (CPG); (ii) muscovite-bearing peraluminous granites (MPG); (iii) K-feldspar porphyritic, calc-alkaline granitoids (KCG) and (iv) Mg-K-rich (monzo)diorites and lamprophyres ("vaugnerites"). New results of LA-SF-ICP-MS U-Pb zircon and monazite dating on 33 samples from all groups indicate that both granites and mafic rocks emplaced together over a long period of 40 million years throughout the Carboniferous, as shown by intrusion ages between 337.4 ± 1.0 and 298.9 ± 1.8 Ma for the granitoids, and between 335.7 ± 2.1 and 299.1 ± 1.3 Ma for the vaugnerites. Low zircon saturation temperatures and abundant inherited zircons with predominant late Ediacaran to early Cambrian ages indicate that the CPG and MPG formed through muscovite or biotite dehydration melting of ortho- and paragneisses from the Lower Gneiss Unit. The KCG and vaugnerites contain very few inherited zircons, if any, suggesting higher magma temperatures and consistent with a metasomatized lithospheric mantle source for the vaugnerites. The KCG can be explained by interactions between the CPG/MPG and the vaugnerites, or extensive differentiation of the latter. The new dataset provides clear evidence that the eastern FMC was affected by a long-lived magmatic episode characterized by coeval melting of both crustal and mantle sources. This feature is suggested here to result from a lithospheric-scale thermal anomaly, triggered by the removal of the lithospheric mantle root. The spatial

  16. The composition of near-solidus melts of peridotite in the presence of CO 2 and H 2O between 40 and 60 kbar

    NASA Astrophysics Data System (ADS)

    Foley, S. F.; Yaxley, G. M.; Rosenthal, A.; Buhre, S.; Kiseeva, E. S.; Rapp, R. P.; Jacob, D. E.

    2009-11-01

    Partial melting experiments at 40, 50 and 60 kbar pressure on three peridotite compositions with 0.5-0.63 wt.% H 2O and 2.0-3.2 wt.% CO 2 added indicate melting temperatures only marginally above continental geotherms. Most experiments were performed on a composition with 1.5 wt.% K 2O added, which causes a further decrease of about 40 °C in melting temperature. Melts progress gradually from carbonate-rich to carbonated silicate in composition: near-solidus melts have Ca/(Ca + Mg) of 0.46-0.53, which fall to < 0.40 more than 50 °C above the solidus. With increasing temperature for the K-enriched peridotite HPK at 50 kbar, melts are characterised by strong increases in SiO 2 (< 3 to > 30 wt.%) and Al 2O 3 (< 1 to > 9 wt.%) and concomitant decrease in CaO (> 20 to < 3 wt.%), with little change in MgO. K 2O and TiO 2 exhibit maxima at intermediate temperatures, reflecting the stability of phlogopite and ilmenite above the solidus, indicating the presence of up to 13 wt.% K 2O and 2.6 wt.% TiO 2 in carbonate-rich melts with only 13 wt.% SiO 2. Of 30 trace elements, only Cr, Mn, Ni, and Zn are compatible in the residue, whereas U, Rb, Ba and the LREE are most enriched in the melts. Low melt fractions exhibit troughs in trace element patterns for Hf, Nb, Ta and Cs that are diminished or eliminated at higher degrees of melting. Apart from these features and larger LREE/HREE ratios, trace element compositions are similar to silicate melts of peridotite in CO 2-free conditions. Partial melts of peridotite with CO 2 and H 2O are too low in MgO to resemble kimberlites, but will act as effective metasomatic agents enriching the lithosphere in K and carbonates, of relevance for ultramafic lamprophyres and kamafugites. Higher-degree melts (15-35%) have > 20 wt.% SiO 2, are only mildly enriched in trace elements, and will not cause large time-integrated isotopic in-growth except over long geological time intervals. The temperature interval over which melts are carbonatitic with

  17. Geology and Fluorspar Deposits of the Levias-Keystone and Dike-Eaton Areas, Crittenden County, Kentucky

    USGS Publications Warehouse

    Trace, Robert Denny

    1962-01-01

    The fault systems of the Levias-Keystone and Dike-Eaton areas, in the Kentucky-Illinois fiuorspar district, are a complex northeastward-trending sys- tem and a simple northwestward-trending system of steeply dipping normal faults, associated in part with a lamprophyre dike. Fluorspar mining started in the area about 1900 and, as of 1945, more than 200,000 tons of crude ore probably has been mined; most of the ore was from the Levias-Keystone area. A small quantity of zinc and lead ore also is present in the Dike-Eaton area. The deposits are localized along faults that displace fiat-lying or low-dipping limestones, sandstones, and shales of the Meramec and Chester series of Missis- sippian age. Movement along most of the faults was principally vertical, with displacement as much as 600 feet. Some horizontal movement occurred along at least one fault. Geologic mapping of the surface and data from underground workings have revealed 13 faults in an area of four-fifths of a square mile. Only a few of these faults are known to contain economically important deposits of fiuorspar. The most abundant vein minerals are calcite and fiuorite with subordinate quantities of sphalerite, galena, barite, and quartz. Some weathering products of sphalerite and galena are present also. The veins are dominantly calcite that contains fiuorite lenses but in places are mainly fiuorite having lesser quantities of calcite. Sphalerite- and galena-bearing deposits are present in the Dike-Eaton area. The ore bodies mainly are the result of fissure filling and replacement of calcite by fiuorite; in addition a small amount of limestone wallrock probably has been replaced. Residual concentrations of high-grade fluorspar in the overburden above faults have yielded some so-called gravel fiuorspar. The position of the veins within the faults may be related to one or more factors such as type of wallrock, change in dip of the fault, and amount of displacement.

  18. Archaean multiphase Porosozero sanukitoid pluton of the Kola region: petrological, geochronological and geochemical data

    NASA Astrophysics Data System (ADS)

    Kudryashov, Nikolai; Mokrushin, Artem; Petrovsky, Michail; Elizarov, Dmitry

    2013-04-01

    The Porosozero sanukitoid intrusion is located in the greenstone belt of the Kolmozero-Voronja, north-eastern part Fennoscandian (Baltic) Shield. The Porosozero multiphase pluton was formed as a result of the 4 magmatic phases during the period ca. 60 million years. The main phase is represented by a differentiated series of gabbro-diorite - quartz monzodiorite - granodiorite - granite. The zircon TIMS ages of granodiorite and quartz monzodiorites are 2733±6 Ma and 2734±4 Ma, respectively. The second phase is composed of leucogranites formed during intrusion of the residual melt portion from intracrustal source. The age of zircon from leucogranite is 2712±6 Ma. The third phase is represented by the lamprophyre dykes with the zircon age 2680±8 Ma. The late pegmatite veins were formed during the fourth final phase. The volume relationships between the gabbro-diorite, quartz monzodiorites, granodiorites and granites are 5:55:27:13, respectively. The medium weighted composition of the initial melt, calculated from the rock compositions of the first phase is andesite (wt.%): SiO2 = 61.53, TiO2 = 0.58, Al2O3 = 15.74, Fe2O3 = 3.75, FeO = 3.07, MnO = 0.10, MgO = 3.06, CaO = 5.83, Na2O = 3.78, K2O = 2.37. The compositional variation is the result of fractional crystallization. The last magmas may have experienced some crustal contamination. All rocks of the first phase are enriched in Ba (500-800 ppm), Sr (450-700 ppm), K2O (1.8-3.2 wt. %), P2O5 (0.15-0.35), LREE [(La/Yb)N=15-23] and contain high concentrations of Cr (150-400 ppm) and Ni (60-140 ppm), possess high mg# values (0.45-0.65), and show a negative Nb-Ta anomaly. Sm-Nd isotopic data for sanukitoids indicate their formation from a mantle source enriched in LILE and LREE with ɛNd (2740) = +1.02 - +0.36, T(DM)=2.9-2.8 Ga. The Porosozero polyphasic pluton is similar to worldwide Archaean and Phanerozoic magmatic sanukitoide series. The Porosozero pluton formation is determined by the processes of mantle

  19. Processes and timescales of melt metasomatism in the continental lower crust of West Greenland

    NASA Astrophysics Data System (ADS)

    Smit, Matthijs; Waight, Tod; Nielsen, Troels

    2017-04-01

    -mediated dissolution and re-precipitation. These melts are either lamprophyric, felsic or carbonatitic, with the latter two occurring only at Sisimiut. Speedometry shows that melts have been present in the Sarfartôq samples since c. 700 Myr before eruption. For the more strongly metasomatized Sisimiut samples, these time scales typically exceed millennia, in particular for carbonatitic and associated felsic melt pockets. These differences are attributed to a fundamental difference in granulite grain size and texture, as well as to the degree of depletion of the underlying mantle, which to a large extent controls the duration of pre-eruptive crustal fluxing and the compositional evolution the metasomatic agents.

  20. B-Be-Li Systematics in the Trans-Mexican Volcanic Belt: Along-Strike Consistencies and Variations

    NASA Astrophysics Data System (ADS)

    Wagner, R.; Grose, C.; Lindsey, M.; Ryan, J. G.

    2007-05-01

    We are examining Li, Be and B abundance variations in mafic lavas along strike in the Trans-Mexican Volcanic Belt (TMVB), building on previous undergraduate research efforts focused on the Colima Graben and two sites in the Michoacan-Guanajuato Volcanic Field (MGVF; Fuller et al 2003; Ryan et al 2005). Our past work indicated that both differentiated calc-alkaline and alkaline (i.e., lamprophyric) TMVB lavas show evidence for assimilation of crustal materials variably enriched in boron (i.e., Hochstaedter et al 1996), while more mafic lavas appear to preserve signatures reflecting their magma sources. We have thus far examined basaltic lavas from the Mascota volcanic field and Volcan San Juan to the west; calc-alkaline lavas from monogenetic centers of the Michoacan- Guanajuato and Chichinautzin volcanic fields, and the Palma Sola volcanic field in the easternmost TMVB. In general, B, Be, and Li systematics for basalts in other TMVB centers are similar to those at Colima: Be is higher in alkaline lavas than calc-alkaline lavas, while B contents are low relative to other arcs. All the lavas show elevated Li/Y and Li/Yb, and K/Li-La/Yb trends indicate slab-derived alkali enrichments and amphibole crystallization. However, along-arc changes are evident in mean B/Be (~7 in west TMVB centers to ~20 in the east) and Li/Yb (~11 in the west, ~6 in the east). Be/Nd ratios are essentially constant along the TMVB, but mean Be/Ti declines from ~1.3 in the west to ~0.5 in the east, implying increases in the mean extent of partial melting from W to E. Be/Ti varies inversely with the age of the downgoing plate, and positively with inferred slab temperatures (Curry et al, 2002), so it is possible that deeper transport of slab fluids to arc depths in E-TMVB leads to higher degrees of mantle melting, an inference consistent with B/Be variations. That Li/Yb and Be/Ti correlate positively may mean that the slab flux of Li changes minimally along the arc and changing melt extents

  1. Late Palaeoproterozoic mafic dyking in the Ukrainian Shield of Volgo-Sarmatia caused by rotation during the assembly of supercontinent Columbia (Nuna)

    NASA Astrophysics Data System (ADS)

    Bogdanova, Svetlana V.; Gintov, Oleg B.; Kurlovich, Dzmitry M.; Lubnina, Nataliya V.; Nilsson, Mimmi K. M.; Orlyuk, Mykhailo I.; Pashkevich, Inna K.; Shumlyanskyy, Leonid V.; Starostenko, Vitaly I.

