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Sample records for lamprophyres

  1. Mesozoic lamprophyres of Gorny and Mongolian Altay

    NASA Astrophysics Data System (ADS)

    Vasyukova, Elena

    2015-04-01

    The Chuya complex consists of more then 400 early Mesozoic lamprophyre dikes that occur in the vast territory in the structures of the Gorny and Mongolian Altay. Based on the irregular distribution of the dikes, various researchers have distinguished from 3 to 6 separate dike swarms or areas. Each of them is spatially connected with a specific simultaneous ore deposit. For example, in the Aktash area, there are the Aktash, Chagan-Uzun and other Sb-Hg deposits, in the territory of the South-Chuya area there are the Kalguta Mo-W and Chagan-Burgasy Ag-Pb deposits and within the Yustyd area there are the Askhatin-Gol Ni-Co-As deposit, Asgat, Ozernoe and Tolbonour Ag-Sb deposits. But the genetic link between the magmatic rocks and close in time and space ore deposits has not yet been proven. In this work samples of lamprophyre dikes from the largest areas (Yustyd and South Chuya) were studied. The dikes are extraordinarily similar in mineralogical and chemical aspects. The greatest differences are in the isotopic characteristics of the rocks. Lamprophyres and syenites of the South-Chuya area have negative eNd (~-4) and an elevated 87Sr/86Sr (>0.711) ratio whereas lamprophyres of the Yustyd area are close to BSE (eNd~0, 87Sr/86Sr=0.705-0.707)/ Using data on the composition of rock-forming minerals, study of chemical characteristics and composition of lamprophyre fluid inclusions, we propose different sources with similar geochemical characteristics and varying degrees of metasomatic mantle material provoked different isotopic composition. The resulting liquid rich in carbonates and composite fluids in conjunction with low degrees of melting generates approximately petrochemical and mineralogical similar compositions newly formed rocks.

  2. Geochemical fingerprints of Late Triassic calc-alkaline lamprophyres from the Eastern Pontides, NE Turkey: A key to understanding lamprophyre formation in a subduction-related environment

    NASA Astrophysics Data System (ADS)

    Karsli, Orhan; Dokuz, Abdurrahman; Kaliwoda, Melanie; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Fehr, Karl-Thomas

    2014-05-01

    The Eastern Pontides in NE Turkey is one of the major orogenic belts in Anatolia. In this paper, we report our new 40Ar/39Ar dating, mineral chemistry, major and trace elements and Sr-Nd-Pb isotopic analyses of the lamprophyre intrusions in this region. The lamprophyres are widely scattered and intrude Late Carboniferous granitoid rocks. The lamprophyres exhibit fine-grained textures and are mineralogically uniform. Hornblende 40Ar/39Ar dating yielded a plateau age of 216.01 ± 10.64 Ma. Based on their geochemistry, mineral compositions and paragenesis, the lamprophyres are classified as calc-alkaline lamprophyres in general and spessartites in particular, which are rich in large ion lithophile elements (e.g., Rb, Ba, K) but depleted in Nb and Ti. Our samples exhibit moderate fractionation in LREE patterns approximately 100 times that of chondrite but HREE abundances less than 10 times that of chondrite. These calc-alkaline lamprophyres display a range of ISr (216 Ma) values from 0.70619 to 0.71291 and ɛNd (216 Ma) values from - 1.4 to 4.1, with TDM = 1.11 to 2.20 Ga. Their Pb isotopic ratios indicate an enriched mantle source. The enrichment process is related to metasomatism of a subcontinental lithospheric mantle source, which is caused by a large quantity of H2O-rich fluids, rather than sediments released from oceanic crust at depth during the closure of the Paleotethys Ocean in Triassic times. All of the geochemical data and the trace element modeling suggest that the primary magma of the calc-alkaline to high-K calc-alkaline spessartites was generated at depth by a low degree of partial melting (~ 1-10%) of a previously enriched lithospheric mantle wedge consisting of phlogopite-bearing spinel peridotite. The ascendance of a hot asthenosphere triggered by extensional events caused partial melting of mantle material. The rising melts were accompanied by fractional crystallization and crustal contamination en route to the surface. All of the geochemical

  3. Origin of sapphires from a lamprophyre dike at Yogo Gulch, Montana, USA: Clues from their melt inclusions

    NASA Astrophysics Data System (ADS)

    Palke, Aaron C.; Renfro, Nathan D.; Berg, Richard B.

    2016-09-01

    Gem corundum (sapphire) has been mined from an ultramafic lamprophyre dike at Yogo Gulch in central Montana for over 100 years. The sapphires bear signs of corrosion showing that they were not in equilibrium with the lamprophyre that transported them; however, their genesis is poorly understood. We report here the observation of minute glassy melt inclusions in Yogo sapphires. These inclusions are Na- and Ca-rich, Fe-, Mg-, and K-poor silicate glasses with compositions unlike that of the host lamprophyre. Larger, recrystallized melt inclusions contain analcime and calcite drawing a striking resemblance to leucocratic ocelli in the lamprophyre. We suggest here that sapphires formed through partial melting of Al-rich rocks, likely as the lamprophyre pooled at the base of the continental crust. This idea is corroborated by MELTS calculations on a kyanite-eclogite protolith which was presumably derived from a troctolite precursor. These calculations suggest that corundum can form through peritectic melting of kyanite. Linking the melt inclusions petrologically to the lamprophyre represents a significant advancement in our understanding of sapphire genesis and sheds light on how mantle-derived magmas may interact with the continental crust on their ascent to the surface.

  4. Isotope and trace element geochemistry of lamprophyres and syenites from different areas of South-Chuya complex, SE Altai.

    NASA Astrophysics Data System (ADS)

    Vasyukova, Elena

    2016-04-01

    Major and trace elements and radiogenic isotope data are reported for lamprophyres and syenites of South-Chuya complex associated with ore districts in South East of Gornyi Altai, Russia. Dikes of lamprophyres form big area, elongated from north-west to south-east. Within the area of complex dikes distribute irregularly accompanied the fault zones. Lamprophyres of three largest areas, named Aktash, South Chuya and Yustyd were characterized in terms of geology, petro- and geochemistry, isotopic composition. Some of the lamprophyres judging by the high mg'>60 reveal mantle signatures. They reveal round TRE patterns typical of the primitive low degree partial melts but with the negative Nb- Ta anomalies. The others with the lower mg' suggest their differentiation and contamination in crust material. They reveal slightly lower level of TRE and lower troughs of all HFSE. All dikes had intruded in the period of 250-235 Ma, have similar mineralogical, petro- and geochemistry characteristics which were the reasons for unite all of them in one complex. On the most of geochemistry diagrams dikes from 3 areas form their own, but intersected clusters. But on the isotopic diagrams (Sm/Nd and Rb/Sr systems) they show the principle dissimilarity between dikes from various areas. Yustyd lamprophyres initial isotopic characteristics are close to the BSE. The south-chuya rocks isotopic compositions are more enriched by 87Sr/86Sr and have negative ɛNd (-2.84..-4.05). Contamination by the lower crust material suggested at the early stage during the formation of the lamprophyres. Bu the Yustyd lamprophyres were contaminated also during the ascend by the upper crust. Two competitive hypotheses n the isotopic composition are dicussed: 1) different sources or 2) different proportions between the material from the same sources, which ensemble generate the parental magma for the rocks.

  5. Lamprophyre dike intrusion and the age of the Alpine fault, New Zealand

    SciTech Connect

    Cooper, A.F.; Barreiro, B.A.; Kimbrough, D.L.; Mattinson, J.M.

    1987-10-01

    The orientations of intrusive rocks from a carbonatitic lamprophyre dike swarm and the history of emplacement relative to country-rock schist structures are compatible with intrusion into tension fractures and Riedel shears formed during initiation of the dextral wrench system of the Alpine fault. New U-Pb and Rb-Sr dates indicate a late Oligocene-early Miocene time of intrusion which, in turn, suggests a mid-Tertiary history for propagation of the Alpine fault plate boundary through South Island, New Zealand.

  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. 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

  9. Geochemistry of lamprophyres at the Daping gold deposit, Yunnan Province, China: Constraints on the timing of gold mineralization and evidence for mantle convection in the eastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Chen, Yaohuang; Yao, Shuzhen; Pan, Yuanming

    2014-10-01

    Cenozoic lamprophyre dykes occur widely along the Ailao-Shan-Red-River (ASRR) shear zone related to the Indian-Eurasian collision. Two generations of lamprophyres have been found at the Daping gold deposit in the southern part of the ASRR shear zone and have been investigated by using phlogopite 40Ar/39Ar dating and whole-rock major and trace element as well as Sr and Nd isotope geochemical analyses. The 40Ar/39Ar plateau ages of phlogopite from the two generations of lamprophyres bracket the emplacement of auriferous quartz veins in the Daping deposit between 36.8 ± 0.2 Ma and 29.6 ± 0.2 Ma, consistent with the timing of gold mineralization in other parts of the ASRR shear zone. Geochemical data suggest that these lamprophyres most likely originated from a subduction-modified mantle source consisting of phlogopite-bearing spinel lherzolite, which underwent partial melting with contributions from crust materials. In particular, the second generation lamprophyres are characterized by more primitive geochemical features than the first, suggesting that secular source evolution probably resulted from post-collisional slab break-off mantle convection and remelting from ascending asthenosphere after subducted lithosphere break-off. Widespread and episodic occurrences of lamprophyres and other potassic volcanism in the eastern Tibetan Plateau were probably related to the onset of transtensional tectonics along the ASRR shear zone during Oligocene. A genetic model involving transtensional tectonics has been proposed for lamprophyres and gold mineralization in the ASRR shear zone.

  10. Unusual carbonate-rich dikes and lamprophyres in Porcupine Dome, east-central Montana

    SciTech Connect

    Doden, A.G.; Gold, D.P. . Dept. of Geosciences)

    1992-01-01

    Isolated carbonate dikes and lamprophyric plugs are exposed in Porcupine dome, a Laramide structure in east-central Montana. En echelon sets of carbonate dikes strike N70E, consistent with regional lineaments and local normal faults. Individual dikes are steeply dipping, only 30--70 cm in width, and up to 1 km in length. These dikes exhibit unequivocal magmatic characteristics, including chilled margins, flow-aligned micas, multiple intrusive stages, country rock xenoliths, and local small blows'' containing well-rounded carbonate autoliths. Spatially associated with the dikes are small plugs of olivine-phlogopite-garnet-carbonate-bearing silicate rocks and a diatreme of bedded tuffs with xenoliths of country rocks. The dikes consistent primarily of calcite and dolomite, phlogopite, and opaque oxides. Although the dikes are relatively homogeneous mineralogically along strike, some chemical variations are apparent in the vicinity of the plugs/diatreme. Phlogopites and carbonates, common to both dikes and plugs, may provide a genetic link between these spatially associated intrusions. These unusual associations of dikes, plugs and diatremes are not restricted to Porcupine dome, but extend at least as far as the Grassrange - Winnett area, 100 km to the NW. The regional distribution of these small carbonatite bodies suggests a different magmatic process from typical carbonatites and alkaline complexes. The closest analogy is the carbonate dikes in the Premier Diamond Mine, South Africa.

