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Sample records for a-type granitic magmatism

  1. Nature and origin of Proterozoic A-type granitic magmatism in the southwestern United States of America

    NASA Astrophysics Data System (ADS)

    Anderson, J. Lawford; Bender, E. Erik

    1989-06-01

    .75. Such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust. The high-f O 2 Holy Moses and Hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust. This boundary is also approximately equivalent to significant changes in the Nd and Pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane. On a global scale, the crust-forming orogenies ended by 1.6 Ga ago and the continents entered a long-lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite, mafic dike swarms, charnockite and anorthosite. The absence of orogenic deformation implies that plate consumption became intraoceanic during this time. The profuse and widespread nature of the igneous activity has no Phanerozoic analogue and is considered to be unique to the Proterozoic. A crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle, the eventual rise of mantle plumes, and the transfer of heat into the youthful, undifferentiated Proterozoic crust. Subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization, a process that would continue until both the mantle and crust reached a stable configuration.

  2. Grenvillian magmatism in the northern Virginia Blue Ridge: Petrologic implications of episodic granitic magma production and the significance of postorogenic A-type charnockite

    USGS Publications Warehouse

    Tollo, R.P.; Aleinikoff, J.N.; Borduas, E.A.; Dickin, A.P.; McNutt, R.H.; Fanning, C.M.

    2006-01-01

    Grenvillian (1.2 to 1.0 Ga) plutonic rocks in northern Virginia preserve evidence of episodic, mostly granitic magmatism that spanned more than 150 million years (m.y.) of crustal reworking. Crystallization ages determined by sensitive high resolution ion microprobe (SHRIMP) U-Pb isotopic analyses of zircon and monazite, combined with results from previous studies, define three periods of magmatic activity at 1183-1144 Ma (Magmatic Interval I), 1120-1111 Ma (Magmatic Interval II), and 1078-1028 Ma (Magmatic Interval III). Magmatic activity produced dominantly tholeiitic plutons composed of (1) low-silica charnockite, (2) leucogranite, (3) non-leucocratic granitoid (with or without orthopyroxene (opx)), and (4) intermediate biotite-rich granitoid. Field, petrologic, geochemical, and geochronologic data indicate that charnockite and non-charnockitic granitoids were closely associated in both space and time, indicating that presence of opx is related to magmatic conditions, not metamorphic grade. Geochemical and Nd isotopic data, combined with results from experimental studies, indicate that leucogranites (Magmatic Intervals I and III) and non-leucocratic granitoids (Magmatic Intervals I and II) were derived from parental magmas produced by either a high degree of partial melting of isotopically evolved tonalitic sources or less advanced partial melting of dominantly tonalitic sources that also included a more mafic component. Post-orogenic, circa 1050 Ma low-silica charnockite is characterized by A-type compositional affinity including high FeOt/(FeOt + MgO), Ga/Al, Zr, Nb, Y, and Zn, and was derived from parental magmas produced by partial melting of potassic mafic sources in the lower crust. Linear geochemical trends defined by leucogranites, low-silica charnockite, and biotite-rich monzogranite emplaced during Magmatic Interval III reflect differences in source-related characteristics; these features do not represent an igneous fractionation sequence. A

  3. Mesozoic Granitic Magmatism in Macao, Southeast China

    NASA Astrophysics Data System (ADS)

    Quelhas, P. M.; Mata, J.; Lou, U. T.; Ribeiro, M. L.; Dias, Á. A.

    2016-12-01

    Macao ( 30 Km2) is a territory characterized by small granitic intrusions, located along the coastal region of Southeast China (Cathaysia Block). Granitoids occur as different facies, including microgranite dykes, with distinct textural, mineralogical and geochemical features, for which a middle-upper Jurassic age ( 164 Ma) has been proposed. New data suggest that these granitoids are mostly high-K calc-alkaline metaluminous (A/CNK = 0.8 - 1.1) biotite granites, consistent with total absence of primary muscovite. They show variable amounts of SiO2 (67-77%), reflecting different degrees of magmatic evolution. There is also variability in terms of trace elements, particularly Rare Earth Elements (REEs), evidenced by decreasing (La/Sm)N, (Gd/Lu)N, (Ce/Yb)N and (Eu/Eu*)N towards the more evolved samples, which can be partly attributed to fractional crystallization processes. Most of the granitoids are characterized by (La/Yb)N = 3 - 10.8, showing negative Ba, Nb, Sr, Zr, P, Ti and Eu anomalies. On the other hand, microgranite dykes, along with a few more evolved granites, show an opposite tendency, being usually enriched in HREEs relatively to LREEs with (La/Yb)N = 0.4 - 1.1. Our data suggests intermediate genetic affinities between I-type and A-type granites. Although these granitoids are mostly metaluminous (characteristic of I-types), Ga/Al ratios, usually used to identify A-types, are close to the accepted boundary between A-type and other granite types. The affinities with A-type granites are more marked for the more evolved facies, which depict higher values of FeOt/MgO (14 - 60) and K2O/MgO (60 - 250). Their trace element characteristics are also transitional between WPG (Within-plate granites) and Syn-COLG (Collision Granites). We interpret those transitional characteristics (A/I and WPG/Syn-COLG) of Macao granitoids as reflecting an origin by melting of infracrustal sources over a period of high heat transfer from mantle to crust during an extensional tectonic

  4. The Late Cretaceous I- and A-type granite association of southeast China: Implications for the origin and evolution of post-collisional extensional magmatism

    NASA Astrophysics Data System (ADS)

    Zhao, Jiao-Long; Qiu, Jian-Sheng; Liu, Liang; Wang, Rui-Qiang

    2016-01-01

    We present new geochronological, mineralogical, and geochemical data for granitic plutons that crop out within the Zhoushan archipelago, northeastern coastal Zhejiang Province, in order to constrain their origin, and the genetic relationship between the I- and A-type granites. These granites can be divided into two groups: (1) the northern I-type Putuoshan (PTS) and Dadong'ao (DDA) plutons; and (2) the southern A-type Daqingshan (DQS), Taohuadao (THD), and Xiazhidao (XZD) plutons. Zircon LA-ICP-MS U-Pb dating yielded ages of 98-96 Ma for the northern I-type plutons and 89-86 Ma for the southern A-type plutons. All of these granites are highly siliceous, K-rich, and have similar total alkali and total rare earth element (REE) abundances. However, there are also geochemical differences between the I-type and the A-type granites. The northern I-type alkali-feldspar granites are high-K calc-alkaline, metaluminous to mildly peraluminous, contain low concentrations of the high field strength elements (HFSE; e.g., Nb, Ta, Zr, and Hf), and have low Ga/Al ratios (2.04-2.44). In contrast, the southern A-type granites are peralkaline and F-rich, and have lower CaO and Al2O3 concentrations, and higher Fe2O3T and HFSE concentrations and Ga/Al ratios (3.25-3.86). Meanwhile, they have slightly higher heavy REE (HREE) concentrations, and are more depleted in Ba, Sr, P, Ti, and Eu than the northern I-type granites. Both the I- and A-type granites have homogeneous whole-rock Nd and highly variable zircon Hf isotopic compositions. Of note, the southern peralkaline A-type granites appear to have more radiogenic Nd and Hf isotope compositions than the northern I-type granites. The present data, together with the results of a previous study on mafic enclaves within the PTS pluton, suggest that the northern I-type alkali-feldspar granites were generated by mixing of mantle-derived material with crustal-derived magmas that formed by dehydration melting of mica-bearing basaltic rocks

  5. Zircon U-Pb ages and geochemistry of Devonian A-type granites in the Iraqi Zagros Suture Zone (Damamna area): New evidence for magmatic activity related to the Hercynian orogeny

    NASA Astrophysics Data System (ADS)

    Abdulzahra, Imad Kadhim; Hadi, Ayten; Asahara, Yoshihiro; Azizi, Hossein; Yamamoto, Koshi

    2016-11-01

    The Damamna granite (DG) is located in the Shalair Valley area in northeast Iraq within the Sanandaj Sirjan Zone (SSZ). The zircon U-Pb ages for the DG rocks are 364-372 Ma, indicating crystallization of the granitic body. The DG rocks are A-type granites, hypersolvus and peraluminous. They are enriched in SiO2, alkalis, Ga/Al, Ga, Zr and Rb/Sr and depleted in CaO, MgO, Sr, P, and Ti. These rocks show steep REE patterns, with LREE enrichment relative to HREE ((La/Yb)N = 5.7-42.5) and pronounced negative Eu anomalies reflecting feldspar fractionation. The geochemical characteristics and relationships suggest that the DG rocks are anorogenic and were emplaced in an extensional tectonic regime having an OIB-like magma affinity. The DG rocks are characterized by low Y/Nb ratios (0.2-1.5) and positive εNd (371 Ma) values (+ 1.6 to + 4.2), which indicate a mantle origin. In the Y/Nb-Yb/Ta diagram, the DG rocks plot in the A1-type granite field, with slightly higher Y/Nb values and a tendency of transitioning from A1 to the nearby A2 field, which possibly indicates a slight crustal contamination effect. The isotopic and geochemical data suggest that a combination of enriched mantle source magma with crustal contamination and fractional crystallization contributed to the generation of the magma for the DG. The geochemical and geochronological results for the DG rocks in the SSZ suggest an extensional zone that probably represents an early stage of Neo-Tethys opening during the Late Devonian or earlier, and this was associated with the Hercynian orogeny and tectono-magmatic activity in northern Arabia and northwestern Iran.

  6. Magnetic Properties of Hydrothermalized A-type Red Granites

    NASA Astrophysics Data System (ADS)

    Trindade, R. I. F.; Nédélec, A.; Peschler, A.; Archanjo, C. J.; Poitrasson, F.; Bouchez, J. L.

    Hydrothermalized A-type granites are commonly identified by their pink to red-brick colour attributed to tiny flakes of hematite in the alkali feldspars. These inclusions can be of interest in magnetic studies, but their timing and process of formation are still unclear. Formation of chlorite after biotite is the commonest effect of hydrother- malization and may occur quite early after crystallization due to late-magmatic or externally-derived fluids. The reddish colour appears at a later stage. Five cases of A-type granites were investigated for their magnetic mineralogy and properties. The selected cases range from nearly unmodified granites (Panafrican stratoid granites of Madagascar) to strongly hydrothermalized ones (Meruoca, Brazil; Tana, Corsica); in- termediate cases are : Mount Scott (Oklahoma), Bushveld (granitic core kindly pro- vided by R.G. Cawthorn) and. Hydrothermal alteration is often associated to a de- crease of the magnetic susceptibility magnitude (K) and of the anisotropy degree (P). It also strongly affects the rockt's bulk coercivity parameters, since alteration changes the relative amounts of coarse-grained primary magnetite, fine-grained PSD to SD sec- ondary magnetite, and hematite. Correspondingly, most samples plot away from the magnetite trend in the Dayt's diagram, but the different groups identified after coer- civity parameters do not directly correlate with whole-rock colour. In addition, IRM- acquisition curves and thermal demagnetization of tri-axial IRM show that hematite occurs in almost all analysed samples despite their colour. Various hematite coercivity ranges are also evidenced. In fact, hematite can be formed either in feldspar crys- tals or after magnetite. Tiny hematite within feldspars can appear either by exsolu- tion process or, more likely, by precipitation from a fluid phase. For these reasons, hematite inclusions may carry a remanence acquired shortly after granite crystalliza- tion or, conversely, a recent

  7. Preface to special issue: Granite magmatism in Brazil

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; de Pinho Guimarães, Ignez; Nardi, Lauro Valentim Stoll

    2016-07-01

    Granites are important both to the geologic evolution and to the economy of Brazil. Deposits of precious and rare metals, such as Au, Sn and many others, are directly or indirectly associated with granites, especially in the geologically under-explored Amazon region. On the opposite eastern side of the country, expanding exploitation of natural granite as dimension stone makes Brazil currently the world's second largest exporter of granite blocks. Granites are a major constituent of the Brazilian Archean-Proterozoic cratonic domains (the Amazon and São Francisco cratons) and their surrounding Neoproterozoic fold belts. The granites are thus fundamental markers of the major events of crustal generation and recycling that shaped the South American Platform. As a result, Brazilian granites have received great attention from the national and international community, and a number of influential meetings focused on the study of granites were held in the country in the last three decades. These meetings include the two International Symposia on Granites and Associated Mineralization (Salvador, January 21-31, 1987, and August 24-29, 1997), the Symposium on Rapakivi Granites and Related Rocks (Belém, August 2-5, 1995) and the Symposium on Magmatism, Crustal Evolution, and Metallogenesis of the Amazonian Craton (Belém, August 2006). Special issues dedicated to contributions presented at these meetings in the Journal of South American Earth Sciences (Sial et al., 1998), Lithos (Stephens et al., 1999), Canadian Mineralogist (Dall'Agnol and Ramo, 2006), Precambrian Research (Ramo et al., 2002) and Anais da Academia Brasileira de Ciências (Dall'Agnol and Bettencourt, 1997; Sial et al., 1999a) are still important references on the knowledge of Brazilian granites and granite petrology in general.

  8. Comparison of Proterozoic and Phanerozoic rift-related basaltic-granitic magmatism

    NASA Astrophysics Data System (ADS)

    Haapala, Ilmari; Rämö, O. Tapani; Frindt, Stephen

    2005-03-01

    This paper compares the 1.67-1.47 Ga rapakivi granites of Finland and vicinity to the 1.70-1.68 Ga rapakivi granites of the Beijing area in China, the anorogenic ˜130 Ma granites of western Namibia, and the 20-15 Ma granites of the Colorado River extensional corridor in the Basin and Range Province of southern Nevada. In Finland and China, the tectonic setting was incipient, aborted rifting of Paleoproterozoic or Archean continental crust, in Namibia it was continental rifting and mantle plume activity that led to the opening of southern Atlantic at ˜130 Ma. The 20-15 Ma granites of southern Nevada were related to rifting that followed the Triassic-Paleogene subduction of the Farallon plate beneath the southwestern United States. In all cases, extension-related magmatism was bimodal and accompanied by swarms of diabase and rhyolite-quartz latite dikes. Rapakivi texture with plagioclase-mantled alkali feldspar megacrysts occurs in varying amounts in the granites, and the latest intrusive phases are commonly topaz-bearing granites or rhyolites that may host tin, tungsten, and beryllium mineralization. The granites are typically ferroan alkali-calcic metaluminous to slightly peraluminous rocks with A-type and within-plate geochemical and mineralogical characteristics. Isotope studies (Nd, Sr) suggest dominant crustal sources for the granites. The preferred genetic model is magmatic underplating involving dehydration melting of intermediate-felsic deep crust. Juvenile mafic magma was incorporated either via magma mingling and mixing, or by remelting of newly hybridized lower crust. In Namibia, partial melting of subcontinental lithospheric mantle was caused by the Tristan mantle plume, in the other cases the origin of the mantle magmatism is controversial. For the Fennoscandian suites, extensive long-time mantle upwelling associated with periodic, migrating melting of the subcontinental lithospheric mantle, governed by heat flow and deep crustal structures, is

  9. ASTEROIDAL GRANITE-LIKE MAGMATISM 4.53 GYR AGO

    SciTech Connect

    Terada, Kentaro; Bischoff, Addi

    2009-07-10

    Constraining the timescales for the evolution of planetary bodies in our solar system is essential for a complete understanding of planet-forming processes. However, frequent collisions between planetesimals in the early solar system obscured and destroyed much of the primitive features of the old, first-generation planetary bodies. The presence of differentiated, achondritic clasts in brecciated chondrites and of chondritic fragments in achondritic breccias clearly witness multiple processes such as metamorphism, magmatism, fragmentation, mixing, and reaccretion. Here, we report the results of ion microprobe Pb-Pb dating of a granite-like fragment found in a meteorite, the LL3-6 ordinary chondrite regolith breccia Adzhi-Bogdo. Eight spot analyses of two phosphate grains and other co-genetic phases of the granitoid give a Pb-Pb isochron age of 4.48 {+-} 0.12 billion years (95% confidence) and a model age of 4.53 {+-} 0.03 billion years (1{sigma}), respectively. These ages represent the crystallization age of a parental granite-like magma that is significantly older than those of terrestrial (4.00-4.40 Gyr) and lunar granites (3.88-4.32 Gyr) indicating that the clast in Adzhi-Bogdo is the oldest known granitoid in the solar system. This is the first evidence that granite-like formation is not only a common process on Earth, but also occurred on primitive asteroids in the early solar system 4.53 Gyr ago. Thus, the discovery of granite magmatism recorded in a brecciated meteorite provides an innovative idea within the framework of scenarios for the formation and evolution of planetary bodies and possibly exoplanetary bodies.

  10. Riftogenic A-type granites of the Polar Urals, Russia

    NASA Astrophysics Data System (ADS)

    Udoratina, Oksana; Kulikova, Ksenia; Shuysky, Alexander

    2016-04-01

    There are granitoids-markers of the riftogenic geodynamic setting in the Polar Urals. Isotope-geochronological and petrographic-petrogeochemical data on granitoids indicate the post-collisional conditions of their formation. Granitoids along with other alkaline massifs North Urals mark rifting in this part of the Urals. These granitoids formed after the collision peak of Timanides formation, after 520 Ma in the absolute chronology, when the intensity of magmatism fell sharply and only small volumes of rhyolite and A-type granites were formed. Granitoid massifs occur within the Northern Urals fragment of the Central Ural uplift composed of preuralide complexes. According to the recent data (U-Pb, SIMS) for single zircon the granitoids of the massifs (hereinafter Ma): Syadatayakhinsky (516±2, 503±6.3), Ochetinsky (500±5), Ingilorsky (487.3±6.9, 503±5), the northern part of Gerdizsky (496.2±7.1), Marunkeu Ridge (495±2.4) and part of massifs of kharbeysky complex of Laptayugansky and Evyugansky domes (497±3 and 487.1±2.1) were formed in the Late Cambrian-Early Ordovician time. Within rare metal ore deposits of Taykeyusky ore unit, except for older granitoids with ages 600-560-540 Ma, the granitoids occur with the following ages: Longotyugansky (512±8, 482±8, 511±11), Taykeusky (513±3.4, 518.6±3.9, 477±12), Ust-Mramorny (516±16). There are the following situation localization of granites in the area of the Central Urals uplift: 1) in Ochetinsky and Syadatayakhinsky blocks without significant tectonic deformations among greenschist metamorphites; 2) in the areas of intense tectonic transformations (Longotyugansky, Taykeusky, Ust-Mramorny), but also among greenschist metamorphites; 3) in highly metamorphized rocks (Marunkeu Ridge, Ingilorsky, Gerdizsky, small bodies of Kharbeysky complex). Granitoids differ by the material and structural-textural features of the rocks. Some are massive with preserved granite fabric (1), the other have clearly expressed

  11. Geochemical evolution of magmatism in Archean granite-greenstone terrains

    NASA Astrophysics Data System (ADS)

    Samsonov, A. V.; Larionova, Yu. O.

    2006-05-01

    Evolution of Archean magmatism is one of the key problems concerning the early formation stages of the Earth crust and biosphere, because that evolution exactly controlled variable concentrations of chemical elements in the World Ocean, which are important for metabolism. Geochemical evolution of magmatism between 3.5 and 2.7 Ga is considered based on database characterizing volcanic and intrusive rock complexes of granite-greenstone terrains (GGT) studied most comprehensively in the Karelian (2.9-2.7 Ga) and Kaapvaal (3.5-2.9 Ga) cratons and in the Pilbara block (3.5-2.9 Ga). Trends of magmatic geochemical evolution in the mentioned GGTs were similar in general. At the early stage of their development, tholeiitic magmas were considerably enriched in chalcophile and siderophile elements Fe2O3, MgO, Cr, Ni, Co, V, Cu, and Zn. At the next stage, calc-alkaline volcanics of greenstone belts and syntectonic TTG granitoids were enriched in lithophile elements Rb, Cs, Ba, Th, U, Pb, Nb, La, Sr, Be and others. Elevated concentrations of both the “crustal” and “mantle-derived” elements represented a distinctive feature of predominantly intrusive rocks of granitoid composition, which were characteristic of the terminal stage of continental crust formation in the GGTs, because older silicic rocks and lithospheric mantle were jointly involved into processes of magma generation. On the other hand, the GGTs different in age reveal specific trends in geochemical evolution of rock associations close in composition and geological position. First, the geochemical cycle of GGT evolution was of a longer duration in the Paleoarchean than in the Meso-and Neoarchean. Second, the Paleoarche an tholeiitic associations had higher concentrations of LREE and HFSE (Zr, Ti, Th, Nb, Ta, Hf) than their Meso-and Neoarchean counterparts. Third, the Y and Yb concentrations in Paleoarchean calc-alkaline rock associations are systematically higher than in Neoarchean rocks of the same type

  12. Magmatic and crustal differentiation history of granitic rocks from Hf-O isotopes in zircon.

    PubMed

    Kemp, A I S; Hawkesworth, C J; Foster, G L; Paterson, B A; Woodhead, J D; Hergt, J M; Gray, C M; Whitehouse, M J

    2007-02-16

    Granitic plutonism is the principal agent of crustal differentiation, but linking granite emplacement to crust formation requires knowledge of the magmatic evolution, which is notoriously difficult to reconstruct from bulk rock compositions. We unlocked the plutonic archive through hafnium (Hf) and oxygen (O) isotope analysis of zoned zircon crystals from the classic hornblende-bearing (I-type) granites of eastern Australia. This granite type forms by the reworking of sedimentary materials by mantle-like magmas instead of by remelting ancient metamorphosed igneous rocks as widely believed. I-type magmatism thus drives the coupled growth and differentiation of continental crust.

  13. A Nd- and O-isotope study of the REE-rich peralkaline Strange Lake granite: implications for Mesoproterozoic A-type magmatism in the Core Zone (NE-Canada)

    NASA Astrophysics Data System (ADS)

    Siegel, Karin; Williams-Jones, Anthony E.; Stevenson, Ross

    2017-07-01

    It is well established that A-type granites enriched in high field strength elements, such as Zr, Nb and the REE, form in anorogenic tectonic settings. The sources of these elements and the processes controlling their unusual enrichment, however, are still debated. They are addressed here using neodymium and oxygen isotope analyses of samples from the 1.24 Ga Strange Lake pluton in the Paleoproterozoic Core Zone of Québec-Labrador, an A-type granitic body characterized by hyper-enrichment in the REE, Zr, and Nb. Age-corrected ɛNd values for bulk rock samples and sodic amphiboles (mainly arfvedsonite) from the pluton range from -0.6 to -5.7, and -0.3 to -5.3, respectively. The ɛNd values for the Napeu Kainiut quartz monzonite, which hosts the pluton, range from -4.8 to -8.1. The 147Sm/144Nd ratios of the suite and the host quartz monzonite range from 0.0967 to 0.1659, large variations that can be explained by in situ fractionation of early LREE-minerals (Strange Lake), and late hydrothermal HREE remobilization. Oxygen isotope analyses of quartz of both Strange Lake and the host yielded δ18O values between +8.2 and +9.1, which are considerably higher than the mantle value of 5.7 ± 0.2‰. Bulk rock oxygen isotope analyses of biotite-gneisses in the vicinity of the Strange Lake pluton yielded δ18O values of 6.3, 8.6 and 9.6‰. The negative ɛNd values and positive δ18O values of the Strange Lake and Napeu Kainiut samples indicate that both magmas experienced considerable crustal contamination. The extent of this contamination was estimated, assuming that the contaminants were sedimentary-derived rocks from the underlying Archean Mistinibi (para-) gneiss complex, which is characterized by low ɛNd and high δ18O values. Mixing of 5-15% of a gneiss, having an ɛNd value of -15 and a δ18O value of +11, with a moderately enriched mantle source (ɛNd = +0.9, δ18O = +6.3) would produce values similar to those obtained for the Strange Lake granites. Based on

  14. Emplacement and deformation of the A-type Madeira granite (Amazonian Craton, Brazil)

    NASA Astrophysics Data System (ADS)

    Siachoque, Astrid; Salazar, Carlos Alejandro; Trindade, Ricardo

    2017-04-01

    The Madeira granite is one of the Paleoproterozoic (1.82 Ga) A-type granite intrusions in the Amazonian Craton. It is elongated in the NE-SW direction and is composed of four facies. Classical structural techniques and the anisotropy of magnetic susceptibility (AMS) method were applied to the study of its internal fabric. Magnetic susceptibility measurements, thermomagnetic curves, remanent coercivity spectra, optical microscopy and SEM (scanning electron microscopy) analyses were carried out on the earlier and later facies of the Madeira granite: the rapakivi granite (RG) and the albite granite (AG) respectively. The last one is subdivided into the border albite granite (BAG) and the core albite granite (CAG) subfacies. AMS fabric pattern is controlled by pure magnetite in all facies, despite significant amounts of hematite in the BAG subfacies. Microstructural observations show that in almost all sites, magnetic fabric correlates to magmatic state fabrics that are defined by a weak NE-SW orientation of mafic and felsic silicates. However, strain mechanisms in both subfacies of AG also exhibit evidence for solid-state deformation at high to moderate temperatures. Pegmatite dyke, strike slip fault (SFA-B-C), hydrothermal vein, normal fault (F1-2) and joint (J) structures were observed and their orientation and kinematics is consistent with the magmatic and solid-state structures. Dykes, SFA-C and F1, are usually orientated along the N70°E/40°N plane, which is nearly parallel to the strike of AMS and magmatic foliations. In contrast, veins, SFB, F2 and some J are oriented perpendicular to the N70°E trend. Kinematic analysis in these structures shows evidence for a dextral sense of movement in the system in the brittle regime. The coherent structural pattern for the three facies of Madeira granite suggests that the different facies form a nested pluton. The coherence in orientation and kinematics from magmatic to high-temperature solid-state, and into the brittle

  15. Tonian granitic magmatism of the Borborema Province, NE Brazil: A review

    NASA Astrophysics Data System (ADS)

    Guimarães, Ignez P.; de Fatima L. de Brito, Maria; de A. Lages, Geysson; da Silva Filho, Adejardo F.; Santos, Lucilene; Brasilino, Roberta G.

    2016-07-01

    involvement of distinct proportions of mantle and crustal components in the source of their protoliths. There is no consensus in the literature about the tectonic setting of the CVG ie they have been related to either continental margin magmatic arc, with possible back-arc association, or extention-related setting, with generation of A-type granites. However, all the available geochemical data suggest that the CVG represent extension related magmatism. The geochemical signature associated to bimodal volcanism, including pyroclastic rocks, with similar ages, and absence, up to now, of evidence for metamorphism of Tonian age, support the hypothesis of extension - related magmatism.

  16. Magmatic Enclaves in Granitic Rocks: Paragons or Parasites?

    NASA Astrophysics Data System (ADS)

    Clemens, John; Stevens, Gary; Elburg, Marlina

    2017-04-01

    Granitic rocks form the fundamental building blocks of Earth's continents and provide us with a wide range of resources, so their formation is worth trying to understand. Fine-grained, igneous-textured microgranular enclaves of tonalitic to monzogranitic composition (ME) are common in granitic rocks and their origins have been hotly debated, with some workers suggesting that ME are not igneous. These ME have been studied intensively enough that we are now certain that they are of igneous origin - globules of mingled and quenched magma. Although a mantle connection is evident in many cases, their ultimate origin (including where in the lithosphere they originate) is still debated. This contribution explores the systematics of chemical variation in ME and their host granites, with the aim of uncovering any systematics in their behaviour and modelling the processes that have led to the variations that we measure, comparing host-rock series to their respective ME series. As always, the hope is that the study of ME may lead to improved understanding and modelling of the processes that are responsible for the formation of the host granitic magmas. Using variations between the molecular quantities Ti and M (Fe+Mn+Mg), we demonstrate that the petrogenetic processes that operated within a diverse group of S- and I-type granitic host magmas and their ME suites are dissimilar. Variations within the granitic series result from a variety of what might be called 'orderly' processes, resulting in linear or curvilinear trends in chemical variation diagrams. In contrast, processes that affected the ME series commonly resulted in scattered, chaotic variations. Even in cases in which an ME series displays more orderly variation, it can be shown that the hypothesis of simple mixing between a parent enclave magma and its host granitic magma, to produce the overall variations, cannot be supported. ME magmas had vastly smaller volumes compared with their host granitic magmas. Thus, they

  17. Rapakivi granites in the geological history of the earth. Part 1, magmatic associations with rapakivi granites: Age, geochemistry, and tectonic setting

    NASA Astrophysics Data System (ADS)

    Larin, A. M.

    2009-06-01

    Rapakivi granites characteristic practically of all old platforms are greatly variable in age and irregularly distributed over the globe. Four types of magmatic associations, which include rapakivi granites, are represented by anorthosite-mangerite-charnockite-rapakivi granite, anorthosite-mangerite-rapakivi-peralkaline granite, gabbro-rapakivi granite-foidite, and rapakivi granite-shoshonite rock series. Granitoids of these associations used to be divided into the following three groups: (1) classical rapakivi granites from magmatic associations of the first three types, which correspond to subalkaline high-K and high-Fe reduced A2-type granites exemplifying the plumasitic trend of evolution; (2) peralkaline granites of the second magmatic association representing the highly differentiated A1-type reduced granites of Na-series, which are extremely enriched in incompatible elements and show the agpaitic trend of evolution; and (3) subalkaline oxidized granites of the fourth magmatic association ranging in composition from potassic A2-type granites to S-granites. Magmatic complexes including rapakivi granites originated during the geochronological interval that spanned three supercontinental cycles 2.7-1.8, 1.8-1.0 and 1.0-0.55 Ga ago. The onset and end of each cycle constrained the assembly periods of supercontinents and the formation epochs of predominantly anorthosite-charnockite complexes of the anorthosite-mangerite-charnockite-rapakivi granite magmatic association. Peak of the respective magmatism at the time of Grenvillian Orogeny signified the transition from the tectonics of small lithospheric plates to the subsequent plate tectonics of the current type. The outburst of rapakivi granite magmatism was typical of the second cycle exclusively. The anorthosite-mangerite-charnockite-rapakivi granite magmatic series associated with this magmatism originated in back-arc settings, if we consider the latter in a broad sense as corresponding to the rear parts of

  18. Charnockites and granites of the western Adirondacks, New York, USA: a differentiated A-type suite

    USGS Publications Warehouse

    Whitney, P.R.

    1992-01-01

    Granitic rocks in the west-central Adirondack Highlands of New York State include both relatively homogeneous charnockitic and hornblende granitic gneisses (CG), that occur in thick stratiform bodies and elliptical domes, and heterogeneous leucogneisses (LG), that commonly are interlayered with metasedimentary rocks. Major- and trace-element geochemical analyses were obtained for 115 samples, including both types of granitoids. Data for CG fail to show the presence of more than one distinct group based on composition. Most of the variance within the CG sample population is consistent with magmatic differentiation combined with incomplete separation of early crystals of alkali feldspar, plagioclase, and pyroxenes or amphibole from the residual liquid. Ti, Fe, Mg, Ca, P, Sr, Ba, and Zr decrease with increasing silica, while Rb and K increase. Within CG, the distinction between charnockitic (orthopyroxene-bearing) and granitic gneisses is correlated with bulk chemistry. The charnockites are consistently more mafic than the hornblende granitic gneisses, although forming a continuum with them. The leucogneisses, while generally more felsic than the charnockites and granitic gneisses, are otherwise geochemically similar to them. The data are consistent with the LG suite being an evolved extrusive equivalent of the intrusive CG suite. Both CG and LG suites are metaluminous to mildly peraluminous and display an A-type geochemical signature, enriched in Fe, K, Ce, Y, Nb, Zr, and Ga and depleted in Ca, Mg, and Sr relative to I- and S-type granites. Rare earth element patterns show moderate LREE enrichment and a negative Eu anomaly throughout the suite. The geochemical data suggest an origin by partial melting of biotite- and plagioclase-rich crustal rocks. Emplacement occurred in an anorogenic or post-collisional tectonic setting, probably at relatively shallow depths. Deformation and granulite-facies metamorphism with some partial melting followed during the Ottawan phase

  19. Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

    NASA Astrophysics Data System (ADS)

    Cai, Da-wei; Tang, Yong; Zhang, Hui; Lv, Zheng-Hang; Liu, Yun-long

    2017-06-01

    Most Silurian-Devonian granites in South China are S- or I-type granites, which are suggested to be petrogenetically related to the Wuyi-Yunkai orogeny. In this paper, we present the detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical, and Nd-Hf isotopic data for Xiqin A-type granites in the northeastern Cathaysia Block, SE China. Zircon U-Pb dating results show that the Xiqin granites were emplaced at about 410 Ma, indicating that they were generated at the end of Wuyi-Yunkai orogeny. These granites are high in K2O + Na2O (6.31-8.79 wt%), high field strength elements (Zr + Nb + Ce + Y = 427-699 ppm), rare earth elements (total REE = 221-361 ppm) as well as high Ga/Al ratios (10,000 Ga/Al = 2.50-3.10), and show characteristics typical of A-type granites. εHf(t) values of the Xiqin granites mainly vary from -0.4 to -3.1 and yield Mesoproterozoic T2DM(Hf) (mainly ranging from 1.29 to 1.45 Ga). The εNd(t) values are from -1.23 to -2.11 and T2DM(Nd) vary from 1.25 to 1.32 Ga. These isotopic data suggest that the Xiqin granites were generated by partial melting of metavolcanic rocks with minor metasedimentary rocks in the lower crust. Our data on the Xiqin granites, coupled with previous studies of Silurian-Devonian magmatism, suggest that the tectonic regime had changed to a strongly post-collisional extension environment in the Wuyi-Yunkai orogen at least since 410 Ma, and that delamination, which accounts for the change in stress from the compression to extension and asthenospheric upwelling during the early Paleozoic, plays a significant role in the generation of Xiqin A-type granites.

  20. Origin and evolution of Pliocene Pleistocene granites from the Larderello geothermal field (Tuscan Magmatic Province, Italy)

    NASA Astrophysics Data System (ADS)

    Dini, A.; Gianelli, G.; Puxeddu, M.; Ruggieri, G.

    2005-04-01

    Extensive, mainly acidic peraluminous magmatism affected the Tuscan Archipelago and the Tuscan mainland since late Miocene, building up the Tuscan Magmatic Province (TMP) as the Northern Apennine fold belt was progressively thinned, heated and intruded by mafic magmas. Between 3.8 and 1.3 Ma an intrusive complex was built on Larderello area (Tuscan mainland) by emplacement of multiple intrusions of isotopically and geochemically distinct granite magmas. Geochemical and isotopic investigations were carried out on granites cored during drilling exploration activity on the Larderello geothermal field. With respect to the other TMP granites the Larderello intrusives can be classified as two-mica granites due to the ubiquitous presence of small to moderate amounts of F-rich magmatic muscovite. They closely resemble the almost pure crustal TMP acidic rocks and do not show any of the typical petrographic features commonly observed in the TMP hybrid granites (enclaves, patchy zoning of plagioclase, amphibole clots). On the basis of major and trace elements, as well as REE patterns, two groups of granites were proposed: LAR-1 granites (3.8-2.3 Ma) originated by biotite-muscovite breakdown, and LAR-2 granites (2.3-1.3 Ma) generated by muscovite breakdown. At least three main crustal sources (at 14-23 km depth), characterized by distinct ɛNd( t) and 87Sr/ 86Sr values, were involved at different times, and the magmas produced were randomly emplaced at shallow levels (3-6 km depth) throughout the entire field. The partial melting of a biotite-muscovite-rich source with low ɛNd( t) value (about -10.5) produced the oldest intrusions (about 3.8-2.5 Ma). Afterwards (2.5-2.3 Ma), new magmas were generated by another biotite-rich source having a distinctly higher ɛNd( t) value (-7.9). Finally, a muscovite-rich source with high ɛNd( t) (about -8.9) gave origin to the younger group of granites (2.3-1.0 Ma). The significant Sr isotope disequilibrium recorded by granites belonging to

  1. A-type granite and the Red Sea opening

    USGS Publications Warehouse

    Coleman, R.G.; DeBari, S.; Peterman, Z.

    1992-01-01

    Miocene-Oligocene A-type granite intrudes the eastern side of the Red Sea margin within the zone of extension from Jiddah, Saudi Arabia south to Yemen. The intrusions developed in the early stages of continental extension as Arabia began to move slowly away from Africa (around 30-20 Ma). Within the narrow zone of extension silicic magmas formed dikes, sills, small plutons and extrusive equivalents. In the Jabal Tirf area of Saudi Arabia these rocks occur in an elongate zone consisting of late Precambrian basement to the east, which is gradually invaded by mafic dikes. The number of dikes increases westward until an igneous complex is produced parallel to the present Red Sea axis. The Jabal Tirf igneous complex consists of diabase and rhyolite-granophyre sills (20-24 Ma). Although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion (< 1 km). To the south, in the Yemen, contemporaneous with alkali basaltic eruptions (26-30 Ma) and later silicic eruptions, small plutons, dikes, and stocks of alkali granite invaded thick (1500 m) volcanic series, at various levels and times. Erosion within the uplifted margin of Yemen suggests that the maximum depth of intrusion was less than 1-2 km. Granophyric intrusions (20-30 Ma) within mafic dike swarms similar to the Jabal Tirf complex are present along the western edge of the Yemen volcanic plateau, marking a north-south zone of continental extension. The alkali granites of Yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite. These granites represent water-poor, hypersolvus magmas generated from parent alkali basalt magmas. The granophyric, two-feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension. Initial 87Sr/86Sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and

  2. A-type granite and the Red Sea opening

    NASA Astrophysics Data System (ADS)

    Coleman, Robert G.; DeBari, Susan; Peterman, Zell

    1992-03-01

    Miocene-Oligocene A-type granite intrudes the eastern side of the Red Sea margin within the zone of extension from Jiddah, Saudi Arabia south to Yemen. The intrusions developed in the early stages of continental extension as Arabia began to move slowly away from Africa (around 30-20 Ma). Within the narrow zone of extension silicic magmas formed dikes, sills, small plutons and extrusive equivalents. In the Jabal Tirf area of Saudi Arabia these rocks occur in an elongate zone consisting of late Precambrian basement to the east, which is gradually invaded by mafic dikes. The number of dikes increases westward until an igneous complex is produced parallel to the present Red Sea axis. The Jabal Tirf igneous complex consists of diabase and rhyolite-granophyre sills (20-24 Ma). Although these are intrusine intrusive rocks their textures indicate shallow depths of intrusion (< 1 km). To the south, in the Yemen, contemporaneous with alkali basaltic eruptions (26-30 Ma) and later silicic eruptions, small plutons, dikes, and stocks of alkali granite invaded thick (1500 m) volcanic series, at various levels and times. Erosion within the uplifted margin of Yemen suggests that the maximum depth of intrusion was less than 1-2 km. Granophyric intrusions (20-30 Ma) within mafic dike swarms similar to the Jabal Tirf complex are present along the western edge of the Yemen volcanic plateau, marking a north-south zone of continental extension. The alkali granites of Yemen consist primarily of perthitic feldspar and quartz with some minor alkali amphiboles and acmite. These granites represent water-poor, hypersolvus magmas generated from parent alkali basalt magmas. The granophyric, two-feldspar granites associated with the mafic dike swarms and layered gabbros formed by fractional crystallization from tholeiitic basalt parent developed in the early stages of extension. Initial 87Sr/ 86Sr ratios of these rocks and their bulk chemistry indicate that production of peralkaline and

  3. Petrogenesis and tectonic implications of Late Carboniferous A-type granites and gabbronorites in NW Iran: Geochronological and geochemical constraints

    NASA Astrophysics Data System (ADS)

    Moghadam, Hadi Shafaii; Li, Xian-Hua; Ling, Xiao-Xiao; Stern, Robert J.; Santos, Jose F.; Meinhold, Guido; Ghorbani, Ghasem; Shahabi, Shirin

    2015-01-01

    Carboniferous igneous rocks constitute volumetrically minor components of Iranian crust but preserve important information about the magmatic and tectonic history of SW Asia. Ghushchi granites and gabbronorites in NW Iran comprise a bimodal magmatic suite that intruded Ediacaran-Cambrian gneiss and are good representatives of carboniferous igneous activity. Precise SIMS U-Pb zircon ages indicate that the gabbronorites and granites were emplaced synchronously at ~ 320 Ma. Ghushchi granites show A-type magmatic affinities, with typical enrichments in alkalis, Ga, Zr, Nb and Y, depletion in Sr and P and fractionated REE patterns showing strong negative Eu anomalies. The gabbronorites are enriched in LREEs, Nb, Ta and other incompatible trace elements, and are similar in geochemistry to OIB-type rocks. Granites and gabbronorites have similar εNd(t) (+ 1.3 to + 3.4 and - 0.1 to + 4.4, respectively) and zircon εHf(t) (+ 1.7 to + 6.2 and + 0.94 to + 6.5, respectively). The similar variation in bulk rock εNd(t) and zircon εHf(t) values and radiometric ages for the granites and gabbronorites indicate a genetic relationship between mafic and felsic magmas, either a crystal fractionation or silicate liquid immiscibility process; further work is needed to resolve petrogenetic details. The compositional characteristics of the bimodal Ghushchi complex are most consistent with magmatic activity in an extensional tectonic environment. This extension may have occurred during rifting of Cadomian fragments away from northern Gondwana during early phases of Neotethys opening.

  4. Petrochemical evolution of the White Mfolozi Granite pluton: Evidence for a late Palaeoarchaean A-type granite from the SE Kaapvaal Craton, South Africa

    NASA Astrophysics Data System (ADS)

    Misra, Saumitra; Reinhardt, Jürgen; Wilson, Allan H.

    2017-08-01

    One of the major limitations in understanding the geochemical evolution of the Kaapvaal Craton, South Africa, is the scarcity of whole rock trace element data of the granitoid and other rocks compared to the vastness of this cratonic block. Here we present new XRF major oxide and ICP-MS trace element analyses of the White Mfolozi Granitoid (WMG) pluton, SE Kaapvaal Craton, which suggest that the 3.25 Ga (U-Pb zircon age) old WMG pluton is a peraluminous A-type granite and could be equivalent to the intrusive potassic granite phase of the Anhalt Granitoid suite, occurring to the North of the WMG pluton. The pluton was generated by batch partial melting of a pre-existing TTG source in two major phases under relatively anhydrous conditions, and the heat of partial melting could have been provided by a voluminous mantle-derived mafic magma, which intruded into mid-crustal levels (c. 17 km), perhaps during a period of crustal extension. The estimated pressure and temperature of generation of the WMG parent magma with average molar [or/(or + ab)] 0.48 could be 500 MPa and close to 1000 °C, respectively, when compared with the results of experimental petrology. Interstitial occurrence of relatively iron-rich biotite [Mg/(Mg + Fe) 0.41-0.45] suggests that the final temperature of crystallization of the pluton was close to 800 °C. An important magmatic event following the main phase of partial melting was limited mixing between the intrusive mafic magma and co-existing newly generated granitic melt. This magma mixing resulted in distinct variations in SiO2 and a low initial Sr isotopic ratio (0.7013) of the WMG pluton. Although both the models of partial melting of quartzo-feldspathic sources and fractional crystallization of basaltic magmas with or without crustal assimilation have been proposed for the origin of A-type granites, the model of magmatic evolution of the WMG pluton presented here can also be an alternative model for the generation of A-type granites. In

  5. The Neocene Magmatism in South Gangdese, Tibet and its tectonic significance: Evidences from Namuru Granitic Complex

    NASA Astrophysics Data System (ADS)

    Dong, G.; Mo, X.

    2011-12-01

    There are lots of granitic intrusions in the western Gangdese, Tibet. Namuru granite complex is one of the typical intrusions with various gabbro inclusions and mafic micro-granular enclaves (shortly MME). Field investigation has found the gradually transitional relationship between the gabbro inclusions and granite with abundant MMEs. It is lithologically biotite granite and few granodiorite for Namuru complex. The chemical analyses show that the SiO2 varies from 65-76%, average 73% for the granite and 48.5-55.6%, average 51%. The total alkali contents are high in both the granite (K2O+Na2O= 5.50%~8.71%) and mafic rocks (4.42~6.7%). The REE pattern is flat and slightly declining with no clearly Eu anomaly with the total content from up to 284.75ppm and lowest of 105.35ppm in the granite and up to 120.38ppm, and lowest 72.48×10-6 in the gabbro rocks. The normalized trace element spider is quite similar in the both with K element enriched and Nb, Ti depleted. Zircon LA-ICP-MS U-Pb dating for 4 samples both granite and gabbro inclusions gave the age of 46.11±0.78Ma, 45.47±0.4Ma, 46.7±2.9Ma and 45.4±1.4Ma respectively, falling into a range of 45.4-46.7Ma of crystalling age. All the characters indicated that magma mixing had happened between granite and mafic magma during the Neocene (45.4-46.7Ma), forming the vast granitic and gabbro rocks as an important magmatic event in western Gangdese. It happens to be consistent with the duration (40.0-52.5Ma) for the known magma mixing and underplating in eastern to middle Gangdese, such as Quxu and Xigarze. It probably represents the giant magma event with magma mixing and underplating in Gangdese during early Neocene. Therefore it was inferred, on the basis of magmatic rocks, that the collision between India-Eurasian continents are acting simultaneously in both eastern and western Gangdese in Eocene, resulting in basaltic magma underplating below and then magma mixing along whole Gangdese belt and formation of the

  6. Magmatic and post-magmatic phenomena in the Karkonosze granite and its metamorphic envelope (West Sudetes, SW Poland)

    NASA Astrophysics Data System (ADS)

    Kozłowski, Andrzej; Ilnicki, Sławomir; Matyszczak, Witold; Marcinowska, Agnieszka

    2016-09-01

    Mineralogical studies of the Karkonosze granite (ca. 322-312 Ma) and its surroundings in West Sudetes (SW Poland) have provided data on Nb-Ta-REE minerals from pegmatites in the NE part of the pluton and several new finds of Ag minerals and 15 oxygenic Bi phases, hitherto not reported from the massif. The Karkonosze pegmatites are enriched in HREE as fergusonite-(Y) or xenotime-(Y) appear in almost every studied pegmatite, together with a subordinate assemblage of the aeschynite, euxenite or columbite group. The abundance of LREE minerals such as allanite-( Ce) and the monazite group, correlates inversely with the Nb-Ta-Ti minerals, whilst an early generation of monazite-(Ce) revealed an exceptionally high amount of Nd (up to 22 wt.% of Nd2O3 ). The physical and chemical conditions during the magmatic and post-magmatic processes were reconstructed and the effects of contact metamorphism in amphibolites from hornfelsed zones examined. Changes in solution composition and concentration at the early magmatic stage (825-920°C), pegmatitic stage overlapping with hydrothermal (560°C which ended at 160-90°C) and clearly hydrothermal stage (400 to 110°C) were studied in detail by means of melt and fluid inclusions in quartz. Furthermore, post-magmatic fluids, including some enriched in Li and B, were identified in rock-forming quartz from the whole pluton. In turn, study of the amphibolites indicates that the pair cummingtonite + anorthite or the presence of Ca-rich plagioclase with actinolite seem to be reliable mineral proxies of the thermal impact of the granitoid body on amphibolites in its envelope. The inferred conditions of the contact processes (450-550°C, 2.5- 4.8 kbar) point to an elevated geothermal gradient (ca. 32-45°C/km) probably reflecting the heat flow induced by the Karkonosze intrusion. Moreover, despite the textural and mineral changes imposed by regional and contact metamorphism, the amphibolites have their pre-metamorphic (magmatic) geochemical

  7. Magmatic immiscibility and fluid phase evolution in the Mount Genis granite (southeastern Sardinia, Italy)

    NASA Astrophysics Data System (ADS)

    Frezzotti, Maria Luce

    1992-01-01

    The Mount Genis granite is one of the post-tectonic intrusives emplaced late in the magmatic history of the Hercynian batholith in Sardinia. Devitrified silicate melt inclusions are present in some (magmatic) rock-forming and miarolitic quartz. These magmatic remnants show initial melting at 680- 720°C. High-temperature observations (700-800°C) revealed the presence in some of the inclusions of mixed hydrosaline melt (L1) and silicate melt (L2), with extremely variable L1/L2 ratios. Electron microprobe analyses indicate L1 to be K-Na dominated chlorides. Inclusions of mixed silicate and hydrosaline melts are interpreted to have been formed by heterogeneous trapping of two immiscible fluid phases (silicate-hydrosaline) after second boiling, most likely during the final crystallization stage. Magma-derived brines (63 eq wt% NaCl) circulated at subsolidus conditions from ≈600°C and were retained in the miarolitic cavities down to about 400°C. Fluid unmixing occurred locally in the miarolitic cavities from 550° to 412°C. At temperatures of ≈400° to 100°C the microgranite was invaded by diluted waters (≈4-5 eq wt% NaCl). A possible model for fluid evolution begins with a hydrosaline melt exsolving from the magma at the late-magmatic stage. The absence of boiling within the volatile (hydrosaline) system shows that brines can occur by direct magmatic immiscibility. The comprehensive hydrothermal evolution suggests a nearly isobaric cooling path, with local boiling episodes in the miaroles, probably in coincidence with invasion of external waters.

  8. Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Lamarão, Claudio Nery; Borges, Régis Munhoz Krás; Dall'Agnol, Roberto

    2014-04-01

    The trace element content in zircons from A-type granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Pará, Amazonas and Goiás states, Brazil) and Variscan (Krušné Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites, it is a late-crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende-biotite and biotite granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing granites may be strongly enriched in Hf (up to 10 wt.% HfO2), Th (up to 10 wt.% ThO2), U (up to 10 wt.% UO2), Y (up to 12 wt.% Y2O3), Sc (up to 3 wt.% Sc2O3), Nb (up to 5 wt.% Nb2O5), Ta (up to 1 wt.% Ta2O5), W (up to 3 wt.% WO3), F (up to 2.5 wt.% F), P (up to 11 wt.% P2O5), and As (up to 1 wt.% As2O5). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type granites, the Zr/Hf value decreases from 41-67 (porphyritic granite) to 16-19 (equigranular granite) in the Kymi stock, Finland, and from 49-52 (biotite granite) to 18-36 (leucogranite) in the Pedra Branca pluton, Brazil. In the in situ strongly

  9. The late Variscan ferroan granite magmatism of southern Sardinia: inferences from Mo metallogenesis

    NASA Astrophysics Data System (ADS)

    Naitza, Stefano; Conte, Aida Maria; Cuccuru, Stefano; Fadda, Sandro; Fiori, Maddalena; Oggiano, Giacomo; Secchi, Francesco

    2017-04-01

    Metallogeny is a powerful tool to investigate crustal evolution; a good example is offered by the Variscan basement of Sardinia and its Mo deposits. Mo ores are poorly represented in Variscan metallogenic provinces of Europe: however, in Sardinia, numerous small Mo deposits, often associated to Sn, W and F ores, are present, invariably related to an early Permian intrusive peak bracketed at about 290 Ma (Fadda et al., 2015; Naitza et al., 2017). In Sardinia, two main magmatic peaks have been schematized at pre-300 and 290 Ma. In southern Sardinia, the 290 magmatic peak is made up of several intrusive F-bearing rock-suites (Conte et al., 2016), belonging to ilmenite series, showing a slight peraluminous character and mostly classifiable as ferroan granites (sensu Frost and Frost, 2011). Mo-bearing granites form a distinct suite of relatively small plutons, emplaced at very shallow depth (about 1kb) in an exhumed Variscan low-grade basement. Peculiar characters of Mo-bearing granites are the occurrence of greisenized microgranite and granophyre cupolas, with fayalite-bearing pegmatites, and ilmenite, xenotime-(Y), monazite, fluorite, and local topaz as accessory phases. Recently, Conte et al. (2016) interpreted these granites as originated by partial melting of low crustal felsic metaigneous photoliths enriched in granophiles (Mo, Sn, W). Mo ores occur as: a) endo- and exo- quartz-muscovite greisens with molybdenite±Fe-Cu sulphides, and b) quartz-molybdenite±wolframite±Fe-Cu-Zn sulphides±fluorite±topaz hydrothermal veins and stockworks, hosted in granites or in country rocks. Redox state of magmas exerts a strong control on Mo metallogeny, as in Mo districts worldwide ores are usually hosted by high-fO2 magnetite series intrusions (Ishihara, 1981). The close field association of Sardinian Mo mineralization with ferroan, low-fO2 ilmenite-series granites may be explained in terms of Mo-enriched crustal sources of magmas, and very efficient geochemical

  10. Paleoproterozoic gabbro-diorite-granite magmatism of the Batomga Rise (NE Aldan Shield): Sm-Nd isotope geochemical evidence

    NASA Astrophysics Data System (ADS)

    Kuzmin, V. K.; Bogomolov, E. S.; Glebovitskii, V. A.

    2016-02-01

    The geochemical similarity and almost simultaneous (2055-2060 Ma) formation of Utakachan gabbro-amphibolite, Jagdakin granodiorite-diorite, Khoyunda granitoid, and Tygymyt leucogranite complexes, which inruded metamorphic formations of the Batomga Group are evidence of their formaton from unified magmatic source. All this makes it possibble to combine aforementioned complexes into the unified Early Proterozoic diferentiated gabbro-diorite-granite complex.

  11. Geochemistry, geochronology, and origin of the Neoarchean Planalto Granite suite, Carajás, Amazonian craton: A-type or hydrated charnockitic granites?

    NASA Astrophysics Data System (ADS)

    Feio, G. R. L.; Dall'Agnol, R.; Dantas, E. L.; Macambira, M. J. B.; Gomes, A. C. B.; Sardinha, A. S.; Oliveira, D. C.; Santos, R. D.; Santos, P. A.

    2012-10-01

    New whole-rock geochemistry and LA-MC-ICPMS and Pb-evaporation geochronological data were obtained on zircon from the Neoarchean Planalto suite granites and associated charnockitic rocks of the Canaã area of the Carajás province, eastern Amazonian craton, Brazil. The Pb-evaporation ages of three samples from the Planalto suite are around 2730 Ma (2733 ± 2 Ma, 2731 ± 1 Ma and 2736 ± 4 Ma), whereas U-Pb LA-MC-ICPMS concordia ages obtained for these samples are 2729 ± 17 Ma, 2710 ± 10 Ma, and 2706 ± 5 Ma, respectively. An orthopyroxene quartz gabbro associated with the Pium complex and Planalto suite yielded a U-Pb concordia age of 2735 ± 5 Ma, interpreted as its crystallization age. The Planalto suite granites and the charnockitic rocks associated with the Mesoarchean Pium complex were probably crystallized at 2730 ± 10 Ma. The Planalto granites have ferroan character and are similar geochemically to reduced A-type granites. In previous studies, they have been classified as such, despite the fact that they are syntectonic. The tectonic setting and the association between the Planalto suite and charnockitic series led us to classify these biotite-hornblende granites as hydrated granites of the charnockitic series. The Planalto suite and the Neoarchean charnockitic magmas were more probably derived by partial melting of mafic to intermediate tholeiitic orthopyroxene-bearing rocks similar to those of the Pium complex. At 2.76 Ga, upwelling of asthenospheric mantle in an extensional setting propitiated the formation of the Carajás basin. Later on, at ca. 2.73 Ga, heat input associated with underplate of mafic magma induced partial melting of mafic to intermediate lower crustal rocks, originating the Planalto and charnockitic magmas. The emplacement of these magmas occurred under active regional stress and resultant major shear zones found in the Canaã dos Carajás area. The close association between the Planalto suite and charnockitic rocks suggests that they

  12. Grenville-age A-type and related magmatism in southern Laurentia, Texas and New Mexico, U.S.A.

    NASA Astrophysics Data System (ADS)

    Li, Yujia; Barnes, Melanie A.; Barnes, Calvin G.; Frost, Carol D.

    2007-08-01

    Large Grenville-age plutons are known to be present in the 1340-1370 Ma basement in Texas and eastern New Mexico, but their distribution and compositional ranges are poorly known. New U-Pb zircon dates (SHRIMP-RG, Stanford University) on subsurface samples have identified widespread presence of compositionally diverse Grenville-age (1070-1110 Ma) plutonic rocks. In the Texas Panhandle, core from a > 175 m thick, sill-like gabbroic intrusion yielded a date of 1081 ± 8.3 Ma. In situ differentiation of this tholeiitic magma led to a ˜ 7-fold increase in incompatible element concentrations as REE patterns remained essentially flat. Trace element data suggest an E-MORB-like source. To the south, alkali-feldspar granite with A-type affinities was recovered from drill core from the Abilene gravity minimum near Albany, Texas. It yielded a date of 1078 ± 23 Ma; similar to undeformed (post-orogenic) granites in the Llano uplift. Further west, an anorthosite xenolith from the Eocene Three Sisters intrusion in El Paso, Texas yielded a date of 1068 ± 30 Ma which is within error of the 1110 ± 19 Ma age determined for the main stage of the nearby A-type Red Bluff granitic suite. Xenoliths from Potrillo maar volcano in the center of the southern Rio Grande rift include monzonitic xenoliths with granulitic texture which yielded dates of ˜ 1072 Ma. In contrast, Potrillo maar xenoliths with igneous textures yielded U-Pb dates of ˜ 27 Ma. Development of the granulitic texture is interpreted to reflect granulite facies metamorphism during Tertiary time (26-27 Ma) on the basis of age zoning and U concentrations in the zircon crystals. Our results show that Grenville-age magmatism in the Texas and New Mexico subsurface was widespread and was coeval with syn- and post-deformation granites in the Llano uplift of central Texas. The compositions of dated samples suggest that mafic magmas were broadly tholeiitic in character and that granitic magmas were "A-type". These magmatic

  13. Zircon dating and mineralogy of the Mokong Pan-African magmatic epidote-bearing granite (North Cameroon)

    NASA Astrophysics Data System (ADS)

    Tchameni, R.; Sun, F.; Dawaï, D.; Danra, G.; Tékoum, L.; Nomo Negue, E.; Vanderhaeghe, O.; Nzolang, C.; Dagwaï, Nguihdama

    2016-09-01

    We present the mineralogy and age of the magmatic epidote-bearing granite composing most of the Mokong pluton, in the Central Africa orogenic belt (North Cameroon). This pluton intrudes Neoproterozoic (~830 to 700 Ma) low- to high-grade schists and gneisses (Poli-Maroua group), and is crosscut or interleaved with bodies of biotite granite of various sizes. The pluton is weakly deformed in its interior, but solid-state deformation increases toward its margins marked by narrow mylonitic bands trending NNE-SSW. The magmatic epidote granitic rocks are classified as quartz monzodiorite, granodiorite, monzogranite, and syenogranite. They are medium- to coarse-grained and composed of K-feldspar + plagioclase + biotite + amphibole + epidote + magnetite + titanite + zircon + apatite. In these granites, the pistacite component [atomic Fe+3/(Fe3+ + Al)] in epidote ranges from 16 to 29 %. High oxygen fugacity (log ƒO2 - 14 to -11) and the preservation of epidote suggest that the magma was oxidized. Al-in hornblende barometry and hornblende-plagioclase thermometry indicate hornblende crystallization between 0.53 and 0.78 GPa at a temperature ranging from 633 to 779 °C. Zircon saturation thermometry gives temperature estimates ranging from 504 to 916 °C, the latter being obtained on samples containing inherited zircons. U/Pb geochronology by LA-ICP-MS on zircon grains characterized by magmatic zoning yields a concordia age of 668 ± 11 Ma (2 σ). The Mokong granite is the only known occurrence magmatic epidote in Cameroon, and is an important milestone for the comparison of the Central Africa orogenic belt with the Brasiliano Fold Belt, where such granites are much more abundant.

  14. A-type and I-type granitoids and mylonitic granites of Hassan Salaran area of SE Saqqez, Kurdistan, Iran

    NASA Astrophysics Data System (ADS)

    Abdullah, Fakhraddin Mohammad; Saeed Ahmad, Sheler

    2014-05-01

    The Hassan Salarn area is located 20km to southeast of Saqqez city in Kurdistan Province, western Iran. In this area there are two distinct granitic rock suites consisting A-type and I-type granites and also mylonitic granites. These A-type and I-type granites have various petrological and geochemical characteristics. They also have different origins and petrogenesis. A-type granitoids comprise alkali feldspar granite, syenogranite and quartz alkali feldspar syenite, whereas I-type granitoids are composed of monzogranite, granodiorite and tonalite. Geochemically, A-type granitoids are peralkaline and acmite-normative but I-type granitoids are subalkaline (calc-alkaline), metaluminous and diopside-normative. A-type granitoids are also ferroan alkali and ferroan alkali-calcic whereas I-type granitoids are magnesian and calcic. A-type granitoids resemble to within plate granites and post-orogenic granites whereas I-type granitoids resemble to volcanic arc granites. A-type granitoids contain higher concentrations of alkalies, Zr, Rb, Nb, Y, Th, Ce, high FeO/MgO ratios and lower concentrations of Mg, Ca and Sr, resembling post-orogenic A-type granites. It is possible that heat from a mantle-derived magma which intruded into the lower crust, and/or rapid crustal extension have been essential generation of approriate melts producing A-type granitoids. Thus we can conclude that A-type granitoids were generated from a mixed mantle-crust source. Negative Nb anomalies and low contents of Ti and P probably indicate a subduction-related origin for protolith of I-type granitoids. Negative Nb anomalies and enrichment in Ce relative to its adjacent elements can be related to involvement of continental crust in magmatic processes. I-type granitoids are also enriched in Rb, Ba, K, Th, Ce and depleted in Nb, Zr and Y, indicating that they have had interacted with crust. I-type granitoids may result from contamination of mantle-derived magmas by continental crust during a subduction

  15. Two-mica andalusite-bearing granite with no primary muscovite: constraints on the origin of post-magmatic muscovite in two-mica granites

    NASA Astrophysics Data System (ADS)

    Puziewicz, Jacek; Pietranik, Anna

    2016-12-01

    The two-mica granite from Gęsiniec (Strzelin Granitic Massif, SW Poland) consists of quartz, K-feldspar, normally zoned plagioclase (30 ± 7 % An), subordinate biotite and muscovite and magmatic andalusite. Andalusite crystallised before the outer parts of plagioclase grains were formed. Biotite has constant Fe/(Fe + Mg) ratio of approximately 0.81. Five textural types of muscovite occur in the granite: (1) muscovite replacing andalusite, (2) embayed interstitial muscovite, (3) muscovite forming aggregates with biotite, (4) muscovite accompanying biotite and chlorite in microfissures and (5) fine muscovite forming fringes at the contact between larger muscovite plates and K-feldspar. They are commonly associated with albite. Crystallisation of muscovite started significantly below the granite solidus, mostly by the replacement of andalusite. Formation of muscovite continued during cooling of host rock. The growth of individual plates was initiated at different undercoolings and the plates whose crystallisation was frozen at different stages of growth occur. Those that were formed earlier are richer in titanium and iron relative to the later ones. As the rock contains no Ti and Fe saturating phases, the content of Ti and Mg in muscovite depends on their local availability. The homogeneous Fe/(Fe + Mg) ratio of biotite indicates that it was re-equilibrated at the post-magmatic stage.

  16. Granitoid magmatism of Alarmaut granite-metamorphic dome, West Chukotka, NE Russia

    NASA Astrophysics Data System (ADS)

    Luchitskaya, M. V.; Sokolov, S. D.; Bondarenko, G. E.; Katkov, S. M.

    2009-04-01

    structural data indicate temporal relation between magmatism, metamorphism and deformations, accompanying formation of dome structure. Structural data also indicate the dome formation between two regional strike-slips. Strike-slip deformations of terminal stage of collision might have resulted in local zones of extensions [6, 8]. Intrusive contacts of studied granitoid plutons with already deformed host deposits indicate their postcollisional origin. Wide petrographical spectrum of granitoids, hornblende and biotite existence in granites, metaluminous high-K and shoshonite character, biotites compositions allow belonging them to high-K granites of I-type. Appearance of I-type granites in postcollisional setting is usually related to crustal anatexis under the influence of hot asthenospheric mantle due to delamination of lower parts of lithosphere. At the same time the processes of mingling of magmas of different composition, assimilation, fractional crystallization take place. Thus, in tectonic scenario of Alarmaut dome formation except dominating submergence of Chukotka microcontinent margin beneath the structures of North-Asian craton active margin we should assume slab-breakoff or delamination of lithospheric mantle which might have facilitated heat transfer, necessary for melting of granite magma. Aptian-Albian volcanism, localized in postcollisional extensional structures, confirms this assumption. Interrelations of major oxides in granitoids show that compositions of Alarmaut intermediate rocks fall in the fields of melts, experimentally obtained during partial melting of amphibolites, and compositions of granodiorites and granites, along the boundary zone of partial melts of greywackes and dacites, tonalites. Heterogeneity of granitoids source composition or different level of magma contamination by ancient crustal material is confirmed by Sr-Nd data. It is expressed in significant dispersal of ɛNd(Т) and 87Sr/86Sr values in granitoids. Work is carried out at the

  17. U-Pb-Nd-Hf isotope geochemistry of the Mesoproterozoic A-type granites in Mannefallknausane, western Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Ramo, O. T.; Kurhila, M.; Luttinen, A. V.; Andersen, T.

    2009-12-01

    The bedrock of western Dronning Maud Land, Antarctica records several stages of anorogenic magmatism. The Grenvillean-age metamorphic basement gneisses of Heimefrontfjella and Mannefallknausane were intruded by mafic dikes (Bauer et al., 2003) and A-type granite plutons (Jacobs, 1991) at circa 1 Ga. A 590 Ma suite of mafic dikes manifests a subsequent episode of Proterozoic anorogenic magmatism (Bauer et al., 2003). Jurassic (180 Ma) continental flood basalts (CFBs), their intrusive equivalents, and associated alkaline mafic rocks represent the third and youngest episode of anorogenic magmatism (Luttinen et al., 1998; Romu and Luttinen, 2007). The crystalline bedrock in western Dronning Maud Land is composed of the Archean Grunehogna craton and the Mesoproterozoic Maud mobile belt. About 100 km south of Archean-Proterozoic transition, in the Proterozoic realm, nunataks of Mannefallknausane (74.5oS, 15oW) are dominated by Precambrian granitoid rocks and rare paragneisses. Three principal granites can be identified: a white, garnet-bearing K-feldspar-megacrystic biotite granite; a red biotite-hornblende±clinopyroxene granite with or without plagioclase-mantled K-feldspar-megacrysts (rapakivi texture); and a dark green porphyritic charnockite with orthopyroxene and hornblende. The presence of rapakivi texture, the mode of occurrence, and geochemical composition of the granites of Mannefallknausane imply A typology. For two varieties of the red granite (wiborgite and pyterlite), our new U-Pb data imply crystallization ages of 1073 ± 6 Ma and 1084 ± 8 Ma, respectively. These are compatible with a U-Pb zircon upper intercept age of 1073 ± 8 Ma of the charnockite (Arndt et al., 1991). The initial Nd isotope composition of these rocks is relatively radiogenic [epsilon-Nd (1075 Ma) value of the biotite granite -0.5; red granite +0.3, +0.5; charnockite +1.4], as is that of a country-rock gneiss from the surrounding bedrock (+1.0). Initial zircon epsilon-Hf values of the

  18. Zircon U-Pb SHRIMP dating of Palaeoproterozoic Isla Mala granitic magmatism in the Rio de la Plata Craton, Uruguay

    NASA Astrophysics Data System (ADS)

    Hartmann, Léo A.; Piñeyro, Daniel; Bossi, Jorge; Leite, Jayme A. D.; McNaughton, Neal J.

    2000-05-01

    An important event of K-rich granitic magmatism occurred at ca. 2.07 Ga in the Rio de la Plata Craton, Uruguay, as determined by U-Pb zircon SHRIMP geochronology of two Isla Mala Suite granitic rocks. Previous indications of Archaean ages are not confirmed. The absence of recrystallization or new zircon growth suggests that the investigated region of the craton remained unaffected by major Meso- or Neoproterozoic orogenies, although less intense deformation may have occurred and remained unregistered in the zircons.

  19. Origin of Mesoproterozoic A-type granites in Laurentia: Hf isotope evidence

    NASA Astrophysics Data System (ADS)

    Goodge, John W.; Vervoort, Jeffrey D.

    2006-03-01

    Granitic rocks are commonly used as a means to study chemical evolution of continental crust. In particular, their isotopic compositions reflect the relative contributions of mantle and crustal sources in their genesis. In Laurentia, a distinctive belt of Mesoproterozoic A-type or "anorogenic" granites of ˜ 1.4 Ga age was emplaced within composite, heterogeneous Proterozoic crust. Zircons are an ideal mineral to constrain the granite petrogenetic history because they are repositories of both age (U-Pb geochronology) and tracer (Lu-Hf isotopic) information. We measured the Hf isotope composition of zircons from 31 previously dated A-type granites intruding Proterozoic basement provinces from the southwest U.S. to the upper mid-continent. Isotopic compositions for all granites are broadly similar, with average 176Hf/ 177Hf(i) ratios of 0.281871-0.282153. Averages for granites within different crustal provinces yield present-day ɛHf values between - 31.9 and - 21.9. Initial ɛHf values discriminate the granites by age of the 2.0-1.6 Ga crust which they intrude, but are independent of intrusion age, as follows (basement formation ages in parentheses): southern Granite-Rhyolite (1.5-1.3 Ga), + 7.0 ± 0.9; central Yavapai (1.8-1.7 Ga), + 5.4 ± 0.9; western Yavapai (1.8-1.7 Ga), + 3.3 ± 1.1; Granite-Rhyolite (1.5-1.3 Ga), + 1.4 ± 0.6; Mojave (1.8-1.7 Ga), + 0.2 ± 0.8; and Penokean (1.9-1.8 Ga), - 0.1 ± n/d. The narrow ranges of Hf isotopic signatures within these regional groupings of granites reflect the age and isotopic composition of the basement provinces they intrude. Granites in the southern Granite-Rhyolite and central Yavapai provinces have the highest initial ɛHf, reflecting their more juvenile sources, whereas Mojave and Penokean granites show contributions from more evolved crustal sources. Simple calculations indicate that all the granites represent dominantly crustal melts; although a mantle contribution cannot be ruled out, if present it must be

  20. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry

    NASA Astrophysics Data System (ADS)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa

    2016-07-01

    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  1. Petrogenesis of selected A-type granitic intrusions from Central Eastern Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Hassan, Tharwat; Asran, Asran; Amron, Taha; Hauzenberger, Christoph

    2014-05-01

    The Pan-African orogeny in the Arabian-Nubian Shield was terminated by intrusion of A-type granites (~ 595 Ma; Greenberg, 1981) and its volcanic equivalents. Subsequent to the intrusions of these granitic bodies the shield was exhumed. Eroded A-type granite pebbles were found in the molasse sediments that were deposited in intermountain basins. Therefore the A-type granites provide information about the last stage of the Pan-African geochemical system. Preliminary whole-rock geochemical data of three granitic intrusions (Kadabora, Um Naggat and El shiekh Salem) from the Central Eastern Desert of Egypt; indicate that all of them are peraluminous and with A-type characteristics. These intrusions show low CaO content (average 0.43 %wt), high FeOT/MgO ratio (10.46-121.88), high Na2O+K2O (average 8.04 %wt), marked enrichment of high field strength elements (Y, Nb and Ga except Zr), depletion in MgO (0.01-0.11 %wt) and with low concentration of Sr and Ba. The studied granitoids were emplaced in within plate tectonic regime. References: Greenberg, J.K. (1981): Characteristic and origin of Egyptian younger granites. Bull. Geol. Soc. Am. Part 1, v.92: 224-232.

  2. Schlieren-bound Magmatic Structures Formed by the Unmixing of Granitic Magmas: A Case Study from Pothole Dome, Sierra Nevada

    NASA Astrophysics Data System (ADS)

    Ardill, K. E.; Paterson, S. R.; Memeti, V.