    2013-08-01

    The Ukrainian Shield comprises the exposed crust of the large Palaeoproterozoic protocraton Volgo-Sarmatia, which together with the Fennoscandian crustal segment constitutes the East European Craton ("Baltica"). Geological and geophysical data indicate that 1.80 to 1.75 Ga mafic dykes related to anorthosite-mangerite-charnockite-granite (AMCG) plutons are widespread within the Ukrainian Shield. We examined their ages, distribution patterns, orientations and compositions in three different crustal blocks (Volyn, Ingul and Azov), and found close spatial relationships with major strike-slip fault systems developed during two phases of extension. The early, 1.80-1.77 Ga, generation of mafic dykes mostly follows NW (330 ± 20°) and more rarely N-S- or E-W-trending faults corresponding to major NE-SW extension (the Submoshorino phase). These dykes contain olivine dolerites, picrites, camptonites, lamprophyres, kimberlites and other rocks belonging to tholeiitic and subalkaline jotunitic series. The compositions of these dykes differ between the host blocks, but all feature upper mantle geochemical signatures such as high contents of Ni and Cr, and positive values of εNd(1800) up to + 2.8. High degrees of REE fractionation indicate deep levels of mantle melting, which is particularly characteristic of the Ingul block as marked by the most extensive and dense mafic dyke swarms. The later, 1.76-1.75 Ga, dyke swarms occur close to the most voluminous AMCG suites of similar age and were emplaced during the second (Korsun) phase of faulting when all the older strike-slip fault zones were reactivated and partly transformed to tensional faults by E-W extension. These dyke swarms mainly trend 030 ± 20°. They are jotunitic and their isotopic signatures indicate a greater participation of crustal sources in the parent melts. The overall transtensional tectonic setting of the mafic dyking associated with the AMCG magmatism in Volgo-Sarmatia was created by convergent tectonics

  2. Alkaline magmatism in the Amambay area, NE Paraguay: The Cerro Sarambí complex

    NASA Astrophysics Data System (ADS)

    Gomes, C. B.; Velázquez, V. F.; Azzone, R. G.; Paula, G. S.

    2011-07-01

    considerably more pronounced in the carbonatites. Chondrite-normalized REE patterns point to the high concentration of these elements and to the strong LRE/HRE fractionation. The Amambay rocks are highly enriched in radiogenic Sr and have TDM model ages that vary from 1.6 to 1.1 Ga, suggesting a mantle source enriched in incompatible elements by metasomatic events in Paleo-Mesoproterozoic times. Data are consistent with the derivation of the Cerro Sarambí rocks from a parental magma of lamprophyric (minette) composition and suggest an origin by liquid immiscibility processes for the carbonatites.

  3. Mineral paragenesis, geochemistry and geochronology investigations of the Carlin-type gold deposits at the Goldstrike property, northern Nevada: Implications for ore genesis, igneous petrogenesis and mineral exploration

    NASA Astrophysics Data System (ADS)

    Almeida, Carolina Michelin De

    The Goldstrike property is located in northern Nevada and contains one of the largest and highest-grade Carlin-type gold deposits. The majority of the Eocene Au mineralization (e.g., Ore I) is hosted in intensely altered Paleozoic lower plate impure carbonate rocks, and is characterized by strong to moderate silicification, higher calculated pyrite and ore-related element concentrations (e.g., As, Cu, Hg, Ni, Tl, Sb, W, and Zn) than Ore II, which is weakly altered. However, both ore types contain similar Au concentration in whole rock and pyrite chemistry analyses. Lithogeochemical and microprobe data suggest that the Paleozoic sedimentary rocks may have been a major source of Cd, Mo, Ni, U, V, and Zn and minor As, Cu, Hg, and Se. The Jurassic lamprophyre dikes might have been a significant source of Ba, Co, and Se, and minor Au, and some of the Jurassic and Eocene intrusive rocks may have provided some Fe. Moreover, the Eocene magmas are interpreted to be the main source of auriferous mineralizing fluids. Trace element abundances and ratios of the Jurassic intrusive rocks suggest that they are shoshonitic and formed from a metasomatized mantle-derived magma, crystal fractionation, and crustal contamination. The Eocene dikes, also shoshonitic, are considerably more evolved and contaminated than the studied Jurassic rocks. Furthermore, Ar-Ar results show that the Jurassic rocks were negligibly affected by the Eocene thermal event, and that temperature of mineralizing fluids were below the closure temperature of biotite (< 350°C). A magmatic-related model is proposed to explain the formation of the Carlin-type gold deposits at the studied area. In this model, Au and the ore-related elements were exsolved along with volatiles by degassing of a deep and large plutonic complex during its early stage of crystallization. As these magmatic-hydrothermal fluids moved upward along major conduits (e.g., NNW-striking faults), they may have interacted with a Fe-rich fluid

  4. Rare earth element deposits in China

    USGS Publications Warehouse

    Xie, Yu-Ling; Hou, Zeng-qian; Goldfarb, Richard J.; Guo, Xiang; Wang, Lei

    2016-01-01

    China is the world’s leading rare earth element (REE) producer and hosts a variety of deposit types. Carbonatite- related REE deposits, the most significant deposit type, include two giant deposits presently being mined in China, Bayan Obo and Maoniuping, the first and third largest deposits of this type in the world, respectively. The carbonatite-related deposits host the majority of China’s REE resource and are the primary supplier of the world’s light REE. The REE-bearing clay deposits, or ion adsorption-type deposits, are second in importance and are the main source in China for heavy REE resources. Other REE resources include those within monazite or xenotime placers, beach placers, alkaline granites, pegmatites, and hydrothermal veins, as well as some additional deposit types in which REE are recovered as by-products. Carbonatite-related REE deposits in China occur along craton margins, both in rifts (e.g., Bayan Obo) and in reactivated transpressional margins (e.g., Maoniuping). They comprise those along the northern, eastern, and southern margins of the North China block, and along the western margin of the Yangtze block. Major structural features along the craton margins provide first-order controls for REE-related Proterozoic to Cenozoic carbonatite alkaline complexes; these are emplaced in continental margin rifts or strike-slip faults. The ion adsorption-type REE deposits, mainly situated in the South China block, are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits, although Caledonian (early Paleozoic) granites are also of local importance. The primary REE enrichment is hosted in various mineral phases in the igneous rocks and, during the weathering process, the REE are released and adsorbed by clay minerals in the weathering profile. Currently, these REE-rich clays are

  5. Petrology of Mafic Bodies Associated with the Eocene "A-type" Golden Horn Batholith, North Cascades, WA

    NASA Astrophysics Data System (ADS)

    Berkelhammer, S.; Tepper, J. H.; Petro, G. T.; Eckles, E. H.

    2012-12-01

    The 49 Ma Golden Horn batholith, the only "A-type" granite in the WA Cascades, is associated with coeval mafic bodies that represent samples of mantle-derived magmas that were present during melting and emplacement of the batholith. The most voluminous mafic rocks are dikes up to 10 m wide that occur in a NW-trending 48 Ma swarm roughly parallel to (but outside of) the SW margin of the batholith. Dike lithologies include hornblende lamprophyres, biotite-hornblende diorites, and hornblende-biotite tonalites. Mafic rocks also occur as plutons within the batholith, one studied example being the 48.4 Ma olivine-bearing pyroxene diorite at Cutthroat Peak. All of the Golden Horn mafic rocks have spidergrams with HFSE depletions that suggest an arc setting. They can be divided on the basis of chemistry into 5 types: low-silica adakites (LSA), high-silica adakites (HSA), Nb-enriched basalts (NEB), high-Nb basalts (HNB), and "typical" arc basalts (TAB). HSA traits (800-1400 ppm Sr, La/Ybn = 11-23, low HREE contents, SiO2 >60 wt. %) are consistent with an eclogite (slab) source. Conversely, the LSA (860-1100 ppm Sr, La/Ybn = 21-25, up to 650 ppm Cr, SiO2 <60 wt. %), NEB and HNB (both with 380-550 ppm Cr, 22-57 ppm Nb, La/Ybn = 13-26) require contributions from both eclogite and peridotite sources. Traits of the TAB, represented by the Cutthroat Peak diorite (46-50 wt. % SiO2; La/Ybn = 3.5-6.1) suggest derivation from a mantle wedge without slab melt (eclogite) involvement. We suggest that the LSA, NEB, and HNB originated by melting of mantle wedge that had been enriched with (or assimilated by) slab melts, the latter possibly represented by the HSA. Elevated temperatures necessary for slab melting are associated with slab windows, and plate motion reconstructions (Engebretson et al., 1985) are compatible with migration of the Kula-Farallon slab window beneath the Golden Horn area during the mid-Eocene. Passage of this slab window provides an explanation for adakite formation

  6. Compositional Variability of the Mantle beneath West Antarctica and its Relationship to Terrane Tectonics: Evidence from Mantle Xenoliths

    NASA Astrophysics Data System (ADS)

    Ross, A. J.; Gibson, S. A.; Leat, P. T.; Vaughan, A. P. M.

    2009-04-01

    This work examines the petrography and mineral chemistry of sixteen previously undescribed mantle xenoliths suites from the West Antarctic Peninsula. The xenoliths are from the Jones Mountains (a Palaeozoic volcanic arc terrane on the margin of Gondwana), Adelaide Island (a Mesozoic volcanic arc terrane) and Alexander Island (an accretionary complex). They were entrained by subduction and rift-related magmatism, including 50 Ma calc-alkaline lamprophyres (Adelaide Island) and 10-5 Ma alkali basalts (Alexander Island and Jones Mountains). The xenoliths range in composition from pyroxenites (Adelaide Island) to spinel peridotites (Alexander Island and Jones Mountains). At Alexander Island, the spinel peridotites occur as both ‘fertile' lherzolites and ‘depleted' harzburgites. The xenoliths show a wide variation in mineral chemistry, for example olivine varies from Fo91.5 in the harzburgites to Fo71 in the pyroxenites. Significant variations have also been observed in the major-element chemistry of the pyroxenes. Those in the spinel peridotites are Cr-diopsides whereas those in the pyroxenites are Al-augites. Rare-earth element patterns of clinopyroxenes and Cr/(Cr+Al) ratios of spinels provide information on the origin of the xenoliths. We conclude that the harzburgites experienced a complex evolution involving extraction of up to 20% melt, perhaps in the mantle wedge, followed by accretion on to the base of the lithosphere and enrichment in Cr by large degree hydrous melts (boninites). There is also evidence of enrichment in strongly incompatible trace elements by carbonate melts and fluids from the subducted Phoenix plate. However, some of the spinel lherzolites from Alexander Island, and also those from the Jones Mountains, have compositions that are similar to fertile mantle and have not been subjected to large scale melting. The pyroxenites from Adelaide Island are believed to represent samples of veined lithospheric mantle caused by percolation and reaction

  7. Petrogenesis of orbicular ijolites from the Prairie Lake complex, Marathon, Ontario: Textural evidence from rare processes of carbonatitic magmatism

    NASA Astrophysics Data System (ADS)

    Zurevinski, Shannon E.; Mitchell, Roger H.

    2015-12-01

    A unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1.1 Ga Prairie Lake Carbonatite Complex (Marathon, Ontario, Canada), and is the only known occurrence of this textural type in a rock of ijolitic composition. This mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites, granites, diorites and lamprophyres. The orbicules occur along distinct, densely packed bands in equigranular nepheline-rich ijolite and range up to 6 cm in diameter. Macroscopically, the orbicules show variability in the mineralogy of their cores. Detailed imaging of the cores shows evidence of quench textures. Radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules. The mineralogy of the orbicules consists of: nepheline; diopside; calcite; apatite; andradite-melanite garnet; titanite; Fe-rich phlogopite; titaniferous magnetite; perovskite; with secondary natrolite, calcite and cancrinite. The mineralogy of the host ijolite is similar to that of the orbicules. Mineral compositions from the orbicular ijolite and the host ijolite are similar. Within the orbicules, anhedral minerals are found occurring in a 'matrix' of garnet throughout the distinct concentric bands. The textures within the concentric bands of the orbicules are best described as annealing recrystallization textures. The rims of the orbicules form interlocking crystals with the host ijolite resulting in near-indistinguishable boundaries. The orbicules are interpreted to represent interaction of a partially-crystallized quenched ijolitic melt, which was in contact with a second pulse of consanguineous ijolite magma. Immersion in the latter resulted in sub-solidus diffusion and annealing recrystallization. Orbicular textures were produced from previously formed quenched ijolite, which was

  8. Geology and resources of thorium and associated elements in the Wet Mountains area, Fremont and Custer counties, Colorado

    USGS Publications Warehouse

    Armbrustmacher, T.J.