  11. 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.

  12. Petrology and geodynamical interpretation of mantle xenoliths from Late Cretaceous lamprophyres, Villány Mts (S Hungary)

    NASA Astrophysics Data System (ADS)

    Nédli, Zsuzsanna; M. Tóth, Tivadar; Downes, Hilary; Császár, Géza; Beard, Andrew; Szabó, Csaba

    2010-06-01

    A Late Cretaceous lamprophyre dyke in the Villány Mts (S Hungary), situated in the Tisza unit, contains abundant spinel lherzolite xenoliths with porphyroclastic textures. Mineral chemistry suggests a relatively fertile mantle, which experienced only 5-7% melt extraction. Differences in porphyroclast and neoblast chemistry and thermobarometric calculations suggest that the mantle section represented by the xenoliths experienced recrystallization at lower PT as it was transported to shallow mantle depths close to the plagioclase stability field, followed by later relaxation. Based on volcanological and sedimentological constraints from the Villány Mts and the neighboring Mecsek Mts, we suggest that the uprise of the subcontinental mantle material was related to a Cretaceous rifting event and lithospheric deformation of the southwestern part of the Tisza unit. Mantle upwelling and formation of lamprophyre melts can be related to generation or reactivation of deep fractures of the lithosphere, during a period of lithospheric extension between the major nappe emplacements (Albian-Cenomanian and Paleocene) of the region.

  13. Geochemistry and radiogenic isotope characteristics of xenoliths in Archean diamondiferous lamprophyres: Implications for the Superior Province cratonic keel

    NASA Astrophysics Data System (ADS)

    Wyman, D. A.; Hollings, P.; Conceição, R. V.

    2015-09-01

    Xenoliths retrieved from lamprophyric hosts in the Michipicoten belt fall into four groups defined by Al-Mg contents but do not include mantle peridotite. Based on immobile trace element abundances, the xenoliths are derived from magmas associated with the main phase of arc volcanism between 2.75 and 2.70 Ga or are co-genetic with the orogenic shoshonite suite. Trace elements distinguish two styles of metasomatism characterized either by LILE enrichment or both LILE and Zr-Hf (± Nb-Ta). The first is likely associated with a hydrous fluid while the second is related to melts that permeated underplated shoshonitic mafic magmas and cumulates or the older sub-arc mantle. The Sm-Nd isotopic compositions of the xenoliths indicate that an aged, highly depleted, source was tapped during the orogenic event. The formation depths of the lamprophyric magmas, and the xenoliths they contain, contrast with the calculated depths to the base of the depleted lithosphere based on xenoliths retrieved from post-Archean kimberlites. The differences imply a late docking of the ~ 150-160 km deep Archean keel beneath the Abitibi-Wawa terrane following the emplacement of major orogenic gold deposits.

  14. Episodic magmatism at 105 Ma in the Kinki district, SW Japan: Petrogenesis of Nb-rich lamprophyres and adakites, and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Imaoka, T.; Nakashima, K.; Kamei, A.; Itaya, T.; Ohira, T.; Nagashima, M.; Kono, N.; Kiji, M.

    2014-01-01

    Cretaceous episodic magmatism produced Nb-rich lamprophyres and adakitic granitoids in the Kinki district of SW Japan. K-Ar dating of minerals from the lamprophyres, adakites, and hornblende peridotite xenoliths yielded ages of 109-99 Ma, indicating a short-lived episodic magmatism. The lamprophyres generally display primitive high-Mg basaltic to basaltic andesite compositions with high Mg# and high Cr and Ni contents that preclude substantial differentiation. Some high-Nb basalt (HNB) and Nb-enriched basalt (NEB) compositions also occur. The lamprophyres have high large-ion lithophile element (LILE) and high field-strength element (HFSE) contents and variable (La/Yb)n ratios, and can be divided into high-(La/Yb)n (12.5-22.1) and low-(La/Yb)n (3.6-6.1) groups. The former contains nepheline-normative rocks with positive initial ɛNd(T) values, whereas the latter contains hypersthene-normative subalkaline rocks with negative initial ɛNd(T) values. The adakitic granitoids have relatively high TiO2, Nb, and Ta contents compared to more typical high-silica adakites elsewhere, indicating that they were produced by high temperatures (ca. 920 to 970 °C) during slab melting.

  15. Svecofennian post-collisional shoshonitic lamprophyres at the margin of the Karelia Craton: Implications for mantle metasomatism

    NASA Astrophysics Data System (ADS)

    Woodard, Jeremy; Kietäväinen, Riikka; Eklund, Olav

    2014-09-01

    Petrographic, geochemical, and geochronological data from shoshonitic lamprophyres from the North Savo region, eastern Finland, and the NW Ladoga region, northwest Russia are presented. The two areas are found ~ 250 km apart along a roughly 450 km long palaeosuture between the Archaean Karelia Craton and the Proterozoic Svecofennian Domain. Two of the samples from North Savo are kersantites, while the remaining ten samples (from both North Savo and NW Ladoga) are minettes. Two morphologically different populations of zircon were identified from these lamprophyres and analysed by secondary ionisation mass spectrometry. Concordant analyses of inherited crustal zircon xenocrysts gave both Archaean and Proterozoic 207Pb/206Pb ages. In the NW Ladoga region, these are the first reported Archaean ages from south of the Meijeri Thrust zone. Large, homogeneous and relatively U- and Th-depleted zircons are interpreted as xenocrysts from the metasomatised mantle. U-(Th)-Pb analyses of these zircons resulted in ages of 1790 ± 3 Ma, 1784 ± 4 Ma, 1785 ± 5 Ma and 1781 ± 20 Ma, representative of the timing of dyke emplacement. Geochemical characteristics of the dykes indicate that the source mantle experienced at least two types of metasomatic enrichment. The first of these was caused by a hydrous alkaline silicate melt, resulting in enrichment in SiO2, Al2O3, FeO, K2O, LILE and LREE. The second was caused by a carbonatitic melt that further enriched the source area in Ba, Th, U, Sr, P and LREE. Infiltration of melt along fractures in the mantle wedge probably resulted in a vein assemblage of biotite - (potassic) amphibole - apatite ± carbonate within unreacted mantle peridotite. The most likely source of the metasomatising melts was from partial melting of subducted carbonate-rich pelitic sediment.

  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. 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

  2. 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.

  3. 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.

  4. Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria)

    NASA Astrophysics Data System (ADS)

    Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin

    2016-06-01

    Dykes in the Strudengau area (SW Moldanubian Zone, Austria) can be mineralogically divided into lamprophyres (spessartites and kersantites) and felsic dykes (granite porphyries, granitic dykes and pegmatoid dykes). Geochemical analyses of 11 lamprophyres and 7 felsic dykes show evidence of fractional crystallization. The lamprophyres are characterized by metaluminous compositions, intermediate SiO2 contents and high amounts of MgO and K2O; these rocks have high Ba (800-3000 ppm) and Sr (250-1000 ppm) contents as well as an enrichment of large-ion lithophile elements over high field strength elements, typical for enriched mantle sources with variable modifications due to fractionation and crustal contamination. This geochemical signature has been reported from durbachites (biotite- and K feldspar-rich mela-syenites particularly characteristic of the Variscan orogen in Central Europe). For most major elements, calculated fractionation trends from crystallization experiments of durbachites give an excellent match with the data from the Strudengau dykes. This suggests that the lamprophyres and felsic dykes were both products of fractional crystallization and subsequent magma mixing of durbachitic and leucogranitic melts. Rb-Sr geochronological data on biotite from five undeformed kersantites and a locally deformed granite porphyry gave cooling ages of c. 334-318 Ma, indicating synchronous intrusion of the dykes with the nearby outcropping Weinsberger granite (part of the South Bohemian Batholith, c. 330-310 Ma). Oriented matrix biotite separated from the locally deformed granite porphyry gave an Rb-Sr age of c. 318 Ma, interpreted as a deformation age during extensional tectonics. We propose a large-scale extensional regime at c. 320 Ma in the Strudengau area, accompanied by plutonism of fractionated magmas of syncollisional mantle-derived sources, mixed with crustal components. This geodynamic setting is comparable to other areas in the Variscan belt documenting an

  5. 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.

  6. Geochronology, geochemistry and Hf isotope of Late Triassic magmatic rocks of Qingchengzi district in Liaodong peninsula, Northeast China

    NASA Astrophysics Data System (ADS)

    Duan, Xiaoxia; Zeng, Qingdong; Yang, Jinhui; Liu, Jianming; Wang, Yongbin; Zhou, Lingli

    2014-09-01

    The initiation timing and mechanism of lithospheric thinning of the North China Craton (NCC) was still controversial. Late Triassic igneous rocks especially mantle derived mafic rocks would provide constrains on Early Mesozoic lithospheric mantle geodynamics and initiation of lithospheric thinning. This paper reports Late Triassic magmatic rocks, including lamprophyre, diorite dykes and biotite monzogranite cropped out in Qingchengzi district of Liaodong peninsula, northeastern NCC. LA-ICPMS zircon U-Pb dating yield ages of 210-227 Ma and 224 Ma for lamprophyres and biotite monzogranite respectively. Lamprophyre is ultrapotassic, strongly enriched in REE and LILEs, depleted in HFSEs, and negative Hf isotopes, which are discriminating signatures of crustal source, but distinguishingly high compatible element contents indicate the primary magma originated from mantle source-a fertile one. Lamprophyre derived from partial melting of an enriched lithospheric mantle, which was modified by slab-derived hydrous fluids/melts associated with deep subduction between the Yangtze Craton and the NCC. The diorite displays distinct features with relatively enriched Nb, Ta, HREE and depleted Th, U, which suggest it derived from a relatively depleted source. The depletion was caused by break-off of the Yangtze slab during deep subduction introducing asthenospheric mantle into the source. The biotite monzogranite shows adakitic affinity, and originated from partial melting of the thickened lower crust with addition of small proportion of mantle material. The recognition of Late Triassic magmatism implies extensional tectonic settings in Liaodong peninsula and suggests initiation of lithospheric thinning of North China Craton in eastern segment might begin early in Late Triassic.