    2015-12-01

    There is ongoing debate regarding the mobility of crystal mush zones in granitic magmas and their ability to mix and interact with intrusive batches to form compositional heterogeneity in plutons. Magmatic structures, localized zones of compositional diversity, enable evaluation of the significance of magmatic flow and convection vs. chemical diffusion in magmatic systems by determining their mode of formation. With further study, magmatic structures are potentially powerful tools recording syn-emplacement tectonic activity. Pothole Dome, in the Cathedral Peak Granodiorite of the Tuolumne Intrusive Complex is an ideal location to investigate magmatic structures since a variety of plumes, pipes, mafic ellipsoids, and schlieren troughs are densely clustered. Previous workers have established patterns in the orientations of different Pothole Dome magmatic structures that are indicative of a broad pattern of movement and younging directions at the kilometer scale. Preliminary whole-rock geochemical and isotopic data compare variations between the normal Cathedral magmas and a plume, trough, tube, potassium feldspar cluster and granitic dyke to investigate plausible mechanisms for the formation of the distinct compositional diversity formed in the structures. Schlieren, abundant in biotite, hornblende, apatite, sphene and zircon show relatively high levels of titanium, calcium and magnesium relative to the feldspar cluster and dyke. Schlieren are also enriched in minor elements including Zr, Y, Sr and Ce relative to the felsic structures. Both elemental and isotopic data for schlieren defining the plumes and troughs and the late leucogranitic dikes and k-feldspar clusters all plot outside the typical mixing line for Cathedral Peak Granodiorite compositions. We postulate that this may be a result of an unmixing process during physical flow of previously mixed populations of chemically distinct crystals in the Cathedral Peak.

  3. Geochronological, geochemical and Nd-Hf isotopic constraints on the petrogenesis of Late Cretaceous A-type granites from the southeastern coast of Fujian Province, South China

    NASA Astrophysics Data System (ADS)

    Zhao, Jiao-Long; Qiu, Jian-Sheng; Liu, Liang; Wang, Rui-Qiang

    2015-06-01

    We present comprehensive petrological, geochronological, major and trace element, and Nd-Hf isotopic data for the Baishishan, Jingangshan, and Wushan granitic plutons on the southeastern coast of Fujian Province, South China, with the aims of elucidating their origin and gaining new insights into the petrogenesis of aluminous A-type granites. Zircon U-Pb ages obtained by laser ablation-inductively coupled plasma-mass spectrometry show that the three investigated plutons were emplaced at 92-86 Ma, indicating that they were generated during a Late Cretaceous magmatic event. The granites from the three plutons are composed mainly of perthite, quartz, plagioclase, and minor biotite; they have high SiO2 contents, and low CaO, MnO, Fe2O3tot, and MgO contents, and show a metaluminous to slightly peraluminous signature. The granites are enriched in some large ion lithophile elements (e.g., Rb, Th, and U) and high field strength elements (e.g., Nb and Ta) with elevated Ga/Al ratios, and spidergrams show strong depletions in Ba, Sr, Ti, and P. Chondrite-normalized REE patterns show relative enrichments in light rare earth elements, flat heavy rare earth element profiles, and strongly negative Eu anomalies. These mineralogical and geochemical characteristics suggest that all three plutons can be classified as aluminous A-type granites. The plutons exhibit nearly identical whole-rock Nd and zircon Hf isotopic compositions, and yield Mesoproterozoic two-stage model ages (1.4-1.1 Ga) for both Nd and Hf isotopes. Based on a synthesis of the geochemical and isotopic data and petrogenetic modelling, we suggest that these A-type granitic rocks were most likely formed by variable degrees of fractional crystallization of magmas produced by the partial melting of a tonalitic to granodioritic source, with plagioclase-rich residual phases in the middle to lower crust, and emplaced at shallow crustal levels along the Changle-Nan'ao Fault. Our data on the Baishishan, Jingangshan, and

  4. The geochemical characteristics of Haiyang A-type granite complex in Shandong, eastern China

    NASA Astrophysics Data System (ADS)

    Li, He; Ling, Ming-xing; Ding, Xing; Zhang, Hong; Li, Cong-ying; Liu, Dun-yi; Sun, Wei-dong

    2014-07-01

    Haiyang granite complex consists of K-feldspar granite and syenite, with a total exposure area of ~ 600 km2. The K-feldspar granite is metaluminous (A/CNK = 0.70 to 0.99) and the syenite is slightly peraluminous (A/CNK = 1.01 to 1.10), both of which have typical characteristics of A-type granite with high total alkali contents and FeOT/(FeOT + MgO) ratios. Zircon U-Pb age are 116.8 ± 1.7 Ma and 115.8 ± 2.2 Ma, for the K-feldspar granite and the syenite, respectively. This is consistent with field observation that the syenite intruded into the K-feldspar granite. Varied zircon O isotope (5.65-7.78‰ for K-feldspar granite and 4.68-7.08‰ for syenite) with peak values that are marginally higher than those of mantle zircon reflects important mantle contributions. These together with large variation of zircon εHf(t) values of K-feldspar granite (- 22.4 to - 15.6) and syenite (- 24.6 to - 13.5), can best be explained by the involvement of at least two components, e.g., enriched lithospheric mantle +/- subducted materials, and upwelling asthenosphere. Apatite has right decline REE pattern. The apatite from K-feldspar granite has higher Cl contents than those of syenite, implying more influence from a subduction released fluid in K-feldspar granite source. This distinction is supported by the systematically higher oxygen fugacity of K-feldspar granite as indicated by zircon Ce4 +/Ce3 + ratios. In the Yb/Ta-Y/Nb, Ce/Nb-Y/Nb diagrams, both K-feldspar granite and syenite plot in A1-type, with K-feldspar granite plotting closer to A2. In the Nb-Y-3Ga and Nb-Y-Ce charts, syenite plots near the boundary between A1 and A2, whereas some K-feldspar granite samples plot in A2 field, indicating a tendency of transition originally from A2 to A1. In general A1 granites form in intraplate settings, whereas A2 granite forms in post-collision. It is likely that mantle components metasomatized by subduction released fluids are easier to be partially melted, forming K-feldspar granite

  5. Magma flow recorded by magmatic and magnetic fabrics in a shallow granitic pluton: La Gloria Pluton, central Chile

    NASA Astrophysics Data System (ADS)

    Payacán, I. J.; Gutiérrez, F. J.; Gelman, S. E.; Bachmann, O.; Parada, M. A.

    2013-12-01

    To better understand the dynamics of a small, shallow, silicic magma reservoir, magmatic and magnetic (AMS) fabrics are compared in samples obtained from La Gloria Pluton (LGP), a 10 Ma granitic intrusion located in southern Andes. The magnetic fabric of LGP, mainly given by magnetite, is characterized by oblate shapes. Magnetic lineations have a NW trend with subhorizontal dip, following the main pluton elongation, while magnetic foliation planes have dips varying gradually from vertical at the walls to subhorizontal toward the center and the roof of the pluton. On the basis of numerical simulations, magnetic fabric was interpreted to represent the shear record induced by magmatic convection along solidification fronts as the reservoir reached its rheological locking point. Magmatic fabric (mineral orientation) was determined on 12 samples along the pluton. Three mutually orthogonal thin sections were produced for each sample, perpendicular to the AMS tensor axes. Size and orientation of individual crystals were obtained by image analysis. A 2-D tensor for two mineral groups (plagioclase and amphibole+biotitie) was defined in each mineral plane projecting the crystal lengths on the main crystal orientation (given by Bingham statistics). A 3-D magmatic fabric tensor was obtained. In order to compare the magmatic and magnetic fabrics, magmatic anisotropy parameters were defined similar to the AMS tensors. Magmatic fabric and anisotropy parameter values vary depending on the location inside the pluton: (1) Samples located at the borders exhibit vertical foliations and lineations with a NW trend, similar to the magnetic fabric tensors and higher anisotropy values for plagioclase than amphibole+biotite,; (2) samples located at the center of the LGP commonly present subvertical foliations/lineations, which differ from the magnetic fabric, and higher magmatic anisotropy degree values for amphibole+biotite than plagioclase. Based on numerical simulations of the fluid

  6. Cambro-Ordovician post-collisional granites of the Ribeira belt, SE-Brazil: A case of terminal magmatism of a hot orogen

    NASA Astrophysics Data System (ADS)

    Valeriano, Claudio de Morisson; Mendes, Julio Cezar; Tupinambá, Miguel; Bongiolo, Everton; Heilbron, Monica; Junho, Maria do Carmo Bustamante

    2016-07-01

    This work presents an overview of the geology and chemical composition of the Cambrian-Ordovician post-collisional (COPC) granites and associated rocks of Ribeira belt, SE-Brazil. These COPC granites make up some of the most picturesque and highest (>2000 m) rocky peaks and cliffs of Rio de Janeiro state, an accessible case of post-orogenic granitic magmatism associated with the terminal stages of a hot Ediacaran-Cambrian (Brasiliano-Panafrican) orogen. The COPC magmatism intruded tonalitic to granitic orthogneisses of the Rio Negro arc (∼790-600 Ma) and associated paragneisses of the São Fidelis Group. Post-collisional magmatism started ∼10 m.y. after the latest collisional event, the Buzios Orogeny, lasting discontinuously from ∼510 Ma until ∼470 Ma. The 15 largest intrusive bodies in Rio de Janeiro State are referred to in the literature as the Parati/Mangaratiba, Vila Dois Rios, Pedra Branca, Suruí, Silva Jardim, Favela, Andorinha, Teresópolis, Frade, Nova Friburgo, Conselheiro Paulino, São José do Ribeirão, Sana and Itaoca granites. They crop out as rounded/elliptical stocks or gently-dipping sheets, always with sharp contacts with the country rocks, along with pegmatite and aplitic veins and dykes. COPC granites are grey and pink undeformed medium-grained biotite monzogranites with (K-feldspar) porphyritic, mega-crystic, equigranular and serial textures. Magmatic flow foliation is frequently observed. Peripheric xenolith zones are common as well as isolated xenoliths from the country rocks. In a compilation of more than 100 chemical compositions, SiO2 contents display a major mode at 71wt%. The COPC magmatism generated high-K calc-alkaline granites and quartz monzonites with predominantly metaluminous granites. Meso to melanocratic gabbroic and dioritic enclaves also have calc-alkaline affinity and likely represent more resistant mafic xenoliths from the Rio Negro Arc.

  7. Major magmatic events in Mt Meredith, Prince Charles Mountains: First evidence for early Palaeozoic syntectonic granites

    USGS Publications Warehouse

    Gongurov, N.A.; Laiba, A.A.; Beliatsky, B.V.

    2007-01-01

    Precambrian rocks at Mt Meredith underwent granulite-facies metamorphism M1. Zircon isotope dating for two orthogneisses revealed the following age signatures: 1294±3 and 957±4Ma; 1105±5 and 887±2Ma. The oldest ages could reflect the time of orthogneiss protolith crystallization and the latest age determinations date Grenvillian metamorphism. The metamorphic rocks were intruded by two-mica and garnet-biotite granites. The granites and host rocks underwent amphibolite-facies metamorphism M2. Zircon isotope analysis of the two-mica granites showed age estimation within 550-510Ma and zircon dating of the garnet-biotite granites revealed the ages of 1107±5, 953±8, and 551±4Ma. As Pan-African age signatures were obtained from only the granite samples, it is possible to suggest that the granites were formed at the time of 510-550Ma and the zircons with greater age values were captured by granites from the host rocks.

  8. Geochronological, geochemical and Sr-Nd-Hf isotopic constraints on the petrogenesis of Late Cretaceous A-type granites from the Sibumasu Block, Southern Myanmar, SE Asia

    NASA Astrophysics Data System (ADS)

    Jiang, Hai; Li, Wen-Qian; Jiang, Shao-Yong; Wang, He; Wei, Xiao-Peng

    2017-01-01

    The Late Cretaceous to Paleogene granitoids occur widespread in the Sibumasu block within Myanmar (SE Asia), which show a close association with tin-tungsten mineralization. However, the precise timing, petrogenesis and tectonic significance of these granitoids are poorly constrained so far. In this study, we present a detailed study on geochronology, elemental and Sr-Nd-Hf isotopic geochemistry for the Hermyingyi and Taungphila granites in southern Myanmar, with the aim of determining their petrogenesis and tectonic implications. LA-ICP-MS U-Pb dating of zircon grains from the two granites yield ages of 69-70 Ma, indicating a Late Cretaceous magmatic event. These granitic rocks are weakly peraluminous and belong to the high-K calc-alkaline series. They are both characterized by high SiO2, K2O + Na2O, FeOT/(FeOT + MgO) and Ga/Al ratios and low Al2O3, CaO, MgO, P2O5 and TiO2 contents, enriched in Rb, Th, U and Y, but depleted in Ba, Sr, P, and Eu, suggesting an A-type granite affinity. Moreover, they display prominent tetrad REE patterns and non-CHARAC trace element behavior, which are common in late magmatic differentiates with strong hydrothermal interaction or deuteric alteration. The granites belong to A2-type and probably formed at a high temperature and anhydrous condition. They have zircon εHf(t) values from - 12.4 to - 10.0 and whole-rock εNd(t) values from - 11.3 to - 10.6, with Paleoproterozoic TDM2 ages (1741-1922 Ma) for both Hf and Nd isotopes. Geochemical and isotopic data suggest that these A-type granites were derived from partial melting of the Paleoproterozoic continental crust dominated by metaigneous rocks with tonalitic to granodioritic compositions, without significant input of mantle-derived magma and followed by subsequent fractional crystallization. By integrating all available data for the regional tectonic evolution in SE Asia and adjacent regions, we attribute the formation of the Late Cretaceous A-type granites to a back-arc extension

  9. Collision vs. subduction-related magmatism: Two contrasting ways of granite formation and implications for crustal growth

    NASA Astrophysics Data System (ADS)

    Moyen, J.-F.; Laurent, O.; Chelle-Michou, C.; Couzinié, S.; Vanderhaeghe, O.; Zeh, A.; Villaros, A.; Gardien, V.

    2017-04-01

    Earth's continental crust is dominantly made of buoyant, felsic igneous material (granitoids), that was ultimately extracted from the mantle as a result of Earth's differentiation. Since felsic melts are not in chemical equilibrium with the mantle, they can originate either from melting of older crustal lithologies, or from differentiation of a primitive mantle melt; only the latter case will contribute to crustal growth. To understand the mechanisms of continental crust growth and differentiation through time, it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites. In modern Earth, granitoids are chiefly generated in convergent plate boundaries (subduction and collision). This paper examines the granitic suites in a late-collision environment, the Variscan French Massif Central (FMC), and compares them with the suites found in an oceanic arc. We therefore describe, and compare, two end-members sites of granite generation. In the FMC, several main types of granites are described. Muscovite and Cordierite bearing Peraluminous Granites (resp. MPG and CPG) contain large amounts of inherited zircons, and their chemistry demonstrates that their sources were older crustal material (resp. metasediments and metaigneous). On the other hand, Potassic Calc-alkaline Granites (KCG), associated to potassic diorites (vaugnerites) do not contain inherited zircons, and ultimately derive from the vaugnerites. The vaugnerites in turn form by partial melting of a mantle contaminated by the regional crust. Therefore, although they are isotopically similar to the crust, the KCG are net contributors to crustal growth. Thus we conclude that although late-orogenic settings are dominated by crustal melting and recycling, they may be sites of net crustal growth, even though this is not visible from isotopes only. In contrast, arc granitoids are purely or almost purely mantle derived. However, the preservation

  10. Long-lived Paleoproterozoic granitic magmatism in the Seridó-Jaguaribe domain, Borborema Province-NE Brazil

    NASA Astrophysics Data System (ADS)

    Hollanda, Maria Helena B. M.; Archanjo, Carlos J.; Souza, Laécio C.; Dunyi, Liu; Armstrong, Richard

    2011-12-01

    The northeastern part of the Borborema Province is dominated by Paleoproterozoic migmatitic tonalitic to granitic orthogneisses (Caicó Complex) that are the basement for younger, metavolcanosedimentary rock assemblages. Within this complex gneissified, porphyritic metagranitoid rocks (the G2-type augen gneisses) are fairly common and supposed to define a synorogenic magmatism at c. 2.0 Ga. New U-Pb (SHRIMP) on zircons and Sm-Nd data shows that these augen gneisses do not differ significantly from the metaplutonic rocks of the basement complex regarding their nature and emplacement age of the primary magmas. U-Pb ages cluster in a time interval between 2.17 and 2.25 Ga and are correlated with Nd parameters (older tDM model ages and negative initial ɛNd values) indicating an origin from recycling of an older, probably Neoarchean crust. The regional host rocks that accommodate the augen gneiss could be c. 2.4-2.3 Ga supracrustal sequences presently preserved as small remnants in the Caicó Complex. The Paleoproterozoic magmatic activity extends to the Late Paleoproterozoic with the intrusion of the Serra Negra pluton (now a coarse augen gneiss) which yielded a (semi) concordant U-Pb age of c. 1.75 Ga. This magmatic activity, until now unsuspected in the Caicó Complex, was probably related to crustal extension and rifting over large areas that include the NE Brazil and the Nigerian shield in Africa.

  11. Neoproterozoic granitic magmatism along the Ailao Shan-Red River belt: U-Pb zircon geochronology, Lu-Hf isotopes and tectonic implications

    NASA Astrophysics Data System (ADS)

    Chen, Xiaoyu; Liu, Junlai; Qi, Yinchuan; Fan, Wenkui; Burg, Jean-Pierre

    2017-04-01

    The Neoproterozoic tectonic characteristics of the high grade metamorphic massifs along the Ailao Shan-Red River belt are debated. Controversies are on 1) whether the massifs were parts of the Yangtze block to the northeast or 2) parts of the Indochina block to the southwest and 3) the magmatic rocks represent arc magmatism or rifting linked to break-up of the Rodinia supercontinent. This study presents new and precise LA-ICP-MS U-Pb age dating and geochemical and Hf isotopic analyses of granitic intrusions along the Ailao Shan-Red River belt in an attempt to elucidate the Neoproterozoic magmatic evolution of this belt. In general, zircon U-Pb ages of the studied granitic rocks are between 804 and 724Ma, with a weighted mean of ca. 770 Ma, thus confirming Neoproterozoic magmatism. All samples plot into the peraluminous domain, indicating a major crustal resource. In consistency with these conclusions, most of the Neoproterozoic granitoids show negative ɛHf (t) values near the chondrite line. A few samples possess low positiveɛ Hf (t) values, being signatures of mantle sources. It is therefore concluded that the Neoproterozoic magmatism along the ASRR belt originated from mantle sources with important contributions through anatexis of ancient lower crust. Discrimination diagrams of tectonic settings suggest continental arc magmatism. Neoproterozoic magmatism is widely reported along the margins of the Yangtze block, especially in the northern margin. However, there are fewer reports about Neoproterozoic magmatic activity along the southern and southwestern margins. The geochronology spectrum and geochemisty of the studied Neoproterozoic granitic rocks are similar to those along the western margin of the Yangtze block. The present study, combined with previous results, suggests that oceanic subduction contributed to the generation of the arc magmatisms along the western and southwestern margin of the Yangtze plate and along the ASRR belt (as part of the

  12. Possible genetic link between I-type granite and orogenic gold deposits in Egypt (metamorphic-magmatic interaction?)

    NASA Astrophysics Data System (ADS)

    Abd El Monsef, Mohamed

    2015-04-01

    The orogenic gold deposits are a distinctive type of deposits that revealed unique temporal and spatial association with an orogeny. Where, the system of gold veins and related ore minerals was confined to hydrothermal solutions formed during compressional to transpressional deformation processes at convergent plate margins in accretionary and collisional orogens, with the respect to ongoing deep-crustal, subduction-related thermal processes. In Egypt, most of vein-type and dyke-type gold mineralization are restricted to granitic rocks or at least near of granitic intrusion that seems to have had an important influence on gold mineralization. Shear zone-related, mesothermal gold deposits of Fatira and Gidami mines in the northern Eastern Desert of Egypt are found within granitic bodies or at the contact between granites and metavolcanic rocks. The hosting-granitic rocks in Fatira and Gidami areas are mainly of granodioritic composition (I-Type granite) which is related to calc-alkaline magmatic series. However, Fatira granitoids were developed within island arc tectonic settings related to mature island arc system (Late-orogenic stage), at relatively low temperature (around 660° C) and medium pressure between (5 - 10 Kbar). On the other hand, Gidami granitoids were developed during the collision stage in continental arc regime related to active continental margin (Syn-orogeny), which were crystallized at relatively high temperature (700-720° C) and low pressure (around 0.1 Kbar). The ore mineralogy includes pyrite, chalcopyrite, sphalerite, covellite, ilmenite, goethite ± pyrrhotite ± pentlandite ± galena ± molybdenite. Native gold is detected only in Gidami mineralization as small inclusions within pyrite and goethite or as tiny grains scattered within quartz vein (in close proximity to the sulfides). In Fatira deposits, it is detected only by microprobe analysis within the crystal lattice of pyrite and jarosite. Fluid inclusions study for the mineralized

  13. A-type stratoid granites of Madagascar: evidence of Rodinia rifting at ca 790 Ma

    NASA Astrophysics Data System (ADS)

    Nedelec, Anne; Paquette, Jean-Louis; Bouchez, Jean-Luc

    2015-04-01

    The so-called stratoid granites are sheet-like granites emplaced as conformable sills in the Precambrian basement of central Madagascar. Most of them have A-type affinities (Nédélec et al. 1995). They are everywhere characterized by the same structural pattern evidencing two stages of deformation. The first one (foliations mildly dipping to the west and lineations trending WSW) is regarded as the consequence of synkinematic magma emplacement. The second stage, characterized by interference folds, steeply dipping foliations and subhorizontal lineations trending to the north, corresponds to a more or less pronounced reworking in ductile conditions, regarded as the result of Late Pan-African transcurrent tectonics. To the north of Antananarivo, the stratoid granites are associated with comagmatic quartz-syenites. New U-Pb zircons ages obtained by in situ analyses reveal two group of ages: upper intercept ages of ca 790 Ma, and younger ages of ca 550 Ma corresponding to crystal rims. These new data question the geological significance of former TIMS ages of ca 630 Ma formerly obtained from the same rocks (Paquette & Nédélec 1998). It is suggested that the stratoid granites and syenites were emplaced during a crustal thinning event corresponding to an early Rodinia rifting stage. The Pan-African imprint on these rocks is therefore limited to reheating, tectonic reworking and deep fluid transfer in the vicinity of Late-Neoproterozoic shear zones at ca 550 Ma (Nédélec et al. 2014).

  14. An Overview of the Origin of A-type Silicic Magmatism Along the Snake River Plain-Yellowstone Hotspot Track

    NASA Astrophysics Data System (ADS)

    Christiansen, E. H.; Bindeman, I. N.; Leishman, J. R.

    2015-12-01

    Disparate models have been proposed for the origin of A-type rhyolites--a volumetrically minor part of modern terrestrial magmatism. But understanding the origin of A-type granites and rhyolites has significance for understanding the formation of the Earth's first silicic crust and for planetary magmatism--small volumes of such granitic materials have been found in lunar rocks, martian and asteroidal meteorites, and have been speculated to have formed on Venus. On other planets, vertical tectonics and plume-like mantle convection dominate, not the recycling of wet, oxidized plates of lithosphere as on Earth. Thus, understanding the origins of A-type silicic magma is important on multiple levels. Voluminous A-type rhyolite were produced on the Snake River Plain-Yellowstone hotspot track and provide the opportunity to better understand these important silicic magmas. Detailed petrologic studies suggest that most Snake River Plain rhyolites ultimately formed by partially melting of previously emplaced basaltic intrusions rather than by fractional crystallization of basalt or melting of Archean crust. This hypothesis is favored because of the bimodal association of rhyolite and basalt without linking intermediate compositions. In addition, incompatible element ratios (e.g., La/Nb, Pb/Ce), a lack of old zircon antecrysts, low-U inherited zircon, high ɛNd and ɛHf values, high eruption temperatures (1050°C to 850°C), low fO2 (near QFM), and H2O (as low as 1.5%), link the rhyolites to a plume-derived basaltic parent through partial melting with lesser incorporation of the Archean to Mesozoic crust that underlies the plain. Moreover, the contrast with wetter, lower temperature rhyolites that must have formed by direct crustal melting (e.g., Arbon Valley Tuff) strengthens this interpretation. Many of the rhyolites also have low δ18O values that must be produced in two stages: first by partial melting of already hydrothermally altered basalt, and subsequently in single

  15. Osa Creek gabbro-granite ring complex, Sierra Nevada, CA, by degassing-driven subsidence of mafic-magmatic sheets

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.; Moore, J. G.

    2010-12-01

    Intrusive ring complexes commonly represent the shallow substrates of calderas, with arcuate intrusions forming as ring dikes engulfing subsiding caldera blocks, and as cone sheets injected during magmatic repressurization. The Osa Creek ring complex, southern Sierra Nevada batholith, differs in having formed by axial subsidence of solidifying gabbro-diorite sheets that injected a coeval mushy granitic magma body. The result is a remarkable nearly circular (6×10 km) steep-sided bimodal intrusive body, exposed 60 km east of Porterville and 30 km southwest of Owens Lake on the east side of the Kern Canyon. Zircon ages (SHRIMP) of both gabbro and granite are 146 ±1.5 Ma (1-sigma), slightly younger than, or concurrent with, the Independence Dike Swarm. Much of the structure is hornblende-biotite gabbro and diorite (SiO2, 47-51 wt %) emplaced as sheets 0.1-5 m thick, with each mafic sheet commonly chilled against and separated by thin (1-25 cm) septa of lighter colored and coarser rock ranging from granite to hornblende-plagioclase pegmatite. Mutually intrusive relations indicate that the septa were partly molten during sheet injection. In the outer portions of the complex the mafic sheets strike parallel to the margins and dip vertically-to-steeply radially inward. Dips of mafic sheets shallow toward the center of the complex, and are sub-horizontal in the center, defining a cup or basin structure. At least 28 thicker (5-250 m) conformable granitic sheets (SiO2, 70-77 wt. %) are spaced through the gabbroic layers and are increasingly thicker and abundant toward the higher elevation outer edges of the structure. Granite sheets also dip steeply inward, further defining the basin-shaped structure. Subsidence of the complex’s interior is indicated by rotation of igneous geopetal (way-up) indicators. These are in the form of small flames and pipes (to ~10 cm across) of the comagmatic inter-sheet septa granitoids that inject adjacent mafic sheets consistently toward the

  16. An early Paleozoic monzonorite-granite suite in the South China block: implications for the intracontinental felsic magmatism

    NASA Astrophysics Data System (ADS)

    Xu, Wenjing; Xu, Xisheng

    2017-01-01

    Large granitoid complexes within the continental crust are believed to be closely linked to mantle-derived magmas based on field observations and isotopic studies. However, details on the contribution of mantle-derived magmas in the generation of felsic magmas deep in the lower to middle crust, especially the interaction between the mantle-derived mafic magmas and the generated felsic melts, are not well constrained by petrological and mineralogical studies. Here we present a detailed study of an early Paleozoic monzonorite-granite suite from the South China Block and comparison with the other coeval magmatic rocks ( 22,000km2) in the region, to provide more details on the underplating/intraplating of mantle-derived magmas and the generation of felsic magmas in intracontinental settings. It is shown that the monzonorite has signatures of both mantle-derived magmas (substantial contents of MgO, Cr, and Ni; presence of olivine and orthopyroxene) and crust-derived magmas (substantial contents of SiO2, K2O, Rb, Ba, and light rare-earth elements; presence of K-feldspar, quartz and low-calcium plagioclase). Interestingly, the monzonorite, granite and the mafic microgranular enclaves (MME) are remarkably uniform in Sr-Nd-Hf isotopic compositions, with high initial 87Sr/86Sr ratios (0.7081-0.7098), low ɛNd (t) values (-6.8 to -6.3) and low zircon ɛHf (t) values (-8.0 to -7.4). An integrated study of petrological, mineralogical, and geochemical data of the monzonorite-granite suite and coeval magmatic rocks from the same region makes it clear that the input of crustal components is essential to explain the unusual signatures of the monzonorite. Petrogenetic modelling and isotopic compositions suggest that the contribution of mantle-derived mafic magmas in the generation of crust-derived felsic magmas is represented by heat input and minor mass input, and in the meantime, we prefer to explain the unusual geochemical signatures of the monzonorite by selective contamination

  17. Petrogenesis of the Yangzhuang Nb- and Ta-rich A-type granite porphyry in West Junggar, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Mao, Wei; Li, Xiaofeng; Wang, Guo; Xiao, Rong; Wang, Mou; Li, Yanlong; Ren, Manchuan; Bai, Yanping; Yang, Feng

    2014-06-01

    West Junggar is featured with a wide spread of Late Carboniferous-Early Permian A-type granites. Systematic comparison of the Yangzhuang granite porphyry and the regional coeval A-type granites (RCAG) shows that: (1) all the Late Carboniferous-Early Permian A-type granites are of the A2 group except the Yangzhuang granite porphyry; (2) the Nb and Ta contents of the Yangzhuang granite porphyry are nearly 10 times that of the RCAG while Ti content is more depleted; (3) εNd (t) of the Yangzhuang granite porphyry is slightly lower and the Sr isotope has a wider range relative to the RCAG. Previous research revealed that highly incompatible elements including Nb and Ta can be transferred into the mantle wedge by precipitation of amphibole from the ascending fluids generated by dehydration of subducted slab. It is inferred that enhanced heat flux brought by the Late Carboniferous ridge subduction decomposed amphibole in the mantle wedge to generate Nb and Ta-rich melt and finally produced the Yangzhuang granite porphyry.

  18. Linking the initial subduction of the South Tianshan Oceanic Plate and associated magmatism to Kazakhstan orocline: insights from petrogenesis of granites in the southern Yili Block

    NASA Astrophysics Data System (ADS)

    Bao, Zihe; Cai, Keda; Sun, Min; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping

    2017-04-01

    The Kazakhstan orocline is a striking collage system of the Central Asian Orogenic Belt. It has been documented to be a composite continent via assembly of several orogenic components by the Devonian and finally to attain its U-shaped structure through oroclinal bending in the Late Paleozoic. In order to reveal the relationship between the Kazakhstan orocline and regional magmatism, granitic rocks including monzogranites and K-feldspar granites in the south limb of the orocline have been conducted geochronological and geochemical studies. Zircon LA-ICP-MS U-Pb dating of the monzogranites gave crystallization ages of 360±1.8 Ma and 360.5±1.7 Ma, and the K-feldspar granites have a coeval age (361.3±1.8 Ma). Both of the granites are high-K granites, and show enrichment in light rare earth elements (LREE) and obvious negative Eu anomalies. They display negative anomalies in Ba, Nb, Sr, Eu, and Ti. The K-feldspar granites have higher SiO2, K2O contents and lower MgO, Fe2O3T, Zr contents than those of the monzogranites. Geochemical data support that the K-feldspar granites are highly fractionated I-type granites, and the monzogranites are unfractionated I-type granites. Distinguishable Nd and Hf isotope suggest that the K-feldspar granites and the monzogranites may share a common magma chamber. The negative Eu anomalies and depletions of Ba and Sr possibly imply plagioclase as residue in the magma source. The Sr-Nd isotopic data and the ɛHf(t) values (-3.6 - 2.9) indicate that the parental magma was probably derived from crustal rock with minor mantle-derived melt. The new geochemical data and regional geology evidences indicate that the granites may be generated in a continental back-arc environment, which was inferred to be a response to the initial subduction of the South Tianshan Oceanic Plate. Given that the Kazakhstan orocline was developed during this period, it is plausible to link the initial subduction of the South Tianshan Oceanic Plate and associated

  19. F-rich strongly peraluminous A-type magmatism in the pre-Andean foreland Sierras Pampeanas, Argentina: Geochemical, geochronological, isotopic constraints and petrogenesis

    NASA Astrophysics Data System (ADS)

    Morales Cámera, Matías M.; Dahlquist, Juan A.; Basei, Miguel A. S.; Galindo, Carmen; da Costa Campos Neto, Mario; Facetti, Nicolás

    2017-04-01

    The petrogenetic nature of A-type granites is a controversial problem. The Vinquis batholith in the Sierras Pampeanas of Argentina contains unusual F-rich and strongly peraluminous A-type monzogranites. A new LA-MC-ICP-MS U-Pb zircon crystallization age of 355 ± 7 Ma indicates emplacement in latest Devonian or earliest Carboniferous time, overlapping with extensive metaluminous A-type magmatism in the area. The monzogranites have a restricted range of SiO2 content (71.5-74.8 %), they are poor in Ca (0.54-1.4% CaO) and rich in FeOt, with relatively high FeOt/(FeOt+MgO) values ranging from 0.77 to 0.86 (average = 0.80) Both [FeOt/ (FeOt+MgO)] vs. SiO2 and [(Na2O+K2O)-CaO] vs. SiO2 plots indicate ferroan and alkali-calcic signatures typical of A-type granitoids. The samples have MgO/TiO2 > 1.2 and are moderately enriched in total alkalis (average 8.18%), with high K2O/Na2O values of 1.40-2.24. The granites are strongly peraluminous, with ASI (molar Al2O3/[CaO + Na2O + K2O]) values of 1.2 to 1.3. The high P2O5 content (0.23-0.37%) is distinctive and close to values reported for other Paleozoic F-rich peraluminous A-type granites in the Sierras Pampeanas. They have moderate contents of high field strength elements (e.g., Zr, Nb, Th, Y, etc.) and moderately fractionated to flat REE patterns [(La/Yb)N in the range 4.8-19.6] showing significant negative Eu anomalies (Eu/Eu* = 0.41). Biotite has a distinctive composition, with relatively high Fe2 +/(Fe2 + + Mg) ratios (0.61-0.74) and high F (0.55-1.42 wt.%) content. Together with the whole-rock chemistry this may be useful in identifying strongly peraluminous A-type granites. In addition, the Rb/Sr vs. Th + Zr + Ce diagram may be an appropriate discriminant between metaluminous and peralkaline A-type granites, strongly peraluminous A-type granites and strongly peraluminous orogenic granites. The geochemical evidence indicates that differentiation of the granitic rocks occurred by mineral fractionation from a F

  20. Timing and sources of granite magmatism in the Ribeira Belt, SE Brazil: Insights from zircon in situ U-Pb dating and Hf isotope geochemistry in granites from the São Roque Domain

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; Andrade, Sandra; Vasconcellos, Antonio Carlos B. C.; Henrique-Pinto, Renato; Ulbrich, Horstpeter H. G. J.

    2016-07-01

    Eight new in situ U-Pb zircon age determinations by SHRIMP and LA-MC-ICPMS reveal that the main granitic magmatism in the São Roque Domain, which is largely dominated by metaluminous high-K calc-alkaline monzogranites with subordinate peraluminous leucogranites, occurred between 604 ± 3 and 590 ± 4 Ma. This small temporal range is ca. 20-30 Ma younger than previously admitted based on U-Pb TIMS dates from literature, some of which obtained in the same occurrences now dated. The observed discrepancy seems related to the presence of small Paleoproterozoic inherited cores in part of the zircon populations used for TIMS multigrain dating, which could also respond for the unusually high (up to 10 Ma) uncertainty associated with most of these dates. The younger age range now identified for the São Roque granite magmatism has important implications for the evolution of the Ribeira Fold Belt. Whilst previously admitted ages ca. 620-630 Ma substantiated correlations with the widespread and intensely foliated high-K calc-alkaline granitoid rocks of the neighbor Socorro-Guaxupé Nappe (potentially associated with an accretionary continental margin), the ˜600-590 Ma interval seems more consistent with a late deformation tectonic setting. Strongly negative ɛHf(t) characterize the magmatic zircons from the São Roque Domain granites. An eastward increase from -22 in the São Roque Granite to -11 in the Cantareira Granite and neighboring stocks suggests an across-domain shift in granite sources. Such eastward younging of sources, also indicated by Sm-Nd isotope data from granites and supracrustal sequences in neighboring domains, is suggestive that some of the first-order limits and discontinuities in this belt are not defined by the strike-slip fault systems traditionally taken to separate distinct domains. Although the negative ɛHf(t) and ɛNd(t) indicate sources with long crustal residence for all studied granite plutons, the observed range is more radiogenic than the

  1. Role of magma pressure, tectonic stress and crystallization progress in the emplacement of syntectonic granites. The A-type Estrela Granite Complex (Carajás Mineral Province, Brazil)

    NASA Astrophysics Data System (ADS)

    Barros, C. E. M.; Barbey, P.; Boullier, A. M.

    2001-12-01

    The Archaean, syntectonic, A-type Estrela Granite Complex (Carajás Mineral Province, Brazil) consists of three plutons emplaced in a greenstone sequence under low-pressure conditions (180< P<310 MPa). It is composed mainly of annite-, ferropargasite (±hedenbergite)- and ilmenite-bearing monzogranites. The contact aureole is affected by a subvertical penetrative schistosity conformable with the limits of the plutons. Meso- to microstructures and mineral reactions in the granites indicate that deformation occurred in a continuum from above-solidus to low- T subsolidus conditions. Two distinct planar structures are observed: (i) a concentrical primary foliation (S 0) corresponding to rhythmic, isomodal, phase layering associated with a faint grain shape fabric; it is horizontal in the centre and vertical towards the edges of the plutons; and (ii) a steep to subvertical foliation (S 1) associated with the deformation of S 0 and accompanied with emplacement of synplutonic dykes and veins of leucocratic granites and pegmatites. Emplacement, differentiation and consolidation of the Estrela Granite Complex are considered to result from a continuous evolution under decreasing temperatures in a single-stage strained crust (transpression), with two main periods. (1) The first period is controlled by body forces, and it corresponds to inflation with magma ponding. As long as the rheology is melt dominated, magma pressure is the critical parameter and almost no strain is recorded. With decreasing T, magmas crystallize and differentiate leading to a concentrical magmatic phase layering. The growing magmatic bodies are mechanically decoupled from the country rocks and their evolution depends on internal magma chamber processes. (2) For higher amount of crystallization (residual melt fraction F<0.5), the role of magma pressure becomes insignificant. Establishment of a continuous crystal framework leads to the coupling of plutons with their surroundings, and deformation in

  2. The Wisconsin magmatic terrane: An Early Proterozoic greenstone-granite terrane formed by plate tectonic processes

    NASA Technical Reports Server (NTRS)

    Schulz, K. J.; Laberge, G. L.

    1986-01-01

    The Wisconsin magmatic terrane (WMT) is an east trending belt of dominantly volcanic-plutonic complexes of Early Proterozoic age (approx. 1850 m.y.) that lies to the south of the Archean rocks and Early Proterozoic epicratonic sequence (Marquette Range Supergroup) in Michigan. It is separated from the epicratonic Marquette Range Supergroup by the high-angle Niagara fault, is bounded on the south, in central Wisconsin, by Archean gneisses, is truncated on the west by rocks of the Midcontinent rift system, and is intruded on the east by the post-orogenic Wolf river batholith. The overall lithologic, geochemical, metallogenic, metamorphic, and deformational characteristics of the WMT are similar to those observed in recent volcanic arc terranes formed at sites of plate convergence. It is concluded that the WMT represents an evolved oceanic island-arc terrane accreated to the Superior craton in the Early Proterozoic. This conclusion is strengthened by the apparent absence of Archean basement from most of the WMT, and the recent recognition of the passive margin character of the epicratonic Marquette Range Supergroup.

  3. The giant Pan-African Hook Batholith, Central Zambia: A-type magmatism in a syn-collisional setting

    NASA Astrophysics Data System (ADS)

    Milani, Lorenzo; Lehmann, Jérémie; Naydenov, Kalin V.; Saalmann, Kerstin; Kinnaird, Judith A.; Daly, J. Stephen; Frei, Dirk; Lobo-Guerrero Sanz, Alberto

    2015-04-01

    production of the thickened crust, and is in agreement with the high radioactivity of the pluton. A tectono-thermal model where crustal accretion is accompanied by slab retreat and lithospheric mantle thinning, can reconcile coeval orogenic contraction in the crust and A-type magmatism. The emplacement of the Hook Batholith further supports the idea that A-type granites, commonly considered to be restricted to extension-related environments, can also occur in compressional regimes.

  4. Cause of large negative Eu anomaly in the highly evolved A-type granites with REE tetrad pattern

    NASA Astrophysics Data System (ADS)

    Lee, S.; Asahara, Y.; Tanaka, T.; Lee, M.; Lee, S. R.

    2013-12-01

    REE tetrad pattern with strongly large negative Eu anomaly is one of the specific geochemical phenomena observed in the highly evolved, fractionated granite or A-type granite. The large negative Eu anomaly from the highly evolved or fractionated granites related with REE tetrad effect was discussed in a lot of literatures (e.g. [1] Muecke and Clarke, 1981; [2] Irber, 1999; [3] Jahn et al., 2001). Recently, Lee et al.[4] also suggested that Eu anomalies and REE tetrad pattern from the highly fractionated A-type Muamsa and Weolaksan granites in the Okcheon Metamorphic Belt, Korea, might be associated with a fractionation between the residual melt and a coexisting aqueous high temperature fluid. Their origin and geochemical significance are ongoing yet. In order to clarify cause of large negative Eu anomaly in the granite with REE tetrad effect more clearly, we reanalyzed REE abundance of the Muamsa and Weolaksan granites using MC-ICP-MS at the origins laboratory of the University of Chicago. We also measured REE abundances of the constituent minerals using quadruple ICP-MS at the Korea Polar Research Institute. In this report, we show the re-analyzed REE data from the whole rock as well as new REE data from constituent minerals of the granite with REE tetrad effect. Then, we discuss the cause of large negative Eu anomaly in the highly evolved granite with REE tetrad effect. Especially, the granites with very large negative Eu anomaly also show large negative Ce anomaly. Lee et al. [4] mentioned that negative Ce anomalies were formed after granite emplacement. However, our new data indicate that negative Ce anomaly might be formed during the same geochemical process with very large negative Eu anomaly. This suggests that the REE tetrad effect may be related with a change of oxidation state during a magma evolution. Therefore, we will discuss REE tetrad effect, negative Eu and Ce anomaly as an indicator for the change of oxidation state of magma during the emplacement

  5. The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic-hydrothermal contributions

    NASA Astrophysics Data System (ADS)

    Huston, David L.; Relvas, Jorge M. R. S.; Gemmell, J. Bruce; Drieberg, Susan

    2011-07-01

    characterised by chloritic and sericitic alteration assemblages and lacks aluminous advanced argillic alteration assemblages, is typical of many VHMS deposits around the world, suggesting that for "garden variety" VHMS deposits, a significant magmatic-hydrothermal contribution is not required. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic-hydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, with the Sn closely associated with Cu and in having formed from high 18O-rich fluids (δ18Ofluid ˜8.5‰). We consider these characteristics, particularly the last, as diagnostic of a significant magmatic hydrothermal contribution. Our analysis indicates that two subgroups of VHMS deposits have a major magmatic-hydrothermal contribution: Cu/Au-rich deposits with aluminous alteration assemblages and reduced, very Sn-rich deposits in which Sn was introduced in a high-temperature ore assemblage. Comparison with "normal" VHMS deposits suggests that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu/Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of "normal" VHMS deposits in which relatively dry granites (In this contribution, we use the term granite sensu latto) formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear; however, thick continental crust below the ore-hosting basin may be critical, as it is in other Sn deposits.

  6. Geochronology and geochemistry of late Carboniferous-middle Permian I- and A-type granites and gabbro-diorites in the eastern Jiamusi Massif, NE China: Implications for petrogenesis and tectonic setting

    NASA Astrophysics Data System (ADS)

    Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Xu, Wen-Liang; Yang, Jin-Hui; Xing, De-He; Chen, Hui-Jun

    2016-12-01

    Late Carboniferous-middle Permian magmatism in the Jiamusi Massif of northeast China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), provides critical evidence regarding the tectonic history and geodynamic processes in the region. The gabbro-diorites of the Longtouqiao pluton and two groups of coeval granite in the study area comprise a bimodal magmatic suite. Precise LA-ICP-MS U-Pb zircon ages indicate that the granitoids and gabbro-diorites were emplaced in the late Carboniferous-middle Permian (302-267 Ma). Group I granites have high SiO2 (70.75-77.04 wt.%) and K2O (3.65-5.89 wt.%) contents, are enriched in LILEs (e.g., Rb, Th, and U) relative to HFSEs and LREEs, and have negative Nb, Ta, P, and Ti anomalies, which collectively indicate affinities with subduction-related magmas. Group II granites are weakly peraluminous (A/CNK = 1.03-1.07) and are characterized by enrichment in alkalis (Na2O + K2O = 8.22-8.90 wt.%), low MgO (0.04-0.09 wt.%) and P2O5 (0.01-0.04 wt.%) contents, high Zr and Nb contents, high 10,000 × Ga/Al ratios, and they are geochemically similar to aluminous A-type granites. All the magmatic zircons in these granitoids have great variations of εHf(t) (+ 7.89 to - 5.60) and two-stage Hf model ages (TDM2) of 0.8-1.7 Ga, which suggest that the precursor magmas originated from a heterogeneous source that involved juvenile components derived from a depleted mantle source during magma generation. The aluminous A-type granite magmas were probably derived by high-temperature partial melting of a felsic crustal source, whereas the other granite magmas probably resulted from partial melting of a mafic lower crust. The gabbro-diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for large positive anomalies in Ba, K, and Pb. These features reflect a limited degree of crustal contamination associated with the subduction-related magmatic processes. These data

  7. Evolution by Replenishment Fractional Crystallization (RFC) of Midproterozoic Magmatic Enclaves in Granites of the Eastern Llano Uplift, central Texas, U.S.A

    NASA Astrophysics Data System (ADS)

    Smith, R. K.; Gray, W.

    2009-12-01

    The Llano Uplift is a gentle structural dome exposing both island-arc and continental margin blocks emplaced along the southern margin of Laurentia during the Grenville orogeny (locally the Llano orogeny). These ~1370 to 1230 Ma metaigneous and metasedimentary rocks were subsequently intruded by a number of ~1119 to 1070 Ma post-to syntectonic granitic plutons collectively known as the Town Mountain Granite. The eastern most of these plutons (Lone Grove, Kingsland, and Marble Falls plutons) contain sparse microgranular magmatic enclaves of intermediate composition (56-68 wt.% SiO2). The enclaves display sharp borders in contact with the host granite suggesting magma quenching with little or no physical exchange between host granite and enclave magma. The origin of the enclave magma(s) is uncertain, as no synchronous mafic to intermediate rocks are exposed in the Uplift. New major- and trace-element analyses are providing clues as to the possible origins and evolution of the enclave magmas. Numerical modeling reveals that neither fractional crystallization nor simple mixing can explain the trace-element trends. However, assuming source magmas similar to primitive continental arc andesites, the trends can be adequately replicated by a replenishment fractional crystallization(RFC) model. The model assumes that replenishment/hybridization events are accompanied by 20%-30% fractionation of plagioclase + clinopyroxene + magnetite. Modeling further reveals that results are relatively insensitive to the number of replenishment events (from 50 to 1000), as well as perturbations in the mineral percentages, suggesting that RFC is a very plausible and robust explanation for the chemical evolution of the enclaves. As suggested by Weibe et al. (1997), RFC and lack of magma exchange may be indicative of enclave magma ponding and hybridization at the base of the host granite magma chamber, followed by occasional dispersment into the host granite. Origin from a primitive

  8. Crustally derived granites in Dali, SW China: new constraints on silicic magmatism of the Central Emeishan Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Zhu, Bei; Peate, David W.; Guo, Zhaojie; Liu, Runchao; Du, Wei

    2017-03-01

    We have identified a new crustally derived granite pluton that is related to the Emeishan Large Igneous Province (ELIP). This pluton (the Wase pluton, near Dali) shows two distinct SHRIMP zircon U-Pb age groups ( 768 and 253 Ma). As it has an intrusive relationship with Devonian limestone, the younger age is interpreted as its formation, which is related to the ELIP event, whereas the 768 Ma Neoproterozoic-aged zircons were inherited from Precambrian crustal component of the Yangtze Block, implying the pluton has a crustally derived origin. This is consistent with its peraluminous nature, negative Nb-Ta anomaly, enrichment in light rare earth elements, high 87Sr/86Sr(i) ratio (0.7159-0.7183) and extremely negative ɛ(Nd)(i) values (-12.15 to -13.70), indicative of melts derived from upper crust materials. The Wase pluton-intruded Devonian strata lie stratigraphically below the Shangcang ELIP sequence, which is the thickest volcanic sequence ( 5400 m) in the whole ELIP. The uppermost level of the Shangcang sequence contains laterally restricted rhyolite. Although the rhyolite has the same age as the Wase pluton, its geochemical features demonstrate a different magma origin. The rhyolite displays moderate 87Sr/86Sr(i) (0.7053), slightly negative ɛ(Nd)(i) (-0.18) and depletions in Ba, Cs, Eu and Sr, implying derivation from differentiation of a mantle-derived mafic magma source. The coexistence of crustally and mantle-derived felsic systems, along with the robust development of dike swarms, vent proximal volcanics and thickest flood basalts piles in Dali, shows that the Dali area was probably where the most active Emeishan magmatism had once existed.

  9. Late-magmatic immiscibility during batholith formation: assessment of B isotopes and trace elements in tourmaline from the Land's End granite, SW England

    NASA Astrophysics Data System (ADS)

    Drivenes, Kristian; Larsen, Rune B.; Müller, Axel; Sørensen, Bjørn E.; Wiedenbeck, Michael; Raanes, Morten P.

    2015-06-01

    Quartz-tourmaline orbicules are unevenly distributed in the roof segment of the Land's End granite, SW England. This study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization, and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes. Trace elements and boron isotope fractionation can be tracked in tourmaline, and create a timeline for crystallization. Tourmaline from the granite matrix has higher V, Cr and Mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline. Overgrowths of blue tourmaline, occurring together with quartz showing hydrothermal cathodoluminescence textures, crystallized from an aqueous fluid during the very last crystallization, and are significantly higher in Sr and Sn, and isotopically heavier. Tourmaline associated with Sn mineralization is also high in Sr and Sn, but has boron isotopic compositions close to that of the magmatic tourmaline, and is not formed by the same fluids responsible for the blue overgrowths. The ore-forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite, but exsolved deeper in the magma chamber, and at a later stage than orbicule formation. Tourmaline from massive quartz-tourmaline rocks is concentrically zoned, with major and trace element compositions indicating crystallization from a similar melt as for the orbicules, but shows a more evolved signature.

  10. Rb-Sr and Sm-Nd study of granite-charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

    NASA Astrophysics Data System (ADS)

    Sekaran, M. Chandra; Bhutani, Rajneesh; Balakrishnan, S.

    2016-04-01

    Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ˜550 Ma. The initial Nd isotope ratios (\\varepsilon _{ {Nd}}t=-20 to -22) and Nd depleted-mantle model ages (TDM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (\\varepsilon _{ {Nd}}t= -29 and TDM = > 3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an `apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which `prepared' the residual crust to sustain the high P- T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

  11. Characterization and origin of the Taishanmiao aluminous A-type granites: implications for Early Cretaceous lithospheric thinning at the southern margin of the North China Craton

    NASA Astrophysics Data System (ADS)

    Wang, Changming; Chen, Liang; Bagas, Leon; Lu, Yongjun; He, Xinyu; Lai, Xiangru

    2016-07-01

    Late Mesozoic magmatic rocks from the Taishanmiao Batholith were collected for LA-ICP-MS dating, Sr-Nd-Hf isotope systematics, and whole-rock major and trace element geochemistry to help understand the nature of collisional and extensional events along the southern margin of the North China Craton. The batholith consists of three texturally distinguishable phases of a 125 ± 1 Ma medium- to coarse-grained syenogranite, a 121 ± 1 Ma fine- to medium-grained syenogranite, and a 113 ± 1 Ma porphyritic monzogranite. Most of the units in the batholith are syenogranitic in composition with high levels of silica (70-78 wt% SiO2), alkalis (8.0-8.6 wt% Na2O + K2O), Fe* (FeOT/(FeOT + MgO) = 0.76-0.90), and depletion in CaO (0.34-1.37 wt%), MgO (0.12-0.52 wt%), TiO2 (0.09-0.40 wt%), and A/CNK (Al2O3/(Na2O + K2O + CaO)) molar ratios of 1.00-1.11. All samples have high proportions of Ga, Nb, Zr, Ga/Al, and REE, and depletions in Ba, Sr, Eu, and compatible elements, indicating that the batholith consists of A-type granites. The zircon saturation temperature for these units yields a mean value of 890 °C, and zircons with Early Cretaceous magmatic ages have ɛNd( t) values of -14.0 to -12.0, ɛHf( t) values ranging from -18.7 to -2.1, and corresponding Hf model ages of 2339-1282 Ma. These geochemical and isotopic characteristics allowed us to conclude that the primary magma for the Taishanmiao Batholith originated from partial melting of Precambrian crustal rocks in the medium-lower crust. However, the high Nb and Ta contents and low normalized Nb/Ta values for the Taishanmiao granites are due to fractionation in Nb- and Ta-rich amphibole (or biotite). It is further proposed that these aluminous A-type granites were generated in an extensional tectonic setting during the Early Cretaceous, which was induced by lithospheric thinning and asthenospheric upwelling beneath eastern China toward the Paleo-Pacific Plate.

  12. Production of hybrid granitic magma at the advancing front of basaltic underplating: Inferences from the Sesia Magmatic System (south-western Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Sinigoi, Silvano; Quick, James E.; Demarchi, Gabriella; Klötzli, Urs S.

    2016-05-01

    The Permian Sesia Magmatic System of the southwestern Alps displays the plumbing system beneath a Permian caldera, including a deep crustal gabbroic complex, upper crustal granite plutons and a bimodal volcanic field dominated by rhyolitic tuff filling the caldera. Isotopic compositions of the deep crustal gabbro overlap those of coeval andesitic basalts, whereas granites define a distinct, more radiogenic cluster (Sri ≈ 0.708 and 0.710, respectively). AFC computations starting from the best mafic candidate for a starting melt show that Nd and Sr isotopic compositions and trace elements of andesitic basalts may be modeled by reactive bulk assimilation of ≈ 30% of partially depleted crust and ≈ 15%-30% gabbro fractionation. Trace elements of the deep crustal gabbro cumulates require a further ≈ 60% fractionation of the andesitic basalt and loss of ≈ 40% of silica-rich residual melt. The composition of the granite plutons is consistent with a mixture of relatively constant proportions of residual melt delivered from the gabbro and anatectic melt. Chemical and field evidence leads to a conceptual model which links the production of the two granitic components to the evolution of the Mafic Complex. During the growth of the Mafic Complex, progressive incorporation of packages of crustal rocks resulted in a roughly steady state rate of assimilation. Anatectic granite originates in the hot zone of melting crust located above the advancing mafic intrusion. Upward segregation of anatectic melts facilitates the assimilation of the partially depleted restite by stoping. At each cycle of mafic intrusion and incorporation, residual and anatectic melts are produced in roughly constant proportions, because the amount of anatectic melt produced at the roof is a function of volume and latent heat of crystallization of the underplated mafic melt which in turn produces proportional amounts of hybrid gabbro cumulates and residual melt. Such a process can explain the

  13. New U Pb SHRIMP zircon age for the Schurwedraai alkali granite: Implications for pre-impact development of the Vredefort Dome and extent of Bushveld magmatism, South Africa

    NASA Astrophysics Data System (ADS)

    Graham, I. T.; De Waal, S. A.; Armstrong, R. A.

    2005-12-01

    The Schurwedraai alkali granite is one of a number of prominent ultramafic-mafic and felsic intrusions in the Neoarchaean to Palaeoproterozoic sub-vertical supracrustal collar rocks of the Vredefort Dome, South Africa. The alkali granite intruded the Neoarchaean Witwatersrand Supergroup and has a peralkaline to peraluminous composition. A new zircon SHRIMP crystallization age of 2052 ± 14 Ma for the Schurwedraai alkali granite places it statistically before the Vredefort impact event at 2023 ± 4 Ma and within the accepted emplacement interval of 2050-2060 Ma of the Bushveld magmatic event. The presence of the alkali granite and associated small ultramafic-mafic intrusions in the Vredefort collar rocks extends the southern extremity of Bushveld-related intrusions to some 120 km south of Johannesburg and about 150 km south of the current outcrop area of the Bushveld Complex. The combined effect of these ultramafic-mafic and felsic bodies may have contributed to a pronouncedly steep pre-impact geothermal gradient in the Vredefort area, and to the amphibolite-grade metamorphism observed in the supracrustal collar rocks of the Vredefort Dome.

  14. Boron and boron isotope systematics in the peralkaline Ilímaussaq intrusion (South Greenland) and its granitic country rocks: A record of magmatic and hydrothermal processes

    NASA Astrophysics Data System (ADS)

    Kaliwoda, Melanie; Marschall, Horst R.; Marks, Michael A. W.; Ludwig, Thomas; Altherr, Rainer; Markl, Gregor

    2011-07-01

    Concentrations of boron in whole rocks and minerals of the peralkaline, 1.16 Ga Ilímaussaq intrusion and its granitic country rocks (South Greenland) were analysed using secondary ion mass spectrometry (SIMS) and prompt gamma neutron activation (PGNAA) analysis. The intrusion consists of an early augite-syenite shell, a later alkali-granite sheet and still later nepheline syenites, which dominate the Complex. Boron concentrations are high (250-280 μg/g) in all rocks containing fresh sodalite, whereas boron is constantly low in the sodalite-free augite syenites (4-6 μg/g) and in the alkali granites (7-22 μg/g). Rocks with sodalite altered to analcime contain only low amounts of boron (2-7 μg/g), which records boron extraction by late-magmatic fluids. Concentration profiles of B in the analysed minerals (olivine, amphibole, clinopyroxene, aenigmatite, eudialyte, biotite, feldspar, nepheline and sodalite) record magmatic fractionation to various extents, late-magmatic to hydrothermal fluid/rock interaction, and sub-solidus diffusion. Whole-rock concentration data cannot be directly translated into the geochemical evolution of the peralkaline melts, since they are largely affected by cumulate fractionation of sodalite and amphibole and furthermore by late-stage hydrothermal alteration processes resulting in B loss. However, trace-element concentrations of mineral zones representing equilibrium fractionation from magmatic liquids can be used in combination with mineral-melt partition coefficients to unravel the enrichment processes of elements in the melt. Boron isotope values of minerals from the intrusion and the country rocks resemble the trend observed for Li isotopes in an earlier study. Amphibole and feldspar display a clear trend from light boron in the inner nepheline syenitic part of the intrusion (δ11B = -20‰ and -17‰ for amphibole and feldspar, respectively) through intermediate values in the outer augite syenites (δ11B = -10‰ and -6‰ for

  15. Geochronology- and Geochemistry of Late Carboniferous-Middle Permian I- and A-Type Granites and Gabro-Diorites in the Eastern Jimausi Massif, NE, China: Implications for a Tectonic Transition

    NASA Astrophysics Data System (ADS)

    Bi, Junhui; Ge, Wenchun

    2016-04-01

    The late Paleozoic magmatism in the Jiamusi Massif of northeast China, located in the eastern segment of the Central Asian Orogenic Belt (CAOB), was dominated by an active continental margin environment due to subduction of the paleo-oceanic plate. Nevertheless, what deep geodynamic processes controlled the late Paleozoic evolution of the Jiamusi Massif are still poorly constrained. In this contribution, we present zircon U-Pb ages and geochemical data of late Carboniferous-middle Permian magmatism in the Jiamusi Massif, aiming to provide constraints on the question. Precise LA-ICP-MS U-Pb zircon ages indicate that the granitoids and gabbro-diorites were emplaced in the late Carboniferous-middle Permian (302-267 Ma). The granites belong to a high-potassium calc-alkaline series, are weakly peraluminous I- and A-type granites, and show high SiO2 and K2O contents; they are depleted in high field strength elements (HFSEs), enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), show weakly to mildly fractionated REE patterns, and on spidergrams show arc-type affinities with strong depletions in Nb, Ta, and Ti. The combination of heterogeneous values of ɛHf(t) for magmatic zircons in all granitoids (ranging from +7.9 to -5.6) and two-stage Hf model ages (TDM2) of 0.8-1.7 Ga suggests that the granites originated from partial melting of a predominantly "old" Meso-Neoproterozoic crustal source. The gabbro-diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for marked large positive anomalies in Ba, K, and Pb. These features reflect limited degrees of crustal contamination associated with subduction-related magma processes. These data, together with previously reported data and the occurrence of arc magmatic rocks along the eastern part of the Jiamusi Massif, suggest that the intrusive rocks formed during westward subduction of the Paleo-Pacific Ocean lithosphere

  16. Age, tectonic setting, and metallogenic implication of Phanerozoic granitic magmatism at the eastern margin of the Xing'an-Mongolian Orogenic Belt, NE China

    NASA Astrophysics Data System (ADS)

    Chen, Cong; Ren, Yunsheng; Zhao, Hualei; Yang, Qun; Shang, Qingqing

    2017-08-01

    The eastern margin of the Xing'an-Mongolian Orogenic Belt is characterised by widespread Phanerozoic granitic magmatism, some of which is closely related to significant ore mineralisation. This paper presents new geochronological, petrogenetic, and tectonic data for selected intrusions. Zircon U-Pb geochronology for five granitoid plutons indicates they were emplaced during the middle-late Permian (264-255 Ma) and Cretaceous (106-94 Ma), and thus granitic magmatism occurred throughout the Phanerozoic, Permian (268-252 Ma), Early-Middle Triassic (248-240 Ma), Early Jurassic (183 Ma), and Cretaceous (112-94 Ma). The Permian granitoids consist of monzogranite, granodiorite, tonalite, and quartz diorite, characterised by enrichment in Na2O (3.60-4.72 wt.%), depletion in K2O (0.97-2.66 wt.%), and a negative correlation between P2O5 and SiO2. Together with the presence of hornblende, these geochemical features are indicative of an I-type affinity. The Permian granitic magmatism is associated with quartz-vein-type tungsten deposits (252 Ma; unpublished Sm-Nd isochron age), which formed in an active continental margin setting related to subduction of the Palaeo-Asian Ocean. The Cretaceous quartz diorites have an adakitic affinity, having relatively high Sr (374-502 ppm), low Yb (0.51-0.67 ppm) and Y (8.7-10.7 ppm), and high Sr/Y (39.4-46.8) and (La/Yb)N values (16.2-34.7), suggesting that they were related to the partial melting of subducted oceanic crust. In addition, they are associated with porphyry Au-Cu deposits. We conclude that the Cretaceous granitic rocks and associated porphyry Au-Cu mineralisation occurred in an extensional tectonic setting related to the subduction of the Palaeo-Pacific Plate beneath the Eurasian Plate. In addition, the large-scale Early-Middle Triassic syn-collisional granite belt at the eastern margin of the Xing'an-Mongolian Orogenic Belt extends from the middle of Jilin Province to the Wangqing-Hunchun region, constraining the timing of the

  17. A-type magmatism in a syn-collisional setting: The case of the Pan-African Hook Batholith in Central Zambia

    NASA Astrophysics Data System (ADS)

    Milani, Lorenzo; Lehmann, Jérémie; Naydenov, Kalin V.; Saalmann, Kerstin; Kinnaird, Judith A.; Daly, J. Stephen; Frei, Dirk; Lobo-Guerrero Sanz, Alberto

    2015-02-01

    The Pan-African Hook Batholith formed during the assembly of the Gondwana supercontinent as a result of syn-collisional stage interaction between the Congo and Kalahari Cratons. The bimodal magmatism (mafic to predominantly felsic) is characterized by both an alkali-calcic and an alkalic suite, with typical A-type, metaluminous, high Fe/Mg and K/Na geochemical signature. Occasionally, sodic granitoids have been documented. Compositions were driven to more differentiated products by fractional crystallization, while Sr-Nd isotopes exclude crustal assimilation during crystallization. Recent new U-Pb age data constrain most of the felsic magmatism between 550 and 540 Ma. Scattered outcrops of gabbroic rocks, both tholeiitic and alkaline, testify to periodic input of mantle material, and, in some cases, to interaction with metasomatizing fluids. Crystallization ages on mafic rocks span from 570 to 520 Ma, thus indicating that they were contemporaneous with the major granitic intrusion, which was the result of a number of successive felsic batches, eventually forming a coalescing batholith. Highly radiogenic Pb isotopic values attest to the radiogenic character of the rocks. Such an anomalous signature was acquired during, or soon after, magma emplacement, perhaps as result of metasomatizing fluids. Enrichment in Th-U of large portions of the crust along this part of the margin of the Congo Craton is suggested. Geochemical and isotopic evidence support the interaction between mantle components and portions of the deep crust at pressure of < 10 kbar, while decompression melting of rising asthenospheric mantle ponding at the base of the crust heated, and ultimately melted, crustal material. An additional and crucial contribution to the crustal melting was likely provided by internal radiogenic heat production of the thickened crust, and is in agreement with the high radioactivity of the pluton. A tectono-thermal model, implying crustal accretion accompanied by slab

  18. Geochemistry and petrogenesis of Mesoproterozoic (~ 1.1 Ga) magmatic enclaves in granites of the eastern Llano Uplift, central Texas, USA

    NASA Astrophysics Data System (ADS)

    Smith, R. K.; Gray, Walt

    2011-07-01

    Mesoproterozoic (~ 1.1 Ga) plutons of the eastern Llano Uplift, central Texas, USA contain two types of magmatic enclaves (< 1% by vol.). Although volumetrically insignificant, the enclaves contain important petrogenetic information. Type I enclaves are felsic in composition (70-75 wt.% SiO2), with mineral assemblages and chemical compositions comparable with the host granites, but typically display a finer grained texture. They are interpreted as partly chilled disrupted material from the margins and roof of the plutons. Type II enclaves are intermediate in composition (~ 56-69 wt.% SiO2), with many elements defining trends continuous with the host granites. Both types of enclaves display sharp borders in contact with the host granite suggesting magma quenching with little or no physical exchange between host granite and enclave magma. Type II enclaves contained within the Marble Falls (MF) and Lone Grove (LG) plutons exhibit enrichments in Y, Nb, and Zr relative to their respective host granites. Enrichments in these incompatible trace elements at low SiO2, renders unlikely the possibility that the MF and LG Type II enclaves are the result of partial melting (anatexis) of mafic crustal rocks. Numerical modeling of fractional crystallization and simple mixing fails to explain the observed trace element trends. Because no coeval mafic to intermediate rocks are exposed in the uplift, characteristics of Type II enclave source magma(s) is uncertain. However, assuming source magmas similar to primitive continental arc basaltic andesite, trace-element trends (i.e., incompatible element enrichment and compatible element depletion) can be adequately replicated by a replenishment fractional crystallization (RFC) model. Chemistry of the MF and LG Type II enclaves suggest repeated replenishment of primitive magmas with only limited interaction with the host granitic magmas; the more primitive enclave magmas evolving in near chemical isolation by RFC processes. However

  19. Fault controlled Carboniferous A-type magmatism in the proto-Andean foreland (Sierras Pampeanas, Argentina): Geochemical constraints and petrogenesis

    NASA Astrophysics Data System (ADS)

    Dahlquist, Juan A.; Alasino, Pablo H.; Eby, G. Nelson; Galindo, Carmen; Casquet, César

    2010-03-01

    The intrusion of granitoids into the Eastern Sierras Pampeanas in the Early Carboniferous took place after a long period of mainly compressional deformation that included the Famatinian (Ordovician) and Achalian (Devonian) orogenies. These granitoids occur as small scattered plutons emplaced in a dominant extensional setting, within older metamorphic and igneous rocks, and many of them are arranged along a reactivated large shear zone. A set of 46 samples from different granitic rocks: Huaco granitic complex, San Blas pluton, and the La Chinchilla stock from the Sierra de Velasco, Zapata granitic complex from Sierra de Zapata, and the Los Árboles pluton from Sierra de Fiambalá, display high and restricted SiO 2 contents between 69.2 and 76.4 wt.%. On both FeO/(FeO + MgO) vs. SiO 2 and [(Na 2O + K 2O) - CaO] vs. SiO 2 plots the samples plot in the ferroan and alkaline-calcic to calco-alkaline fields (FeO/(FeO + MgO) = 0.88-1.0%;[(Na 2O + K 2O) - CaO] = 6.3-8.3%), thus showing an A-type granitoid signature. The high concentrations for the High Field Strength Elements (HSFE), such as Y, Nb, Ga, Ta, U, Th, etc. and flat REE patterns showing significant negative Eu anomalies are also typical features of A-type granites. Our petrogenetic model supports progressive fractional crystallization with dominant fractionation of feldspar and a source mineral assemblage enriched in plagioclase. Biotites have distinctive compositions with high FeO/MgO ratios (7.8-61.5), F (360-5610 ppm), and Cl (120-1050 ppm). The FeO/MgO ratios together with the F and Cl content of igneous biotites seem to reflect the nature of their parental host magmas and may be useful in identifying A-type granitoids. The isotopic data (Rb-Sr and Sm-Nd) confirm that the A-type granites represent variable mixtures of asthenospheric mantle and continental crust and different mixtures lead to different subtypes of A-type granite (illustrating the lack of consensus about A-type magma origin). We conclude that

  20. The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

    NASA Astrophysics Data System (ADS)

    Simons, B.; Shail, Robin K.; Andersen, Jens C. Ø.

    2016-09-01

    not exhibit the typical geochemical characteristics of intraplate A-type granites.

  1. Long-lived interaction between hydrothermal and magmatic fluids in the Soultz-sous-Forêts granitic system (Rhine Graben, France)

    NASA Astrophysics Data System (ADS)

    Gardien, Véronique; Rabinowicz, Michel; Vigneresse, Jean-Louis; Dubois, Michel; Boulvais, Philippe; Martini, Rossana

    2016-03-01

    The 5 km deep drilling at Soultz-sous-Forêts samples a granitic intrusion under its sedimentary cover. Core samples at different depths allow study of the evolving conditions of fluid-rock interaction, from the syn-tectonic emplacement of Hercynian granites at depth until post-cooling history and alteration close to the surface. Hydrogen, carbon and oxygen isotope compositions of CO2 and H2O have been measured in fluid inclusions trapped in magmatic quartz within samples collected along the drill core. Early Fluid Inclusions Assemblage (FIA) contains aqueous carbonic fluids whereas the latest FIA are H2O-rich. In the early FIA, the amount of CO2 and the δ13C value both decrease with depth, revealing two distinct sources of carbon, one likely derived from sedimentary carbonates (δ13C = - 2‰ V-PDB) and another from the continental crust (δ13C = - 9‰ V-PDB). The carbon isotope composition of bulk granites indicates a third carbon source of organic derivation (δ13C = - 20‰ V-PDB). Using a δD - δ18O plot, we argue that the water trapped in quartz grains is mainly of meteoric origin somewhat mixed with magmatic water. The emplacement of the Soultz-sous-Forêts granite pluton occurred in a North 030-040° wrench zone. After consolidation of the granite mush at 600 °C, sinistral shear (γ 1) concentrated the final leucocratic melt in vertical planes oriented along (σ1, σ2). Crystallization of this residual leucocratic melt occurred while shearing was still active. At a temperature of 550 °C, crystallization ended with the formation of vertical quartz veins spaced about 5 mm, and exhibiting a width of several cm. The quartz veins form a connected network of a few kilometers in height, generated during hydrothermal contraction of the intrusion. Quartz crystallization led to the exsolution of 30% by volume of the aqueous fluid. As quartz grains were the latest solid phase still plastic, shearing localized inside the connected quartz network. Aqueous fluid was

  2. The physical hydrology of magmatic-hydrothermal systems: High-resolution 18O records of magmatic-meteoric water interaction from the Yankee Lode tin deposit (Mole Granite, Australia)

    NASA Astrophysics Data System (ADS)

    Fekete, Szandra; Weis, Philipp; Driesner, Thomas; Heinrich, Christoph A.; Baumgartner, Lukas; Bouvier, Anne-Sophie

    2016-04-01

    Magmatic-hydrothermal ore deposits are important economic Cu, Au, Mo and Sn resources (Sillitoe, 2010, Kesler, 1994). The ore formation is a result of superimposed enrichment processes and metals can precipitate due to fluid-rock interaction and/or temperature drop caused by convection or mixing with meteoric fluid (Heinrich and Candela 2014). Microthermometry and LA-ICP MS trace element analyses of fluid inclusions of a well-characterized quartz sample from the Yankee Lode quartz-cassiterite vein deposit (Mole Granite, Australia) suggest that tin precipitation was driven by dilution of hot magmatic water by meteoric fluids (Audétat et al.1998). High resolution in situ oxygen isotope measurements of quartz have the potential to detect changing fluid sources during the evolution of a hydrothermal system. We analyzed the euhedral growth zones of this previously well-studied quartz sample. Growth temperatures are provided by Audétat et al. (1998) and Audétat (1999). Calculated δ 18O values of the quartz- and/or cassiterite-precipitating fluid show significant variability through the zoned crystal. The first and second quartz generations (Q1 and Q2) were precipitated from a fluid of magmatic isotopic composition with δ 18O values of ˜ 8 - 10 ‰. δ 18O values of Q3- and tourmaline-precipitating fluids show a transition from magmatic δ 18O values of ˜ 8 ‰ to ˜ -5 ‰. The outermost quartz-chlorite-muscovite zone was precipitated from a fluid with a significant meteoric water component reflected by very light δ 18O values of about -15 ‰ which is consistent with values found by previous studies (Sun and Eadington, 1987) using conventional O-isotope analysis of veins in the distal halo of the granite intrusion. Intense incursion of meteoric water during Q3 precipitation (light δ 18O values) agrees with the main ore formation event, though the first occurrence of cassiterite is linked to Q2 precipitating fluid with magmatic-like isotope signature. This

  3. Temporal and compositional variation within the Early Paleogene Silhouette/North Island A-type Granite Complex, Seychelles

    NASA Astrophysics Data System (ADS)

    Shellnutt, G.; Lee, T. Y.; Yeh, M. W.