    1988-01-01

    Thorium in potentially economic amounts occurs in three types of deposits in the Wet Mountains area of Colorado: (1) quartz-baritethorite veins and fracture zones, (2) carbonatite dikes, and (3) red syenite dikes. The quartz-barite-thorite veins and fracture zones contain the largest resources of thorium; they cut all Precambrian and Paleozoic rock types in the area and tend to strike normal to the foliation in the Proterozoic metasedimentary and metavolcanic rocks. The veins and fracture zones are end products of the episode of Cambrian alkaline magmatism that also produced rocks of the McClure Mountain Complex, the Gem Park Complex, the complex at Democrat Creek, and associated dikes of carbonatite, lamprophyre, and red syenite. The veins and fracture zones contain an average of 0.46 percent ThO2, 0.21 percent SLREE (total light rare-earth elements), 0.14 percent SHREE (total heavy rare-earth elements), and 0.012 percent Nb2O5; They contain reserves of 64,200 tons ThO2, 29,300 tons SLREE, 19,540 tons SHREE, 1,675 tons Nb2O5; they contain probable potential resources of 160,500 tons ThO2, 73,270 tons SLREE, 48,850 tons SHREE, and 4,185 tons Nb2O5. The carbonatite dikes form two distinct groups: replacement carbonatites and primary magmatic carbonatites. The latter group appears to be the better source of potentially economic commodities. The primary magmatic carbonatites contain an average of 0.17 percent ThO2, 0.0097 percent Nb2O5, 0.0031 percent U3O5, and 2.15 percent total rare-earth oxides. The seven largest dikes contain reserves of 131 tons ThO2, 40 tons Nb2O5, 17 tons U3O5, and 2,500 tons SRE203 (total rare-earth oxides), and probable potential resources of 753 tons ThO2, 228 tons Nb2O5, 105 tons U3O5, and 14,300 tons SRE2O3. The red syenite dikes contain anomalous amounts of thorium, uranium, niobium, and rare-earth elements. Although reserves and probable potential resources have not been calculated, they are likely to be small.

  9. PGE geochemistry and Re Os dating of massive sulfide ores from the Baimazhai Cu Ni deposit, Yunnan province, China

    NASA Astrophysics Data System (ADS)

    Sun, Xiaoming; Wang, Shengwei; Sun, Weidong; Shi, Guiyong; Sun, Yali; Xiong, Dexin; Qu, Wenjun; Du, Andao

    2008-09-01

    The Baimazhai deposit in Yunnan Province is one of the largest Cu-Ni sulfide deposits hosted in mafic-ultramafic intrusions in China. Concentrations of platinum-group elements (PGE) in massive sulfide ores and host rocks from Baimazhai were determined by using inductively coupled plasma mass spectrometry (ICP-MS) following nickel sulfide fire assay pre-concentration. The results show that the total PGE (ΣPGE) are quite low, decreasing gradually from central massive ores (78.2-556 ppb) to olivine pyroxenite (0.472-67.0 ppb), gabbro (0.847 ppb) and, websterite (0.76-0.809). The intruded lamprophyre dykes also show low ΣPGE (2.98-4.07 ppb). The ΣPGE exhibit obvious positive correlations with Au, Ni and Cu contents. Primitive mantle normalized PGE patterns of the massive Cu-Ni ores are of the Pt-Pd type with relatively steep and trough-like patterns, which are similar to those of the host rocks. In addition, the Pt/Pd and Cu/Pd ratios of the massive sulfide ores are similar to those of olivine pyroxenite, gabbro and websterite. These characteristics suggest that sulfides in the massive ores are of magmatic origin, co-genetic with their host rocks. The relatively high Pt/Pd ratios of the Baimazhai massive sulfide ores (averaging 0.83) and their host rocks imply that the Baimazhai sulfides formed in a single sulfide saturation event, but not through multiple sulfide injections. High Ir contents (0.77-5.52 ppb, averaging 2.35 ppb) and dramatically variable Pd/Ir ratios (4.76-296, averaging 138) of the massive sulfide ores suggest that the Baimazhai sulfide ores might have suffered significant late stage hydrothermal alteration. The Baimazhai massive sulfide ores yield a Re-Os isochron age of 259 ± 20 Ma (MSWD = 0.025), which is the same as the major eruption stage of the Emeishan large igneous province and the Baimazhai intrusion, further supporting their magmatic origin. The initial 187Os/ 188Os value of 0.456 ± 0.026 indicates that crustal contamination has played

  10. Protracted, coeval crust and mantle melting during Variscan late-orogenic evolution: U-Pb dating in the eastern French Massif Central

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Couzinié, Simon; Zeh, Armin; Vanderhaeghe, Olivier; Moyen, Jean-François; Villaros, Arnaud; Gardien, Véronique; Chelle-Michou, Cyril

    2017-03-01

    The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt, which makes it akin to "hot" orogens. These processes resulted in the development of large granite-migmatite complexes, the largest of which being the 305-300-Ma-old Velay dome in the eastern French Massif Central (FMC). This area also hosts a wide range of late-Variscan plutonic rocks that can be subdivided into four groups: (i) cordierite-bearing peraluminous granites (CPG); (ii) muscovite-bearing peraluminous granites (MPG); (iii) K-feldspar porphyritic, calc-alkaline granitoids (KCG) and (iv) Mg-K-rich (monzo)diorites and lamprophyres ("vaugnerites"). New results of LA-SF-ICP-MS U-Pb zircon and monazite dating on 33 samples from all groups indicate that both granites and mafic rocks emplaced together over a long period of 40 million years throughout the Carboniferous, as shown by intrusion ages between 337.4 ± 1.0 and 298.9 ± 1.8 Ma for the granitoids, and between 335.7 ± 2.1 and 299.1 ± 1.3 Ma for the vaugnerites. Low zircon saturation temperatures and abundant inherited zircons with predominant late Ediacaran to early Cambrian ages indicate that the CPG and MPG formed through muscovite or biotite dehydration melting of ortho- and paragneisses from the Lower Gneiss Unit. The KCG and vaugnerites contain very few inherited zircons, if any, suggesting higher magma temperatures and consistent with a metasomatized lithospheric mantle source for the vaugnerites. The KCG can be explained by interactions between the CPG/MPG and the vaugnerites, or extensive differentiation of the latter. The new dataset provides clear evidence that the eastern FMC was affected by a long-lived magmatic episode characterized by coeval melting of both crustal and mantle sources. This feature is suggested here to result from a lithospheric-scale thermal anomaly, triggered by the removal of the lithospheric mantle root. The spatial

  11. Geochemical and isotopic constraints on the petrogenesis of the Puesto La Peña undersaturated potassic complex, Mendoza province, Argentina: Geodynamic implications

    NASA Astrophysics Data System (ADS)

    Zappettini, Eduardo O.; Villar, Luisa M.; Hernández, Laura B.; Santos, João O.

    2013-03-01

    Major and trace element and radiogenic and stable isotope data are reported for the Miocene Puesto La Peña undersaturated potassic complex, located in the Argentine Precordillera. The complex is composed of a pyroxenite core surrounded by a malignite-borolanite association, followed by radial and ring dikes composed of alkaline lamprophyres, tephrite to phonolite and intermediate varieties, porphyritic microledmorite, benmoreite, alkaline trachyte and a swarm of ultrabasic ouachitite dikes. Late trachytic to phonolitic volcanic necks and associated dikes crop out surrounding the malignitic-borolanitic massif. Major and trace element data are consistent with their derivation by partial melting from an enriched, probably lithospheric, metasomatized heterogeneous mantle involving spinel- and garnet-facies mantle sources. The trace element and isotope data indicate that all rock types are derived from a common parental magma and are thus cogenetic. Sr, Nd and Pb variations in the different studied lithologies are restricted, except for the evidence of Sr decoupling in the ouachitite samples. Their Sr-Nd isotope compositions follow the "mantle array" defined by oceanic basalts, within the OIB field, consistent with an intraplate depleted source. The genesis of the ouachitite is interpreted to be related to mixing between asthenospheric magma and melts from the lower lithosphere consisting of K-rich metasomatic layers. The Dupal like Pb isotopes signature suggests a mantle modification by introduction of continental crust material in the upper mantle; this is consistent with the Sr-Nd isotope data from the late silica-undersaturated felsic dikes and volcanic necks. Multistage mantle extraction would have occurred by the end of Neoproterozoic to lower Paleozoic times as indicated by the isotopic data. Partial melting was initiated by mantle upwelling decompression during lithosphere extension. Back-arc extensional conditions during the latest Early Miocene (19 Ma

  12. Pre-eruptive conditions of the Hideaway Park topaz rhyolite: Insights into metal source and evolution of magma parental to the Henderson porphyry molybdenum deposit, Colorado

    USGS Publications Warehouse

    Mercer, Celestine N.; Hofstra, Albert H.; Todorov, Todor I.; Roberge, Julie; Burgisser, Alain; Adams, David T.; Cosca, Michael A.

    2015-01-01

    partitioned. Given that the Henderson deposit contains anomalous abundances of not only Mo, but also W, Pb, Zn, Cu, Bi, Ag, and Mn, we suggest that these metals were sourced from similar fluids exsolved from unerupted portions of the same magmatic system. Trace element ratios imply that Mo was sourced deep, from either the lower crust or metasomatized mantle. The origin of sulfur remains unresolved; however, given the extremely low S solubility of rhyolite melts in the shallow crust we favor the possibility that another source of S might supplement or account for that present in the ore deposit, probably the comagmatic, mantle-derived lamprophyres that occur in minor quantities with the voluminous topaz rhyolites in the area. To account for the 437 Mt of MoS2 (∼1·0 × 106 t Mo) present in the Henderson ore deposit, a volume of ∼45 km3 of Hideaway Park rhyolite magma would have been necessary to supply the Mo (a cylindrical pluton measuring 3·1 km × 6·0 km) along with sparging of ∼6·8 × 105 t of S from ∼0·05 km3 of lamprophyre magma. Based on a weighted mean 40Ar/39Ar age of 27·58 ± 0·24 Ma, similar melt geochemistry, and characteristically F-rich biotite phenocrysts, we conclude that the Hideaway Park tuff was cogenetic with the intrusions at Red Mountain that formed the Henderson deposit.

  13. Petrology of the Rainy Lake area, Minnesota, USA-implications for petrotectonic setting of the archean southern Wabigoon subprovince of the Canadian Shield

    USGS Publications Warehouse

    Day, W.C.

    1990-01-01

    The Rainy Lake area in northern Minnesota and southwestern, Ontario is a Late Archean (2.7 Ga) granite-greenstone belt within the Wabigoon subprovince of the Canadian Shield. In Minnesota the rocks include mafic and felsic volcanic rocks, volcaniclastic, chemical sedimentary rocks, and graywacke that are intrucded by coeval gabbro, tonalite, and granodiorite. New data presented here focus on the geochemistry and petrology of the Minnesota part of the Rainy Lake area. Igneous rocks in the area are bimodal. The mafic rocks are made up of three distinct suites: (1) low-TiO2 tholeiite and gabbro that have slightly evolved Mg-numbers (63-49) and relatively flat rare-earth element (REE) patterns that range from 20-8 x chondrites (Ce/YbN=0.8-1.5); (2) high-TiO2 tholeiite with evolved Mg-numbers (46-29) and high total REE abundances that range from 70-40 x chondrites (Ce/YbN=1.8-3.3), and (3) calc-alkaline basaltic andesite and geochemically similar monzodiorite and lamprophyre with primitive Mg-numbers (79-63), enriched light rare-earth elements (LREE) and depleted heavy rare-earth elements (HREE). These three suites are not related by partial melting of a similar source or by fractional crystallization of a common parental magma; they resulted from melting of heterogeneous Archean mantle. The felsic rocks are made up of two distinct suites: (1)low-Al2O3 tholeiitic rhyolite, and (2) high-Al2O3 calc-alkaline dacite and rhyolite and consanguineous tonalite. The tholeiitic felsic rocks are high in Y, Zr, Nb, and total REE that are unfractionated and have pronounced negative Eu anomalies. The calcalkaline felsic rocks are depleted in Y, Zr, and Nb, and the REE that are highly fractionated with high LREE and depleted HREE, and display moderate negative Eu anomalies. Both suites of felsic rocks were generated by partial melting of crustal material. The most reasonable modern analog for the paleotectonic setting is an immature island arc. The bimodal volcanic rocks are

  14. Stratigraphy and structure of the western Kentucky fluorspar district

    USGS Publications Warehouse

    Trace, R.D.; Amos, D.H.