  7. 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. PMID:18506262

  8. 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

  9. High to ultrahigh potassic alkaline volcanic belt along the Ankara-Erzincan suture (northern Turkey): new geochemical and Ar-Ar data constraining petrogenesis with implications for the late Cretaceous subduction of the Neotethys Ocean

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Remnants of some high- to ultrahigh-K alkaline volcanic rocks crop out as isolated small and discontinuous bodies along the Ankara-Erzincan suture belt in northern Turkey. These rocks are represented by leucite-bearing lavas (LB), basaltic andesites, trachytes, monzonite/syenites) and lamprophyres. Leucite-bearing rocks are small stocks, dikes and lava flows. Pebbles and blocks of the LB are found in the coeval volcanic debris avalanche deposits and volcanoclastic breccias. Leucite-bearing rocks are mainly phonotephrite, tephriphonolite, trachyandesite and basaltic trachyandesites (shoshonite) and have mineral assemblages of lct + cpx + ol + pl + Kfs + mag+ ap. Leucites were almost totally analcimized. Trachytes and monzonite/syenites, which are seen as small stocks and dikes, are characterized by amp + bt + pl + Kfs + spn + ap + opq paragenesis. Lamprophyres are mica-rich melanocratic dikes, and include cpx + mica (phlogopitic) + Kfs + ap + opq. Rarely leucite, olivine and plagioclase are also present. Ar-Ar data reveal that this volcanic activity occurred between 73.6±0.18 and 76.78±0.19 Ma, corresponding to latest Cretaceous. All the samples from the high- and ultrahigh-K volcanic belt are alkaline in nature. Leucite-bearing lavas are characterized by their MgO (2.70-5.81, av. 4.58 wt.%), K2O (0.79-4.81, av. 2.35 wt.%), Na2O (4.86-7.48, av. 3.58 wt.%) and K2O/Na2O (0.13-0.92, av. 0.42 wt.%). The low K2O and K2O/Na2O contents of these rocks are due to extensive analcimization of the leucites. Major oxide contents in lamprophyric rocks are 3.25-7.48 (MgO), 1.35-7.76 (K2O), 1.77-4.00 (Na2O) and 0.31-2.69 (K2O/Na2O). The silica content of these rocks are variable and range from 47.18-50.26 (wt.%) (LB) to 39.14-53.28 (lamprophyres). Based on their major element contents, these rocks are classified as plagioleucitites or ultrapotassic rocks of the active orogenic zones (Foley, 1992). Leucite-bearing rocks, lamprophyres and the trachytes (with their hypabyssal

  10. Geochemistry and petrogenesis of the late Cretaceous potassic-alkaline volcanic rocks from the Amasya Region (northern Turkey)

    NASA Astrophysics Data System (ADS)

    Gülmez, Fatma; Genç, Can; Tüysüz, Okan; Karacık, Zekiye; Roden, Mike; Billor, Zeki; Hames, Willis

    2013-04-01

    The Cretaceous Lokman Formation (Alp, 1972) , is a volcano-sedimantary unit that comprises high- to ultra high-K alkaline volcanic rocks in Amasya Region (40°N, 35°E). The volcanic rocks expose as small outcrops and interfingered with pyroclastic and epiclastic rocks, and are classified as leucitite, tephriphonolite (LT), lamprophyres, trachytes and rarely andesites. LT and lamprophyres occur as dikes cutting each other, and rare lava flows. Trachytes are observed as small domes in the field and lots of pebbles and blocks within the clastic deposits derived from the domes. Samples of LT comprise lct+cpx (diopsite)+plg+mag+ap and classified as leucite-basanite mineralogically and tephri-phonolite geochemically. Ar-Ar age dating from leucites show that the leucite-bearing volcanic activity formed 75.6±3.7 Ma. The mineralogic composition of melanokratic lamprophyre dikes are represented by Kfs+cpx+mica+ap+mag. They defined geochemically as phono-tephrite and phonolite. The Ar-Ar plateau ages from the phlogopites from two different outcrops are 76.78 and 77.48 Ma. The main minerals of trachytic rocks are amp + bt + pl + Kfs + spn + ap +opq. They are classified as alkaline trachyandesite, geochemically. Radiometric age data from Kfs minerals reveal that the trachytic volcanism occurred 75.83±0.09 Ma. Except one andesitic sample, lamprophyres and trachytes of the Lokman Formation are the high- and ultra high-K and alkaline rocks. LT and lamprophyres are characterized by relatively high MgO (3.25-7.04 wt.%), K2O (4.34-6.54 wt.%), Na2O (3.42-5.74 wt.%). Total analcimization of leucite minerals let to decreasing its K2O, and increasing the Na2O contents. Therefore, K2O/Na2O values for LT and the lamprophyres (0.92-2.27) are relatively low. Trachytic suite is also high-K and alkaline in nature. On MORB normalized plots, all of the volcanic rocks from Lokman Formation display enrichment of LIL elements significantly relative to HFSE, and depletions of Nb-Ta and Ti

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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. PMID:10736267

  17. 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

  18. 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

  19. 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

  20. 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

  1. Geochronology and geochemistry of the Early Cretaceous Jigongshan and Qijianfeng batholiths in the Tongbai orogen, central China: implications for lower crustal delamination

    NASA Astrophysics Data System (ADS)

    Zhang, Jinyang; Ma, Changqian; Li, Jianwei; She, Zhenbing; Zhang, Chao

    2013-06-01

    The Jigongshan and Qijianfeng batholiths in the Tongbai orogen consist mainly of porphyritic hornblende-biotite monzogranite, biotite monzogranite, and biotite syenogranite, which are variably intruded by lamprophyre, diorite, and syenogranite dykes. Mafic microgranular enclaves commonly occur in the hornblende-biotite monzogranite, whereas surmicaceous enclaves are found in the biotite monzogranite. Both batholiths have zircon U-Pb ages ranging from ca. 139 to 120 Ma, indicating their emplacement in the Early Cretaceous. The hornblende-biotite monzogranite has an adakitic affinity marked by relatively high Sr/Y and (La/Yb) N ratios, lack of Eu anomalies, low MgO and Ni contents, and Na2O > K2O. Its chemical compositions, combined with enriched Sr-Nd isotopic signatures, suggest formation by dehydration melting of mafic rocks in a thickened lower crust. This thickened crust resulted from the Permo-Triassic subduction-collision between the North China and South China blocks and persisted until the Early Cretaceous. The biotite monzogranite and biotite syenogranite have low Al2O3, CaO, and Sr contents, low Rb/Sr, FeOt/MgO, and (Na2O + K2O)/CaO ratios, and flat HREE patterns with moderate to weak Eu anomalies. They were produced by partial melting of crustal materials under relatively low pressure. Partial melting at different crustal levels could have significantly contributed to mechanical weakening of the crust. The diorite and lamprophyre dykes show linear trends between SiO2 and major or trace elements on Harker diagrams, with two lamprophyre samples containing normative nepheline and olivine. These rocks have high La/Yb and Dy/Yb ratios, both displaying co-variation with contents of Yb. They were originated from relatively deep lithospheric mantle followed by fractionation of olivine + clinopyroxene + apatite + Fe-Ti oxides. Extensive partial melting in the lithospheric mantle indicates relatively high temperatures at this level. We suggest that the presence of

  2. 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

  3. Geochemistry and petrogenesis of intrusions at the Golden Pride gold deposit in the Nzega greenstone belt, Tanzania

    NASA Astrophysics Data System (ADS)

    Kwelwa, Shimba; Manya, Shukrani; Vos, Ivo M. A.

    2013-10-01

    The greenstone sequence at Golden Pride gold deposit in Nzega greenstone belt of northern Tanzania is cross-cut by several intrusions whose geochemistry and petrogenesis is unknown. We present major and trace elements geochemistry of the Golden Pride igneous intrusions with the aim of constraining their petrogenesis and their ancient tectonic setting. The Golden Pride intrusions are geochemically categorized into two main rock suites: the granodiorites (which include the porphyries) and the lamprophyres (formerly intermediate intrusions). The granodiorites are characterized by SiO2 contents of 54.5-69.9 wt%, elevated MgO (1.22-3.59 wt%) Cr (up to 54 ppm), Mg# (35-55) pointing to a mantle component in the source. Compared to the TTG and adakites, the granodiorites are characterized by higher K2O (1.52-4.30 wt%), medium HREE (Gd/ErCN = 2.13-3.77) and marked enrichment in Ba and Sr (Ba + Sr = 819-2922 ppm) and are in these respects similar to Archean high Ba-Sr sanukitoids. The rocks in this suite are interpreted to have formed by partial melting of an enriched mantle wedge through two metasomatic events: subduction-related fluids/melts and by metasomatism related to asthenospheric mantle upwelling caused by slab break-off. Compared to the granodiorites, the lamprophyres have higher MgO contents (2.37-3.81 wt%), Cr (60-298 ppm), Co (31-57 ppm) and Mg# (32-40). They also show slight enrichment of the LREE relative to HREE (La/YbCN = 3.3-7.1), moderate Nb-Ti depletion and sub-chondritic Zr/Hf ratios (34-41). These geochemical features are attributed to derivation of the Golden Pride lamprophyres by partial melting of the amphibole-rich metasomatized mantle by slab derived hydrous fluids. Both of the Golden Pride intrusion suites show strong affinity to subduction related magmas and we interpret that the entire greenstone sequence and the associated intrusions at Golden Pride gold deposit formed in a late Archaean convergent margin.

  4. The Aiguablava dyke swarm: emplacement and paleostress in a fractured basement

    NASA Astrophysics Data System (ADS)

    Martínez-Poza, Ana Isabel; Druguet, Elena; Castaño, Lina Marcela; Carreras, Jordi

    2013-04-01

    A structural analysis has been performed in the Upper Permian lamprophyric dyke swarm of Aiguablava (NE Spain). Dyke emplacement is related to the presence of a widespread joint network, likely developed during the cooling and decompression of the late Variscan granitic host rocks. In order to characterize the patterns of both the joint system and the dyke swarm, a trend frequency analysis has been performed using the circular scanlines method (Mauldon et al., 2001). The sub-vertical joint pattern consists on two major orthogonal sets at ≈N23°, ≈N113° and secondary sets at ≈N0° and ≈N90°, among others. These four fracture sets are interpreted as previous to the lamprophyre intrusion event, because they are either exploited or cross-cut by the lamprophyres. The subvertical dykes have a mean N113° trend, which corresponds to the trend of one of the main joint sets. Despite this overall orientation of dykes, segmentation is a noticeable feature at the Dm- to cm-scale, and this is probably related to the localized dyke intrusion into the other pre-existing secondary joint sets. Dyke opening directions has been measured from matching dyke jogs or markers in the host rock, with a mean orientation of 021/04. A three-dimensional paleostress analysis has been carried out from dyke orientations, applying the Mohr circle construction of Jolly and Sanderson (1997), and the parameters R' (driving pressure ratio, R'= 0.156) and φ (stress ratio, φ = 0.45) were calculated. From this analysis, we have obtained a sub-vertical maximum (σ1) and a NNE-SSW minimum (σ3) stress axes, consistent with the sub-horizontal mean trend of dyke opening measured in the field. It is inferred that many of the pre-existing joint sets were exploited by magmatic dykes, being the ≈N113° joint set (normal to σ3) the most favourable for dyke emplacement. At that time, magmatic pressure related to dyke intrusion, Pm, was lower than the intermediate principal stress axis, σ2 . Our

  5. 1.8 Ga Svecofennian post-collisional shoshonitic magmatism in the Fennoscandian shield

    NASA Astrophysics Data System (ADS)

    Eklund, O.; Konopelko, D.; Rutanen, H.; Fröjdö, S.; Shebanov, A. D.