    2016-12-01

    The Main Islands of the Seychelles are primarily composed of Neoproterozoic ( 750 Ma to 800 Ma) granites that were formed at an Andean-type margin. The Early Paleogene Silhouette/North Island volcano-plutonic complex is located to the NW of the Main Islands and is attributed to magmatism associated with the eruption of the Deccan Traps and rifting of the Seychelles microcontinent from India. The zircon 206Pb/238U ages show that the silicic volcanic and plutonic rocks from Silhouette are generally older (i.e. 64.9 ± 1.6 Ma to 62.3 ± 0.8 Ma) than the rocks from North Island (i.e. 61.0 ± 0.8 Ma to 60.6 ± 0.7 Ma). The Danian-Selandian age of the Silhouette/North Island complex is younger than the peak eruption time of the Deccan Traps (i.e. 65 ± 1 Ma) suggesting that it was emplaced during the continental rifting/sea-floor spreading transition. The granitic rocks from both islands are compositionally ferroan and alkalic (ACNK < 1; Na+K/Al = 0.8 to 1.1) and correspond to within-plate granites. The whole rock Sr and Nd and zircon Hf isotopes reveal that there are subtle differences between the islands with Silhouette generally have higher 87Sr/86Sri (0.7035 to 0.7061) ratios, and lower ɛNd(t) (+0.5 to +2.9) and ɛHf(t) (+3.8 to +5.2) values than North Island (87Sr/86Sri = 0.7036 to 0.7041; ɛNd(t) = +1.4 to +3.8; ɛHf(t) = +4.6 to +6.2). The granitic rocks were likely derived by fractional crystallization of parental magmas similar to the composition of the volumetrically minor mafic intrusive rocks found on each island. The modeling conditions that produce the best results are hydrous (H2O ≤ 1.5 wt%), slightly reducing (FMQ ≤ 0) and shallow pressure (≤ 0.3 GPa). Crustal contamination is documented within the rocks from Silhouette but appears to be negligible or absent within the North Island rocks. The spatial and temporal differences between the two islands can be explained by the movement of the plate over the magma source as the Seychelles microcontinent

  4. Petrogenesis of A-type granites and origin of vertical zoning in the Katharina pluton, Gebel Mussa (Mt. Moses) area, Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Katzir, Y.; Eyal, M.; Litvinovsky, B. A.; Jahn, B. M.; Zanvilevich, A. N.; Valley, J. W.; Beeri, Y.; Pelly, I.; Shimshilashvili, E.

    2007-05-01

    ; the δ18O (Fsp) values point to magmatic origin of fluids. The stable and radiogenic isotope data [ δ18O (Zrn) = 5.82 ± 0.06‰, ISr = 0.7022 ± 0.0064, ɛNd ( T) values are + 3.6 and + 3.9] indicate that the granite magma was generated from a 'juvenile' source, which is typical of the rocks making up most of the Arabian-Nubian shield.

  5. The molybdenum isotopic compositions of I-, S- and A-type granitic suites

    NASA Astrophysics Data System (ADS)

    Yang, Jie; Barling, Jane; Siebert, Christopher; Fietzke, Jan; Stephens, Ed; Halliday, Alex N.

    2017-05-01

    This study reports Mo isotopic compositions for fifty-two Palaeozoic granitic rocks with contrasting source affinities (A-, I- and S-type) from the Lachlan Fold Belt (LFB) and the New England Batholith (NEB), both in SE Australia, and three compositionally zoned plutons (Loch Doon, Criffell, and Fleet) located in the Southern Uplands of Scotland. The results show relatively large variations in δ98Mo for igneous rocks ranging from -1.73‰ to 0.59‰ with significant overlaps between different types. No relationships between δ98Mo and δ18O or ASI (Alumina Saturation Index) are observed, indicating that Mo isotopes do not clearly distinguish igneous vs. sedimentary source types. Instead, effects of igneous processes, source mixing, regional geology, as well as hydrothermal activity control the Mo isotope compositions in these granites. It is found that Mo is mainly accommodated in biotite and to a lesser extent in hornblende. Hornblende and Fe3+-rich minerals may preferentially incorporate light isotopes, as reflected by negative correlations between δ98Mo and K/Rb and [Fe2O3]. There is a positive correlation between initial 87Sr/86Sr and δ98Mo in I-type granitic rocks, reflecting the admixing of material from isotopically distinct sources. Granitic rocks from Scotland and Australia display strikingly similar curvilinear trends in δ98Mo vs. initial 87Sr/86Sr despite the differing regional geology. Localized hydrothermal effects can result in low δ98Mo in granite, as seen in three samples from Loch Doon and Criffell which have anomalously light δ98Mo of <-1‰. Based on this study, an estimate of δ98Mo = 0.14 ± 0.07‰ (95% s.e.) for the Phanerozoic upper crust is proposed. This is slightly heavier than basalts indicating an isotopically light lower crust and/or a systematic change to the crust resulting from subduction of isotopically light dehydrated slab and/or pelagic sediment over time.

  6. A-type granites from the Guéra Massif, Central Chad: Petrology, geochemistry, geochronology, and petrogenesis.

    NASA Astrophysics Data System (ADS)

    Pham, Ngoc Ha T.; Shellnutt, J. Gregory; Yeh, Meng-Wan; Lee, Tung-Yi

    2017-04-01

    The poorly studied Saharan Metacraton of North-Central Africa is located between the Arabian-Nubian Shield in the east, the Tuareg Shield in the west and the Central African Orogenic Belt in the south. The Saharan Metacraton is composed of Neoproterozoic juvenile crust and the relics of pre-Neoproterozoic components reactivated during the Pan-African Orogeny. The Republic of Chad, constrained within the Saharan Metacraton, comprises a Phanerozoic cover overlying Precambrian basement outcroppings in four distinct massifs: the Mayo Kebbi, Tibesti, Ouaddaï, and the Guéra. The Guéra massif is the least studied of the four massifs but it likely preserves structures that were formed during the collision between Congo Craton and Saharan Metacraton. The Guéra Massif is composed of mostly granitic rocks. The granitoids have petrologic features that are consistent with A-type granite, such as micrographic intergrowth of sodic and potassic feldspar, the presence of sodic- and iron-rich amphibole, and iron-rich biotite. Compositionally, the granitic rocks of the Guéra Massif have high silica (SiO2 ≥ 68.9 wt.%) content and are metaluminous to marginally peraluminous. The rocks are classified as ferroan calc-alkalic to alkali-calcic with moderately high to very high Fe* ratios. The first zircon U/Pb geochronology of the silicic rocks from the Guéra Massif yielded three main age groups: 590 Ma, 570 Ma, 560 Ma, while a single gabbro yielded an intermediate age ( 580 Ma). A weakly foliated biotite granite yielded two populations, in which the emplacement age is interpreted to be 590 ± 10 Ma, whereas the younger age (550 ± 11 Ma) is considered to be a deformation age. Furthermore, inherited Meso- to Paleoproterozoic zircons are found in this sample. The geochemical and geochronology data indicate that there is a temporal evolution in the composition of rocks with the old, high Mg# granitoids shifting to young, low Mg# granitoids. This reveals that the A-type granites in

  7. Pan-African alkali granites and syenites of Kerala as imprints of taphrogenic magmatism in the South Indian shield

    NASA Technical Reports Server (NTRS)

    Santosh, M.; Drury, S. A.; Iyer, S. S.

    1988-01-01

    Granite and syenite plutons with alkaline affinities ranging in age from 550 to 750 Ma sporadically puncture the Precambrian granulites of the Kerala region. All the bodies are small (20 to 60 sq km), E-W to NW-SE elongated elliptical intrusives with sharp contacts and lie on or close to major late Proterozoic lineaments. Geochemical plots of A-F-M and An-Ab-Or relations show an apparent alkali enrichment trend on the former, but the plutons define relatively distinct fields on the latter. Most of the plutons are adamellitic to granitic by chemistry. The variations of SiO2 with log sub 10 K2O/MgO (1) brings out the distinct alkaline nature of the plutons. Some of the granites are extremely potassic, like the Peralimala pluton, which shows up to 11.8 percent K2O. On a SiO2-Al2O3-Na2O+K2O (mol percent) plot, the plutons vary from peraluminous to peralkaline, but none are nepheline normative. Low MgO, low to moderate CaO and high Fe2O3/FeO values are other common characteristics. Among trace elements, depletion of Ba, Sr and Rb with high K/Ba and K/Rb values are typical. Overall, the plutons show a trend of decreasing K/Rb ratio with increasing K content. Individual plutons show more clearly defined trends similar to those from granitic masses characterized by plagioclase fractionation.

  8. Origin of high Sr/Y-type granitic magmatism in the southwestern of the Alxa Block, Northwest China

    NASA Astrophysics Data System (ADS)

    Zhou, Xiao-Chun; Zhang, Hong-Fei; Luo, Bi-Ji; Pan, Fa-Bin; Zhang, Sha-Sha; Guo, Liang

    2016-07-01

    The petrogenesis of high Sr/Y-type magmas is still open to debate. Usually, such magmas could result from melting under high-pressure settings (> 12 kbar). In this paper, we gave an example that some high Sr/Y-type magmas could originate from melting of crustal materials at pressure of 10-12 kbar. We carried out a study of petrogenesis for Devonian high Sr/Y granites from the Beidashan batholith (397-411 Ma), southwestern Alxa Block, Northwest China. The Beidashan granites have SiO2 (69.21-74.60 wt.%) and Al2O3 (14.01-16.20 wt.%) with A/CNK ratios of 0.99-1.08. According to their trace element compositions and whole-rock zirconium saturation temperatures (TZr), the Beidashan granites can be divided into two groups: Group I ((Dy/Yb)N = 1.2-3.0, Eu/Eu* = 0.77-1.3, TZr = 761-856 °C), resulted from fluid-absent partial melting of mafic to intermediate crustal materials leaving garnet residuum at pressure of ~ 12 kbar, and Group II ((Dy/Yb)N = 0.76-2.16, Eu/Eu* = 1.7-5.3, TZr = 651-785 °C), formed by fluid-present melting of mafic to intermediate crustal materials with residual amphibole in the source at pressure of ~ 10 kbar. Both Group I and Group II show high Sr/Y and (La/Yb)N features. They show ISr = 0.7134-0.7180, εNd(t) = - 6.61 to - 9.71, T2DM = 1.7-1.9 Ga; εHf(t) = - 5.6 to - 9.9 and TDMC = 1.7-2.0 Ga, indicating that the Beidashan high Sr/Y granites were derived from melting of crustal basement materials. Our results suggest that some high Sr/Y-type granites formed under relatively lower pressure conditions (~ 10-12 kbar), and they could not be an indicative of partial melting of thickened crust.

  9. Fractionation of Li, Be, Ga, Nb, Ta, In, Sn, Sb, W and Bi in the peraluminous Early Permian Variscan granites of the Cornubian Batholith: Precursor processes to magmatic-hydrothermal mineralisation

    NASA Astrophysics Data System (ADS)

    Simons, Beth; Andersen, Jens C. Ø.; Shail, Robin K.; Jenner, Frances E.

    2017-05-01

    The Early Permian Variscan Cornubian Batholith is a peraluminous, composite pluton intruded into Devonian and Carboniferous metamorphosed sedimentary and volcanic rocks. Within the batholith there are: G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz) granites. G1-G2 and G3-G4 are derived from greywacke sources and linked through fractionation of assemblages dominated by feldspars and biotite, with minor mantle involvement in G3. G5 formed though flux-induced biotite-dominate melting in the lower crust during granulite facies metamorphism. Fractionation enriched G2 granites in Li (average 315 ppm), Be (12 ppm), Ta (4.4 ppm), In (74 ppb), Sn (18 ppm) and W (12 ppm) relative to crustal abundances and G1 granites. Gallium (24 ppm), Nb (16 ppm) and Bi (0.46 ppm) are not significantly enriched during fractionation, implying they are more compatible in the fractionating assemblage. Sb (0.16 ppm) is depleted in G1-G2 relative to the average upper and lower continental crust. Muscovite, a late-stage magmatic/subsolidus mineral, is the major host of Li, Nb, In, Sn and W in G2 granites. G2 granites are spatially associated with W-Sn greisen mineralisation. Fractionation within the younger G3-G4 granite system enriched Li (average 364 ppm), Ga (28 ppm), In (80 ppb), Sn (14 ppm), Nb (27 ppm), Ta (4.6 ppm), W (6.3 ppm) and Bi (0.61 ppm) in the G4 granites with retention of Be in G3 granites due to partitioning of Be into cordierite during fractionation. The distribution of Nb and Ta is controlled by accessory phases such as rutile within the G4 granites, facilitated by high F and lowering the melt temperature, leading to disseminated Nb and Ta mineralisation. Lithium, In, Sn and W are hosted in biotite micas which may prove favourable for breakdown on ingress of hydrothermal fluids. Higher degrees of scattering on trace element plots may be attributable to fluid-rock interactions or variability within the magma chamber. The G3-G4 system is more boron

  10. Neoproterozoic A-type granitoids of the central and southern Appalachians: Intraplate magmatism associated with episodic rifting of the Rodinian supercontinent

    USGS Publications Warehouse

    Tollo, R.P.; Aleinikoff, J.N.; Bartholomew, M.J.; Rankin, D.W.

    2004-01-01

    Emplacement of compositionally distinctive granitic plutons accompanied two pulses (765-680 and 620-550Ma) of crustal extension that affected the Rodinian craton at the present location of the central Appalachians during the Neoproterozoic. The dominantly metaluminous plutons display mineralogical and geochemical characteristics of A-type granites including high FeO t/MgO ratios, high abundances of Nb, Zr, Y, Ta, and REE (except Eu), and low concentrations of Sc, Ba, Sr, and Eu. These dike-like, sheet complexes occur throughout the Blue Ridge province of Virginia and North Carolina, and were emplaced at shallow levels in continental crust during active extension, forming locally multiple-intrusive plutons elongated perpendicular to the axis of extension. New U-Pb zircon ages obtained from the Polly Wright Cove (706??4Ma) and Suck Mountain (680??4Ma) plutons indicate that metaluminous magmas continued to be replenished near the end of the first pulse of rifting. The Suck Mountain body is presently the youngest known igneous body associated with earlier rifting. U-Pb zircon ages for the Pound Ridge Granite Gneiss (562??5Ma) and Yonkers Gneiss (563??2Ma) in the Manhattan prong of southeastern New York constitute the first evidence of plutonic felsic activity associated with the later period of rifting in the U.S. Appalachians, and suggest that similar melt-generation processes were operative during both intervals of crustal extension. Fractionation processes involving primary minerals were responsible for much of the compositional variation within individual plutons. Compositions of mapped lithologic units in a subset of plutons studied in detail define overlapping data arrays, indicating that, throughout the province, similar petrologic processes operated locally on magmas that became successively more chemically evolved. Limited variation in source-sensitive Y/Nb and Yb/Ta ratios is consistent with results of melting experiments and indicates that metaluminous

  11. In-situ zircon U-Pb age and Hf-O isotopic constraints on the origin of the Hasan-Robat A-type granite from Sanandaj-Sirjan zone, Iran: implications for reworking of Cadomian arc igneous rocks

    NASA Astrophysics Data System (ADS)

    Honarmand, Maryam; Li, Xian-Hua; Nabatian, Ghasem; Neubauer, Franz

    2017-01-01

    The Lower Permian Hasan-Robat syenogranite occurs as a single pluton and intruded the Upper Carboniferous-Lower Permian sandstones and dolomitic limestones in the central part of the Sanandaj-Sirjan zone. This syenogranitic intrusion shows A-type granitic affinity and is a good representative of Early Permian igneous activity in Iran. SIMS U-Pb zircon analyses indicate a crystallization age of 294.2 ± 2.5 Ma for the Hasan-Robat A-type granite. In-situ Lu-Hf and oxygen isotope analyses of magmatic zircons were carried out to infer the magma sources and evolution of the Hasan-Robat A-type syenogranite. The Hf-O zircon isotopic compositions are relatively homogeneous, with nearly chondritic ɛHf(t) values of -0.8 to +2.4 corresponding to two-stage zircon Hf model ages of 1.15-1.36 Ga. The δ18O values of zircon range from +7.6 to +8.6‰. The Hf model ages of the Hasan-Robat zircons is within the range of those reported from the Cadomian granitoids in Iran. The isotopic features of the Hasan-Robat syenogranite are in good agreement with Hf isotopic values and Hf and Nd model ages reported from the Cadomian arc magmatic suites in Iran. Thus, partial melting of these Cadomian igneous rocks would be the favorite source for the Hasan-Robat syenogranitic magma during the opening of the Neotethys Ocean and separation of Iranian terranes from the northern margin of Gondwana.

  12. Source-inherited compositional diversity in granite batholiths: The geochemical message of Late Paleozoic intrusive magmatism in central Calabria (southern Italy)

    NASA Astrophysics Data System (ADS)

    Fiannacca, Patrizia; Cirrincione, Rosolino; Bonanno, Fiorenza; Carciotto, Manuele Mario

    2015-11-01

    The Serre Batholith, in central Calabria, is a Late Paleozoic granitoid complex that makes up the middle portion, ca. 13 km thick, of a continuous and nearly complete section of the continental crust. The batholith displays a large compositional variety, with granitoid rocks ranging with continuity from quartz diorite to syenogranite, a distinct group of leucotonalites also occur. The granitoids are on the whole magnesian and calcic to calc-alkalic, with only some of the more evolved rocks showing a ferroan calc-alkalic to alkali-calcic composition. Quartz diorites and tonalites are metaluminous to weakly peraluminous, while granodiorites and granites are weakly to strongly peraluminous, with two-mica porphyritic types being the only population with a genuine strongly peraluminous character. Fe*-number, MALI and ASI features highlight a strong affinity of the Serre Batholith rocks with Cordilleran granitoids, inherited from the compositions of the source rocks rather than reflecting the real tectonic environment of the magmas. Major trace element and existing Sr-Nd data are consistent with an origin of the Serre Batholith from the assembling of several batches of magmas with specific original compositions derived by fluid-absent melting of different crustal sources. Quartz diorites and tonalites originated from a metabasaltic magma source, whereas metagraywackes with various mafic and pelitic contents appear the most likely sources of weakly peraluminous granodiorites and strongly peraluminous granodiorites and granites. Biotite ± amphibole granodiorites could also have been derived from mafic-intermediate metaigneous sources. Two-mica porphyritic leucogranites are the only rock types representing pure crustal melts, resulting from melting of mafic pelitic sources. The other granitoid compositions are too silica-poor and MgO + FeOt rich to represent pure melts, so they need to include other components, such as solid restitic/peritectic material entrained from the

  13. The Northeast Kingdom batholith, Vermont: magmatic evolution and geochemical constraints on the origin of Acadian granitic rocks

    USGS Publications Warehouse

    Ayuso, R.A.; Arth, Joseph G.

    1992-01-01

    Five Devonian plutons (West Charleston, Echo Pond, Nulhegan, Derby, and Willoughby) that constitute the Northeast Kingdom batholith in Vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution. The batholith consists of metaluminous quartz gabbro, diorite and quartz monzodiorite, peraluminous granodiorite and granite, and strongly peraluminous leucogranite. Contents of major elements vary systematically with increasingSiO40) and have small negative Eu anomalies. The strongly peraluminous Willoughby leucogranite has unique trace-element abundances and ratios relative to the rest of the batholith, including low contents of Hf, Zr, Sr, and Ba, low values of K/Rb (80-164), Th/Ta (<9), Rb/Cs (7-40), K/Cs (0.1-0.5), Ce/Pb (0.5-4), high values of Rb/Sr (1-18) low to moderate REE contents and light-REE enriched patterns (with small negative Eu anomalies). Flat REE patterns (with large negative Eu anomalies) are found in a small, hydrothermally-altered area characterized by high abundances of Sn (up to 26 ppm), Rb (up to 670 ppm), Li (up to 310 ppm), Ta (up to 13.1 ppm), and U (up to 10 ppm). There is no single mixing trend, fractional crystallization assemblage, or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the Northeast Kingdom batholith. The plutons originated by mixing mantle-derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment. Hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks (<50% by mass), and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals. ?? 1992 Springer-Verlag.

  14. Mineral chemistry and geochemistry of the Late Neoproterozoic Gabal Abu Diab granitoids, Central Eastern Dessert, Egypt: Implications for the origin of rare metal post-orogenic A-type granites

    NASA Astrophysics Data System (ADS)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Ahmed, Awaad F.; Mohamed, Haroun A.

    2015-04-01

    within A-type granite worldwide. According to Zhang et al., 2012, the garnet crystallized at the expense of biotite from the MnO-rich evolved melt after fractionation of biotite, plagioclase, K-feldspar, zircon, apatite, and ilmenite. The granitoids are alkali feldspar granites showing distinct geochemical features and most likely, belong to the post-orogenic younger Egyptian granitoids. They are peraluminous A-type alkaline rocks but they have lower Fe2O3, MgO, MnO, CaO, TiO2, P2O5, Sr, Ba, V, and higher SiO2, Na2O, K2O, Nb, Ta, U, Zr, Th, Ga/Al and Rb than the typical rocks of this type. The positive correlation between Ba and Sr, and the negative correlation between Rb and K/Rb reveal fractional crystallization of alkali feldspar. The similarity in most geochemical characteristics suggests that Abu Diab granitoids are genetically related to each other and extremely enrichment in incompatible elements such as Nb and Ta, indicating that they crystallized from extremely differentiated magmas. References: Zhang, J., Ma, C. and She, Z., 2012. An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen, central China: Petrological, mineralogical and geochemical constraints. Geoscience Frontiers 3 (5), 635-646.

  15. Post-collisional, Late Neoproterozoic, high-Ba-Sr granitic magmatism from the Dom Feliciano Belt and its cratonic foreland, Uruguay: Petrography, geochemistry, geochronology, and tectonic implications

    NASA Astrophysics Data System (ADS)

    Lara, Pablo; Oyhantçabal, Pedro; Dadd, Kelsie

    2017-04-01

    Post-collisional, granitic magmatism with high-barium-strontium (HiBaSr) content and shoshonitic affinity has been recently recognized both in the southern section of the Dom Feliciano Belt of Uruguay and its cratonic foreland. This group of granitic rocks has a distinctive age, mineralogy, chemistry and field characteristics. New zircon U-Pb LA-ICP-MS data for three of the plutons confirm their Late Neoproterozoic age; 634 ± 7.3 (Sierra de los Caracoles), 604 ± 3.0 Ma (Cortez Blanco) and 597 ± 3.6 Ma (Guayabo). Similar ages were published previously for the Solis de Mataojo Granitic Complex (584 ± 13 Ma) as well as Las Flores (586 ± 2.7 Ma) and Sobresaliente plutons (585 ± 2.5 Ma). Mineral assemblages of the studied quartz-monzonites, granodiorites and monzogranites comprise quartz, orthoclase and microcline, plagioclase (Ab10-30), hornblende, green biotite, apatite, titanite and allanite. They plot predominantly in the high-K calc-alkaline field with the exception of a few that plot in the shoshonitic field; characteristically they are relatively high in Na2O (normally > 4.5%) in acid varieties (SiO2 > 65%) decreasing to between 3 and 4% for more basic types; K2O normally exceeds 3.5% but can be as low as < 2% in the basic varieties. The Uruguayan HiBaSr granitoids show high abundances of Ba (> 700 ppm), Sr (> 500 ppm) and light REEs alongside low Nb, Ta and heavy REEs. The Eu anomalies are negligible to slightly positive. Intermediate initial 87Sr/86Sr values (0.7077 to 0.7090) and very low initial epsilon Nd values (- 15.8 to - 19.3) at 600 Ma with high Nd TDM (2.2-2.8 Ga) suggest a recycling of ancient Paleoproterozoic to Late Archaean sources. Late Neoproterozoic granitoids of Uruguay have been emplaced within a post-collisional tectonic setting controlled by major shear zones and strike-slip fault zones. Current field and analytical data suggest that these granitoids could have been mostly generated through the partial melting of an intermediate to

  16. Vertical zonality of fractionated granite plutons reflected in zircon chemistry: the Cínovec A-type versus the Beauvoir S-type suite

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Škoda, Radek

    2012-11-01

    We studied vertical changes in the chemical composition of zircon from two contrasting Variscan granite systems. The Beauvoir system (Massif Central, France) composed of three successive intrusions (B1, B2, B3) represents typical peraluminous S-type granite extremely enriched in P, F, Li, Rb, Cs, Be, Sn, Nb, Ta, and poor in Zr, Th, REE and Y. The Cínovec system (Krušné hory Mts/Erzgebirge, Czech Republic/Germany) composed of two successive intrusions (protolithionite granite, zinnwaldite granite) is only slightly peraluminous, P-poor, F, Li, Rb, Cs, U, Th, REE, Y, Sc, Sn, W, Nb, Ta-rich granite, which may be classified as A-type. In both localities, the most fractionated intrusions are located on the top of the system. Samples from borehole GPF-1 (Beauvoir) represent an 800 m long vertical section through the entire granite stock, while CS-1 borehole (Cínovec) reached a depth of 1600 m. Chemical compositions of zircons from both granite systems show distinct vertical zonality, but their shape and elemental speciation is highly contrasting. At Beauvoir, zircon shows a remarkable increase in Hf-content from 2-4 wt. % HfO2 (~0.03 apfu Hf) in the deepest B3-unit to 15-19 wt. % HfO2 (up to 0.18 apfu Hf) in the uppermost B1-unit. The highest contents of F, P, and U were detected in the intermediate unit B2 at a depth of 400-600 m. At Cínovec, Hf shows only moderate enrichment from ca. 2 wt. % HfO2 in the deeper protolithionite granite to 5-10 wt. % HfO2 in the uppermost part of the zinnwaldite granite. High contents of Th (3-8 wt. % ThO2) are entirely bound in the uppermost section of the granite copula to a depth of 200 m, but below this level the contents only sporadically exceed 1 wt. % ThO2. Concentrations of U, Y, HREE, Sc and Bi also reach their highest values in the uppermost parts of the zinnwaldite granite, but their decrease downward is much gentler. Extreme enrichment of outer zones of zircon crystals from some granites with Hf or high contents of Th, U

  17. An investigation of cathodoluminescence in albite from the A-type Georgeville granite, Nova Scotia

    SciTech Connect

    Dalby, Kim N.; Anderson, Alan J.; Mariano, Anthony N.; Gordon, Robert A.; Mayanovic, Robert A.; Wirth, Richard

    2009-12-15

    Cathodoluminescence (CL) reveals red and blue colors within single, non-turbid albite (Ab{sub 98-99}) grains from the Georgeville granite, Nova Scotia. A 720 nm X-ray excited optical luminescence (XEOL) peak characterizes red CL regions, while a 280 nm XEOL feature dominates blue CL regions. Synchrotron X-ray fluorescence results indicate that red CL and the 720 nm XEOL peak intensities relate to total Fe concentrations. The relationship between red CL and Fe content is confirmed by electron microprobe (EMPA) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS). The XEOL technique is used to exclude the Fe K-edge as the cause of red CL. X-ray absorption spectroscopy results indicate that Fe in both the red and blue CL regions is Fe{sup 3+}, and that red CL activation may relate to the Si-Al order of the feldspar and to the distribution of Fe on tetrahedral sites. The CL textures, combined with EMPA and LA-ICPMS analyses, indicate that blue CL albite (Ab98) regions contain higher concentrations of Ca, Ti, Pb and rare earth elements, and were replaced, in part, by a more Fe-rich, trace element depleted albite (Ab99) which displays red CL. Complex diffraction contrasts and amorphous deposits identified in transmission electron microscope images suggest that aqueous fluids have reacted with both red and blue CL regions. Fluid inclusion homogenization temperatures of up to 430 C provide a lower estimate of the fluid temperature.

  18. Geochemical and zircon U-Pb geochronological study of the Yangshan A-type granite: Insights into the geological evolution in south Anhui, eastern Jiangnan Orogen

    NASA Astrophysics Data System (ADS)

    Gu, Huangling; Yang, Xiaoyong; Deng, Jianghong; Duan, Liuan; Liu, Lei

    2017-07-01

    The Early Cretaceous Yangshan granite is an A-type granitic intrusion that was emplaced along the eastern Jiangnan Orogen in southern Anhui Province, South China. The Yangshan intrusion mainly consists of syenite porphyry (127.0 ± 0.6 Ma) and alkali-feldspar granite porphyry (126.0 ± 1.0 Ma). As a part of Qingyang-Jiuhuashan complex intrusion, the Yangshan A-type granites have lower MgO, CaO, Co, Sr, and higher Rb, Nb, Th and HREE contents, with enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and slightly negative Eu anomalies. However, the syenite porphyry and the alkali-feldspar granite porphyry differ in terms of zircon εHf(t) values: small variations in the syenite porphyry from - 5.5 to - 3.7, corresponding to Hf model ages (tDMC) between 1.42 Ga and 1.53 Ga, and large variations in the alkali-feldspar granite porphyry from - 6.4 to + 4.4, yielding tDMC of 0.90-1.59 Ga. While both rocks also have similar εNd(t) values ranging from - 7.02 to - 5.47, corresponding Nd model ages (TDMC) are 1.37-1.49 Ga, falling within the Hf model ages. We take these features to indicate that the Qingyang I-type granites, which are isotopically similar, and Yangshan A-type granites were originated from partial melting of Mesoproterozoic-Neoproterozoic crust, with minor juvenile crust input for the alkali-feldspar granite porphyry, followed by fractional crystallization. In combination with previous studies, we propose that the Cretaceous A-type granitic rocks formed between 135 Ma and 122 Ma, implying an important Mesozoic extensional event in eastern Jiangnan Orogen, which facilitated underplating of mantle-derived magma and crustal heating. This may have occurred in a back-arc extension in response to the drift of subduction direction of the Paleo-Pacific plate, which started as early as 135 Ma ago.

  19. Geochemistry, mineralogy, and zircon U-Pb-Hf isotopes in peraluminous A-type granite xenoliths in Pliocene-Pleistocene basalts of northern Pannonian Basin (Slovakia)

    NASA Astrophysics Data System (ADS)

    Huraiová, Monika; Paquette, Jean-Louis; Konečný, Patrik; Gannoun, Abdel-Mouhcine; Hurai, Vratislav

    2017-08-01

    Anorogenic granite xenoliths occur in alkali basalts coeval with the Pliocene-Pleistocene continental rifting of the Pannonian Basin. Observed granite varieties include peraluminous, calcic to peralkalic, magnesian to ferroan types. Quartz and feldspars are dominant rock-forming minerals, accompanied by minor early ilmenite and late magnetite-ulvöspinel. Zircon and Nb-U-REE minerals (oxycalciopyrochlore, fergusonite, columbite) are locally abundant accessory phases in calc-alkalic types. Absence of OH-bearing Fe, Mg-silicates and presence of single homogeneous feldspars (plagioclase in calcic types, anorthoclase in calc-alkalic types, ferrian Na-sanidine to anorthoclase in alkalic types) indicate water-deficient, hypersolvus crystallization conditions. Variable volumes of interstitial glass, absence of exsolutions, and lacking deuteric hydrothermal alteration and/or metamorphic/metasomatic overprint are diagnostic of rapid quenching from hypersolidus temperatures. U-Pb zircon ages determined in calcic and calc-alkalic granite xenoliths correspond to a time interval between 5.7 and 5.2 Ma. Positive ɛHf values (14.2 ± 3.9) in zircons from a 5.2-Ma-old calc-alkalic granite xenolith indicate mantle-derived magmas largely unaffected by the assimilation of crustal material. This is in accordance with abundances of diagnostic trace elements (Rb, Y, Nb, Ta), indicating A1-type, OIB-like source magmas. Increased accumulations of Nb-U-REE minerals in these granites indicate higher degree of the magmatic differentiation reflected in Rb-enrichment, contrasting with Ba-enrichment in barren xenoliths. Incipient charnockitization, i.e. orthopyroxene and ilmenite crystallization from interstitial silicate melt, was observed in many granite xenoliths. Thermodynamic modeling using pseudosections showed that the orthopyroxene growth may have been triggered by water exsolution from the melt during ascent of xenoliths in basaltic magma. Euhedral-to-skeletal orthopyroxene growth

  20. Magmatic inclusions in rhyolites of the Spor Mountain Formation, western Utah: Limitations on compositional inferences from inclusions in granitic rocks

    NASA Astrophysics Data System (ADS)

    Christiansen, Eric H.; Venchiarutti, Daniel A.

    1990-10-01

    Inclusions of quenched mafic magma occur in a 21 Ma rhyolite lava and precursory non-welded tuff that form the Spor Mountain Formation in west-central Utah. The mafic inclusions are not lithic inclusions; no comparable volcanic unit was present at the surface when the Spor Mountain Formation erupted. Mineral and bulk compositions preclude liquid immiscibility. The mafic inclusions show clear morphologic and textural effects of magma mingling shortly before eruption of the rhyolite. Globular inclusions from both units are vesicular, phenocryst-poor, plagioclase-sanidine-clinopyroxene-orthopyroxene-magnetite-ilmenite latites and trachytes with quench temperatures of about 1000°C. Although overlapping in SiO2, TiO2, Zr, and Hf concentrations, inclusions from the underlying tuff lack negative Eu anomalies and are enriched in P2O5, K2O, Al2O3, Sr, Pb, Cr, and Ni whereas those hosted in the overlying lava have small negative Eu anomalies and two-fold enrichments in Fe2O3, MnO, HREE, Y, Ta, Th, Rb, and Cs. The most reasonable explanation for the differences between the two sets of inclusions lies in selective chemical exchange between the rhyolite lava and the mafic inclusions after eruption. Limited mechanical mixing occurred after the inclusions solidified and became chemically modified. The textures of the inclusions in the lavas and the elements selectively mobilized in the inclusions imply that vapor-phase transport occurred in this low-pressure volcanic environment. If such substantial variations in inclusion compositions can arise during what must have been a short period of time before chemical reactions were halted by rapid cooling, it seems unlikely that the compositions of mafic inclusions formed by magma mingling in slowly cooled granites preserve their original compositions, mineralogies, or information about their ultimate sources. Using the compositions of such chemically modified inclusions as end-members for mixing calculations may lead to erroneous

  1. Crystallization conditions and evolution of magmatic fluids in the Harney Peak Granite and associated pegmatites, Black Hills, South Dakota—Evidence from fluid inclusions

    NASA Astrophysics Data System (ADS)

    Sirbescu, Mona-Liza C.; Nabelek, Peter I.

    2003-07-01

    A microthermometric study of inclusions in granites and pegmatites in the Proterozoic Harney Peak Granite system identified four types of inclusions. Type 1 inclusions are mixtures of CO 2 and H 2O and have low salinities, on average 3.5 wt.% NaCl eq; type 2 inclusions are aqueous solutions of variable salinities, from 0 to 40% wt.% NaCl eq; type 3 inclusions are carbonic, dominated by CO 2, with no detectable water; and type 4 inclusions consist of 20 to 100% solids, with the remaining volume occupied by a CO 2-H 2O fluid. Many inclusions have a secondary character; however, a primary character can be unambiguously established in several occurrences of the type 1 inclusions. These inclusions were trapped above the solidus and represent the exsolved magmatic fluid. The secondary populations of types 1, 2, and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions. Type 4 inclusions are primary and are interpreted to be trapped, fluid-bearing, complex silicate melts that subsequently solidified or underwent other posttrapping changes. It is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex, Li-bearing Tin Mountain pegmatite were trapped along the two-fluid phase boundary in the system CO 2-H 2O-NaCl eq. Consequently, the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions—on average 340°C and 2.7 kbar. These conditions indicate that this Li-, Cs-, Rb-, P-, and B-rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust. An internally consistent, empirical solvus surface in P- T- XCO2 coordinates was generated for the pseudobinary CO 2-(H 2O-4.3 wt.% NaCl eq) pegmatite fluid system. Distribution coefficients for the

  2. Partitioning of F between H2O and CO2 fluids and topaz rhyolite melt - Implications for mineralizing magmatic-hydrothermal fluids in F-rich granitic systems

    USGS Publications Warehouse

    Webster, J.D.

    1990-01-01

    Fluid/melt distribution coefficients for F have been determined in experiments conducted with peraluminous topaz rhyolite melts and fluids consisting of H2O and H2O+CO2 at pressures of 0.5 to 5 kbar, temperatures of 775??-1000??C, and concentrations of F in the melt ranging from 0.5 to 6.9 wt%. The major element, F, and Cl concentrations of the starting material and run product glasses were determined by electron microprobe, and the concentration of F in the fluid was calculated by mass balance. The H2O concentrations of some run product glasses were determined by ion microprobe (SIMS). The solubility of melt in the fluid phase increases with increasing F in the system; the solubility of H2O in the melt is independent of the F concentration of the system with up to 6.3 wt% F in the melt. No evidence of immiscible silica- and fluoriderich liquids was detected in the hydrous but water-undersaturated starting material glasses (???8.5 wt% F in melt) or in the water-saturated run product glasses. F concentrates in topaz rhyolite melts relative to coexisting fluids at most conditions studied; however, DF (wt% F in fluid/wt% F in melt) increases strongly with increasing F in the system. Maximum values of DF in this study are significantly larger than those previously reported in the literature. Linear extrapolation of the data suggests that DF is greater than one for water-saturated, peraluminous granitic melts containing ???8 wt% F at 800?? C and 2 kbar. DF increases as temperature and as (H2O/H2O+CO2) of the fluid increase. For topaz rhyolite melts containing ???1 wt% F and with H2O-rich fluids, DF is independent of changes in pressure from 2 to 5 kbar at 800?? C; for melts containing ???1 wt% F and in equilibrium with CO2-bearing fluids the concentrations of F in fluid increases with increasing pressure. F-and lithophile element-enriched granites may evolve to compositions containing extreme concentrations of F during the final stages of crystallization. If F in the

  3. Rhyacian A-type tholeiitic granites in southern Brazil: Geochemistry, U-Pb zircon ages and Nd model ages

    NASA Astrophysics Data System (ADS)

    Mesquita, Maria José; Bitencourt, Maria de Fátima; Nardi, Lauro Stoll; Picanço, Jefferson; Chemale, Farid, Jr.; Pimenta, Vanessa de Almeida

    2017-04-01

    In the southern South American platform, 2.5 to 2.0 Ga terranes, probably related to the Atlantica supercontinent, occur mainly as minor reworked inliers within Neoproterozoic, Brasiliano/Pan-African orogenic belts, as the Ribeira Belt in southern Brazil. The dispersion of such fragments has generated uncertainties about their geotectonic reconstruction, and their study has been supported mainly by elemental and isotope geochemistry. The southern Ribeira Belt lies between the Paranapanema and Luiz Alves cratons and contains reworked Neoarquean and Paleoproterozoic terranes which outcrop as basement nuclei in supracrustal sequences, as the Setuva Complex. The Água Comprida Suite, situated in the northern part of the Setuva Complex, consists of Amphibole-Biotite Syenogranite (ABS), Porphyritic Biotite Syenogranite (PBS), and Equigranular Biotite Syenogranite (EBS). All granites are foliated and intensively deformed. The oldest foliation (Sn) is marked by augen feldspars set in a recrystallized matrix, followed by a crenulation cleavage (Sn+1) which evolves to discrete shear zones. ABS is a metaluminous, reduced A-type granite with FeOt / (FeOt + MgO) > 0.9, with high HFSE and REE contents, corresponding to magmas related to continental medium to high-K tholeiitic series. PBS and specially EBS are highly differentiated, metaluminous to peraluminous (EBS), oxidized granites. The increase of Al2O3 and Rb, and decrease of HFS and RE elements relative to ABS indicate their evolution from tholeiitic magmas. The Água Comprida Suite granites are cogenetic rocks evolved from a within-plate mantle source, marked by high Nb, Ta, and Y. The influence of previously metasomatised mantle sources is evidenced by negative Nb, Ti, and P anomalies. The age of ABS is 2187 ± 26 Ma, and that of PBS is between 2180 ± 13 to 2186 ± 22 Ma. The Nd model age of 2.4 Ga, and ɛNd(2.18 Ga) between - 0.23 and - 0.27 support the interpretation of ABS being formed from juvenile material with a

  4. Eocene magmatic processes and crustal thickening in southern Tibet: Insights from strongly fractionated ca. 43 Ma granites in the western Gangdese Batholith

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Zhu, Di-Cheng; Cawood, Peter A.; Zhao, Zhi-Dan; Liu, Sheng-Ao; Chung, Sun-Lin; Zhang, Liang-Liang; Liu, Dong; Zheng, Yuan-Chuan; Dai, Jin-Gen

    2015-12-01

    This study reports zircon U-Pb age and Hf isotope, whole-rock major and trace element, and Sr-Nd-Pb-Hf isotope data for the Dajia pluton, western Gangdese Batholith, in southern Tibet. These data indicate that the pluton consists of moderately (Group 1) and strongly (Group 2) fractionated granites that were emplaced synchronously at ca. 43 Ma. Group 1 samples have SiO2 contents of 69-72 wt.% and vary in terms of the differentiation index (DI = 84-93). These rocks are depleted in Ba, Nb, Sr, P, and Ti, with moderate negative Eu anomalies, and display low heavy rare earth elements (HREEs) and Y abundances. Group 2 samples are characterized by high SiO2 (75-78 wt.%) and DI (95-97); significantly negative Eu anomalies; marked concave-upward middle REE (Gd-Ho) patterns; and Ba, Sr, P, and Ti anomalies that are significantly more negative than those of Group 1 samples. Group 1 samples have whole-rock εNd(t) (- 5.9 to - 6.0), εHf(t) (- 4.0 to - 4.5), and zircon εHf(t) (- 6.0 to + 5.8) values identical to those of Group 2 samples [εNd(t) = - 5.7 to - 6.7, εHf(t) = - 3.5 to - 2.9, and zircon εHf(t) = - 2.0 to + 4.2], as well as similar initial Pb isotopic compositions. These data indicate that the two groups were derived from a common source region with garnet as a residual mineral phase. Group 1 samples were most likely derived from partial melting of garnet-bearing amphibolite (rather than eclogite) within the juvenile southern Lhasa crust and mixed with the enriched components from the subducting ancient Indian continental crust and/or the ancient central Lhasa basement. Group 2 samples are interpreted as the products of extensive fractional crystallization (plagioclase, K-feldspar, biotite, apatite, allanite, titanite, monazite, and ilmenite) of the melts represented by Group 1 samples. Low HREEs and Y abundances of the Dajia pluton, together with the presence of strongly fractionated granites (Group 2) identified for the first time in the Gangdese Batholith

  5. Geochemical associations between fluorite mineralization and A-type shoshonitic magmatism in the Keban-Elazig area, East Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Akgul, Bunyamin

    2015-11-01

    Keban fluorite mineralizations are closely related Coniacian-Campanian subvolcanics intruded into Permian-Triassic Keban metamorphites; this event caused pyrometasomatic, porphyry, and vein-type Pb-Zn-Ag, Cu, W, and Pb-Zn-Ag-Mo-F mineralizations. These rocks are syenitic and syenomonzonitic in composition and have high Al2O3, alkali (Na2O + K2O), FeO*/MgO, Zr, Nb, Ta, Ga, Rb, Y, and rare earth element (REE) contents. They are A-type, metaluminous, and all fall in the shoshonitic series field in K2O vs SiO2 and Th/Yb vs Ta/Yb diagrams. The trace element contents and discriminations indicate that the Keban syenitoids were derived from lithospheric mantle metasomatized by oceanic-crust/sediment fluids. The metal and halogen contents of the Keban mineralizations apparently originated from metasomatized mantle and were transported to the crust by syenitoid magmas. Clear resemblances in chondrite-normalized REE patterns, LREE-HREE partionation, and high LILE contents of the magmatics and fluorites indicate a close kinship between the syenitoids and fluorite mineralizations. The HFSE contents of the fluorites are lower than those of the magmatics, as HFSEs are not soluble in aqueous fluids. The fluorites are products of early-phase alkali magmatism (LREE > HREE). The high contents of Rb, Sr, and Ba of fluorites are inherited from the magma, which also has very high contents of these elements. In Sc-∑REE, (La/Yb)n-(Eu/Eu*)n and (Tb/La)n-(Tb/Ca)n diagrams, Keban fluorites fall into distinct areas from Akcakisla-Akdagmadeni and Celikhan-Adiyaman fluorites.

  6. Two Late Cretaceous A-type granites related to the Yingwuling W-Sn polymetallic mineralization in Guangdong province, South China: Implications for petrogenesis, geodynamic setting, and mineralization

    NASA Astrophysics Data System (ADS)

    Zheng, Wei; Mao, Jingwen; Zhao, Haijie; Zhao, Caisheng; Yu, Xiaofei

    2017-03-01

    Major and trace elements, whole rock Sr-Nd-Pb isotopes, LA-ICP-MS U-Pb zircon dating, zircon trace elements and Hf isotope data are reported for a suite of A-type granites from Yingwuling pluton in western Guangdong province, South China. Zircon U-Pb ages obtained by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) show that biotite granite and alkali feldspar granite were emplaced in 81.3 ± 0.6 Ma and 80.6 ± 0.5 Ma, respectively. Both of the two suites have the petrographic and geochemical characteristics of A-type granite. These granitic rocks are metaluminous to weakly peraluminous and have pronounced contents of total alkalis (Na2O + K2O = 7.80-8.84%), Fe2O3T/MgO and Ga/Al ratios. They exhibit low MgO, CaO and TiO2 contents, enrichment in some LILEs and HFSEs (except for Zr, Eu and Y), depletion in Ba, Sr, P and Ti. They show A2 subtype affinity and were probably formed a temperature of 800 °C. The Yingwuling biotite granite has relatively high (87Sr/86Sr)i ratios of 0.70655 to 0.70928, low εNd(t) values of - 5.8 to - 4.2 and zircon εHf(t) values (- 5.70-1.37). Whole-rock Nd isotopic and zircon Hf isotopic two-stages model ages mostly vary from 1057 to 1506 Ma. The alkali feldspar granite display bulk rock εNd(t) values and (87Sr/86Sr)i ratios in the range of - 6.6 to - 6.1 and 0.70640 to 0.71077, respectively, and zircon εHf(t) values from - 5.44 to 0.54, with Mesoproterozoic T2DM for both Nd and Hf isotopes. Geochemical and isotopic data indicate the Yingwuling A-type granitic magmas were drived from mantle-crust interaction. Zircon grains of Yingwuling granites have relatively low Eu/Eu* and Ce4 +/Ce3 + ratios, indicating low oxygen fugacity. The visible tetrad effect in the Yingwuling granites indicates that it experienced strong fractionation and is close relationship to the W-Sn mineralization. Our new data together with previous published data indicate that Late Mesozoic A-type granitiods or alkaline intrusive rocks in South

  7. A new U-Pb LA-ICP-MS age of the Rumburk granite (Lausitz Block, Saxo-Thuringian Zone): constraints for a magmatic event in the Upper Cambrian

    NASA Astrophysics Data System (ADS)

    Zieger, J.; Linnemann, U.; Hofmann, M.; Gärtner, A.; Marko, L.; Gerdes, A.

    2017-07-01

    The basement of the Saxo-Thuringian Zone consists of Upper Neoproterozoic (c. 650-570 Ma) Cadomian arc sediments (Lusatian greywackes) and voluminous intrusions of Early Cambrian granitoids with ages of c. 540 Ma (Lausitz Block and Karkonosze-Izera Massif). The latter basement complexes comprise several c. 505 Ma granites, granodiorites, and gneisses emplaced during the change from a collisional tectonic setting to rift-related geotectonics. We present a new age for the Rumburk granite of 504 ± 3 Ma linking Late Cambrian plutonism at the northern margin of Gondwana with the initial phase of a Cambro-Ordovician rift event. Trace element analysis points to a linkage of the Rumburk granite with other Late Cambrian aged rocks of the Karkonosze-Izera Massif. Furthermore, geochemical data also provide evidence of a melting and recycling of Lusatian greywackes by the intrusion of the Rumburk granite. The youngest age peak of the Rumburk granite at c. 504 Ma is considered to be the age of emplacement. Older inherited age populations at c. 540 and c. 610 Ma are present and likely the result of a melting and recycling of Lusatian granitoids and greywackes. The appearance of Neoproterozoic inheritance and Lu-Hf similarities with the Rumburk granite strongly suggest the Lusatian greywackes as source rocks. There is a significant age gap of c. 35 Ma between Cambrian plutonic and volcanic rocks in Saxo-Thuringia. Hence, we consider two distinct pulses of magmatic activity during the transition from the Cadomian orogeny to the opening of the Rheic Ocean.

  8. Magmatic origin and fluid alteration versus inheritance: Complex history of accessory minerals from I-type granites from northern Victoria Land (Antarctica)

    NASA Astrophysics Data System (ADS)

    Menneken, M.; John, T.; Läufer, A.; Berndt, J.; Henjes-Kunst, F.; Giese, J.

    2016-12-01

    When reconstructing the formation and evolution of Earths earliest crust, one is still heavily reliant on information that can be gathered from detrital zircon grains, which have been proven to be a useful tool concerning the various isotopic, chemical, and mineralogical features that can be utilized within. However, detailed investigations have shown that some of these tracers might be prone to alteration and will not necessarily reflect conditions during formation [1, 2]. In this study, zircons and their host rocks from the Granite Harbour Intrusives (GHI) of northern Victoria Land, Antarctica, have been investigated with respect to regional evolution of continental crust as well as the reliability of zircon as a recorder of crustal formation. Here we present U-Pb, δ18O, trace element and inclusion data of zircons from Cambro-Ordovician granitoids, as well as geochemical analyses of accessory apatites. Our initial results show that even in I-type granitoids with a presumably simple formation history, U-Pb-age data and related isotopic, chemical, or mineralogical features have to be evaluated carefully in order to constrain the timing of magmatic events, inheritance or fluid alteration events. They do, for example, incorporate a large portion of recycled material, which is clearly reflected by a strong component of inherited U-Pb-zircon ages, but can also be inferred by comparing main- and trace-element compositions of apatite inclusions in zircon with accessory apatites. Apatite inclusions from all investigated samples for example, are clearly higher in F concentration, than their accessory counterparts. However, not all zircon grains record the youngest event, emphasizing that not only alteration might be a key factor to consider when evaluating zircon characteristics with respect to their host rock, but also, the timing and preservation of predating features. [1] Rasmussen et al. (2011) Metamorphic replacement of mineral inclusions in detrital zircon from Jack

  9. Timing of granitic magmatism in the northern Borborema Province, Brazil: a U Pb study of granitoids from the Alto Pajeú Terrain

    NASA Astrophysics Data System (ADS)

    Bastos Leite, P. R.; Bertrand, J.-M.; de Lima, E. S.; Leterrier, J.

    2000-11-01

    The Alto Pajeú Terrain (APT) is a SW-NE trending fold belt in the Neoproterozoic Borborema Province (NE Brazil), formed by metasedimentary sequences interlayered with metavolcanosedimentary units, both intruded by granitic rocks of different compositions and ages. The tectonic evolution of the APT involves Mesoproterozoic and Neoproterozoic transtensional and contractional tectonic events. In this study, we present U-Pb zircon ages of five granitoids selected according to a generally accepted relative chronology: (a) the Tuparetama granite and Tuparetama migmatitic granite with low angle gneissic foliation represent syn-tangential rocks presumably related to a Transamazonian event; (b) the Amparo granite with high angle gneissic foliation related to the Brazilian/Pan-African event; and (c) the Tabira and Jabitacá post-strike-slip granites. The results obtained do not confirm the generally accepted chronology of events. Granites previously classified in different groups (Tuparetama, Amparo, and Jabitacá) belong to the same orogenic cycle (Brazilian). Large batholiths, previously suspected to have been emplaced after the strike-slip deformation, represent older crustal remnants within them. In each case they consist of particular rock types — an alkaline high-temperature granite (Tabira) and a 'granulite' (Tuparetama migmatitic granite). These older ages imply that pre-Brazilian crust-forming events such as the Transamazonian Orogeny (Tuparetama migmatitic granite estimated at ca. 2050 Ma) and Cariris Velhos event (Tabira granite at ca. 972 Ma) occurred in the APT, and their records survived the intense recycling which characterizes the Brazilian/Pan-African orogeny.

  10. Late Carboniferous bimodal volcanic rocks and coeval A-type granite in the Suman Khad area, Southwest Mongolia: Implications for the tectonic evolution

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Zhang, Fochin; Fan, Jingjing; Miao, Laicheng; Baatar, Munkhtsengel; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo; Ganbat, Ariuntsetseg

    2017-08-01

    The volcanic rocks in the Suman Khad area in Southwest Mongolia form a bimodal suite consisting mainly of peralkaline rhyolites with subordinate basalts. The rhyolite sample collected from the bimodal suite yielded a SHRIMP zircon U-Pb age of 314 ± 5 Ma (MSWD = 1.41, n = 12), which was interpreted to represent formation time of the bimodal volcanic suite. The basalts were characterized by enrichment in LILE and LREE, and depletion in HFSE, indicating their formation was related to subduction processes. These features, together with their positive εNd (t) values (6.3-6.7), suggest that the basalts were likely derived from a depleted mantle source metasomatized by subduction-related fluids. In various tectonic discrimination diagrams, the basalts exhibited a transition from true arc basalts to intraplate basalts and thus were suggested to from in a back-arc tectonic setting. The rhyolites show a close affinity to A-type granites with enrichment in LILE and LREE, depletion in Nb, Ta and Ti and positive εNd (t) values (6.0-6.4). Considering the observed distinct compositional gap between the endmembers of the bimodal suite, the rhyolites are proposed to originate from partial melting of juvenile basaltic crustal rocks rather than fractional crystallization of basaltic melt. The granite associated with the bimodal volcanic rocks yielded a SHRIMP zircon U-Pb ages of 312 ± 5 Ma (MSWD = 0.75, n = 13), indicating that the granite is contemporaneous with the bimodal volcanic suite. The granite samples showed typical A-type granitic geochemical affinities and are considered to have been formed by partial melting of crustal rocks in a within-plate tectonic setting. Based on a combination of the available data, we suggest that the Late Carboniferous bimodal volcanic suite together with the coeval A-type granites in the Suman Khad region probably document a back-arc basin extensional environment, which probably related to the roll-back of the Paleo-Asian oceanic plate during

  11. Late Permian to Early Oligocene granitic magmatism of the Phan Si Pan uplift area, NW Vietnam: their relationship to Phanerozoic crustal evolution of Southwest China

    NASA Astrophysics Data System (ADS)

    Pham, T. T.; Shellnutt, G.

    2015-12-01

    The Phan Si Pan uplift area of NW Vietnam is a part of the Archean to Paleoproterozoic Yangtze Block, Southwest China. This area is of particular interest because it experienced a number of Phanerozoic crustal building events including the Emeishan Large Igneous Province, the India-Eurasia collision and Ailaoshan - Red River Fault displacement. In the Phan Si Pan uplift area, there are at least three different geochronological complexes, including: (1) Late Permian, (2) Eocene and (3) Early Oligocene. (1) The Late Permian silicic rocks are alkali ferroan A1-type granitic rocks with U/Pb ages of 251 ± 3 to 254 ± 3 Ma. The Late Permian silicic rocks of Phan Si Pan uplift area intrude the upper to middle crust and are considered to be part of the ELIP that was displaced during the India-Eurasian collision along the Ailaoshan-Red River Fault shear zone and adjacent structures (i.e. Song Da zone). Previous studies suggest the Late Permian granitic rocks were derived by fractional crystallization of high - Ti basaltic magma. (2) The Eocene rocks are alkali ferroan A1-type granites (U/Pb ages 49 ± 0.9 Ma) and are spatially associated with the Late Permian granitic rocks. The trace element ratios of this granite are similar to the Late Permian rocks (Th/Nb=0.2, Th/Ta = 2.5, Nb/U = 24, Nb/La =1.2, Sr/Y=1). The origin of the Eocene granite is uncertain but it is possible that it formed by fractional crystallization of a mafic magma during a period of extension within the Yangtze Block around the time of the India-Eurasia collision. (3) The Early Oligocene granite is characterized as a peraluminous within-plate granite with U/Pb ages of 31.3 ± 0.4 to 34 ± 1 Ma. The Early Oligocene granite has trace element ratios (Th/Nb = 2.1, Th/Ta = 22.6, Nb/U = 4.4, Nb/La = 0.4, Sr/Y = 60.4) similar to crust melts. The high Sr/Y ratio (Sr/Y = 20 - 205) indicates a lower crust source that was garnet-bearing. The Phan Si Pan uplift was neither a subduction zone nor an arc environment

  12. Contrasted crustal sources as defined by whole-rock and Sr-Nd-Pb isotope geochemistry of neoproterozoic early post-collisional granitic magmatism within the Southern Brazilian Shear Belt, Camboriú, Brazil

    NASA Astrophysics Data System (ADS)

    Florisbal, Luana Moreira; de Assis Janasi, Valdecir; de Fátima Bitencourt, Maria; Stoll Nardi, Lauro Valentim; Heaman, Larry M.

    2012-11-01

    The early phase of post-collisional granitic magmatism in the Camboriú region, south Brazil, is represented by the porphyritic biotite ± hornblende Rio Pequeno Granite (RPG; 630-620 Ma) and the younger (˜610 Ma), equigranular, biotite ± muscovite Serra dos Macacos Granite (SMG). The two granite types share some geochemical characteristics, but the more felsic SMG constitutes a distinctive group not related to RPG by simple fractionation processes, as indicated by its lower FeOt, TiO2, K2O/Na2O and higher Zr Al2O3, Na2O, Ba and Sr when compared to RPG of similar SiO2 range. Sr-Nd-Pb isotopes require different sources. The SMG derives from old crustal sources, possibly related to the Paleoproterozoic protoliths of the Camboriú Complex, as indicated by strongly negative ɛNdt (-23 to -24) and unradiogenic Pb (e.g., 206Pb/204Pb = 16.0-16.3; 207Pb/204Pb = 15.3-15.4) and confirmed by previous LA-MC-ICPMS data showing dominant zircon inheritance of Archean to Paleoproterozoic age. In contrast, the RPG shows less negative ɛNdt (-12 to -15) and a distinctive zircon inheritance pattern with no traces of post-1.6 Ga sources. This is indicative of younger sources whose significance in the regional context is still unclear; some contribution of mantle-derived magmas is indicated by coeval mafic dykes and may account for some of the geochemical and isotopic characteristics of the least differentiated varieties of the RPG. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas despite their emplacement within a low-strain zone. It may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of Paleoproterozoic orthogneisses from the Camboriú Complex.

  13. Th-REE- and Nb-Ta-accessory minerals in post-collisional Ediacaran felsic rocks from the Katerina Ring Complex (S. Sinai, Egypt): An assessment for the fractionation of Y/Nb, Th/Nb, La/Nb and Ce/Pb in highly evolved A-type granites

    NASA Astrophysics Data System (ADS)

    Moreno, J. A.; Molina, J. F.; Bea, F.; Abu Anbar, M.; Montero, P.

    2016-08-01

    The relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios in A-type felsic rocks from the Ediacaran Katerina Ring Complex, northernmost Arabian-Nubian Shield (ANS; S. Sinai, Egypt), are investigated in this work to understand their behavior during generation of highly evolved granitic magmas and to explore the nature of magma sources. Textural and compositional relationships of cognate Th-REE- and Nb-Ta-accessory minerals in Katerina felsic rocks show that chevkinite-group minerals (CGM), monazite, thorite, allanite and xenotime formed from residual liquids in quartz syenite porphyries, quartz monzonites and peralkaline granites, whereas in aluminous granites, allanite and monazite crystallized early, and thorite and columbite formed from residual liquids. Relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios with Zr/Hf ratios in the aluminous granites and with Be abundances in the peralkaline granites suggest a decrease in La/Nb and Ce/Pb ratios in the former, and in Y/Nb and La/Nb ratios in the latter with crystallization progress. This contrasts with absence of systematic variations of Th/Nb and Ce/Pb ratios in the peralkaline compositions and of Y/Nb ratio in the aluminous ones. In this latter, Th/Nb ratio can present a significant decrease only in highly evolved compositions. An analysis of Y/Nb, Th/Nb, La/Nb and Ce/Pb relationships in worldwide OIB and subduction-related magmatic suites reveals that A-type felsic rocks with (Th/Nb)N < 1.3, (La/Nb)N < 1.3, and (Ce/Pb)N > 1 may have A1-type affinity, and those with (Th/Nb)N > 2, (La/Nb)N > 2, and (Ce/Pb)N < 1 tend to present A2-type affinity. The crystal fractionation of Th-LREE- and Nb-Ta-accessory minerals and mixing of components derived from the two granite groups may cause deviations from these compositional limits that can be evaluated using constraints imposed by Th/Nb-La/Nb, Ce/Pb-Th/Nb and Ce/Pb-La/Nb relationships in OIB and subduction-related magmatic suites. Three mantle sources might have been

  14. Granites in the Sawuer region of the west Junggar, Xinjiang Province, China: Geochronological and geochemical characteristics and their geodynamic significance

    NASA Astrophysics Data System (ADS)

    Zhou, Taofa; Yuan, Feng; Fan, Yu; Zhang, Dayu; Cooke, David; Zhao, Guochun

    2008-12-01

    the A-type granites were emplaced in an extensional setting. We concluded that the Sawuer as well as the whole Junggar region in northern Xinjiang were involved in tectonism that gradually changed from compressional to extensional between the late Carboniferous and early Permian. This late Paleozoic granitic magmatism contributed to vertical crustal growth in the region.

  15. The Temaguessine Fe-cordierite orbicular granite (Central Hoggar, Algeria): U Pb SHRIMP age, petrology, origin and geodynamical consequences for the late Pan-African magmatism of the Tuareg shield

    NASA Astrophysics Data System (ADS)

    Abdallah, Nachida; Liégeois, Jean-Paul; De Waele, Bert; Fezaa, Nassima; Ouabadi, Aziouz

    2007-11-01

    The Temaguessine high-level subcircular pluton is intrusive into the LATEA metacraton (Central Hoggar) Eburnian (2 Ga) basement and in the Pan-African (615 Ma) granitic batholiths along a major NW-SE oriented major shear zone. It is dated here (SHRIMP U-Pb on zircon) at 582 ± 5 Ma. Composed of amphibole-biotite granite and biotite syenogranite, it comprises abundant enclaves: mafic magmatic enclaves, country-rock xenoliths and remarkable Fe-cordierite (#Fe = 0.87) orbicules. The orbicules have a core rich in cordierite (40%) and a leucocratic quartz-feldspar rim. They are interpreted as resulting from the incongruent melting of the meta-wacke xenoliths collapsed into the magma: the breakdown of the biotite + quartz assemblage produced the cordierite and a quartz-feldspar minimum melt that is expelled, forming the leucocratic rim. The orbicule generation occurred at T < 850° and P < 0.3 GPa. The Fe-rich character of the cordierite resulted from the Fe-rich protolith (wacke with 4% Fe 2O 3 for 72% SiO 2). Strongly negative ɛNd (-9.6 to -11.2), Nd TDM model ages between 1.64 and 1.92 Ga, inherited zircons between 1.76 and 2.04 Ga and low to moderately high ISr (0.704-0.710) indicate a Rb-depleted lower continental crust source for the Temaguessine pluton; regional considerations impose however also the participation of asthenospheric material. The Temaguessine pluton, together with other high-level subcircular pluton, is considered as marking the end of the Pan-African magma generation in the LATEA metacraton, resulting from the linear delamination along mega-shear zones, allowing asthenospheric uprise and melting of the lower continental crust. This implies that the younger Taourirt granitic province (535-520 Ma) should be considered as a Cambrian intraplate anorogenic event and not as a very late Pan-African event.

  16. Petrogenesis of post-collisional A-type granitoids from the Urumieh-Dokhtar magmatic assemblage, Southwestern Kerman, Iran: Constraints on the Arabian-Eurasian continental collision

    NASA Astrophysics Data System (ADS)

    Dargahi, Sara; Arvin, Mohsen; Pan, Yuanming; Babaei, Abbed

    2010-03-01

    Three plutons (Deh-Siahan, Bande-Bagh and Baghe-Khoshk Sharghi, collectively referred to as the DBB hereafter) in southwestern Kerman, in the southeastern part of the Urumieh-Dokhtar magmatic assemblage (UDMA) of the Zagros orogenic belt differ from the typical calc-alkaline metaluminous, I-type intrusions of the region. The DBB intrusions have a distinct lithological assemblage varying from diorite through monzogranite and monzonite to alkali feldspar syenite and alkali granite. The DBB granitoids are metaluminous to slightly peraluminous, alkaline to shoshonitic in composition and have high total alkali contents with K 2O > Na 2O, high FeO T/MgO values, and low CaO and MgO contents. They are enriched in some LILEs (such as Rb and Th) and HFSEs (such as Zr, Y and REEs except Eu) and depleted in Sr and Ba relative to primordial mantle, and have low concentrations of transitional metals. These features along with various geochemical discriminant diagrams suggest that the DBB granitoids are post-collisional A-type granitoids, which had not been recognized previously in the UDMA. The chondrite-normalized REE patterns of the DBB granitoids show slightly enriched light REEs [(La/Sm) N = 2.26-4.13], negative Eu anomalies [(Eu/Eu*) N = 0.19-0.74] and flat heavy REE patterns [(Gd/Yb) N = 0.80-1.87]. The negative Eu anomaly indicates an important role for plagioclase and/or K-feldspar during fractional crystallization. Whole-rock Rb-Sr isotope analysis yields an isochron age of 33 ± 1 Ma with an initial 87Sr/ 86Sr value of 0.7049 ± 0.0001. Whole-rock Sm-Nd isotope analysis gives ɛNdt values from + 2.56 to + 3.62 at 33 Ma. The positive ɛNdt and low ISr values of the DBB granitoids together with their TDM of 0.6-0.7 Ga suggest their formation from partial melting of a lithospheric mantle source, modified by fluids or melts from earlier subduction processes. Melting of lithospheric mantle occurred via a dehydration melting process at pressures below the garnet stability

  17. Geochemical and isotopic characterization of the granitic magmatism along the Remígio - Pocinhos shear zone, Borborema Province, NE Brazil

    NASA Astrophysics Data System (ADS)

    de Lima, Jefferson V.; Guimarães, Ignez de P.; Santos, Lucilene; Amorim, José Victor A.; Farias, Douglas José S.

    2017-04-01

    Two granitoid plutons (Pilõezinhos and Curral de Cima) intruded along the Remígio - Pocinhos shear zone, eastern part of the Borborema Province. The Pilõezinhos and Curral de Cima granites were dated at 566 ± 3 Ma and 618 ± 5 Ma respectively. The granitoids from both plutons have distinct initial 143Nd/144Nd ratios, expressed by εNd(t) values, i.e. the granitoids of Pilõezinhos pluton have lower εNd(t) values (-15.47 to -15.81) and negative εHf (t = 570 Ma) values (-16.0 to -18.6), while the granitoids of the Curral de Cima pluton have εNd(t) values between -1.12 and -5.23. The granitoids of the Curral de Cima pluton are epidote bearing, magnesian calcalkaline I-type granitoids, crystallized under high fO2 conditions. The granitoids of the Pilõezinhos pluton are alkaline, low-fO2, ferroan, ilmenite-series, A2-type granite intrusions. The geochemical and isotopic signatures suggest that the origin of magma of the Curral de Cima granitoids involved mixing/mingling at depth between crustal and mantle magmas, associated to decompression (lateral escape) during the convergent stage of Brasiliano/Pan/African orogeny, which lead the asthenosphere melts to rise into the lower crust. The source of magma of the granitoids of the Pilõezinhos pluton involved a strong crustal component with geochemical and isotopic signatures similar to the orthogneisses of the Serrinha-Pedro Velho Complex, and small mantle component. The emplacement of the Pilõezinhos pluton is associated to an extensional space formed during high-T strike-slip shearing developed by the synchronic movement of the Matinhas sinistral shear zone and Remígio - Pocinhos dextral shear zone.

  18. Mineralogy and geochemistry of the Paleoproterozoic, tin-mineralized Bom Jardim granite of the Velho Guilherme Suite, eastern Amazonian craton

    NASA Astrophysics Data System (ADS)

    Lamarão, Claudio Nery; Cordovil Pinho, Sabrina Cristina; de Paiva, Antonio Lima; Galarza, Marco Antônio

    2012-10-01

    The Bom Jardim granite is located to the south of São Felix do Xingu town and is intrusive in the intermediate to felsic volcanic rocks of the Uatumã Group. It is formed dominantly of coarse- to medium-grained isotropic monzogranite and syenogranite, both affected by intense late- to post-magmatic alteration. Biotite, generally chloritized, is the main primary mafic phase, with rare amphibole being found in the monzogranite. Hydrothermally altered and greisenized rocks, containing small primary concentrations of cassiterite + wolframite, as well as quartz veins with millimeter- to centimeter-sized crystals of wolframite + pyrite + fluorite occur in pervasively altered cupolas. Presently, alluvial cassiterite and wolframite (±columbite, tantalite) are mined in the Pedra Preta mine, located in the northern part of the pluton. SEM data showed that Sn-W mineralization is dominantly associated with syenogranite and greisenized rocks. EDS Semi-quantitative analysis revealed that the zircon crystals of the Bom Jardim granite are characteristically enriched in Hf, Y, U, and Th and display Zr/Hf ratios decreasing from monzogranite/leucomonzogranite toward syenogranite and greisenized syenogranite rocks, suggesting that magmatic differentiation significantly contributed for this particular feature. The Bom Jardim granite is slightly peraluminous and displays geochemical affinities with A-type granites. The Bom Jardim granite varieties evolved dominantly by fractional crystallization and their REE patterns are similar to those of the tin-specialized granites of the Velho Guilherme suite. It is concluded that the more evolved granites and associated greisenized rocks of the Bom Jardim pluton are tin-specialized granites. The similarities observed between the granites of the Velho Guilherme suite and the Bom Jardim granite allow to include the latter in this important granite suite.