    1984-01-01

    Rivers and their major tributaries. Many mafic dikes and a few mafic sills are present. The mafic rocks are mostly altered mica peridotites or lamprophyres that are composed of carbonate minerals, serpentine, chlorite, and biotite and contain some hornblende, pyroxene, and olivine. Most of the dikes are in a north-north west-trending belt 6 to 8 mi wide and strike N. 20 0 -30 0 W. The dikes dip from 80 0 to 90 0 and are commonly 5 to 10 ft wide. Radioisotopic study indicates that the dikes are Early Permian in age. The district is just southeast of the intersection of the east-trending Rough Creek-Shawneetown and northeast-trending New Madrid fault systems. The district's principal structural features are a northwest-trending domal anticline, the Tolu Arch, and a series of steeply dipping to nearly vertical normal faults and fault zones that trend dominantly northeastward and divide the area into elongated northeast-trending grabens and horsts. Formation of these grabens and horsts was one of the major tectonic events in the district. Vertical displacement may be as much as 3,000 ft but commonly ranges from a few feet to a few hundred feet; no substantial horizontal movement is believed to have taken place. Many cross faults having only a few feet of displacement trend northwestward and are occupied at places by mafic dikes. Faulting was mostly post-Early Permian to pre-middle Cretaceous in age. Many theories have been advanced to explain the structural history of the district. A generally acceptable overall hypothesis that would account for all the structural complexities, however, is still lacking. Useful structural data, such as the structural differences between the grabens and the horsts, have been obtained, however, from the recently completed geologic mapping. Mapping also has more clearly shown the alinement of the Tolu Arch, the belt of dikes, and an unusually deep graben (the Griffith Bluff graben); this alinement suggests that possibl

  15. Petrology of the Rainy Lake area, Minnesota, USA-implications for petrotectonic setting of the archean southern Wabigoon subprovince of the Canadian Shield

    NASA Astrophysics Data System (ADS)

    Day, Warren C.

    1990-08-01

    The Rainy Lake area in northern Minnesota and southwestern, Ontario is a Late Archean (2.7 Ga) granite-greenstone belt within the Wabigoon subprovince of the Canadian Shield. In Minnesota the rocks include mafic and felsic volcanic rocks, volcaniclastic, chemical sedimentary rocks, and graywacke that are intrucded by coeval gabbro, tonalite, and granodiorite. New data presented here focus on the geochemistry and petrology of the Minnesota part of the Rainy Lake area. Igneous rocks in the area are bimodal. The mafic rocks are made up of three distinct suites: (1) low-TiO2 tholeiite and gabbro that have slightly evolved Mg-numbers (63 49) and relatively flat rare-earth element (REE) patterns that range from 20 8 x chondrites (Ce/YbN=0.8 1.5); (2) high-TiO2 tholeiite with evolved Mg-numbers (46 29) and high total REE abundances that range from 70 40 x chondrites (Ce/YbN=1.8 3.3), and (3) calc-alkaline basaltic andesite and geochemically similar monzodiorite and lamprophyre with primitive Mg-numbers (79 63), enriched light rare-earth elements (LREE) and depleted heavy rare-earth elements (HREE). These three suites are not related by partial melting of a similar source or by fractional crystallization of a common parental magma; they resulted from melting of heterogeneous Archean mantle. The felsic rocks are made up of two distinct suites: (1)low-Al2O3 tholeiitic rhyolite, and (2) high-Al2O3 calc-alkaline dacite and rhyolite and consanguineous tonalite. The tholeiitic felsic rocks are high in Y, Zr, Nb, and total REE that are unfractionated and have pronounced negative Eu anomalies. The calcalkaline felsic rocks are depleted in Y, Zr, and Nb, and the REE that are highly fractionated with high LREE and depleted HREE, and display moderate negative Eu anomalies. Both suites of felsic rocks were generated by partial melting of crustal material. The most reasonable modern analog for the paleotectonic setting is an immature island arc. The bimodal volcanic rocks are

  16. Unusual Cathodoluminescence in Diamonds: Evidence for Metamorphism or a Source Characteristic

    NASA Astrophysics Data System (ADS)

    Bruce, L. F.; Longo, M.; Kopylova, M.; Ryder, J.

    2009-05-01

    Cathodoluminescence (CL) is a useful means of diamond "fingerprinting". CL-active cratonic macrodiamonds usually cathodoluminesce blue or yellow, and always exhibit prominent wide CL emittance peaks at 430-450 nm and 480-490 nm. Exceptions to this norm are diamond suites recently discovered in the Archean rocks metamorphosed in the greenschist facies. These macrodiamonds cathodoluminesce red, orange and yellow, and invariably exhibit the most prominent CL peak at 520 nm. The diamond suites with the unusual CL are derived from two different locations within the Michipicoten Greenstone Belt (Southern Superior craton), near the town of Wawa (Ontario). One suite is extracted from the 2.68-2.74 Ga polymict volcanic breccias and lamprophyres and the other suite - from the 2.68 Ga sedimentary conglomerates grading into overlying sandstones of the Dore assemblage. The diamondiferous conglomerates are found in an area 8 km south of the breccias and 12 km northeast of Wawa. CL emittance of macrodiamonds (> 0.5 mm) extracted from the breccias consists of a broad band at 520 nm, a sharp peak at 575.5 nm, and several lines at 550-670 nm. The conglomerate macrodiamonds mostly show a dominant peak at 520 nm, whereas corresponding microdiamonds exhibit two peaks at about 576 and 600 nm. None of the diamonds show a maximum peak at 420 nm. Polycrystalline stones from conglomerates show distinct CL spectra and colours for all intergrown crystals in the same diamond. The relative abundances of the CL colors of the conglomerate diamonds are orange-red (46%), yellow (28%), orange-green (10%), green (6%), and non-uniform colors (10%). These colours are more diverse than mostly orange CL colours in the breccia diamonds; this results from a larger variety of positions and intensity of CL peaks in the conglomerate diamonds. We propose two models for explaining the presence of the 520 nm CL peak in the breccia and conglomerate diamonds in Wawa. The first model suggests metamorphism as the

  17. Cathodoluminescence of diamond as an indicator of its metamorphic history

    NASA Astrophysics Data System (ADS)

    Kopylova, Maya; Bruce, Loryn; Longo, Micaela; Ryder, John; Dobrzhinetskaya, Larissa

    2010-05-01

    Diamond displays a supreme resistance to chemical and mechanical weathering, ensuring its survival through complex and prolonged crustal processes, including metamorphism and exhumation. For these reasons, volcanic sources and secondary and tertiary collectors for detrital placer diamonds, like Ural or Bingara diamonds, may be difficult to determine. If metamorphic processes leave their marks on diamond, they can be used to reconstruct crustal geologic processes and ages of primary diamondiferous volcanics. Four diamond suites extracted from metamorphic rocks have been characterized using optical CL, infrared and CL spectroscopy, and photoluminescence at the liquid nitrogen temperature. The studied diamonds are from the ~2.7 Ga sedimentary conglomerate and lamprophyric breccia metamorphosed in the greenschist facies (Wawa, Northern Ontario, Canada) during the 2.67 Ga Kenoran orogeny, and from the ultra-high pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany) exhumated in the Paleozoic. Wawa diamonds (Type IaAB and Type II) displayed green, yellow, orange, and red CL colours controlled by the CL emittance at 520, 576 nm, and between 586 and 664 nm. The UHP terranes diamonds show much weaker CL; few luminescent stones display CL peaks at 395, 498, 528 nm and a broad band at 580-668 nm. In contrast, most common diamonds found in unmetamorphosed rocks, i.e. octahedrally grown Type IaAB stones, luminescence blue emitting light at ~415-440 nm and 480-490 nm. There is a noticeable difference between cathodoluminescence of these diamonds and diamonds in metamorphic rocks. The studied diamonds that experienced metamorphism show a shift of CL emission to longer wavelengths (above 520 nm) and to green, yellow and red CL colours. Photoluminescence has the high resolution necessary to assign luminescence to specific optical centers of diamond. Diamonds in metamorphic rocks contain H3 (pairs of substitutional nitrogen atoms separated by a vacancy) and NVo

  18. Natural radioactivity in stream sediments of Oltet River, Romania

    NASA Astrophysics Data System (ADS)

    Ion, Adriana

    2017-04-01

    The concentration of naturally occurring radionuclides (U-238, Th-232 and K-40) in stream sediments of the Oltet River was measured in order to establish the primary sources of radionuclides, the transport pathways and the geochemical factors favouring their mobilisation and concentration in the existing geological context. The Oltet River has a length of 185 Km and crosses the southern central part of the country, being the right tributary of the Olt River. The range in elevation of the watercourse varies between 1963 m in the springs area (Parîng Mountains) and 200 m at the confluence with the Olt River, whereas the relief of the Oltet Basin has a varied character, manifested by the presence of diverse forms of relief, starting with major mountainous heights and ending with low-lying plains regions. In cross section from North to South, the Olteț River cuts metamorphic rocks (schist, gneisses, quartzite, marble, mica-schist's), magmatic rocks (granite and granitoid massifs - intruded by veins of microgranite, aplite, pegmatite and lamprophyre) and limestone, followed by deposits composed of clays, marls, sands and gravels, that are characterized by the presence of lignite seams. 44 stream sediment samples were collected in summer of 2016 from sampling points distributed along the river with an equidistance of about 4 - 5 km. The activity concentrations of the U-238, Th-232 and K-40 were measured by gamma ray spectrometry using HPGe detector (ORTEC) with 26% relative efficiency in multilayer shielding. The reference materials used were IAEA - RGK-1 and IAEA - 314. Analysis was performed on the <2 mm fraction of sediment sample, each sample was counted for 24,000 s. U-238 specific activity in the stream sediments varies between 6.18 and 68.76 Bq/Kg and Th-232 specific activity from 8.12 to 89.28 Bq/Kg, whereas the K-40 specific activity in sediments ranges from 99.01 to 312.16 Bq/Kg. In the upper sector of the Oltet River, concentrations of U-238, Th-232 and K-40

  19. Dyke belt in North Western margin of Siberian platform

    NASA Astrophysics Data System (ADS)

    Ryabov, Victor

    2015-04-01

    The Early Triassic dyke swarm belt is strengthening at about 500 km (50-60 km width) along the northern margin of Siberian platform. Its locations is limited from the north by rift structure of the Yenisei-Khatanga trough, and from the south by Kystyktah-Ayan-Ambardah uprise. From west to east dyke belt is crossing Norilsk, Kamensky and Maimecha-Kotuiskaya province. In this direction the composition of dykes changing from basic rthrough alkali-basic to alkali-ultramafic varieties. The sickness of dykes varies from 0,5-10m up to 90 m and length - from 5-15 m to 140 km. The orientation of the bulk of dykes coincides with the direction of the major structural and tectonic lineaments of the region. Dykes are often refer to the fault planes. The composition of dykes may vary along the stretches. The density of hundreds of basaltic dykes and small intrusions in the dyke swarms is not permanent and sometimes essentially uneven. They form a compact dyke swarms of dykes, stocks and sub layering bodies veins. In dyke package on Huor-Uyallah river here are 20 subparallel dykes of different chemical composition at a distance of 2 km Lack of the evidence of the dykes crossing allows to assume their formation during the same magmatic cycle. Dykes cross cut through the entire incision of basaltic plateau. They did not created the flow effusions and refer to the final stage trap magmatism. Ar/Ar age of the youngest dykes in the province Kamenska 238-247 Ma. the age of lamproite dyke in Norilsk province is 235 Ma. Dykes are represented by dolerites trachydolerites, syenites, minettes, lamprophyres (camptonite, spessartite, vosgesite), avgitites, melanephelinite, alnoites, limburgites alkaline picrites, meimechites. Their content vary widely: SiO2 - 35,7-62,6; TiO2- 0,4-7,5; Al2O3- 4,4-17,5; Fe2O3- 4,6-20,6; MnO- 0,08-0,44; MgO- 0,8-31,5; CaO- 0,7-15,4; Na2O- 0,01-6,5; K2O 0,8-5,3 wt.%; P2O5 0,1-1,2 wt.%. The h Bolsheavamskaya volcanic basin in Kamensky province is most abundant in