    1998-12-01

    At least 14 small (1-11 km across) 1.8 Ga Svecofennian post-collisional bimodal intrusions occur in southern Finland and Russian Karelia in a 600-km-long belt from the Åland Islands to the NW Lake Ladoga region. The rocks range from ultramafic, calc-alkaline, apatite-rich potassium lamprophyres to peraluminous HiBaSr granites, and form a shoshonitic series with K 2O+Na 2O>5%, K 2O/Na 2O>0.5, Al 2O 3>9% over a wide spectrum of SiO 2 (32-78%). Although strongly enriched in all rocks, the LILE Ba and Sr and the LREE generally define a decreasing trend with increasing SiO 2. Depletion is noted for HFSE Ti, Nb and Ta. Available isotopic data show overlapping values for lamprophyres and granites within separate intrusions and a cogenetic origin is thus not precluded. Initial magmas (Mg#>65) in this shoshonitic association are considered to be generated in an enriched lithospheric mantle during post-collisional uplift some 30 Ma after the regional Svecofennian metamorphic peak. However, prior to the melting episode, the lithospheric mantle was affected by carbonatite metasomatism; more extensively in the east than in the west. The melts generated in the more carbonate-rich mantle are extremely enriched in P 2O 5˜4%, F˜12,000 ppm, LILE: Ba˜9000 ppm, Sr˜7000 ppm, LREE: La˜600 ppm and Ce˜1000 ppm. The parental magma underwent 55-60% fractionation of biotite+clinopyroxene+apatite+magnetite+sphene whereupon intermediate varieties were produced. After further fractionation, 60-80%, of K-feldspar+amphibole+plagioclase±(minor magnetite, sphene and apatite), leucosyenites and quartz-monzonites were formed. In the west, where the source was less affected by carbonatite metasomatism, calc-alkaline lamprophyres (vogesites, minettes and spessartites) and equivalent plutonic rocks (monzonites) were formed. Removal of about 50% of biotite, amphibole, plagioclase, magnetite, apatite and sphene produced peraluminous HiBaSr granites. The impact of crustal assimilation is considered

  6. Crust and Upper Mantle Structure in the Sarfartoq Kimberlite Province, West Greenland: A Receiver Function Study

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, Trine; Voss, Peter H.; Møller Steensgaard, Bo; Pinna, Line G.

    2015-04-01

    A marked change in crustal thickness is seen at the deformation boundary between undisturbed Archean core in the south and reworked Archean gneiss in the foreland of the Nagssugtoqidian orogen in West Greenland. In addition, intra-crustal boundaries can be tentativly interpreted. Interpretations on upper mantle structures are less clear. This is the first information on crust and upper mantle structure in the area, which is known for kimberlite, carbonatite and ultramafic lamprophyre occurrences, and diamond exploration. The data consists of two summer seasons of passive seismological data recorded on 5 broad-band seismological stations placed on an almost 200 km long profile crossing the deformation boundary. The stations were installed in the remote area with solar panels and batteries, and recorded two summer seasons. Between 7 and 28 events on the stations were used for the Receiver Function analysis.

  7. Crust and Upper Mantle Structure in the Sarfartoq Kimberlite Province, West Greenland: A Receiver Function Study

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, T.; Voss, P.; Larsen, L. M.; Steensgaard, B. M.; Pinna, L. G. B.

    2014-12-01

    A marked change in crustal thickness is seen at the deformation boundary between undisturbed Archean core in the south and reworked Archean gneiss in the foreland of the Nagssugtoqidian orogen in West Greenland. In addition, intra-crustal boundaries can be tentativly interpreted. Interpretations on upper mantle structures are less clear. This is the first information on crust and upper mantle structure in the area, which is known for kimberlite, carbonatite and ultramafic lamprophyre occurrences, and diamond exploration. The data consists of two summer seasons of passive seismological data recorded on 5 broad-band seismological stations placed on an almost 200 km long profile crossing the deformation boundary. The stations were installed in the remote area with solar panels and batteries, and recorded two summer seasons. Between 7 and 28 events on the stations were used for the Receiver Function analysis.

  8. 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).

  9. 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.

  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. 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.

  12. 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.

  13. 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.

  14. Geochronology and geochemistry of Early Cretaceous igneous units from the central Sulu orogenic belt: Evidence for crustal delamination during a shift in the regional tectonic regime

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Chang, Su-Chin; Wang, Kuo-Lung; Lu, Hong-Bo; Zhang, Hai-Chun

    2015-11-01

    Widespread Late Mesozoic igneous events in northern China have been intensively investigated over the past decades and provide evidence for regional lithospheric thinning. The underlying mechanism causing lithospheric thinning remains unclear however. This study reports U-Pb zircon ages, geochemical data and isotopic ratios for Cretaceous igneous units from the central Sulu orogenic belt as it occurs in the Shandong Peninsula. LA-ICP-MS U-Pb analyses of magmatic zircons identified a relatively restricted population of ages ranging from 123 ± 2 Ma to 120 ± 2 Ma from four representative samples of igneous units in the study area. Geochemical analysis of the samples revealed LREE and LILE enrichment, HREE depletion, high initial 87Sr/86Sr values ranging from 0.7040 to 0.7096, and low negative εNd(t) values from -22.0 to -12.2. The data suggest lamprophyres derived separately from heterogeneous mantle inputs, which experienced crust-mantle interaction, andesitic porphyrites and syenogranites derived from enriched lithospheric mantle and rhyolites derived from partial melting of an ancient crustal component. Assimilation and fractionation processes did not contribute to lamprophyre formation, but did play an important role in generating andesitic porphyrites, syenogranites and rhyolites. The petrogenetic history of these rocks indicates intensive lithospheric thinning of the upper mantle and lower crust beneath the Sulu orogenic belt at 123-120 Ma. Given the timing and regional tectonic framework in which these units formed, thinning was likely caused by an abrupt change in the direction of the subducting Pacific plate.

  15. A comparative petrological study of the Siberian and Ethiopian Large Igneous Provinces (LIPs) and a case study on Triassic mafic rocks in Chukotka, NE Russia

    NASA Astrophysics Data System (ADS)

    Desta, M. T.; Ishiwatari, A.; Machi, S.; Ledneva, G. V.; Sokolov, S. D.; Artem, M. V.; Bazylev, B. A.

    2012-12-01

    This study is mainly targeted to find the possible eastern marginal extension of Siberian LIP and to compare them with the central Siberian LIP and is also aimed to compare and contrast the geochemical and petrological characteristics of Siberian LIP (~ 250 Ma) with the Ethiopian LIP (~ 30 Ma) to consider the mantle and crustal processes in view of magmatic diversity among those LIPs. A review of previous geochemical data from the Siberian and Ethiopian LIP confirms notable differences in their major and trace element compositions. Siberian LIP comprises a variety of rocks (such as basalts, basaltic andesites, picrites and meimechites) with a wide range of SiO2 (40-62 wt. %). In contrast, Ethiopian LIP is characterized by bimodal volcanism with the absence of intermediate rock. The Ethiopian high-Ti basalts and picrites have higher TiO2 (3-6 wt. %), lower CaO/Al2O3 (0.5-1.5) and MgO (5-26 wt. %) than the Siberian high-Ti picrites and meimechites (2-4, 1.8-2.3 and 13-36 wt. % respectively). Siberian LIP shows more significant depletion in HFSE (mainly Nb) and higher La/Sm ratios than Ethiopian LIP. This may suggest contamination of Siberian LIP magma by crustal component. Triassic volcanic and intrusive rock samples are collected in 2009 from the Chukotka province (Northeast Russia), where geographically far to the east from the central Siberian flood basalt province. The petrography of the studied samples includes basaltic rocks (i.e. hornblende basalt, lamprophyre, pyroxene basalt, and ankaramite) and gabbroic rocks (i.e. amphibole-bearing type-I and amphibole free type-II). Clinopyroxenes (diopside to augite) both from basalts and gabbros show only low-Ti (<1 wt. %) characteristics. Amphiboles are pargasite in lamprophyres and type-I gabbros, tschermakite in hornblende-basalt, edenite in ankaramite and edenite-hornblende in type-II gabbros. Plagioclase ranges from An100 to An45.6 in type-I gabbros, An54.5 to An0.9 in type-II gabbros and An73.4 to An1.3 in

  16. Petrogenesis of Cretaceous adakite-like intrusions of the Gangdese Plutonic Belt, southern Tibet: Implications for mid-ocean ridge subduction and crustal growth

    NASA Astrophysics Data System (ADS)

    Zheng, Yuan-chuan; Hou, Zeng-qian; Gong, Ying-li; Liang, Wei; Sun, Qing-Zhong; Zhang, Song; Fu, Qiang; Huang, Ke-Xian; Li, Qiu-Yun; Li, Wei

    2014-03-01

    We have conducted a whole-rock geochemical, U-Pb zircon geochronological, and in situ zircon Hf-O isotopic compositional study of rocks in southern Tibet from the Langxian igneous suite (including a lamprophyre dyke, mafic enclaves, a granodiorite, and a two-mica granite) and the Nuri igneous suite (a quartz-diorite). U-Pb zircon dating indicates that the timing of crystallization of the mafic enclaves and host granodiorite of the Langxian suite are ca. 105 Ma and 102 Ma, respectively, that the Langxian lamprophyre dyke and the two-mica granite were emplaced at ca. 96 Ma and 80-76 Ma, respectively, and that the Nuri quartz-diorite was emplaced at ca. 95 Ma. With the exception of the lamprophyre dyke and mafic enclaves in the Langxian area, felsic rocks from the Langxian and Nuri igneous suites all show signs of a geochemical affinity with adakite-like rocks. The high Mg-numbers, high abundance of compatible elements, high ɛNd(t) (2.7 and 2.8) and δ18O (8.9 and 9.2‰) values, elevated zircon ɛHf(t) (11.0-17.0) values, and low 87Sr/86Sr(i) ratios (0.7040), collectively indicate that the Nuri adakite-like quartz-diorite was derived from partial melting of the low temperature altered Neo-Tethyan oceanic crust, and that these dioritic magmas subsequently interacted with peridotite as they rose upwards through the overlying mantle wedge. The observation of identical differentiation trends, similar whole-rock Sr-Nd and zircon Hf isotopic compositions, and consistently low (Dy/Yb)N ratios among the Langxian igneous suite rocks, indicates that the adakite-like granodiorite was produced by low-pressure fractional crystallization of precursor magmas now represented by the (relict) mafic enclaves. However, relatively high Al2O3 contents, low MgO, Cr and Ni contents, and low (La/Yb)N and (Dy/Yb)N values indicate that the two-mica granite was derived from partial melting of the southern Tibetan mafic lower crust in the absence of garnet, while isotopic data suggest that at

  17. 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

  18. Calc-alkaline rear-arc magmatism in the Fuegian Andes: Implications for the mid-cretaceous tectonomagmatic evolution of southernmost South America

    NASA Astrophysics Data System (ADS)

    Guillot, Mauricio González; Escayola, Mónica; Acevedo, Rogelio

    2011-02-01

    The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500-2000 ppm, Sr 800-1400 ppm), HFSE (Th 7-23 ppm, Nb 7-13 ppm, Ta 0.5-1.1 ppm) and LREE (La 16-51 ppm) contents, along with relatively low HREE (Yb 1.7-1.3 ppm) and Y (9-19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60-65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11-38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic

  19. 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

  20. 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

  1. Early Carboniferous (Viséan) emplacement of the collisional Kłodzko-Złoty Stok granitoids (Sudetes, SW Poland): constraints from geochemical data and zircon U-Pb ages