  19. Tin-carrier minerals in metaluminous granites of the western Nanling Range (southern China): Constraints on processes of tin mineralization in oxidized granites

    NASA Astrophysics Data System (ADS)

    Wang, Ru Cheng; Xie, Lei; Chen, Jun; Yu, Apeng; Wang, Lubin; Lu, Jianjun; Zhu, Jinchu

    2013-09-01

    Huashan, Guposhan and Qitianling are three similar and representative metaluminous A-type tin granites in the western Nanling Range, China. They all have a high oxidization state with magnetite as the dominant Fe-Ti oxide. This study presents an understanding of systematic mineralogy of Sn-bearing minerals (biotite, titanite, magnetite and cassiterite) in the three granites. Biotite has an annite composition and both electron-microprobe and LA-ICP-MS analyses indicate trace amounts of tin in biotite (approximately 100-20 ppm). Chloritization of biotite is accompanied by formation of Sn-rich rutile and cassiterite. Titanite has a long history of crystallization from the early-magmatic stage through the late-magmatic stage to the hydrothermal stage. Owing to its solid-solution relationship with malayaite (CaSnSiO5), titanite always contains tin to various extents. Early-magmatic titanite contains about 0.5 wt.% SnO2, while the late-magmatic titanite is markedly enriched in tin (on average 14.8 and 3.4 SnO2 in titanite from the Qitianling and Huashan granites, respectively). Magnetite grains typically display a trellis structure with ilmenite lamellae, where microinclusions of cassiterite (<1 μm in size) are present. This is likely consistent with features of the "oxy-exsolution" process of Sn-bearing titanomagnetite precursor. Cassiterite may be observed as late-magmatic phase, but most commonly appears as an alteration product of other primary minerals. All tin-bearing minerals in the three granites record a complete process of tin mineralization in granite. The features of tin in primary biotite, titanite and magnetite reflect an initial enrichment during the early stage of magmatic crystallization of the Huashan, Guposhan and Qitianling granites. Association of interstitial Sn-titanite and cassiterite suggests further tin enrichment related to fractional crystallization of granitic magmas. Fluids and alteration of primary minerals play an important role in the

  20. The Serra das Araras Batholith: An example of Ediacaran syntectonic peraluminous granitic magmatism in the southwestern Paraíba do Sul Domain

    NASA Astrophysics Data System (ADS)

    Retamal, Iuri; Machado, Rômulo; Philipp, Ruy Paulo; Lana, Cristiano; Gonçalves, Guilherme O.

    2017-10-01

    The Serra das Araras Batholith (SAB), located at the southwest portion of the Paraíba do Sul Domain, Central Ribeira Belt, is composed of orthogneisses with peraluminous character. Combined LA-ICP-MS U-Pb and Lu-Hf isotopic analyses have been performed in zircon grains for a representative sample (SA-3H) of SAB. Data point to Rhyacian to Orosirian (ca. 2.1-1.8 Ga) inherited zircon cores with positive ɛHf(t) values and Ediacaran U-Pb crystallization age (595 ± 8 Ma). A leucogranite dyke (SA-3D), 15-25 cm thick, which crosscuts SAB and a biotite-hornblende quartz diorite enclave (SA-06) have been analyzed. Crystallization ages for the three samples (ca. 600-590 Ma) and ɛHf(t) values, ranging from -5.6 to -29.4 for Neoproterozoic zircon grains, indicate an Ediacaran crustal magmatism involving mid to lower crust anatexis and the reworking of Paleoproterozoic juvenile and crustal rocks.

  1. REE enrichment in granite-derived regolith deposits of the southeast United States: Prospective source rocks and accumulation processes

    USGS Publications Warehouse

    Foley, Nora K.; Ayuso, Robert A.; Simandl, G.J.; Neetz, M.

    2015-01-01

    The Southeastern United States contains numerous anorogenic, or A-type, granites, which constitute promising source rocks for REE-enriched ion adsorption clay deposits due to their inherently high concentrations of REE. These granites have undergone a long history of chemical weathering, resulting in thick granite-derived regoliths, akin to those of South China, which supply virtually all heavy REE and Y, and a significant portion of light REE to global markets. Detailed comparisons of granite regolith profiles formed on the Stewartsville and Striped Rock plutons, and the Robertson River batholith (Virginia) indicate that REE are mobile and can attain grades comparable to those of deposits currently mined in China. A REE-enriched parent, either A-type or I-type (highly fractionated igneous type) granite, is thought to be critical for generating the high concentrations of REE in regolith profiles. One prominent feature we recognize in many granites and mineralized regoliths is the tetrad behaviour displayed in REE chondrite-normalized patterns. Tetrad patterns in granite and regolith result from processes that promote the redistribution, enrichment, and fractionation of REE, such as late- to post- magmatic alteration of granite and silicate hydrolysis in the regolith. Thus, REE patterns showing tetrad effects may be a key for discriminating highly prospective source rocks and regoliths with potential for REE ion adsorption clay deposits.

  2. Fractionated alkaline rare-metal granites: two examples

    NASA Astrophysics Data System (ADS)

    Liverton, Timothy; Botelho, Nilson F.

    2001-04-01

    Two suites of tin-related alkaline granites are compared: the Seagull-Thirtymile granites of the Yukon, which were emplaced in a cordilleran setting and the Paranã suite of Goiás, which were emplaced in an incipient rift environment. The geochemistry of these two suites is similar and both have evolved small volumes of Li-Rb rich alkali feldspar leucogranites. Both fall partly, but not wholly, within the compositional fields defined for 'A-types' on various tectonic discrimination diagrams. Halogen contents and major element chemistry of Fe-Li micas from the Seagull-Thirtymile suite indicate that these plutons were reduced magmas that evolved magmatic/hydrothermal systems with increasing Cl content in a shallow, at least periodically 'open' system. The most important Sn-granites of the Paranã suite of Goiás were also emplaced at shallow depth and developed extensive greisen in active shear zones, which contrasts with a more passive environment for the Seagull granites. Both of these suites may be classified as low-P 2O 5 alkaline types and they display particularly Fe 2+-rich biotite micas that separate the alkaline plutons from S-type tin granites.

  3. 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.

  4. Synchronous alkaline and subalkaline magmatism during the late Neoproterozoic-early Paleozoic Ross orogeny, Antarctica: Insights into magmatic sources and processes within a continental arc

    NASA Astrophysics Data System (ADS)

    Hagen-Peter, Graham; Cottle, John M.

    2016-10-01

    Extensive exposure of intrusive igneous rocks along the Ross orogen of Antarctica-an ancient accretionary orogen on the margin of East Gondwana-provides an exceptional opportunity to study continental arc magmatism. There is significant petrologic and geochemical variability in igneous rocks within a 500-km-long segment of the arc in southern Victoria Land. The conspicuous occurrence of carbonatite and alkaline silicate rocks (nepheline syenite, A-type granite, and alkaline mafic rocks) adjacent to large complexes of subalkaline granitoids is not adequately explained by traditional models for continental arc magmatism. Extensive geochemical analysis (> 100 samples) and zircon U-Pb geochronology (n = 70) confirms that alkaline and carbonatitic magmatism was partially contemporaneous with the emplacement of large subduction-related igneous complexes in adjacent areas. Major pulses of subalkaline magmatism were compositionally distinct and occurred at different times along the arc. Large bodies of subalkaline orthogneiss and granite (sensu lato) were emplaced over similar time intervals (ca. 25 Myr) to the north (ca. 515-492 Ma) and south (ca. 550-525 Ma) of the alkaline magmatic province, although the initiation of these major pulses of magmatism was offset by ca. 35 Myr. Alkaline and carbonatitic magmatism spanned at least ca. 550-509 Ma, overlapping with voluminous subalkaline magmatism in adjacent areas. The most primitive rocks from each area have similarly enriched trace element compositions, indicating some common characteristics of the magma sources along the arc. The samples from the older subalkaline complex have invariably low Sr/Y ratios (< 40), consistent with relatively shallow magma generation and differentiation. The younger subalkaline complex and subalkaline rocks within the area of the alkaline province extend to higher Sr/Y ratios (up to 300), indicative of generation and differentiation at deeper levels. The significant spatial and temporal

  5. Geochronology and geochemistry of the Triassic bimodal volcanic rocks and coeval A-type granites of the Olzit area, Middle Mongolia: Implications for the tectonic evolution of Mongol-Okhotsk Ocean

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Zhang, Fochin; Miao, Laicheng; Baatar, Munkhtsengel; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo

    2016-05-01

    The Olzit volcanism in Middle Mongolia comprises a bimodal suite of basalts and peralkaline rhyolites adjacent to the Main Mongolia Lineament. The basalts are characterized by enrichment in LILE and LREE, and depletion in HFSE with typical Sr-Nd isotopic signatures (εNd(t) = -2.50 to -0.38 and (87Sr/86Sr)i = 0.7058-0.7063), indicating they were likely derived from partial melting of an enriched lithospheric mantle, modified by subducted slab-derived fluids. The rhyolites show a close affinity to A-type granites with enrichment in LILE and LREE, and depletion in Nb, Ta and Ti. They also show a significant negative Eu anomaly, and have εNd(t) values ranging from 0.50 to 1.38 and initial 87Sr/86Sr ratios ranging from 0.7022 to 0.7200, suggesting the rhyolites stem from partial melting of crustal rocks rather than fractional crystallization of the basaltic melt. The rhyolite porphyry yields a SHRIMP zircon U-Pb age of 207 ± 2 Ma (MSWD = 1.42), indicating the bimodal volcanic suite formed in the Late Triassic. The miarolitic per-alkaline granite and biotite-bearing granite, which are associated with the bimodal volcanic rocks, show typical A-type granitic geochemical affinity with εNd(t) = 0.89-0.91 and (87Sr/86Sr)i = 0.7021-0.7043, indicating they are likely generated by partial melting of crustal rocks similar to the rhyolitic end-member of bimodal suite. The miarolitic per-alkaline granite and biotite-bearing granite yielded SHRIMP zircon U-Pb ages of 209 ± 2 Ma (MSWD = 0.91) and 213 ± 3 Ma (MSWD = 1.65) respectively, which are nearly coeval with the age of the bimodal volcanic suites. In view of the new geochemical and chronological data in this study, we suggest the Olzit Late Triassic bimodal volcanic rocks together with the coeval A-type granites represent a back-arc basin extensional environment, which probably related to the roll-back of Mongol-Okhotsk oceanic plate during the southward subduction under the Central Mongolia microcontinent.

  6. Geochemical and zircon U-Pb and Hf isotopic study of the Baijuhuajian metaluminous A-type granite: Extension at 125-100 Ma and its tectonic significance for South China

    NASA Astrophysics Data System (ADS)

    Wong, Jean; Sun, Min; Xing, Guangfu; Li, Xian-hua; Zhao, Guochun; Wong, Kenny; Yuan, Chao; Xia, Xiaoping; Li, Longming; Wu, Fuyuan

    2009-10-01

    The Early Cretaceous Baijuhuajian pluton is an A-type granitic intrusion, emplaced along the Jiangshan-Shaoxing (JSSX) fault zone in western Zhejiang Province, SE South China. It intruded into a Late Jurassic volcanic basin bounded by Proterozoic sandstone and siltstone. The granite has a coarse-grained, porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of K-feldspar, quartz, plagioclase and biotite. The pluton has a clear A-type geochemical signature, e.g. it is metaluminous (A/CNK ~ 1.0) and has high SiO 2 (75 to 78 wt.%), total alkalis (Na 2O + K 2O = 4.8 to 8.5 wt.%), rare earth elements (total REE = 228 to 438 ppm), HFSE and Fe* [FeO t/(FeO t + MgO) = 0.87 to 0.97]. On the other hand, it is characterized by low CaO (0.51 to 1.01 wt.%), TiO 2 (0.06 to 0.13 wt.%), P 2O 5 (below detection) and Sr (7.0 to 9.5 ppm). The hypersolvus texture and fine-grained groundmass indicate emplacement at a shallow-depth. SHRIMP U-Pb zircon dating yielded a weighted mean 206Pb/ 238U age of 126 ± 3 Ma and zircons from this pluton give ɛHf( T) values between - 0.52 and + 4.24, suggesting the importance of juvenile material in the magma source. Most of the plutonic rocks in southeast China are calc-alkaline, subduction-related intrusions of Jurassic and Cretaceous age. Previous studies suggested that the sparse A-type granites in South China were emplaced in two episodes: 190-155 Ma in the inland area and ~ 100 Ma along the coastal area in SE South China. Our study of the Baijuhuajian granite, together with the coeval Suzhou A-type granite (123 Ma) in Jiangsu Province, defines an important extensional event between 125 and 100 Ma. Considering the available data for the Mesozoic igneous rocks in South China, we suggest that subduction of the Pacific plate in the Mesozoic produced voluminous calc-alkaline granitoids and volcanic rocks with a younging trend from west to east. The A-type granites were generated during periods of local extension at 190

  7. Geochronology and isotopic geochemistry of the A-type granites from the Huanggang Sn-Fe deposit, southern Great Hinggan Range, NE China: Implication for their origin and tectonic setting

    NASA Astrophysics Data System (ADS)

    Zhou, Zhen-Hua; Mao, Jing-Wen; Lyckberg, Peter

    2012-04-01

    The Huanggang Sn-Fe deposit, Inner Mongolia, is located in southern Great Hinggan Range metallogenic belt. LA-ICP-MS zircon U-Pb dating show that the K-feldspar granite and granite-porphyry in the Huanggang mine were formed at 136.7 ± 1.1 Ma and 136.8 ± 0.57 Ma, respectively. Sr-Nd-Pb isotope of the rocks and In situ zircon Hf isotopic systematics show that (87Sr/86Sr)i values range from 0.70211 to 0.70729, close to the (87Sr/86Sr)i of oceanic basalts and lower than those of continental crust. The ɛNd(t) values and Nd model ages (TDM) vary from -0.8 to 0.9 and 855 to 993 Ma, respectively. The Pb isotopic compositions are also variable with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18.974-26.107, 15.554-15.914 and 38.894-39.890, respectively, suggesting that the lead is derived from a mixed source. The 176Hf/177Hf values range from 0.282744 to 0.282922, with corresponding ɛHf(t) values ranging from 1.9 to 18.3, and two-stage Hf model ages (TDM2) of between 561 and 888 Ma. The isotope composition shows that Huanggang granites were derived from partial melting of juvenile lower crust that originated from depleted mantle, perhaps contaminated by small amounts of ancient continental crust. Younger Nd, Hf isotope model ages imply that an important crustal growth event took place in this area during the Neoproterozoic. Integrating our data with previously published results and the Late Mesozoic regional tectonic setting, we conclude that the Huanggang granites were generated in an intraplate tectonic-magmatic setting. Asthenospheric mantle upwelling due to lithospheric delamination and magma underplating, caused the partial melting of a mantle wedge metasomatized by the fluids released from subducted oceanic crust or by decompression of depleted mantle. This resulted in remelting, differentiation and a continued evolution of the mafic juvenile crust, producing a large quantity of granitic magma. The tectonic setting for these processes may be linked to the

  8. Gallium and germanium geochemistry during magmatic fractionation and post-magmatic alteration in different types of granitoids: a case study from the Bohemian Massif (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Gardenová, Nina; Kanický, Viktor; Vaculovič, Tomáš

    2013-06-01

    Contents of Ga and Ge in granites, rhyolites, orthogneisses and greisens of different geochemical types from the Bohemian Massif were studied using inductively coupled plasma mass spectrometry analysis of typical whole-rock samples. The contents of both elements generally increase during fractionation of granitic melts: Ga from 16 to 77 ppm and Ge from 1 to 5 ppm. The differences in Ge and Ga contents between strongly peraluminous (S-type) and slightly peraluminous (A-type) granites were negligible. The elemental ratios of Si/1000Ge and Al/1000Ga significantly decreased during magmatic fraction: from ca. 320 to 62 and from 4.6 to 1.2, respectively. During greisenization, Ge is enriched and hosted in newly formed hydrothermal topaz, while Ga is dispersed into fluid. The graph Al/Ga vs. Y/Ho seems to be useful tool for geochemical interpretation of highly evolved granitoids.

  9. Synkinematic emplacement of the magmatic epidote bearing Major Isidoro tonalite-granite batholith: Relicts of an Ediacaran continental arc in the Pernambuco-Alagoas domain, Borborema Province, NE Brazil

    NASA Astrophysics Data System (ADS)

    Silva, Thyego R. da; Ferreira, Valderez P.; Lima, Mariucha M. Correia de; Sial, Alcides N.; Silva, José Mauricio R. da

    2015-12-01

    The Neoproterozoic Major Isidoro batholith (˜100 km2), composed of metaluminous to slightly peraluminous magmatic epidote-bearing tonalite to granite, is part of the Águas Belas-Canindé composite batholith, which intruded the Pernambuco-Alagoas Domain of the Borborema Province, northeastern Brazil. These rocks contain biotite, amphibole, titanite and epidote that often shows an allanite core as key mafic mineral phases. K-diorite mafic enclaves are abundant in this pluton as well as are amphibole-rich clots. The plutonic rocks are medium-to high-K calc-alkaline, with SiO2 varying from 59.1 to 71.6%, Fe# from 0.6 to 0.9 and total alkalis from 6.1 to 8.5%. Chondrite-normalized REE patterns are moderately fractionated, show (La/Lu)N ratios from 13.6 to 31.8 and discrete negative Eu anomalies (0.48-0.85). Incompatible-element spidergrams exhibit negative Nb-Ta and Ti anomalies. This batholith was emplaced around 627 Ma (U-Pb SHRIMP zircon age) coevally with an amphibolite-facies metamorphic event in the region. It shows Nd-model age varying from 1.1 to 1.4 Ga, average ɛNd(627Ma) of -1.60 and back-calculated (627 Ma) initial 87Sr/86Sr ratios from 0.7069 to 0.7086. Inherited zircon cores that yielded 206Pb/238U ages from 800 to 1000 Ma are likely derived from rocks formed during the Cariris Velhos (1.1-0.9 Ga) orogenic event. These isotopic data coupled with calculated δ18O(w.r.) value of +8.75‰ VSMOW indicate an I-type source and suggest a reworked lower continental crust as source rock. A granodioritic orthogneiss next to the Major Isidoro pluton, emplaced along the Jacaré dos Homens transpressional shear zone, yielded a U-Pb SHRIMP zircon age of 642 Ma, recording early tectonic movements along this shear zone that separates the Pernambuco-Alagoas Domain to the north, from the Sergipano Domain to the south. The emplacement of the Major Isidoro pluton was synkinematic, coeval with the development of a regional flat-lying foliation, probably during the peak of

  10. Magmatism and polymetallic mineralization in southwestern Qinzhou-Hangzhou metallogenic belt, South China

    NASA Astrophysics Data System (ADS)

    Huang, Xudong; Lu, Jianjun; Wang, Rucheng; Ma, Dongsheng

    2016-04-01

    As Neoproterozoic suture zone between the Yangtze Block and Cathaysia Block, Qinzhou-Hangzhou metallogenic belt is one of the 21 key metallogenic belts in China. Intensive multiple-aged felsic magmatism and related polymetallic mineralization take place in this belt. Although Neoproterozoic, Paleozoic, Triassic granites and associated deposits have been found in southwestern Qinzhou-Hangzhou metallogenic belt, Middle-Late Jurassic (150-165 Ma) magmatism and related mineralization is of the most importance. Three major kinds of Middle-Late Jurassic granitoids have been distinguished. (Cu)-Pb-Zn-bearing granitoids are slightly differentiated, calc-alkaline and metaluminous dioritic to granodioritic rocks. Sn-(W)-bearing granites contain dark microgranular enclaves and have high contents of REE and HFSE, suggesting affinities of aluminous A-type (A2) granites. W-bearing granites are highly differentiated and peraluminous rocks. (Cu)-Pb-Zn-bearing granitoids have ɛNd(t) values of -11 ˜ -4 and ɛHf(t) values of -12 ˜ -7, corresponding to TDMC(Nd) from 1.4 to 1.8 Ga and TDMC(Hf) from 1.6 to 2.0 Ga, respectively. The ɛNd(t) values of W-bearing granites vary from -11 to -8 with TDMC(Nd) of 1.6 ˜ 1.9 Ga and ɛHf(t) values change from -16 to -7 with TDMC(Hf) of 1.5 ˜ 2.0 Ga. Compared with (Cu)-Pb-Zn-bearing granitoids and W-bearing granites, the Sn-(W)-bearing granites have higher ɛNd(t) (-8 ˜ -2) and ɛHf(t) (-8 ˜ -2) values and younger TDMC(Nd) (1.1 ˜ 1.6 Ga) and TDMC(Hf) (1.2 ˜ 1.8 Ga) values, showing a more juvenile isotopic character. Sn-(W)-bearing granites originate from partial melting of granulitized lower crust involved with some mantle-derived materials. W-bearing granites are derived from partial melting of crust. (Cu)-Pb-Zn-bearing granitoids are also derived from crust but may be influenced by more mantle-derived materials. For (Cu)-Pb-Zn deposits, skarn and carbonate replacement are the most important mineralization types. Cu ore bodies mainly

  11. First magmatism in the New England Batholith, Australia: forearc and arc-back-arc components in the Bakers Creek Suite gabbros

    NASA Astrophysics Data System (ADS)

    McKibbin, Seann J.; Landenberger, Bill; Fanning, C. Mark

    2017-04-01

    The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite-gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ˜ 305 Ma) forearc basalt-like component with low Th / Nb and with high Y / Zr and Ba / La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc-back-arc like gabbroic magmas (305-304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ˜ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ˜ 10 Myr) timescales for such melting.

  12. Intermittent 1630 1220 Ma magmatism in central Mazatzal province: New geochronologic piercing points and some tectonic implications

    NASA Astrophysics Data System (ADS)

    Tapani Rämö, O.; McLemore, Virginia T.; Hamilton, Michael A.; Kosunen, Paula J.; Heizler, Matt; Haapala, Ilmari

    2003-04-01

    The northern Burro Mountains in southwestern New Mexico reveal three distinct, intimately juxtaposed Mesoproterozoic magmatic suites in southern Laurentia. At 1633 Ma, the newly formed Mazatzal crust was intruded by tholeiitic diabase with a depleted-mantle type Nd isotope composition but with enriched incompatible trace element abundances. A potassic granite-minette suite was emplaced ca. 1460 Ma, and a tholeiitic A-type granite-anorthosite suite intruded ca. 1225 1220 Ma. The diabase-minette-anorthosite sequence and the associated silicic rocks record dominantly juvenile additions to the cratonic margin and imply subcontinental enrichment events ca. 1650 Ma (accretion), prior to 1460 Ma (potassic metasomatism), and ca. 1220 Ma (magmatic underplating). The latter two may have been controlled by a major transcurrent structure along the south margin of Laurentia.

  13. Experimental constraints on the Qitianling granite in south China: phase equilibria and petrogenetic implications

    NASA Astrophysics Data System (ADS)

    Huang, Fangfang; Scaillet, Bruno; Wang, Rucheng; Erdmann, Saskia; Chen, Yan; Faure, Michel; Liu, Hongsheng; Xie, Lei; Wang, Bo; Zhu, Jinchu

    2016-04-01

    In South China, the huge distribution of the Mesozoic metallogenic province reflects the abundant magmatism and associated mineralizations which occurred during that period. Building up the phase equilibrium diagrams of representative Mesozoic granites allows us to better understand Mesozoic magmatic events, an approach so far little applied to granites of South China. The Qitianling ganite is a representative Jurassic A-type metaluminous pluton which is associated with tin mineralization in South China. The dominant rock-types are hornblende-biotite monzonitic granites, biotite±hornblende bearing granites and fine-grained biotite-bearing granites. Three metaluminous granite samples (QTL38C, QTL14A and QTL13), of varying mafic character but all bearing hornblende, were chosen for constraining crystallization and magma generation conditions of the Qitianling composite batholith. Crystallization experiments were performed in the 100-700 MPa range, albeit mainly at 200 MPa, at an fO2 at NNO-1 or NNO +2.5, in a temperature range 700°C to 900°C. At 200 MPa, the water content in melt varies between 3 wt% and 6.5 wt% (water-saturated). Experimental results show that under H2O-saturated conditions and at NNO-1, ilmenite, magnetite and pyroxene are the liquidus phases, followed by hornblende, biotite and plagioclase. Hornblende is present only in the most mafic sample (QTL38C), below 900°C and above 5 wt% H2O. In contrast, for H2O-saturated conditions and at NNO+2.5, magnetite, pyroxene crystallize first, followed by biotite while ilmenite is rarely observed. Petrographic observations of natural samples show that magnetite and ilmenite coexist, whereas pyroxene is never observed. The Fe# value (Fe/Mg+Fe) of natural amphibole goes up to 0.69, being on average at 0.67. Experiments indicate that the crystallization of pyroxene occurs at early magmatic stages, but it breaks down to hornblende and biotite at low temperatures, explaining its absence in natural assemblages

  14. 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

    The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

  15. Oxygen isotope studies of early Precambrian granitic rocks from the Giants Range batholith, northeastern Minnesota, U.S.A.

    USGS Publications Warehouse

    Viswanathan, S.

    1974-01-01

    Oxygen isotope studies of granitic rocks from the 2.7 b.y.-old composite Giants Range batholith show that: (1) ??(O18)quartz values of 9 to 10 permil characterize relatively uncontaminated Lower Precambrian, magmatic granodiorites and granites; (2) granitic rocks thought to have formed by static granitization have ??(O18)quartz values that are 1 to 2 permil higher than magmatic granitic rocks; (3) satellite leucogranite bodies have values nearly identical to those of the main intrusive phases even where they transect O18-rich metasedimentary wall rocks; (4) oxygen isotopic interaction between the granitic melts and their O18-rich wall rocks was minimal; and (5) O18/O18 ratios of quartz grains in a metasomatic granite are largely inherited from the precursor rock, but during the progression - sedimentary parent ??? partially granitized parent ??? metasomatic granite ??? there is gradual decrease in ??(O18)quartz by 1 to 2 permil. ?? 1974.

  16. Two-mica granites of northeastern Nevada.

    USGS Publications Warehouse

    Lee, D.E.; Kistler, R.W.; Friedman, I.; Van Loenen, R. E.

    1981-01-01

    The field settings are described and analytical data are presented for six two-mica granites from NE Nevada. High delta 18O and 87Sr/86Sr values indicate that all are S-type granite, derived from continental crust. The major element chemistry and accessory mineral contents of these rocks also are characteristic of S-type granites. Chemical, X ray, and other data are presented for the micas recovered from these granites. The muscovites are notably high in Fe2O3, FeO, and MgO. Except for one hydrobiotite, each of the biotites has an MgO content near 6.0 wt%. Two different types of two-mica granites are recognized in the area of this study. One type is distinguished by the presence of many biotite euhedra within muscovite phenocrysts and by an unusual suite of accessory minerals completely devoid of opaque oxides. This type probably resulted from anatexis of late Precambrian argillites under conditions of relatively low oxygen fugacity, along a line that roughly coincides with the westward disappearance of continental basement. In the other textural type of two-mica granite the micas are equigranular and there is a greater variety of accessory minerals. The magmatic evolution of this type also appears to reflect the influence of late Precambrian argillites; there may be age differences between the two types of two-mica granites.-Author

  17. Zircon U-Pb geochronology and geochemistry of two episodes of granitoids from the northwestern Zhejiang Province, SE China: Implication for magmatic evolution and tectonic transition

    NASA Astrophysics Data System (ADS)

    Li, Zilong; Zhou, Jing; Mao, Jianren; Santosh, M.; Yu, Minggang; Li, Yinqi; Hu, Yizhou; Langmuir, Charles H.; Chen, Zhongxing; Cai, Xiongxiang; Hu, Yanhua

    2013-10-01

    Granitoids (175-80 Ma) representing a prominent Yanshanian (Jurassic to Cretaceous) magmatic event in South China widely intrude the Precambrian crystalline basement and Paleozoic strata. Here we report zircon U-Pb age data, geochemical characteristics and Sr-Nd isotopes of the Late Jurassic and Early Cretaceous granitoids from the northwestern Zhejiang Province (ZXB) of southeastern China. Our results reveal two distinct episodes for the Yanshanian magmatism. The Jiemeng and Datongkeng granodiorites formed at 148.6 ± 1.1 Ma, whereas the Huangshitan, Jiuligang and Ruhong aluminous A-type granites were generated between 129.0 ± 0.6 Ma and 126.1 ± 1.1 Ma. The two magmatic phases represent a tectonic transition from an active continental margin to post-orogenic setting during the Late Jurassic (ca. 150 Ma) to Early Cretaceous (ca. 128 Ma). Geochemically, these intrusions are granodioritic to granitic in composition and show an affinity of S-type and A-type granitoids, respectively. The S-type granodiorites of Jiemeng and Datongkeng are characterized by moderate SiO2 (65.0-69.6 wt.%), high K2O + Na2O (5.0-7.6 wt.%), K2O/Na2O (1.2-1.5), Zr (31-109 ppm), Sr (71-190 ppm) and high field strength elements, low to intermediate Mg#, and moderate Nb depletion. The A-type granites of Huangshitan, Jiuligang and Ruhong are characterized by high SiO2 (72.7-77.2 wt.%), K2O + Na2O (6.9-8.8 wt.%), K2O/Na2O (1.3-2.1), FeT/(FeT + Mg), Ga (17-29 ppm, > 20 ppm commonly), Zr (96-197 ppm) and Sr (8-45 ppm) with slight Nb depletion. The S-type granodiorites have higher Mg#, A/NK, Sr, Sr/Ba, Sr/Y, (La/Yb)N, and LREE/HREE, and lower SiO2, K2O + Na2O, Ga and Zr with weak negative Eu anomalies compared to those of the A-type granites with negative Eu anomalies. All these rocks show Y/Nb ratios > 1.2, high initial 87Sr/86Sr (ISr) ratios and low ɛNd(t), and are depleted in Nb, Ti and Sr, indicating crustal origin with subduction zone signatures. We suggested that the ZXB S-type granitic

  18. Conventional U-Pb dating versus SHRIMP of the Santa Barbara Granite Massif, Rondonia, Brazil

    USGS Publications Warehouse

    Sparrenberger, I.; Bettencourt, Jorge S.; Tosdal, R.M.; Wooden, J.L.

    2002-01-01

    The Santa Ba??rbara Granite Massif is part of the Younger Granites of Rondo??nia (998 - 974 Ma) and is included in the Rondo??nia Tin Province (SW Amazonian Craton). It comprises three highly fractionated metaluminous to peraluminous within-plate A-type granite units emplaced in older medium-grade metamorphic rocks. Sn-mineralization is closely associated with the late-stage unit. U-Pb monazite conventional dating of the early-stage Serra do Cicero facies and late-stage Serra Azul facies yielded ages of 993 ?? 5 Ma and 989 ?? 13 Ma, respectively. Conventional multigrain U-Pb isotope analyses of zircon demonstrate isotopic disturbance (discordance) and the preservation of inherited older zircons of several different ages and thus yield little about the ages of Sn-granite magmatism. SHRIMP U-Pb ages for the Santa Ba??rbara facies association yielded a 207Pb/206Pb weighted-mean age of 978 ?? 13 Ma. The textural complexity of the zircon crystals of the Santa Ba??rbara facies association, the variable concentrations of U, Th and Pb, as well as the mixed inheritance of zircon populations are major obstacles to using conventional multigrain U-Pb isotopic analyses. Sm-Nd model ages and ??Nd (T) values reveal anomalous isotopic data, attesting to the complex isotopic behaviour within these highly fractionated granites. Thus, SHRIMP U-Pb zircon and conventional U-Pb monazite dating methods are the most appropriate to constrain the crystallization age of the Sn-bearing granite systems in the Rondo??nia Tin Province.

  19. Transition from adakitic to bimodal magmatism induced by the paleo-Pacific plate subduction and slab rollback beneath SE China: Evidence from petrogenesis and tectonic setting of the dike swarms

    NASA Astrophysics Data System (ADS)

    Xia, Yan; Xu, Xisheng; Liu, Lei

    2016-02-01

    The late Mesozoic magmatic record of SE China is dominated by felsic volcanics and intrusions. However, this magmatism mainly occurred in coastal areas at 110-80 Ma, in contrast to poorly researched dike swarms that were emplaced inland at 165-120 Ma. Here, we focus on Early Cretaceous mafic and felsic dike swarms that provide new insights into the tectono-magmatic evolution of SE China. The swarms were intruded into Neoproterozoic plutons and include granodioritic porphyry, granitic porphyry, and diabase dikes. The granodioritic porphyry (128 ± 2 Ma) dikes are geochemically similar to adakitic rocks, suggesting that inland adakitic magmatism occurred between ca. 175 and ca. 130 Ma. The majority of these adakitic rocks are calc-alkaline and have Sr-Nd-Hf-O isotopic compositions that are indicative of derivation from a Neoproterozoic magmatic arc source within the lower crust. The granitic porphyry and diabase dikes were emplaced coevally at ca. 130 Ma, and the former contain high alkali and high field strength element (HFSE; e.g., Zr, Nb, Ce, and Y) concentrations that together with their high Ga/Al and FeOT/(FeOT + MgO) ratios imply an A-type affinity. The widespread ca. 130 Ma magmatism that formed the A-type granites and coeval diabase dikes defines a NE-SW trending inland belt of bimodal magmatism in SE China. The presence of mafic enclaves in some of the A-type granites, and the Sr-Nd-Hf isotopic compositions of the latter are indicative of inadequate mixing between the basement sediment-derived and coeval mantle-derived basaltic melts that define the bimodal magmatism. The transition from adakitic rocks to bimodal magmatism in the inland region of SE China indicates a change in the prevailing tectonic regime. This change was associated with an increase in the dip angle of the northwestward-subducting paleo-Pacific Plate beneath SE China between the Middle Jurassic and the Early Cretaceous. This resulted in a transition from a local intra-plate extensional

  20. Formation of a Granite Bodies in Depleted Granulite Terranes: the Wuluma Granite, Central Australia

    NASA Astrophysics Data System (ADS)

    Lavaure, S.; Sawyer, E. W.

    2009-05-01

    replaced by biotite (or chlorite), although, small crystals of garnet within the matrix persist locally. Virtually all of the granite contains a magmatic foliation, and this together with the presence of small dykes of granite in shears and in fold hinges indicates that the granite body formed during regional deformation (the local D3 event). Thus, the Wuluma granite did not form by in situ partial melting. Rather, it formed at a site where small increments of anatectic melt extracted from the surrounding granulite terrane during regional deformation were able to accumulate.

  1. Geodynamics of late Paleozoic magmatism in the Tien Shan and its framework

    NASA Astrophysics Data System (ADS)

    Biske, Yu. S.; Konopelko, D. L.; Seltmann, R.

    2013-07-01

    suprasubduction process (I-granites, etc.) with transition to the bimodal type in the Tien Shan segment of the Kazakhstan paleocontinent that formed; (2) superposition of A-granites on the outer Hercynides and foredeep at the margin of the Tarim paleocontinent (Kokshaal-Halyktau) and emplacement of various granitoids (I, S, and A types, up to alkali syenite) in the linear Kyzylkum-Alay Orogen; and (3) within-plate basalts and alkaline intrusions in the Tarim paleocontinent. Synchronism of the maximum manifestation and atypical combination of igneous rock associations with spreading of magmatism over the foreland can be readily explained by the effect of the Tarim plume on the lithosphere. Having reached maximum intensity by the Early Permian, this plume could have imparted a more distinct thermal expression to collision. The localization of granitoids in the upper crust was controlled by postcollision regional strike-slip faults and antiforms at the last stage of Paleozoic convergence.

  2. Magmatic tritium

    SciTech Connect

    Goff, F.; Aams, A.I.; McMurtry, G.M.; Shevenell, L.; Pettit, D.R.; Stimac, J.A.; Werner, C.

    1997-07-01

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory. Detailed geochemical sampling of high-temperature fumaroles, background water, and fresh magmatic products from 14 active volcanoes reveal that they do not produce measurable amounts of tritium ({sup 3}H) of deep origin (<0.1 T.U. or <0.32 pCi/kg H{sub 2}O). On the other hand, all volcanoes produce mixtures of meteoric and magmatic fluids that contain measurable {sup 3}H from the meteoric end-member. The results show that cold fusion is probably not a significant deep earth process but the samples and data have wide application to a host of other volcanological topics.

  3. AMS studies in Portuguese variscan granites

    NASA Astrophysics Data System (ADS)

    Sant'Ovaia, Helena; Martins, Helena; Noronha, Fernando

    2014-05-01

    A large volume of Variscan granitic rocks outcrop in Central Iberian Zone which are well documented concerning geological mapping, petrography and geochemistry but whose magnetic characteristics and fabric remain unknown. In this study we summarize the available AMS data from approximately 644 sampling stations (5152 samples) on different massifs of Variscan Portuguese granites. Despite their different geological, petrographic and geochemical characteristics, magnetic susceptibility (K) values obtained for the majority of the studied granites range from 15 to 300 × 10-6 SI. The dominant paramagnetic behaviour of the granite bodies reflects the presence of ilmenite as the main iron oxide. This feature indicates the reduced conditions involved in the granite melt formation during the Variscan orogeny. The two-mica granites show K values ranging between 15 to 70 × 10-6 SI which are lower than values displayed by the biotite-rich facies scattered within the interval of 70 and 300 × 10-6 SI. The magnetite-bearing granites are scarce but represented in Lavadores, Gerês and Manteigas. Even so, only the Lavadores body could be considered as a true magnetite-type granite (K >3.0 × 10-3 SI) in face of its K, comprised between 1550 and 19303 × 10-6 SI. Magnetic anisotropy can be used as a "marker" for the deformation experienced by granite mushes during their crustal emplacement and further cooling. Magnetic anisotropy can thus be correlated with the finite deformation of a rock, as record by mineral fabrics. Post-tectonic granites, such as those from Vila Pouca de Aguiar, Pedras Salgadas, Caria, Vila da Ponte, Chaves and Lamas de Olo, have a magnetic anisotropy <2.5% which corresponds to a deformation hardly visible to the naked eye. Nevertheless, at microscopic scale, these granites display almost ubiquitous magmatic to submagmatic microstructures (rare wavy extinction in quartz, erratic subgrain boundaries in quartz and, eventually, folded or kinked biotites). For

  4. Uralian magmatism: an overview

    NASA Astrophysics Data System (ADS)

    Fershtater, G. B.; Montero, P.; Borodina, N. S.; Pushkarev, E. V.; Smirnov, V. N.; Bea, F.

    1997-07-01

    This paper is an attempt to summarize current knowledge of Uralian magmatism, focusing on those aspects relevant for understanding its geodynamic evolution. The Urals consist of three tectonomagmatic domains: a Suture Sector, in the west, and two N-S imbricated Island-Arc Continental Sectors in the east. The Suture Sector comprises lower Palaeozoic mafic-ultramafic complexes which show eastward impoverishment in LILE, thus reflecting the transition of the subcontinental lithospheric mantle of the Russian plate to the suboceanic lithospheric mantle of the subducted Uralian palaeo-ocean. The two Island-Arc Continental Sectors represent the transition from oceanic to continental environments in the middle and south Urals. Collisional magmatism started in the Silurian and persisted till the Permian, migrating progressively eastward and increasing in abundance of LILE and {87Sr }/{86Sr initial}. Magmatic polarity is very similar to that of modern subduction zones and indicates that the subducted slab was dipping eastward during that period. The Northern and Southern Island-Arc Continental Sectors show many similarities regarding the nature and spatial-temporal distribution of magmatism, but there are also some important differences which probably indicate somewhat different geodynamic regimes. In the Northern Sector, Carboniferous tonalite-granodiorite batholiths have features compatible with an origin by melting of the oceanic crust in the subducted slab. In the Southern Sector, however, Carboniferous tonalite-granodiorite batholiths have features more consistent with a melting event within the lower continental crust above the subduction zone than with melting within the subducted slab. Upper Carboniferous-Permian granites have high {87Sr }/{86Sr initial} in the north (e.g., 0.7120 in the Murzinka batholith) but very low {87Sr }/{86Sr initial} in the south (e.g., 0.7045 in the Dzhabyk batholith) in spite of rocks from both batholiths being equally peraluminous and

  5. Fe isotopes and the contrasting petrogenesis of A-, I- and S-type granite

    NASA Astrophysics Data System (ADS)

    Foden, John; Sossi, Paolo A.; Wawryk, Christine M.

    2015-01-01

    We present new Fe isotope data of 42 S-, I- and A-type (ferroan) granites from the Cambrian Delamerian orogen in South Australia, the Palaeozoic Lachlan Fold Belt and Western USA. Interpretation of these data, together with modelling suggests that magmatic processes do result in quite complex Fe-isotopic differentiation trends and can lead to granites with isotopically heavy iron with δ57Fe > 0.35‰. By comparison Mid-Ocean Ridge Basalts (MORBs) have δ57Fe = 0.15‰ (Teng et al., 2013). These variations are similar to those previously reported (Poitrasson and Freydier, 2005; Heimann et al., 2008; Telus et al., 2012), but, contrary to some interpretations (Beard and Johnson, 2006; Heimann et al., 2008), heavy values are not necessarily the product of late-stage hydrothermal fluid loss, though this process is undoubtedly also an important factor in some circumstances. A-type (ferroan) granites reach very heavy δ57Fe values (0.4-0.5‰) whereas I-types are systematically lighter (δ57Fe = 0.2‰). S-type granites show a range of intermediate values, but also tend to be isotopically heavy (δ57Fe ≈ 0.2-0.4‰). Our results show that the iron isotopic values and trends are signatures that reflect granite generation processes. A modelling using the Rhyolite-MELTS software suggests that contrasting trajectories and end-points in Fe isotope evolution towards granite depend on: oxidation state of the evolving magma and, whether or not the system is oxygen-buffered. Iron isotopic evolution supports an origin of ferroan A-type granite from protracted, closed magma chamber fractionation of moderately reduced mafic magmas. In these systems magnetite saturation is delayed and the ferric iron budget is finite. I-type systems originate with the supply of relatively oxidised, hydrous, subduction-related magmas from the mantle wedge to the upper plate crust. These then experience oxygen-buffered open-system AFC processes in lower crustal hot-zones. S-type magmas are crustal

  6. Zircon Lu-Hf isotopes and granite geochemistry of the Murchison Domain of the Yilgarn Craton: Evidence for reworking of Eoarchean crust during Meso-Neoarchean plume-driven magmatism

    NASA Astrophysics Data System (ADS)

    Ivanic, Timothy J.; Van Kranendonk, Martin J.; Kirkland, Christopher L.; Wyche, Stephen; Wingate, Michael T. D.; Belousova, Elena A.

    2012-09-01

    New in situ Lu-Hf data on zircons from GSWA geochronology samples has provided a unique isotopic dataset with a high temporal resolution for the Murchison Domain of the Yilgarn Craton in Western Australia. These data identify extended periods of juvenile mantle input (positive ɛHf values) into the crust firstly at c. 2980 Ma and then from c. 2820 Ma to c. 2640 Ma with significant pulses of crustal recycling at c. 2750 Ma and c. 2620 Ma (highly negative ɛHf values). Geochemical data from well-characterised granitic suites of the Murchison Domain provide additional constraints on the crustal evolution of the area and indicate a prolonged period of crustal melting and remelting at progressively shallower depths from c. 2750 to c. 2600 Ma. At c. 2760-2753 Ma, widespread calc-alkaline, intermediate to silicic volcanic rocks of the Polelle Group were erupted, accompanied by intrusion of felsic to intermediate melts derived from a variety of crustal sources that likely formed by partial mixing with basaltic melts. The intrusive rocks include a wide geochemical array of rocks in the Cullculli and Eelya suites that were sourced over a wide range of crustal depths. At this time a major departure to negative ɛHf values (<-5) occurred, indicating sampling of c. 3.80 Ga model aged source rocks as well as continued juvenile input. Post-volcanic granitic rocks emplaced between c. 2710 and c. 2600 Ma show geochemical evidence for progressive fractionation through time and derivation from an evolving crustal source. We interpret the driving force for this protracted history of mantle and crustal melting to be two mantle plumes at 2.81 and 2.72 Ga. These data document the process of cratonization through progressive melt depletion of the lower crust, progressively fractionating and shallower melts, culminating with a final phase of crustal recycling (ɛHf < - 5) and the cessation of juvenile input at c. 2630-2600 Ma during intrusion of the Bald Rock Supersuite, resulting in

  7. Magmatic Enclaves

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.

    2011-12-01

    Over the past three decades, the term "magmatic enclave" has become widely accepted for small (typically <1 m) spheroidal bodies of igneous rock that are compositionally distinct from their coeval lava or intrusive hosts (e.g., Didier and Barbarin, 1991). Certain magmatic enclaves are crystal cumulates but most are globs of magma more mafic and hotter than their host. Understanding the origins and scientific utility of enclaves is aided by their common occurrence in both plutonic and volcanic rocks. Enclaves were noticed and described by geologists and petrographers for decades (e.g., Lacroix, 1890; Pabst, 1928; Williams, 1931) before it was demonstrated that many enclaves were introduced into their hosts while both were in a magmatic state: For example, in plutons by Wager and Bailey (1953), Walker and co-workers (1960's), Didier (1973), Wiebe (1980), and Vernon (1984), and in volcanic rocks by Wilcox (1944), Eichelberger (1980), and Bacon (1986). Spheroidal forms, crenulated or fine-grained margins, and crystal textures of enclaves are evidence of magmatic behavior. On entrapment, an enclave rapidly loses heat to its host and grows groundmass crystals whose size and morphology reflect the degree of enclave undercooling that is closely related to compositional contrast. At depth, some of the water dissolved in enclave magma may enter hydrous silicates but much can exsolve, including during partial crystallization. Vapor exsolution creates spherical vesicles and irregular gas pockets between crystals that give most volcanic enclaves porous textures. A vapor pressure gradient between an incompletely crystallized rigid enclave interior and host magma can drive residual melt into segregation vesicles and even out of the enclave by gas-driven filter pressing. Such enclaves have cores with cumulate-like compositions. Felsic droplets in mafic inclusions in plutonic rocks are interpreted as crystallized segregation vesicles. Enclaves are samples of magma that may not

  8. Early Carboniferous magmatism in Lhasa generated in passive continental margin: constrained by new SIMS dating from Carboniferous arc in Qiantang terrane, Tibet

    NASA Astrophysics Data System (ADS)

    Zhang, X. Z.; Dan, W.; Wang, Q.; Hao, L. L.; Qi, Y.

    2016-12-01

    In today's oceans, they are rarely undergone subduction on one side and extension on the opposite side. In contrast, there are a few magmatisms in the passive continental margins in the Tethys Ocean. However, because of their long and complex evolution of the northern continental margin of the Gondwana, the geodynamics of the magmatism occurred in this area is speculative or highly depute. One of these examples is the geodynamics of the 360-350 Ma magmatism in southern Lhasa, Tibet. Many authors speculated that it was generated in back-arc setting. Our recent new high-resolution SIMS zircon U-Pb dating reveals that there is a subduction arc with ages of 370-350 Ma in the Qiangtang terrane. The arc rocks compose of andesites, plagiogranites, A-type granites and cumulated gabbros, indicating an initial subduction. This initial subduction arc is located on the north margin of the eastern Paleo-Tethys Ocean, and it was formed slightly earlier than the 360-350 Ma magmatism in southern Lhasa, located on the south margin of the eastern Paleo-Tethys Ocean. Combined with similar aged magmatism generating the back-arc basin in the Sanjiang area, the 360-350 Ma magmatism in southern Lhasa was proposed to be generated in a passive continental margin, and induced by the regional extensional setting related to the subduction in the north margin of the eastern Paleo-Tethys Ocean.

  9. FROGS (Friends of Granites) report

    NASA Astrophysics Data System (ADS)

    Miller, Calvin

    This VGP News, which is devoted to petrology, is a good one for noting the existence of FROGS. FROGS is, as the name suggests, an informal organization of people whose research relates in one way or another to granitic rocks. Its purpose has been to promote communication among geoscientists with different perspectives and concerns about felsic plutonism. Initially, a major focus was experimental petrology and integration of field-oriented and lab-oriented viewpoints; now that there is the opportunity to communicate with the Eos readership, an obvious additional goal will be to bring together volcanic and plutonic views of felsic magmatism.FROGS first gathered in late 1982 under the guidance of E-an Zen and Pete Toulmin (both at U.S. Geological Survey (USGS), Reston, Va.), who saw a need for greater interaction among those interested in granites and for renewed, focused experimental investigations. They produced two newsletters (which were sent out by direct mail) and organized an informal meeting at the Geological Society of America meeting at Indianapolis, Ind., and then turned over the FROG reins to Sue Kieffer (USGS, Flagstaff, Ariz.) and John Clemens (Arizona State University, Tempe). They generated another newsletter, which was directly mailed to a readership that had grown beyond 200.

  10. The Keimoes Suite redefined: The geochronological and geochemical characteristics of the ferroan granites of the eastern Namaqua Sector, Mesoproterozoic Namaqua-Natal Metamorphic Province, southern Africa

    NASA Astrophysics Data System (ADS)

    Bailie, Russell; Macey, Paul Hugh; Nethenzheni, Sedzani; Frei, Dirk; le Roux, Petrus

    2017-10-01

    Voluminous granite gneisses and granites straddle the boundary between the Kakamas and Areachap Terranes in the eastern Namaqua Sector (NS) of the Mesoproterozoic Namaqua-Natal Metamorphic Province (NNMP). These rocks have been previously poorly defined and loosely grouped into the Keimoes Suite, but a recent U-Pb age study has suggested the suite be subdivided into syn-tectonic and post-tectonic groups relative to the main phase of the Namaqua Orogeny. This study adds new whole rock geochemical, isotopic and age data for these granites that confirms the subdivision is appropriate. The older group of syn-tectonic granite gneisses, dated between 1175 and 1146 Ma, have penetrative foliations and are largely derived from fractionated, leucogranitic metaluminous to peraluminous magmas with low maficity, low Ti, Mn and Ca. They were derived from mildly depleted sources (εNd(t): -1.47 to 1.78), with Meso-to Paleoproterozoic Nd model ages (1.57-1.91 Ga), and high initial Sr ratios (0.71970-0.75567) suggesting mixing between younger depleted and older, arc-like sources imparting an arc-like signature to the magmas. High initial Sr ratios appear to be an intrinsic character of these granites reflecting those of granites in the region and the highly radiogenic nature of the NS. The weakly to unfoliated late-to post-tectonic megacrystic granodiorites and monzogranites, including charnockites, intruded between 1110 and 1078 Ma and constitute the Keimoes Suite proper. They have I-type characteristics, being strongly metaluminous and locally hornblende- and orthopyroxene-bearing with moderate SiO2 and with arc-type affinities (LILE enrichment relative to the HFSE, Ta-Nb, Ti and P anomalies). However, the granitoids also have high Fe/Mg ratios, along with high HFSE, LILE and REE contents more indicative of A-type granites. They show an increasing maficity, metaluminous character, and general decreasing degree of fractionation with decreasing age. They are similar to the syn

  11. Geochemical study of granites from Chinmen (Quemoy) and Hong Kong, southeastern China

    NASA Astrophysics Data System (ADS)

    Sun, Li-Min; Chen, Ju-Chin

    Eighteen granite samples from Chinmen and 31 granite samples from Hong Kong were chemically analyzed. All granite specimens contain essentially quartz, potash-feldspar and albite with a minor amount of biotite. Chinmen granites are chemically similar to Hong Kong granites and both show the characteristics of S-type granite defined by Chappell and White (1974), indicating that Chinmen and Hong Kong granites originated from continental crustal material. Negative europium anomalies observed in Chinmen and Hong Kong granites suggest that both Chinmen and Hong Kong granites have evolved through magmatic differentiation with Ca-rich plagioclase being separated out in the early stage of the differentiation. It is inferred that the parental magmas of Chinmen and Hong Kong granites were derived from partially melted SiO 2, Na 2O, K 2O-enriched material during the Yenshan orogeny in southeastern China in Late Mesozoic, associated with the rapid spreading of the Pacific plate. The Chinmen granites are relatively higher in Al, Ca, Na, Ni and Sc but lower in Fe, K, Ba, Hf, Y and Ce when compared with Hong Kong granites, indicating that there might be slight differences in the parental crustal material and/or differentiation process.

  12. Voluminous granitic magmas from common basaltic sources

    USGS Publications Warehouse

    Sisson, T.W.; Ratajeski, K.; Hankins, W.B.; Glazner, A.F.

    2005-01-01

    Granitic-rhyolitic liquids were produced experimentally from moderately hydrous (1.7-2.3 wt% H2O) medium-to-high K basaltic compositions at 700 MPa and f O2 controlled from Ni-NiO -1.3 to +4. Amount and composition of evolved liquids and coexisting mineral assemblages vary with fO2 and temperature, with melt being more evolved at higher fO2s, where coexisting mineral assemblages are more plagioclase- and Fe-Ti oxide-rich and amphibole-poor. At fO2 of Ni-NiO +1, typical for many silicic magmas, the samples produce 12-25 wt% granitic-rhyolitic liquid, amounts varying with bulk composition. Medium-to-high K basalts are common in subduction-related magmatic arcs, and near-solidus true granite or rhyolite liquids can form widely, and in geologically significant quantities, by advanced crystallization-differentiation or by low-degree partial remelting of mantle-derived basaltic sources. Previously differentiated or weathered materials may be involved in generating specific felsic magmas, but are not required for such magmas to be voluminous or to have the K-rich granitic compositions typical of the upper continental crust. ?? Springer-Verlag 2005.

  13. Determination of geochemical affinities of granitic rocks from the Aue-Schwarzenberg zone (Erzgebirge, Germany) by multivariate statistics

    USGS Publications Warehouse

    Forster, H.-J.; Davis, J.C.

    2000-01-01

    Variscan granites of the Erzgebirge region can be effectively classified into five genetically distinct major groups by canonical analysis of geochemical variables. The same classification procedure, when applied to small plutons in the Aue-Schwarzenberg granite zone (ASGZ), shows that all ASGZ granites have compositional affinities to low-F biotite or low-F two-mica granite groups. This suggests that the ASGZ granites were emplaced during the first, late-collisional stage of silicic magmatism in the region, which occurred between about 325 and 318 Ma. The numerous biotite granite bodies in the zone are geochemically distinct from both the neighboring Kirchberg granite pluton and the spatially displaced Niederbobritzsch biotite granite massif. Instead, these bodies seem to constitute a third sub-group within the low-F biotite granite class. The ASGZ biotite granites represent three or more genetically distinct bodies, thus highlighting the enormous compositional variability within this group of granites. Least evolved samples of two-mica granites from the ASGZ apparently reflect the assimilation of low-grade metamorphic country rocks during emplacement, altering the original composition of the melts by enhancing primary Al content. The same genesis is implied for the rare "cordierite granite" facies of the Bergen massif, the type pluton for the low-F two-mica granite group in the Erzgebirge.

  14. Petrogenesis of Sveconorwegian magmatism in southwest Norway; constraints from zircon U-Pb-Hf-O and whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Roberts, Nick M. W.; Slagstad, Trond; Parrish, Randall R.; Norry, Michael J.; Marker, Mogens; Horstwood, Matthew S. A.; Røhr, Torkil

    2013-04-01

    The Sveconorwegian orogen is traditionally interpreted as a Himalayan-scale continental collision, and the eastward continuation of the Grenville Province of Laurentia; however, it has recently been proposed that it represents an accretionary orogen without full-scale continental collision (Slagstad et al., in press). We suggest that magmatism is one of the key constraints to differentiate between different types of orogens; thus, detailed investigation of the timing and petrogenesis of the magmatic record is a requirement for better understanding of the Sveconorwegian orogen as a whole. Here, we present new U-Pb geochronology, zircon Hf-O isotope, and whole-rock geochemical data to constrain the petrogenesis of the early -Sveconorwegian Sirdal Magmatic Belt (SMB). The SMB is a batholithic-scale complex of intrusions that intrudes into most of the Rogaland-Hardangervidda Block in southwest Norway. Current age constraints put emplacement between ~1050 to 1020 Ma. New ages from the Suldal region indicate that the onset of SMB magmatism can be put back to 1070 Ma, which is some 30-50 Myrs prior to high-grade metamorphism. Average initial ɛHf signatures range from ~0 to 4; these overlap with later post-Sveconorwegian granites and with early-/pre-Sveconorwegian ferroan (A-type) granites. Average δ18O signatures range from ~5.7 to 8.7, except for one anomalous granite at ~11.6. The Hf-O signatures are compatible with a mixed mantle-crustal source. Crustal sources may include ~1500 Ma Telemarkian or ~1200 Ma juvenile crust. Hf-O bulk-mixing modelling using a 1500 Ma crustal source indicates >50 % mantle input. Although much further mapping and geochronological work is required, granitic magmatism appears to have persisted throughout much of the ~1100 to 900 Ma period that spans the Sveconorwegian orogen. This magmatism is consistently ferroan (i.e. dry); however, the SMB marks a clear transition to magnesian (i.e. wet) magmatism, with a return to ferroan magmatism at

  15. Metallogenetic systems associated with granitoid magmatism in the Amazonian Craton: An overview of the present level of understanding and exploration significance

    NASA Astrophysics Data System (ADS)

    Bettencourt, Jorge Silva; Juliani, Caetano; Xavier, Roberto P.; Monteiro, Lena V. S.; Bastos Neto, Artur C.; Klein, Evandro L.; Assis, Rafael R.; Leite, Washington Barbosa, Jr.; Moreto, Carolina P. N.; Fernandes, Carlos Marcello Dias; Pereira, Vitor Paulo

    2016-07-01

    The Amazonian Craton hosts world-class metallogenic provinces with a wide range of styles of primary precious, rare, base metal, and placer deposits. This paper provides a synthesis of the geological database with regard to granitoid magmatic suites, spatio temporal distribution, tectonic settings, and the nature of selected mineral deposits. The Archean Carajás Mineral Province comprises greenstone belts (3.04-2.97 Ga), metavolcanic-sedimentary units (2.76-2.74 Ga), granitoids (3.07-2.84 Ga) formed in a magmatic arc and syn-collisional setting, post-orogenic A2-type granites as well as gabbros (ca. 2.74 Ga), and anorogenic granites (1.88 Ga). Archean iron oxide-Cu-Au (IOCG) deposits were synchronous or later than bimodal magmatism (2.74-2.70 Ga). Paleoproterozoic IOCG deposits, emplaced at shallow-crustal levels, are enriched with Nb-Y-Sn-Be-U. The latter, as well as Sn-W and Au-EGP deposits are coeval with ca. 1.88 Ga A2-type granites. The Tapajós Mineral Province includes a low-grade meta-volcano-sedimentary sequence (2.01 Ga), tonalites to granites (2.0-1.87 Ga), two calc-alkaline volcanic sequences (2.0-1.95 Ga to 1.89-1.87 Ga) and A-type rhyolites and granites (1.88 Ga). The calc-alkaline volcanic rocks host epithermal Au and base metal mineralization, whereas Cu-Au and Cu-Mo ± Au porphyry-type mineralization is associated with sub-volcanic felsic rocks, formed in two continental magmatic arcs related to an accretionary event, resulting from an Andean-type northwards subduction. The Alta Floresta Gold Province consists of Paleoproterozoic plutono-volcanic sequences (1.98-1.75 Ga), generated in ocean-ocean orogenies. Disseminated and vein-type Au ± Cu and Au + base metal deposits are hosted by calc-alkaline I-type granitic intrusions (1.98 Ga, 1.90 Ga, and 1.87 Ga) and quartz-feldspar porphyries (ca. 1.77 Ga). Timing of the gold deposits has been constrained between 1.78 Ga and 1.77 Ga and linked to post-collisional Juruena arc felsic magmatism (e.g., Col

  16. The peculiarities of the processes of forming, accumulation and migration of the graniteic melt

    NASA Astrophysics Data System (ADS)

    Anfilogov, V.

    2003-04-01

    The peculiarity of the processes of forming, accumulation and migration of granitic melts in katazone, mesozone and epizone are discussed. It is shown, that if fluid phase is present, the forming of the eutectic granitic melt by melting of the substrate realizes without the contact between grain of quartz and alkaline fieldspars.The leaf-by-leaf migmatites are able to form by the way of contrary diffusion of the components of granitic eutectic through the fluid. This way do not demand the addition of the components from outside The accumulation of big volume of granitic melt in katazone and the forming of granit - gneiss domes do not conected with metasomatism. They are formed as the result of leaf-by-leaf flow of the partialy melted material of migmatite. The granitic batholthes in mesozone are formed from the melt, which is generated in katazone. The zone of anatexis and the zone of the accumulation of granitic melt in batholithes are formed in thia case the united magmatic system. Our experiments show, that if the concentration of Na_2O and K_2O in fluid are constant the composition of granitic melt is constant too, in spite of the fact its temperature more than 100o higher than the temperature of granitic eutectic. Granitic melt is able to migrate up to 4 - 5 km without crystalization in this condition. The forming of batholithe is going graduately, layer by layer from its upper boundary to the down one. Experiments on interaction of ,basalt with chloride solutions at temperature 700 - 800 o C allow to construct the model of granitic melt origin from basaltic substrate. It is shown that the forming of big volume of granitic melt in the areas of active basaltic volcanism goes by three steps: autometasomatic transformation of the basalt, partialy melting of the meyasomatic products and migration of granitic melt to the upper part of the magmatic system.

  17. Petrogenesis of two Triassic A-type intrusions in the interior of South China and their implications for tectonic transition

    NASA Astrophysics Data System (ADS)

    Sun, Li-Qiang; Ling, Hong-Fei; Shen, Wei-Zhou; Wang, Kai-Xing; Huang, Guo-Long

    2017-07-01

    The evolution of the tectonic regime that was responsible for the Indosinian granitoids in the South China Block (SCB) is still controversial. Investigations on A-type granites can provide important information regarding this tectonic evolution. A detailed study that utilizes whole-rock elemental, Sr-Nd isotopic, in situ zircon U-Pb and Lu-Hf isotopic geochemistry is conducted on the Miantuwo biotite granite in northern Guangdong Province and the Pingtian biotite monzogranite in southern Jiangxi Province, South China. The new data indicate that both the Miantuwo and Pingtian granites were emplaced at 233 ± 2 Ma and show metaluminous to slightly peraluminous A-type granite affinity. The two granites are characterized by high amounts of rare earth elements (total REEs = 247 ppm-557 ppm and 251 ppm-342 ppm) and high field strength elements (Zr + Nb + Ce + Y = 325 ppm-605 ppm and 343 ppm-496 ppm) and high Ga/Al ratios (10,000 × Ga/Al = 2.50-2.98 and 2.62-2.70). Calculations from a zircon saturation thermometer and apatite saturation thermometer indicate that the magmatic temperatures were 800 °C-980 °C for both granites. Both the Miantuwo and Pingtian granites show relatively high initial 87Sr/86Sr ratios (0.7151-0.7185 and 0.7170-0.7189), low εNd(t) values (- 9.8 to - 8.6 and - 9.7 to - 9.1) and low to moderate zircon εHf(t) values (- 10.4 to - 6.6 and - 9.5 to - 4.6). Based on these data, we suggest that these two A-type granites were derived from the partial melting of existing mafic to intermediate rocks in the lower crust in response to the underplating and/or intraplating of mantle-derived magma. Our study on the Miantuwo and Pingtian granites, alongside previous studies on other Triassic A-type granites in South China, indicates an extensional tectonic environment during the Late Triassic in the interior of the Cathaysia Block. Alongside existing geological observations and the tectonic evolution in the SCB, we suggest that the interior of the SCB was

  18. Thermometers and thermobarometers in granitic systems

    USGS Publications Warehouse

    Anderson, J.L.; Barth, A.P.; Wooden, J.L.; Mazdab, F.; ,

    2008-01-01

    including Fe-Ti oxides, pyroxene, fayalitic olivine, quartz, sphene, and/or biotite, some of which have been recently revised, can provide additional information on temperature and oxygen fugacity. Oxygen fugacity can range over several orders of magnitude in different magmatic systems and can have profound influence on the mineralogy and mineral compositions in granitic magmas. It also forms the foundation of the popular magnetite- versus ilmenite-series granite classification. Copyright ?? Mineralogical Society of America.

  19. Relationships between deformation and magmatism in the Pan-African Kandi Shear Zone: Microstructural and AMS studies of Ediacaran granitoid intrusions in central Bénin (West Africa)

    NASA Astrophysics Data System (ADS)

    Adissin Glodji, L.; Bascou, J.; Yessoufou, S.; Ménot, R.-P.; Villaros, A.

    2014-09-01

    Relationships between the metamorphic basement, granitic intrusions and the Kandi Shear Zone (KSZ) in central Bénin have been investigated using petrological and structural approaches, in order to better understand the space and time parameters of the Pan-African shear deformation and the Ediacaran magmatism. In central Bénin, metamorphic rocks from the KSZ display a steep to vertical N-S trending foliation, a sub-horizontal mineral lineation together with kinematic indicators in agreement with a dextral transcurrent mega-shear zone. Four granitic intrusions (Dassa, Tré, Gobada and Tchetti) show many petrological similarities. They are biotite ± amphibole - ilmenite ± magnetite monzogranites with ferrous and metaluminous I-type features derived from high-K calk-alkaline magma. A fifth intrusion (Fita) is an alkali-feldspar, biotite, magnetite and ilmenite bearing granite crystallized from an alkaline magma. Moreover, high K2O, Zr, Y, Nb and low CaO, MgO and Al2O3 contents together with high (FeOt/MgO) and low LIL/HFS elements ratios suggesting an A-type granite affinity. Microstructural and AMS investigations presented in this paper show (i) solid-state deformation evidence for Dassa pluton and (ii) a magmatic deformation for the Tré, Tchetti, Gobada and Fita granitoids. Foliation in Dassa is parallel to the mesoscopic planar mylonitic foliation of the metamorphic basement. In the Tré, Tchetti, Gobada and Fita granitoids, magmatic textures and magnetic fabrics are coherent with the KSZ activity. These data suggest (i) a syn-kinematic nature for most of the intrusions (Tré, Gobada, Tchetti and Fita), except Dassa which correspond to an earlier event (ii) the succession of high-K calk-alkaline (Dassa, Tré, Gobada, Tchetti) evolves toward alkaline magmas (Fita) during the KSZ strike-slip tectonics. These observations highlight the changing nature of magma composition, magmatic processes and the different sources during KSZ activity in the Bénin Nigerian

  20. Late Triassic granites from Bangka, Indonesia: A continuation of the Main Range granite province of the South-East Asian Tin Belt

    NASA Astrophysics Data System (ADS)

    Ng, Samuel Wai-Pan; Whitehouse, Martin J.; Roselee, Muhammad H.; Teschner, Claudia; Murtadha, Sayed; Oliver, Grahame J. H.; Ghani, Azman A.; Chang, Su-Chin

    2017-05-01

    The South-East Asian Tin Belt is one of the most tin-productive regions in the world. It comprises three north-south oriented granite provinces, of which the arc-related Eastern granite province and the collision-related Main Range granite province run across Thailand, Singapore, and Indonesia. These tin-producing granite provinces with different mineral assemblages are separated by Paleo-Tethyan sutures exposed in Thailand and Malaysia. The Eastern Province is usually characterised by granites with biotite ± hornblende. Main Range granites are sometimes characterised by the presence of biotite ± muscovite. However, the physical boundary between the two types of granite is not well-defined on the Indonesian Tin Islands, because the Paleo-Tethyan suture is not exposed on land there. Both hornblende-bearing (previously interpreted as I-type) and hornblende-barren (previously interpreted as S-type) granites are apparently randomly distributed on the Indonesian Tin Islands. Granites exposed on Bangka, the largest and southernmost Tin Island, no matter whether they are hornblende-bearing or hornblende-barren, are geochemically similar to Malaysian Main Range granites. The average ɛNd(t) value obtained from the granites from Bangka (average ɛNd(t) = -8.2) falls within the range of the Main Range Province (-9.6 to -5.4). These granites have SIMS zircon U-Pb ages of ca. 225 Ma and ca. 220 Ma, respectively that are both within the period of Main Range magmatism (∼226-201 Ma) in the Peninsular Malaysia. We suggest that the granites exposed on Bangka represent the continuation of the Main Range Province, and that the Paleo-Tethyan suture lies to the east of the island.

  1. High-spatial resolution SIMS U-Pb zircon dating on Malay tin granites: New insights to crustal evolution of the Malaysian Peninsula

    NASA Astrophysics Data System (ADS)

    Ng, S.; Searle, M. P.; Whitehouse, M. J.; Chung, S.; Robb, L. J.; Ghani, A. A.; Sone, M.

    2012-12-01

    The Southeast Asian tin granite province has previously been recognized as comprising three distinct granitic belt (Cobbing et al., 1986): (1) Middle Permian - Late Triassic Eastern Province with mainly subduction-related I-type granites associated with Cu-Au deposits, (2) Late Permian - Early Jurassic Main Range Province with mainly S-type granites associated with Sn-W deposits, and (3) Late Triassic - Cretaceous Western Province with mixed I- and S-type granites associated with Sn-W deposits. These ages were obtained mainly using whole rock Rb-Sr and K-Ar geochronology in the 70s and 80s, methods that are no longer considered suitable for obtaining crystallization ages of granites due to unstable behaviour of these isotopes in hydrothermal systems. During 2011 we collected over 50 samples of granites across all three zones in Northern Malaysia for U-Pb dating using high-spatial resolution precision SIMS at the Swedish Museum of Natural History. The results reveal a westward younging trend across the Malay Peninsula. The Eastern Province hornblende- and biotite-granites in Eastern Malaysia formed by subduction-related processes have ages lying between 220-285 Ma. The Main Range Province dominantly S-type granites in west and central Malaysia have ages lying between 206-226 Ma. These include dominantly biotite granites with less common tourmaline+biotite leucocratic granites related to crustal thickening processes following collision of Sibumasu with Indochina and closing of the Palaeo-Tethyan Bentong-Raub suture zone. Some enigmatic young Cretaceous zircon rim ages (c. 81-80 Ma) may indicate a young hydrothermal - metasomatic origin for some tin mineralization from both the Eastern Province (Tioman Island) and the Western province (Phuket, Thailand) (Searle et al., 2012). Granites in Malaysia cannot be simply categorized as I-, S- or A-type as most of them failed to show distinctive minerals for classification and there is considerable overlap in geochemical

  2. Zircon and whole-rock Zr/Hf ratios as markers of the evolution of granitic magmas: Examples from the Teplice caldera (Czech Republic/Germany)

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Škoda, Radek

    2017-09-01

    Hafnium contents and Zr/Hf ratios were studied in zircons and their parent rocks from three magmatic suites associated with the Teplice caldera, Eastern Erzgebirge: rhyolite and dacite from the peraluminous Schönfeld Unit, relatively younger A-type Teplice rhyolite, and post-caldera A-type biotite and zinnwaldite granite and greisen. New data suggest that zircon crystallizing from a geochemically less evolved volatile- and water-poor melt is, compared to the host rock, relatively Hf-depleted, while zircon crystallizing from an evolved volatile- and water-rich melt has a Zr/Hf value approximately identical to that of the parental melt. Zr/Hf values in zircon did not change substantially either during greisenization, or during low-temperature alteration after metamictization. Zr/Hf values in the whole rock may serve as a sensitive indicator of magmatic fractionation of evolved granitic melts, as they are only negligibly influenced by the following hydrothermal processes. Zr/Hf values in individual cogenetic zircon grains are scattered but their general evolution trend in the rock series is consistent with the evolution of the whole-rock Zr/Hf values.