  20. Along-Strike Tectonic Segmentation of the Mesozoic Central Orogenic Belt, China: Insights from the Eastern Qinling Magmatic Syntaxis

    NASA Astrophysics Data System (ADS)

    Ma, C.; Sun, Y.; Li, J.; Xu, W.; magmatism; mineralization

    2011-12-01

    Along-strike tectonic segmentation is an important feature of the active continental margin. However, the tectonic segmentation of collisional orogenic belts is yet not to be well constrained. The Triassic Central Orogenic belt in China extends nearly 5,000 km, and is a collisional belt between the North China and Yangtze cratons. Influenced by the subduction of the paleo-Pacific plate, and the lithospheric thinning of the North China craton, this Orogenic belt is superimposed on multi-stage magmatism and mineralization, showing a typical along-strike segmentation. This paper takes the Eastern Qinling magmatic syntaxis as an example, and attempts to understand the manifestation of the structural segmentation and its formation mechanism. The Eastern Qinling magmatic syntaxis can be divided into two parts bounded by a line extending from the Xiaoqinling - Xiong'ershan region in the southern North China craton to Ankang region in the southern Qinling zone(hereafter referred to Xiao-an line). Both sides of the line have distinct geological and geophysical characteristics. (1) Middle-Late Triassic intrusive rocks are widespread in the west of the Xiao-an line, and their rock types include adakitic and shoshonite-series granitoids, rapakivi granites and a small volume of lamprophyre dykes. Triassic igneous rocks are lack in the east of the Xiao-an line, but the late Jurassic (~153Ma) monzogranites and granodiorite, and early Cretaceous (130-108 Ma) alkali-feldspar granites and syenites are widely distributed in the east, probably in response to the subduction of the paleo-Pacific plate and the lithosphere thinning of the North China craton. (2) In the east of the Xiao-an line, the gold mineralization of quartz-veins and altered-rock took place in the late Mesozoic, while in the west, the carlin-like gold deposits formed in the early Mesozoic.In the east of the line there is late Mesozoic molybdenum ore belt, the largest molybdenum ore belt in China. However, in the west

  1. Geological, mineralogical and geochemical characteristics of the Radzimowice Au As Cu deposit from the Kaczawa Mountains (Western Sudetes, Poland): an example of the transition of porphyry and epithermal style

    NASA Astrophysics Data System (ADS)

    Mikulski, Stanislaw Z.

    2005-03-01

    The sheeted quartz sulfide veins of the Radzimowice Au As Cu deposit in the Kaczawa Mountains are related to Upper Carboniferous post-collisional potassic magmatism of the composite Zelezniak porphyry intrusion. Multiple intrusive activity ranges from early calc-alkaline to sub-alkaline and alkaline rocks and is followed by multiple hydrothermal events. Early crustally derived dacitic magma has low mg# (<63) and very low concentrations of mantle-compatible trace elements, high large-ion lithophile elements (LILE), moderate light rare-earth elements (LREE), and low high-field-strength elements (HFSE). Later phases of more alkaline rocks have higher mg# (60 70), and LILE, LREE, and HFSE characteristics that indicate mafic magma contributions in a felsic magma chamber. The last episode of the magmatic evolution is represented by lamprophyre dikes which pre-date ore mineralization and are spatially related to quartz sulfide carbonate veins. The dikes consist of kersantite and spessartite of calc-alkaline affinity with K2O/Na2O ratios of 1.1 1.9, mg# of 77 79, and high abundances of mantle-compatible trace elements such as Cr, Ni, and V. They have high LILE, low LREE, and low HFSE contents suggesting a subduction-related post-collisional arc-setting. The mineralization started with arsenopyrite that was strongly brecciated and overprinted by multiple quartz carbonate phases associated with base-metal sulfides and Au Ag Bi Te Pb±S minerals. The sulfur isotope composition of sulfides ranges from -1.1 to 2.8‰ δ34S and suggests a magmatic source. At least two generations of gold deposition are recognized: (1) early refractory, and (2) subsequent non-refractory gold mineralization of epithermal style. Co-rich arsenopyrite with refractory gold and pyrite are the most abundant minerals of the early stage of sulfide precipitation. Early arsenopyrite formed at 535 345°C along the arsenopyrite pyrrhotite loellingite buffer and late arsenopyrite crystallized below 370

  2. Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

    2013-08-01

    of the Mianlue Ocean between the South Qinling Belt and the South China Block. Voluminous late-stage (225-185 Ma) magmatism evolved from early I-type to later I-A-type granitoids associated with contemporaneous lamprophyres, representative of a transition from syn- to post-collisional setting in response to the collision between the North China and the South China blocks. Late Mesozoic (158-100 Ma) granitoids, located in the southern margin of the North China Block and the eastern part of the North Qinling Belt, are characterized by I-type, I- to A-type, and A-type granitoids that were emplaced in a post-orogenic or intraplate setting. The first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process. These suggest that the tectonic evolution of the Qinling Orogen is very complicated.

  3. Spinels from tuffites of the Bulkur anticline: comparative analysis of macro- and microcrysts

    NASA Astrophysics Data System (ADS)

    Biller, Anastasia; Oleinikov, Oleg; Babushkina, Svetlana

    2017-04-01

    The northeastern Siberian platform is famous for a unique association of placer diamonds including specific diamond varieties (V-VII, following the classification by L.Yu. Orlov (1973). Such diamonds have been found in none of the kimberlite pipes of Yakutia. The petrochemical nature of the primary source for these placer deposits and the conditions of their formation in the mantle are as yet poorly understood. Diamonds with a large amount of associate minerals such as garnets and chrome-spinels occur in the basal horizon of the volcanogenic-sedimentary rocks aged at 226-228 Ma (U-Pb zircon dating, Grakhanov, Smelov, 2011). This paper presents the results of studying spinel macrocrysts and microcrysts from the tuffites' groundmass. The analyses were performed on a JEOL JSM 64800 LV scanning electron microscope with an Oxford INCA Energy Dispersive Spectrometer at the Diamond and Precious Metals Geology Institute, SB RAS. Chemically, the microcrystal spinels are characterized by a wide range of their major components: 17.14-56.53 wt% Cr2O3, 3.57-24.96 wt% Al2O3, 0.82-11.32 wt% TiO2, and 1.74-13.31 wt% MgO.Comparison between the microcrystal spinels from the tuffites and those from the Yakutian Kimberlite Province (YaKP) showed that the bulk of the spinels belong to high-Cr and medium-Cr picrochromites that are also typical of the diamondiferous kimberlites in the region. On the diagrams after Mitchel and Bergman (1991) they tend to the lamprophyric rocks trend. Chemical composition of the macrocrystal spinels also exhibits large variations: 24.9-60.5 wt% Cr2O3, 4.32-8.99 wt% TiO2 (with rare grains containing less than 1 wt%), 1.39-36.06 wt% Al2O3, and 13.53-55.67 wt% Fe(total). There is no essential difference in composition between the macrocrystal spinels with inclusions and those without them. For comparison, we plotted on various diagrams the compositions of spinels from the highly diamondiferous Mir pipe. It was found that compositions of spinels from the

  4. Petrology of the Northern Anabar alkaline-ultramafic rocks (the Siberian Craton, Russia) and the role of metasomatized lithospheric mantle in their genesis

    NASA Astrophysics Data System (ADS)

    Kargin, Alexey; Golubeva, Yulia; Demonterova, Elena

    2017-04-01

    produced several carbonatite pipes and dykes. Their geochemical composition indicates the predominance of the carbonate component in the source region and a decrease of the thickness of the lithospheric mantle. This study was supported by Russian Science Foundation №16-17-10068. Tappe S., Foley S.F., Jenner G.A. et al. 2006. Genesis of Ultramafic Lamprophyres and Carbonatites at Aillik Bay, Labrador: a Consequence of Incipient Lithospheric Thinning beneath the North Atlantic Craton // J. Petrology. V. 47 (7). P. 1261-1315. Sun J., Liu C.Z., Tappe S. et al. 2014. Repeated kimberlite magmatism beneath Yakutia and its relationship to Siberian flood volcanism: Insights from in situ U-Pb and Sr-Nd perovskite isotope analysis // Earth Planet. Sci. Lett. V. 404. P. 283-295. Zaytsev A.I., Smelov A.P., 2010. Isotope Geochronology of Kimberlite Formation Rocks from Yakutian Province // Publication of the Institute of Diamonds Geology, Siberian branch of the Russian Academy of Sciences, Yakutsk (107 pp. (in Russian)).

  5. Petrology and mineralogy of the La Peña igneous complex, Mendoza, Argentina: An alkaline occurrence in the Miocene magmatism of the Southern Central Andes

    NASA Astrophysics Data System (ADS)

    Pagano, Diego Sebastián; Galliski, Miguel Ángel; Márquez-Zavalía, María Florencia; Colombo, Fernando

    2016-04-01

    The La Peña alkaline igneous complex (LPC) is located in the Precordillera (32°41‧34″ S - 68°59‧48″ W) of Mendoza province, Argentina, above the southern boundary of the present-day flat-slab segment. It is a 19 km2 and 5 km diameter subcircular massif emplaced during the Miocene (19 Ma) in the Silurian-Devonian Villavicencio Fm. The LPC is composed of several plutonic and subvolcanic intrusions represented by: a cumulate of clinopyroxenite intruded by mafic dikes and pegmatitic gabbroic dikes, isolated bodies of malignite, a central intrusive syenite that develops a wide magmatic breccia in the contact with clinopyroxenite, syenitic and trachytic porphyries, a system of radial and ring dikes of different compositions (trachyte, syenite, phonolite, alkaline lamprophyre, tephrite), and late mafic breccias. The main minerals that form the LPC, ordered according to their abundance, are: pyroxene (diopside, hedenbergite), calcium amphibole (pargasite, ferro-pargasite, potassic-ferro-pargasite, potassic-hastingsite, magnesio-hastingsite, hastingsite, potassic-ferro-ferri-sadanagaite), trioctahedral micas (annite-phlogopite series), plagioclase (bytownite to oligoclase), K-feldspar (sanidine and orthoclase), nepheline, sodalite, apatite group minerals (fluorapatite, hydroxylapatite), andradite, titanite, magnetite, spinel, ilmenite, and several Cu-Fe sulfides. Late hydrothermal minerals are represented by zeolites (scolecite, thomsonite-Ca), epidote, calcite and chlorite. The trace element patterns, coupled with published data on Sr-Nd-Pb isotopes, suggest that the primary magma of the LPC was generated in an initially depleted but later enriched lithospheric mantle formed mainly by a metasomatized spinel lherzolite, and that this magmatism has a subduction-related signature. The trace elements pattern of these alkaline rocks is similar to other Miocene calc-alkaline occurrences from the magmatic arc of the Southern Central Andes. Mineral and whole

  6. Vestiges of the Kerguelen Plume in alkalic mafic-ultramafic, carbonatitic complexes and flood basalts in NE India

    NASA Astrophysics Data System (ADS)

    Basu, A. R.; Ghatak, A.