    NASA Astrophysics Data System (ADS)

    Mikulski, Stanisław Z.; Williams, Ian S.; Bagiński, Bogusław

    2013-06-01

    Sensitive high-resolution ion microprobe zircon U-Pb dating and geochemical data of igneous rocks from the composite Kłodzko-Złoty Stok (KZS) Granite Pluton, Sudetic Block, indicate that the granitoids represent an Early Carboniferous Viséan phase of Variscan metaluminous, high-K, I-type, syn-collisional granite magmatism within the Saxothuringian Zone of the Central European Variscides. Igneous zircon records hypabyssal magmatism that produced various granitoids and lamprophyre (spessartite) emplaced from ca. 340 to 331 Ma. The KZS granitoids have compositions ranging from granodiorite to monzonite, low A/CNK ratios (<1), and are associated with abundant mafic members. Most of them are alkaline, highly potassic, and moderately evolved. The major and trace element contents of the KZS granitoids suggest geochemical heterogeneity, and the hybrid nature of magmas derived from a range of sources in the middle crust, with a strong input of material from the upper mantle. Mixing of magmas of mantle origin with high-K material from partly melted continental crust was probably a more important factor than fractional crystallization, in controlling the evolution of the magmas. The mean Pb-U ages of the main population of igneous zircon from a quartz monzodiorite (Żelazno) and hornblende monzonite (Droszków) are 340.2 ± 2.5 Ma and 339.5 ± 3.1 Ma, respectively. A slightly younger biotite-hornblende granodiorite from Chwalisław, 336.7 ± 2.5 Ma, was cut by a spessartite dyke at 333.1 ± 3.1 Ma. This indicates that mafic magmas were immediately intruded into fractured, probably incompletely solidified, granodiorites. The lamprophyric dyke also contains igneous zircon of Neoproterozoic age, 566.3 ± 6.4 Ma, typical of the crust in the Saxothuringian Zone. Tonalite from Ptasznik Hill near Droszków is of similar age to the spessartite, 331.5 ± 2.6 Ma. High REE contents in the tonalite and its igneous zircon indicate advanced differentiation of granitic magma, producing a

  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. The application aeromagnetic data for dyke swarm mapping (an example the Ladoga region, Russia)

    NASA Astrophysics Data System (ADS)

    Vasilieva, T.; Frank-Kamenetsky, D.

    2003-04-01

    interesting lamprophyre dykes could not be detected and mapped with this method because of their low magnetic susceptibility. These Riphean dolerites and warm of lamprophyre dykes (approximate age is about 1.8 Ga) expanding on the most part of NW Ladoga region indicate the main stages of the geological history after Svecofennian orogeny. Supposed by grant N 330 for Young Scientists, RAS

  4. 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.

  5. 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

  6. Uranium in Precambrian granitic rocks of the St. Francois Mountains, southeastern Missouri: with comments on uranium resource potential

    USGS Publications Warehouse

    Nash, J. Thomas

    1977-01-01

    Red granites of the St. Francois Mountains are highly radioactive and contain 4 to 34 parts per million (ppm) uranium. The most radioactive is the Graniteville Granite which contains an average of 16.9 ppm U and 42.6 ppm Th. The Butler Hill and Breadtray Granites also contain anomalous amounts, averaging 6.2 and 5.6 ppm U and 23.5 and 20.5 ppm Th respectively. Other Precambrian granitic rocks have normal concentrations of- U and Th. Fission track 'maps' indicate that high concentrations of uranium are associated with magnetite in the red granites; this uranium is presumed to be readily leachable by hydrothermal or supergene solutions. No uranium minerals or ore grade concentrations of uranium were observed in or near the granites, but there-are conceptual reasons for the possible existence of uranium deposits in intragranitic veins and onlapping Cambrian-Ordovician sedimentary rocks. Although the red granites constitute a good potential source of uranium, there is not much evidence for uranium having been mobilized. Identification of features such as lamprophyre dikes and 'episyenite' alteration, or sedimentary rocks containing reductants, would be of value for exploration and would permit more favorable resource appraisal.

  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. 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.

  9. 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.

  10. Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil

    NASA Astrophysics Data System (ADS)

    Comin-Chiaramonti, Piero; Gomes, Celso B.; De Min, Angelo; Ruberti, Excelso; Girardi, Vicente A. V.; Slejko, Francesca; Neder, Renato D.; Pinho, Francisco E. C.

    2014-12-01

    The Planalto da Serra igneous rocks form plugs, necks and dykes of carbonate-rich ultramafic lamprophyres (aillikites and glimmerites with kamafugitic affinity) and carbonatites (alvikites and beforsites). Phlogopite and/or tetraphlogopite, diopside and melanitic garnet are restricted to aillikitic rock-types, whereas pyroclore occurs only in carbonatites. Aillikites and carbonatites are altered to hydrotermalites, having chlorite and serpentine as dominant minerals. Planalto da Serra igneous rock association has kamafugitic affinity (i.e. effusive, ultrapotassic. High LREE/HREE fractionation, incompatible elements data and Sr-Nd isotopes, suggest that the K-ultramafic alkaline and carbonatite rocks originated from a variably metasomatized mantle source enriched in radiogenic Sr. Crustal contamination is negligible or absent. Age values of 600 Ma rule out the geochronological relationship between the investigated intrusions and the Mesozoic alkaline bodies from the Azimuth 125° lineament. The TDM model ages allow to conclude that Planalto da Serra magma is derived from the partial melting of a mantle source metasomatised by K-rich carbonatated melt during the Early to Late Neoproterozoic. On the basis of alkaline magmatism repetitions at 600 Ma and 90-80 Ma we question the subsistence of a stationary mantle plume for so long time.

  11. The geology and mineralisation at the Golden Pride gold deposit, Nzega Greenstone Belt, Tanzania

    NASA Astrophysics Data System (ADS)

    Vos, I. M. A.; Bierlein, F. P.; Standing, J. S.; Davidson, G.

    2009-10-01

    The Golden Pride gold deposit (˜3 Moz) is located in the central part of the Nzega Greenstone Belt at the southern margin of the Lake Victoria Goldfields in Tanzania. It represents an inferred Late Archaean, orogenic gold deposit and is hosted in intensely deformed meta-sedimentary rocks in the hanging wall of the approximately E-W striking Golden Pride Shear Zone. The hanging-wall sequence also includes felsic (quartz porphyritic) to mafic (lamprophyric) intrusions, as well as banded iron formations. Hydrothermal alteration phases associated with mineralisation are dominated by sericite and chlorite. Two main ore types can be distinguished, chlorite and silica ore, both occupying dilational sites and structural intersections in the hanging wall of the main shear zone. Sulphide minerals in both ore types include pyrrhotite, arsenopyrite, pyrite and accessory sphalerite, galena, sulphosalts and Ni-Co-Bi sulphides. Gold and tellurides are late in the paragenetic sequence and associated with a secondary phase of pyrrhotite deposition. Sulphur isotope compositions range from -6 to 7 per mil and are interpreted to reflect contributions from two distinct sources to the mineralising fluids in the Golden Pride gold deposit. A redox change, potentially induced by the intrusion of mafic melts, together with structural elements in the hanging wall of the Golden Pride Shear Zone, are interpreted to be the main controls on gold mineralisation in this deposit.

  12. Petrology, geochemistry and geochonology of the Jacupiranga ultramafic, alkaline and carbonatitic complex (southern Brazil)

    NASA Astrophysics Data System (ADS)

    Chmyz, Luanna; Arnaud, Nicolas; Biondi, João Carlos

    2015-04-01

    Brazilian carbonatitic complexes are located at the edges of the Paleozoic basins and are usually associated to tectonic crustal flexuring or deep fault zones. The Jacupiranga Complex is a 65 km² ultrabasic-alkaline carbonatitic intrusive body outcroping at the northeastern border of the Paraná Basin, South of São Paulo State (Brazil). The northern portion of the unit is mostly composed of peridotitic rocks, while the southern part contains ijolites, melteigites, clinopyroxenites and carbonatites which host a phosphate deposit, mined since 1966. Even though the carbonatites only represent 1% of the Complex's area, they have concentrated most of the historical petrogenetic studies, leaving almost unknown the petrogenetic and the geochronological characteristics of other rocks. This explains why the few petrogenetic models from the literature are very partial and mostly unsatisfactory. While the peridotitic rocks are largely hindered by the absence of fresh outcrops, the regolith thickness and the high serpentinization degree, field observations and petrographic data notably show a heterogeneous zone around the peridotitic body. That zone is composed of a large variety of lithotypes over a relatively small area (~9 km²), comprising diorites, monzodiorites, alkali feldspar syenites, trachytes, lamprophyres and syenites. Moreover, these rocks present a restricted lateral continuity (decametric) and a lack of the magmatic bedding characteristic of the ijolitic and clinopyroxenitc rocks. The southern clinopyroxenitic zone (~20 km²) is composed of clinopyroxenite and melteigite with prominent magmatic layering, probably of cumulative origin, and a body of carbonatites which outcrops over less than 1 km2 essentially composed of sovite and beforsite, with abundant apatite. The Jacupiranga Complex characteristics indicate that its formation possibly comprises at least five magmatic events which cannot at present be surely ordinated in time: a) the emplacement of the

  13. 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

  14. 1.8 Ga magmatism in the Fennoscandian Shield; lateral variations in subcontinental mantle enrichment

    NASA Astrophysics Data System (ADS)

    Andersson, U. B.; Eklund, O.; Fröjdö, S.; Konopelko, D.

    2006-01-01

    The ca. 1.8 Ga post-collisional magmatism in the southern part of the 2.1-1.86 Ga Svecofennian domain of the Fennoscandian Shield have been studied with particular reference to the character and sources of the mafic rocks in a traverse from the Archaean craton margin in east, across the juvenile Svecofennian domain to its western margin. For this purpose three key areas were selected in the eastern, central and western parts of the domain: (i) in the western part of the domain, the Tjällmo-Vättern zone (southern Sweden) of the Transscandinavian Igneous Belt (TIB) consists of extensive areas of dominantly alkali-calcic granitoids associated with calc-alkaline to tholeiitic mafic rocks. Initial ɛNd for the mafic rocks vary from around 0 to above +3. (ii) In the central part of the domain (SW Finland), the post-collisional rocks are represented by small intrusions consisting of calc-alkaline high-Ba-Sr granites associated with shoshonitic lamprophyres and their plutonic equivalents. Initial ɛNd for the rocks in this series vary between 0 and +1. (iii) In the easternmost part of the Svecofennian domain (Russian Karelia and SE Finland) shoshonitic associations occur, comprising lamprophyres and their plutonic equivalents (apatite and magnetite-rich monzodiorites), which are related to syenites and high-Ba-Sr granites by fractional crystallization. All the rock types in this shoshonitic association have strongly elevated contents of P 2O 5, LREE and LILE. Initial ɛNd for all rocks in Karelia fall between 0 and -1. Geochemical and isotopic results indicate that the post-collisional rocks in the central and eastern part of the domain stem from lithospheric mantle sources that were enriched during the preceding Svecofennian orogeny. The HFSE depletion, combined with the strong Sr, LILE and LREE enrichment, recall signatures of increasingly carbonate-dominated metasomatism of the mantle eastwards towards the craton margin. In contrast, the mainly LILE enriched mafic

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Geochronology and Geochemistry of Volcanic Suites from the Middle Sulu Orogenic Belt, Eastern China: Implication for Petrogenesis and Tectonic Setting

    NASA Astrophysics Data System (ADS)

    Wang, J.; Chang, S. C.; Lu, H.; Zhang, H.