  3. Petrogenesis, zircon U-Pb age, and geochemistry of the A-type Mogou syenite, western Henan Province: Implications for Mesozoic tectono-magmatic evolution of the Qinling Orogen

    NASA Astrophysics Data System (ADS)

    He, Xinyu; Wang, Jionghui; Wang, Changming; Carranza, Emmanuel John M.; Chen, Liang; Wu, Bin

    2016-04-01

    The Mogou syenite intruded into the Mesoproterozoic Xiong'er Group is the main lithostratigraphic unit, along the southern margin of the North China Craton (NCC). This paper reports zircon LA-ICP-MS data, whole-rock major and trace element compositions of late Triassic magmatic rocks in the Mogou syenite, in order to constrain the formation age of the Mogou syenite, research the origin and evolution of the magma and analyse the geodynamic setting of the Qinling Orogen (QO) in Late Triassic. These rocks consist of medium- to coarse-grained syenite and fine-grained quartz syenite. Zircon U-Pb dating yields a crystallization age of 226.5±2.7 Ma. The syenites are characterized by high SiO2 (63.49-72.17%), alkali (K2O+Na2O of 11.18-15.38%) and potassium (K2O/Na2O of 2.88-28.11), are peralkaline or metaluminous (molar A/CNK of 0.87-1.02) and belong to shoshonite series. The syenites have ΣREE of 33.01-191.30 ppm, LREE/HREE of 14-20, (La/Yb)N of 11-24, with LREE-rich distribution pattern and obvious differentiation between HREE and LREE. Eu anomalies are positive for the medium- to coarse-grained syenite and weakly negative for the fine-grained quartz syenite. In addition, the syenites are enriched in large-ion lithophile elements (Ba, K, Sr, and Pb) but depleted in high strength field elements (Ti, Ta, Nb, Zr, and Hf), and have high differentiation indices of 91.69-97.06. These geochemical features indicate that the primary magma of the Mogou syenite most likely originated from a mantle source with minor crustal component, and underwent a fractional crystallization process during its emplacement. The late Triassic A-type Moguo syenite along the southern margin of the NCC was generated in the late stage of the syn-collision event of QO, recording a transition period from compression to extension at around 227 Ma.

  4. Oxygen isotope compositions of selected laramide-tertiary granitoid stocks in the Colorado Mineral Belt and their bearing on the origin of climax-type granite-molybdenum systems

    USGS Publications Warehouse

    Hannah, J.L.; Stein, H.J.

    1986-01-01

    Quartz phenocrysts from 31 granitoid stocks in the Colorado Mineral Belt yield ??18O values less than 10.4???, with most values between 9.3 and 10.4???. An average magmatic value of about 8.5??? is suggested. The stocks resemble A-type granites; these data support magma genesis by partial melting of previously depleted, fluorine-enriched, lower crustal granulites, followed by extreme differentiation and volatile evolution in the upper crust. Subsolidus interaction of isotopically light water with stocks has reduced most feldspar and whole rock ??18O values. Unaltered samples from Climax-type molybdenumbearing granites, however, show no greater isotopic disturbance than samples from unmineralized stocks. Although meteoric water certainly played a role in post-mineralization alteration, particularly in feldspars, it is not required during high-temperature mineralization processes. We suggest that slightly low ??18O values in some vein and replacement minerals associated with molybdenum mineralization may have resulted from equilibration with isotopically light magmatic water and/or heavy isotope depletion of the ore fluid by precipitation of earlier phases. Accumulation of sufficient quantities of isotopically light magmatic water to produce measured depletions of 18O requires extreme chemical stratification in a large magma reservoir. Upward migration of a highly fractionated, volatile-rich magma into a small apical Climax-type diapir, including large scale transport of silica, alkalis, molybdenum, and other vapor soluble elements, may occur with depression of the solidus temperature and reduction of magma viscosity by fluorine. Climax-type granites may provide examples of 18O depletion in magmatic systems without meteoric water influx. ?? 1986 Springer-Verlag.

  5. Oxygen isotope compositions of selected laramide-tertiary granitoid stocks in the Colorado Mineral Belt and their bearing on the origin of climax-type granite-molybdenum systems

    NASA Astrophysics Data System (ADS)

    Hannah, Judith L.; Stein, Holly J.

    1986-07-01

    Quartz phenocrysts from 31 granitoid stocks in the Colorado Mineral Belt yield δ 18O values less than 10.4‰, with most values between 9.3 and 10.4‰. An average magmatic value of about 8.5‰ is suggested. The stocks resemble A-type granites; these data support magma genesis by partial melting of previously depleted, fluorine-enriched, lower crustal granulites, followed by extreme differentiation and volatile evolution in the upper crust. Subsolidus interaction of isotopically light water with stocks has reduced most feldspar and whole rock δ 18O values. Unaltered samples from Climax-type molybdenumbearing granites, however, show no greater isotopic disturbance than samples from unmineralized stocks. Although meteoric water certainly played a role in post-mineralization alteration, particularly in feldspars, it is not required during high-temperature mineralization processes. We suggest that slightly low δ 18O values in some vein and replacement minerals associated with molybdenum mineralization may have resulted from equilibration with isotopically light magmatic water and/or heavy isotope depletion of the ore fluid by precipitation of earlier phases. Accumulation of sufficient quantities of isotopically light magmatic water to produce measured depletions of 18O requires extreme chemical stratification in a large magma reservoir. Upward migration of a highly fractionated, volatile-rich magma into a small apical Climax-type diapir, including large scale transport of silica, alkalis, molybdenum, and other vapor soluble elements, may occur with depression of the solidus temperature and reduction of magma viscosity by fluorine. Climax-type granites may provide examples of 18O depletion in magmatic systems without meteoric water influx.

  6. On the Eighth Hutton Symposium on Granites and Related Rocks

    NASA Astrophysics Data System (ADS)

    de Fátima Bitencourt, Maria; de Assis Janasi, Valdecir; Sawyer, Edward

    2017-04-01

    The Eighth Hutton Symposium was held on September 20-25, in the coastal city of Florianópolis, south Brazil, situated on the Neoproterozoic Florianópolis Batholith. During the mid-symposium field trip shallow-level granites, rhyolites and mafic dikes were visited in several large exposures along the shore. A 4-day pre-meeting field trip took place to see the Quadrilátero Ferrífero Province Archaean basement in Minas Gerais (southeast Brazil). After the meeting, another field trip took participants to the southern Brazilian coast to see Neoproterozoic, syntectonic granite magmatism within a transpressive orogen and to discuss crust and mantle contribution to granite generation.

  7. Textural and chemical evolution of a fractionated granitic system: the Podlesí stock, Czech Republic

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Müller, Axel; Leichmann, Jaromír; Gabašová, Ananda

    2005-03-01

    The Podlesí granite stock (Czech Republic) is a fractionated, peraluminous, F-, Li- and P-rich, and Sn, W, Nb, Ta-bearing rare-metal granite system. Its magmatic evolution involved processes typical of intrusions related to porphyry type deposits (explosive breccia, comb layers), rare-metal granites (stockscheider), and rare metal pegmatites (extreme F-P-Li enrichment, Nb-Ta-Sn minerals, layering). Geological, textural and mineralogical data suggest that the Podlesí granites evolved from fractionated granitic melt progressively enriched in H 2O, F, P, Li, etc. Quartz, K-feldspar, Fe-Li mica and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. Changes in chemical composition between individual crystal zones and/or populations provide evidence of chemical evolution of the melt. Variations in rock textures mirror changes in the pressure and temperature conditions of crystallization. Equilibrium crystallization was interrupted several times by opening of the system and the consequent adiabatic decrease of pressure and temperature resulted in episodes of nonequilibrium crystallization. The Podlesí granites demonstrate that adiabatic fluctuation of pressure ("swinging eutectic") and boundary-layer crystallization of undercooled melt can explain magmatic layering and unidirectional solidification textures (USTs) in highly fractionated granites.

  8. Magma emplacement mechanisms and syn-magmatic deformation - a new approach to the Knaben area in Vest Agder, Norway

    NASA Astrophysics Data System (ADS)

    Stormoen, Martin Austin; Slagstad, Trond; Henderson, Iain

    2014-05-01

    The Knaben area, known for its molybdenite mining, defines a N-S striking (~30 degrees dip towards the east) belt, consisting of porphyry granite with a varying density of amphibolite and varieties of deformed granite, lying within the Sirdal Magmatic Belt, is important for understanding the emplacement- and deformation mechanisms of the batholith. Detailed geological mapping combined with geochronology, geochemistry, and structural geology will be the focus areas. Last autumn's fieldwork indicated that several of the formerly mapped enclaves of amphibolite and deformed granite are more coherent then previously indicated, and some have been followed for a few kilometres. Several varieties of granite make up the area, mainly a dominating red porphyry granite, and a grey molybdenite-bearing finer grained granite. Structural investigations revealed consistent "top to the west" compressional kinematics on mappable shear zone networks often displaying west-directed duplex geometries. The Knaben area could possibly comprise a boundary between two individual plutons in the Sirdal Magmatic Belt, or a zone with remaining host rock. Geochronology of the eastern and western plutons will be done. Currently, largely different paleomagnetic vectors of the eastern and western porphyry granites indicate that they are separate plutons. Exploring how the emplacement- and deformation mechanisms have acted and are related, will be one of the main objectives. If the deformed granite is host rock, or syn- to post-magmatic deformed porphyry granite has been one of the major questions. A better understanding of the formation of the Knaben area, also regarding the emplacement of molybdenite, will prove useful for understanding the regional batholith, and possibly the possibility for molybdenite to occur elsewhere. The Sirdal Magmatic Belt, and also Knaben, seem to be of great value for studying magmatic processes.

  9. Petrological features of the Santa Teresa Granitic Complex Southeastern Uruguay

    NASA Astrophysics Data System (ADS)

    Muzio, Rossana; Artur, Antonio Carlos

    1999-09-01

    The Santa Teresa Granitic Complex, located in the north-eastern region of the Rocha Department (Eastern Uruguay), is an epizonal Late-Brasiliano granite intruded in the low-grade metasedimentary sequence of the Rocha Group. Twelve different facies types, each with distinctive structural-petrographic features, were recognized during detailed mapping (1:50,000) of the central-eastern part of the granitic complex and form two magmatic suites. The Santa Teresa Calk-alkaline Suite is composed of mostly porphyritic 3a-3b granites with variable amounts of biotite, sphene, allanite, magnetite and microgranular enclaves and belongs to a middle to high potassium calk-alkaline series with high silica contents. In contrast, the Sierra de la Blanqueada Peraluminous Suite has a great variation of grain size, including 3a-3b granitic facies with variable content of muscovite, biotite, tourmaline, ilmenite and monazite. Zircon morphology was studied in both suites and also shows their calk-alkaline and peraluminous nature. The Santa Teresa Calk-alkaline Suite had a Late- to Post-orogenic setting whereas the Sierra de la Blanqueada Peraluminous Suite was formed during the crustal thickening related to a syn-collisional environment.

  10. Nb-Ta-Ti-W-Sn-oxide minerals as indicators of a peraluminous P- and F-rich granitic system evolution: Podlesí, Czech Republic

    NASA Astrophysics Data System (ADS)

    Breiter, K.; Škoda, R.; Uher, P.

    2007-11-01

    The strongly peraluminous, P- and F-rich granitic system at Podlesí in the Krušné Hory Mountains, Czech Republic, resembles the zonation of rare element pegmatites in its magmatic evolution (biotite → protolithionite → zinnwaldite granites). All granite types contain disseminated Nb-Ta-Ti-W-Sn minerals that crystallized in the following succession: rutile + cassiterite (in biotite granite), rutile + cassiterite → ferrocolumbite (in protolithionite granite) and ferrocolumbite → ixiolite → ferberite (in zinnwaldite granite). Textural features of Nb-Ta-Ti-W minerals indicate a pre-dominantly magmatic origin with only minor post-magmatic replacement phenomena. HFSE remained in the residual melt during the fractionation of the biotite granite. An effective separation of Nb + Ta into the melt and Sn into fluid took place during subsequent fractionation of the protolithionite granite, and the tin-bearing fluid escaped into the exocontact. To the contrast, W contents are similar in both protolithionite and zinnwaldite granites. Although the system was F-rich, only limited Mn-Fe and Ta-Nb fractionation appeared. Enrichment of Mn and Ta was suppressed due to foregoing crystallization of Mn-rich apatite and relatively low Li content, respectively. The content of W in columbite increases during fractionation and enrichment in P and F in the melt. Ixiolite (up to 1 apfu W) instead of columbite crystallized from the most fluxes-enriched portions of the melt (unidirectional solidification textures, late breccia).

  11. The geochemical evolution of syncollisional magmatism and the implications for significant magmatic-hydrothermal lead-zinc mineralization (Gangdese, Tibet)

    NASA Astrophysics Data System (ADS)

    Zhou, Jinsheng; Yang, Zhusen; Hou, Zengqian; Liu, Yingchao; Zhao, Xiaoyan; Zhang, Xiong; Zhao, Miao; Ma, Wang

    2017-09-01

    In addition to well-known subduction processes, the collision of two continents also generates abundant ore deposits, as in the case of the Tibetan Plateau, which is the youngest and most spectacular collisional belt on Earth. During the building history of the Gangdese magmatic belt, several magmatic flare-up events developed, however, significant magmatic-hydrothermal lead-zinc mineralization dominantly accompanied the magmatism during the syncollisional period ( 65-41 Ma). Based on integrated geochemical and isotopic data, we provide insights into the genesis and evolution of syncollisional magmas, and their implications for significant magmatic-hydrothermal lead-zinc mineralization. The Sr-Nd isotopic compositions of most syncollisional igneous rocks (87Sr/86Sr = 0.7034-0.7123; εNd(t) = - 9.0 to + 1.8) indicate a mixing origin between mantle-derived basaltic magmas and ancient crustal melts, and fractional crystallization is a fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions. Most lead-zinc mineralization-related plutons are high silica (76.14% wt.% SiO2 on average), high oxygen fugacity (average ΔFMQ + 2.5) granites with highly evolved chemical signatures [average Eun/Eun* = 0.33, high Rb/Sr (average = 3.9)], and they represent the final products from primary magmas. Due to the contribution of ancient crustal melts to the genesis of mineralization-related parent magmas, the spatial distribution of Pb-Zn deposits within the northern Gangdese magmatic belt is controlled by the lithospheric architecture. In compressional environments, magmas have low evacuation efficiency and long magma chamber lifespan, which is favorable for basaltic parents evolved to high silica granites through sufficient fractional crystallization. This scenario contributes to our understanding of the significant magmatic-hydrothermal lead-zinc mineralization that occurred in the syncollisional period.

  12. Geochemistry and geochronology of the rapakivi granites and associated rocks in the midwest portion of the Serra da Providência composite batholith, SW of Amazonian craton, Rondônia, Brazil

    NASA Astrophysics Data System (ADS)

    Costa, Manoel Augusto Corrêa da; Sousa, Maria Zélia Aguiar de; Dall'Agnol, Roberto; Scandolara, Jaime E.; Ruiz, Amarildo Salina

    2016-08-01

    The Serra da Providência batholith includes the type area of the homonymous suite, the oldest rapakivi magmatic assemblage in the SW of the Amazonian craton (1.60-1.53 Ga). In the midwest portion of this massif, besides wiborgites/pyterlites and granophyric syenogranites, a leucosyenogranite facies and porphyritic rhyolites constitute new rock varieties recently described in that area. Usbnd Pb LA-MC-ICP-MS zircon ages of 1574 ± 9 Ma and 1604 ± 3 Ma, respectively, were obtained for these new varieties and confirm their link with the Serra da Providência magmatism, whereas the subvolcanic rocks are older than the main rock varieties and were formed in a precursor event. These granitic facies are metaluminous to peraluminous, alkali-calcic, A2-type, ferroan granites. Their FeOt/(FeOt + MgO) ratios vary from 0.83 to 0.98 and suggest that these rocks were crystallized from oxidized-to reduced-A-type magmas, where the leucosyenogranites and granophyric sienogranites tend to be formed under more reduced conditions. They show fractionated REE patterns with very pronounced to weak negative Eu anomalies. The presence of granophyric textures and miarolitic cavities in equigranular syenogranitic facies suggests that these rocks were formed at shallow crustal depths, lower than 3 km. Three samples of leucosyenogranite have silica contents higher than 75% and low K/Rb ratios (<150), similarly to the tin specialized granites described in the Amazonian craton. Two distinctive groups of mafic rocks were recognized in the study area: porphyritic and equigranular gabbronorites. They correspond to tholeiitic basalts, with #Mg varying from 37 to 41 in porphyritic gabbronorites and 51 to 65 in equigranular gabbronorites. The low to moderate #Mg suggests that these rocks were crystallized from more evolved basaltic magmas. The porphyritic gabbronorites are enriched in TiO2, FeOt, K2O, P2O5 and REE compared to the equigranular gabbronorites that are enriched in MgO and CaO. The

  13. Late Paleozoic granitic rocks of the Chukchi Peninsula: Composition and location in the structure of the Russian Arctic

    NASA Astrophysics Data System (ADS)

    Luchitskaya, M. V.; Sokolov, S. D.; Kotov, A. B.; Natapov, L. M.; Belousova, E. A.; Katkov, S. M.

    2015-07-01

    An Early Carboniferous (352-359 Ma) U-Pb (TIMS, SIMS) age is established for granitic rocks of the Kibera pluton, quartz sienites of the Kuekvun pluton, and granites from the pebbles in the basement of Carboniferous rocks of the Kuul and Kuekvun uplifts in the Central Chukotka region. These data support the suggestion of granitic magmatism to occur in the region in the Late Paleozoic. The petrogeochemistry of most granitic rocks of the Kibera and Kuekvun plutons is similar to that of I-type granites, and their age coincides with tectonic events of Ellesmerian Orogeny in the Arctic region at the Late Devonian-Early Carboniferous boundary. The Devonian-Early Carboniferous granitic complexes extend to the territories of the Arctic Alaska, Yukon, and Arctic Canada, which indicates a common geological evolution within the Chukotka-Arctic Alaska block, which experienced a motion away from Arctic Canada.

  14. Transpressional granite-emplacement model: Structural and magnetic study of the Pan-African Bandja granitic pluton (West Cameroon)

    NASA Astrophysics Data System (ADS)

    Sandjo, A. F. Yakeu; Njanko, T.; Njonfang, E.; Errami, E.; Rochette, P.; Fozing, E.

    2016-02-01

    The Pan-African NE-SW elongated Bandja granitic pluton, located at the western part of the Pan-African belt in Cameroon, is a K-feldspar megacryst granite. It is emplaced in banded gneiss and its NW border underwent mylonitization. The magmatic foliation shows NE-SW and NNE-SSW strike directions with moderate to strong dip respectively in its northern and central parts. This mostly, ferromagnetic granite displays magnetic fabrics carried by magnetite and characterized by (i) magnetic foliation with best poles at 295/34, 283/33 and 35/59 respectively in its northern, central and southern parts and (ii) a subhorizontal magnetic lineation with best line at 37/8, 191/9 and 267/22 respectively in the northern, central and southern parts. Magnetic lineation shows an `S' shape trend that allows to (1) consider the complete emplacement and deformation of the pluton during the Pan-African D 2 and D 3 events which occurred in the Pan-African belt in Cameroon and (2) reorganize Pan-African ages from Nguiessi Tchakam et al. (1997) compared with those of the other granitic plutons in the belt as: 686 ±17 Ma (Rb/Sr) for D 1 age of metamorphism recorded in gneiss; and the period between 604-557 Ma for D 2-D 3 emplacement and deformation age of the granitic pluton in a dextral ENE-WSW shear movement.

  15. Experimental and theoretical investigation of the production of HCl and some metal chlorides in magmatic/hydrothermal systems

    SciTech Connect

    Not Available

    1992-01-01

    In the calculations we have assumed that all apatites are magmatic. The presence of chlorite and altered plagioclase within the granite and quartz-monzodiorite suggests that alteration may play a role in leading to erroneous estimates of initial melt Cl and F for 2 reasons: (1) the apatites may in fact not be magmatic in origin, but are hydrothermal, and (2) the halogen signature of magmatic apatite may be changed due to subsolidus exchange with a hydrothermal fluid. We are currently endeavoring to develop criteria for determining whether apatite composition represents earlier or later stages of magmatic-hydrothermal development.

  16. Onset of the Sveconorwegian orogeny: 1220-1130 Ma bimodal magmatism, sedimentation and granulite-facies metamorphism

    NASA Astrophysics Data System (ADS)

    Bingen, Bernard; Viola, Giulio; Engvik, Ane K.; Solli, Arne

    2013-04-01

    The Grenville orogen of Laurentia and the Sveconorwegian orogen of Baltica are generally interpreted as long-lived, hot, collisional orogens resulting from collision of a possibly joined Laurentia-Baltica margin with another major plate, possibly Amazonia. Here we report new mapping, petrologic and SIMS U-Pb geochronological data from S Norway, to address the pre- to early-Sveconorwegian evolution between 1220 and 1130 Ma. The Sveconorwegian belt includes from west to east the Telemarkia terrane characterized by 1520-1480 Ma magmatism and the Idefjorden terrane characterized by Gothian active margin 1660-1520 Ma magmatism. The Idefjorden terrane is thrusted eastwards onto the parauthochthonous Eastern Segment. The Kongsberg and Bamble are two small terranes between the Idefjorden and Telemarkia terranes. They have a strong N-S and NE-SW structural grain, respectively, and are thrust westwards on top of the Telemarkia terrane. Basement metavolcanic and metaplutonic rocks in the Kongsberg terrane range from c. 1534 to 1500 Ma (5 new samples) and in Bamble from c. 1572 to 1460 Ma, overlapping with both the Telemarkia and Idefjorden terranes. New and published data show the following: (1) In Telemark, a c. 1200 Ma granitoid from the Flåvatn complex and a c. 1195 Ma granite sheet in the bimodal Nissedal supracrustals demonstrate that 1220-1180 Ma comparatively juvenile magmatism is the dominant rock type over much of southern part of Telemark. (2) A rhyolite dated at 1155 Ma complement available data showing low grade bimodal mafic-felsic volcanism interlayered with immature clastic sediments in central Telemark between 1169 and 1145 Ma (the ex-Bandak group). These supracrustals are intruded by c. 1153-1144 Ma A-type granite plutons. (3) Ten samples of foliated commonly porphyritic ganitoid and one granite dyke in gabbro collected in Kongsberg and along the Kongsberg-Telemark boundary demonstrate that c. 1171-1147 Ma bimodal plutonism occurred in Kongsberg. This

  17. Juvenile crustal recycling in an accretionary orogen: Insights from contrasting Early Permian granites from central Inner Mongolia, North China

    NASA Astrophysics Data System (ADS)

    Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Liu, Fulin

    2016-11-01

    Coeval high-K calc-alkaline to alkaline granites constitute important components of post-collisional to post-orogenic igneous suites in most orogenic belts of various ages on Earth and their genesis harbors a key to ascertaining critical geodynamic controls on continental crustal formation and differentiation. This zircon U-Pb dating and geochemical study documents three contrasting Early Permian granites from Erenhot of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB) and reveals concurrent high-K calc-alkaline to alkaline granite association derived from successive partial melting of distinct protoliths. The ca. 280 Ma Gancihuduge (GCG) pluton shows a calc-alkaline I-type character, with initial 87Sr/86Sr ratios of 0.7035 to 0.7039, εNd(t) of + 1.87 to + 4.70, zircon εHf(t) of + 8.0 to + 13.2 and δ18O from 7.4 to 8.7‰. The ca. 276 Ma Cailiwusu (CLS) pluton is magnesian and peraluminous, with initial 87Sr/86Sr ratios of 0.7036 to 0.7040, εNd(t) of + 1.9 to + 2.4, zircon εHf(t) of + 6.5 to + 12.1 and δ18O from 9.7 to 10.9‰. These features are consistent with partial melts of mixed sources composed of newly underplated meta-basaltic to -andesitic protoliths and variable supracrustal components, with distinctively higher proportion of the latter in the CLS pluton. By contrast, the ca. 279 Ma Kunduleng (KDL) suite exhibits an A-type magmatic affinity, with typical enrichment in alkalis, Ga, Zr, Nb and Y, εNd(t) of + 2.39 to + 3.55, zircon εHf(t) from + 8.3 to + 12.3 and δ18O values from 6.8 to 7.5‰. These features suggest that they stem from high-temperature fusion of dehydrated K-rich mafic to intermediate protoliths. Besides presenting a snapshot into a stratified crustal architecture in δ18O, these contrasting granites could not only serve as a temporal marker for monitoring post-collisional extension in the aftermath of a retreating subduction zone, but also present spatial magmatic proxy for tracing crustal formation and

  18. Measurement and interpretation of strain in the syntectonic Solı´s de Mataojo Granitic Complex, Uruguay

    NASA Astrophysics Data System (ADS)

    Oyhantçabal, Pedro; Heimann, Adriana; Miranda, Sara

    2001-05-01

    The Neoproterozoic Solı´s de Mataojo Granitic Complex is an intrusive body, elongate north-south, emplaced in the Sarandı´ del Yı´-Arroyo Solı´s Grande Shear Zone. In the present work, a quantification of the magmatic strain has been made by analysis of fabric, enclave geometry and minor structures. Structural evidence indicates that deformation began in the magmatic state and continued through the sub-solidus stage. The observed distribution of magmatic foliations and lineations, the fabric, the geometry of the enclaves and the late to post-magmatic structures, are related to a non-coaxial flattening regime that took place after the emplacement, and late in the magmatic history. These structures reveal that magmatic strain involved a shortening of the order of 80% with a simple shear component ( γ) between 3 and 4.5. The solid-state deformation records an additional mean γ of 2.7.

  19. Mineral chemistry and magnetic petrology of the Archean Planalto Suite, Carajás Province - Amazonian Craton: Implications for the evolution of ferroan Archean granites

    NASA Astrophysics Data System (ADS)

    Cunha, Ingrid Roberta Viana da; Dall'Agnol, Roberto; Feio, Gilmara Regina Lima

    2016-04-01

    The Planalto Suite is located in the Canaã dos Carajás subdomain of the Carajás Province in the southeastern part of the Amazonian Craton. The suite is of Neoarchean age (∼2.73 Ga), ferroan character, and A-type affinity. Magnetic petrology studies allowed for the distinction of two groups: (1) ilmenite granites showing low magnetic susceptibility (MS) values between 0.6247×10-3 and 0.0102 × 10-3 SI and (2) magnetite-ilmenite-bearing granites with comparatively higher but still moderate MS values between 15.700×10-3 and 0.8036 × 10-3 SI. Textural evidence indicates that amphibole, ilmenite, titanite, and, in the rocks of Group 2, magnetite also formed during magmatic crystallization. However, compositional zoning suggests that titanite was partially re-equilibrated by subsolidus processes. The amphibole varies from potassian-hastingsite to chloro-potassian-hastingsite and shows Fe/(Fe + Mg) > 0.8. Biotite also shows high Fe/(Fe + Mg) ratios and is classified as annite. Plagioclase porphyroclasts are oligoclase (An25-10), and the grains of the recrystallized matrix show a similar composition or are albitic (An9-2). The dominant Group 1 granites of the Planalto Suite were formed under reduced conditions below the FMQ buffer. The Group 2 granites crystallized under more oxidizing conditions on or slightly above the FMQ buffer. Pressures of 900-700 MPa for the origin and of 500-300 MPa for the emplacement were estimated for the Planalto magmas. Geothermometers suggest initial crystallization temperatures between 900 °C and 830 °C, and the water content in the magma is estimated to be higher than 4 wt%. The Neoarchean Planalto Suite and the Estrela Granite of the Carajás Province reveal strong mineralogical analogies, and their amphibole and biotite compositions have high total Al contents. The latter characteristic is also observed in the same minerals of the Neoarchean Matok Pluton of the Limpopo Belt but not in those of the Proterozoic rapakivi A-type

  20. The Late Neoproterozoic granitoid magmatism of the Pelotas Batholith, southern Brazil

    NASA Astrophysics Data System (ADS)

    Philipp, Ruy Paulo; Machado, Rômulo

    2005-09-01

    Geological mapping, petrography, geochemistry, and isotope studies enable the division of the Pelotas Batholith into six granitic suites: Pinheiro Machado (PMS), Erval (ES), Viamão (VS), Encruzilhada do Sul (ESS), Cordilheira (CS), and Dom Feliciano (DFS). The rocks of the PMS show a large compositional range (granite through granodiorite to tonalite), and the suite is considered pre- to syncollisional. Other suites show restricted compositional variations (granite to granodiorite) and are late to postcollisional. In general, the suites are metaluminous to slightly peraluminous (PMS, ES, and VS) or peraluminous (CS) or have alkaline tendencies (ESS and DFS). The magmatic evolution corresponds to high-K calc-alkaline to alkaline magmatism. The suites are enriched in K, Rb, and REE compared with rocks of typical calc-alkaline series. Initial 87Sr/ 86Sr ratios vary from 0.705 to 0.716, except in the CS, where they attain values of 0.732-0.740. Sm-Nd T DM model ages vary between 0.98 and 2.0 Ga, with initial ɛ Nd values ranging from -0.3 to -10. U-Pb zircon dates of samples from PMS, VS, and ESS suggest an age between 0.63 and 0.59 Ga for magmatism. Rb-Sr dates of samples of alkaline granites from DFS present ages between 0.57 and 0.55 Ga. The main tectonic controls of the magmatism of the Pelotas Batholith are high-dip sinistral shear zones.

  1. Geology of Nicholson's point granite, Natal Metamorphic Province, South Africa: the chemistry of charnockitic alteration and origin of the granite

    NASA Astrophysics Data System (ADS)

    Grantham, G. H.; Allen, A. R.; Cornell, D. H.; Harris, C.

    1996-10-01

    by destabilisation of biotite by a low aH 20 fluid phase, possibly hypersaline brines. The Nicholson's Point granite has geochemical characteristics typical of within-plate granites, A-type granites and rapakivi granites, however the stable and radiogenic isotope characteristics suggest a significant crustal component in the source.

  2. The GRANIT spectrometer

    SciTech Connect

    Baessler, Stefan; Beau, M; Kreuz, Michael; Nesvizhevsky, V.; Kurlov, V; Pignol, G; Protasov, K.; Vezzu, Francis; Voronin, Vladimir

    2011-01-01

    The existence of quantum states of matter in a gravitational field was demonstrated recently in the Institut Laue-Langevin (ILL), Grenoble, in a series of experiments with ultra cold neutrons (UCN). UCN in low quantum states is an excellent probe for fundamental physics, in particular for constraining extra short-range forces; as well as a tool in quantum optics and surface physics. The GRANIT is a follow-up project based on a second-generation spectrometer with ultra-high energy resolution, permanently installed in ILL. It has been constructed in framework of an ANR grant; and will become operational in 2011.

  3. Sequence of mineral assemblages in differentiated granitic pegmatites.

    USGS Publications Warehouse

    Norton, J.J.

    1983-01-01

    The sequence of mineral assemblages in internally zoned granitic pegmatites recognized by Cameron et al. (1949) is modified here to account for an observed vertical component, especially in feldspar compositions, in addition to the recognized outer contact-to-inner core differentiation process, and the importance of primary lithium minerals other than spodumene, such as petalite. The zonal patterns of 11 well-known granitic pegmatites are consistent with this revised sequence, with additional explanations for the repeated monomineralic zones of quartz or pollucite, etc. The crystallization history of zoned pegmatites is described in general terms, beginning with the magmatic crystallization which produces the outer zones. Aqueous fluid is exsolved continuously from the magma as relatively anhydrous phases precipitate, and plays an important role in the formation of the inner zones; its evolution is thought to be a major cause of pegmatite differentiation.-J.E.S.

  4. Linking magmatism with collision in an accretionary orogen

    PubMed Central

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

  5. Linking magmatism with collision in an accretionary orogen.

    PubMed

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-05-11

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251-245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  6. Geochronology, geochemistry and tectonic implications of Late Triassic granites in the Mongolian Altai Mountains

    NASA Astrophysics Data System (ADS)

    Dash, Batulzii; Boldbaatar, Enkhjargal; Zorigtkhuu, Oyun-Erdene; Yin, An

    2016-03-01

    Although the closure of the Paleo-Asian Ocean in western China and western Mongolia occurred in the Late Carboniferous and Early Permian, widespread intra-continental magmatism continued to occur across this region from the Late Permian to the end of the Triassic. In this study we document field relationships and geochemical characterization of a Late Triassic felsic intrusive complex in the western Mongolian Altai. The plutonic complex occurs as sills, dikes, and small stocks and its composition varies from biotite granite, two-mica granite, to leucogranite. Structurally, the plutonic complex occurs in the hanging wall of a segment of the regionally extensively (>1500 km long) Irtysh-Ertix-Bulgan thrust zone. As the plutonic bodies both cut and are deformed by the shear fabrics in this regional thrust shear zone, the duration of felsic magmatism and regional thrusting was temporally overlapping. This suggests that magmatism was coeval with crustal thickening. Major- and trace-element data and isotopic analysis of granitoid samples from our study area indicate that the felsic intrusions were derived from partial melting of meta-sediments, with the biotite and two-mica granite generated through vapor-absent melting and the leucogranite from flux melting. Although the Mongolian Altai intrusions were clearly originated from anatexis, coeval granite in the Chinese Altai directly west of our study area in the hanging wall of the Irtysh-Ertix-Bulgan thrust was derived in part from mantle melting. To reconcile these observations, we propose a Himalayan-style intracontinental-subduction model that predicts two geologic settings for the occurrence of felsic magmatism: (1) along the intracontinental thrust zone where granite was entirely generated by anatexis and (2) in the hanging wall of the intracontinental thrust where convective removal and/or continental subduction induced mantle melting.

  7. LA-ICPMS zircons U/Pb dating of Permo-Triassic and Cretaceous magmatisms in Northern Vietnam - Geodynamical implications

    NASA Astrophysics Data System (ADS)

    Roger, Françoise; Maluski, Henri; Lepvrier, Claude; Vu Van, Tich; Paquette, Jean-Louis

    2012-04-01

    In northeastern Vietnam, the major tectonic episode responsible for nappes emplacement is Triassic. These allochtonous structures are intruded by granitic melts. Two post-tectonic massifs showing no sign of deformation have been dated by the LA-ICPMS zircon U-Pb techniques. Dating reveals a multiphase history with zircon cores showing evidence of Proterozoic magmatism. The emplacement of the Phia Bioc granite intrusive in allochtonous units is 248-245 Ma, an age which assesses a younger limit for the major nappes tectonic. This tectonic could be synchronous of the tectonometamorphic strike-slip faulting events (250-245 Ma) defined in the Truong Son Belt as the Indosinian orogen. The Phia Bioc intrusion is probably linked with the intra-plate magmatism of the Emeishan Large Igneous Province or with magmatism associated with the Paleotethys closure. The age of the Phia Oac granite intrusion in displaced units is much younger, at 87.3 ± 1.2 Ma. This granite is probably linked to the magmatic activity produced during the Paleo-Pacific plate subduction under the SE Asia continental plate during the Mesozoic. Although the Cenozoic Red River fault system is close to these two plutons, this last thermotectonic episode has not been strong enough to disturb the U/Pb system. Zircons rims do not show any Tertiary magmatic or metamorphic overprint.

  8. Geology of the Andover Granite and surrounding rocks, Massachusetts

    USGS Publications Warehouse

    Castle, Robert O.

    1964-01-01

    Field and petrographic studies of the Andover Granite and surrounding rocks have afforded an opportunity for an explanation of its emplacement and crystallization. The investigation has contributed secondarily to an understanding of the geologic history of southeastern New England, particularly as it is revealed in the Lawrence, Wilmington, South Groveland, and Reading quadrangles of Massachusetts. The Andover Granite and Sharpners Pond Tonalite together comprise up to 90 percent of the Acadian(?) subalkaline intrusive series cropping out within the area of study. The subalkaline series locally invades a sequence of early to middle Paleozoic and possibly Precambrian metasedimentary and metavolcanic rocks. Much of the subalkaline series and most of the Andover Granite is confined between two prominent east-northeast trending faults or fault systems. The northern fault separates the mildly metamorphosed Middle Silurian(?) Merrimack Group on the north from a highly metamorphosed and thoroughly intruded Ordovician(?) sequence on the south. The southern 'boundary '' fault is a major structural discontinuity characterized by penetrative, diffuse shearing over a zone one-half mile or more in width. The magmatic nature of the Andover Granite is demonstrated by: (1) sharply crosscutting relationships with surrounding rocks; (2) the occurrence of tabular-shaped xenoliths whose long directions parallel the foliation within the granite and whose internal foliation trends at a high angle to that of the granite; (3) continuity with the clearly intrusive Sharpners Pond Tonalite; (4) the compositional uniformity of the granite as contrasted with the compositional diversity of the rocks it invades; (5) its modal and normative correspondence with (a) calculated norms of salic extrusives and (b) that of the ternary (granite) minimum for the system NaAlSi3O8-KAlSi3O8-SiO2. Orogenic granites, as represented by the Andover, contrast with post-orogenic granites, represented locally by

  9. Middle Neoproterozoic (ca. 705-716 Ma) arc to rift transitional magmatism in the northern margin of the Yangtze Block: Constraints from geochemistry, zircon U-Pb geochronology and Hf isotopes

    NASA Astrophysics Data System (ADS)

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Xu, Xianbing; Deng, Qi; Fu, Xuehai

    2017-09-01

    The South Qinling Belt in Central China is an important window to investigate the Neoproterozoic tectono-magmatic processes along the northern margin of the Yangtze Block. Here we present whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes of a suite of Middle Neoproterozoic intrusion from the Wudang Uplift in South Qinling. Zircon LA-ICP-MS U-Pb ages reveal that these rocks were formed at ca. 705-716 Ma. Geochemical features indicate that the felsic magmatic rocks are I-type granitoids, belong to calcic- to calc-alkaline series, and display marked negative Nb, Ta and Ti anomalies. Moreover, the enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs), combined with depletion of heavy rare earth elements (HREEs) support that these rocks have affinity to typical arc magmatic rocks formed in Andean-type active continental margins. The REE patterns are highly to moderately fractionated, with (La/Yb)N = 5.13-8.10 in meta-granites, and 2.32-2.35 in granodiorite. The granitoids have a wide range of zircon εHf(t) values (-29.91 to 14.76) and zircon Hf two-stage model ages (696-3482 Ma). We suggest that the ca. 705-716 Ma granitoids were sourced from different degrees of magma mixing between partial melting of the overlying mantle wedge triggered by hydrous fluids released from subducted materials and crustal melting. The hybrid magmas were emplaced in the shallow crust accompanied by assimilation and fractional crystallization (AFC). Both isotopic and geochemical data suggest that the ca. 705-716 Ma felsic magmatic rocks were formed along a continental arc. These rocks as well as the contemporary A-type granite may mark a transitional tectonic regime from continental arc to rifting, probably related to slab rollback during the oceanic subduction beneath the northern margin of Yangtze Block.

  10. Cretaceous rift related magmatism in central-western South America

    NASA Astrophysics Data System (ADS)

    Viramonte, J. G.; Kay, S. M.; Becchio, R.; Escayola, M.; Novitski, I.

    1999-03-01

    The Cretaceous-Paleocene Andean basin system of central-western South America, comprises northwestern Argentina and southwestern Bolivia. It is situated between 62°-68°W and 18°-27°S, but extends westward to northern Chile and northward to Bolivia and Peru. These basins have been interpreted as an aborted foreland rift. In a general sense, it may be possible to relate this rift to the opening of the South Atlantic Ocean, however it was directly associated, in a backarc position, with the subduction of the Nazca Plate below the South American Plate. Three main magmatic episodes were recognized: the pre-rift stage (130-120 Ma) which is characterized by an early phase of anorogenic plutonism, with subalkaline and alkaline granitic intrusives; the syn-rift volcanic episode which started with a mainly alkaline volcanic activity (110-100) in which alkaline rocks prevail; a second more voluminous volcanic episode (80-75 Ma) which is characterized by an alkaline suite represented by basanites and tephriphonolites; and the last volcanic episode (65-60 Ma) which consists of lamproitic sills and basic K rich lava flows. Petrography, chemistry and chronology of the Cretaceous plutonic bodies indicate anorogenic pre-rift related A-type granite complexes closely related to the further evolution of the Cretaceous rift basin. The petrology and geochemistry of the Cretaceous volcanic rocks show strong alkaline affinities and suggest a similar rift-related origin. The geochemical and isotopic characteristics of the alkaline basalts suggest that they originated through low degrees of partial melting of a depleted mantle subcontinental lithosphere which was previously enriched by processes such as the introduction of veins rich in amphibole, high Ti phlogopite, and apatite. Cretaceous plutonic and volcanic rocks from central-southwestern South America are related to an intracontinental rift environment and although their ages are correlative with those of the Paraná volcanic

  11. Multiple-staged granite evolution and TaNb mineralization in South China

    NASA Astrophysics Data System (ADS)

    Lin, Yin; Jinchu, Zhu; Shouxi, Hu

    Nb mineralized granites have very special geochemical compositions. The TaNb mineralized granites are characterized by high Na 2O, Na 2O/K 2O ratios (>1 wt%), Al 2O 3, Li and F and very low TiO 2, MnO, MgO and CaO. Most typically, nearly all the TaNb mineralized granites bear very low total REE contents (less than 50 ppm), low Sr and Zr (both usually less than 30 ppm) and very high Rb (more than 700 to 3000 ppm). Geochemical features, excluding the contribution of post-magmatic alteration, change gradually from the earlier to the later phases in a granite complex, showing some trends of magmatic evolution. For example, two good negative exponential correlation curves on the RbSr diagrams (or a correlogram for other elements) of Yichun ad Dengfuxian multiple-stage granite plutons indicate a fractional crystallization mechanism which might have been an effective way to enrich the rare metal elements. The granite-type TaNb deposits, where Ta is economically more important than Nb, will be the only TaNb mineralization type discussed in this paper.

  12. Late Neoproterozoic magmatism in South Qinling, Central China: Geochemistry, zircon U-Pb-Lu-Hf isotopes and tectonic implications

    NASA Astrophysics Data System (ADS)

    Wang, Ruirui; Xu, Zhiqin; Santosh, M.; Yao, Yuan; Gao, Li'e.; Liu, Chunhua

    2016-06-01

    The Neoproterozoic tectonic evolution of the northern margin of the Yangtze Block in South China remains debated. In this study, we present results from LA-ICP-MS zircon U-Pb geochronology on a suite of intermediate-felsic rocks in South Qinling, Central China which show a mean age of ca. 630 Ma. The zircon εHf(t) values of these rocks mostly range from + 0.44 to + 14.78. Geochemically, the granites and syenite show high total alkali contents, with enrichment in LREE, LILE (Rb, Ba, and K), and HFSE (Th, U, Nb, Ta, Zr, and Hf), and depletion in Sr, P, and Ti, similar to the features of A-type granites. The meta-diorite shows high Na2O, with depletion in Eu, Ti, and LILE (Sr, Rb, Ba, and K), and enrichment in HFSE (Th, U, Nb, Ta, Zr, and Hf). The geochemical features are consistent with formation of the intermediate-felsic suite through fractionation from underplated basaltic magma that originated from sub-continental lithospheric mantle metasomatized by asthenosphere-derived oceanic-island-basalt-like (OIB-like) melts, coupled with minor crustal contamination. We correlate the ca. 630 Ma magmatism with a back-arc rift setting that probably developed in relation to slab tearing during continued slab rollback.

  13. Climax granite test results

    SciTech Connect

    Ramspott, L.D.

    1980-01-15

    The Lawrence Livermore Laboratory (LLL), as part of the Nevada Nuclear Waste Storage Investigations (NNWSI) program, is carrying out in situ rock mechanics testing in the Climax granitic stock at the Nevada Test Site (NTS). This summary addresses only those field data taken to date that address thermomechanical modeling for a hard-rock repository. The results to be discussed include thermal measurements in a heater test that was conducted from October 1977 through July 1978, and stress and displacement measurements made during and after excavation of the canister storage drift for the Spent Fuel Test (SFT) in the Climax granite. Associated laboratory and field measurements are summarized. The rock temperature for a given applied heat load at a point in time and space can be adequately modeled with simple analytic calculations involving superposition and integration of numerous point source solutions. The input, for locations beyond about a meter from the source, can be a constant thermal conductivity and diffusivity. The value of thermal conductivity required to match the field data is as much as 25% different from laboratory-measured values. Therefore, unless we come to understand the mechanisms for this difference, a simple in situ test will be required to obtain a value for final repository design. Some sensitivity calculations have shown that the temperature field is about ten times more sensitive to conductivity than to diffusivity under the test conditions. The orthogonal array was designed to detect anisotropy. After considering all error sources, anisotropic efforts in the thermal field were less than 5 to 10%.

  14. The anatectic effect on the zircon Hf isotope composition of migmatites and associated granites

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Xiang; Gao, Peng; Zheng, Yong-Fei

    2015-12-01

    Zircon Hf isotope composition is widely used to trace the growth and evolution of continental crust. However, it is controversial whether the Hf isotope composition of magmatic zircons can faithfully reflect that of their sources, especially for S-type granites. In order to provide an insight into this issue, we have revisited the published Lu-Hf isotope data of zircons from well-studied migmatites and associated granites in the Sulu orogen and the Cathaysian terrane, respectively. The results show greatly elevated 176Hf/177Hf ratios (by more than 10ε units) for newly grown zircon domains compared to the relict zircon domains. This indicates considerable contributions from non-zircon Hf to anatectic melts during crustal anatexis and subsequent magmatism. Furthermore, this more radiogenic Hf isotope signature was not erased during magmatic processes such as crystal fractionation during melt ascent and emplacement. The budget of Hf isotopes in source rocks with respect to mineral Lu/Hf ratios suggests the involvement of Hf-bearing major minerals in anatectic reactions by dissolving Hf-bearing major minerals into the anatectic melts. The significant Hf isotope variations in some anatectic and magmatic zircon domains from the migmatites and granites suggest not only the source heterogeneity but also the variable non-zircon Hf contributions. As such, the Hf isotope compositions of anatectic and magmatic zircons are substantially dictated by the mass balance between the non-zircon Hf from anatectic reactions and the zircon-Hf from the dissolution of protolith zircons into the anatectic melts. They are primarily controlled by P-T conditions and mechanism of crustal anatexis, and the magmatic processes during melt evolution. The present study highlights the important contribution of non-zircon Hf to the anatectic and magmatic zircon domains. In this regard, the greatly elevated 176Hf/177Hf ratios for newly grown zircon domains in the migmatites and granites cannot reflect

  15. Geochronology and tectonic significance of Middle Proterozoic granitic orthogneiss, North Qaidam HP/UHP terrane, Western China

    USGS Publications Warehouse

    Mattinson, C.G.; Wooden, J.L.; Liou, J.G.; Bird, D.K.; Wu, C.L.

    2006-01-01

    Amphibolite-facies para- and orthogneisses near Dulan, in the southeast part of the North Qaidam terrane, enclose minor ultra-high pressure (UHP) eclogite and peridotite. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. Ion microprobe U-Pb and REE analyses of zircons from two granitic orthogneisses indicate magmatic crystallization at 927 ?? Ma and 921 ?? 7 Ma. Zircon rims in one of these samples yield younger ages (397-618 Ma) compatible with partial zircon recrystallization during in-situ Ordovician-Silurian eclogite-facies metamorphism previously determined from eclogite and paragneiss in this area. The similarity between a 2496 ?? 18 Ma xenocrystic core and 2.4-2.5 Ga zircon cores in the surrounding paragneiss suggests that the granites intruded the sediments or that the granite is a melt of the older basement which supplied detritus to the sediments. The magmatic ages of the granitic orthogneisses are similar to 920-930 Ma ages of (meta)granitoids described further northwest in the North Qaidam terrane and its correlative west of the Altyn Tagh fault, suggesting that these areas formed a coherent block prior to widespread Mid Proterozoic granitic magmatism. ?? Springer-Verlag 2006.

  16. Mobilité des terres rares au cours des altérations hydrothermales: l'exemple du granité de Serra Branca, Brésil central

    NASA Astrophysics Data System (ADS)

    Pinto-Coelho, Cristina; Botelho, Nilson F.; Roger, Guy

    1999-05-01

    The Middle Proterozoic granitic massif, in the Goiás Tin Province, is affected by pervasive post-magmatic hydrothermal alterations, chiefly by eastward, increasingly developed greisenization. Hydrothermal alteration results in strong mineralogical and chemical modifications of granite composition, but nevertheless the effect of fluid circulations is probably limited to a dilution of the initial REE content in magmatic rocks without any important fractionation, as suggested by the similarity between chondrite-normalized patterns for all rocks, from the less altered granite to the muscovite-topaz-bearing greisen.

  17. A Global compilation of Heat Production in Granitic Rocks

    NASA Astrophysics Data System (ADS)

    Jakobsen, Kiki; Sørensen, Nanna K.; Nielsen, Louise S. K.; Thybo, Hans; Artemieva, Irina M.

    2017-04-01

    Knowledge of the heat production in the crust is important for understanding the energy balance in Earth. It is assumed that the crust produces a substantial part of the heat in Earth, but its proportion in comparison to the mantle and the contribution from core solidification is not well known. Knowledge of the crustal heat production is required for assessing the mantle heat flow at the crust-mantle interface. Granites probably are the main heat producing rock types in the crust, and therefore their heat production is of crucial importance for understanding Earth heat balance. As part of a B.Sc. thesis study we have compiled a new database based on published values of heat production in various types of granites. The database has about 500 entries for concentrations of U, Th, and K and the total heat generation in different continental regions. The database also includes information on crustal age and the emplacement age of granites, where available. Some of the main conclusions that may be drawn from analyses of this new database are: • Distribution of heat production values is narrow in Archean-early Proterozoic granites but very broad in middle-late Proterozoic granites. • We observe no correlation between granite type and heat production. • Some correlation may be inferred between age and heat production - heat production is relatively low in Archaean-early Proterozoic granites. • Proterozoic granites are dominated by A-type which have high heat production; the I-type Archean granitic rocks seem to have the highest Th/U ratio. • The Th/U ratio is supposed to be 3.7-4.0 based on relative time constants. This is in general correct with a global average value of 3.7. However, it is ca. 3.8 for Phanerozoic and Archaean-early Proterozoic granites and 3.3 for middle-late Proterozoic granites. We speculate if this variation may be caused by major plate reorganization or perhaps by change in global plate tectonic style?

  18. Dirty or Tidy ? Contrasting peraluminous granites in a collapsing Orogen: Examples from the French Massif Central

    NASA Astrophysics Data System (ADS)

    Villaros, Arnaud; Pichavant, Michel; Moyen, Jean-François; Cuney, Michel; Deveaud, Sarah; Gloaguen, Eric; Melleton, Jérémie

    2013-04-01

    Post collisional collapse commonly enhances crustal melting. Such melting typically produces peraluminous granitic magmas. In the French Massif Central, a mid-crustal segment of the western Variscan belt, two large granitic bodies were produced during the collapse of the Variscan Belt. The St Sylvestre Leucogranitic Complex (SSyL) in the western part of the Massif Central and the Velay Migmatitic Complex (VMC) in the Eastern part. Although these two complexes are formed in similar geodynamic context they present meaningful petrological and geochemical differences. The VMC (~305 Ma) is clearly intrusive in migmatitic terranes. The migmatitic host recorded two successive melting events M3 (720 °C and 5kb) dated between 335 and 315 Ma and M4 (850°C and 4 kb) dated at 305 Ma. The compositions of the VMC are strictly H2O-undersaturated and ranges from leucogranitic to granodioritic. Three main successive granite types have been distinguished (1) A heterogeneous banded biotite granite, (2) A main biotite-cordierite granite, where cordierite can be prismatic, as cockade or pseudomorphic (3) a late magmatic with large K-feldspar phenocryst and prismatic cordierite. The compositions of the VMC granites are quite similar to typical Australian S-type granites in the sense that they also show a positive correlation between ferromagnesian abundance and aluminosity. The SSyL (~320 Ma) is intrusive in upper greenschist facies to upper amphibolite migmatitic metasediment and orthogneiss (~3kb). The compositional variety observed in the SSyL suggests a continuous trend from a moderately mafic, peraluminous magma (cd- and sill- granite) to a H2O saturated granite ("two-mica" granite) facies and finally to an extremely felsic, H2O-saturated magma. Three granitic units have been recognized in the SSyL: (1) the western "Brame Unit" composed of the less evolved cd- and sill- granite facies (2) the central "St Sylvestre Unit", composed mainly by U-rich two-mica granite, intruded by two

  19. [Study on the fine structure of K-feldspar of Qichun granite].

    PubMed

    Du, Deng-Wen; Hong, Han-Lie; Fan, Kan; Wang, Chao-Wen; Yin, Ke

    2013-03-01

    Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR), and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization. The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry. K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening [131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp [131] peak and is honiogeneously monoclinic. The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer (1974). The 640 cm-1 absorption band increases while the 540 cm-' absorption band decreases with increase in K-feldspar ordering index, also, the 1,010 cm-1 absorption band separates into 1,010 and 1,046 cm-1 absorption bands, with a change in the band shape from widening to sharp outline. The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements, and the granite exhibits better mineralization background, K-feldspar of the potassic alteration veins has markedly lower Sr and Ba, indicating that the alteration fluid originated from the granitic magmatism, and hence, potassic alteration is a good indicator for molybdenite exploration.

  20. Experimental and theoretical investigation of the production of HCl and some metal chlorides in magmatic/hydrothermal systems. Annual report, 1991--1992

    SciTech Connect

    Not Available

    1992-12-31

    In the calculations we have assumed that all apatites are magmatic. The presence of chlorite and altered plagioclase within the granite and quartz-monzodiorite suggests that alteration may play a role in leading to erroneous estimates of initial melt Cl and F for 2 reasons: (1) the apatites may in fact not be magmatic in origin, but are hydrothermal, and (2) the halogen signature of magmatic apatite may be changed due to subsolidus exchange with a hydrothermal fluid. We are currently endeavoring to develop criteria for determining whether apatite composition represents earlier or later stages of magmatic-hydrothermal development.

  1. Granite Symposia and Working Groups

    NASA Astrophysics Data System (ADS)

    Miller, Calvin

    In addition to the Hutton Symposium on Granites and Related Rocks to be held in Canberra, Australia, Sept. 23-28, 1991, two other international symposia on granitoids will take place during 1991: the inaugural meeting and field excursion of the proposed IGCP project Rapakivi Granites and Related Rocks, to be held in Helsinki, Finland, July 29-August 4, and Granites and Geodynamics, to be held in Moscow, August 6-9. Contacts for these meetings are: Hutton Symposium, Bruce Chappell, Dept. of Geology, Australian National University, GPO Box 4, Canberra, ACT 2601, Australia; Rapakivi Granites, Ilmari Haapala or Tapani Ramo, Dept. of Geology, Division of Geology and Mineralogy, University of Helsinki, Snelmaninkatu 5, 60170 Helsinki 17, Finland. Melt segregation and migration in partly molten rocks will be the topic of a special session at the Geological Association/Mineralogical Association of Canada meeting in Toronto, May 27-29, 1991.

  2. Bimodal magmatism produced by progressively inhibited crustal assimilation.

    PubMed

    Meade, F C; Troll, V R; Ellam, R M; Freda, C; Font, L; Donaldson, C H; Klonowska, I

    2014-06-20

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.

  3. Bimodal magmatism produced by progressively inhibited crustal assimilation

    NASA Astrophysics Data System (ADS)

    Meade, F. C.; Troll, V. R.; Ellam, R. M.; Freda, C.; Font, L.; Donaldson, C. H.; Klonowska, I.

    2014-06-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.

  4. Granite petrogenesis revealed by combined gravimetric and radiometric imaging

    NASA Astrophysics Data System (ADS)

    Tartèse, Romain; Boulvais, Philippe; Poujol, Marc; Vigneresse, Jean-Louis

    2011-03-01

    In peneplaned terranes, it is often impossible to get a full 3D view of geological objects. In the case of granitic plutons, for which intrusive relationships between constituent units can provide first order information regarding their petrogenesis, this lack of 3D field evidence is a major issue. Indirect observations can be provided by geophysical surveys. Here, we interpret field gravity data and airborne gamma ray radiometric maps with whole rock geochemistry data in order to obtain information on granite petrogenesis. First, we test our proposed combined geophysical and geochemical approach on the Huelgoat Variscan intrusion (Armorican Massif, France) and we show that ternary radiometric maps are a good proxy for the distribution of K, U and Th radioelements. Then, we apply our method to the Lizio and Questembert Variscan granitic intrusions (Armorican Massif) and show that some features characteristic of the intrusions, such as the feeding zones, can be localised by geophysical imaging. Indeed, radiometric maps constitute a frozen image of the latest stage of the magmatic building of plutons.

  5. Geochemical characteristics and origin of the Lebowa Granite Suite, Bushveld Complex

    USGS Publications Warehouse

    Hill, M.; Barker, F.; Hunter, D.; Knight, R.

    1996-01-01

    The ??? 2052-Ma Lebowa Granite Suite (LGS) represents the culminating phase of an Early Proterozoic magmatic cycle in the Central Transvaal area of the Kaapvaal Province. Following extrusion of at least 200,000 km3 of intermediate to acid volcanics (Rooiberg Felsite), mafic and ultramafic magmas intruded at 2065 Ma to form the Rustenburg Layered Suite (RLS). The LGS includes the Nebo, Makhutso, Bobbejaankop, Lease, and Klipkloof granites. The Nebo Granite intruded the Rooiberg Felsite as sheets up to 4 km thick above the RLS. Smaller stocks of the other granites crosscut the Nebo. We determined major- and trace-element compositions and oxygen, Rb-Sr, and Sm-Nd isotope ratios for samples of: Nebo Granite; Rooiberg Felsite; granophyre and granophyric granite; Makhutso, Bobbejaankop, and Lease granites; and feldspar porphyry from areas throughout the exposed area of the LGS (Dennilton, Verena Balmoral, Enkeldoorn, Sekhukhune Plateau, Zaaiplaats-Potgeitersrus, and Western Transvaal). Coherent floor-to-roof geochemical trends exist in some areas, although it is not possible to model them convincingly. Regional variations in geochemistry exist and likely are related to source variations in the estimated 200,000 km3 of the Nebo Granite sheets. ??18O for the LGS range from +5.9??? to +9.5???; if these are approximate primary magmatic values, pelitic sediments cannot have been an important source for the LGS. The Rb-Sr isotope system has been altered, a finding consistent with previous studies. A mineral isochron for Nebo Granite near Dennilton yields a York regression age of 1995 ?? 99 Ma, with initial 143Nd/144Nd = 0.50978??8 and ???CHUR=-5.12. Samples from the Sekhukhune Plateau have higher 143Nd/144Nd ratios than do Dennilton-area samples, suggesting that the former originated from older or less LREE-enriched sources. We suggest that intrusion of mafic to ultramafic magmas at depth in the continental crust triggered melting of Archean quartzofeldspathic crystalline

  6. Petrogenesis of Oxidized Arfvedsonite Granite Gneiss from Dimra Pahar, Hazaribagh, Eastern India: Constraints from Mineral Chemistry and Trace Element Geochemistry

    NASA Astrophysics Data System (ADS)

    Basak, Ankita; Goswami, Bapi

    2017-04-01

    The arfvedsonite granite gneiss of Dimra Pahar occurs along the North Purulia Shear Zone (NPSZ) which pivots the Proterozoic Chotannagpur Gneissic Complex (CGC), Eastern India. Although minerals like arfvedsonite and aegirine depict the peralkaline nature of the pluton, the geochemistry of the rock reflects its composition varying from peralkaline to mildly peraluminous. K-feldspar, quartz, arfvedsonite, albite with accessory aegirine, titaniferous iron oxides and zircon form the dominant mineralogy of this alkali feldspar granite (IUGS, 2000) gneiss. The zircon saturation temperature corresponds to 747oC-1066oC. The granitic magma contains low water content evidenced by the absence of any pegmatite associated with this pluton. Geochemically these granites are classified as ferroan and alkalic (cf. Frost et al., 2001). These highly evolved granites possess enrichment of SiO2, Na2O + K2O, FeO(t)/MgO, Ga/Al, Zr, Nb, Ga, Y, Ce and rare earth elements (REE) with low abundance of CaO, MgO, Ba and Sr which characterize their A-type nature while standard discrimination diagrams ( cf. Eby, 1992; Grebennikov, 2014) help to further discriminate them as A1 type. Tectonic discriminations diagrams (Pearce et al., 1984; Maniar and Piccoli, 1989; Batchelor and Bowden, 1985) constrain the tectonic setting of the magma to be anorogenic, within plate, rift-related one. The REE compositions show moderately fractionated patterns with (La/Yb)N 2.57-10.5 and Eu/Eu* 0.16-0.70. Multielement spider diagram and various trace element ratio together with oxidized nature (ΔNNO: +2) of these granites further suggest that these have been derived from OIB-type parental magma. The peralkaline nature of the granite and its lack of subduction- related geochemical features are consistent with an origin in a zone of regional extension. The extremely high Rb/Sr ratios combined with the extreme Sr, Ba, P, Ti and Eu depletions clearly indicate that these A-type granites were highly evolved and require

  7. Southern complex: geology, geochemistry, mineralogy, and mineral chemistry of selected uranium- and thorium-rich granites

    SciTech Connect

    Hoffman, M.A.

    1987-01-01

    Four major rock groups are defined in the Southern Complex: the Bell Creek Granite (BCG), the Clotted Granitoids (CGR), the Albite Granite (AGR), and the Migmatite Complex. Metatexites of the Migmatite Complex are the oldest rocks and include paleosome of a metasedimentary and metavolcanic protolith represented by Banded Iron Formation, Banded Amphibolite, and Banded Gneisses, and interlayered or crosscutting leucogranites. The CGR span the range from metatexite to diatexite and represent in-situ partial melting of metapelitic layers in the protolith during intrusion of the BCG. The BCG cuts the migmatites, is locally cut by the CGR, and was derived by partial melting of a dominantly metasedimentary protolith at some depth below the presently exposed migmatites during a regional tectonothermal event. The Albite Granite is a 2km diameter, muscovite-fluorite-columbite-bearing intrusive stock that cuts all other major units. The thorium history of the BCG is a function of the history of monazite. The thorium history of the CGR is also dominated by monazite but the thorium content of this unit cannot be entirely accounted for by original restite monazite. The uranium history of the BCG and CGR was dominated by magmatic differentiation and post magmatic, metamorphic and supergene redistributions and is largely independent of the thorium history. The thorium and uranium history of the AGR was dominated by magmatic/deuteric processes unlike the BCG and CGR.

  8. Hydrothermal alteration and permeability changes in granitic intrusions related to Sn-W deposits : case study of Panasqueira (Portugal)

    NASA Astrophysics Data System (ADS)

    Launay, Gaetan; Sizaret, Stanislas; Guillou-Frottier, Laurent; Gloaguen, Eric; Melleton, Jérémie; Pichavant, Michel; Champallier, Rémi; Pinto, Filipe

    2017-04-01

    The Panasqueira Sn-W deposit occurs as a dense network of flat wolframite and cassiterite-bearing quartz veins concentrated in the vicinity of a hidden greisen cupola, and to a lesser extent as disseminated cassiterites in the greisen. Previous studies (Thadeu 1951; 1979) have suggested that the Panasqueira deposit is genetically related to magmatic activity for which the most part is unexposed, and being only represented by the greisen cupola. Hydrothermal fluid circulation during the final stages of granite crystallisation has probably led to the greisenisation of the cupola followed by the deposition of the mineralization in the veins system. Mineral replacement reactions that occurred during the greisenisation could affect rock properties (porosity, density and permeability) which control fluid circulation in the granite. This study aims to investigate effects of greisenisation reactions on the dynamic (time varying) permeability that ultimately leads to fluid circulation in the greisen cupola. To do so, petrological study and experimental determinations of hydrodynamic features (porosity and permeability) for different granite alteration levels and petrographic types (unaltered granite to greisen) are combined and then integrated in coupled numerical models of fluid circulation around the granitic intrusion. Greisen occurs in the apical part of the granitic body and results in the pervasive alteration of the granite along the granite-schist contact. This greisen consists mainly of quartz and muscovite formed by the replacement of feldspars and bleaching of biotites of the initial granite. Otherwise, greisen is generally vuggy which suggests a porosity increase of the granite during hydrothermal alteration processes. This porosity increase has a positive effect on the permeability of the granitic system. Indeed, experimental measurements of permeability with the Paterson press indicate that the initial granite is impermeable (10-20 m2) whereas the greisen is

  9. The geochemical and Srsbnd Nd isotopic characteristics of Paleozoic fractionated S-types granites of north Queensland: Implications for S-type granite petrogenesis

    NASA Astrophysics Data System (ADS)

    Champion, David C.; Bultitude, Robert J.

    2013-03-01

    Moderately to strongly fractionated S-type granites crop out extensively (> 2500 km2) in the central and eastern parts of the Hodgkinson Province, north Queensland, Australia. The granites have been subdivided in two major supersuites: the garnet-bearing Whypalla and cordierite-bearing Cooktown Supersuites; and a number of minor suites—including the extremely fractionated Wangetti and Mount Alto Suites. Early formed magmatic tourmaline is a feature of the Wangetti and Mount Alto granites. Almost all of the S-type granites contain metasedimentary enclave material, while microdioritic enclaves are mostly notably absent. The S-type granites are felsic with a moderate SiO2 range (68-77%). Most elements are negatively correlated with increasing differentiation, including TiO2, FeOtot, MgO, CaO, Ba, Sr, Th, LREE, Eu, Zr, Hf, and ratios such as K/Rb; many decrease to very low levels. There are very few positively correlated elements: Rb, U, and to some extent Na2O. Geochemical differences between supersuites include higher CaO, Ba, Sr, Pb, and lower Rb, Sn, B, V in the Whypalla Supersuite. Geochemical variation within the granites is largely due to extensive crystal fractionation. Some of the S-type granites have FeO* and MgO contents of 2.5-3.0% or more indicating they do not represent simple sedimentary melts, but rather represent the presence of both cumulate and restitic material. Variable Nd and Sr signatures (ɛNd between - 2 and - 6.5; initial Sr ratios between 0.709 and 0.715), suggest multiple components. The S-type granites intrude a very extensive, siliciclastic turbidite sequence that is isotopically evolved (e.g., ɛNd mostly - 12.0 to - 15.0 at 270 Ma), and generally too mature (too CaO poor) to produce S-type granites. Isotopic and chemical modeling show that although magma-mixing is permissible, the levels permissible (< ca. 20-25% basaltic input), are not large enough to explain the signature of the granites. Instead the data suggest that the S

  10. Changing magmatic and tectonic styles along the paleo-Pacific margin of Gondwana and the onset of early Paleozoic magmatism in Antarctica

    NASA Astrophysics Data System (ADS)

    Encarnación, John; Grunow, Anne

    1996-12-01

    Basement rocks of the Transantarctic Mountains are believed to record a change in the paleo-Pacific margin of Gondwana from a passive to a tectonically active margin. Widespread emplacement of calc-alkaline batholiths (Granite Harbor intrusives) occurred during the active margin phase. We present new concordant zircon and titanite U-Pb ages for these magmatic rocks in southern Victoria Land and the Scott Glacier area. Most magmatic rocks previously associated with a pre-late Early Cambrian (>530 Ma) deformational event(s) (Beardmore orogeny) have yielded younger crystallization ages. The lack of definite arc magmatism prior to ˜530 Ma suggests that deformation may have been associated with a strike or oblique-slip regime, although shallow subduction without significant arc magmatism cannot be ruled out. Local transpressional and transtensional domains may account for compressional deformation and rare alkaline and carbonatite magmatism during this early period. The oldest and most voluminous magmatic rocks were emplaced after ˜530 Ma. This magmatism has been associated with active subduction, and suggests a fundamental change in the plate boundary at ˜530 Ma. Ductile shearing of plutons and contractional deformation of supracrustal rocks after ˜530 Ma (Ross orogeny) may have been due to transpressional tectonics in an oblique subduction setting and/or a collision. Compressional deformation associated with the Ross orogeny may have ceased by ˜500 Ma along the southern Victoria Land-Scott Glacier segment of the Antarctic margin, as indicated by undeformed magmatic rocks of this age, although magmatic activity continued to at least ˜485 Ma.

  11. An Early Neoproterozoic gabbro-granite association in the Bureya Continental Massif (Central Asian fold belt): First geochemical and geochronological data

    NASA Astrophysics Data System (ADS)

    Sorokin, A. A.; Ovchinnikov, R. O.; Kudryashov, N. M.; Sorokina, A. P.

    2016-12-01

    The fact that gneissose granites and gabbros of the Nyatygran Complex in the Bureya Continental Massif are not Palaeoproterozoic in age, as previously thought, but Neoproterozoic, 933 Ma is proved. New data with the first direct evidence of Early Neoproterozoic magmatism in continental massifs composing the Bureya-Jiamusi Superterrane are given. At the moment, the obtained age estimates are the oldest for the magmatic rocks of this superterrane.

  12. Magmatic responses to Late Cretaceous through Oligocene tectonic evolution of the western Alaska Range

    NASA Astrophysics Data System (ADS)

    Todd, E.; Jones, J. V., III; Karl, S.; Ayuso, R. A.; Bradley, D. C.; Box, S. E.; Haeussler, P. J.