    2011-12-01

    The Archean East Indian craton was affected by the Kerguelen plume at ~117 Ma causing flood-basalt eruptions at the cratonic margin giving rise to the Rajmahal-Bengal-Sylhet Traps. Rajmahal-age volcanics are wide-spread in and around the Bengal Basin, from the intrusive lamproites and lamprophyres in the west and Sikkim in the north, to the Sylhet basalts and alkalic-carbonatitic-ultramafic intrusives of the Shillong plateau and the Mikir hills in northeastern India. These volcano-plutonic complexes are exposed over an approximate area of 0.8 million km2 in and around the Bengal Basin. This study demonstrates that all these diverse volcanic rocks are caused by the Kerguelen plume activity. We provide isotopic and geochemical data of the Rajmahal Traps, and associated alkalic-carbonatitic-mafic-ultramafic complexes, and relate them to the Sylhet Traps in northeastern India, some contemporaneous Kerguelen Plateau basalts, and associated volcanics in the Southern Indian Ocean. Specifically, we report here Nd-Sr-Pb-isotopic and multiple trace element data of discrete lava flows from the Rajmahal Traps; mafic, alkalic, ultrabasic, and carbonatitic rocks from four alkalic complexes, and three ultramafic dikes from the Bokaro coal fields southwest of the Rajmahal Traps. In Nd-Sr-Pb isotopes, the Rajmahal Traps lavas of this study show remarkable similarity with previously reported Rajmahal Groups I and II basalts, Sylhet Traps, Bunbury basalts and lavas from the southern Kerguelen Plateau. The combined geochemical data and their correlation with the Rajmahal, Bunbury basalts, and some Kerguelen Plateau lavas in the Indian Ocean imply a relatively primitive Kerguelen plume source for the Rajmahal lavas similar to the Rajmahal Group I basalts. We estimate the average composition of this plume source to be: ɛNd(I)=+2, 87Sr/86Sr(I)=0.7045, with relatively flat rare earth element (REE) patterns. Rajmahal lavas similar to the Group II Rajmahal basalts have slightly enriched

  7. Two Distinct Sets of Magma Sources in Cretaceous Rocks From Magnet Cove, Prairie Creek, and Other Igneous Centers of the Arkansas Alkaline Province, USA

    NASA Astrophysics Data System (ADS)

    Duke, G. I.; Carlson, R. W.; Eby, G. N.

    2008-12-01

    Two distinct sets of magma sources from the Arkansas alkaline province (~106-89 Ma) are revealed by Sr-Nd-Pb isotopic compositions of olivine lamproites vs. other alkalic rock types, including carbonatite, ijolite, lamprophyres, tephrite, malignite, jacupirangite, phonolite, trachyte, and latite. Isotopic compositions of diamond-bearing olivine lamproites from Prairie Creek and Dare Mine Knob point to Proterozoic lithosphere as an important source, and previous Re-Os isotopic data indicate derivation from subcontinental mantle lithosphere. Both sources were probably involved in lamproite generation. Magnet Cove carbonatites and other alkalic magmas were likely derived from an asthenospheric source. Lamproite samples are isotopically quite different from other rock types in Sr-Nd-Pb isotopic space. Although three lamproite samples from Prairie Creek have a large range of SiO2 contents (40-60 wt %), initial values of ɛNd (-10 to -13), 206Pb/204Pb (16.61-16.81), 207Pb/204Pb (15.34-15.36), and 208Pb/204Pb (36.57-36.76) are low and similar. Only 87Sr/86Sr(i) displays a wide range in the Prairie Creek lamproites (0.70627-0.70829). A fourth lamproite from Dare Mine Knob has the most negative ɛNd(i) of -19. Lamproite isotope values show a significant crustal component and isotopically overlap subalkalic rhyolites from the Black Hills (SD), which assimilated Proterozoic crust. Six samples of carbonatite, ijolite, and jacupirangite from Magnet Cove and Potash Sulphur Springs exhibit the most depleted Sr-Nd isotopic signatures of all samples. For these rock types, 87Sr/86Sr(i) is 0.70352 - 0.70396, and ɛNd(i) is +3.8 - +4.3. Eight other rock types have a narrow range of ɛNd(i) (+1.9 - +3.7), but a wide range of 87Sr/86Sr(i) (0.70424 - 0.70629). These 14 samples comprise a fairly tight cluster of Pb isotopic values: 206Pb/204Pb (18.22-19.23), 207Pb/204Pb (15.54-15.62), and 208Pb/204Pb (38.38-38.94), suggesting very little crustal assimilation. They are most similar to EM-2

  8. Tracking traces of "hidden" UHPM rocks in deep Earth

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, Larissa; Green, Harry; Yang, Juing-Sui; Wirth, Richard

    2010-05-01

    mantle-derived grt-pyroxenite xenolith from Hawaii. Diamonds of 20-nm-size occur within the Si-rich glass together with Fe Cu, FeS, FeS2, ZnS, AgS phases. Yet, another diamond was discovered inside the OsIr inclusion from chromite pod from dunite-harzburgite section of the Luobasa ophiolite, Tibet. The polycrystalline coesite found in the same chromite ore suggests its replacement after stishovite. Other forms of UHP-HP carbon-bearing minerals such as moissonite (SiC) as well as metal nitrides [osbornite (TiN) and cubic boron nitride (cBN)] are discovered within UHPM rock-fragment incorporated in the mantle section of the Loubasa ophiolite of Tibet. The new finding demonstrates that some fragments of oceanic lithosphere also include UHP phases derived from deep within the upper mantle, but that their protolith probably had a near-surface origin according to carbon isotopes signatures of moissanite. Diamond in CPx from a Cenozoic lamprophyre dike was discovered in a forearc setting, Japan. A pressure of 5.5 GPa was calculated for the forearc diamond formation; it suggests that the diamond-bearing rocks rose to the forearc region from depths of about 160 km. This implies that mantle flow in convergent plate boundaries occurs on a larger scale than was previously recognized. We need a new understanding the interactions among magma generation and mantle convection and upwelling beneath oceanic islands, forearcs, and the mid-oceanic floor.

  9. New Geological Settings for Ultra-High Pressure Rocks

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L. F.; Wirth, R.; Yang, J.; Green, H. W.

    2009-05-01

    400 km. Diamond in CPx from a Cenozoic lamprophyre dike was discovered in a forearc setting, Japan [3]. A pressure of 5.5 GPa was calculated for the forearc diamond formation; it suggests that the diamond-bearing rocks rose to the forearc region from depths of about 160 km. This implies that mantle flow in convergent plate boundaries occurs on a larger scale than was previously recognized. We need a new understanding the interactions among magma generation and mantle convection beneath oceanic islands, forearcs, and the mid-oceanic floor. [1] Wirth & Rocholl (2003) EPSL 211, 357-369. [2] Frezotti & Peccerillo (2007) EPSL 262, 273-283. [3] Muzukami et al. (2008) Geology 36, 219-222.

  10. Age and isotopic marks of K-rich Manning Massif trachybasalts: an evidence for Lambert-Amery rift-system initiation (East Antarctica)

    NASA Astrophysics Data System (ADS)

    Leitchenkov, German; Belyatsky, Boris; Lepekhina, Elena; Antonov, Anton; Krymsky, Robert; Andronikov, Alex; Sergeev, Sergey

    2017-04-01

    source of contamination was an ancient material (> 2.4 Ga) and/or with high μ (26.5). The initial isotope characteristics of the studied basalts are the same for different individual flows: ɛNd=-3.4±0.4; 87Sr/86Sri=0.7061±0.0003, 206Pb/204Pbi=18.421±0.001; 207Pb/204Pbi=15.667±0.001; 208Pb/204Pbi=39.845±0.001; 187Os/186Osi = 0.2012±0.0004 and reflect minimal influence of host-rock contamination during or after melts crystallization and correspond to enriched mantle source signatures akin to plume-like. Thus the Manning Massif K-rich basalts correlate with the time of formation of the Late-Paleozoic coal-bearing sediments of the Lambert Glacier Rift and basic dykes of Jetty Peninsula [Mikhalsky, Sheraton, 1993] and can be interpreted to mark the earliest, Lower Carboniferous stage of the rifting. This event corresponds to the initial intracontinental stretching in the Eastern Gondwana wich was previously detected only in Perth Basin of western Australia. The research was done under financial support by RSF grant N 16-17-10139. References: Andronikov A.V., Foley S.F., Beliatsky B.V. 1998. Sm-Nd and Rb-Sr isotopic systematics of the East Antarctic Manning Massif alkaline trachybasalts and the development of the mantle beneath the Lambert-Amery rift. Mineral. Petrol. 63. 243-261. Mikhalsky E.V., Sheraton J.W. 1993. Association of dolerite and lamprophyre dykes, Jetty Peninsula (Prince Charles Mountains, East Antarctica). Antarctic Sciences. 5(3). 297-307.

  11. Seeking the mantle contribution for the formation of giant ore deposits: Contemporaneous alkaline lamproites and carbonatites in the Kalmakyr and Muruntau ore districts, Tienshan, Uzbekistan

    NASA Astrophysics Data System (ADS)

    Seltmann, Reimar; Choulet, Flavien

    2014-05-01

    The decline in discoveries of ore deposits contrasted by the rising demand for e-tech metals requires the global mining industry to continuously seek innovation in exploration. Unravelling the source of metals is among the crucial questions in exploration targeting and geologists have often had to recourse to indirect determinations based on the nature of the magma conveying the metals. The relative contributions of mantle and crust in metallogenic processes and the origin of the magmas from either shallow or deep mantle are not fully understood in the current models of ore genesis. To help to resolve this dilemma, research must establish the link between anorogenic (within-plate) and orogenic processes by using a holistic approach featuring crustal processes, mantle dynamics and crust-mantle interactions that may contribute to the magma fertilization. To achieve this, our study focuses on indicators for the involvement of deep-mantle intrusions (lamproites, lamprophyres, etc.), which have the potential to encapsulate pristine samples of the mantle (xenoliths) during magma ascent [1,2]. The Tienshan belt hosting many giant ore deposits is quite exemplary for understanding mantle-crust interactions and identifying the nature of mantle contribution to ore systems. Sr-Nd-Hf-Pb isotope systematics on granitoids [3] showed a variation of crustal to mixed signatures, indicating involvement of both older crustal sources and mantle-derived material, but the mantle source is not clearly assessed. As objects for our case study in Uzbekistan we choose the Kalmakyr Cu-Au porphyry deposit (~ 315 Ma; Chatkal-Kurama continental arc of Middle Tienshan) and the Muruntau orogenic Au deposit (~290 Ma, Turkestan-Alai / Kyzylkum accretionary complex of South Tienshan) to investigate the impact of associated alkaline magmas on the ore-bearing intrusions and mineralization. Field observations and geochronological data shed light on the spatial and temporal relationships between the

  12. Petrogenesis of Late Mesozoic granitoids and coeval mafic rocks from the Jiurui district in the Middle-Lower Yangtze metallogenic belt of Eastern China: Geochemical and Sr-Nd-Pb-Hf isotopic evidence

    NASA Astrophysics Data System (ADS)

    Xu, Yao-Ming; Jiang, Shao-Yong; Zhu, Zhi-Yong; Yang, Shui-Yuan; Zhou, Wei

    2014-03-01

    Large-scale Cu-Au mineralization is associated with the Late Mesozoic granitoids in the Jiurui district of the Middle-Lower Yangtze Mineralization Belt in Eastern China. To constrain the petrogenesis of these granitoids and coeval mafic rocks, a detailed geochemical and Sr-Nd-Pb-Hf isotopic study was performed. The Jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry. These granitoids are characterized by SiO2 and K2O contents of 58.8 wt.% to 68.6 wt.% and 1.9 wt.% to 5.7 wt.%, respectively. These granitoids show relatively high MgO contents (1.0 wt.% to 3.1 wt.%, average 2.1 wt.%) and high Mg# values (39 to 70, average 54). The Jiurui granitoids are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE), and compatible trace elements (Cr, Ni and V) but are relatively depleted in Nb, Ta, Y and Yb. These rocks show a negligible negative Eu anomaly (Eu/Eu* = 0.76-1.13, average 0.91) and nearly no negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7060 to 0.7092, and the ɛNd(t) values vary from - 5.4 to - 2.0. The granitoids show radiogenic Pb isotopic ratios with values of 206Pb/204Pb (17.93-18.21), 207Pb/204Pb (15.55-15.58), and 208Pb/204Pb (38.16-38.56) for the plagioclases. The zircon Hf isotopic compositions show ɛHf(t) values from - 11.8 to 2.4. The coeval mafic rocks consist of lamprophyre, diabase and fine-grained mafic dyke. These rocks are characterized by SiO2 contents ranging from 47.6 wt.% to 54.8 wt.%, with a negative Eu anomaly and a positive to negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7059 to 0.7071, and the ɛNd(t) values vary from - 3.8 to - 1.4. By comparing the geochemical and isotopic compositions of the Jiurui granitoids and the coeval mafic rocks, we conclude that the granitoids are similar to adakites that were likely related to the delamination processes, and the coeval mafic rocks may have originated directly from

  13. High-mg granitoids (sanukitoids) of the Baltic Shield geological setting, geochemical characteristics and implications for the origin of mantle-derived melts.