    2014-12-01

    The widely distributed Late Mesozoic igneous events in North China have been intensively studied in the past decades and proposed to be accounted by lithospheric thinning. However, mechanism of the lithospheric thining is still in debate. In this study, we report U-Pb zircon ages, geochemical data and Sr-Nd isotopic data for the Cretaceous mafic and associated felsic intrusions from the middle Sulu orogenic belt in the Shandong Peninsula. The ICP-MS U-Pb zircon analyses show consistent crystallization ages ranging from 120.2 ± 2.1 Ma to 123.3 ± 1.6 Ma for four representative samples. These rocks are characterized by LREE and LILE enrichment, HREE depletion, high initial 87Sr/86Sr values ranging from 0.70401 to 0.70966, low negative ɛNd(t) values from -22.0 to -12.2. These features suggest that they were derived from a common enriched lithospheric mantle source. Geochemical and isotopic data indicate that the original magma of these rocks was produced by partial melting of an ancient lithospheric mantle, which was variably mixed with lower crustal eclogite derived melts. The lamprophyres, andesitic porphyrites and syenogranite may have been attributed to subsequent fractional crystallization of olivine and pyroxene, whereas the rhyolite resulted from K-feldspar and plagioclase fractionation, without any crustal contamination affection. Tectonically, the petrogenesis process of these rocks favors an intense lithospheric extensional regime beneath the Sulu orogenic belt at 120 ~ 124 Ma, which was resulted by the widespread removal of the upper mantle and lower crust that driven by the abrupt change of the subducting direction of the Pacific plate.

  2. 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.

  3. Petrology of Quaternary volcanic rocks and related plutonic xenoliths from Gölcük volcano, Isparta Angle, Turkey: Origin and evolution of the high-K alkaline series

    NASA Astrophysics Data System (ADS)

    Platevoet, Bernard; Elitok, Ömer; Guillou, Hervé; Bardintzeff, Jacques-Marie; Yagmurlu, Fuzuli; Nomade, Sébastien; Poisson, André; Deniel, Catherine; Özgür, Nevzat

    2014-10-01

    The Quaternary volcanism of Isparta, south-western Anatolia, belongs to the post-collisional alkali-potassic to ultrapotassic magmatism, active since Miocene, from Afyon to Isparta. In the so-called Isparta Angle, the magmatism is contemporaneous with the Aegean extensional regime initiated during the Late Miocene and active throughout the Pliocene and Quaternary. The Gölcük volcano-forming stages consist of three main eruptive cycles: Cycle I comprising 200 m-thick pyroclastic flow deposits; Cycle II consisting of tephriphonolitic lava dome-flows extruded throughout the caldera; and Cycle III characterized by tuff-ring deposits related to the last phreatoplinian events. These late explosive events sampled plutonic xenoliths that allow to better constrain magma fractionation processes that operated at depth in the magma chamber. Magma evolution was first controlled by accumulation of clinopyroxene, phlogopite and apatite, then by phlogopite, amphibole and feldspars, with apatite, magnetite, titanite and zircon as accessories. Crystallization of clinopyroxene, phlogopite and amphibole probably controlled the silica-saturation trend of the whole series and faithfully reflect intensive H2O variations in the magma that were responsible of explosive cyclic events. The parental magma may have had a lamprophyric-tephritic composition. Trace element and isotope ratios indicate a prevalent asthenospheric source versus lithospheric one. Geochemical features, such as strong enrichment of LILE, REE, HFSE in the Gölcük magma point to the involvement of a asthenospheric OIB-type melt with a possible carbonatitic component, that interacted with remnants of the delaminated lithosphere during upwelling.

  4. 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.

  5. 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.

  6. 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., Jr.

    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.

  7. 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.

  8. The temporal evolution of sanukitoids in the Karelian Craton, Baltic Shield: an ion microprobe U Th Pb isotopic study of zircons

    NASA Astrophysics Data System (ADS)

    Bibikova, E. V.; Petrova, A.; Claesson, S.

    2005-01-01

    The U-Th-Pb isotopic systematics of zircons from six sanukitoid intrusions in the Karelian Craton has been investigated, using the secondary ion mass spectrometer (SIMS). Our results show that Karelian sanukitoids formed between 2745 and 2705 Ma ago and that there is an age difference of about 30 Ma between sanukitoids in the eastern and western Karelia. Results for intrusions made up of a number of magmatic phases show no internal age variation. In the east of the study region, zircons from a monzodiorite and two quartz monzonites from the Panozero pluton were dated at 2737±11, 2739±11, and 2741±8 Ma; in the Hautavaara pluton, a monzodiorite and a subalkaline granite were dated at 2743±8 and 2742±23 Ma, and a quartz diorite from the Elmus pluton gave an age of 2741±7 Ma. In addition, a lamprophyre dyke within the Sjargozero pluton gave an age of 2742±14 Ma. In the west, zircons from a quartz monzonite and a granodiorite in the Njuk intrusion gave ages of 2709±10 and 2716±11 Ma. In the Kurgelampi pluton, zircons from a diorite and two granodiorites were dated at 2707±9, 2719±6, and 2712±9 Ma, respectively. Zircons from the granodiorites and the alkaline granites contain older cores with 207Pb/ 206Pb ages greater than 2800 Ma. The absence of inherited zircons in the more mafic sanukitoids is attributed to their higher saturation levels for zirconium. Sanukitoid zircons have Th/U ratios above 0.5 and often higher, whereas nearby tonalite-tondhjemite-granodiorites (TTGs) have Th/U ratios below 0.5. Typically, tonalites are older than sanukitoids by more than 100 Ma and it is possible that tectonic processes associated with the collision of the Belomorian Mobile Belt provided the heat necessary to initiate the generation of the sanukitoid melts.

  9. Structural controls on Tertiary orogenic gold mineralization during initiation of a mountain belt, New Zealand

    NASA Astrophysics Data System (ADS)

    Craw, D.; Begbie, M.; MacKenzie, D.

    2006-10-01

    Two types of structurally controlled hydrothermal mineralization have occurred during folding of fissile schist in southern New Zealand: fold-related mineralization and normal fault-related mineralization. Both types have the same mineralogy and textures, and are dominated by quartz-ankerite veins and silicified breccias with ankeritic alteration. Most mineralized zones are thin (centimetre scale), although host schist is commonly impregnated with ankerite up to 20 m away. Thick (up to 5 m wide) mineralized zones are generally gold-bearing and contain pyrite and arsenopyrite with stibnite pods locally. Some of these auriferous zones have been extensively mined historically despite rugged topography and difficult access. Mineralization occurred during regional tectonic compression in the initial stages of development of the Southern Alps mountain belt at the Pacific-Australian plate boundary in the Miocene. Most of the gold-bearing deposits occur in east to south-east, striking normal faults that cut across mesoscopic folds in a belt that coincides with the southern termination of a regional-scale north trending antiform. Mineralized zones have similar structural control and relative timing to a nearby swarm of Miocene lamprophyre dykes and carbonatites. Limited stable isotopic data (C and O) and trace element geochemistry suggest that there was probably no genetic link between the igneous activity and gold mineralization. However, these two types of fluid flow have been controlled by the same tectonically created crustal plumbing system. This Miocene hydrothermal activity and gold deposition demonstrates that orogenic (mesothermal) mineralization can occur during the inception of an orogenic belt, not just in the latter stages as is commonly believed. These Miocene structures have been preserved in the orogen because the locus of uplift has moved northwards, so the early-formed gold deposits have not yet been structurally overprinted or eroded.

  10. 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.

  11. 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. PMID:10504135

  12. 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.

  13. 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.

  14. Age and origin of post collision Baltoro granites, south Karakoram, North Pakistan: Insights from in-situ U-Pb, Hf and oxygen isotopic record of zircons

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Mahéo, Gweltaz; Goodell, Philip C.; Pavlis, Terry L.

    2014-09-01

    Origin of post collision plutonism is critical to understand the tectonothermal evolution of the over thickened continental crust in collision zones. This has proven difficult to reconcile with the conventional whole rock geochemical and field based studies alone. We report in-situ study of zircon U-Pb, Hf and O isotopes from five samples of the Baltoro Plutonic Unit (BPU) in south Karakoram. The plutonic unit is the western part of the southern Asian margin of the India-Asia convergent zone. Baltoro granites and a biotite-rich enclave yielded similar and overlapping U-Pb ages ranging from 26 to 15 Ma. Hafnium isotopic composition (εHf (0)) is very heterogeneous ranging from - 17.1 to + 4.4 while the oxygen isotopic composition of the granites is homogeneous with mean δ18O ranging from 7.2 to 9.4‰. Based on U-Pb geochronology and Hf-O isotopic composition, the involvement of two main sources is suggested (1) Cretaceous calc-alkaline Karakoram crust and (2) Karakoram gneisses. Moreover, possible involvement of metasomatized Asian lithospheric mantle is supported by elevated oxygen composition of granites and identical Hf composition of biotite-rich enclave to the mantle derived Baltoro lamprophyre. However, direct contribution from juvenile pristine mantle is unlikely as no juvenile mantle type Hf and oxygen values were obtained. This also precludes the involvement of southward juvenile arc related component of Kohistan-Ladakh batholith. Our new U-Pb and Hf data are comparable to the Mesozoic Karakoram batholith, Miocene two-mica leucogranites in the Pangong Range and magmatism from the Lhasa terrane in south Tibet, suggesting a genetic link between the Karakoram and the rocks to the east. This magmatic event is best explained by lower crust partial melting promoted by both thermal equilibration following crustal thickening and heat advection by ultrapotassic magmas associated with the breakoff of the Indian continental margin.

  15. 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.

  16. 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.

  17. 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

  18. Post-collisional and intraplate Cenozoic volcanism in the rifted Apennines/Adriatic domain

    NASA Astrophysics Data System (ADS)

    Bianchini, G.; Beccaluva, L.; Siena, F.

    2008-02-01

    -dependent, with generation of tholeiites to nephelinites/alkaline lamprophyres by decreasing degrees of partial melting ( F = 25 to ≤ 5%) of lherzolite lithospheric sources at progressively increasing depths (ca. 40 to 100 km). Moreover, geochemical features of these anorogenic magmas testify that their mantle sources are remarkable homogeneous, as also confirmed by lack of veining in the VVP mantle xenoliths. This homogeneity suggests that Na-metasomatic agents pervasively affected the overlying Adriatic lithospheric mantle by porous flow mechanisms without causing significant inhomogeneities at a regional scale.