    2014-12-01

    New geochemistry, U/Pb geochronology, and radiogenic isotopes, together with existing datasets, contribute to a refined model of the petrogenetic history of magmatism in the western Alaska Range. Plutons within the study area were emplaced into Kahiltna basin Mesozoic turbiditic strata. The Kahiltna sequence overlies Mesozoic Peninsular oceanic terrane rocks in the SE half of the basin and Proterozoic to Paleozoic Farewell continental terrane rocks to the NW. This study focuses on successive intrusion suites, most of which are thought to intrude Kahiltna or underlying Farewell terrane rocks, but include older, perhaps more deeply exhumed rocks emplaced in Peninsular terrane basement to the SE. The chemically diverse sequence records magmatism associated with major tectonic reorganization events on the southern Alaska circum-Pacific subduction margin. The oldest pluton suite (~100-80 Ma) is mostly intermediate to evolved calcalkaline granite and coincides with final closure of the Kahiltna basin and a regional transition to transpression-dominated tectonics. The post-closure magmatic pulse (~75-67 Ma) is compositionally varied, including primitive subalkaline melts, peraluminous high-K granites, and a subset of sodic, adakite-like granites. A Paleocene (~63-57 Ma) magmatic flare-up follows, dominated by extremely fractionated subalkaline melts. Rare, more primitive melts of this suite are metaluminous, from gabbro to syenite. This stage may represent relaxed melt productivity or shallowing of the slab dip, yielding more laterally diffuse melting. An early Eocene magmatic hiatus precedes middle Eocene circum-Pacific tectonic reorganization, regionally resulting in initiation of proto-Aleutian/Meshik arc magmatism, and locally in the 44-37 Ma emplacement of subalkaline intermediate to felsic plutons associated with andesite to rhyolite volcanic deposits. An Oligocene (~31-25 Ma) magmatic pulse involved emplacement of a compositionally variable suite ranging from

  13. Cretaceous ongonites (topaz-bearing albite-rich microleucogranites) from Ongon Khairkhan, Central Mongolia: Products of extreme magmatic fractionation and pervasive metasomatic fluid: rock interaction

    NASA Astrophysics Data System (ADS)

    Dostal, Jaroslav; Kontak, Daniel J.; Gerel, Ochir; Gregory Shellnutt, J.; Fayek, Mostafa

    2015-11-01

    Ongonites were defined at their type locality at Ongon Khairkhan, central Mongolia, as pristine magmatic topaz-bearing albite-quartz-keratophyres with up to 4 wt. % F and containing phenocrysts of albite, K-feldspar, quartz and rare mica and topaz hosted in a groundmass composed of the same minerals. However, detailed petrographic and SEM-EDS studies indicate that these rocks underwent considerable subsolidus exchange with deuteric fluids, as evidenced by the presence of albitic plagioclase (Ab~ 100) and end-member orthoclase (Or~ 100), secondary Li-Fe-rich mica (zinnwaldite) enriched in rare metals (Sn, W, Ta, Nb), pitted feldspars containing fluid inclusions, and disseminated fluorite. The ~ 120 Ma old dyke rocks, emplaced at a high structural level in the crust, are strongly peraluminous leucogranites characterized by high Al and alkalis that are also enriched in Rb, Cs, Ga and Ta, depleted in Mg, Ca, Zr, Ba, Sr and Eu, and have anomalous K/Rb, Rb/Sr, Zr/Hf and Nb/Ta ratios compared to the average continental crust. However, the suite has Nd isotopic ratios (ɛNd(120) ~- 1) similar to those of contemporaneous A-type granites of the Mongolian-Transbaikalian igneous province of the Central Asian Orogenic Belt. The inferred primary δ18O (~+ 6 to + 7‰) and Pb isotopic values are consistent with a granitic parent magma and interaction with orthomagmatic fluids. The ongonites and constituent minerals record (1) an extensive and protracted crystal fractionation history, in part due to the presence of volatiles (particularly F) which depressed the solidus temperature of the felsic rocks and extended its duration of crystallization and (2) subsolidus exchange with fluids which includes late flux of heated meteoric water as indicated by modified whole rock δ18O values (+ 0.5 to +2.7‰). The interaction of the ongonites with internally derived orthomagmatic fluids is considered to result in enrichment and/or redistribution of several incompatible elements, but not to

  14. Effects of magma mingling in the granites of Mount Desert Island, Maine

    SciTech Connect

    Seaman, S.J.; Ramsey, P.C. )

    1992-07-01

    Textures and compositional relationships associated with dark-colored, fine-grained enclaves in the Cadillac Mountain and Somesville granites, Mount Desert Island, Maine, preserve abundant evidence for contamination of host granitic magmas by enclave liquids. Fine-grained enclaves, which apparently represent chilled magmatic droplets, have affected the composition and texture of the host granites by three possible mechanisms: (1) crystallization of feldspar-quartz-hornblende pegmatite pods from fluids of enclave origin in the granite surrounding enclaves, and the disaggregation of the pods and dispersion of crystals into the granite; (2) ionic exchange between enclaves and granitic magmas; (3) the generation around enclaves of rinds consisting of an inner alkali feldspar-quartz zone and an outer zone of hornblende-enriched granite. Thermal calculations suggest that the alkali feldspar-quartz zones of the rinds surrounding enclaves may result from resorption of alkali feldspar and quartz crystals in the granitic magma by heat of cooling and crystallization of enclave material. The interaction between the hot enclave and the alkali feldspar-quartz composition liquid may be analogous to that between a pluton and meteoric water in a hydrothermal system. The segregation of alkali feldspar-quartz and hornblende-rich zones may result from the minimum melt composition fluid migrating toward the enclave, leaving behind unmelted hornblende, as part of a convection circuit set up by the enclave. Alternatively, hornblende-rich zones concentric to and outside of the alkali feldspar-quartz rinds may record limit of movement of a front of hydrous fluid driven from the enclave boundary down a thermal gradient.

  15. Rheology of Granitic Magmas During Ascent and Emplacement

    NASA Astrophysics Data System (ADS)

    Petford, Nick

    Considerable progress has been made over the past decade in understanding the static rheological properties of granitic magmas in the continental crust. Changes in H2O content, CO2 content, and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid/fluid mixture. Although the strengths of granitic magmas over the crystallization interval are still poorly constrained, theoretical investigations suggest that during magma ascent, yield strengths of the order of 9 kPa are required to completely retard the upward flow in meter-wide conduits. In low Bagnold number magma suspensions with moderate crystal contents (solidosities 0.1 0.3), viscous fluctuations may lead to flow differentiation by shear-enhanced diffusion. AMS and microstructural studies support the idea that granite plutons are intruded as crystal-poor liquids ( 50%), with fabric and foliation development restricted to the final stages of emplacement. If so, then these fabrics contain no information on the ascent (vertical transport) history of the magma. Deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt, resulting in a range of local macroscopic flow structures, including layering, crystal alignment, and other mechanical instabilities such as shear zones. As the suspension viscosity varies with stress rate, it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear. New theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved.

  16. Getting granite dikes out of the source region

    NASA Technical Reports Server (NTRS)

    Rubin, Allan M.

    1995-01-01

    Whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow. Various formulations are developed for a viscous fluid at temperature T(sub m) intruding a growing crack in an elastic solid. The initial solid temperature equals T(sub m) at the source and decreases linearly with distance from the source. If T(sub m) is the unique freezing temperature of the fluid, dike growth is initially self-similar and an essentially exact solution is obtained; if T(sub m) is above the solidus temperature, the solution is approximate but is designed to overestimate the distance the dike may propagate. The ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness. Perhaps more intuitively, one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus, necessary for dikes to propagate far into subsolidus rock. It is concluded that for reasonable material properties and source conditions, most basalt dikes will have little difficulty leaving the source region, but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus. While these results can explain why granitic dikes are common near granitic plutons but rare elsewhere, the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes. Nonetheless, these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies.

  17. The density of dry and hydrous granitic magmas

    NASA Astrophysics Data System (ADS)

    Malfait, W. J.; Sanchez-Valle, C.; Seifert, R.; Petitgirard, S.; Perrillat, J.

    2011-12-01

    Large volumes of granitic magmas form through partial melting of the lower crust and are subsequently emplaced in the higher crustal levels [1]. In addition, granite-like liquids may form through partial melting of subducted sediments [2] or as an end-product of magmatic differentiation [3]. Moreover, water rich magmas of granitic composition are a major source of explosive volcanism. The physical properties of granitic melts, and particularly their density, are key controls on the migration rate and emplacement depth of granitic intrusions. However, because of the high viscosity of granitic liquids, density and compressibility measurements with the sink/float method and sound velocity measurements are challenging. As a result, the density and compressibility of dry and volatile-bearing granitic liquids is poorly constrained, particularly for the pressure-temperature conditions relevant for their formation and emplacement. In this study, we present in situ experimental data on the density of dry and hydrous haplogranitic melts (5 and 10 wt% water) at pressure and temperature conditions relevant for the crust and the subducting slab (1.0-2.7 GPa, 1350-1720 K). The experiments were performed with a panoramic Paris-Edinburgh press installed at the ID27 beamline of ESRF. The samples were contained in a cylindrical diamond capsule, capped with a platinum disk on either side, surrounded by hexagonal boron nitride (hBN) and placed inside a graphite heater and boron epoxy gasket. Pressure and temperature were determined from the X-ray diffraction patterns of hBN and platinum using the double-isochore method [4]. The density of the melts was determined from the X-ray absorption contrast between the sample and the diamond capsule (Mo edge, 20 keV). The molten state of the sample at the condition of the density measurements was verified by X-ray diffraction. The run products were analyzed by electron microprobe and infrared spectroscopy to verify the chemical composition and

  18. Vermont granite workers' mortality study.

    PubMed

    Costello, J; Graham, W G

    1988-01-01

    A cohort mortality study was carried out in Vermont granite workers who had been employed between the years 1950 and 1982. The cohort included men who had been exposed to high levels of granite dust prior to 1938-1940 (average cutters to 40 million parts/cubic foot), and those employed at dust levels after 1940, which on average were less than 10 million parts/cubic foot. Deaths were coded by a qualified nosologist and standardized mortality ratios were calculated. The results confirm previous studies that show that death rates from silicosis and tuberculosis, the major health threats in the years before 1940, were essentially eliminated after dust controls. However, we found excessive mortality rates from lung cancer in stone shed workers who had been employed prior to 1930, and hence had been exposed to high levels of granite dust. When information was available, 100% of those dying from lung cancer had been smokers.

  19. Alteration and breakdown of xenotime-(Y) and monazite-(Ce) in granitic rocks of the Western Carpathians, Slovakia

    NASA Astrophysics Data System (ADS)

    Broska, Igor; Williams, C. Terry; Janák, Marian; Nagy, Géza

    2005-05-01

    In the granitic rocks of the Western Carpathians, xenotime-(Y) occurs both as a late-stage magmatic mineral, and as a secondary post-magmatic phase. Magmatic xenotime occurs with monazite and displays minor compositional zonation involving Si, Th and U. The source of elements for the formation of secondary xenotime-(Y) in the granitic rocks results from leaching of P and (Y+REE), mainly from zircon and apatite. Both xenotime-(Y) and monazite-(Ce) are unstable during fluid-activated overprinting. Low temperature alteration of monazite in S-type granites leads to the formation of apatite enriched in the britholite component, but low to medium grades of metamorphism result in the formation of apatite and LREE enriched epidote (partly allanite) as a corona enclosing the monazite-(Ce) core. Xenotime-(Y) shows a similar alteration pattern, but with different REE distributions within the products. At greenschist/amphibolite facies, rims of secondary Y-rich apatite and Y-rich epidote form around xenotime-(Y). In low-Ca granites however, apatite is missing from this alteration assemblage as xenotime-(Y) breaks down directly to Y-enriched epidote. The relative mobilities of the heavy and light REE are different during breakdown of monazite and xenotime. The fluid responsible for the breakdown of monazite and xenotime contains elements released from alteration of anorthite (Ca) and biotite (Si, Al and F).

  20. New methodical developments for GRANIT

    SciTech Connect

    Baessler, Stefan; Nesvizhevsky, V.; Toperverg, B; Zhernenkov, K.; Gagarski, A; Lychagin, E; Muzychka, A; Strelkov, A; Mietke, A

    2011-01-01

    New methodical developments for the GRANIT spectrometer address further improvements of the critical parameters of this experimental installation, as well as its applications to new fields of research. Keeping in mind an extremely small fraction of ultra cold neutrons (UCN) that could be bound in gravitational quantum states, we look for methods to increase statistics due to: developing UCN sources with maximum phase-space density, counting simultaneously a large fraction of neutrons using position-sensitive detectors, and decreasing detector backgrounds. Also we explore an eventual application of the GRANIT spectrometer beyond the scope of its initial goals, for instance, for reflectometry with UCN.

  1. Status of LLNL granite projects

    SciTech Connect

    Ramspott, L.D.

    1980-12-31

    The status of LLNL Projects dealing with nuclear waste disposal in granitic rocks is reviewed. This review covers work done subsequent to the June 1979 Workshop on Thermomechanical Modeling for a Hardrock Waste Repository and is prepared for the July 1980 Workshop on Thermomechanical-Hydrochemical Modeling for a Hardrock Waste Repository. Topics reviewed include laboratory determination of thermal, mechanical, and transport properties of rocks at conditions simulating a deep geologic repository, and field testing at the Climax granitic stock at the USDOE Nevada Test Site.

  2. The magmatism and metamorphism at the Malayer area, Western Iran

    NASA Astrophysics Data System (ADS)

    Ahadnejad, V.; Valizadeh, M. V.; Esmaeily, D.

    2009-04-01

    The Malayer area is located in the NW-SE aligned Sanandaj-Sirjan metamorphic belt, western Iran and consists mainly of Mesozoic schists so-called Hamadan Phyllites, Jurassic to Tertiary intrusive rocks and related contact metamorphic aureoles, aplites and pegmatites. The Sanandj-Sirjan Zone is produced by oblique collisional event between Arabian plate and Central Iran microcontinent. Highest level of regional metamorphism in the area is greenschist facies and injection of felsic magmas is caused contact metamorphism. Magmatism is consist of a general northwest trend large felsic to intermediate intrusive bodies. The main trend of structural features i.e. faults, fractures and other structural features is NW-SE. The Malayer granitoid complex is ellipsoid in shape and has NW-SE foliation especially at the corners of the intrusions. Petrography of the magmatic rocks revealed recrystallization of quartz and feldspars, bending of biotite, and aligment of minerals paralle to the main trend of magmatic and metamorphic country rocks. These indicated that intrusion of felsic magma is coincide to the regional metamorphism and is syn-tectoinc. Non-extensive contact metamorphism aureoles and rareness of pegmatite and aplite in the area are interpreted as injection of felsic magmas into the high-strain metamorphic zone. The regional metamorphic rocks mainly consist of meta-sandstone, slate, phyllite, schist. These gray to dark metasedimentary rocks are consist of quartz, muscovite, turmaline, epidote, biotite and chlorite. Sheeted minerals form extended schistosity and study of porphyroblast-matrix relationships shows that injection of granitic magma into the country rocks is syn to post-tectonic. Syn-tectonic indicating porphyroblast growth synchronous with the development of the external fabric. The thermal contact area of the granite can be observed in the contact margin of granite and regional metamorphic rocks, where it produced hornfelses, andalusit-garnet schists and

  3. Pluton emplacement in a releasing bend in a transpressive regime: the arrozal granite in the Paraíba do Sul shear belt, Rio de Janeiro.

    PubMed

    Nummer, Alexis R; Machado, Rômulo; Dehler, Nolan M

    2007-06-01

    The Arrozal Granite, situated in the southwestern region of the State of Rio de Janeiro, has a granitic to granodioritic composition. It contains a strong mylonitic foliation along its border, passing gradually to a well-developed magmatic foliation towards its center. Structural analysis indicates that the Arrozal Granite was emplaced along the Além-Paraíba Shear Zone in a dextral transpressive tectonic regime. A regional shift of the trend along this shear zone from NE-SW to E-W, observed in the area, is interpreted to be casually related to the creation of space for the emplacement of the granite. Our data indicate that releasing bends may have played an important role for space generation during the emplacement of the Arrozal Granite and other plutons.

  4. The Capilla del Monte pluton, Sierras de Córdoba, Argentina: the easternmost Early Carboniferous magmatism in the pre-Andean SW Gondwana margin

    NASA Astrophysics Data System (ADS)

    Dahlquist, Juan A.; Pankhurst, Robert J.; Rapela, Carlos W.; Basei, Miguel A. S.; Alasino, Pablo H.; Saavedra, Julio; Baldo, Edgardo G.; Murra, Juan A.; da Costa Campos Neto, Mario

    2016-07-01

    New geochronological, geochemical, and isotopic data are reported for the Capilla del Monte two-mica granite pluton in the northeastern Sierras de Córdoba. An Early Carboniferous age is established by a U-Pb zircon concordia (336 ± 3 Ma) and a Rb-Sr whole-rock isochron (337 ± 2 Ma). Zircon saturation geothermometry indicates relatively high temperatures (735-800 °C). The granites have high average SiO2 (74.2 %), Na2O + K2O (7.8 %), and high field-strength elements, high K2O/Na2O (1.7) and FeO/MgO ratios (5.1), with low CaO content (0.71 %). REE patterns with marked negative Eu anomalies (Eu/Eu* 0.14-0.56) indicate crystal fractionation, dominantly of plagioclase and K-feldspar, from a peraluminous magma enriched in F. Isotope data (87Sr/86Srinitial = 0.7086, ɛ Nd336 = -5.5 to -4.4 with T DM = 1.5 Ga, zircon ɛ Hf336 +0.8 to -6.1; mean T DM = 1.5 Ga) suggest a Mesoproterozoic continental source, albeit with some younger or more juvenile material indicated by the Hf data. The pluton is the easternmost member of a Carboniferous A-type magmatic suite which shows an increase in juvenile input toward the west in this part of the pre-Andean margin. The petrological and geochemical data strongly suggest a similar intraplate geodynamic setting to that of the nearby but much larger, Late Devonian, Achala batholith, although Hf isotope signatures of zircon suggest a more uniformly crustal origin for the latter. Further studies are required to understand whether these bodies represent two independent magmatic episodes or more continuous activity.

  5. Age and tectonic setting of the early Paleozoic magmatism of the Mamyn Terrane, Central Asian Orogenic Belt, Russia

    NASA Astrophysics Data System (ADS)

    Sorokin, A. A.; Kudryashov, N. M.; Kotov, A. B.; Kovach, V. P.

    2017-08-01

    -Early Ordovician trachyrhyodacite and rhyodacite units in this area are high-K and calc-alkaline or are shoshonitic and are enriched in K, Rb, the rare earth elements (REE), Y, Nb, Ta, and Zr, and are depleted in Sr and have A-type granite affinities. However, these units do not contain alkali amphibole or pyroxene and have high FeOtot/MgO ratios (6.7-12.7) that indicate they formed from highly fractionated magmas. Therefore, these volcanic rocks represent extreme melt differentiates that also formed the coeval granites. The early Paleozoic magmatic events within the Mamyn Terrane have also been identified in the Argun, Bureya, and Jiamusi areas of the eastern CAOB, suggesting that all of these areas have a common geodynamic history.

  6. Early Mesozoic granites in the Nanling Belt, South China: Implications for intracontinental tectonics associated with stress regime transformation

    NASA Astrophysics Data System (ADS)

    Song, Meijia; Shu, Liangshu; Santosh, M.

    2016-04-01

    The link between two tectono-magmatic events during Early and Late Mesozoic periods in the Nanling Belt of South China remains debated. Here we present zircon U-Pb geochronology, Hf isotopes and whole-rock geochemistry of granitic intrusions from Zhuguangshan in the Nanling Belt. The zircon data exhibit two magmatic episodes with 206Pb/238U ages of ca. 230 Ma and 150 Ma, representing the Indosinian (Early-Middle Triassic period) and Early Yanshanian (Jurassic-Cretaceous period) events, respectively. The Indosinian granites are characterized by strongly peraluminous nature with high A/CNK values (> 1.1), whereas the Early Yanshanian granites are weakly peraluminous (average A/CNK value of 1.06). Although the Early Yanshanian granites bear higher HREE contents and lower LREE/HREE ratios, the two-phase granites show enrichment in LREE, Rb, Th, U and Pb, depletion in Eu and negative Ba, Sr, Nb and Ti anomalies. All samples show variably negative εHf(t) values (- 5 to - 16) with two-stage Hf model ages clustered around 1.8-2.1 Ga. Our data indicate that the two-phase granitic magmas were generated from the partial melting of early Paleoproterozoic basement rocks with no input of mantle material. Combined with other geological evidence, we infer that the Indosinian tectono-magmatic event was closely related to intracontinental orogeny triggered by collisions along the boundaries of South China Craton, in relation to processes associated with the E-W trending Tethys tectonic domain. We envisage that the Early Yanshanian event might be a response to the back-arc extension of NW-directed paleo-Pacific plate subduction. The Nanling Belt is a critical zone that records the transformation from Tethys to paleo-Pacific tectonic regimes.

  7. Post-magmatic solid solutions of CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-bearing epidote in miarolitic pegmatites of Permian Baveno granite (Verbania, central-southern alps, Italy)

    NASA Astrophysics Data System (ADS)

    Guastoni, Alessandro; Nestola, Fabrizio; Schiazza, Mariangela

    2017-06-01

    CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and rare earth element (REE)-bearing epidote occur as globular aggregates and platy prismatic crystals in miarolitic cavities in a niobium, yttrium, fluorine (NYF) granitic pegmatite at Baveno, Verbania, Southern Alps, Italy. These samples were investigated by means of an electron probe micro-analyser (EPMA) and single-crystal X-ray diffraction. Our EPMA results show that the globular aggregates have the highest REE content in the core portion and decreases to REE-bearing epidote towards the rim whereas the prismatic crystals are characterized by marked oscillatory zoning that have the highest REE contents at the rim of the crystal. The unit-cell parameters of "allanites" have an intermediate unit-cell between CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-free epidote, because reflect the strong chemical heterogeneity of the samples which form complete solid solutions. Hydrothermal fluids control the activity and precipitation of incompatible elements like high field strength elements (HFSE), Sc and REE by hydrous F-rich fluids below the critical temperature which allow to deposit accessory minerals in the cavities with decreasing temperature. The source of REE and Y are the sheet and REE-silicates like siderophyllite-annite, and gadolinite-(Y) which underwent partial to complete decomposition by the activity of aggressive F-rich hydrothermal fluids.

  8. Post-magmatic solid solutions of CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-bearing epidote in miarolitic pegmatites of Permian Baveno granite (Verbania, central-southern alps, Italy)

    NASA Astrophysics Data System (ADS)

    Guastoni, Alessandro; Nestola, Fabrizio; Schiazza, Mariangela

    2016-09-01

    CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and rare earth element (REE)-bearing epidote occur as globular aggregates and platy prismatic crystals in miarolitic cavities in a niobium, yttrium, fluorine (NYF) granitic pegmatite at Baveno, Verbania, Southern Alps, Italy. These samples were investigated by means of an electron probe micro-analyser (EPMA) and single-crystal X-ray diffraction. Our EPMA results show that the globular aggregates have the highest REE content in the core portion and decreases to REE-bearing epidote towards the rim whereas the prismatic crystals are characterized by marked oscillatory zoning that have the highest REE contents at the rim of the crystal. The unit-cell parameters of "allanites" have an intermediate unit-cell between CaCeAl2(Fe3+ 2/3□1/3)[Si2O7][SiO4]O(OH), allanite-(Ce) and REE-free epidote, because reflect the strong chemical heterogeneity of the samples which form complete solid solutions. Hydrothermal fluids control the activity and precipitation of incompatible elements like high field strength elements (HFSE), Sc and REE by hydrous F-rich fluids below the critical temperature which allow to deposit accessory minerals in the cavities with decreasing temperature. The source of REE and Y are the sheet and REE-silicates like siderophyllite-annite, and gadolinite-(Y) which underwent partial to complete decomposition by the activity of aggressive F-rich hydrothermal fluids.

  9. Geochemistry and petrogenesis of Proterozoic granitic rocks from northern margin of the Chotanagpur Gneissic Complex (CGC)

    NASA Astrophysics Data System (ADS)

    Yadav, Bhupendra S.; Wanjari, Nishchal; Ahmad, Talat; Chaturvedi, Rajesh

    2016-07-01

    This study presents the geochemical characteristics of granitic rocks located on the northern margin of Chotanagpur Gneissic Complex (CGC), exposed in parts of Gaya district, Bihar and discusses the possible petrogenetic process and source characteristics. These granites are associated with Barabar Anorthosite Complex and Neo-proterozoic Munger-Rajgir group of rocks. The granitic litho-units identified in the field are grey, pink and porphyritic granites. On the basis of geochemical and petrographic characteristics, the grey and pink granites were grouped together as GPG while the porphyritic granites were named as PG. Both GPG and PG are enriched in SiO2, K2O, Na2O, REE (except Eu), Rb, Ba, HFSE (Nb, Y, Zr), depleted in MgO, CaO, Sr and are characterised by high Fe* values, Ga/Al ratios and high Zr saturation temperatures (GPGavg˜ 861 ∘C and PGavg˜ 835 ∘C). The REE patterns for GPG are moderately fractionated with an average (La/Yb)N˜ 4.55 and Eu/Eu* ˜ 0.58, than PG which are strongly fractionated with an average (La/Yb)N˜ 31.86 and Eu/Eu* ˜ 0.75. These features indicate that the granites have an A-type character. On the basis of geochemical data, we conclude that the granites are probably derived from a predominant crustal source with variable mantle involvement in a post-collisional setting.

  10. Cambrian-Ordovician magmatism in the Thiel Mountains, Transantarctic Mountains, and implications for the Beardmore orogeny

    NASA Astrophysics Data System (ADS)

    Pankhurst, R. J.; Storey, B. C.; Millar, I. L.; MacDonald, D. I. M.; Vennum, W. R.

    1988-03-01

    New field and laboratory studies result in a redefinition of the three main lithostratigraphic units of the Thiel Mountains. These are (1) the Thiel Mountains porphyry, a massive hypersthene-bearing monzonite, faulted against (2) the Mount Walcott Formation, a sequence of shallow-water volcaniclastic sedimentary rocks and dacitic tuffs or flows, and (3) the Reed Ridge granites, coarse-grained biotite granite/granodiorite stocks that cut the porphyry. Genetic relations between the porphyry and both the sedimentary rocks and the granite are proposed. Evidence for a Phanerozoic age indicated by the presence of fossils in the sediments is reinforced by Rb-Sr whole-rock dating that has conclusively established a Late Cambrian or Early Ordovician age (502 ±5 Ma) for the entire sequence. The stratigraphic and tectonic consequences refute all evidence for magmatism in the Transantarctic Mountains associated with the Precambrian "Beardmore orogeny," the age and status of which are now in doubt.

  11. Hydrothermal alteration of Variscan granites, southern Schwarzwald, Federal Republic of Germany

    NASA Astrophysics Data System (ADS)

    Simon, K.

    1990-03-01

    Hercynian S-type granites from the southeastern Schwarzwald granite series represent cogenetic biotite-and two-mica granites. Oxygen- and hydrogen-isotope data show that hydrothermal alteration invoking isotopically light surface waters resulted in a drastic reduction in δ18O and δ D and pronounced disequilibrium between the minerals. Effective water-rock ratios are calculated to be high, about 0.8 vol units. A shift in the18O/16O and the chemical composition of the fluid due to water-rock interaction is continuously traced from pure H2O with meteoric isotopic character in the deep-seated biotite granites to slightly saline water with rock-equilibrated isotopic composition in the two-mica granites at a shallower level. Substantial retrograde hydrometamorphism in the temperature range 500° to 200° C resulted mineralogically in high-temperature chloritization of biotite, and low-temperature muscovitization as well as feldspar alteration, respectively. Another result of the re-equilibration of cations is strong disturbance of the Rb-Sr system which affects measured ages and initial87Sr/86Sr values. Hydrothermal differentiation and alteration probably overlap to a very large extent magmatic differentiation processes.

  12. A zircon vs titanite geochronometres by SHRIMP IIe as a tool in multistage magmatic intrusion problems

    NASA Astrophysics Data System (ADS)

    Wiszniewska, Janina; Krzemińska, Ewa

    2017-04-01

    Most of crystalline basement area of NE Poland is represented by late Svecofennian (1.84-1.80 Ga) orogenic granitoids and supracrustal succession. These early rock assemblages were intruded by plutons of the Mezoproterozoic AMCG suite, which occupies most of W-E trending belt of the so called Mazury Complex. This suite is dominated by A-type granitoids of rapakivi-like texture. The subsequent important components are gabbro-norite, anorthosite and locally mangerite and charnockite rock variations. Anorthosite occurs at three autonomic massifs Sejny, Suwałki(SAM) and Ketrzyn. The basic geochronological investigation was carried out previously using mainly the U-Pb-Th system of zircon and monazite geochronometers. The AMCG suite yielded ages mainly in the range between 1548 to 1500 Ma. The isotopic work also reveals sporadic ages recorded on titanite (1526±11 Ma), considered as the crystallization age of the titanites under subsolidus conditions (Dörr et al.,2002). The geochemical and isotopic whole rock investigation suggests that formation of the AMCG suite was a complex process with multiple magma batches sequentially differentiating, and probably undergoing mixing and crustal assimilation. In this study, we report sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon and titanite single grain age data from upper part of drill section (Krasnopol 6, depth 1003m) located within easternmost vicinity of the SAM. Both of mineral phases have been selected from the contact between A-type granitoid with Pb-Pb TIMS age of 1525±5 Ma (op cit) and mafic chilled margin interpreted as next magma input. Dating of 20 single zircons from the contact zone yielded concordia ages of 1510±10 Ma for most of grains defined as emplacement age with inheritance at 1850±10 Ma. It evidenced a younger dose of the melt on the top of plutonic body and some input of older crustal material, detected also by whole rock isotopic signatures. Single titanite grains from the same zone

  13. Granitoids in the Dalat zone, southern Vietnam: age constraints on magmatism and regional geological implications

    NASA Astrophysics Data System (ADS)

    Nguyen, Thuy Thi Bich; Satir, Muharrem; Siebel, Wolfgang; Chen, Fukun

    The Dalat zone in southern Vietnam comprises a Cretaceous Andean-type magmatic arc with voluminous granitoids and contemporary volcanic rocks. On the basis of petrographical and mineralogical studies, the granitoids were subdivided into three suites: Dinhquan, Deoca and Cana. Rocks of the Dinhquan suite are hornblende-biotite diorites, granodiorites and minor granites. The Cana suite encompasses mainly leucocratic biotite-bearing granites with scarce hornblende. The Deoca suite is made up of granodiorites, monzogranites and granites. Geochemically, the granitoids are of subalkaline affinity, belong to the high-K, calc-alkaline series, and most of them display typical features of I-type granites. This paper presents the new Rb-Sr mineral and U-Pb zircon and titanite age data for the granitoids, which establish the ages of the plutonic suites as: the Dinhquan at 112-100 Ma, Cana at 96-93 Ma and Deoca at 92-88 Ma. These ages are significantly different from earlier publications, and indicate that the earliest magmatism in the Dalat zone began at 112 Ma ago, that is 30-50 Ma later than previously thought. Our geochronological data are also support the continuation of an Andean-type arc running from SE China via southern Vietnam to SW Borneo.

  14. Natural polish in granitic rocks

    NASA Astrophysics Data System (ADS)

    Siman-Tov, S.; Brodsky, E. E.; Stock, G. M.; White, J. C.

    2016-12-01

    Fault mirrors are highly smooth and reflective rock surfaces that are found in many shear zones around the world. Recent studies suggest that fault mirrors are formed during high velocity slip on faults and therefore may serve as an indicator for seismic slip. In contrast, other studies suggest that fault mirrors may form under high normal stress at sub-seismic velocities and at room temperature. Fault mirrors are observed within the fault core of many rock type environments including limestone, dolomite, chert and rhyolite. However, to the best of our knowledge, they are missing in faults hosted in granite. Moreover, mirror-like surfaces form during high velocity rotary shear experiments in many types of rock but not in sheared granite blocks. The absence of fault mirrors in granite is surprising, particularly since there exists extensive glacial polish on granitic bedrock. Glacial polish describes the smooth and reflective rock surfaces formed at the base of glaciers that carved the underlying bedrock. In addition to their import for studies of glacial dynamics and geomorphology, glacially polished surfaces may hold some significance for fault mechanics. Glacial polish and fault mirrors share many similarities. At field exposures they both present highly smooth surfaces and striations that clearly point in the slip direction. Studies on carbonate fault mirrors showed that individual highly reflective surfaces are composed of a thin nanograin layer. Preliminary SEM observations on samples collected from granitic rocks at Yosemite National Park suggest that these polished surfaces are also coated by an ultrathin cohesive layer composed of nanograins. Although there are clear differences between glacial and fault-zone environments, the similarity between these textures, and the fact that both are formed during shear, suggest that a similar mechanism is responsible for their formation. The comparison raises questions about the importance of high fluid contents and

  15. Geochemistry and petrogenesis of the Mesoarchean granites from the Canaã dos Carajás area, Carajás Province, Brazil: Implications for the origin of Archean granites

    NASA Astrophysics Data System (ADS)

    Feio, G. R. L.; Dall'Agnol, R.

    2012-12-01

    Four Mesoarchean (2.93 to 2.83 Ga) granite units, which encompass the Canaã dos Carajás, Bom Jesus, Cruzadão and Serra Dourada granites, were recognized in the Canaã dos Carajás area of the Archean Carajás Province. The Mesoarchean units are composed dominantly of biotite leucomonzogranites. They are compared with the Neoarchean Planalto suite (2.73 Ga) which encompasses biotite-hornblende monzogranites to syenogranites. The Canaã dos Carajás, Bom Jesus and the variety of the Cruzadão granite with higher (La/Yb)N are geochemically more akin to the calc-alkaline granites, whereas the other varieties of the Cruzadão granite are transitional between calc-alkaline and alkaline granites. The Serra Dourada granite has an ambiguous geochemical character with some features similar to those of calc-alkaline granites and other peraluminous granites. The Planalto granites have ferroan character, are similar geochemically to reduced A-type granites and show a strong geochemical contrast with the Mesoarchean studied granites. The Mesoarchean granites described in the Canaã dos Carajás area are geochemically distinct to those of the Rio Maria domain of the Carajás Province. The Canaã dos Carajás and Bom Jesus granites are similar to the high-Ca granites, whereas the Cruzadão and Serra Dourada are more akin to the low-CaO granites of the Yilgarn craton. The geochemical characteristics of the Mesoarchean studied granites approach those of the biotite granite group of Dharwar but the latter are enriched in HFSE and HREE compared to the Canaã dos Carajás granites. The Neoarchean Planalto suite granite has no counterpart in the Mesoarchean Rio Maria domain of the Carajás Province, neither in the Yilgarn and Dharwar cratons. Geochemical modeling suggests that partial melting of a source similar in composition to an Archean basaltic andesite of the Carajás Province could give origin to the Bom Jesus and Cruzadão granites. In the case of the Bom Jesus granite the

  16. Petrogenesis of middle Ordovician peraluminous granites in the Baoshan block: Implications for the early Paleozoic tectonic evolution along East Gondwana

    NASA Astrophysics Data System (ADS)

    Li, Gong-Jian; Wang, Qing-Fei; Huang, Yu-Han; Gao, Lei; Yu, Li

    2016-02-01

    Peraluminous granitic magmatism in the Baoshan block is long-lasting roughly from 500 Ma to 450 Ma. The petrogenesis and geodynamics for this long-lived magmatism remain controversial. To address this controversy, this study reports the zircon U-Pb age and Hf-isotope, and bulk-rock major and trace element data of the granites from the Shuangmaidi and Mengmao areas in the Baoshan block. LA-ICPMS zircon U-Pb dating reveals that the granitic rocks from the two areas were emplaced between 470 and 459 Ma. These rocks are high silicic and strongly peraluminous, with SiO2 = 73.6-77.6 wt.%, A/CNK ratios of 1.0-1.6, and CIPW normative corundum contents of 0.7-5.3 wt.%. They are enriched in LREEs, LILEs (e.g., Rb, Th, U, and K) and Pb, and depleted in HFSEs (e.g., Nb, Ta, P, Zr, and Ti), Eu, Sr, and Ba. The εHf(t) values for co-magmatic zircons of the Shuangmaidi coarse- and fine-grained porphyritic granites show wide ranges from - 11.6 to + 5.2 and from - 8.1 to + 7.0, concentrating in - 7.1 to + 0.5 and - 8.1 to + 0.7, respectively; and those of the Mengmao granites concentrate between - 4.6 and - 0.5. The primary magmas of these granites can be mainly attributed to the partial melting of ancient metasedimentary rocks, while small amounts of mantle-derived components were introduced into the magma sources for the Shuangmaidi granites. The primary magma of the Shuangmaidi granites experienced biotite-dominant mineral fractionation, and that of the Mengmao granite mainly fractionated K-feldspar and plagioclase. Combining our data with the regional sedimentary unconformity, multi-type magmatism, and high-pressure metamorphism in the Baoshan and its periphery blocks, we propose that these ca. 470-460 Ma peraluminous granites were formed in the tectonic setting of the thickened lithospheric delamination following the final amalgamation of outboard Asian microcontinents onto the East Gondwana margin at ca. 490-475 Ma. Our study favors that the long-lasted (ca. 500-450 Ma

  17. Do S-type granites commonly sample infracrustal sources? New results from an integrated O, U-Pb and Hf isotope study of zircon

    NASA Astrophysics Data System (ADS)

    Appleby, Sarah K.; Gillespie, Martin R.; Graham, Colin M.; Hinton, Richard W.; Oliver, Grahame J. H.; Kelly, Nigel M.

    2010-07-01

    In contrast to I-type granites, which commonly comprise infracrustal and supracrustal sources, S-type granites typically incorporate predominantly supracrustal sources. The initial aim of this study was to identify the sources of three Scottish Caledonian (~460 Ma) S-type granites (Kemnay, Cove and Nigg Bay) by conducting oxygen, U-Pb and Hf isotope analyses in zircon in order to characterise one potential end-member magma involved in the genesis of the voluminous late Caledonian (~430-400 Ma) I-type granites. Field, whole-rock geochemical and isotopic data are consistent with the generation of the S-type granites by melting their Dalradian Supergroup country rocks. While Hf isotope compositions of magmatic zircon, U-Pb data of inherited zircons, and high mean zircon δ18O values of 9.0 ± 2.7‰ (2SD) and 9.8 ± 2.0‰ for the Kemnay and Cove granites support this model, the Nigg Bay Granite contains zircons with much lower δ18O values (6.8 ± 2.1‰), similar to those found in Scottish I-type granites. This suggests that the Nigg Bay Granite contains low-δ18O material representing either altered supracrustal material, or more likely, an infracrustal source component with mantle-like δ18O. Mixing trends in plots of δ18O vs. ɛHf for S-type granite zircons indicate involvement of at least two sources in all three granites. This pilot study of Scottish Caledonian S-type granites demonstrates that, while field and whole-rock geochemical data are consistent with local melting of only supracrustal sources, the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources.

  18. Petrogenesis of Jurassic tungsten-bearing granites in the Nanling Range, South China: Evidence from whole-rock geochemistry and zircon U-Pb and Hf-O isotopes

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Yang, Jin-Hui; Chen, Jing-Yuan; Wang, Hao; Xiang, Yuan-Xin

    2017-05-01

    The Nanling Range (NLR) is the largest tungsten metallogenic province in China and perhaps in the world. The tungsten mineralization is believed to be related to Jurassic granitic magmatism. However, the petrogenesis of these granites and their relation to the tungsten mineralization are still debated. Whole-rock geochemical and Sr-Nd-Hf isotopic data and zircon in situ U-Pb ages and Hf-O isotopes are reported for W-bearing granitic intrusions from the southern Jiangxi Province in the NLR, in order to constrain their magmatic sources and petrogenesis. The NLR granites include biotite granites, two-mica granites and garnet muscovite granites. SIMS and LA-ICPMS U-Pb dating of zircons and monazites give emplacement ages of 161-154 Ma for these rocks. The granites are metaluminous to strongly peraluminous with high SiO2 (> 72.3 wt.%) and high K2O (> 3.7 wt.%). Petrographic and geochemical features show that they are highly fractionated I-type granites. The biotite granites are enriched in light rare earth elements (LREEs) relative to heavy REEs, have weakly negative Eu anomalies and are depleted in Nb, Ba, P and Ti. In contrast, the two-mica and garnet-bearing muscovite granites have tetrad-type REE patterns with strongly negative Eu anomalies and are extremely depleted in Ba, Nb, Sr, P and Ti. Magmatic garnets are mainly almandine and spessartine, and have low-Mn cores and high-Mn rims. Their (Y + HREE) contents are high and generally decrease from core (1.2 wt.%) to rim (average = 4955 ppm). All of these granites are characterized by variable whole-rock initial 87Sr/86Sr (0.7053-0.8000), εNd(t) (- 12.6 to - 9.4) and εHf(t) (- 12.3 to - 8.5), as well as variable zircon εHf(t) and δ18O, with values of - 16.3 to - 7.4 and 7.6 to 10.0‰, respectively. They contain abundant zircon xenocrysts and xenoliths of micaceous schist. All of these features are consistent with a process of crystal fractionation of crustally-derived magmas coupled with strong assimilation of

  19. Late Triassic syn-exhumation magmatism in central Qiangtang, Tibet: Evidence from the Sangehu adakitic rocks

    NASA Astrophysics Data System (ADS)

    Liu, Han; Wang, Bao-di; Ma, Long; Gao, Rui; Chen, Li; Li, Xiao-bo; Wang, Li-quan

    2016-12-01

    The geodynamic setting of Late Triassic magmatic activity along the Longmu Co-Shuanghu suture zone (LSSZ) in central Qiangtang, Tibet is a matter of debate. This paper presents zircon LA-ICP-MS U-Pb ages, zircon Hf isotopic compositions, and whole-rock geochemical data for the Sangehu (SGH) granitic intrusion in central Qiangtang, and addresses the petrogenesis of Late Triassic magmatism, and the history of collision between the northern and southern Qiangtang terranes. The SGH pluton consists mainly of biotite adamellite with mafic microgranular enclaves (MMEs), and small amounts of K-feldspar granite. The biotite adamellite, MMEs, and K-feldspar granite give ages of 207.8 ± 3.0 Ma, 212.4 ± 31 Ma, and 211.6 ± 3.8 Ma, respectively. The MMEs show magmatic textures and acicular apatite, and are coeval with the host biotite adamellite, suggesting they were produced by magma mixing. All samples from the SGH pluton show high Sr and low Y contents, and positive Eu anomalies, similar to adakitic rocks. The high K2O contents and low Mg#, Cr, and Ni contents, and enriched Hf isotopic characteristics of the zircons indicate that these magmas were derived from the partial melting of thickened crust. However, the whole-rock geochemical data and zircon Hf isotopic compositions also reveal heterogeneity at the source. The combined magmatic and metamorphic records suggest that Triassic magmatic activity in central Qiangtang was closely related to the collision of the northern and southern Qiangtang terranes. The large-scale Late Triassic (225-200 Ma) magmatic event in central Qiangtang may have resulted from the breakoff of the Longmu Co-Shuanghu Tethys Ocean lithospheric slab in the early Late Triassic (236-230 Ma). The Late Triassic magmatic rocks, including adakitic rocks, are coeval with retrograde high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in central Qiangtang, and show characteristics of syn-exhumation magmatism. The early adakitic rocks (>220 Ma

  20. Petrogenesis and geochemistry of circa 2.5 Ga granitoids in the Zanhuang Massif: Implications for magmatic source and Neoarchean metamorphism of the North China Craton

    NASA Astrophysics Data System (ADS)

    Wang, Junpeng; Kusky, Timothy; Wang, Lu; Polat, Ali; Wang, Songjie; Deng, Hao; Fu, Jianmin; Fu, Dong

    2017-01-01

    The tectonic framework of the North China Craton (NCC) during late Archean to early Paleoproterozoic (circa 2.5 Ga) is still lacking comprehensive understanding due to subsequent strong deformation and metamorphic overprinting events. Circa 2.5 Ga magmatic and metamorphic activities are widely spread throughout the NCC, which can be used as an efficient target to better understand the tectonic evolution at this period. In this study, based on a detailed field, structural, geochemical, geochronological and Sm-Nd isotopic study, we focus our work on the Haozhuang granitoids in the Zanhuang Massif located at the eastern margin of the Central Orogenic Belt of the NCC. The granitoids mainly include undeformed pegmatite and granodiorite. One pegmatite and two granodiorite samples yield zircon 207Pb/206Pb ages of 2513 ± 29 Ma, 2511 ± 36 Ma and 2528 ± 18 Ma, respectively. The granodiorites show metaluminous and shoshonitic to high-K calc-alkaline series characteristics with A-type granite affinity. The circa 2.5 Ga granodiorites have highly negative εNd(t) values (- 29.22 - 33.12) and TDM model ages between 2671 Ma and 3151 Ma. This work shows clearly, from whole-rock major and trace elements and Sm-Nd isotopic studies, that the Haozhuang granodiorites were derived from partial melting of old and thickened TTG crust rather than mantle sources, and formed in a subduction-related tectonic setting. With geochemical comparison studies to other similar-aged granitic rocks in the Zanhuang Massif, we suggest that these granitic rocks possibly have a certain correlation during the magma evolution. Coupled with our previous geochemical and isotopic studies on circa 2.5 Ga mafic dike swarms, we propose that the similar-aged granitic rocks and mafic dike swarms were produced by an east-dipping subduction polarity reversal event following an arc-continent collision between the Fuping/Wutai island arc and Eastern Block of the NCC above a west-dipping slab. The east

  1. Venus magmatic and tectonic evolution

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Hansen, V. L.

    1993-01-01

    Two years beyond the initial mapping by the Magellan spacecraft, hypotheses for the magmatic and tectonic evolution of Venus have become refined and focused. We present our view of these processes, attempting to synthesize aspects of a model for the tectonic and magmatic behavior of the planet. The ideas presented should be taken collectively as an hypothesis subject to further testing. The quintessence of our model is that shear and buoyancy forces in the upper boundary layer of mantle convection give rise to a spatially and temporally complex pattern of strain in a one-plate Venusian lithosphere and modulate the timing and occurrence of magmatism on a global basis.

  2. Emanation of radon from household granite.

    PubMed

    Kitto, Michael E; Haines, Douglas K; Arauzo, Hernando Diaz

    2009-04-01

    Emanation of radon (222Rn) from granite used for countertops and mantels was measured with continuous and integrating radon monitors. Each of the 24 granite samples emitted a measurable amount of radon. Of the two analytical methods that utilized electret-based detectors, one measured the flux of radon from the granite surfaces, and the other one measured radon levels in a glass jar containing granite cores. Additional methods that were applied utilized alpha-scintillation cells and a continuous radon monitor. Measured radon flux from the granites ranged from 2 to 310 mBq m-2 s-1, with most granites emitting <20 mBq m-2 s-1. Emanation of radon from granites encapsulated in airtight containers produced equilibrium concentrations ranging from <0.01 to 11 Bq kg-1 when alpha-scintillation cells were used, and from <0.01 to 4.0 Bq kg-1 when the continuous radon monitor was used.

  3. U-Pb Zircon Geochronology of Hermit's Peak Batholith Granite, Northern New Mexico: Implications for Tectonic Quiescence at 1.4 GA

    NASA Astrophysics Data System (ADS)

    Lindline, J.; Cedillo, D. N.; Romero, A.

    2012-12-01

    The Hermit's Peak batholith, a Proterozoic metamorphic-plutonic massif in the southern Sangre de Cristo Mountains, is located in the transition zone between the Yavapai and Mazatzal Precambrian provinces. We conducted zircon geochronology at the University of Arizona's LaserChron Center on granitic phases within the Hermit's Peak batholith to establish the timing of granite magmatism relative to Proterozoic orogenesis. Two analyses (core and rim) of more than 20 zircon crystals were incorporated into a final age calculation for each sample. Within the batholith, early granitoid intrusions form centimeter- to meter-wide coarse-grained tabular sheets and layers within Paleoproterozoic host rock gneisses. The intrusions were deformed during isoclinal folding along with their host rocks, suggesting that the early granites are pre- or syntectonic with contractional deformation associated with Yavapai-Mazatzal collision. These granites show a fine- to medium-grained anhedral granular texture with quartz microstructures indicative of dynamic strain and solid state deformation, including undulose extinction, subgrain development, and serrated grain boundaries. All zircon crystals are euhedral with aspect ratios of 2:1 to 3:1 and lengths ranging from 100-300 μm. Cathodoluminescence imaging shows that most crystals have oscillatory zonation indicating they are igneous in origin. Elemental U/Th ratios are all low (<10) indicating an igneous origin as well. Most crystals show a bright rim (high U) suggesting a late-stage fluid interaction. However, there was no discordance between core and rim age analyses. The granitic gneiss yielded a weighted mean 207Pb/206Pb age of 1.705 ± 0.017 Ga placing its emplacement prior to or early in the Mazatzal orogeny. A small (< 1.0 km2) nonfoliated coarse-grained anhedral granular granite intrudes the granitic gneiss. All zircon crystals are euhedral with aspect ratios of 2:1 to 3:1 and lengths ranging from 100-300 μm. Cathodoluminescence

  4. Yingmailai Granitic Intrusion in the Southern Tianshan:Magnetite-series or Ilmenite-series?

    NASA Astrophysics Data System (ADS)

    Ma, L.; Zhang, Z.

    2015-12-01

    The Yingmailai granitic intrusion is located in the middle part of the southern Tianshan. It consists predominantly of biotite K-feldspar granite with minor two-mica K-feldspar granite. They have similar whole-rock geochemical characteristics, but distinct mineralogy. Opaque minerals in biotite K-feldspar granite are ilmenite, whereas they are magnetite in two-mica K-feldspar granite. Primary muscovite has been recognized in two-mica K-feldspar granite, which is characterized by high Mg/Fe in biotite, An contents of plagioclase and Ab contents of perthite. According to Ishihara's classification(1977), biotite K-feldspar granite can undoubtedly be classified to ilmenite-series. For instance, opaque oxide minerals are less than 1 vol%, in which ilmenite is unique recognized; Fe-rich biotite (high FeO+Fe2O3) and low MgO, high FeO+Fe2O3/ FeO+Fe2O3+MgO ratio (0.957~0.980), low Mg numbers (<0.6), mostly Fe2+>1.1, and low Fe3+/(Fe3++Fe2+). Although some characteristics, e.g., presence of magnetite and Mg-rich biotite, suggest magnetite-series, it should be noted that the magnetite in two-mica K-feldspar granite is formed by post magmatism. In combination with low Fe3+/(Fe3++Fe2+)ratio and presence of indicating mineral—muscovite, it can be inferred that it also belongs to ilmenite-series. The factors which control the appearance of secondary magnetite are sudden change of fO2, pressure, temperature during magma emplacement rather than their source. In addition, Yingmailai granitic intrusion's characteristics, such as mineralogy, CaO(wt%)<3.7, w(Na2O)/w(K2O)<1, high SiO2 and (87Sr/86Sr)t, low temperature during the process of forming, indicate S type granitoids, suggesting that ilmenite-series defined by Ishihara (1977) correspond to S-type granite in the south Tienshan. This research also suggests that the south Tianshan had not experienced within plate during early Permian.

  5. Origin of allanite in gneiss and granite in the Dabie orogenic belt, Central East China

    NASA Astrophysics Data System (ADS)

    Guo, Haihao; Xiao, Yilin; Xu, Lijuan; Sun, He; Huang, Jian; Hou, Zhenhui

    2017-03-01

    Allanite is a common accessory mineral phase, representing an important carrier of rare earth elements, Th, U, Sr and other trace elements in most continental rocks. As Th and U can be incorporated into the allanite lattice, the mineral is a good geochronological tool for constraining geological events. Moreover, the trace element features δEu, Th/U ratio and common lead content of allanite are indicators of the forming conditions. Allanite and coexisting epidote-group minerals are abundant in ultrahigh-pressure (UHP) metamorphic rocks from the Dabie-Sulu orogen in central East China. However, if these minerals formed in the Neoproterozoic as magmatic phases, or in the Triassic as metamorphic phases is a matter of long-standing controversy. We report major and trace element analyses of whole rocks, allanite and coexisting epidote-group minerals, together with U-Th-Pb isotopic compositions of allanite in UHP gneiss from the Dabie-Sulu orogen, and allanite in the adjacent Jingshan granite. The granite is emplaced along the southeastern margin of the North China Craton and considered a product of partial melting of the subducted Dabie-Sulu gneiss. Trace elements (low Th/U and La/Sm, high δEu and high Sr) and high common lead concentrations indicate a metamorphic origin of allanite-epidote in the UHP gneiss. On the other hand, coarse-grained allanite from the Jingshan granite shows a corrosion core and a magmatic rim with common 208Pb up to 70% in the core and less than 30% in the rim. The allanite cores are of peritectic and the rims of magmatic origin with ages of ∼160 Ma, consistent with the granite crystallization age. In combination with previous studies, we conclude that the allanite of the Jingshan granite has form from the subducted and remolten Dabie-Sulu gneiss. Allanite records Triassic UHP metamorphic ages as well as Jurassic peritectic-magmatic ages as a part of the evolution of the Dabie-Sulu orogen.

  6. Chronology (SHRIMP II) of magmatism in the Kalguty rare-metal-tungsten-molybdenum ore-magmatic system, Gorny Altai, Russia

    NASA Astrophysics Data System (ADS)

    Gusev, N. I.

    2011-06-01

    The Kalguty ore-magmatic system (OMS) contains economic greisen and vein rare-metal-tungsten-molybdenum mineralization. The data on U-Pb zircon (SHRIMP II) age of nine samples of igneous rocks from the Kalguty OMS are accompanied by chemical, ICP-MS, and ICP-AES analyses of the main rock varieties. Porphyritic biotite granite of the main phase of the Kalguty pluton is characterized by the concordant age of 207.5 ± 1.7 Ma (MSWD = 0.034). The concordant age of the leucogranitic dikes pertaining to the East Kalguty Complex is 204 ± 2 Ma (MSWD = 0.65) for elvan and 200.8 ± 1.1 Ma (MSWD = 0.72) for ultrapotassic rhyolite porphyry. The two-mica and muscovite leucogranite of the Eastern stock is significantly younger: 195 ± 2.7 Ma (MSWD = 0.076) and 193.1 ± 2.1 Ma (MSWD = 0.0009). Thus, the Chingadatui Complex (the main phase of the Kalguty pluton) and dikes of the East Kalguty Complex are Late Triassic in age. The two-mica leucogranites of the Eastern, Zhumaly, and other stocks are most likely correlated to the Early Jurassic Alacha Complex of rare-metal granites. The superposition of greisen mineralization on elvan and ongonite dikes may be related to the emplacement of younger, Early Jurassic ore-forming two-mica and muscovite granites. Judging from zircon xenocrysts in granites, the Mesoproterozoic igneous rocks dated at 1.5 Ga and products of erosion of the rocks dated at 1.7 and 2.5 Ga occur in the basement of the Kalguty volcanic-tectonic structure. This is sound evidence for the occurrence of ancient continental crustal blocks in the southwestern part of the Altai-Sayan region.

  7. Thermomechanical properties of Stripa granite

    NASA Astrophysics Data System (ADS)

    Myer, L.

    1982-09-01

    The Stripa material properties testing program was initiated to study, by laboratory testing, the thermomechanical behavior of the Stripa rock mass and to provide material properties for input into numerical programs for simulation of the in situ heater experiments at Stripa. Measurement of elastic moduli and coefficients of thermal expansion of dry, intact samples of Stripa granite was completed in fiscal year 1980. A summary of the most significant findings resulting from tests on six samples are presented.

  8. Magmatism evolution on the last Neoproterozoic development stage of the western Siberian active continental margin

    NASA Astrophysics Data System (ADS)

    Vernikovskaya, Antonina E.; Vernikovsky, Valery A.; Matushkin, Nikolay Yu.; Kadilnikov, Pavel I.; Romanova, Irina V.

    2017-04-01

    Rocks from active continental margin complexes are characterized by a wide variety of chemical compositions from depleted in alkali to alkali differentiates. When addressing issues of geodynamic settings in which such rocks form, it is important to understand the evolution of the host tectonic structure, as well as the chemical affiliation of the various rocks composing it. The Yenisey Ridge orogen located in the south-western framing of Siberia is one of the more studied regions with a long history of Neoproterozoic magmatic events. This orogen was formed during the collision of the Central Angara terrane with Siberia, which took place 761-718 Ma. Subsequent subduction-related events in the orogen have been recorded in the coeval magmatism (711-629 Ma) of two complexes: one is the active continental margin complex (Nb enriched igneous rocks - gabbroids, trachybasalts, A-type granites and carbonatites, including contact metasomatites zones with Nb mineralization), and the other one is an island arc complex (differentiated series volcanics, gabbroids and plagiogranites). The rocks of these complexes are respectively located in two suture zones: the Tatarka-Ishimba zone that formed due to the collision mentioned above, and the Yenisei suture marking the subduction zone [Vernikovsky et al., 2003; 2008]. The final Neoproterozoic stage in the evolution of the active margin of Siberia is manifested as adakite-gabbro-anorthosite magmatism in the 576-546 Ma interval. Our results indicate a genetic relationship between the adakites and their host NEB-type metabasites of the Zimovey massif. These Neoproterozoic adakites could have formed in a setting of transform-strike-slip drift of lithospheric plates after the subduction stopped, both from a crustal and mantle-crustal source, similarly to the Cenozoic magmatic complexes of the transform margin in the eastern framing of Eurasia [Khanchuk et al., 2016]. Vernikovsky V.A., Vernikovskaya A.E., Kotov A.B., Sal'nikova E

  9. Early Permian East-Ujimqin mafic-ultramafic and granitic rocks from the Xing'an-Mongolian Orogenic Belt, North China: Origin, chronology, and tectonic implications

    NASA Astrophysics Data System (ADS)

    Cheng, Yinhang; Teng, Xuejian; Li, Yanfeng; Li, Min; Zhang, Tianfu

    2014-12-01

    The East-Ujimqin complex, located north of the Erenhot-Hegenshan fault, North China, is composed of mafic-ultramafic and granitic rocks including peridotite, gabbro, alkali granite, and syenite. We investigated the tectonic setting, age, and anorogenic characteristics of the Xing'an-Mongolian Orogenic Belt (XMOB) through field investigation and microscopic and geochemical analyses of samples from the East-Ujimqin complex and LA-MC-ICP-MS zircon U-Pb dating of gabbro and alkali granite. Petrographic and geochemical studies of the complex indicate that this multiphase plutonic suite developed through a combination of fractional crystallization, assimilation processes, and magma mixing. The mafic-ultramafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from a mantle source. The mafic-ultramafic magmas triggered partial melting of the crust and generated the granitic rocks. The granitic rocks are alkali and metaluminous and have high Fe/(Fe + Mg) characteristics, all of which are common features of within-plate plutons. Zircon U-Pb geochronological dating of two samples of gabbro and alkali granite yielded ages of 280.8 ± 1.5 and 276.4 ± 0.7 Ma, placing them within the Early Permian. The zircon Hf isotopic data give inhomogeneous εHf(t) values of 8.2-14.7 for gabbroic zircons and extraordinary high εHf(t) values (8.9-12.5) for the alkali granite in magmatic zircons. Thus, we consider the East-Ujimqin mafic-ultramafic and granitic rocks to have been formed in an extensional tectonic setting caused by asthenospheric upwelling and lithospheric thinning. The sources of mafic-ultramafic and granitic rocks could be depleted garnet lherzolite mantle and juvenile continental lower crust, respectively. All the above indicate that an anorogenic magma event may have occurred in part of the XMOB during 280-276 Ma.

  10. Origin, distribution and glaciological implications of Jurassic high heat production granites in the Weddell Sea rift, Antarctica

    NASA Astrophysics Data System (ADS)

    Leat, Phil T.; Jordan, Tom A. R. M.; Ferraccioli, Fausto; Flowerdew, Michael; R, Riley, Teal; Vaughan, Alan P. M.; Whitehouse, Martin

    2013-04-01

    The distribution of heat flow in Antarctic continental crust is critical to understanding ice sheet nucleation, growth and basal rheology and hydrology. We identify a group of High Heat Production granites intruded into Palaeozoic sedimentary sequences which may contribute to locally high heat flow beneath the central part of the West Antarctic Ice Sheet. Four of the granite plutons are exposed above ice sheet level at Pagano Nunatak, Pirrit Hills, Nash Hills and Whitmore Mountains. A new U-Pb zircon age from Pirrit Hills of 177.9 ± 2.3 Ma confirms earlier Rb-Sr dating that suggested an Early-Middle Jurassic age for the granites, coincident with the Karoo-Ferrar large igneous province and the first stage of Gondwana break-up. Our recently-acquired aerogeophysical data indicate that the plutons are distributed unevenly over 1000 km2 and were intruded into the actively extending, locally transcurrent, Jurassic Weddell Sea Rift [1]. In the NW part of the rift, the Pirrit Hills, Nash Hills and Whitmore Mountains granites form small isolated intrusions within weakly deformed upper crust. In the SE part of the rift, where granite intrusion was strongly structurally controlled within transtensional structures, the Pagano Nunatak granite is the only outcrop of a probably multiphase, ca 180 km long granite intrusion. The granites are weakly peraluminous, S-type and have Th and U abundances up to 61 and 19 ppm respectively. Heat production of analysed granite samples is ca. 2.9-9.1 µWm-3, toward the upper limit of values for High Heat Production granites globally. The granites are thought to have been generated during mafic underplating of the Weddell Rift during eruption of the contemporaneous Karoo-Ferrar magmatism [2]. The high Th and U abundances may be related to fractionation of the high Th-U Ferrar basaltic magmas combined with assimilation of pelitic sedimentary rocks. The granites correspond to an area of West Antarctica that may have heat flow significantly above

  11. Contrasting evolution of low-P rare metal granites from two different terranes in the Hoggar area, Algeria

    NASA Astrophysics Data System (ADS)

    Kesraoui, Mokrane; Nedjari, Samia

    2002-05-01

    Two mineralogically different rare metal granites located in two distinct terranes from the Tuareg area are compared: the Tin-Amzi granite in the north of the Laouni Terrane and the Ebelekan granite in the Assodé-Issalane Terrane. The Tin-Amzi granite is enclosed within Eburnean granulitic gneisses, and consists of albite, quartz, protolithionite, K-feldspar and topaz granite (PG). The accessory minerals include columbite tantalite, U- and Hf-rich zircon, Th-uraninite, wolframoixiolite and wolframite. This facies is characterised by a mineralogical evolution from the bottom to the top underlined by a strong resorption of K-feldspar and albite and the crystalliK-feldspar of more abundant topaz and protolithionite II which is further altered in muscovite and Mn-siderite. It is underlain by an albite, K-feldspar, F-rich topaz, quartz and muscovite granite (MG), with W-Nb-Ta oxides, wolframite, Nb-rutile, zircon and scarce uranothorite as accessories. The Ebelekan granite intrudes into a coarse-grained biotite granite enclosed within upper amphibolite-facies metasediments. It comprises a zinnwaldite, albite, topaz porphyritic granite (ZG) with "snow ball" quartz and K-feldspar. The accessories are zircon, monazite, uranothorite, Ta bearing cassiterite, columbite tantalite and wodginite. It is capped by a banded aplite-pegmatite (AP). The geochemistry of Tin-Amzi and Ebelekan granites is nearly comparable. Both are peraluminous (A/CNK=1.10-1.29; ASI=1.17-1.31), sodolithic and fluorine rich with high SiO 2, Al 2O 3, Na 2O+K 2O, Rb, Ga, Li, Ta, Nb, Sn and low FeO, MgO, TiO 2, Ba, Sr, Y, Zr and REE contents. These rare metal Ta bearing granites belong to the P-poor subclass, relating to their P 2O 5 content ( 0.03-0.15 wt.%). Nevertheless, they are distinguished by their concentration of W, Sn and Ta. The Tin-Amzi granite is W-Ta bearing with high W/Sn ratio whereas the Ebelekan granite is Ta-Sn bearing with insignificant W content. At Tin-Amzi the W-Nb-Ta minerals define

  12. Late-orogenic, post-orogenic, and anorogenic granites: Distinction by major-element and trace-element chemistry and possible origins

    SciTech Connect

    Rogers, J.J.W.; Greenberg, J.K. )

    1990-05-01

    Granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different among groups. Orogenically related granites include late-orogenic varieties (LO) associated with calc-alkaline batholiths, and post-orogenic varieties (PO), which occur in broad zones of isolated diapiric plutons in recently deformed orogenic belts. Inclined REE patterns, moderate Sr contents, and K{sub 2}O-SiO{sub 2} relationships show that late-orogenic granites formed by fractionation of plagioclase, clinopyroxene, and amphibole from calcalkaline magmas. Flatter REE patterns and K{sub 2}O contents near 5%, plus the absence of associated magmatic rocks, indicate that the post-orogenic granites developed by partial melting of subduction-produced mafic/intermediate magmatic rocks. Both the late- and post-orogenic granites can be part of material newly added to continental crust as a result of orogeny. Anorogenic granites in anorthosite/rapakivi complexes (AR) or alkaline ring complexes (RC) have LIL contents too high to have been equilibrated with a mafic mineral assemblage. These anorogenic rocks probably formed by partial melting of preexisting sialic crust and do not represent new crustal increment.

  13. Triassic granitoids in the eastern Songpan Ganzi Fold Belt, SW China: Magmatic response to geodynamics of the deep lithosphere

    NASA Astrophysics Data System (ADS)

    Yuan, Chao; Zhou, Mei-Fu; Sun, Min; Zhao, Yongjiu; Wilde, Simon; Long, Xiaoping; Yan, Danping

    2010-02-01

    The Songpan Ganzi Fold Belt (SGFB), SW China, was developed from a passive continental margin into an orogenic belt with the consumption of the Paleo-Tethys. During the evolution of the SGFB, numerous Late Triassic granitic plutons formed and exhibited a progressive development from adakite/I-type granite, high Ba-Sr granite, A-type granite and monzonite. Representative Late Triassic plutons were studied to unravel the bewildering evolution of the eastern SGFB. The Menggu Pluton (224 ± 3 Ma) consists of granites with high alkali (K 2O+Na 2O = 7.85-10.4 wt.%) and adakitic characteristics (Sr/Y = 19-38). The ɛNd T values (- 2.77 to - 5.03), initial 87Sr/ 86Sr ratios (0.7050-0.7063) and low Nb/Ta ratios (8-10) are indicative of an origin by partial melting of amphibolitic lower crust. Rocks from the Niuxingou Pluton (215 ± 3 Ma) are richer in K than Na (K 2O/Na 2O = 1.1-1.5) and contain high Sr (1006-1662 ppm) and Ba (1277-2009 ppm), typical of shoshonite and high Ba-Sr granite. They have less enriched ɛNd T values (+ 0.08 to - 2.04) and less radiogenic 87Sr/ 86Sr i ratios (0.7047-0.7048), and formed from a mixed melt derived from upwelling asthenosphere and the overlying metasomatised lithospheric mantle. The Taiyanghe Pluton (205 ± 3 Ma) consists of monzonites, with high Al 2O 3 (> 20 wt.%), but low MgO (0.94-1.39 wt.%). The rocks are richer in Na than K (K 2O/Na 2O < 0.7), contain high large ion lithophile element (LILE) (681-834 ppm Sr and 2142-9453 ppm Ba) and display strongly fractionated REE patterns ((La/Yb) N = 35-63). These features, together with their enriched Nd-Sr isotopic compositions (ɛNd T = - 4.78 to - 6.50; 87Sr/ 86Sr i = 0.7074-0.7090), suggest that the monzonite probably formed from low degrees of partial melting of metasomatised lithospheric mantle. Although a continuous compressional regime during the Mid- and Late Triassic has been invoked for the SGFB, the generation of crustally derived adakitic and shoshonitic plutons reflect

  14. Magmatic Evolution of the Skye Igneous Center, Western Scotland

    NASA Astrophysics Data System (ADS)

    Fowler, S. J.; Bohrson, W. A.; Spera, F. J.

    2003-12-01

    Geochemically complex igneous suites are the result of interplay between deep and crustal-level processes. Quantitatively modeling the contribution that crustal-level processes such as magma recharge, crustal assimilation, and fractional crystallization have is critical for developing realistic models of how magma transport/storage systems evolve. The Energy-Constrained Recharge, Assimilation, and Fractional Crystallization simulator (EC-RAFC, Spera & Bohrson, 2001, 2002; Bohrson & Spera, 2001, 2003) provides a means to model thermal, compositional, and magma volume data for complex magmatic systems. The Skye igneous center, western Scotland, spanning the period 60.53 +/- 0.08 Ma - 53.5 +/- 0.8 Ma and characterized by a well-documented suite of lavas and intrusive rocks of picritic to granitic composition, is the first natural data set to which the EC-RAFC model has been applied in detail. Based on analysis of published field, stratigraphic, petrographic, and chemical data, we propose that the Skye Tertiary magmatic sequence be divided into four petrogenetically related lineages. EC-RAFC results indicate that each lineage is characterized by a unique parental magma that has undergone distinct episodes of RAFC. Model results, constrained by published data on the nature of the crust beneath Skye, indicate that the character of the assimilant changes upsection, suggesting that the associated magma reservoirs migrated to shallower levels as the magmatic system matured. The magmatic products of each group also record the fingerprint of multiple episodes of magma recharge, where the character of the recharge magma also evolves with time. The image of the magma transport system that emerges is one in which magma is initially intruded at lower crustal levels and undergoes a distinct RAFC episode. Residual magma from this event then migrates to shallower levels, where mid-crustal wallrock is assimilated; recharge magma is characterized by increasingly crustal chemical and

  15. Understanding Granites: Integrating New and Classical Techniques

    NASA Astrophysics Data System (ADS)

    Candela, Philip A.

    Many aspects of granite geology are covered in Understanding Granites: Integrating New and Classical Techniques, a 288-page volume edited by Antonio Castro, Carlos Ferñandez, and Jean-Louis Vigneresse. However, the topics chosen for this collection lean toward the physical, rather than the chemical end of the spectrum. In the introduction to this 16-chapter collection, the authors set the stage by reviewing the groundwork laid by Hutton, Reed, and Bowen; they then discuss the landmark work of Chappell and White, first published in the 1970s, which ushered in the new era of granite research—one that has continued unabated to the present day. Finally, the editors outline some of the perennial questions of granite science, such as the “room problem,” granite ascent and emplacement, and the thermal and petrochemical requirements for granite genesis.

  16. Late Cenozoic crustal extension and magmatism, southern Death Valley region, California

    USGS Publications Warehouse

    Calzia, J.P.; Rämö, O.T.

    2000-01-01

    The late Cenozoic geologic history of the southern Death Valley region is characterized by coeval crustal extension and magamatism. Crustal extension is accommodated by numerous listric and planar normal faults as well as right- and left-lateral strike slip faults. The normal faults sip 30°-50° near the surface and flatten and merge leozoic miogeoclinal rocks; the strike-slip faults act as tear faults between crustal blocks that have extended at different times and at different rates. Crustal extension began 13.4-13.1 Ma and migrated northwestward with time; undeformed basalt flows and lacustrine deposits suggest that extension stopped in this region (but continued north of the Death Valley graben) between 5 and 7 Ma. Estimates of crustal extension in this region vary from 30-50 percent to more than 100 percent. Magmatic rocks syntectonic with crustal extension in the southern Death Valley region include 12.4-6.4 Ma granitic rocks as well as bimodal 14.0-4.0 Ma volcanic rocks. Geochemical and isotopic evidence suggest that the granitic rocks get younger and less alkalic from south to north; the volcanic rocks become more mafic with less evidence of crustal interaction as they get younger. The close spatial and temporal relation between crustal extension and magmatism suggest a genetic and probably a dynamic relation between these geologic processes. We propose a rectonic-magmatic model that requires heat to be transported into the crust by mantle-derived mafic magmas. These magmas pond at lithologic or rheologic boundaries, begin the crystallize, and partially melt the surrounding crustal rocks. With time, the thermally weakened crust is extended (given a regional extensional stress field) concurrent with granitic magmatism and bimodal volcanism.

  17. The discovery of late Triassic mylonitic granite and geologic significance in the middle Gangdese batholiths, southern Tibet

    NASA Astrophysics Data System (ADS)

    Ma, Shiwei; Meng, Yuanku; Xu, Zhiqin; Liu, Xiaojia

    2017-02-01

    The Gangdese magmatic belt, located in the southern margin of the Lhasa terrain and carrying significant copper poly-metallic mineralization, preserves important information related to the tectonics associated with the Neo-Tethys Ocean subduction, Indian-Asian collision and the crustal growth of southern Tibet. Here, we investigated the Namling batholiths in the central domain of the Gangdese magmatic belt and report for the first time the occurrence of late Triassic mylonitic granite, and present its petrologic, zircon U-Pb-Hf isotopes and the whole-rock chemistry dataset. Zircon LA-ICP-MS U-Pb dating from three mylonitic granitic samples yields crystallization ages of 209.4 ± 1.1 Ma, 206.7 ± 1.1 Ma and 212 ± 1.1Ma, indicating a late Triassic magmatic event in the Gangdese magmatic belt. Geochemically, the mylonitic granite exhibits magnesian genesis and calcic and calc-alkalic features. The depletions of Nb, Ta and Ti and enrichments of LREEs together suggest that the magmas from which these rocks crystallized were generated in an active continental margin. Besides, all the analyzed samples also demonstrate highly positive εHf(t) values of 8.95-12.91 (mean value 10.84), corresponding to single stage model ages (tDM1) in the range of 326 Ma-486 Ma (mean 414 Ma), attesting to crustal growth in southern Lhasa terrain. The mylonitic pluton are likely sourced from partial melting of the lower crustal components (amphibolite or basaltic stuff) that was heated and metasomatized by underplating basaltic magmas, and subsequently might undergo fractional crystallization and upper sediments contamination during parental magmas ascent. In light of the distribution of the early Mesozoic magmatic events and robust sedimentary evidence together suggest that the northward subduction of the Neo-Tethys oceanic crust beneath the Lhasa terrain should commence prior to late Triassic (∼210 Ma).