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, S.; Chekulaev, V.; Arestova, N.; Kovalenko, A.; Ivanikov, V.; Gooseva, N.; Rollinson, H.

    2003-04-01

    . We propose that the presence of fluid during melting is mainly responsible for the distinction of these trends: the presence of H2O during melting will promote silica oversaturation, whereas in the presence of CO2 melts will be undersaturated in silica [Mysen &Boettcher,1975; Shirie &Hanson,1984] and enriched in K2O [Lamb et al.,1986]. Some sanukitoid plutons are associated with mafic-ultrumafic rocks (Shaaravalampi, Panozero in Karelia, Roaring River Complex, Lac des Iles pluton, OttoStock in Canada [Sutcliffe et al.,1990; Stern&Hanson,1991]. In the Panozero pluton ultramafic rocks occur as net-veins within the felsic rocks, cumulate layers and as fragments within explosive breccias forming pipes and dykes. Mineral composition of the geodes which are composed by calk-spar and actinolith indicates on important role of CO2 in fluid composition. The parental melt of sanukitoids in many studies had composition of Qu-diorite (or monzodiorite) which was formed by partial melting of metasomatised mantle. However, the large volume of mafic-ultramafic units within the sanukitoid plutons and mafic lamprophyres push to assumption of more mafic composition of initial melt followed by differentiation in place of crystallization and /or in intermediate camerae. Mafic initial melt can be produced by incremental batch melting of the depleted mantle (Kushiro,1984) which was metasomatised by H2O-CO2 fluid enriched in some LIL and LRE elements.

  14. Nontraditional 'Deliverers' of UHP Rocks from Earth's Deep Interior to the Surface

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L.; Wirth, R.; Yang, J.; Green, H. W.

    2008-12-01

    chromites (Dobrzhinetskaya et al., 2007; Yamamoto et al., 2007), suggesting depth of their possible origin over 400 km. Solid-state transport within massive chromitite appears the only vehicle capable of transporting these phases and preserving their low-fO2 environment at the very high temperatures of oceanic spreading centers. Similar findings have now been made in other ophiolites. Microdiamond in clinopyroxene from a Cenozoic lamprophyre dike was discovered in a forearc setting on Shikoku island, Japan (Mizukami et al., 2008). Studies provide a pressure constraint of 5.5 GPa, which suggests that the diamond-bearing rocks rose to the forearc region from depths of ~160 km. This implies that mantle flow in convergent plate boundaries occurs on a larger scale than was previously recognized. The discoveries of UHP minerals in rocks located within 'forbidden' geological settings indicate that a new understanding is needed of the interactions between mantle convection and oceanic islands, forearcs, and oceanic spreading centers, as well as the depths of their magma formation.

  15. Alteration and arenization processes of granitic waste rock piles from former uranium Mines in Limousin, France.

    NASA Astrophysics Data System (ADS)

    Kanzari, Aisha; Boekhout, Flora; Gérard, Martine; Galoisy, Laurence; Phrommavanh, Vannapha; Descostes, Michael

    2014-05-01

    France counts approximately 200 former uranium mines, 50 of which are located in the Limousin region. Mining activities between 1945 and 2001 have generated close to 200 000 tons of waste rocks in the Limousin, with uranium levels corresponding essentially to the geological background. Waste rock piles from three former mining sites in this region, were selected according to their age, uranium content and petrological signature. These sites are part of the two-mica granitic complex of St Sylvestre massif, formed 324 million years ago. Granitic blocks that build up the waste rock piles have experienced different processes and intensities of alteration before their emplacement at the surface. These processes are responsible for the petrological heterogeneity throughout the waste rock pile at the time of construction. It is important to make a distinction within waste rocks between natural-cut-off waste rocks and economic-cut-off waste rocks. The latter represents a minority and is linked to stock prices. Natural-cut-off waste rocks contain about 20 ppm of uranium; economic-cut-off waste rocks contain about 100 to 300 ppm of uranium. The aims of this study are to 1) assess the neo-formation of U-bearing minerals hosted by these rocks, and 2) to characterize the weathering processes since the construction of the rock piles, including both mechanical and chemical processes. The structure of the waste rocks piles, from metric blocks to boulders of tens centimeters, induces an enhanced weathering rate, compared to a granitic massif. Mechanical fracturing and chemical leaching by rainwater (arenization) of the waste rocks produce a sandy-silty alteration phase. Silty-clay weathering aureoles of submetric-granitic blocks evolving into technic soil are mainly located below growing birch trees. Sampling on the rock piles was restricted to surface rocks. Samples collected consist mainly of granites, and rare lamprophyres with a high radiometric signal, thereby especially

  16. Experimental study of the P-T stability of phlogopite in metasomatised peridotite with varying H2O contents in the deep cratonic lithosphere

    NASA Astrophysics Data System (ADS)

    Yaxley, Greg; Rosenthal, Anja

    2014-05-01

    Phlogopite is an important metasomatic, hydrous, potassic phase in peridotite from on- and off-cratonic lithospheric mantle. It is significant in petrogenesis of exotic mantle-derived magmas such as micaceous kimberlites, ultramafic lamprophyres, kamafugites, lamproites and olivine basanites[1-6]. Along with other potassic hydrous agents (fluids/melts), phlogopite is a major repository for potassium, H2O and F in K-enriched peridotitic mantle down to ~200 km or more (≡6 GPa[7-10]). Although some recent studies delineated phlogopite stability in peridotite at a given bulk H2O content1[1,8-10,12], we lack experimental investigations close to the limits of phlogopite stability in a model mantle composition enriched in K (i.e. by metasomatic agents) with varying amounts of H2O over a pressure range of 4-6 GPa, i.e. from ≡120 to 200 km deep. Variations in the %H2O available however determine the shape and location of the solidus, and hence the onset of partial melting of a K-enriched mantle enriched[8,13]. Our experimental base composition (HPK2) is fertile peridotite + 0.5wt% K2O. Mixes HPK2-0 and HPK2-13 were prepared by blending powdered high purity oxides or carbonates of Si, Ti, Al, Mg, Cr, Ni, Mn, Ca, Na and K. Mg(OH)2 was included in HPK2-13 to produce a mix with 13wt% H2O. HPK2-0 is anhydrous. HPK2-0 and HPK2-13 were blended to create 3 additional mixes with identical compositions but varying H2O contents, nominally 0.2, 2 and 5wt% H2O. Experiments were run in Au, AuPd or graphite (in Pt) capsules at 4-6 GPa and 1050-1350°C. Run products were analysed by EDS on a SEM. Experiments crystallized assemblages of olivine + orthopyroxene ± clinopyroxene ± garnet ± rutile ± phlogopite. We define the temperature stability limit of phlogopite in potassic-peridotite between 1200 and 1250°C at 4 GPa and <1300°C at 5 GPa, consistent with interpolation of data from previous lower[1] and higher pressure[14] investigations. We also demonstrate the leaching effect of

  17. Mixing of fluids in hydrothermal ore-forming (Sn,W) systems: stable isotope and rare earth elements data

    NASA Astrophysics Data System (ADS)

    Sushchevskaya, T. M.; Popova, J. A.; Velivetskaya, T. A.; Ignatiev, A. V.; Matveeva, S. S.; Limantseva, O. A.

    2012-04-01

    Experimental and physico-chemical modeling data witness to important role of mixing of different type of fluids during tin and tungsten ore formation in hydrothermal systems. Mixing of magmatogeneous fluids, exsolved from granite melts, with exogenic, initially meteoric waters in hydrothermal ore-forming systems may change chemical composition of ore-forming fluid, causing cassiterite and/or wolframite precipitation (Heinrich, 1990; Sushchevskaya, Ryzhenko, 2002). We studied the process of genetically different fluids mixing for two economic Sn-W deposits, situated in the Iultin ore region (North-East of Russia, Chukotka Penninsula). The Iultin and Svetloe deposits are located in the apical parts of close situated leucogranite stocks, formed at the final stage of the Iultin complex emplacement. Both deposits are composed of a series of quartz veins among the flyschoid rocks (T 1-2), cut by the dikes (K1) of lamprophyre, granodiorite porphyre and alpite. The veins of the deposits are dominated by the productive quartz-wolframite-cassiterite-arsenopyrite-muscovite mineral assemblage. Topaz, beryl, fluorite, and albite occur sporadically. The later sulfide (loellingite-stannite-chalcopyrite) and quartz-fluorite-calcite assemblages show insignificant development. The preore quartz veinlets in host hornfels contain disseminated iron sulfides, chalcopyrite, muscovite. Isotopic (H, O, Ar) study of minerals, supplemented by oxygen isotope data of host granites and metamorphic rocks gave us possibility to conclude, that at the Iultin and the Svetloye deposits fluid mixing was fixed on the early stages of deposit formation and could be regarded as probable cause of metal (W, Sn) precipitation. During postore time the intensive involvement of isotopically light exogenic waters have changed: a) the initial character of oxygen isotope zonality; b) the initial hydrogen isotope composition of muscovites, up to meteoric calculated values for productive fluid (while the δ18O

  18. Andesite petrogenesis in a hybrid arc-rift setting: the Western Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Gómez-Tuena, A.; Vázquez-Duarte, A.; Díaz-Bravo, B.; Mori, L.

    2011-12-01

    The western sector of the Mexican subduction zone is characterized by the steep subduction of one of the youngest slabs on the planet (Rivera plate), and by the existence of a continental rift at ~230 km to the north from the trench (the so-called Tepic-Zacoalco rift, TZR), under which the subducted slab is either extremely deep or even absent (>250 km). The volcanic front is located at ~170 km from the trench and contains abundant potassic-alkaline lamprophyres with strong subduction (Ba/Ta= 1600-6000) and garnet signatures (Gd/Yb= 2-8), that have been recently interpreted as influenced by deep K2O-rich slab melts or supercritical fluids (Gómez-Tuena et al., 2011, GCA). In contrast, the most mafic rocks within the TZR are high-Nb, intraplate-like basalts that appear to derive from low extents of melting of a dryer (Ba/Ta= 800-60) and shallower (Gd/Yb= 2-2.5) mantle source. Even though a simple transition from an arc environment to an extensional tectonic regime is apparent when only the most primitive volcanic rocks are taken into account, the scenario becomes more complicated since at least five stratovolcanoes have been erupting typical arc andesites within the TZR over the last million years (San Juan, Sanganguey, Tepetiltic, Ceboruco and Tequila). Surprisingly, true calc-alkaline basalts that could be parental to andesites have not been found, indicating that andesites may have a direct mantle origin. Indeed, mayor and trace element compositions of volcanic rocks from western Mexico arrange in discrete suites with linear trends that are indicative of mixing, but they form sub-parallel arrays that do not converge to a common primitive basaltic melt, and often follow diverging trends in trace element-ratio plots. Melt-crust interactions likely occurred during magma ascent, since the volcanic rocks frequently include xenoliths and disequilibrium textures, but correlations among isotopic compositions and indexes of fractionation are not clearly observed in the

  19. Petrological and geochemical constraints on the origin of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc, NE Turkey

    NASA Astrophysics Data System (ADS)

    Aydin, Faruk; Oguz, Simge; Baser, Rasim; Uysal, Ibrahim; Sen, Cüneyt; Karsli, Orhan; Kandemir, Raif