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. The magmatic record in the Arghash region (northeast Iran) and tectonic implications

    NASA Astrophysics Data System (ADS)

    Alaminia, Zahra; Karimpour, Mohammad Hassan; Homam, Seyed Massoud; Finger, Fritz

    2013-09-01

    Eocene magmatism in the Arghash Massif is interpreted as related to thermal anomalies in crust and mantle that developed when the Sabzevar subduction system collapsed. The youngest magmatic activities in the Arghash Massif are lamprophyres and small intrusions of quartz-monzodiorite porphyries, which cut through all other rocks including an Oligocene-Miocene conglomerate cover series.

  4. 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

  5. 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

  6. 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

  7. 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

  8. K-T magmatism of western Rajasthan, India: Manifestation of Reunion plume activity or extensional lithospheric tectonics?

    NASA Astrophysics Data System (ADS)

    Sharma, K.

    2004-12-01

    A number of alkaline plutons have been recorded at the K-T (Cretaceous-Tertiary) boundary in western Rajasthan, India. Significant magmatism occurred at Mundwara, Barmer, Sarnu-Dandali and Tavider. The evolution of the Cambay-Sanchor-Barmer rift during the K-T period resulted in these alkaline complexes at the rift margins. Sedimentary basins are developed in the Barmer and Jaiselmer regions. The magmatism of Mundwara and Sarnu-Dandali is dated at 68.50 Ma and considered as an early pulse of Deccan volcanism. Several workers correlated K-T sedimentary basin evolution, magmatism and other tectonic features of western Rajasthan with the Reunion plume-interaction in the northwestern Indian shield. Alkaline igneous complexes along the rift from the southern part are reported from Phenai Mata, Amba Dongar and Seychelles. The Seychelles was part of the northwestern Indian shield prior to Deccan volcanism. The Mundwara igneous complex represents three distinct circular plutonic bodies - Toa, Mer and Mushala, which are situated in the periphery of an area three kilometers in radius. Besides these, there are numerous concentric and radial dykes of lamprophyre, carbonatite, dolerite and amphibolite. All these three bodies represent different phases of intrusion and are not similar to each other. The alkaline rocks of Sarnu-Dandali occur as dykes and isolated plugs in the desert sand. Carbonatite dykes are also reported from southeast of Barmer. The Tavider outcrop is devoid of any plutonic rock and consists of rhyolite, andesite and basalt. These rocks occur along the Precambrian Malani magmatic lineaments. The development of the Cambay-Sanchor-Barmer rift caused reactivation of Precambrian fractures and resulted in magmatism at the basin margin. The Gondwanaland fragmentation during the Mesozoic era caused extensional tectonics in the northwestern Indian shield. This led to the development of rift basins in Gujarat and western Rajasthan. Deccan volcanism, separation of the

  9. 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.

  10. The Archaean sanukitoid series of the Baltic Shield: geological setting, geochemical characteristics and implications for their origin

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, S. B.; Rollinson, H. R.; Chekulaev, V. P.; Arestova, N. A.; Kovalenko, A. V.; Ivanikov, V. V.; Guseva, N. S.; Sergeev, S. A.; Matukov, D. I.; Jarvis, K. E.

    2005-01-01

    Archaean high-Mg granitoids (sanukitoids) occur in the Karelian granite-greenstone terrain in the Baltic Shield in two distinct zones. In the west of the Shield sanukitoid intrusions formed between 2700 and 2720 Ma and consist of a single igneous phase that varies in composition from diorite to granite. In the Eastern part of the Shield, sanukitoid intrusions formed between 2730 and 2745 Ma and are strongly differentiated, varying in composition from ultramafic to felsic. All the sanukitoids are enriched in light rare earth elements (LREE: La≤80 ppm, Ce≤150 ppm, La N/Yb N≤30-40), Sr≤2000 ppm, Ba≤2500 ppm, P 2O 5≤1.5%, alkalis (Na 2O+K 2O=5-10%), possess high mg# values (0.50-0.65), and show a negative Nb-Ta anomaly. They are spatially and temporally related to syenite intrusions and lamprophyre dykes. Sanukitoid intrusions in the Western and Eastern zones differ in composition. In the west, they have higher SiO 2 (mainly>60%) and lower alkalis, Sr, Ba, LREE than in the Eastern zone intrusions. The most differentiated intrusion, the Panozero intrusion in the Eastern zone, was formed in two magmatic cycles separated by ductile deformation. In the first cycle, ultramafic to monzonitic rocks formed, whereas, in the second cycle, the magmas were monzodioritic to quartz monzonite. Ultramafic and mafic rocks make up about 10% of the outcrop and occur as enclaves in monzonites and monzodiorites, and, as dykes, implies a number of discrete magmatic events. All rocks of the Panozero intrusion have high K 2O, and the composition of the initial melt, calculated from the weighted average of the first cycle magmas is monzodiorite (SiO 2=52%, mg#=0.55, Na 2O+K 2O˜6%). The presence of magmatic hornblende and biotite, a high carbonate content, widely distributed explosive breccias and evidence of liquid immiscibility are consistent with a high H 2O-CO 2 content in the sanukitoid melt. The geodynamic model which most satisfactorily explains our geological and

  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. Petrology of an unusual orthopyroxene-bearing minette suite from southeastern Peru, Eastern Andean Cordillera: Al-rich lamproites contaminated by peraluminous granites

    NASA Astrophysics Data System (ADS)

    Carlier, Gabriel; Lorand, Jean-Pierre; Audebaud, Etienne; Kienast, Jean-Robert

    1997-01-01

    The Puno minettes (Eastern Andean Cordillera, southern Peru) are phlogopite-phyric rocks with a groundmass consisting mainly of phlogopite, alkali feldspar and apatite microphenocrysts and/or microlites. They display the strong large-ion-lithophile-element enrichments that characterize potassic to ultrapotassic rocks of the lamprophyre clan (Rb, Ba, Sr up to 10 3× Primordial Mantle, REE up to 6.10 2× CI-chondrites). In addition to their close association with granitoids, the rocks of this series show many features of minettes occurring in arc-related collisional zones, i.e., absence of mantle xenoliths, up to 30 vol.% felsic xenocrysts and strong negative Nb and Ti anomalies. However, they are distinguished by unusual phenocryst phases, whole-rock compositions and groundmass mineralogy. Some minettes contain only a few per cent of biotite±quartz±plagioclase xenocrysts immersed in a typical minette groundmass whereas those richer in xenocrysts display the complete liquidus paragenesis of the coexisting peraluminous granite (biotite+quartz+plagioclase+alkali feldspar+cordierite+zircon+pyrite) in a high-K latitic to trachydacitic groundmass. Field relations, radiometric ages, whole-rock data and felsic xenocrysts all indicate that the Puno minettes result from a mixing process involving Al-rich lamproites and peraluminous monzogranites. The most common phenocryst assemblage (highly magnesian phlogopite+olivine±titanian Cr-spinel±Ca-rich enstatite±magnesian ilmenite±Al- and Ti-poor diopside) is similar to that reported in Al-rich phlogopite lamproites from southeastern Spain. Likewise, the host rocks have diagnostic features of Spanish phlogopite lamproites (e.g., K 2O/Al 2O 3 ratios >9, CaO contents <2 wt.%, negative Ba and Sr anomalies in primitive mantle-normalized multi-element plots, La N/Nd N<1.5). Graphite in the groundmass and Cr-spinel and ilmenite compositions devoid of Fe 3+ suggest strongly reduced conditions of formation. Another phenocryst

  13. Magmatic origin of alkaline meta-igneous rocks from Chamberlindalen, SW Svalbard

    NASA Astrophysics Data System (ADS)

    Goluchowska, Karolina; Barker, Abigail; Manecki, Maciej; Czerny, Jerzy; Majka, Jaroslaw

    2014-05-01

    This study focuses on the late Neoproterozoic meta-igneous rocks of SW Svalbard to determine their magmatic evolution, conditions of magma storage and origin. The samples from the Chamberlindalen area form an alkaline igneous suite, from which thin dikes and intrusive bodies have been collected. The rocks in question intrude Late Neoproterozoic metasediments and are surrounded by occurrences of Neoproterozoic metabasalts in contrast to highly alkaline the Chamberlindalen intrusions. The rocks from Chamberlindalen are divided into two groups based on their geochemistry, mineralogy and field relationships. The dikes, classify as minettes, belonging to the lamprophyre group and contain mainly euhedral, elongated phlogopite and additionally clinopyroxene and feldspar. The rest of the samples are highly magnesian and are classified as alkali gabbro. The alkali gabbros contain primary magmatic minerals such as clinopyroxene, calcic amphibole and mica in different proportions. The alkali gabbros are enriched in LREE and HFSE and depleted in P, K and HREE. The minette dikes are always more enriched in HFSE and REE in comparison to the alkali gabbros. The mineral chemistry of the alkali gabbros reveals that pyroxenes are represented by diopside with Wo46-51 En35-46 Fs6-14, and calcic amphibole by kaersutite. The Mg# number for diopside is from 72 - 88, whereas for kaersutite Mg# number is 51 - 74. Thermobarometry calculations for diopside and kaersutite have been performed. In the alkali gabbros from Chamberlindalen, diopside crystallized between 0.7 - 8 kbar and 1152 - 1233°C. Results for kaersutite reveal that they crystallized between 5 - 17 kbar and 1043 - 1215°C. For diopside the main crystallization was between 10 and 38 km, whereas for kaersutite, the main crystallization was between 30 and 50 km. Clinopyroxene and minor kaersutite also show a zone of crystallization at 2 to 10 km. This reflects a main crystallization zone at 10 - 50 km throughout the continental

  14. Chemical and isotopic composition of the lower crust beneath the Meguma Lithotectonic Zone, Nova Scotia: evidence from granulite facies xenoliths

    NASA Astrophysics Data System (ADS)

    Eberz, G. W.; Clarke, D. B.; Chatterjee, A. K.; Giles, P. S.

    1991-03-01

    Granulite-facies xenoliths from an Upper Devonian lamprophyre dyke near Tangier, Nova Scotia, provide new information about the lower crust in the Meguma Zone. Two mineralogically and chemically distinet groups of xenoliths occur. Both groups contain quartz+feldspar+biotite+Fe-Ti oxides+sulfides. In addition, group A contains garnet+graphite±[aluminosilicates+spinel±sapphirine (hight Al2O3 subgroups A1 and A2)] or [clinopyroxene+sphene+apatite (high CaO sub-group A3)]. Group B has highly variable proportions of orthopyroxene (B1), clinopyroxene (B2), and amphibole (B3). Trace-element contents of the highly aluminous xenoliths compare closely with average to upper crustal model compositions and are similar in many aspects to other “undepleted” granulite-facies rocks. Low P-T sedimentary assemblages of quartz-chlorite-clay minerals-calcite-albite or paragonite can account for the compositions of group A xenoliths. Within group B, a high-MgO (MgO>13 wt%) subgroup with high transition-metal contents, and low-MgO (MgO<9 wt%) sub-groups with higher LIL (large-ion-lithophile) element contents exist. Although the rare-earth and high-field-strength elements indicate a tholeiitic or low-K calc-alkaline chemistry, the LIL elements are as high as those from high-K calc-alkaline volcanic are rocks. Isotopically, group A ranges from ɛNdt=-2.56 to-0.80 and87Sr/86Sr t =0.7046 to 0.7182 for t=370 Ma. For group B these values are +1.45 to +5.33 and 0.7028 to 0.7048, respectively. Model ages (TCHUR) are correspondingly low and are tightly constrained (544±52 Ma). These “young” ages contrast with the middle Proterozoic Nd model ages of the overlying Meguma Zone low-grade flysch. This time-inverted stratigraphy appears to be the product of a tectonic break between a younger autochthonous Tangier lower crust (≡Avalon), and an older allochthonous Meguma Group upper crust.