  18. Correlation between magnetic fabrics, strain and biotite microstructure with increasing mylonitisation in the pretectonic Wyangala Granite, Australia

    NASA Astrophysics Data System (ADS)

    Lennox, P. G.; de Wall, H.; Durney, D. W.

    2016-04-01

    The Wyangala Granite is a foliated, porphyritic Silurian granite from the Palaeozoic Circum-Pacific type Eastern Lachlan Orogen (ELO) of Australia. It is a paramagnetic ilmenite-bearing, S/marginal I type two-mica- to mainly biotite-granite with different biotite contents and local chlorite alteration. Very highly strained quartz-epidote bands are present. In this contribution, anisotropy of magnetic susceptibility (AMS) is compared with independently measured intensity and 3D style of strain, biotite microstructure and degree of mylonitisation for low-strain granites with weak S-foliations, through medium-strain protomylonitic granites with moderate S- and C-foliations to a high-strain altered granite with a strong single foliation. The samples are further analysed for possible contributions from sample heterogeneity, magmatic flow and 'sub-magmatic' deformation. A good correlation, P‧AMS ~ 1.02 + 0.04 ln P‧(e)Qtz, is obtained between site-average degree of AMS (P‧AMS) in the granite and degree of finite-strain anisotropy (P‧(e)Qtz) from aspect ratios of quartz aggregates in S-foliations in hand specimen and outcrop (P‧AMS 1.03-1.14, P‧(e)Qtz 1.4-19). The magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the March model. The observed quartz strains, however, exceed the AMS March strains and are near neutral, plano-linear character. The geological factors that may have contributed to these differences include intra- and inter-crystalline deformation of biotite and bimodality in S and C. Magmatic fabric is not clearly evident in either the AMS or the biotite data. New data for synkinematic oligoclase, low-titanium biotite and low-sodium K-feldspar show that conditions during deformation were approximately transitional greenschist-amphibolite facies: i.e., well below solidus. This agrees with published age data that put the granite emplacement in an extensional, back-arc setting in already deformed

  19. Mesoproterozoic rapakivi granites of the Rondonia Tin Province, southwestern border of the Amazonian craton, Brazil-I. Reconnaissance U-Pb geochronology and regional implications

    USGS Publications Warehouse

    Bettencourt, Jorge S.; Tosdal, R.M.; Leite, W.B.; Payolla, B.L.

    1999-01-01

    Rapakivi granites and associated mafic and ultramafic rocks in the Rondonia Tin Province, southwestern Amazonian craton, Brazil were emplaced during six discrete episodes of magmatism between ca 1600 and 970 Ma. The seven rapakivi granite suites emplaced at this time were the Serra da Providencia Intrusive Suite (U-Pb ages between 1606 and 1532 Ma); Santo Antonio Intrusive Suite (U-Pb age 1406 Ma); Teotonio Intrusive Suite (U-Pb age 1387 Ma); Alto Candeias Intrusive Suite (U-Pb ages between 1346 and 1338 Ma); Sao Lourenco-Caripunas Intrusive Suite (U-Pb ages between 1314 and 1309 Ma); Santa Clara Intrusive Suite (U-Pb ages between 1082 and 1074 Ma); and Younger Granites of Rondonia (U-Pb ages between 998 and 974 Ma). The Serra da Providencia Intrusive Suite intruded the Paleoproterozoic (1.80 to 1.70 Ga) Rio Negro-Juruena crust whereas the other suites were emplaced into the 1.50 to 1.30 Ga Rondonia-San Ignacio crust. Their intrusion was contemporaneous with orogenic activity in other parts of the southwestern Amazonian craton, except for the oldest, Serra da Providencia Intrusive Suite. Orogenic events coeval with emplacement of the Serra da Providencia Intrusive Suite are not clearly recognized in the region. The Santo Antonio, Teotonio, Alto Candeias and Sao Lourenco-Caripunas Intrusive Suites are interpreted to represent extensional anorogenic magmatism associated with the terminal stages of the Rondonian-San Ignacio orogeny. At least the Sao Lourenco-Caripunas rapakivi granites and coeval intra-continental rift sedimentary rocks may, in contrast, represent the products of extensional tectonics and rifting preceding the Sunsas/Aguapei orogeny (1.25 to 1.0 Ga). The two youngest rapakivi suites, the Santa Clara Intrusive Suite and Younger Granites of Rondonia, seemingly represent inboard magmatism in the Rondonian-San Ignacio Province during a younger episode of reworking in the Rio Negro-Juruena Province during the waning stages of the collisional 1.1 to 1.0 Ga

  20. Structure and emplacement of granite plutons in the Paleoproterozoic crust of Eastern Burkina Faso: rheological implications

    NASA Astrophysics Data System (ADS)

    Vegas, Nestor; Naba, Seta; Bouchez, Jean Luc; Jessell, Mark

    2008-11-01

    The Fada N'Gourma area in Burkina Faso is underlain by Paleoproterozoic rocks that make the northeastern West-African Craton. This region is composed of NE-trending volcano-sedimentary belts and foliated tonalites, affected by several shear zones. A generation of younger, ˜2100 Ma-old, non-foliated biotite-bearing granites intrudes the former rock units. We have investigated the younger granite pluton of Kouare that was previously considered as forming a single body with the pluton of Satenga to the west, a pluton which likely belongs to the ˜20 Ma more recent Tenkodogo-Yamba batholith. Magnetic fabric measurements have been combined with microstructural observations and the analysis of field and aeromagnetic data. The granite encloses angular enclaves of the host tonalites. Magmatic microstructures are preserved inside the pluton and solid-state, high-temperature deformation features are ubiquitous at its periphery. The presence of steeply plunging lineations in the pluton of Kouare and its adjacent host-rocks suggests that large volumes of granitic magmas became crystallized while they were ascending through the crust that was softened and steepened close to the contact. Around Kouare, the foliation in the host tonalites conforms with a map-scale, Z-shaped fold in between NNE-trending shear zones, implying a bulk clockwise rotation of the material contained in-between the shear zones, including the emplacing pluton. Regionally, the Fada N'Gourma area is concluded to result from NW-shortening associated with transcurrent shearing and vertical transfer of granitic magmas. This study concludes that the ˜2200 Myears old juvenile crust of Burkina Faso was brittle before the intrusion of the biotite-granites, became softened close to them and that gravity-driven and regional scale wrench tectonics were active together.

  1. Petrochemical and isotopic studies of Transhimalayan granites in Ladakh, NW India

    SciTech Connect

    Srimal, N.; Basu, A.R.; Sinha, A.K.

    1985-01-01

    The India-Asia collision zone in the Transhimalayan Indus and Shyok Tectonic Belts (STB) of Ladakh, NW India is characterized by two major granitic batholiths. The northern, Karakoram Granitic batholith and the southern, Ladakh Granitic batholith are separated by thrust-bound belts of ophiolite, flysch and calc-alkaline volcanics of Mesozoic to Tertiary age. The KGC can be divided into three zones: a northern zone of metaluminous to mildly peraluminous granodiorite, diorite and tonalite with normative corundum, a southern zone of peraluminous two-mica and garnet bearing granites with normative corundum 1.8-3.3%, K/Rb=200-310, Rb/Sr > 0.3 and initial /sup 87/Sr/ /sup 86/Sr > 0.7113, and a central zone with variable K/Rb, Rb/Sr and initial /sup 87/Sr//sup 86/Sr ratios showing characteristics of both the northern and the southern zones. Field and characteristics of both the northern and the southern zones. Field and geochemical data indicate that: 1) the northern granites of the KGC represent an older magmatic arc derived largely from igneous sources with a small admixture of evolved crustal components and 2) the southern granites of the KGC are derived by partial melting of mature crustal material. Preliminary work in the LGC indicate varying source contamination reflected in variable initial /sup 87/Sr//sup 86/Sr ratios (.7041-.7072) and in correlated /sup 87/Sr//sup 86/Sr vs. delta /sup 18/O plot. The authors data suggest: 1) multiple accretion of Gondwanic fragments in the Mesozoic and Tertiary along the southern margin of Asia, 2) absence of extensive crustal anatexis in the source region of the Ladakh batholith, and 3) remobilization of old sutures and crustal anatexis as a result of India-Asia collision.

  2. An evaluation of disequilibrium melting and granitic magma evolution by zircon

    NASA Astrophysics Data System (ADS)

    Wang, X.; Tang, M.

    2012-12-01

    The magma-mixing model has been widely used to explain the isotopic diversity in various granitic systems, although it, in many cases, lacks definite field and petrographic evidence to link the possible mantle input in granitic magma. The issue of disequilibrium melting, however, has seldom been fully evaluated in the formation of granitic rocks and it may readily occur when the melt extraction is fast enough that the melt may fail to attain isotopic equilibrium with the protoliths. In this scenario, melt batches of different stages may continually feed the magma chamber and then crystallize, causing large isotopic heterogeneity within individual pluton/intrusion. In this work, the effect of disequilibrium melting on granitic magmatism was pictured by in-situ geochemical and isotopic analyses on zircons from five representative granite samples in South China. These granites are characterized by significant ɛHf(t) variation (> 5 epsilon units) in zircons on specimen scale, although they do not have evident field or petrographic signs of magma mixing. Zircons from these samples display roughly positive Th/U-T (temperature) correlations with various extents of scatter. Many zircons show reverse thermal zonation, implying complex thermal evolution of the magma chambers, which might result from multiple melt impulses. Such open-system processes may also be responsible for the large ɛHf(t) variations in zircons. Coupled zircon ɛHf(t) variations and extent of scatter in zircon Th/U-T diagram are observed in one sample (Jiuling Pluton), strongly implying that isotopic evolution in the magma chamber may have been controlled by melt recharge frequency, which in turn may be associated with melt extraction rate in the source. Zircon ɛHf(t)-Th/U covariation, which may be expected in the mixing processes between mantle and crust derived magmas, was not observed in any sample of this work.

  3. Geology and mineralization of the Jabalat alkali-feldspar granite, northern Asir region, Kingdom of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Al Tayyar, Jaffar; Jackson, Norman J.; Al-Yazidi, Saeed

    The Jabalat post-tectonic granite pluton is composed of albite- and oligoclase-bearing, low-calcium, F-, Sn- and Rb-rich subsolvus granites. These granites display evidence of late-magmatic, granitophile- and metallic-element specialization, resulting ultimately in the development of post-magmatic, metalliferous hydrothermal systems characterized by a Mo sbnd Sn sbnd Cu sbnd Pb sbnd Zn sbnd Bi sbnd Ag sbnd F signature. Two main types of mineralization are present within the pluton and its environs: (1) weakly mineralized felsic and aplitic dikes and veins enhanced in Mo, Bi, Ag, Pb and Cu; and (2) pyrite—molybdenite—chalcopyrite-bearing quartz and quartz—feldspar veins rich in Mo, Sn, Bi, Cu, Zn and Ag. A satellite stock, 3 km north of the main intrusion, is composed of fine-grained, miarolitic, muscovite—albite—microcline (microperthite) granite. The flanks of this intrusion and adjacent dioritic rocks are greisenized and highly enriched in Sn, Bi and Ag. Quartz veins which transect the satellite stock contain molybdenite and stannite.

  4. Origin of miarolitic pegmatites in the Königshain granite/Lusatia

    NASA Astrophysics Data System (ADS)

    Thomas, Rainer; Davidson, Paul

    2016-09-01

    In this study we examine an interesting occurrence of miarolitic pegmatites in the Königshain granite of the Lusatia region of the Bohemian Massif. This granite is characterized by the extensive development of micro-sized miarolitic pegmatites (typically with diameters of 5 to 15 mm) irregularly distributed through its upper levels, and larger miarolitic pegmatites (up to 1 m) in the uppermost levels. This granite also shows evidence of varied forms of transport of extremely volatile rich residual melts/fluids, in the form of more or less discrete inter-granular melt bodies, and associated magmatic quartz veins formed in tectonic fissures. Together, these provide evidence for the origin of miarolitic pegmatites, both in the specific case of Königshain, and more generally. Our evidence suggests that miarolitic pegmatites form from volatile- and alkali-rich residual melts, ranging from 10 to 50% H2O, far more than typical granitic melts, but far more silicate components than aqueous fluids or vapor suggested by some authors. Using melt inclusions in quartz from the aplitic and graphic granite zones in miarolitic pegmatites in the Königshain granite, we show that two different inclusion populations are present. We provide evidence that the first inclusion population are those related to the primary granite at the level of intrusion, and the second were trapped during the re-crystallization of the granite wall rocks by silicate-rich supercritical fluids moving through the solid crystal framework with a porosity < 25 and a permeability > 0 (see Clarke et al., 2013). Our results show that a significant volume fraction of the miarolitic pegmatites was not created by a pegmatite-forming fluid, but formed in-situ by re-crystallization of wall-rocks, triggered by highly reactive volatiles exsolved from the pegmatite-forming melts. Evidence is also presented which suggests the nature and speed of emplacement of the Königshain granite. This evidence may explain the unusual

  5. U-Pb zircon geochronology of Mesoproterozoic postorogenic rocks and implications for post-Ottawan magmatism and metallogenesis, New Jersey Highlands and contiguous areas, USA

    USGS Publications Warehouse

    Volkert, R.A.; Zartman, R.E.; Moore, P.B.

    2005-01-01

    Postorogenic rocks are widespread in Grenville terranes of the north-central Appalachians where they form small, discordant, largely pegmatitic felsic intrusive bodies, veins, and dikes, and also metasomatic calcic skarns that are unfoliated and postdate the regional 1090 to 1030 Ma upper amphibolite- to granulite-facies metamorphism related to the Grenville (Ottawan) Orogeny. Zircons from magmatic and nonmagmatic rocks from northern New Jersey and southern New York were dated to provide information on the regional tectonomagmatic and metallogenic history following Ottawan orogenesis. We obtained U-Th-Pb zircon ages of 1004 ?? 3 Ma for pegmatite associated with the 1020 ?? 4 Ma Mount Eve Granite near Big Island, New York, 986 ?? 4 Ma for unfoliated, discordant pegmatite that intrudes supracrustal marble at the Buckwheat open cut, Franklin, New Jersey, ???990 Ma for a silicate-borate skarn layer in the Franklin Marble at Rudeville, New Jersey, and 940 ?? 2 Ma for a calc-silicate skarn layer at Lower Twin Lake, New York. This new data, together with previously published ages of 1020 ?? 4 to 965 ?? 10 Ma for postorogenic rocks from New Jersey and southern New York, provide evidence of magmatic activity that lasted for up to 60 Ma past the peak of high-grade metamorphism. Postorogenic magmatism was almost exclusively felsic and involved relatively small volumes of metaluminous to mildly peraluminous melt that fractionated from an A-type granite parent source. Field relationships suggest the melts were emplaced along lithosphere-scale fault zones in the Highlands that were undergoing extension and that emplacement followed orogenic collapse by least 30 Ma. Postorogenic felsic intrusions correspond to the niobium-yttrium-fluorine (NYF) class of pegmatites of C??erny?? (1992a). Geochronologic data provide a temporal constraint on late-stage hydrothermal activity and a metallogenic event in New Jersey at ???990 to 940 Ma that mineralized pegmatites with subeconomic to

  6. Contamination in mafic mineral-rich calc-alkaline granites: a geochemical and Sr-Nd isotope study of the Neoproterozoic Piedade Granite, SE Brazil.

    PubMed

    Leite, Renato J; Janasi, Valdecir A; Martins, Lucelene

    2006-06-01

    The Piedade Granite (approximately 600 Ma) was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit) and core (metaluminous titanite-bearing biotite monzogranite BmgT unit) and felsic pink inequigranular granite (Bmg unit) between them. Bmg has high LaN/YbN (up to 100), Th/U (> 10) and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (approximately 45), Ba and Sr, fractionated REE patterns (LaN/YbN = 45), 87Sr/86Sr(t) approximately 0.710, epsilonNd(t) approximately -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta). The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t) = 0.713-0.714; epsilonNd(t) = -14 to -16), similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

  7. Magmatism on the Moon

    NASA Astrophysics Data System (ADS)

    Michaut, Chloé; Thorey, Clément; Pinel, Virginie

    2016-04-01

    Volcanism on the Moon is dominated by large fissure eruptions of mare basalt and seems to lack large, central vent, shield volcanoes as observed on all the other terrestrial planets. Large shield volcanoes are constructed over millions to several hundreds of millions of years. On the Moon, magmas might not have been buoyant enough to allow for a prolonged activity at the same place over such lengths of time. The lunar crust was indeed formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a particularly light and relatively thick crust. This low-density crust acted as a barrier for the denser primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basins where at least part of the crust was removed by the impact process. Thus, the ascent of lunar magmas might have been limited by their reduced buoyancy, leading to storage zone formation deep in the lunar crust. Further magma ascent to shallower depths might have required local or regional tensional stresses. Here, we first review evidences of shallow magmatic intrusions within the lunar crust of the Moon that consist in surface deformations presenting morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. We then study the preferential zones of magma storage in the lunar crust as a function of the local and regional state of stress. Evidences of shallow intrusions are often contained within complex impact craters suggesting that the local depression caused by the impact exerted a strong control on magma ascent. The depression is felt over a depth equivalent to the crater radius. Because many of these craters have a radius less than 30km, the minimum crust thickness, this suggests that the magma was already stored in deeper intrusions before ascending at shallower depth. All the evidences for intrusions are also preferentially located in the internal

  8. Reduced Magmatic Volatiles

    NASA Astrophysics Data System (ADS)

    Hirschmann, M. M.; Withers, A. C.; Ardia, P.; Stanley, B. D.; Foley, N.

    2012-12-01

    Volatiles in Earth's upper mantle are dominated by H2O and CO2, but under more reduced conditions likely deeper in the mantle, other volatile species may be important or dominant. However, the speciation, solubilities, and effect on physical properties of reduced magmatic volatiles are poorly constrained. Here we summarize results from an experimental campaign to better understand reduced volatiles in magmas. Experiments emphasize spectroscopic and SIMS characterization of dissolved species in experiments for which fluid fugacities are known, thereby facilitating thermodynamic parameterization. Experimental determinations of molecular H2 solubility in basaltic and andesitic liquids show concentrations that are proportional to H2 fugacity. Because H2 increases with fH2 whereas dissolved H2O increases with fH2O1/2, the relative importance of H2 increases with pressure and for more hydrous magmas. At 1 GPa and IW-1, solubility in basalt reaches 0.3 wt.% (equivalent to 2.7 wt.% H2O). Solubilities at pressures of the deep upper mantle have not been explored experimentally (as is also true for H2O and CO2), but H2 could become the dominant hydrous species at 400 km and deeper, and so deep hydrous melts may have chiefly H2 rather than H2O or OH. Experiments suggest an extremely low partial specific density (0.18 kg/m3) for dissolved H2 at low pressure, and so appreciable dissolved H2 in melt atop the 410 km discontinuity or in the lower mantle may promote positive buoyancy. Solubilities of reduced C-species remain poorly known. In contrast to results in Na2O-SiO2 liquids (Mysen et al., 2009), experiments with a haplobasaltic liquid at controlled CH4 fugacities indicated very small (<0.05 wt.%) CH4 solubilities even at very reduced conditions (

  9. The Deep Crust Magmatic Refinery, Part 2 : The Magmatic Output of Numerical Models.

    NASA Astrophysics Data System (ADS)

    Bouilhol, P.; Riel, N., Jr.; Van Hunen, J.

    2016-12-01

    Metamorphic and magmatic processes occurring in the deep crust ultimately control the chemical and physical characteristic of the continental crust. A complex interplay between magma intrusion, crystallization, and reaction with the pre-existing crust provide a wide range of differentiated magma and cumulates (and / or restites) that will feed the upper crustal levels with evolved melt while constructing the lower crust. With growing evidence from field and experimental studies, it becomes clearer that crystallization and melting processes are non-exclusive but should be considered together. Incoming H2O bearing mantle melts will start to fractionate to a certain extent, forming cumulates but also releasing heat and H2O to the intruded host-rock allowing it to melt in saturated conditions. The end-result of such dynamic system is a function of the amount and composition of melt input, and extent of reaction with the host which is itself dependent on the migration mode of the melts. To better constrain lower crust processes, we have built up a numerical model [see Riel et al. associated abstract for methods] to explore different parameters, unravelling the complex interplay between melt percolation / crystallization and degassing / re-melting in a so called "hot zone" model. We simulated the intrusion of water bearing mantle melts at the base of an amphibolitized lower crust during a magmatic event that lasts 5 Ma. We varied several parameters such as Moho depth and melt rock ratio to better constrain what controls the final melt / lower crust composition.. We show the evolution of the chemical characteristics of the melt that escape the system during this magmatic event, as well as the resulting lower crust characteristics. We illustrate how the evolution of melt major elements composition reflects the progressive replacement of the crust towards compositions that are dominated by the mantle melt input. The resulting magmas cover a wide range of composition from

  10. Radioelement distributions in the Proterozoic granites and associated pegmatites of Gabal El Fereyid area, Southeastern Desert, Egypt.

    PubMed

    Abd El-Naby, H H; Saleh, G M

    2003-10-01

    Lithologically, the rock types in the Gabal El Fereyid area are dominantly granites with minor amounts of pegmatites. The granites range in composition from tonalite to granite-adamallite with minor acidic dikes, quartz and pegmatite veins. The granite-adamallite is peraluminous and formed as a result of partial melting of amphibole-bearing rocks at depths of approximately 24-30 km and at temperatures of 800-950 degrees C. Among the different rock types, the muscovite-rich pegmatites had the highest U and Th contents (66 and 38 ppm on average, respectively). The high level of radioactivity in pegmatites is attributed to the presence of the radioactive minerals thorianite, uranophane and allanite as confirmed by XRD analysis. Binary relations of Zr/U, Zr/Th, Ce/U and Ce/Th against either U or Th in the granite-adamellite exhibit significant negative correlations indicating that both elements are not preferentially hosted in the accessory minerals phases such as zircon and monazite, but could be associated with major forming minerals such as biotite, muscovite, plagioclase and quartz, or U is situated within labile sites within granite. The uranium and thorium enrichment in the pegmatites is a two-stage process. The primary stage is magmatic whereas the secondary enrichment is from hydrothermal concentration. The magmatic U and Th are indicated by the presence of thorianite and allanite, whereas evidence of hydrothermal mineralization is the alteration of rock-forming minerals such as feldspar and the formation of secondary minerals such as uranophane and pyrite.

  11. Trace-element geochemistry of postorogenic granites from the northeastern Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Stuckless, John S.; Knight, R.J.; VanTrump, G.; Budahn, J.R.

    1983-01-01

    Concentrations determined for all of the trace elements included in this study of postorogenic granites from the northeastern Arabian Shield are best described by log-normal distributions. The trace elements are divided into two groups: (1) compatible lithophile and siderophile elements (strontium, cobalt, scandium, manganese, europium, and titanium) and (2) incompatible lithophile elements (uranium, thorium, tantalum, rubidium, and rare-earth elements, except europium). The compatible elements exhibit greatest concentrations in the metaluminous postorogenic granites, and concentrations decrease with increasing degree of magma evolution. Economic potential for these elements and other geochemically similar elements is considered to be low. The concentrations of the incompatible elements increase with increasing degree of magma evolution and are greatest in the peralkaline and peraluminous granites. There is some geologic evidence that pegmatite and vein-forming processes were operative toward the end stage of postorogenic magmatism in the northeastern Arabian Shield, and therefore there is some probability for economic potential for these elements. It is suggested that such potential is greatest where highly evolved postorogenic granites intruded volatile (generally water )-rich country rocks.

  12. GRANITE PEAK ROADLESS AREA, CALIFORNIA.

    USGS Publications Warehouse

    Huber, Donald F.; Thurber, Horace K.

    1984-01-01

    The Granite Peak Roadless Area occupies an area of about 5 sq mi in the southern part of the Trinity Alps of the Klamath Mountains, about 12 mi north-northeast of Weaverville, California. Rock and stream-sediment samples were analyzed. All streams draining the roadless area were sampled and representative samples of the rock types in the area were collected. Background values were established for each element and anomalous values were examined within their geologic settings and evaluated for their significance. On the basis of mineral surveys there seems little likelihood for the occurrence of mineral or energy resources.

  13. Mid-Neoproterozoic intraplate magmatism in the northern margin of the Southern Granulite Terrane, India: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deeju, T. R.; Santosh, M.; Yang, Qiong-Yan; Pradeepkumar, A. P.; Shaji, E.

    2016-11-01

    The northern margin of the Southern Granulite Terrane in India hosts a number of mafic, felsic and alkaline magmatic suites proximal to major shear/paleo-suture zones and mostly represents magmatism in rift-settings. Here we investigate a suite of gabbros and granite together with intermediate (dioritic) units generated through mixing and mingling of a bimodal magmatic suite. The massive gabbro exposures represent the cumulate fraction of a basic magma whereas the granitoids represent the product of crystallization in felsic magma chambers generated through crustal melting. Diorites and dioritic gabbros mostly occur as enclaves and lenses within host granitoids resembling mafic magmatic enclaves. Geochemistry of the felsic units shows volcanic arc granite and syn-collisional granite affinity. The gabbro samples show mixed E-MORB signature and the magma might have been generated in a rift setting. The trace and REE features of the rocks show variable features of subduction zone enrichment, crustal contamination and within plate enrichment, typical of intraplate magmatism involving the melting of source components derived from both depleted mantle sources and crustal components derived from older subduction events. The zircons in all the rock types show magmatic crystallization features and high Th/U values. Their U-Pb data are concordant with no major Pb loss. The gabbroic suite yields 206Pb/238U weighted mean ages in the range of 715 ± 4-832.5 ± 5 Ma marking a major phase of mid Neoproterozoic magmatism. The diorites crystallized during 206Pb/238U weighted mean age of 724 ± 6-830 ± 2 Ma. Zircons in the granite yield 206Pb/238U weighted mean age of 823 ± 4 Ma. The age data show broadly similar age ranges for the mafic, intermediate and felsic rocks and indicate a major phase of bi-modal magmatism during mid Neoproterozoic. The zircons studied show both positive and negative εHf(t) values for the gabbros (-6.4 to 12.4), and negative values for the diorites (-7

  14. Lithium and boron in late-orogenic granites - Isotopic fingerprints for the source of crustal melts?

    NASA Astrophysics Data System (ADS)

    Romer, Rolf L.; Meixner, Anette; Förster, Hans-Jürgen

    2014-04-01

    (14.7) of one granite sample (Burgberg), which is similar to δ7Li values of its wall rocks (up to 14.5), may indicate late-magmatic fluid-rock interaction with external, wall rock-derived fluids. Because of the small compositional range of most source lithologies, the Li and B-isotopic variation in the granites is also small indicating that the isotopic composition of Li and B does not represent a particularly sensitive source tracer, with the exception of source lithologies characterized by extreme δ7Li or δ11B values.

  15. Age and nature of Triassic magmatism in the Netoni Intrusive Complex, West Papua, Indonesia

    NASA Astrophysics Data System (ADS)

    Webb, Max; White, Lloyd T.

    2016-12-01

    We report field observations together with petrological, geochemical and geochronological data from granitoids of the Netoni Intrusive Complex of West Papua. Until now, our knowledge of the timing of granitic magmatism in this region has been limited to a wide range of ages (241-6.7 Ma) obtained from K-Ar measurements of hornblende, biotite and plagioclase, primarily from samples of river detritus. We collected in situ samples along several traverses into the intrusive complex to: (1) develop a better understanding of the lithologies within the intrusive complex; and (2) determine the timing of magmatism using U-Pb dating of zircon. We also dated zircons from two river sand samples to identify other potential pulses of magmatism that may have been missed due to a sampling bias. The zircons extracted from the river sands yield age spectra similar to those obtained from the in situ samples. The combined data demonstrate that magmatism in the Netoni Intrusive Complex occurred between 248 Ma and 213 Ma. The petrological and geochemical data indicate that the granitoids were most likely emplaced in an ocean-continent (Andean style) subduction setting. This builds on previous work which suggests that a magmatic belt extended along eastern Gondwana (now New Guinea and eastern Australia) throughout much of the Paleozoic. The volcanic ejecta that were produced along this arc and the subsequent erosion of the mountain chain are a potential source of detritus for Triassic and younger sedimentary rocks in New Guinea, eastern Indonesia and north/northwestern Australia.

  16. Paired Magmatic-Metallogenic Belts in Myanmar - an Andean Analogue?

    NASA Astrophysics Data System (ADS)

    Gardiner, Nicholas; Robb, Laurence; Searle, Michael; Morley, Christopher

    2015-04-01

    contrasting minerals endowment. The Mogok-Mandalay-Mergui (MMM) Belt hosts crustal-melt S-type granites with significant tin-tungsten mineralization, and contains the historically major tungsten deposit of Mawchi. The Wuntho-Popa Arc comprises I-type granites and granodiorites with porphyry-type copper-gold and epithermal gold mineralization, and includes the world-class Monywa copper mine. Recent U-Pb radiometric age dating has shown the potential for the two belts to be both active from the Late Cretaceous to Eocene. The spatial juxtaposition of these two sub-parallel belts, the implication of contemporary magmatism, and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the South American Cordillera. Here we investigate whether they together represent the magmatic and metallogenic expression of an Andean-type setting in Myanmar during the subduction of Neo-Tethys. In this analogue the Wuntho-Popa Arc represents a proximal I-type magmatic belt sited immediately above the eastwards-verging Neo-Tethys subduction zone. Exhibiting porphyry-type copper-gold and epithermal gold mineralization, this would therefore be the Myanmar equivalent of the Andean coastal copper belts. Conversely, the parallel MMM Belt, comprised of more distal crustal-melt S-type tin granites, would have an analogue in the Bolivian tin belt.

  17. 6. Photocopied August 1971 from Photo 13731, Granite Folder #1, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Photocopied August 1971 from Photo 13731, Granite Folder #1, Engineering Department, Utah Power and Light Co., Salt Lake City, Utah. GRANITE STATION, MAY 24, 1915. - Utah Power Company, Granite Hydroelectric Plant, Holladay, Salt Lake County, UT

  18. Lithospheric evolution of the Northern Arabian Shield: Chemical and isotopic evidence from basalts, xenoliths and granites

    NASA Technical Reports Server (NTRS)

    Stein, M.

    1988-01-01

    The evolution of the upper-mantle and the lower-crust (the conteinental lithosphere), is the area of Israel and Sinai was studied, using the chemical composition and the Nd-Sr isotopic systematics from mantle and crustal nodules, their host basalts, and granites. The magmatism and the metasomatism making the lithosphere are related to uprise of mantle diapirs in the uppermost mantle of the area. These diapirs heated the base of the lithosphere, eroded, and replaced it with new hot material. It caused a domal uplift of the lithosphere (and the crust). The doming resulted in tensional stresses that in turn might develop transport channels for the basalt.

  19. Lithospheric evolution of the Northern Arabian Shield: Chemical and isotopic evidence from basalts, xenoliths and granites

    NASA Technical Reports Server (NTRS)

    Stein, M.

    1988-01-01

    The evolution of the upper-mantle and the lower-crust (the conteinental lithosphere), is the area of Israel and Sinai was studied, using the chemical composition and the Nd-Sr isotopic systematics from mantle and crustal nodules, their host basalts, and granites. The magmatism and the metasomatism making the lithosphere are related to uprise of mantle diapirs in the uppermost mantle of the area. These diapirs heated the base of the lithosphere, eroded, and replaced it with new hot material. It caused a domal uplift of the lithosphere (and the crust). The doming resulted in tensional stresses that in turn might develop transport channels for the basalt.

  20. Geochemical Signatures of Neoproterozoic Granites and Granitoid-gneisses from Angavo Belt, Central Madagascar

    NASA Astrophysics Data System (ADS)

    Raharimahefa, T.

    2015-12-01

    The basement rocks of Madagascar record high-grade metamorphism, magmatism, and contractional and extensional structures that accompanied the collision of the eastern and western Gondwana segments of the supercontinent followed by its collapse. In the eastern central Madagascar, granitoids dominate the landscape and occur in a large area near and within the N-S trending highly strained zone known as the Angavo Shear Zone or Angavo belt. The area is a key in understanding the evolution of basement of Madagascar and the reconstruction of the Gondwana supercontinent. These granitoids range from layered to massive and previously published U-Pb zircon dating yielded three distinctive Neoproterozoic magmatisms at 770 Ma to 820 Ma, ca. 660Ma, and ca 550Ma. However, it was unknown whether these ages represent distinct magmatic pulses or reflect a continuous granitoid emplacement. This work contributes to the knowledge of the Malagasy basement rocks and to explore and discuss the origin and petrotectonic evolution of the granites and granitoid-gneisses from this part of the Madagascar. The rock samples are placed into three groups: group A and B for granitoid-gneisses and a third group for the granite layers. Group A and B are metaluminous and slightly peraluminous, respectively. All rocks have typical subduction zone calc-alkaline signatures. Group A is characterized by enrichment in large ion lithophile elements (LILE) but low U, LREE enrichment, depletion in the high field strength elements (HFSE). In contrast, Group B has REE patterns closely similar to Archean sediments. The granite layers show fractionated REE patterns in which HREE patterns show strong correlation with Zr abundances. Trends in major element variation diagrams and the enrichment of incompatible elements could be explained by simple fractional crystallization, while the overall geochemical signatures reflect either (1) melting of ancient crust or (2) crustal contamination of a more evolved magmas that

  1. Contrasting hydrological processes of meteoric water incursion during magmatic-hydrothermal ore deposition: An oxygen isotope study by ion microprobe

    NASA Astrophysics Data System (ADS)

    Fekete, Szandra; Weis, Philipp; Driesner, Thomas; Bouvier, Anne-Sophie; Baumgartner, Lukas; Heinrich, Christoph A.

    2016-10-01

    Meteoric water convection has long been recognized as an efficient means to cool magmatic intrusions in the Earth's upper crust. This interplay between magmatic and hydrothermal activity thus exerts a primary control on the structure and evolution of volcanic, geothermal and ore-forming systems. Incursion of meteoric water into magmatic-hydrothermal systems has been linked to tin ore deposition in granitic plutons. In contrast, evidence from porphyry copper ore deposits suggests that crystallizing subvolcanic magma bodies are only affected by meteoric water incursion in peripheral zones and during late post-ore stages. We apply high-resolution secondary ion mass spectrometry (SIMS) to analyze oxygen isotope ratios of individual growth zones in vein quartz crystals, imaged by cathodo-luminescence microscopy (SEM-CL). Existing microthermometric information from fluid inclusions enables calculation of the oxygen isotope composition of the fluid from which the quartz precipitated, constraining the relative timing of meteoric water input into these two different settings. Our results confirm that incursion of meteoric water directly contributes to cooling of shallow granitic plutons and plays a key role in concurrent tin mineralization. By contrast, data from two porphyry copper deposits suggest that downward circulating meteoric water is counteracted by up-flowing hot magmatic fluids. Our data show that porphyry copper ore deposition occurs close to a magmatic-meteoric water interface, rather than in a purely magmatic fluid plume, confirming recent hydrological modeling. On a larger scale, the expulsion of magmatic fluids against the meteoric water interface can shield plutons from rapid convective cooling, which may aid the build-up of large magma chambers required for porphyry copper ore formation.

  2. Lower Carboniferous post-orogenic granites in central-eastern Sierra de Velasco, Sierras Pampeanas, Argentina: U-Pb monazite geochronology, geochemistry and Sr-Nd isotopes

    NASA Astrophysics Data System (ADS)

    Grosse, Pablo; Söllner, Frank; Báez, Miguel A.; Toselli, Alejandro J.; Rossi, Juana N.; de La Rosa, Jesus D.

    2009-07-01

    in a within-plate setting, possibly as a response to the collapse of the previous Famatinian orogen, extension of the crust and mantle upwelling. They are part of the group of Middle Devonian-Lower Carboniferous granites of the Sierras Pampeanas. The distribution and U-Pb ages of these granites suggests a northward arc-parallel migration of this mainly post-orogenic magmatism with time.

  3. Accretionary history of the Altai-Mongolian terrane: perspectives from granitic zircon U-Pb and Hf-isotope data

    NASA Astrophysics Data System (ADS)

    Cai, Keda; Sun, Min; Xiao, Wenjiao

    2014-05-01

    The Central Asian Orogenic Belt (CAOB) consists of many tectonic terranes with distinct origin and complicated evolutionary history. Understanding of individual block is crucial to reconstruct the geodynamic history of the gigantic accetionary collage. This study presents zircon U-Pb ages and Hf isotopes for the granitoid rocks in the Russian Altai mountain range (including Gorny Altai, Altai-Mongolian terrane and CTUS suture zone between them), in order to clarify the timing of granitic magmatism, source nature, continental crustal growth and tectonic evolution. Our dating results suggest that granitic magmatism of the Russian Altai mountain range occurred in three major episodes including 445~429 Ma, 410~360 Ma and ~241 Ma. Most of the zircons within the Paleozoic granitoids present comparable positive ɛHf(t) values and Neoproterozoic crustal model ages, which favor the interpretation that the juvenile crustal materials produced in the early stage of CAOB were probably dominant sources for the Paleozoic magmatism in the region. The inference is also supported by widespread occurrence of short-lived juvenile materials including ophiolites, seamount relics and arc assemblages in the north CAOB. Consequently, the Paleozoic massive granitic rocks maybe not represent continental crustal growth at the time when they were emplaced, but rather record reworking of relatively juvenile Proterozoic crustal rocks although mantle-derived mafic magma was possibly involved to sever as heat engine during granitic magma generation. The Early Triassic granitic intrusion may be product in an intra-plate environment, as the case of same type rocks in the adjacent areas. The positive ɛHf(t) values (1.81~7.47) and corresponding Hf model ages (0.80~1.16 Ga) together with evidence of petrology are consistent with the interpretation that the parental magma of the Triassic granitic intrusion was produced from enriched mantle-derived sources under an usually high temperature condition

  4. Middle Proterozoic mafic magmatism, east central Idaho: Implications for age of deposition of Belt Supergroup and basin subsidence models

    SciTech Connect

    Chamberlain, K.R. . Dept. of Geology and Geophysics); Doughty, P.T. . Geological Sciences)

    1993-04-01

    In the Salmon River Arch, a ca. 1,365 Ma rapikivi granite intrudes the Proterozoic Yellow Jacket Formation, which is commonly correlated with the basal Belt-Purcell Supergroup. The contact aureole of the granite contains andalusite and overprints greenschist-facies burial metamorphism in the undeformed sedimentary strata. To the north, the granite intrudes amphibolite-facies, migmatitic paragneiss and a mafic igneous complex. Textures within the migmatites attest to deformation during partial melting. Preliminary U-Pb zircon data from a quartz diorite that intrudes the Yellowjacket sediments yield an age of ca. 1,445 Ma. This is consistent with zircon ages from the Crossport C and Moyie sills in northern Idaho and southern BC that constrain the basal Belt Supergroup to be older than 1,440 Ma. U-Pb zircon data from an amphibolitized mafic dike within the mafic igneous complex along the Salmon River are nearly concordant and yield Pb/Pb ages of ca. 1,377 Ma. The zircons exhibit skeletal, magmatic morphologies and the age is interpreted to be the time of primary crystallization. This age is slightly older than the age of the rapikivi granite and overlaps with the U-Pb zircon age of leucosomes in the migmatites. Thus, bimodal magmatism and partial melting occurred ca. 1,370 Ma. Deformation accompanied these events, but was concentrated in the deeper level, high-grade rocks. These processes are syn-depositional, based on age constraints from the intrusive quartz diorite. The authors envision that burial metamorphism, deformation, partial melting mafic magmatism and granite emplacement occurred during extensional deformation in the base of the Yellowjacket basin.

  5. Early Cretaceous (ca. 100 Ma) magmatism in the southern Qiangtang subterrane, central Tibet: Product of slab break-off?

    NASA Astrophysics Data System (ADS)

    Li, Yalin; He, Haiyang; Wang, Chengshan; Wei, Yushuai; Chen, Xi; He, Juan; Ning, Zijie; Zhou, Aorigele

    2016-09-01

    The lack of Early Cretaceous magmatic records with high-quality geochemical data in the southern Qiangtang subterrane has inhibited a complete understanding of the magmatic processes and geological evolution of central Tibet. In this study, we present zircon U-Pb ages, whole-rock geochemistry, and Sr-Nd-Pb and zircon Hf isotopic data for the newly discovered Moku pluton in the southern Qiangtang subterrane. Zircon U-Pb dating reveals that the Moku granites were emplaced in the Early Cretaceous (ca. 100 Ma) and are coeval with the hosted dioritic enclaves. The granites are slightly peraluminous and high-K calc-alkaline I-type granites and characterized by initial (87Sr/86Sr)i ratios of 0.70605-0.70658, negative ɛ Nd(t) values (-4.44 to -3.35), and Nd isotopic model ages of 1.19-1.29 Ga. The granites have a wide range of zircon ɛ Hf(t) values (-24.4 to 2.6) and concordant ratios of (206Pb/204Pb)t = 18.645-18.711, (207Pb/204Pb)t = 15.656-15.666, and (208Pb/204Pb)t = 38.751-38.836. The coeval dioritic enclaves are medium- to high-K calc-alkaline rocks with zircon ɛ Hf(t) values of -13.3 to +3.6. The geochemical signatures of the host granites and coeval dioritic enclaves indicate that the Moku pluton was most likely generated by partial melting of the ancient lower crust with contributions from mantle-derived melts. Our new data, together with other recently published data, indicate that the ca. 100 Ma magmatic rocks were derived from anatexis of the Qiangtang lower crust that mixed with upwelling asthenosphere materials in response to the slab break-off of the northward subduction of the Bangong-Nujiang oceanic lithosphere.

  6. Early Cretaceous (ca. 100 Ma) magmatism in the southern Qiangtang subterrane, central Tibet: Product of slab break-off?

    NASA Astrophysics Data System (ADS)

    Li, Yalin; He, Haiyang; Wang, Chengshan; Wei, Yushuai; Chen, Xi; He, Juan; Ning, Zijie; Zhou, Aorigele

    2017-06-01

    The lack of Early Cretaceous magmatic records with high-quality geochemical data in the southern Qiangtang subterrane has inhibited a complete understanding of the magmatic processes and geological evolution of central Tibet. In this study, we present zircon U-Pb ages, whole-rock geochemistry, and Sr-Nd-Pb and zircon Hf isotopic data for the newly discovered Moku pluton in the southern Qiangtang subterrane. Zircon U-Pb dating reveals that the Moku granites were emplaced in the Early Cretaceous (ca. 100 Ma) and are coeval with the hosted dioritic enclaves. The granites are slightly peraluminous and high-K calc-alkaline I-type granites and characterized by initial (87Sr/86Sr)i ratios of 0.70605-0.70658, negative ɛ Nd( t) values (-4.44 to -3.35), and Nd isotopic model ages of 1.19-1.29 Ga. The granites have a wide range of zircon ɛ Hf( t) values (-24.4 to 2.6) and concordant ratios of (206Pb/204Pb)t = 18.645-18.711, (207Pb/204Pb)t = 15.656-15.666, and (208Pb/204Pb)t = 38.751-38.836. The coeval dioritic enclaves are medium- to high-K calc-alkaline rocks with zircon ɛ Hf( t) values of -13.3 to +3.6. The geochemical signatures of the host granites and coeval dioritic enclaves indicate that the Moku pluton was most likely generated by partial melting of the ancient lower crust with contributions from mantle-derived melts. Our new data, together with other recently published data, indicate that the ca. 100 Ma magmatic rocks were derived from anatexis of the Qiangtang lower crust that mixed with upwelling asthenosphere materials in response to the slab break-off of the northward subduction of the Bangong-Nujiang oceanic lithosphere.

  7. Contrasting Sources Of Granites In The Fosdick Migmatite Dome, West Antarctica

    NASA Astrophysics Data System (ADS)

    Saito, S.; Brown, M.; Korhonen, F.; Siddoway, C. S.

    2007-12-01

    suggest that the granites and leucosomes likely formed by partial melting of the Ford Granodiorite or a sedimentary protolith represented by the Swanson Formation. In terms of trace element compositions, the granites in the dome may be grouped into high-Sr and low-Sr type. Our initial Sr-Nd isotope data suggest that sources of the high-Sr and low-Sr granites are the Ford Granodiorite and the Swanson Formation, respectively. The difference in Sr contents of two granite types may be attributed to different hydrate-breakdown melting reactions in the contrasting sources. Mica-breakdown melting will not contribute a significant amount of Sr to the melt, so we infer that the low-Sr granite likely formed by a mica-breakdown melting reaction in the metasedimentary source. In contrast, hornblende-breakdown melting or hornblende-biotite-breakdown melting of a granodiorite source may contribute Sr to the melt, and we infer the high-Sr granite likely formed by this process. Continuing research will investigate whether these attributes may be used for correlation with contemporaneous magmatism recorded in contiguous parts of the East Gondwana margin, particularly New Zealand (e.g. Tulloch and Kimbrough, 2003, GSA SP374) or Thurston Island (e.g. Bradshaw et al., 1997, Ter. Ant. Pub.).

  8. Distinction between S-type and peraluminous I-type granites: Zircon versus whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Gao, Peng; Zheng, Yong-Fei; Zhao, Zi-Fu

    2016-08-01

    Biotite and two-mica granites are common in continental crust. Although they are generally peraluminous in lithochemistry, their petrogenesis has been controversial. Because they often show a negative correlation between P2O5 and SiO2 and a positive correlation between A/CNK and SiO2, they are commonly considered as the I-type granites of metaigneous origin. However, such lithochemical consideration is not certain in view of their other geochemical characteristics. To constrain the source nature of peraluminous granites, we performed a combined study of in situ U-Pb age, O isotope, and trace element for synmagmatic and relict zircons from Triassic biotite and two-mica granites in the Nanling Range, South China. Zircon U-Pb dating yields concordant ages of 230 ± 3 to 237 ± 3 Ma for synmagmatic zircons, and 335-2379 Ma for relict zircons with two clusters at ca. 440 Ma and ca. 800 Ma, respectively. Both the synmagmatic zircons and the ~ 440 Ma relict zircons are characterized by high δ18O values of 8.8-11.4‰ and 8.6-10.3‰, respectively. In contrast, the majority of the other relict zircons show relatively low δ18O values of 5.1-7.9‰. The high δ18O values for synmagmatic zircons indicate that the Triassic granites were originated from metasedimentary sources. The two age clusters for relict zircons overlap with two episodes of granitic magmatism, respectively, in the early Paleozoic and the middle Neoproterozoic in South China, suggesting their inheritance from the metasedimentary sources. Thus, these Triassic granites were derived from partial melting of metasedimentary rocks rather than metaigneous rocks; they belong to S-type granite although their lithochemical relationships are akin to common I-type granites. As such, the zircon in situ geochemical analyses have the capacity to unravel the source nature of controversial granites. Our data indicate that fractional crystallization of heterogeneous magmas is the possible mechanism for the decoupling

  9. Geological, fluid inclusion and stable isotope studies of Mo mineralization, Galway Granite, Ireland

    NASA Astrophysics Data System (ADS)

    Gallagher, V.; Feely, M.; Högelsberger, H.; Jenkin, G. R. T.; Fallick, A. E.

    1992-09-01

    Mo mineralization within the Galway Granite at Mace Head and Murvey, Connemara, western Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Si-rich alteration, quartz vein(Mace Head) and granite-hosted (Murvey) molybdenite, chalcopyrite, pyrite and magnetite mineralization and a gangue assemblage which includes quartz, muscovite and K-feldspar. Most fluid inclusions in quartz veins homogenize in the range 100 350°C and have a salinity of 1 13 eq. wt.% NaCl. They display Th-salinity covariation consistent with a hypothesis of dilution of magmatic water by influx of meteoric water. CO2-bearing inclusions in an intensely mineralized vein at Mace Head provide an estimated minimum trapping temperature and pressure for the mineralizing fluid of 355°C and 1.2 kb and are interpreted to represent a H2O-CO2 fluid, weakly enriched in Mo, produced in a magma chamber by decompression-activated unmixing from a dense Mo-bearing NaCl-H2O-CO2 fluid. δ34S values of most sulphides range from c. 0‰ at Murvey to 3 4‰ at Mace Head and are consistent with a magmatic origin. Most quartz vein samples have δ18O of 9 10.3‰ and were precipitated from a hydrothermal fluid with δ18O of 4.6 6.7‰. Some have δ18O of 6 7‰ and reflect introduction of meteoric water along vein margins. Quartz-muscovite oxygen isotope geothermometry combined with fluid inclusion data indicate precipitation of mineralized veins in the temperature range 360 450°C and between 1 and 2 kb. Whole rock granite samples display a clear δ18O-δD trend towards the composition of Connemara meteoric waters. The mineralization is interpreted as having been produced by highlyfractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of

  10. Contrasting Modes for Granitic Batholith Construction: the Role of Tectonic Stress

    NASA Astrophysics Data System (ADS)

    Hogan, J. P.

    2005-05-01

    Mental images of felsic magma chambers are inextricably linked to eruption of voluminous high silica ignimbrites which require the presence of even larger volume magma chambers within the crust. Systematic stratigraphic compositional variation within ignimbrites indicate compositionally stratified chambers, with a high silica cap, grading downward to intermediate compositions, all underlain by mafic magma. Influx of basaltic magma keeps the overlying felsic magma liquid and convecting, thus sustaining the large volume chamber. Too large a mafic replenishment can catastrophically extinguish the chamber by triggering an eruption. Silurian granitic batholiths of the coastal Maine magmatic province fit well with an origin as the plutonic roots for such volcanic systems e.g., Mount Desert Igneous Complex (Seaman, 1999), Vinalhaven Igneous Complex (Hawkins and Wiebe, 2004). Large volcanic eruptions are associated with these batholiths. In contrast to "open system" magma chambers, isotopic evidence indicates large "closed system" granitic batholiths can be assembled incrementally from coalescence of discrete smaller batches of felsic magma. Observed heterogeneity in initial isotopic compositions (e.g., Sr, Pb) from these batholiths is interpreted to be inherited form the source region. Preservation of this isotopic heterogeneity eliminates homogenization by convective mixing, indicating discrete batches of magma welded together to form large granitic batholiths. The Devonian Lucerne granite of the coastal Maine magmatic province fits this style of "closed system" batholith construction (Hogan and Sinha, 1991). It is indeterminate as to whether or not the Lucerne magma chamber erupted. The distinction between these two styles of batholith construction, and their magma chambers dynamics, is dependent upon the availability and volume of basaltic magma within the crustal column, which is linked to tectonic stress (Hogan et al., 1998). Increased magma driving pressures during

  11. Geochemical characteristics of the Bulgarmarse Granite of the Fall River Pluton in the Avalonian Superterrane of southeastern New England

    SciTech Connect

    Mancuso, C.I.; Puffer, J.H. . Dept. of Geological Sciences)

    1993-03-01

    The 600 m.y. Bulgarmarsh Granite of the Fall River Pluton crops out along the SE margin of the Pennsylvanian-age Narragansett Basin in the Dedham terrane of the New England Avalonian Superterrane. The Bulgarmarsh is a coarse-grained, quartz-rich, very leucooratic granite, in which mafic minerals, generally less than 5--8%, occur chiefly as chlorite, biotite and garnet disequilibrium intergrowths. Most of the granite is very slightly deformed, but there are many localized zones of deformation, both brittle and plastic, that vary in degree of intensity. The Bulgarmarsh intrudes Basin margin metavolcanics similar to those of Price Neck Formation that crop out within the Basin in Newport and on Gould Island. The Bulgarmarsh Granite has many of the mineralogical and geochemical characteristics of an A-type granite. Its geochemistry places it in the post-orogenic classification of Maniar and Piccoli (1989). New major and minor element geochemical data clearly discriminate between the Bulgarmarsh Granite and the adjacent calc-alkaline Metacom Granite Gneiss. Avalonian Orogeny, occupying a place in geologic history similar to that of the Newport Granite.

  12. Early to late Yanshanian I-type granites in Fujian Province, SE China: Implications for the tectonic setting and Mo mineralization

    NASA Astrophysics Data System (ADS)

    Yang, Yu-Long; Ni, Pei; Yan, Jun; Wu, Chang-Zhi; Dai, Bao-Zhang; Xu, Ying-Feng

    2017-04-01

    The Cathaysia Block is the southeastern part of the South China Block in Southeast (SE) China, and it hosts voluminous late Mesozoic I-, S-, and A-type granitoids, as well as minor highly fractionated granites. We present here zircon U-Pb age data and Nd-Hf isotopic data for the Dayang and Juzhou granites, together with new petrological and geochemical analyses. The Dayang pluton consists of fine-grained two-mica monzonitic granites in which the plagioclases exhibit zoning and poikilitic textures. In contrast, the Juzhou pluton consists of medium- to coarse-grained biotite K-feldspar granites that lack zoning and poikilitic textures. The emplacement ages are 143 ± 2.3 Ma for the Dayang pluton and 133 ± 2.1 Ma for the Juzhou pluton according to zircon U-Pb isotope analyses. The Dayang and Juzhou granites are both metaluminous and belong to the shoshonitic series. The Dayang granite exhibits very flat REE patterns, showing the tetrad effect, and the spidergrams show striking negative Ba, Sr, Nb, and Ti anomalies and a positive Ta anomaly. In contrast, the Juzhou granite has sloping REE patterns, but like the Dayang granite it also has striking negative Ba, Sr, Nb, Ta, and Ti anomalies. Petrographic and geochemical evidence indicates that the Dayang granite is a highly fractionated I-type granite and that the Juzhou granite is a typical I-type granite. The tetrad effect in the Dayang granite can be interpreted in terms of melt-rock interactions at a late stage of magma evolution, whereas the main mechanism during the evolution of the Juzhou magma was fractionation of plagioclase, biotite, hornblende, apatite, zircon, and allanite. Nd-Hf isotope data suggest that the Dayang and Juzhou granites were both formed partial melting of Paleoproterozoic basement rock and juvenile material (underplating basalts or Mayuan Group amphibolites), with the Juzhou granite having a greater contribution from juvenile material than the Dayang granite. Our new data, together with

  13. Fracture process zone in granite

    USGS Publications Warehouse

    Zang, A.; Wagner, F.C.; Stanchits, S.; Janssen, C.; Dresen, G.

    2000-01-01

    In uniaxial compression tests performed on Aue granite cores (diameter 50 mm, length 100 mm), a steel loading plate was used to induce the formation of a discrete shear fracture. A zone of distributed microcracks surrounds the tip of the propagating fracture. This process zone is imaged by locating acoustic emission events using 12 piezoceramic sensors attached to the samples. Propagation velocity of the process zone is varied by using the rate of acoustic emissions to control the applied axial force. The resulting velocities range from 2 mm/s in displacement-controlled tests to 2 ??m/s in tests controlled by acoustic emission rate. Wave velocities and amplitudes are monitored during fault formation. P waves transmitted through the approaching process zone show a drop in amplitude of 26 dB, and ultrasonic velocities are reduced by 10%. The width of the process zone is ???9 times the grain diameter inferred from acoustic data but is only 2 times the grain size from optical crack inspection. The process zone of fast propagating fractures is wider than for slow ones. The density of microcracks and acoustic emissions increases approaching the main fracture. Shear displacement scales linearly with fracture length. Fault plane solutions from acoustic events show similar orientation of nodal planes on both sides of the shear fracture. The ratio of the process zone width to the fault length in Aue granite ranges from 0.01 to 0.1 inferred from crack data and acoustic emissions, respectively. The fracture surface energy is estimated from microstructure analysis to be ???2 J. A lower bound estimate for the energy dissipated by acoustic events is 0.1 J. Copyright 2000 by the American Geophysical Union.

  14. Study on the formation process of composite MMEs (mafic magmatic enclaves) in Taejongdae, Busan Korea.

    NASA Astrophysics Data System (ADS)

    Adam, Mohammed; Kim, Young-Seog; Kim, Taehyung

    2017-04-01

    Mafic Magmatic Enclave (MME) is a common feature in granitic rocks. However, the layered MMEs developed in the outcrop of Cretaceous granite in Taejongdae National Geopark, Busan show various patterns and interesting phenomena providing useful information on the formation of MMEs. We define here the layered MME as MME composed of several contrasting rock shells. Characteristics and origin of MMEs have been studied in several ways; descriptively, geochemically and through isotope studies due to their importance in the evolution of igneous rocks. This study aims to understand the formation mechanism of the composite MMEs, including the reasons for the diversity of the MME rock types. To achieve those tasks, the relationship between the MMEs and the host granite, and difference between the layers were investigated based on petrological, XRF and EPMA analyses. The important results include the followings: the MMEs can be categorized into two main types; Simple-type composed of a single rock type, and Layered-type composed of different surrounded rock shells. Most of the Simple-type have relatively angular shapes and small sizes, and their contacts with the host granite are commonly sharp but some show small dioritic mixing rims. The forming rocks of the simple MMEs are variable from mafic porphyritic, mafic fine to medium grains and felsic coarse-grained dioritic rocks. The layered MMEs have almost circular to elliptical shapes, and show gradual change in composition from mafic and porphyritic texture in the center to fine in the outer shells (like a chilled margin) and again surrounded by a dioritic layer. The dioritic layer shows another chilled margin with the host granite, indicating double cooling mechanism. Some MMEs are injected by granitic materials through cracks. The injection of the granitic materials into the layered MMEs may indicate fracturing during the cooling process. They may indicate two different phases of mingling and one phase of mixing event. The

  15. New perspectives on the origin and emplacement of the Late Jurassic Fanos granite, associated with an intra-oceanic subduction within the Neotethyan Axios-Vardar Ocean

    NASA Astrophysics Data System (ADS)

    Michail, Maria; Pipera, Kyriaki; Koroneos, Antonios; Kilias, Adamantios; Ntaflos, Theodoros

    2016-10-01

    The Fanos granite occurs in the Peonias subzone of the eastern Axios-Vardar zone in northern Greece. The Fanos granite is Late Jurassic (158 ± 1 Ma) and trends N-S, intruding the Mesozoic back-arc Guevgueli ophiolitic complex. The intrusive character of the eastern contact of the Fanos granite with the host ophiolitic complex is well preserved. In turn the western contact is overprinted by a few meters thick, west- to southwest-directed semi-ductile thrust zone, of Late Jurassic-Early Cretaceous age. The Fanos granite is dominated by the typical, isotropic granitoid fabric, although in some places the initial magmatic flow fabric is preserved. The main deformation recognized in the Fanos granite occurred in brittle regime and expressed by Tertiary thrust faults and Neogene-Quaternary normal to oblique normal faults. The origin as well as the possible tectonic setting of the Fanos granite is the main topics that we address in our study. Rock samples of the Fanos granite along with the adjusted Kotza Dere quartz diorite were analyzed for major and trace elements and for Sr and Nd isotopes (only the quartz diorite). The geochemical data show that the granite has peraluminous characteristics, high-K calc-alkaline affinities, and I-type features. The Sr initial isotopic values of the Fanos granite are rather low (0.7053-0.7056) while for the quartz diorite range from 0.7066 to 0.7068. The Nd initial isotopic values range from 0.51235 to 0.51240 for the granite and from 0.51222 to 0.51233 for the quartz diorite. The source of the granitic melt is interpreted to be meta-basaltic amphibolites. These amphibolites are the metamorphic products of enriched mantle melts that underplated the oceanic lithosphere. Taking into account our and published structural and geochemical data for the Fanos granite along with the tectonic data of the broader Axios-Vardar zone, we suggest that the studied granitic rocks were formed during an intra-oceanic subduction within the Neotethyan

  16. Lunar granites with unique ternary feldspars

    NASA Technical Reports Server (NTRS)

    Ryder, G.; Stoeser, D. B.; Marvin, U. B.; Bower, J. F.

    1975-01-01

    An unusually high concentration of granitic fragments, with textures ranging from holocrystalline to glassy, occurs throughout Boulder 1, a complex breccia of highland rocks from Apollo 17, Station 2. Among the minerals included in the granites are enigmatic K-Ca-rich feldspars that fall in the forbidden region of the ternary diagram. The great variability in chemistry and texture is probably the result of impact degradation and melting of a granitic source-rock. Studies of the breccia matrix suggest that this original granitic source-rock may have contained more pyroxenes and phosphates than most of the present clasts contain. Petrographic observations on Apollo 15 KREEP basalts indicate that granitic liquids may be produced by differentiation without immiscibility, and the association of the granites with KREEP-rich fragments in the boulder suggests that the granites represent a residual liquid from the plutonic fractional crystallization of a KREEP-rich magma. Boulder 1 is unique among Apollo 17 samples in its silica-KREEP-rich composition. We conclude that the boulder represents a source-rock unlike the bedrock of South Massif.

  17. Imprints of Late Mesozoic tectono-magmatic events on Palawan Continental Block in northern Palawan, Philippines

    NASA Astrophysics Data System (ADS)

    Padrones, Jenielyn T.; Tani, Kenichiro; Tsutsumi, Yukiyasu; Imai, Akira

    2017-07-01

    A recent investigation in Palawan Island led to the recognition of the Daroctan Granite, a pluton that intruded the Mesozoic mélange in the northernmost part. The occurrence and age of the magmatism is presented in this study as well as the maximum age of deposition for some Late Mesozoic lithostratigraphic units. Geochronological studies on zircon and monazite was carried out to unravel the Late Mesozoic tectonic evolution of this area. Monazite U-Th-total Pb dating was used to determine the age of the Daroctan Granite, which yielded a Late Cretaceous age similar to some of the Mesozoic granites surrounding the South China Sea. Zircon U-Pb and monazite U-Th-total Pb dating were also used to determine the maximum age of deposition of the sedimentary units belonging to the Guinlo Formation and Tumarbong Semi-schist. The results show a Jurassic to Early Cretaceous age range with a Late Cretaceous maximum age of deposition for the meta-sedimentary units. This sliver of the Palawan Continental Block, which is composed of accreted units, might have been located at the margin of the continent-ocean collision during the Mesozoic wherein detrital minerals with mostly Late Cretaceous ages were deposited. It was later intruded by the Daroctan Granite and eventually broke off from the southeastern Eurasian margin. These findings provide additional constraints on the tectonic evolution of the Palawan Continental Block.

  18. Paleoproterozoic postcollisional magmatic belt of the southern Siberian craton

    NASA Astrophysics Data System (ADS)

    Salnikova, E. B.; Larin, A. M.; Kotov, A. B.; Levitsky, V. I.; Reznitsky, L. Z.; Kovach, V. P.; Yakovleva, S. Z.

    2003-04-01

    Paleoproterozoic time is characterized by large-scale collisional and postcollisional magmatic activity evidenced in the most of ancient cratons. This global event is related to the Arctic supercontinent assemblage (Rogers, 1996). The formation of postcollisional magmatic belt at 1.9-1.8 Ga within the south-west flanking of the Siberian craton is a remarkable example of these processes happened during overall lithospheric convergence. This belt is extends for about 3000 km from the southern Enisey ridge at the west to the central Aldan shield at the east. Within the central Aldan shield the latest collisional event occurred 1925+/-5 Ma (Kotov et al, 2003) and post-collisional subalkaline S- and I-type granites emplaced at 1916+/-10 Ma (Bibikova et al., 1989), 1901+/-1 Ma (Frost et al., 1998) and 1899+/-6 Ma (Kotov et al, 2003). However at the southern Olekma terrain (western Aldan shield) the syncollisional granites have formed at 1906+/-4 Ma and postcollisional Kodar granitoids were generated at 1876-1873 Ma (Larin et al., 2000). The is a tendency outlined in timing of postcollision processes to the west (in modern coordinates). Ages of postcollisional Kevakta granitoid plutons (1846+/-8 Ma) and volcanics of North-Baikal volcano-plutonic belt (1869+/-6 Ma 1856+/-3 Ma), Baikal folded area, support this tendency. Emplacement of the Primorsky complex postcollisional rapakivi-type granitoids (southern Baikal lake) occurred at 1859+/-16 Ma (Donskaya et al., 2002). New results of U-Pb single zircon and baddeleyite dating demonstrate that formation of late-synkinematic syenite, charnockite and pegmatitic veins (1856±12 Ma, 1853±20 Ma) and calciphyre (1868±2 Ma) within the eastern part of the Sharyzhalgay block (southern Baikal lake) occurred virtually within the same episode. Postcollisional intrusive charnockite of the Shumikha complex from the western Sharyzhalgay block dated at 1861±1 Ma (Donskaya et al., 2001) and 1871±17 Ma (Levitsky et al., 2002). Subalcaline

  19. Timing of ore-related magmatism in the western Alaska Range, southwestern Alaska

    USGS Publications Warehouse

    Taylor, Ryan D.; Graham, Garth E.; Anderson, Eric D.; Selby, David

    2014-01-01

    This report presents isotopic age data from mineralized granitic plutons in an area of the Alaska Range located approximately 200 kilometers to the west-northwest of Anchorage in southwestern Alaska. Uranium-lead isotopic data and trace element concentrations of zircons were determined for 12 samples encompassing eight plutonic bodies ranging in age from approximately 76 to 57.4 millions of years ago (Ma). Additionally, a rhenium-osmium age of molybdenite from the Miss Molly molybdenum occurrence is reported (approx. 59 Ma). All of the granitic plutons in this study host gold-, copper-, and (or) molybdenum-rich prospects. These new ages modify previous interpretations regarding the age of magmatic activity and mineralization within the study area. The new ages show that the majority of the gold-quartz vein-hosting plutons examined in this study formed in the Late Cretaceous. Further work is necessary to establish the ages of ore-mineral deposition in these deposits.

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

    NASA Astrophysics Data System (ADS)

    Faure, Kevin; Brathwaite, Robert L.

    2006-03-01

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

  1. Geology and mineralogy of the Alakha spodumene granite porphyry deposit, Gorny Altai, Russia

    NASA Astrophysics Data System (ADS)

    Annikova, I. Yu.; Vladimirov, A. G.; Smirnov, S. Z.; Gavryushkina, O. A.

    2016-09-01

    The Alakha lithium-tantalum deposit in the southern Altai, Russia, is represented by a stock of spodumene-bearing granite porphyry localized in the Kalba-Narym-Koktogai lithium-tantalum rare-metal granitic belt, unique in extent (more than 1000 km). This belt is a part of the Altai accretionary-collisional system. Judging from forecasting, the Alakha deposit can be regarded as an uneroded proxy of a pegmatite body both in dimensions and mean Li2O and Ta2O5 contents (0.98 wt % and 114 ppm, respectively); however, the oregenerating potential of this deposit remains insufficiently studied and had not yet been claimed. In this paper, we attempt to fill this gap with a detailed mineralogical study, which allows us to provide insights into the crystallization of Li-bearing high-silicic magma and redistribution of components during magmatic and postmagmatic processes. Accessory mineral assemblages in muscovite-spodumene-K-feldspar granite porphyry and muscovite albitite—the main petrographic rock varieties of the Alakha stock—turned out to be almost identical. A significant similarity in the chemistry of major rock-forming minerals is established for spodumene granite porphyry of the Alakha stock and spodumene pegmatites from large deposits, which makes it possible to suggest that they are close in the petrogenetic mechanism of their formation. The mineral assemblages of muscovite albitite in the apical portion of the Alakha stock are connected by gradual transition with those of spodumene granite porphyry. Such a transition is caused by postmagmatic metasomatic alteration of the latter.

  2. Tectonic significance of Neoproterozoic magmatism of Nakora area, Malani igneous suite, Western Rajasthan, India

    NASA Astrophysics Data System (ADS)

    Kumar, Naresh; Vallinayagam, G.

    2014-05-01

    Three magmatic phases are distinguished in the Neoproterozoic Nakora Ring Complex (NRC) of Malani Igneous Suite (MIS), namely (a) Extrusive (b) Intrusive and (c) Dyke phase. Magmatism at NRC initiated with minor amount of (basic) basalt flows and followed by the extensive/voluminous acid (rhyolites-trachytes) flows. The ripple marks are observed at the Dadawari area of NRC in tuffaceous rhyolite flow which suggests the aqueous condition of flows deposition. The emplacement of the magma appears to have been controlled by a well defined NE-SW tectonic lineament and cut by radial pattern of dykes. These NE-SW tectonic lineaments are the linear zones of crustal weakness and high heat flow. The spheroidal and rapakivi structures in the Nakora acid volcanics indicate the relationship between genetic link and magma mixing. Basalt-trachyte-rhyolite association suggests that the large amount of heat is supplied to the crust from the magma chamber before the eruption. The field (elliptical/ring structures), mineralogical and geochemical characteristics of Nakora granites attest an alkaline character in their evolution and consistent with within plate tectonic setting. The emplacement of these granites and associated volcanics is controlled by ring structures, a manifestation of plume activity and cauldron subsidence, an evidence of extensional tectonic environment. NRC granites are the product of partial melting of rocks similar to banded gneiss from Kolar Schist Belt of India. The present investigations suggest that the magmatic suites of NRC rocks are derived from a crustal source and the required heat supplied from a mantle plume.

  3. Correlations between microstructures, K-feldspar triclinicity and trace element geochemistry in stanniferous and barren granites, northern Nigeria

    NASA Astrophysics Data System (ADS)

    Badejoko, T. A.

    The biotite granites in the Nigerian Younger Granites are a major source of the economic metals Sn, Nb, Zn and W. The textural variations in these rocks are considered together with the composition and structural state of the K-feldspars. The curious disparity in the degree of mineralization of these rocks of similar mineral assemblage is considered to be related to the textural and structural variations. The stanniferous granites are characterized by medium- to fine-grained texture, miarolitic cavities, subsolidus crystallization of biotite and albite; turbidity, coarsening and incoherent perthitic texture of the K-feldspar. The barren granites are usually coarse-grained with few druses, silvery irridescent feldspar grains and coherent perthitic texture. K-feldspars in the stanniferous granites are mainly of maximum microcline structure while the barren ones are characterized by intermediate microcline structure. Compositionally, all the K-feldspars have less than 3% An; they have crystallized in the binary system at temperatures close to 700°C but have now re-equilibrated to various lower temperatures as a result of variable rock-fluid interaction. Positive correlations are observed between Nb, Sn, Rb, Li and F in granites and triclinicity of their K-feldspars. Enhancement of Rb-values is observed in both the stanniferous rocks and their K-feldspar constituents. The variable textures, degree of Al, Si order in the feldspars and enrichment in ore and trace elements are attributed to the presence and abundance of a fluid phase. It is suggested that in the course of magmatic evolution of these rocks an alkali-rich volatile phase developed, accumulated and was trapped in the roof zone of the stanniferous granites.

  4. CO2 laser cutting of natural granite

    NASA Astrophysics Data System (ADS)

    Riveiro, A.; Mejías, A.; Soto, R.; Quintero, F.; del Val, J.; Boutinguiza, M.; Lusquiños, F.; Pardo, J.; Pou, J.

    2016-01-01

    Commercial black granite boards (trade name: "Zimbabwe black granite") 10 mm thick, were successfully cut by a 3.5 kW CO2 laser source. Cutting quality, in terms of kerf width and roughness of the cut wall, was assessed by means of statistically planned experiments. No chemical modification of the material in the cutting walls was detected by the laser beam action. Costs associated to the process were calculated, and the main factors affecting them were identified. Results reported here demonstrate that cutting granite boards could be a new application of CO2 laser cutting machines provided a supersonic nozzle is used.

  5. The South Patagonian batholith: 150 my of granite magmatism on a plate margin

    NASA Astrophysics Data System (ADS)

    Hervé, F.; Pankhurst, R. J.; Fanning, C. M.; Calderón, M.; Yaxley, G. M.