    2015-04-01

    Geological, petrographical and geochemical data of mafic dykes intruding the composite Kaçkar Pluton from the eastern Blacksea magmatic arc (EBMA), NE Turkey, provide new insights into the nature of the metasomatizing agents in subcontinental lithospheric mantle beneath the region during the late Mesozoic-early Tertiary. Mafic dykes from the Çaykara and Hayrat (Trabzon), and also Ikizdere (Rize) areas from the northern margin of the EBMA consist of basalts, dolerites, lamprophyres (basic member) and lesser basaltic andesites and trachyandesites (evolved member). All dykes have no deformation and metamorphism. The outcrops of these dykes vary, with thickness from 0.2 to 10 m. and visible length from 3 to 20 m. In general, the mafic dykes dip steeply and cut directly across the Kaçkar Pluton, and show NW- and NE-trending, roughly parallel to the orientations of the EBMA main faults. Most of the dyke samples display subaphyric to porphyritic texture with phenocrysts of plagioclase (up to 10%), clinopyroxene (5-20%), amphibole (5-15%), and some contain variable amount of biotite (5-20%), lesser quartz (1-2%), and minor euhedral zircon, apatite and Fe-Ti oxides. The basic members of the mafic dykes have SiO2 of 44.1-51.9%, MgO of 4.5-12.1%, and TiO2 >mostly 0.8% (up to 2.3%) with K2O+Na2O of 1.3-6.6% with mostly subalkaline character. They are relatively high in mg-number (0.45-0.73) and transition metals (V=171-376 ppm, Co=22-45 ppm, Ni=3-148 ppm, and Sc=21-49 ppm). The evolved members of the dykes exhibit relatively higher SiO2 (57.1-60.2%) and K2O+Na2O (5.6-9.0%), and lower MgO (2.2-5.9%) and TiO2 (0.5-0.8%) contents than those from the basic dykes. Also, these samples have slightly low mg-number (0.41-0.65) and transition metals (V=99-172 ppm, Co=9-22 ppm, Ni=1-43 ppm, and Sc=9-20 ppm). In the Harker diagrams, all samples of the mafic dykes form a continuous array, and exhibit similar geochemical characteristics. In general, SiO2 inversely correlates with MgO, Fe

  20. Numerical simulation of ground-water flow through glacial deposits and crystalline bedrock in the Mirror Lake area, Grafton County, New Hampshire

    USGS Publications Warehouse

    Tiedeman, Claire R.; Goode, Daniel J.; Hsieh, P.A.

    1997-01-01

    This report documents the development of a computer model to simulate steady-state (long-term average) flow of ground water in the vicinity of Mirror Lake, which lies at the eastern end of the Hubbard Brook valley in central New Hampshire. The 10-km2 study area includes Mirror Lake, the three streams that flow into Mirror Lake, Leeman's Brook, Paradise Brook, and parts of Hubbard Brook and the Pemigewasset River. The topography of the area is characterized by steep hillsides and relatively flat valleys. Major hydrogeologic units include glacial deposits, composed of till containing pockets of sand and gravel, and fractured crystalline bedrock, composed of schist intruded by granite, pegmatite, and lamprophyre. Ground water occurs in both the glacial deposits and bedrock. Precipitation and snowmelt infiltrate to the water table on the hillsides, flow downslope through the saturated glacial deposits and fractured bedrock, and discharge to streams and to Mirror Lake. The model domain includes the glacial deposits, the uppermost 150m of bedrock, Mirror Lake, the layer of organic sediments on the lake bottom, and streams and rivers within the study area. A streamflow routing package was included in the model to simulate baseflow in streams and interaction between streams and ground water. Recharge from precipitation is assumed to be areally uniform, and riparian evapotranspiration along stream banks is assumed negligible. The spatial distribution of hydraulic conductivity is represented by dividing the model domain into several zones, each having uniform hydraulic properties. Local variations in recharge and hydraulic conductivities are ignored; therefore, the simulation results characterize the general ground-water system, not local details of ground-water movement. The model was calibrated using a nonlinear regression method to match hydraulic heads measured in piezometers and wells, and baseflow in three inlet streams to Mirror Lake. Model calibration indicates that

  1. The andesite aqueduct: perspectives on the evolution of intermediate magmatism in west-central (105-99°W) Mexico

    NASA Astrophysics Data System (ADS)

    Carmichael, Ian S.

    2002-09-01

    Intermediate calc-alkaline magma (52-65% SiO2) in western-central Mexico is the focus of this paper, and the typically porphyritic andesites (57-65% SiO2) form large central volcanoes, whereas basaltic andesites (52-57% SiO2) are less porphyritic, and they are found as cones and flows but are absent from central volcanoes. Several studies of experimental phase equilibria on these lavas relate water concentration to the phenocryst assemblages and to the degree of crystallinity, so that the abundance, composition and variety of phenocrysts can be used to constrain the amount of water dissolved in the magmas. Thus, the plagioclase-rich andesites of Volcan Colima, Mexico, become so as a result of decompressional crystallisation at ~950 °C (the pyroxene phenocryst temperature), and lose their dissolved water (2.5 to 4.5 wt% H2O) which is inversely proportional to the modal abundance of plagioclase. The feeding magma to V. Colima, North America's most productive central volcano, is represented by hornblende lamprophyre, a lava type without plagioclase phenocrysts which requires at least 6 wt% water to reproduce the phenocryst assemblage. Thus, degassing of the V. Colima magmas, and of those of the other central volcanoes in the western-central Mexican volcanic belt, contributes essentially all their dissolved water to the conduit or to the atmosphere. The source of this magmatic water is related to the source of the intermediate magmas. For some this must lie in the mantle, as the incorporation of hornblende-lherzolite nodules in a hydrous andesite with hornblende phenocrysts could only have occurred while ascending through the mantle. Consistent with a mantle source is the composition of the olivine phenocrysts in Mexican lavas with 10 to 5% MgO, which is in the mantle range of Fo88-92. Accordingly, basaltic andesites and andesites with >5% MgO are candidates for a mantle source. The equilibration of intermediate magmas with the mantle, as illustrated by the

  2. Mineralogy and petrology of leucite ankaratrites with affinities to kamafugites and carbonatites from the Kayıköy area, Isparta, SW Anatolia, Turkey: Implications for the influences of carbonatite metasomatism into the parental mantle sources of silica-undersaturated potassic magmas

    NASA Astrophysics Data System (ADS)

    Caran, Şemsettin

    2016-07-01

    /Eu, elevated CaO/Al2O3 and (La/Yb)N ratios], (ii) consistency of parental magma compositions with experimental melt compositions for carbonated peridotites, and (iii) geochemical and isotopic affinities to kamafugites and carbonatites, it is inferred that the carbonatitic melts infiltrated the mantle sources of Kayıköy leucite ankaratritic magma, and induced the depletion of its SiO2 contents. Carbonate-bearing phonolitic parental melts formed by mixing of both silicate and carbonate-asthenospheric melts from convecting mantle, react with wall-rock peridotite to form diopside + phlogopite + olivine + apatite metasomatic veins as wehrlitic metasomes. Partial melting of such newly generated wehrlitic metasomes in the subcontinental lithospheric mantle resulted in the parental melts of Kayıköy leucite ankaratrites. Results also imply that the nature and composition of asthenosphere-derived silicate melts (basanitic, phonolitic or tephriphonolitic in composition) and percentage of mixed carbonatitic melts lead to the formation of discrete mantle metasomes within the Inner Isparta Angle lithospheric mantle. These metasomes are conducive to the generation of coeval potassic magmas with contrasting geochemical signatures (e.g., lamproitic, lamprophyric, kamafugitic) in a single tectonic setting. Table 2 Representative chemical compositions (wt.%) of olivines in Kayıköy leucite-ankaratrites. Table 3 Representative chemical compositions (wt.%) of Cr-spinels in olivine from Kayıköyleucite-ankaratrites. Table 4 Representative chemical compositions (wt.%) of clinopyroxenes from Kayıköy leucite-ankaratrites. Table 5 Representative chemical compositions (wt.%) of phlogopites from Kayıköy leucite-ankaratrites. Table 6 Representative chemical compositions (wt.%) of leucites in Kayıköy leucite-ankaratrites. Table 7 Representative chemical compositions (wt.%) of nephelines in Kayıköy leucite-ankaratrites. Table 8 Representative chemical compositions (wt.%) of haüynes in Kay

  3. Geology and ore deposits of the Pioche district, Nevada

    USGS Publications Warehouse

    Westgate, L.G.; Knopf, Adolph

    1932-01-01

    which was discovered accidentally during the prospecting of the fissure veins. The ore deposits of the district comprise three groups (1) silver-bearing fissure veins in quartzite; (2) silver-bearing mineralized granite porphyry; (3) replacement deposits in limestone and dolomite. All of them appear to have been formed at about the same time, in the epoch of mineralization that occurred shortly after the intrusion of the granitic rocks and their allied dikes of granite porphyry and lamprophyre. The entire present output of the district is coming from the replacement deposits in limestone and dolomite, but exploratory work is still in progress on the fissure veins and mineralized porphyry. The replacement deposits include both replacement fissure veins and stratiform ("bedded") replacement deposits. The replacement fissure veins dip steeply and cut across the bedding of the carbonate rocks in which they are inclosed. They are thoroughly oxidized, as deep at least as 1,100 feet, for on none of them have the mine workings penetrated to water level, and they are highly manganiferous and limonitic and low in silica. At-certain horizons stratiform replacement deposits extend out as lateral branches from the fissure veins. Deposits of this kind occur mainly in the Mendha limestone, Highland Peak limestone, and Lyndon limestone. The stratigraphic range is therefore at least 5,500 feet, and as some of the fissure veins extend down through the underlying Pioche shale the indicated range may exceed 6,500 feet. The most notable representatives of the replacement fissure veins are at the Bristol mine, where they yield silver-bearing copper-leadzinc ores. So far unique among the ore bodies of the district is the pipe of wad and pyrolusite ore at the Jackrabbit mine, the periphery of the pipe consisting of a girdle of extraordinarily coarse white calcite spar produced by the recrystallization of the surrounding limestones. The stratiform replacement deposits that are attracting most

  4. Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds

    NASA Astrophysics Data System (ADS)

    Pearson, D. G.; Canil, D.; Shirey, S. B.

    2003-12-01

    samples of mantle available beneath many areas. Because they are erupted rapidly, they freeze in the mineralogical and chemical signatures of their depth of origin, in contrast to massifs which tend to re-equilibrate extensively during emplacement into the crust. In addition, many xenolith suites, particularly those erupted by kimberlites, provide samples from a considerably greater depth range than massifs. Over 3,500 mantle xenolith localities are currently known. The location and nature of many of these occurrences are summarized by Nixon (1987). A historical perspective on their study is given by Nixon (1987) and Menzies (1990a). Mantle xenoliths from any tectonic setting are most commonly described from three main igneous/pyroclastic magma types (where no genetic relationships are implied):(i) Alkalic basalts sensu-lato (commonly comprising alkali basalt-basanites and more evolved derivatives), nephelinites and melilitites.(ii) Lamprophyres and related magmas (e.g., minettes, monchiquites, and alnoites) and lamproites.(iii) The kimberlite series (Group I and Group II or orangeites; Mitchell, 1995).Although mantle xenoliths most commonly occur in primitive members of the above alkaline rocks, rare occurrences have been noted in more evolved magmas such as phonolites and trachytes (e.g., Irving and Price, 1981).To simplify matters and to circumvent the petrographic complexities of alkaline volcanic rocks in general, we will use the term "alkalic and potassic mafic magmas" to include alkalic basalts, nephelinites, melilitites, and lamprophyres. Occurrence of xenoliths in such magmas can be compared to those occurring in kimberlites and related rocks. As a general rule, the spectrum of mantle xenoliths at a given location varies with host rock type. In particular, alkalic and potassic mafic magmas tend to erupt peridotites belonging predominantly to the spinel-facies, whereas kimberlites erupt both spinel and garnet-facies peridotites (Nixon, 1987; Harte and Hawkesworth