  15. 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

  16. 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.

  17. 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

  18. 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

  19. 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

  20. 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

  1. 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

  2. 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

  3. 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

  4. A tale of two magmas: Petrological insights into mafic and intermediate Plinian volcanism at Volcán de Colima, Mexico

    NASA Astrophysics Data System (ADS)

    Crummy, J. M.; Savov, I. P.; Morgan, D. J.; Wilson, M.; Loughlin, S.; Navarro-Ochoa, C.

    2012-12-01

    recrystallisation and re-equilibration within a compositionally different melt. This composition of the clinopyroxene is similar to that of the Group I magmas. Whole-rock geochemical and Sr and Nd isotopic analyses reveal strong trends in the Group II magmas towards the composition of monogenetic cinder cones composed of phlogopite-bearing alkaline lamprophyre situated to the north of Volcán de Colima. The alkaline magmas are thought to have formed from partial melting of metasomatically enriched veins within the lithospheric mantle. We suggest the high Mg clinopyroxene cores of the Group II magmas crystallised from such alkaline melts, which then mixed with the parental mantle-derived melts of the Group I magmas. Geothermometry and hygrometry based on mineral-mineral and mineral-melt equilibria reveal no correlation between variations in eruption temperature (930-1000°C) and magmatic H2O content (3-6 wt.%) with magma composition. This implies magma composition and volatile content are not controlling the highly explosive mafic and intermediate eruptions at Volcán de Colima, but rather, are driven by very fast ascent rates from source to surface.

  5. Qualitative and quantitative analyses of magmatic stoping in the roof of the Proterozoic Åva ring complex

    NASA Astrophysics Data System (ADS)

    Krumbholz, Michael; Burchardt, Steffi

    2013-04-01

    determine their size, orientation, and shape. In addition, we measured the strike of the internal foliation in relation to the undisturbed country rock for each individual xenolith. The spatial xenolith distribution pattern and the close assemblage of fragments of a wide range of sizes indicate that stoping is a rapid and efficient process. The size distribution closely resembles a power-law distribution over several orders of magnitude, even if modified by stereographic effects. The results of the shape analysis indicate that the fragmentation process is strongly controlled by the host-rock foliation, expressed in alternating aspect ratios with respect to the xenolith size. First fragmentation occurs parallel to the foliation, resulting in high aspect ratios of large xenoliths. Further fragmentation reduces block aspect ratios cracking the blocks perpendicular to their long axis, before fragmentation parallel to the foliation becomes dominant again, producing small blocks with high aspect ratios. References Daly, R. A., 1903. The mechanics of igneous intrusion. American Journal of Science 15, 269- 298. Eklund, O. and Shebanov, A. D., 2005. Prolonged postcollisional shoshonitic magmatism in the southern Svecofennian domain - a case study of the Åva granite-lamprophyre ring complex. Lithos 80: 229-247.

  6. Geochemical, zircon U-Pb dating and Sr-Nd-Hf isotopic constraints on the age and petrogenesis of an Early Cretaceous volcanic-intrusive complex at Xiangshan, Southeast China

    NASA Astrophysics Data System (ADS)

    Yang, Shui-Yuan; Jiang, Shao-Yong; Jiang, Yao-Hui; Zhao, Kui-Dong; Fan, Hong-Hai

    2011-01-01

    The Late Mesozoic geology of Southeast China is characterized by extensive Jurassic to Cretaceous magmatism consisting predominantly of granites and rhyolites and subordinate mafic rocks, forming a belt of volcanic-intrusive complexes. The Xiangshan volcanic-intrusive complex is located in the NW region of the belt and mainly contains the following lithologies: rhyodacite and rhyodacitic porphyry, porphyritic lava, granite porphyry with mafic microgranular enclaves, quartz monzonitic porphyry, and lamprophyre dyke. Major and trace-element compositions, zircon U-Pb dating, and Sr-Nd-Hf isotopic compositions have been investigated for these rocks. The precise SHRIMP and LA-ICP-MS zircon U-Pb dating shows that the emplacement of various magmatic units at Xiangshan took place within a short time period of less than 2 Myrs. The stratigraphically oldest rhyodacite yielded a zircon U-Pb age of 135 ± 1 Ma and the overlying rhyodacitic porphyry has an age of 135 ± 1 Ma. Three porphyritic lava samples yielded zircon U-Pb ages of 136 ± 1 Ma, 132 ± 1 Ma, and 135 ± 1 Ma, respectively. Two subvolcanic rocks (granite porphyry) yielded zircon U-Pb ages of 137 ± 1 Ma and 137 ± 1 Ma. A quartz monzonitic porphyry dyke, which represented the final stage of magmatism at Xiangshan, also yielded a zircon U-Pb age of 136 ± 1 Ma. All these newly obtained precise U-Pb ages demonstrate that the entire magmatic activity at Xiangshan was rapid and possibly took place at the peak of extensional tectonics in SE China. The geochemical data indicate that all these samples from the volcanic-intrusive complex have an A-type affinity. Sr-Nd-Hf isotopic data suggest that the Xiangshan volcanic-intrusive complex derived mainly from remelting of Paleo-Mesoproterozoic crust without significant additions of mantle-derived magma. However, the quartz monzonitic porphyry, which has zircon Hf model ages older than the whole-rock Nd model ages, and which has ɛNd(T) value higher than the other rocks

  7. 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.

  8. 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.

  9. 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

  10. Kimberlite and related rocks from Garnet Lake, West Greenland, including their mantle constituents, diamond occurrence, age and provenance

    NASA Astrophysics Data System (ADS)

    Hutchison, Mark T.; Frei, Dirk

    2009-11-01

    around 1258 °C and 6.20 GPa, equivalent to a depth of 195 km along a 41 mWm -2 mantle geotherm. Garnet Lake xenoliths thus lie at the deepest extent of mantle samples recovered from western Greenland lamprophyric rocks and from well within the diamond stability field. Diamonds are typically colourless and occur as fragments or with a dominant octahedral morphology. Crysts exhibit very high quantities of nitrogen (up to 2133 ppm N) and yet are not strongly aggregated to IaB centres (typically about 33% aggregation). This suggests either a short residence time, low residence temperature or likely a combination of both. Employing the restricted range of equilibrium conditions exhibited by mantle xenoliths, calculated diamond formation ages peaking around 583-593 Ma are favoured. This is a short time before the 568 Ma Garnet Lake main sheet emplacement age which coincides with the age of the nearby Sarfartoq carbonatite complex. A model of mantle refertilisation and diamond formation culminating in conditions favourable for creating carbonate-rich melts acting as carriers of mantle constituents to the surface is presented. Data suggest close temporal, chemical and geographic associations between kimberlite, aillikite and carbonatite.

  11. The Aurora volcanic field, California-Nevada: oxygen fugacity constraints on the development of andesitic magma

    NASA Astrophysics Data System (ADS)

    Lange, R. A.; Carmichael, Ian S. E.

    1996-10-01

    The Aurora volcanic field, located along the northeastern margin of Mono Lake in the Western Great Basin, has erupted a diverse suite of high-K and shoshonitic lava types, with 48 to 76 wt% SiO2, over the last 3.6 million years. There is no correlation between the age and composition of the lavas. Three-quarters of the volcanic field consists of evolved (<4 wt% MgO) basaltic andesite and andesite lava cones and flows, the majority of which contain sparse, euhedral phenocrysts that are normally zoned; there is no evidence of mixed, hybrid magmas. The average eruption rate over this time period was ˜200 m3/km2/year, which is typical of continental arcs and an order of magnitude lower than that for the slow-spreading mid-Atlantic ridge. All of the Aurora lavas display a trace-element signature common to subduction-related magmas, as exemplified by Ba/Nb ratios between 52 and 151. Pre-eruptive water contents ranged from 1.5 wt% in plagioclase-rich two-pyroxene andesites to ˜6 wt% in a single hornblende lamprophyre and several biotite-hornblende andesites. Calculated oxygen fugacities fall within 0.4 and +2.4 log units of the Ni-NiO buffer. The Aurora potassic suite follows a classic, calc-alkaline trend in a plot of FeOT/MgO vs SiO2 and displays linear decreasing trends in FeOT and TiO2 with SiO2 content, suggesting a prominent role for Fe-Ti oxides during differentiation. However, development of the calc-alkaline trend through fractional crystallization of titanomagnetite would have caused the residual liquid to become so depleted in ferric iron that its oxygen fugacity would have fallen several log units below that of the Ni-NiO buffer. Nor can fractionation of hornblende be invoked, since it has the same effect as titanomagnetite in depleting the residual liquid in ferric iron, together with a thermal stability limit that is lower than the eruption temperatures of several andesites (˜1040 1080°C; derived from two-pyroxene thermometry). Unless some progressive

  12. 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

  13. 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

  14. 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

  15. The Chineysky layered massif (Siberia, Russia) and Upper Zone of the Bushveld Complex: resemblance and difference features

    NASA Astrophysics Data System (ADS)

    Gongalskiy, B.; Krivolutskaya, N.

    2009-04-01

    : 1) consecutive introduction of magmas of different composition; 2) stratification of different nature; 3) differently grade rhythmicity. The Chineysky massif is thought to have been produced by successive emplacement of magmas, which formed four rock groups. These are the pyroxenite of the first group, titanomagnetite gabbronorites and leucogabbro of the second group, gabbronorites of the third group, and lamprophyres of the fourth group The trace-element patterns of various rocks and the results of simulations by the COMAGMAT-3.5 computer program led us to believe that all four rock groups of the massif were generated by the successive emplacements of several portions of the initial magma, which was a complicatedly differentiated suspension of olivine, plagioclase, and magnetite crystals in ferroabsaltic melt at a temperature of approximately 1130°л. The gravitational separation of these phases in the melt before its emplacement into the chamber and during the subsequent emplacement of various portions of the initial magma into the modern chamber predetermined the heterogeneity of the massif (its block structure). As a result, the bulk of the Chineysky massif is composed of compositionally principally different rocks of the second and third groups, with the predominance of intratelluric plagioclase and magnetite crystals in the former case (gabbronorite and leucogabbro series in the western and southeastern blocks) and orthopyroxene in the latter one (norite series, central block). The rocks of the third group were generated later. The crystallization sequences of minerals modeled for the Chineysky massif can be classed into two major types [2]: (a) "high-Al", which is typical of the "leucogabbro" compositions and characterized by the occurrence of a magnetite-plagioclase cotectic, and (b) "high-Mg", which is typical of the noriteseries and is characterized by the early appearance of olivine on the liquidus or the concurrent crystallization of this mineral with

  16. 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