    2007-09-01

    A new database of 70 U-Pb zircon ages (mostly determined by SHRIMP) indicates that the South Patagonian batholith resulted from the amalgamation of subduction-related plutons from the Late Jurassic to the Neogene. Construction of the batholith began with a voluminous, previously undetected, Late Jurassic bimodal body mainly composed of leucogranite with some gabbro, emplaced along its present eastern margin within a restricted time span (157 to 145 Ma). This episode is, at least in part, coeval with voluminous rhyolitic ignimbrites of the Tobífera Formation, deposited in the deep Rocas Verdes Basin east of the batholith; this was the last of several southwestward-migrating silicic volcanic episodes in Patagonia that commenced in an Early Jurassic extensional tectonic regime. The quasi-oceanic mafic floor of the basin was also contemporaneous with this Late Jurassic batholithic event, as indicated by mutually cross-cutting field relationships. Changes in subduction parameters then triggered the generation of earliest Cretaceous plutons (Cretaceous 1: 144-137 Ma) west of the Late Jurassic ones, a westward shift that culminated at 136-127 Ma (Cretaceous 2) along the present western margin of the batholith. Most mid- to Late Cretaceous (Cretaceous 3: 126-75 Ma) and Paleogene (67-40 Ma) granitoids are represented by geographically restricted plutons, mainly emplaced between the previously established margins of the batholith, and mostly in the far south; no associated volcanic rocks of similar age are known at present in this area. During the final Neogene stage of plutonism (25-15 Ma) a recurrence of coeval volcanism is recognized within and east of the batholith. Typical ɛNdt values for the granitoids vary from strongly negative (- 5) in the Late Jurassic, to progressively higher values for Cretaceous 1 (- 4), Cretaceous 2 (- 0.7), Cretaceous 3 (+ 2) and the Paleogene (+ 5), followed by lower and more variable ones in the Neogene (- 1 to + 5). These variations may reflect different modes of pluton emplacement: large crustal magma chambers developed in the early stages (Late Jurassic to Cretaceous 1), leading to widespread emplacement of plutons with a crustal signature, whereas the Cretaceous 2, Cretaceous 3 and Palaeogene parts of the batholith resulted from incremental assembly of small plutons generated at greater depths and with higher ɛNdt. This does not in itself justify the idea of a reduction in crustal character due to progressive exhaustion of fusible material in the crust through which the magmas passed.

  6. Sediment and weathering control on the distribution of Paleozoic magmatic tin-tungsten mineralization

    NASA Astrophysics Data System (ADS)

    Romer, Rolf L.; Kroner, Uwe

    2015-03-01

    The formation of major granite-hosted Sn and/or W deposits and lithium-cesium-tantalum (LCT) type pegmatites in the Acadian, Variscan, and Alleghanian orogenic belts of Europe and Atlantic Northern America involves weathering-related Sn and W enrichment in the sedimentary debris of the Cadomian magmatic arc and melting of these sedimentary source rocks during later tectonic events, followed by magmatic Sn and W enrichment. We suggest that within this, more than 3,000-km long late Paleozoic belt, large Sn and/or W deposits are only found in regions where later redeposition of the Sn-W-enriched weathered sediments, followed by tectonic accumulation, created large volumes of Sn-W-enriched sedimentary rocks. Melting of these packages occurred both during the formation of Pangea, when continental collision subjected these source rocks to high-grade metamorphism and anatexis, and during post-orogenic crustal extension and mantle upwelling. The uncoupling of source enrichment and source melting explains (i) the diachronous occurrence of tin granites and LCT pegmatites in this late Paleozoic orogenic belt, (ii) the occurrence of Sn and/or W mineralizations and LCT pegmatites on both sides of the Rheic suture, and (iii) the contrasting tectonic setting of Sn and/or W mineralizations within this belt. Source enrichment, sedimentary and tectonic accumulation of the source rocks, and heat input to mobilize metals from the source rocks are three unrelated requirements for the formation of Sn and/or W granites. They are the controlling features on the large scale. Whether a particular granite eventually generates a Sn and/or W deposit depends on local conditions related to source melting, melt extraction, and fractionation processes.

  7. Comments on ;Geochronology and geochemistry of rhyolites from Hormuz Island, southern Iran: A new Cadomian arc magmatism in the Hormuz Formationˮ by N. S. Faramarzi, S. Amini, A. K. Schmitt, J. Hassanzadeh, G. Borg, K. McKeegan, S. M. H. Razavi, S. M. Mortazavi, Lithos, Sep. 2015, V.236-237, P.203-211: A missing link of Ediacaran A-type rhyolitic volcanism associated with glaciogenic banded iron salt formation (BISF)

    NASA Astrophysics Data System (ADS)

    Atapour, Habibeh; Aftabi, Alijan

    2017-07-01

    A critical overview on the petrogeochemistry of Hormuz Island highlights that the Ediacaran Hormuz Complex includes synchronous felsic submarine volcanism associated with diamictite and dropstone-bearing banded iron salt (anhydrite, halite, sylvite) formation (BISF) that formed 558-541 Ma in the Late Neoproterozoic. Our field observations disagree with Faramarzi et al. (2015) on the geological map of the Hormuz Island, in particular on the occurrence of the ferruginous agglomerates in the Hormuz Island, thus the geological data do not provide a robust geological mapping. The agglomerates are commonly related to the strombolian peralkaline basaltic eruptions rather than the submarine felsic volcanism. Based on the tectonogeochemical diagrams extracted from the geochemical data of the authors, the Hormuz rhyolites show an affinity to the A-type or A2-type submarine riftogenic and or intra-plate rhyolites of Eby (1992). However, the authors admitted two sides of the debate and proposed an extensional back arc or rift-related magmatic activity as well as continental arc margin setting. The rhyolites are also similar to the Ediacaran Arabian-Nubian A-type alkaline rhyolites that formed by intra-plate rifting during the Pan-African orogen in the proto-Tethys shallow grabens of the Gondwana supercontinent. The most exceptional feature of the Hormuz rhyolites is related to their co-occurrence with the Ediacaran salt rocks, glaciogenic diamictites and jaspillitic banded iron formations, which have never ever been reported previously.

  8. Multiple sources for the origin of the early Cretaceous Xinxian granitic batholith and its tectonic implications for the western Dabie orogen, eastern China

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Xu, Zhaowen; Chen, Maohong; Yu, Yang

    2016-02-01

    This paper investigates the petrogenesis of the Xinxian granitic batholith and its tectonic implications for the Dabie orogen. Two Xinxian granites yield Early Cretaceous 238U/206Pb ages of 122.7 ± 1.3 Ma and 123.6 ± 2.2 Ma. The granites are metaluminous differentiated I-type granites, with A/NKC ranging from 0.90 to 0.96. The chondrite-normalised REE patterns display significant LREE/HREE enrichments with moderate negative Eu anomalies (Eu/Euδ = 0.30 ~ 0.85). The granites show enrichments in large-ion lithophile elements (LILEs, e.g. Rb, K, Th and U) and depletions in Sr, Ba and high field strength elements (HFSEs, e.g. Nb, Ta and Ti). Inherited zircons of different age (Neoproterozoic, one Early Proterozoic, one Archean and two Triassic inherited metamorphic zircons) are identified. The Early Cretaceous magmatic zircons contain enriched Hf isotopes with ɛ Hf ( t) values ranging from -26.9 to -18.7 (average = -22.5), more enriched than their probable alleged source, i.e. the Dabie Complex, represented by the Neoproterozoic and Triassic inherited zircons. Thus, the Archean and Early Proterozoic crustal materials may represent an enriched end member source for the parental magma of the Xinxian granites. Provenance analysis of the magmatic zircons in the North China and Yangtze blocks demonstrates that the Early Proterozoic inherited zircon in Xinxian has North China affinity. Thus, we proposed a multiple-sourced petrogenetic model for the Xinxian granitic batholith, which suggests that the batholith was formed by the remelting of a mixed crustal assemblage, including the Archean and Early Proterozoic crust of the North China Block, the Neoproterozoic crust of the Yangtze Block, as well as some Triassic collision-related ultra-high pressure (UHP) metamorphic rocks.

  9. Controls on the Mobilization and Transport of Hfse in Ore-Forming Magmatic-Hydrothermal Systems

    NASA Astrophysics Data System (ADS)

    Sanchez-Valle, C.; Louvel, M.

    2015-12-01

    The genesis of economical rare metals (Zr, Nb, REE) ore deposits in largegranitic complexes (e.g., Strange Lake and Thor Lake Nechalacho deposit, Canada; Galineiro complex, Spain) is related to the intrusion of alkaline halogen-rich magmatic bodies. Although the role of exolved magmatic fluids in the mobilization and transport of HFSE is widely recognized, the physico-chemical conditions and atomic-scale mechanisms that control the formation of the ore deposits remain poorly understood. We present new experimental constraints on behavior of HFSE during the exsolution of aqueous fluids from peralkaline granitic magmas at crustal conditions. In situ partitioning and speciation studies of Zr in the haplogranite-(F)-H2O systems using synchrotron X-ray spectroscopies provide evidence for large controls of fluid chemistry and temperature on the mobilization and transport of HFSE in crustal settings. At shallow crustal pressure conditions (> 800 °C and 0.3 GPa), Zr preferentially partitions into the exolved aqueous fluid in the presence of fluorine (Df/mZr = 1.40 ± 0.10) as previously reported for Nb in F- (and Cl-) bearing metaluminous granitic systems at similar conditions. The reverse partitioning of HFSE (Zr and Nb) into the aqueous phase at temperature above 800 °C contrast with the behavior observed at lower temperatures, where the Df/mZr remain lower than 1 at all pressures. The enrichment of the aqueous phase in HFSE (Zr, Nb) in the earlier stages of the magmatic evolution is likely related to the enhanced peralkalinity of low pressure (< 0.4 GPa), F-bearing aqueous fluid coexisting with granitic melts as temperature increases. This particular fluid chemistry provides the favorable conditions for the mobilization of HFSE via the formation of HFSE-O-Si/Na clusters in the fluid as shown by the in situ Zr speciation data. Our results show that the exsolution of highly alkaline early magmatic fluid at pressures below 0.4 GPa has the potential to extract HFSE from F

  10. Potassium-argon dating of the cape granite and a granitized xenolith at sea point.

    PubMed

    Schreiner, G D; Basson, H H; Verbeek, A A

    1968-11-01

    Ages obtained by potassium-argon dating are reported for the total rock, light mineral fraction and heavy mineral fractions of the Cape Granite, and of a granitized xenolith derived from the Malmesbury sediments. These ages lie between 430 and 554 million years. The heavy mineral fractions from each rock type show the oldest age, 540 (granite) and 554 (xenolith) million years. These ages are interpreted as lower limits, and the granite age confirms the age of 553 million years found by rubidium-strontium dating. The coincidence of the ages of the different fractions of the granite and xenolith samples is discussed in the light of the different suggestions about the age of the Malmesbury sediments. The conclusion is reached that all pre-granitization history has been eliminated. The possibility of the use of argon retention as a measure of metamorphic activity is suggested.

  11. The petrogenesis of sodic granites in the Niujuanzi area and constraints on the Paleozoic tectonic evolution of the Beishan region, NW China

    NASA Astrophysics Data System (ADS)

    Yu, Jiyuan; Guo, Lin; Li, Jianxing; Li, Yanguang; Smithies, Robert H.; Wingate, Michael T. D.; Meng, Yong; Chen, Shefa

    2016-07-01

    Ordovician to Devonian sodic granites dominate the newly recognized Luotuojuan composite granite in the Lebaquan-Luotuojuan-Niujuanzi region of Beishan, along the southern margin of the Central Asian Orogenic Belt in NW China. The granites include sodic (K2O/Na2O > 0.5) tonalites with low Y (< 7 ppm), Yb (< 0.7 ppm), high Sr/Y (> 68) that formed during at least two events at c. 435 and c. 370-360 Ma. Their compositions are consistent with high-pressure melting of basaltic crust, although relatively non-radiogenic Nd isotope compositions (εNd(t) + 0.9) require some crustal assimilation. The interpretation that these granites reflect melts of a subducted slab (i.e. adakite) is supported by independent local and regional geological evidence for an oceanic subduction-accretion setting, including a long history of calc-alkaline magmatism and the identification of a series of early Paleozoic ophiolite belts. Other sodic granites forming the Luotuojuan composite granite are mainly quartz-diorite and granodiorite formed between c. 391 and c. 360 Ma. These rocks are not adakites, having Sr concentrations and Sr/Y ratios too low and Y and Yb concentrations too high. They are low- to medium-K calc-alkaline rocks more typical of magmas derived through melting in a subduction modified mantle wedge. Compositional changes from sodic to potassic granites, over time frames consistent with subduction processes, suggest at least two separate cycles, or pulses, of hot subduction in the Lebaquan-Luotuojuan-Niujuanzi region. Although early Paleozoic adakites have been inferred to exist elsewhere in the Beishan region, many of the reported adakitic rocks have compositions inconsistent with melting of subducted oceanic lithosphere and so tectonic interpretation of hot subduction might not be valid in these cases. A study of regional granite data also shows not only that adakite magmatism does not extend into the Permian but that if subduction-accretion processes extended into the late

  12. Landscape Response to Magmatic Uplift

    NASA Astrophysics Data System (ADS)

    O'Hara, D.; Karlstrom, L.

    2016-12-01

    The response of bedrock landscapes to localized perturbations that uplift the land surface remains an outstanding problem in geomorphology. Intrusive magmatism represents the majority of magma input to the crust in volcanic environments, thickening the lithosphere and uplifting the surface. Previous studies have analyzed the effects on channel network and basin geometries caused by long wavelength perturbations in the form of tectonic forcing and dynamic topography from mantle flow. However, the erosional response to small wavelength perturbations caused by magmatic intrusions remains relatively unconstrained. Shallow intrusions may initiate long-term adjustments to the erosional pattern of landscapes through the creation of high-relief landforms. Studying the erosional response to localized uplift may provide contextual clues within modern landscapes that can be used to probe transient incision histories and magmatic flux through time. Using a bedrock landscape evolution model, we analyze landscape response to perturbations similar in scale to laccoliths (shallow magmatic intrusions that uplift overlying bedrock). We study the effects of uplift rate variations, uplift geometry, and position in pre-existing basins on drainage network evolution in the uplifted area and surrounding region. A 1D model provides the template for understanding transient ridge migration induced by localized uplift, which we then extend to a 2D model to study the stability of steady state basin spatial configurations and patterns of transient response. We use a Monte Carlo scheme to sample the wide range of parameters, developing new topographic metrics specific to axisymmetric landforms to characterize intra-basin and channel network reconfigurations and erosion response. We explore the extent to which pre-intruded basin geometries and localized uplift rates can be constrained from modern basin geometry and intruded landform mass distribution.

  13. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Soejono, Igor; Janoušek, Vojtěch; Žáčková, Eliška; Sláma, Jiří; Konopásek, Jiří; Machek, Matěj; Hanžl, Pavel

    2017-09-01

    Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U-Pb data (601 ± 3 Ma, Brno Massif; 634 ± 6 Ma, paraautochtonous core of the Svratka Dome; 568 ± 3 Ma, Bíteš orthogneiss) from the allochtonous Moravicum indicate the prolonged magmatic activity within the Brunovistulian Domain during the Ediacaran. The major- and trace-element and Sr-Nd isotopic signatures show heterogeneous geochemical characteristics of the granitic rocks and suggest a magmatic-arc geotectonic setting. The two-stage Depleted Mantle Nd model ages ( c. 1.3-2.0 Ga) indicate derivation of the granitic rocks from a relatively primitive crustal source, as well as from an ancient and evolved continental crust of the Brunovistulian Domain. These results constrain the magmatic-arc activity to c. 635-570 Ma and provide a further evidence for a long-lived (at least c. 65 Myr) and likely episodic subduction-related magmatism at the northern margin of Gondwana. The presence of granitic intrusions derived from variously mature crustal sources at different times suggests heterogeneous crustal segments to having been involved in the magmatic-arc system during its multistage evolution.

  14. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Soejono, Igor; Janoušek, Vojtěch; Žáčková, Eliška; Sláma, Jiří; Konopásek, Jiří; Machek, Matěj; Hanžl, Pavel

    2016-11-01

    Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U-Pb data (601 ± 3 Ma, Brno Massif; 634 ± 6 Ma, paraautochtonous core of the Svratka Dome; 568 ± 3 Ma, Bíteš orthogneiss) from the allochtonous Moravicum indicate the prolonged magmatic activity within the Brunovistulian Domain during the Ediacaran. The major- and trace-element and Sr-Nd isotopic signatures show heterogeneous geochemical characteristics of the granitic rocks and suggest a magmatic-arc geotectonic setting. The two-stage Depleted Mantle Nd model ages (c. 1.3-2.0 Ga) indicate derivation of the granitic rocks from a relatively primitive crustal source, as well as from an ancient and evolved continental crust of the Brunovistulian Domain. These results constrain the magmatic-arc activity to c. 635-570 Ma and provide a further evidence for a long-lived (at least c. 65 Myr) and likely episodic subduction-related magmatism at the northern margin of Gondwana. The presence of granitic intrusions derived from variously mature crustal sources at different times suggests heterogeneous crustal segments to having been involved in the magmatic-arc system during its multistage evolution.

  15. Tectonic implications of space-time patterns of Cenozoic magmatism in the western United States

    USGS Publications Warehouse

    Snyder, W.S.; Dickinson, W.R.; Silberman, M.L.

    1976-01-01

    Locations of 2,100 radiometrically dated igneous rocks were plotted on a series of 20 maps, each representing an interval within the period 80 m.y. B.P. to present. Derivative maps showing the distributions in space and time of dated granitic intrusive rocks, silicic lavas and domes, ash-flow tuffs, andesitic-dacitic rocks, and basalts depict well the two main petrogenetic assemblages noted previously by others: (1) mainly intermediate andesitic-dacitic suites, including associated granitic intrusive rocks, silicic extrusive rocks, and minor basaltic lavas, are interpreted as reflecting plate interactions related to subduction along the continental margin; and (2) bimodal suites, dominantly basaltic but with minor silicic extrusive rocks, are interpreted as reflecting extensional tectonics. Space-time distribution of the two assemblages suggests that magmatic arcs extended continously parallel to the continental margin from Canada to Mexico in latest Mesozoic and in Oligocene times. An early Cenozoic null in magmatism in the Great Basin may delineate the region where subduction was arrested temporarily by development of the proto-San Andreas fault as a transform in coastal California or, alternatively, may reflect complex subsurface configurations of subducted plates. The late Cenozoic transition from subduction-related magmatism to extention-related basaltic volcanism in the southern Cordillera occurred at different times in different areas in harmony with current concepts about the migration of the Mendocino triple junction as the modern San Andreas transform fault was formed. The plots also reveal the existence of several discrete magmatic loci where igneous activity of various kinds was characteristically more intense and long-lived than elsewhere. ?? 1976.

  16. Grusification of granite (scheme based on the study of granites from Sudety Mts., SW Poland)

    NASA Astrophysics Data System (ADS)

    Kajdas, Bartlomiej; Michalik, Marek

    2014-05-01

    Gruses that are developed on the Karkonosze granite (three outcrops) and the Izera granite (one outcrop) were investigated using optical microscope, scanning electron microscope equipped with EDS and electron microprobe, X-ray diffraction, IR spectrometry, chemical analysis (ICP-AES and ICP-MS), hydrogen and oxygen isotopic ratio determination and K-Ar dating. Three groups of samples were distinguished according to the degree of grusification (group I - compact granite; group II - friable granite; group III - granitic grus). The results of the examination allowed to present the simplified scheme of the grusification: 1. Development of microcracks (caused by tectonic stress, mechanical upload or magma cooling processes) promote circulation of hydrothermal fluids in granites; 2. The presence of the microcracks in granite facilitate the circulation of low-temperature fluids (low-temperature hydrothermal or weathering fluids). Fluids cause hydration and expansion of primary biotite (vermiculitization), what leads to development of secondary cracks in a rock. Fluids can also induce advanced alteration of plagioclases into clay minerals (mainly smectite or vermiculite). Expansion of biotite during vermiculitization is the most important factor in grusification. Other processes of alteration also contribute to grusification. Hydrothermal fluids in granite contribute the increase of alteration degree of primary minerals (e.g. sericitization and albitization of feldspar, chloritization or muscovitization of biotite, decomposition of monazite-(Ce) and formation of secondary REE phosphates). If primary biotite is subjected to muscovitization or chloritization, complete grusification of granite does not occur because of lack of vermiculitation.

  17. Magmatic tempo of Earth's youngest exposed plutons as revealed by detrital zircon U-Pb geochronology.

    PubMed

    Ito, Hisatoshi; Spencer, Christopher J; Danišík, Martin; Hoiland, Carl W

    2017-09-29

    Plutons are formed by protracted crystallization of magma bodies several kilometers deep within the crust. The temporal frequency (i.e. episodicity or 'tempo') of pluton formation is often poorly constrained as timescales of pluton formation are largely variable and may be difficult to resolve by traditional dating methods. The Hida Mountain Range of central Japan hosts the youngest exposed plutons on Earth and provides a unique opportunity to assess the temporal and spatial characteristics of pluton emplacement at high temporal resolution. Here we apply U-Pb geochronology to zircon from the Quaternary Kurobegawa Granite and Takidani Granodiorite in the Hida Mountain Range, and from modern river sediments whose fluvial catchments include these plutons in order to reconstruct their formation. The U-Pb data demonstrate that the Kurobegawa pluton experienced two magmatic pulses at ~2.3 Ma and ~0.9 Ma; whereas, to the south, the Takidani pluton experienced only one magmatic pulse at ~1.6 Ma. These data imply that each of these magmatic systems were both spatially and temporally distinct. The apparent ~0.7 Myr age gap between each of the three magmatic pulses potentially constrains the recharge duration of a single pluton within a larger arc plutonic complex.

  18. Cambro-Ordovician Granites in the Araçuaí Belt, in Brazil: snapshots from a late orogenic collapse

    NASA Astrophysics Data System (ADS)

    De Campos, Cristina P.; Mendes, Júlio Cesar; de Medeiros, Silvia Regina; Ludka, Isabel P.

    2014-05-01

    Along the Brazilian Coast, surrounding the São Francisco Craton and adjacent mobile belts, deep segments of a Neoproterozoic orogen (Araçuaí-West Congo) generated over 120 Ma of successive magmatic episodes of granitic magmatism. The c.630-585 Ma calc-alkaline magmatic arc consists of metatonalite to metagranodiorite, with metadioritic to noritic facies and enclaves. During the syn-collisional and crustal thickening stage (c. 585 to 560 Ma) S-type metagranites have been built by dehydration melting of a diverse package of sediments. Around 545-525 Ma late orogenic crustal remelting formed mostly non-foliated garnet-cordierite leucogranites. In the post-orogenic stage (c. 510-480 Ma) inversely zoned calc-alkaline to alkaline plutons intruded previous units. This work will focus on the youngest post-orogenic magmatism. It will present the state of the art by reviewing structural measurements, detailed mapping of flow patterns and additional geochemical and isotopic data. The architecture of around 10 plutons, ranging from c. 20 to 200 km2 in surface area, unravels deep mushroom- to funnel-like magma chambers and/or conduits. Available data point towards different compositional domains, which are interfingered in complex concentric layers, so that, each pluton depicts a unique internal flow pattern. In the silica-richer structures concentric fragmented or folded layers of granite, in a hybrid K-gabbroic/dioritic matrix, contrast with predominantly homogeneous K-basaltic to gabbroic regions. These may be separated by magmatic shear zones where mixing is enhanced, also resulting in hybrid compositions. Sharp and pillow-like contacts between granitic and K-basaltic rocks locally depict a frozen-in situation of different intrusive episodes. In the silica-poorer plutonic bodies gradational contacts are more frequent and may be the result of convection enhanced diffusion. For all plutons, however, mostly sub-vertical internal contacts between most- and least

  19. Tectonic record, magmatic history and hydrothermal alteration in the Hercynian Guérande leucogranite, Armorican Massif, France

    NASA Astrophysics Data System (ADS)

    Ballouard, C.; Boulvais, P.; Poujol, M.; Gapais, D.; Yamato, P.; Tartèse, R.; Cuney, M.

    2015-04-01

    The Guérande peraluminous leucogranite was emplaced at the end of the Carboniferous in the southern part of the Armorican Massif. At the scale of the intrusion, this granite displays structural heterogeneities with a weak deformation in the southwestern part, whereas the northwestern part is marked by the occurrence of S/C and mylonitic extensional fabrics. Quartz veins and pegmatite dykes orientations as well as lineations directions in the granite and its country rocks demonstrate both E-W and N-S stretching. Therefore, during its emplacement in an extensional tectonic regime, the syntectonic Guérande granite has probably experienced some partitioning of the deformation. The southwestern part is characterized by a muscovite-biotite assemblage, the presence of restites and migmatitic enclaves, and a low abundance of quartz veins compared to pegmatite dykes. In contrast, the northwestern part is characterized by a muscovite-tourmaline assemblage, evidence of albitization and gresenization and a larger amount of quartz veins. The southwestern part is thus interpreted as the feeding zone of the intrusion whereas the northwestern part corresponds to its apical zone. The granite samples display continuous compositional evolutions in the range of 69.8-75.3 wt.% SiO2. High initial 87Sr/86Sr ratios and low εNd(T) values suggest that the peraluminous Guérande granite (A/CNK > 1.1) was formed by partial melting of metasedimentary formations. Magmatic evolution was controlled primarily by fractional crystallization of K-feldspar, biotite and plagioclase (An20). The samples from the apical zone show evidence of secondary muscovitization. They are also characterized by a high content in incompatible elements such as Cs and Sn, as well as low Nb/Ta and K/Rb ratios. The apical zone of the Guérande granite underwent a pervasive hydrothermal alteration during or soon after its emplacement. U-Th-Pb dating on zircon and monazite revealed that the Guérande granite was emplaced

  20. Neutrons and Granite: Transport and Activation

    SciTech Connect

    Bedrossian, P J

    2004-04-13

    In typical ground materials, both energy deposition and radionuclide production by energetic neutrons vary with the incident particle energy in a non-monotonic way. We describe the overall balance of nuclear reactions involving neutrons impinging on granite to demonstrate these energy-dependencies. While granite is a useful surrogate for a broad range of soil and rock types, the incorporation of small amounts of water (hydrogen) does alter the balance of nuclear reactions.

  1. Granite Exfoliation, Cosumnes River Watershed, Somerset, California

    NASA Astrophysics Data System (ADS)

    Crockett, I. Q.; Neiss-Cortez, M.

    2015-12-01

    In the Sierra Nevada foothills of California there are many exposed granite plutons within the greater Sierra Nevada batholith. As with most exposed parts of the batholith, these granite slabs exfoliate. It is important to understand exfoliation for issues of public safety as it can cause rock slides near homes, roads, and recreation areas. Through observation, measuring, and mapping we characterize exfoliation in our Cosumnes River watershed community.

  2. Radiological implications of granite of northern Pakistan.

    PubMed

    Asghar, M; Tufail, M; Sabiha-Javied; Abid, A; Waqas, M

    2008-09-01

    Granite is an igneous rock that contains natural radioactivity of primordial radionuclides. In Pakistan, granite is distributed in a vast area called the Ambela Granitic Complex (AGC) in North West Frontier Province (NWFP). Granite is a hard rock that exists in different colours and is used to decorate floors, kitchen counter tops, etc. The use of granite in a building as a decor material is a potential source of radiation dose; therefore, natural radioactivity has been measured in 20 granite samples of the AGC with an HPGe (high purity germanium) based gamma ray spectrometer. The average specific activities and their range (given in parentheses) for primordial radionuclides (40)K, (226)Ra and (232)Th were 1218 (899-1927), 659 (46-6120) and 598 (92-3214) Bq kg(-1), respectively. The measured activity concentrations were used for the assessment of hazard indices and radiation dose which were evaluated based on the permissible limits defined for these parameters. The measured specific activities and the derived quantities, hazard indices and radiation dose, have been compared with those given in the literature for these parameters.

  3. Permian magmatic sequences of the Bilihe gold deposit in central Inner Mongolia, China: Petrogenesis and tectonic significance

    NASA Astrophysics Data System (ADS)

    Liu, Chunhua; Nie, Fengjun

    2015-08-01

    The Bilihe gold deposit is located in the eastern section of the Ondor Sum-Yanji Suture at the southern margin of the Xing'an-Mongolian Orogenic Belt (XMOB) and the northern margin of the North China Craton (NCC), central Inner Mongolia. The magmatic rocks in the ore district are generally high-K calc-alkaline, enriched in LREE, Zr, and Hf, and depleted in HREE, Nb, Ta, and P. The magmatic evolution sequences are norite gabbro → granodiorite porphyry → granite or norite gabbro → andesite → dacite porphyry → granodiorite, which show a trend of decreasing TiO2, FeO, MgO, CaO, and P2O5 with increasing SiO2. In the Bilihe ore district, hydrothermal processes were coeval with granitic magmatism for a period of ~ 17 Myr (272-255 Ma). The ages of the granite, granodiorite porphyry, granodiorite, and dacite porphyry are 271.5-264.1 Ma, 269.8-255.8 Ma, 268.3 Ma, and 268.6-259.4 Ma, respectively. The magmatic rocks contain magmatic, hydrothermal, and magmatic-hydrothermal zircons. The magmatic zircons have δCe > 4, La < 3 ppm, and SmN/LaN > 2.5; the hydrothermal zircons have δCe < 4, La > 3 ppm, and SmN/LaN < 2.5. The Nb/Ta and Zr/Hf ratios of granodiorite are 12.7-14.99 and 40.2-46.56, respectively. The Zr/Hf ratios successively increase in the sequence of granite (27.4-29.02) → granodiorite porphyry (29.19-32.18) → dacite porphyry (33.54-38.5) → norite gabbro (36.75-38.37), and their Nb/Ta ratios are 9.09-12.38. Zircons in granodiorite yield ε Hf (t) values of - 0.29 to - 56 (n = 13) and 2.07-7.62 (n = 5), and they give a Hf two-stage model age (tDM2) of 807-4765 Ma. The ε Hf (t) values of the zircons in granite, granodiorite porphyry, and dacite porphyry are - 0.46 to 8.03, 3.17 to 10.32, and - 0.78 to 6.58, respectively, and their Hf tDM2 ages are 787-1324 Ma, 638-1091 Ma, and 868-1343 Ma, respectively. Dehydration partial melting of subducted oceanic crust resulted in the formation of dacite porphyry; partial melting of depleted mantle resulted in

  4. The Early Paleozoic Xitieshan syn-collisional granite in the North Qaidam ultrahigh-pressure metamorphic belt, NW China: Petrogenesis and implications for continental crust growth

    NASA Astrophysics Data System (ADS)

    Zhao, Zhixin; Wei, Junhao; Fu, Lebing; Liang, Shengnan; Zhao, Shaoqing

    2017-05-01

    Syn-collisional magmatism produced by partial melting of subducted oceanic and continental crust during the continental collision plays an important role in understanding the orogenic evolution and crustal growth. This contribution reports zircon LA-ICPMS U-Pb ages and Hf isotopic compositions, whole rock major and trace elements and Sr-Nd isotopic compositions of syn-collisional Xitieshan intrusion within the North Qaidam ultrahigh-pressure metamorphic (UHPM) belt, to study its petrogenesis and contribution to continental crust growth. LA-ICPMS zircon U-Pb dating of the Xitieshan granite yields magmatic crystallization ages of 441 ± 2 Ma and 442 ± 2 Ma, which are consistent with the peak age of ultrahigh-pressure eclogite-facies metamorphism in the Xiteishan terrane. The temporal correlation between them confirms that the Xitieshan granite was products of syn-collisional magmatism during the continental collision between Qaidam and Qilian Blocks. These granites show high-K calc-alkaline and slightly peraluminous signature, low zirconium saturation temperatures and high contents of K2O with the S-type characteristics. They have rare earth element and trace element patterns resembling those of bulk continental crust, with strong fractionation of light and heavy rare earth elements ((La/Yb)N = 19-26), moderately Eu negative anomalies (δEu = 0.65-0.71) and the obviously Nb, Ta, P and Ti negative anomalies. The Xitieshan granite also exhibits remarkable Sr-Nd isotopic differences (initial 87Sr/86Sr = 0.70920-0.71080 and εNd(t) = - 4.54-4.11) from the contemporaneous granites within North Qaidam UHPM belt. Combined with the positive εHf (t)(0.5-5.3) and ages of inherited zircons (475-518 Ma), the magmatism is best explained as resulting from melting of subducted oceanic and continental crust during continental collision. Isotopic mixing calculations suggest that ca. 28-35% ocean crust and ca. 65-72% continental materials contribute to the origin of the Xitieshan

  5. Overview of granitic rocks in the Bradfield Canal area, southeastern Alaska

    SciTech Connect

    Koch, R.D. )

    1993-04-01

    Granitic rocks in the Bradfield Canal area of southeastern Alaska are part of the Coast plutonic-metamorphic complex and include rocks representing several different periods of magmatic activity. Units belonging to the previously named Admiralty-Revillagigedo, great tonalite sill, Coast Mountains, and Groundhog Basin-Cone Mountain belts are present. The Texas Creek Granodiorite is located in the southeastern part of the area and is probably 212 Ma or somewhat older. It consists mainly of locally deformed and altered calc-alkalic biotite-hornblende granodiorite and is closely associated with important mineral deposits. Distinguishing features include primary epidote, accessory garnet, and locally a distinctive plagioclase-porphyritic texture. Northeast of the Admiralty-Revillagigedo belt lies the northwest-trending great tonalite sill belt. These rocks are 58--55 Ma and consist of calc-alkalic, generally well-foliated and locally lineated biotite-hornblende and hornblende tonalite, quartz diorite, and granodiorite. The Coast Mountains belt granitic rocks are the most extensive in the area. The granite has been explored for U, Th, and REE deposits. The Coast plutonic-metamorphic complex records dynamothermal and regional contact metamorphic events related to the regional plutonism. Most of the lengthy and complicated magmatic and metamorphic history of the complex is related to Late Cretaceous collision of the Alexander and Wrangellia terranes and juxtaposition of the Gravina overlap assemblage to the west (Superterrane II) against the Yukon prong and Stikine terrane to the east (Superterrane I). An exception is the Texas Creek Granodiorite, which is related to a pre-accretionary Jurassic arc in the Stikine terrane.

  6. Petrology and mineral chemistry of peraluminous Marziyan granites, Sanandaj-Sirjan metamorphic belt (NW Iran)

    NASA Astrophysics Data System (ADS)

    Darvishi, Esmaiel; Khalili, Mahmoud; Beavers, Roy; Sayari, Mohammad

    2015-10-01

    The Marziyan granites are located in the north of Azna and crop out in the Sanandaj-Sirjan metamorphic belt. These rocks contain minerals such as quartz, K-feldspars, plagioclase, biotite, muscovite, garnet, tourmaline and minor sillimanite. The mineral chemistry of biotite indicates Fe-rich (siderophyllite), low TiO2, high Al2O3, and low MgO nature, suggesting considerable Al concentration in the source magma. These biotites crystallized from peraluminous S-type granite magma belonging to the ilmenite series. The white mica is rich in alumina and has muscovite composition. The peraluminous nature of these rocks is manifested by their remarkably high SiO2, Al2O3 and high molar A/CNK (> 1.1) ratio. The latter feature is reflected by the presence of garnet and muscovite. All field observations, petrography, mineral chemistry and petrology evidence indicate a peraluminous, S-type nature of the Marziyan granitic rocks that formed by partial melting of metapelite rocks in the mid to upper crust possibly under vapour-absent conditions. These rocks display geochemical characteristics that span the medium to high-K and calc-alkaline nature and profound chemical features typical of syn-collisional magmatism during collision of the Afro-Arabian continental plate and the Central Iranian microplate.

  7. An example of Precambrian channel flow: Anasagar granite revisited near Ajmer, Rajasthan, India.

    NASA Astrophysics Data System (ADS)

    De, Keyur; Dasgupta, Nandini; Dasgupta, Nilanjan

    2014-05-01

    Anasagar Granite Gneiss is exposed in the northern part of the South Delhi Fold Belt, around Ajmer city, western India. It is a K-feldspar megacrystic granite gneiss, emplaced as a concordant sheet like body emplaced within and deformed along with the metasediments of South Delhi Fold Belt (Lopez et al, 1996). The gneiss and its enveloping supracrustals are deformed by polyphase folding, producing a gneissic dome. Field observation suggests that the grain size of the gneiss varies from core to the contact with the associated meta-sediments. Within the core of the granite megacrysts with lengths of 1 to 5 cm are embedded within a gneissic matrix, defined by alternate medium to fine grained felsic (quartz or feldspar) materials and foliated layers predominantly of mafic (biotite and hornblende) composition. The same granite becomes fine grained looking like quartz-biotite-muscovite schist at the margin. Shearing along the granite margin during subsequent deformation has been proposed (Chattopadhyay et al, 2006), leading to grain refinement. To the contrary we believe that the fine grained nature of the contact zone is a primary feature developed due to quick chilling of the magma along its margin. The map pattern shows that the contact zone in the western part has a persistent thickness of 10m on an average. We test the hypothesis of shearing vis-à-vis granite magma flowage structure and probe the microstructural evidences in support of this hypothesis. We propose that differential flowage between the viscous granite magma in the interior domains with respect to the quickly chilled fine grained boundary during emplacement has rotated, stretched and aligned the crystallizing grains to the flow direction along the magmatic foliation. A comparative study of the types of microstructures between the core and the margin of the granite reveal the extent of annealing during later deformation episodes. There is a positive trend of recrystallization in the quartz grains from

  8. Formation of Hadean granites by melting of igneous crust

    NASA Astrophysics Data System (ADS)

    Burnham, A. D.; Berry, A. J.

    2017-06-01

    The oldest known samples of Earth, with ages of up to 4.4 Gyr, are detrital zircon grains in meta-sedimentary rocks of the Jack Hills in Australia. These zircons offer insights into the magmas from which they crystallized, and, by implication, igneous activity and tectonics in the first 500 million years of Earth’s history, the Hadean eon. However, the compositions of these magmas and the relative contributions of igneous and sedimentary components to their sources have not yet been resolved. Here we compare the trace element concentrations of the Jack Hills zircons to those of zircons from the locality where igneous (I-) and sedimentary (S-) type granites were first distinguished. We show that the Hadean zircons crystallized predominantly from I-type magmas formed by melting of a reduced, garnet-bearing igneous crust. Further, we propose that both the phosphorus content of zircon and the ratio of phosphorus to rare earth elements can be used to distinguish between detrital zircon grains from I- and S-type sources. These elemental discriminants provide a new geochemical tool to assess the relative contributions of primeval magmatism and melting of recycled sediments to the continents over geological time.

  9. Lithospheric delamination in post-collisional setting: Evidence from intrusive magmatism from the North Qilian orogen to southern margin of the Alxa block, NW China

    NASA Astrophysics Data System (ADS)

    Zhang, Liqi; Zhang, Hongfei; Zhang, Shasha; Xiong, Ziliang; Luo, Biji; Yang, He; Pan, Fabin; Zhou, Xiaochun; Xu, Wangchun; Guo, Liang

    2017-09-01

    Post-collisional granitoids are widespread in the North Qilian and southern margin of the Alxa block and their petrogenesis can provide important insights into the lithospheric processes in a post-collisional setting. This paper carries out an integrated study of U-Pb zircon dating, geochemical and Sr-Nd-Hf isotopic compositions for five early Paleozoic intrusive plutons from the North Qilian to southern margin of the Alxa block. The geochronological and geochemical results show that their magmatism can be divided into three periods with distinct geochemical features. The early-period intrusive rocks ( 440 Ma) include the Lianhuashan (LHS) and Mengjiadawan (MJDW) granodiorites. Both of them display high Sr/Y ratios (52-91), coupled with low Y and HREE contents, implying that they were derived from partial melting of thickened lower crust, with garnet in the residue. The middle-period intrusive rocks ( 430 Ma), including the MJDW quartz diorites and Yangqiandashan (YQDS) granodiorites, are high-K calc-alkaline with low Sr/Y values. The geochemical and isotopic data suggest that they are generated from partial melting of lower crust without garnet in the residue. The late-period intrusive rocks (414-422 Ma), represented by the Shengrongsi (SRS) and Xinkaigou (XKG) plutons, are A-type or alkali-feldspar granites. They are possibly derived from partial melting of felsic crustal material under lower pressure condition. Our data show decreasing magma crystallization ages from MJDW pluton in the north and LHS pluton in the south to the SRS and XKG plutons in the central part of the study area. We suggest that such spatial and temporal variations of magmatic suites were caused by lithospheric delamination after the collision between the Central Qilian and the Alxa block. A more plausible explanation is that the delamination propagated from the margin part of the thickened lithosphere to inward beneath the North Qilian and southern margin of the Alxa block.

  10. Structure of the Castillo granite, Southwest Spain: Variscan deformation of a late Cadomian pluton

    NASA Astrophysics Data System (ADS)

    EguíLuz, L.; Apraiz, A.; ÁBalos, B.

    1999-12-01

    A geometrical reconstruction of the 500 Ma old Castillo granite pluton (SW Iberia) is completed on the basis of structural and geophysical (rock magnetism) techniques. The pluton is intrusive into latest Proterozoic-earliest Cambrian metasediments and conforms a tabular intrusion 6 km in diameter and 1.7 km thick that was emplaced at a depth of 10 km. Its magnetic fabric reveals that the strike of moderately to steeply dipping magmatic flow planes forms a high angle to the regional tectonic trends. Magnetic foliations and associated moderately to gently plunging magnetic lineations represent magmatic flow planes and directions. The internal anisotropy of the granite together with the structure shown by the country rocks attest the lateral propagation of the pluton and its latter inflation. The pluton's root zone would correspond to a likely thin, subvertical feeder structure initiated near the orientation of regional σ1 at the time of emplacement. During the Variscan orogeny the pluton was tilted and underwent localized brittle-ductile strain in relation to shear zone deformation in the footwall of a major ductile thrust. Tilting permits the observation and study of a vertical profile of the intrusion. Localized deformation caused superposition of tectonic zonations on the magmatic ones, a reactivation of the basal contact of the pluton, and dismemberment from its root. This and other granitoid plutons of similar age emplaced at a similar depth constrained the creation of crustal mechanical heterogeneity and anisotropy. This controlled the site of pluton emplacement, the nucleation of a major ductile thrust, and localization of deformation and tectonic displacements along the pluton margins during later orogenic reactivation.

  11. Apatite as a Tool for Tracking Magmatic CO2 Contents

    NASA Astrophysics Data System (ADS)

    Riker, J.; Humphreys, M.; Brooker, R. A.

    2014-12-01

    CO2 plays a fundamental role in the evolution of magmatic and volcanic systems, but its low solubility in silicate melts means that direct records of magmatic CO2 concentrations remain elusive. The phosphate mineral apatite is unique among igneous minerals in its capacity to accommodate all major magmatic volatiles (H2O, F, Cl, CO2 and S). Although interest in apatite as a tool for tracking magmatic volatile contents (namely H2O, F, and Cl) has increased in recent years, its potential as a record of magmatic CO2contents remains untapped. We present the results of high-temperature, high-pressure experiments investigating the partitioning behaviour of CO2 between apatite and basaltic melt. Experiments were run in piston cylinder apparatus at 1 GPa and 1250 °C, with a slow initial cooling ramp employed to facilitate crystal growth. Each charge contained the starting basaltic powder doped with Ca-phosphate and variable proportions of H2O, CO2, and F. Run products are glass-rich charges containing 15-25 vol% large, euhedral apatite crystals (± cpx and minor biotite). Experimental apatites and glasses have been characterised by BSE imaging, electron microprobe, and ion microprobe. Apatites range in composition from near-endmember fluorapatite (3.0 wt% F), to near-endmember hydroxyapatite (1.7 wt% H2O), to carbon-rich apatite containing up to 1.6 wt% CO2. Apatite compositions are stoichiometric if all anions (F-, OH-, and CO32—) lie in the channel site, suggesting an "A-type" substitution under these conditions (i.e. CO32— + [] = 2X—, where X is another channel anion and [] is a vacancy; e.g. Fleet et al. 2004). Importantly, CO2 partitions readily into apatite at all fluid compositions considered here. CO2 is also more compatible in apatite than water at our run conditions, with calculated H2O-CO2 exchange coefficients close to or greater than 1. Our results indicate that when channel ions are primarily occupied by H2O and CO2 (i.e. F- and Cl-poor magmatic systems

  12. Tourmaline occurrences within the Penamacor-Monsanto granitic pluton and host-rocks (Central Portugal): genetic implications of crystal-chemical and isotopic features

    NASA Astrophysics Data System (ADS)

    da Costa, I. Ribeiro; Mourão, C.; Récio, C.; Guimarães, F.; Antunes, I. M.; Ramos, J. Farinha; Barriga, F. J. A. S.; Palmer, M. R.; Milton, J. A.

    2014-04-01

    granitic melts, implying loss of B and other volatiles to the surrounding host-rocks during the late-magmatic stages. This process was responsible for tourmalinization at the exocontact of the Penamacor-Monsanto pluton, either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin (vein/breccia tourmalinites), or as replacement of mafic minerals (chlorite or biotite) in the host-rocks (replacement tourmalinites) along the exocontact of the granite. Thermometry based on 18O equilibrium fractionation between tourmaline and fluid indicates that a late, B-enriched magmatic aqueous fluid (av. δ18O ~12.1 ‰, at ~600 °C) precipitated the vein/breccia tourmaline (δ18O ~12.4 ‰) at ~500-550 °C, and later interacted with the cooler surrounding host-rocks to produce tourmaline at lower temperatures (400-450 °C), and an average δ18O ~13.2 ‰, closer to the values for the host-rock. Although B-metasomatism associated with some granitic plutons in the Iberian Peninsula seems to be relatively confined in space, extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of Variscan magmatism and related mineralizations.

  13. Contribution of Columbia and Gondwana Supercontinent assembly- and growth-related magmatism in the evolution of the Meghalaya Plateau and the Mikir Hills, Northeast India: Constraints from U-Pb SHRIMP zircon geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Rino, Vikoleno; Hayasaka, Yasutaka; Kimura, Kosuke; Raju, Shunmugam; Terada, Kentaro; Pathak, Manjari

    2017-04-01

    The Meghalaya Plateau and the Mikir Hills constitute a northeastern extension of the Precambrian Indian Shield. They are dominantly composed of Proterozoic basement granite gneisses, granites, migmatites, granulites, the Shillong Group metasedimentary cover sequence, and Mesozoic-Tertiary igneous and sedimentary rocks. Medium to coarse grained, equigranular to porphyritic Cambrian granite plutons intrude the basement granite gneisses and the Shillong Group. U-Pb SHRIMP zircon geochronology and geochemistry of the granite gneisses and granites have been carried out in order to understand the nature and timing of granite magmatism, supercontinent cycles, and crustal growth of the Meghalaya Plateau and Mikir Hills. Zircons from the Rongjeng granite gneiss record the oldest magmatism at 1778 ± 37 Ma. An inherited zircon core has an age of 2566.4 ± 26.9 Ma, indicating the presence of recycled Neoarchaean crust in the basement granite gneisses. Zircons from the Sonsak granite have two ages: 523.4 ± 7.9 Ma and 1620.8 ± 9.2 Ma, which indicate partial assimilation of an older granite gneiss by a younger granite melt. Zircons from the Longavalli granite gneiss of the Mikir Hills has a crystallization age of 1430.4 ± 9.6 Ma and a metamorphic age of 514 ± 18.6 Ma. An inherited core of a zircon from Longavalli granite gneiss has an age of 1617.1 ± 14.5 Ma. Zircons from younger granite plutons have Cambrian mean ages of 528.7 ± 5.5 Ma (Kaziranga), 516 ± 9.0 Ma (South Khasi), 512.5 ± 8.7 Ma (Kyrdem), and 506.7 ± 7.1 Ma and 535 ± 11 Ma (Nongpoh). These plutons are products of the global Pan-African tectonothermal event, and their formation markedly coincides with the later stages of East Gondwana assembly (570-500 Ma, Kuunga orogen). The older inherited zircon cores (2566.4 ± 26.9 Ma, 1758.1 ± 54.3 Ma, 1617.1 ± 14 Ma) imply a significant role for recycled ancient crust in the generation of Cambrian granites. Thus the Meghalaya Plateau and Mikir Hills experienced

  14. FROGS Report Friends of Granite Summer 1989

    NASA Astrophysics Data System (ADS)

    FROGS Reports present information on current research relevant to felsic magmatism, including commentaries on problems of current interest. Please contact Calvin Miller (6028B, Vanderbilt University, Nashville, TN 37235) concerning your own research, conferences, and ideas for stimulating commentaries.

  15. Magmatic and tectonic modification of convergent margins: An example from southern Alaska

    NASA Astrophysics Data System (ADS)

    Farris, David W.

    Southern Alaska is an excellent natural laboratory to study forearc/arc subduction zone magmatism and tectonics. Understanding these processes are important to understanding the evolution and modification of continental crust. This thesis focuses on the Kodiak Islands, but also examines larger-scale features throughout southern Alaska and cordilleran tectonics. Kodiak Island intrusive rocks differ in character across the Border Ranges fault system (BRF). North of the BRF is the tilted Triassic-Jurassic Talkeetna island arc. This arc section exposes ultramafic mantle through mid to upper crustal plutonic and volcanic rocks all of which are geochemically related, despite being fault-bounded blocks. South of the BRF lie Paleocene intrusive rocks related to eastward spreadingridge subduction migration. These rocks are distributed in two belts: the Kodiak batholith and the trenchward belt. The Kodiak batholith is composed of granitic plutons emplaced as a series of intermingled, 1-8 km wide, viscoelastic diapirs that ascended by downward transport of aureole rocks through and around the magmatic column, and range in age from 59.2-58.4+/-0.2 Ma (SW-NE). These plutons formed from equilibrium crystallization of an argillite/graywacke derived magma, and contain fractally fragmented meta-sedimentary xenoliths. Trenchward belt rocks lie south of the Contact fault and are composed of small gabbroic to granitic plutons, dikes and pillows that range in age from 62.6+/-0.6-60.15+/-0.86 Ma (SW-NE). They formed by assimilation fractional crystallization of MORB with an argillite assimilant. Trenchward belt rocks intruded when a spreading ridge first entered the accretionary prism, whereas the Kodiak batholith formed when a slab window opened at 15-20 km depth. Age differences between the two Paleocene magmatic belts are explained by oblique ridge subduction and Contact fault displacement. The Kodiak batholith is part of the 2100 km Sanak-Baranof belt of forearc magmatism. Along

  16. Crustal Structure And Magmatism, Coast Mountains Orogen, Latitude 52-53 degrees North, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    Rusmore, M. E.; Gehrels, G.; Woodsworth, G. J.

    2007-12-01

    New geologic data and U-Pb ages reveal complex history of arc accretion, crustal thickening and migration of magmatic fronts during deformation. Plutonic ages define distinct western and eastern Jurassic - mid Cretaceous arcs that share a common history after ~90 Ma. Juxtaposition of these arcs occurred during mid- Cretaceous crustal shortening in a dominantly SW-vergent crustal-scale thrust belt. Significant crustal thickening buried 151 Ma granitic clasts to pressures > 6 kb, and mid-Cretaceous plutons were emplaced at this depth along the axis of the orogen. Thrusting continued after establishment of the 90 Ma arc; a regional SW-verging thrust emplaced high-grade metamorphic rocks of the Yukon-Tanana terrane and deep-seated plutons over low- grade rocks of the Alexander and Wrangellia terranes. The shear zone is coincident with the western boundary of 82-89 Ma plutons and a regionally extensive, late-kinematic, sill-like pluton. Dextral shear zones preserved on the flanks of the orogen suggest a component of Late Cretaceous transpression. By 75 Ma, metamorphism, deformation, and magmatism had migrated central portions of the orogen and there is no evidence of ductile deformation and syn-kinematic metarmorphism younger than ~70 - 65 along the western flank of the orogen. The Coast shear zone localized 62-58 Ma synkinematic plutons during NE-side up displacement, creating a sharp western magmatic front. Sparse cooling ages suggest plutons and metamorphic rocks adjacent to the CSZ cooled through 500-600 deg between 54-58 Ma during exhumation along the shear zone. Voluminous granitic plutons were emplaced from ~55-50 Ma, but significant crustal extension that affected the eastern side of the orogen farther north is not evident along this transect. This history supports previous models of crustal subcretion and the generation of arc magmas in thickened crust. Definition of two pre-90 Ma arcs negates models calling for simple Andean-style orogen prior to mid

  17. Variscan Collisional Magmatism and Deformation In The Viseu Area (northern Central Portugal) - Constraints From U-pb Geochronology of Granitoids

    NASA Astrophysics Data System (ADS)

    Azevedo, M. R.; Aguado, B. V.; Scaltegger, U.; Nolan, J.; Martins, M. R.; Medina, J.

    The Viseu area is located in the innermost zone of the Iberian Variscan Fold Belt (the Central Iberian Zone). It consists of abundant post-thickening, collision related grani- toids intruded into upper and middle crustal levels. The ascent of granite magmas took place after an extensional tectonic event (D2) and is coeval with D3 dextral and sinis- tral crustal-scale transcurrent shear zones. In the northern part of the area, the presence of a well preserved Upper Carboniferous tectonic basin filled with deformed conti- nental clastic sediments, bounded by contemporaneously exhumed deep crustal rocks and intruded by late-tectonic granites documents an episode of extension involving basin subsidence, uplift and erosion of the basement and granite magmatism in a post- thickening, but syn-convergent scenario. Convergence is manifested by strike-slip tec- tonics and basin inversion. According to structural criteria, the Variscan granitoids can be subdivided into two major groups: (1) syn-D3 granitoids including two dif- ferent petrological associations, highly peraluminous leucogranite and granodiorite- monzogranite intrusions and (2) late-D3 granitoids comprising slightly metaluminous to peraluminous granodiorites and monzogranites. Four plutons representing the syn- D3 leucogranites (Junqueira) and monzogranites (Maceira and Casal Vasco) and the late-D3 biotite granites (Cota) yielded U-Pb zircon + monazite or monazite ages of 310 Ma, 311 Ma, 311 Ma and 306 Ma, respectively. This points to a synchronous emplacement of the different syn-D3 plutons shortly followed by the intrusion of the late-D3 granites and suggests that the Upper Carboniferous plutonism occurred within a short time span of ca. 5 myr. Stratigraphic markers show that the oldest continental sediments in the Carboniferous basin are Westphalian whilst field relationships in- dicate that the deformation occurred prior to the intrusion of the late-D3 granitoids. Precise U-Pb geochronology proves that basin

  18. Fluid-driven destabilization of REE-bearing accessory minerals in the granitic orthogneisses of North Veporic basement (Western Carpathians, Slovakia)

    NASA Astrophysics Data System (ADS)

    Ondrejka, M.; Putiš, M.; Uher, P.; Schmiedt, I.; Pukančík, L.; Konečný, P.

    2016-10-01

    A variety of rare earth elements-bearing (REE) accessory mineral breakdowns were identified in granitic orthogneisses from the pre-Alpine basement in the Veporic Unit, Central Western Carpathians, Slovakia. The Ordovician granitic rocks were subjected to Variscan metamorphic-anatectic overprint in amphibolite facies. Chemical U-Th-Pb dating of monazite-(Ce) and xenotime-(Y) reveal their primary magmatic Lower to Middle Ordovician age (monazite: 472 ± 4 to 468 ± 6 Ma and xenotime: 471 ± 13 Ma) and/or metamorphic-anatectic Variscan (Carboniferous, Visean) age (monazite: 345 ± 3 Ma). Younger fluid-rock interactions caused breakdown of primary magmatic and/or metamorphic-anatectic monazite-(Ce), xenotime-(Y), fluorapatite and allanite-(Ce). Fluid-induced breakdown of xenotime-(Y) produced numerous tiny uraninite inclusions within the altered xenotime-(Y) domains. The monazite-(Ce) breakdown produced secondary egg-shaped coronal structures of different stages with well-developed concentric mineral zones. Secondary sulphatian monazite-(Ce) (up to 0.15 apfu S) occasionally formed along fluorapatite fissures. Localized fluorapatite and monazite-(Ce) recrystallization resulted in a very fine-grained, non-stoichiometric mixture of REE-Y-Fe-Th-Ca-P-Si phases. Finally, allanite-(Ce) decomposed to secondary REE carbonate minerals (members of the bastnäsite and synchysite groups) and calcite in some places. Although the xenotime alteration and formation of uraninite inclusions is believed to be the result of dissolution-reprecipitation between early magmatic xenotime and late-magmatic granitic fluids, the monazite, apatite and allanite breakdowns were driven by metamorphic hydrothermal fluids. While earlier impact of post-magmatic fluids originated probably from Permian acidic volcanic and microgranitic veins crosscutting the orthogneisses, another fluid-rock interaction event most likely occurred during Late Cretaceous metamorphism in the Veporic basement and covering

  19. Melting mud in Earth's mantle, evidence from sub-Moho S-type granites with extreme oxygen isotope signatures

    NASA Astrophysics Data System (ADS)

    Spencer, C. J.; Cavosie, A. J.; Raub, T. D.; Rollinson, H. R.; Searle, M. P.; Miller, J. A.; Jeon, H.; Evans, N.; McDonald, B.

    2016-12-01

    The role of sediment melting in Earth's mantle and its subsequent incorporation into volcanic arc magmas remains controversial, as direct observation of melt generation in the mantle is not possible. Geochemical fingerprints of sediment provide strong indirect evidence for subduction delivery of surface materials to the mantle, however sediment abundance in mantle-derived melt such as basalt is generally low (0-2%), and difficult to detect. Here, we provide compelling evidence for bulk melting of subducted marine sediment in the mantle through analysis of granite preserved within an exhumed mantle section. Peraluminous granite dykes intruding peridotite below the petrologic Moho in the Oman-UAE ophiolite have unusually high oxygen isotope (δ18O) values for whole rock and quartz, and host magmatic zircon with the highest δ18O values ever reported, up to 27‰ (relative to VSMOW). The extremely high oxygen isotope ratios uniquely restrict the source to high δ18O siliceous marine sediment (i.e. mud; includes shale and chert or siliceous ooze), as no other source rock could produce granite with such anomalously high δ18O. Elemental composition, mineralogy, and zircon Hf identifies the granite suite as S-type, having formed by melting of supracrustal material. Zircon U-Pb ages of 100 Ma confirms a pre-obduction age of the dykes. The formation of high δ18O S-type granite within mantle peridotite has not been documented previously, and requires delivery of high δ18O marine sediment to the asthenosphere by subduction, where it melted and intruded overlying mantle wedge. The S-type granite suite intrusive to the mantle in the Oman-UAE ophiolite contains the most evolved oxygen isotope ratios reported for igneous rocks. Quantifying the extent of sediment melting within the mantle has important consequences for understanding crustal recycling and mantle heterogeneity over time.

  20. Source regions of granites and their links to tectonic environment: examples from the western United States

    NASA Astrophysics Data System (ADS)

    Anthony, Elizabeth Y.

    2005-03-01

    This review, in honor of Ilmari Haapala's retirement, reflects on lessons learned from studies of three granitic systems in western North America: (1) Mesoproterozoic samples from west Texas and east New Mexico; (2) Laramide granitic systems associated with porphyry-copper deposits in Arizona; and (3) granites of the Colorado Mineral Belt. The studies elucidate relationships amongst tectonic setting, source material, and magma chemistry. Mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions. The first suite, the "plutonic province", is dominantly magnesian, calc-alkalic to alkali-calcic, and metaluminous. It has low K 2O/Na 2O and Rb/Sr, and Nd model ages of 1.56 to 1.40 Ga. The second suite, the "Panhandle igneous complex", is magnesian, metaluminous, alkalic, and is part of the Mesoproterozoic belt of magmatism that extends from Finland to southwestern United States. Samples from the Panhandle igneous complex demonstrate three episodes of magmatism: the first pulse was intrusion of quartz monzonite at 1380 to 1370 Ma; the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 Ma. Both of these rock types are high-K to slightly ultra-high-K. The third pulse at 1338 to 1330 Ma was intrusion of ultra-high-K quartz syenite. Nd model ages (1.94 to 1.52 Ga) are distinct from those of the "plutonic province" and systematically older than crystallization ages, implying a substantial crustal input to the magmas. At the Sierrita porphyry-copper deposit in the Mazatzal Province of southeastern Arizona, trace element, Sr, and Nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks (67 Ma) intruded by granodiorite and granite. Isotopic composition and chemical evolution are well correlated throughout the suite. Andesite has the least negative initial ɛNd (-4.3) and lowest 87Sr/ 86Sr i (0.7069). It is also the oldest and chemically most primitive, having low

  1. Origin of late Archean granite: geochemical evidence from the Vermilion Granitic Complex of northern Minnesota

    NASA Astrophysics Data System (ADS)

    Day, Warren C.; Weiblen, P. W.

    1986-07-01

    The 2,700-Ma Vermilion Granitic Complex of northern Minnesota is a granite-migmatite terrane composed of supracrustal metasedimentary rocks, mafic rocks, tonalitic and granodioritic plutonic rocks, and granite. The metasedimentary rocks are predominantly graywacke, which has been regionally metamorphosed to garnet-sillimanite-muscovite-bearing biotite schist, and has locally undergone anatexis. The mafic rocks form early phases within the complex and are of two types: (1) basaltic amphibolite, and (2) monzodiorite and essexite rich in large ion lithophile elements (LILE). The members of the early plutonic suite form small bodies that intrude the metasedimentary rocks and mafic rocks, producing an early migmatite. The granite is of two distinct varieties: (1) white garnet-muscovite-biotite leucogranite ( S-type; Chappell and White 1974) and (2) grayish-pink biotite-magnetite Lac La Croix Granite ( I-type). The leucogranite occurs in the early migmatite and in paragneissic portions of the complex, whereas the Lac La Croix Granite is a late-stage intrusive phase that invades the early migmatite and metasediment (producing a late migmatite) and forms a batholith. This study focuses specifically on the origin of granite in the Vermilion Granitic Complex. Chemical mass-balance calculations suggest that the S-type two-mica leucogranite had a metagraywacke source, and that the I-type Lac La Croix Granite formed via partial fusion of calc-alkaline tonalitic material, which may have been similar to rocks of the early plutonic suite. This model is satisfactory for petrogenesis of similar Late Archean post-kinematic granites throughout the Canadian Shield.

  2. Origin of late Archean granite: geochemical evidence from the Vermilion Granitic Complex of northern Minnesota

    USGS Publications Warehouse

    Day, W.C.; Weiblen, P.W.

    1986-01-01

    The 2,700-Ma Vermilion Granitic Complex of northern Minnesota is a granite-migmatite terrane composed of supracrustal metasedimentary rocks, mafic rocks, tonalitic and granodioritic plutonic rocks, and granite. The metasedimentary rocks are predominantly graywacke, which has been regionally metamorphosed to garnet-sillimanite-muscovite-bearing biotite schist, and has locally undergone anatexis. The mafic rocks form early phases within the complex and are of two types: (1) basaltic amphibolite, and (2) monzodiorite and essexite rich in large ion lithophile elements (LILE). The members of the early plutonic suite form small bodies that intrude the metasedimentary rocks and mafic rocks, producing an early migmatite. The granite is of two distinct varieties: (1) white garnet-muscovite-biotite leucogranite (S-type; Chappell and White 1974) and (2) grayish-pink biotite-magnetite Lac La Croix Granite (I-type). The leucogranite occurs in the early migmatite and in paragneissic portions of the complex, whereas the Lac La Croix Granite is a late-stage intrusive phase that invades the early migmatite and metasediment (producing a late migmatite) and forms a batholith. This study focuses specifically on the origin of granite in the Vermilion Granitic Complex. Chemical mass-balance calculations suggest that the S-type two-mica leucogranite had a metagraywacke source, and that the I-type Lac La Croix Granite formed via partial fusion of calc-alkaline tonalitic material, which may have been similar to rocks of the early plutonic suite. This model is satisfactory for petrogenesis of similar Late Archean post-kinematic granites throughout the Canadian Shield. ?? 1986 Springer-Verlag.

  3. S-type granitic magmas—petrogenetic issues, models and evidence

    NASA Astrophysics Data System (ADS)

    Clemens, J. D.

    2003-04-01

    . They represent globules of quenched, more mafic magma mingled and modified by exchange with the host granitic magma. However, magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas. Likewise, the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and, in some cases, violate constraints from isotopic studies. S- and I-type magmas commonly retain their distinct identities. This suggests limited source mixing, limited magma mixing and limited wall-rock assimilation. Though intermediate types certainly exist, they are probably relatively minor in volume. Crystal fractionation probably plays the major role in the differentiation of very many granitic magmas, including most S-types, especially those emplaced at high crustal levels or in the volcanic environment. Minor mechanisms include magma mixing, wall-rock assimilation and restite unmixing. Isotopic variations within plutons and in granite suites could be caused by source heterogeneities, magma mixing, assimilation and even by isotopic disequilibrium. However, source heterogeneity, coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity. Normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust, and crustal thickening likewise fails to provide sufficient heat. Generally, the mantle must be the major heat source. This might be provided through mantle upwelling and crustal thinning, and possibly through the intra- and underplating of mafic magmas. Upper crustal extension seems to have been common in regions undergoing granitic magmatism. Migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid-present reactions. Granitic magmas are mostly formed by fluid-absent processes. Where we do see rare evidence for arrested fluid-absent partial melting, the melt fraction is invariably

  4. Post-orogenic shoshonitic magmas of the Yzerfontein pluton, South Africa: the `smoking gun' of mantle melting and crustal growth during Cape granite genesis?

    NASA Astrophysics Data System (ADS)

    Clemens, J. D.; Buick, I. S.; Frei, D.; Lana, C.; Villaros, A.

    2017-09-01

    The post-orogenic Yzerfontein pluton, in the Saldania Belt of South Africa was constructed through numerous injections of shoshonitic magmas. Most magma compositions are adequately modelled as products of fractionation, but the monzogranites and syenogranites may have a separate origin. A separate high-Mg mafic series has a less radiogenic mantle source. Fine-grained magmatic enclaves in the intermediate shoshonitic rocks are autoliths. The pluton was emplaced between 533 ± 3 and 537 ± 3 Ma (LA-SF-ICP-MS U-Pb zircon), essentially synchronously with many granitic magmas of the Cape Granite Suite (CGS). Yzerfontein may represent a high-level expression of the mantle heat source that initiated partial melting of the local crust and produced the CGS granitic magmas, late in the Saldanian Orogeny. However, magma mixing is not evident at emplacement level and there are no magmatic kinships with the I-type granitic rocks of the CGS. The mantle wedge is inferred to have been enriched during subduction along the active continental margin. In the late- to post-orogenic phase, the enriched mantle partially melted to produce heterogeneous magma batches, exemplified by those that formed the Yzerfontein pluton, which was further hybridised through minor assimilation of crustal materials. Like Yzerfontein, the small volumes of mafic rocks associated with many batholiths, worldwide, are probably also low-volume, high-level expressions of crustal growth through the emplacement of major amounts of mafic magma into the deep crust.

  5. Re-examination of models for the origin of granite-rhyolite provinces in the midcontinent region, USA

    SciTech Connect

    Van Schmus, W.R. . Dept. of Geology)

    1993-03-01

    New isotopic data for the 1.47 Ga Eastern Granite-Rhyolite Province and the 1.37 Ga Southern Granite-Rhyolite Province require re-examination of models for the origin of these suites of rock. For the most part, eNd(t) values for the granite-rhyolite provinces and A-type plutons intrusive into adjacent Early proterozoic basement are compatible with origin through melting of 1.8 Ga continental crust. However, new data shows that southeastern parts of the granite-rhyolite provinces yield positive [var epsilon]Nd(t) data is an E-W trending belt of intermediate values in northern Oklahoma; [var epsilon]Nd(t) data south of this belt, in s. Oklahoma, are equivalent to that in Kansas and Nebraska, reflecting cal 1.8 Ga lower crust. The granite-rhyolite provinces are not related to any well defined tectonic event, and they have commonly been referred to as anorogenic. The thermal event responsible for producing the silicic melts may have been associated with an extensional regime, in view of the a-type character of the granites.

  6. Estimation of crystallization pressure of granite intrusions

    NASA Astrophysics Data System (ADS)

    Yang, Xue-Ming

    2017-08-01

    A numerical method is presented to estimate the crystallization pressure of granite intrusions based on two polynomial equations obtained by an analysis of the existing haplogranite ternary phase diagram and associated dataset. The results indicate that the pressure is correlated respectively with normative quartz (Qtz) content and with normative albite (Ab) plus orthoclase (Or) contents of granitic rocks as follows. where P is pressure in MPa, and R denotes correlation coefficient. It is noted that the procedure of normalizing the sum of CIPW norm (quartz, albite, orthoclase) contents to 100% is required before using Eqs. (1) and (2). The difference in pressure calculations between these two equations is ≤ 16 MPa for the range of normative quartz contents from 15 to 40 wt%. An example of how to use these equations to estimate the crystallization pressure of a granite intrusion is also provided to show the validity and convenience of this method. The uncertainty of such pressure estimation is not well known, although it must fall into the uncertainty range of the existing experimental work on pressure constraints. The simplicity of this empirical method is appreciable, although its applicability to natural granitoids needs further test. More experimental work is required to constrain the effects of components, such as CaO, FeO, MgO, F, Cl, CO2, on the granite phase equilibria. These equations, however, can be used for estimating crystallization pressures of water-saturated and quartz-oversaturated granitic systems.

  7. Frictional slip of granite at hydrothermal conditions

    USGS Publications Warehouse

    Blanpied, M.L.; Lockner, D.A.; Byerlee, J.D.

    1995-01-01

    To measure the strength, sliding behavior, and friction constitutive properties of faults at hydrothermal conditions, laboratory granite faults containing a layer of granite powder (simulated gouge) were slid. The mechanical results define two regimes. The first regime includes dry granite up to at least 845?? and wet granite below 250??C. In this regime the coefficient of friction is high (?? = 0.7 to 0.8) and depends only modestly on temperature, slip rate, and PH2O. The second regime includes wet granite above ~350??C. In this regime friction decreases considerably with increasing temperature (temperature weakening) and with decreasing slip rate (velocity strengthening). These regimes correspond well to those identified in sliding tests on ultrafine quartz. The results highlight the importance of fluid-assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry, large displacements, higher concentrations of phyllosilicates, and time-dependent fault healing. -from Authors

  8. Origin of peralkaline granites of Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Radain, A. A. M.; Fyfe, W. S.; Kerrich, R.

    1982-01-01

    Small volumes of peralkaline granites were generated as the final phase of a Pan African calc-alkaline igneous event which built the Arabian Peninsula. The peralkaline granites are closely associated with trends or sutures related to ophiolites. Peralkaline rocks are chemically heterogeneous, with anomalous abundances of Zr (average 2,150 ppm±2,600 1σ), Y (200±190), and Nb (105±100), representing up to ten-fold enrichments of these elements relative to abundances in calc alkaline granite counterparts. Large enrichments of some rare earth elements and fluorine are also present. The peralkaline granites have scattered whole rock 18O values, averaging 8.7±0.6% in the Hadb Aldyaheen Complex and 10.7±1% in the Jabal Sayid Complex. Quartz-albite fractionations of 0.5 to 1.5% signify that the heavier whole rock δ-values probably represent the oxygen isotope composition of the peralkaline magma. Small variable enrichments of 18O, in conjunction with slightly elevated 87Sr/86Sr initial ratios relative to broadly contemporaneous calc alkaline granites, are both suggestive of a small degree of involvement of crustal, or crustal derived material in the peralkaline magmas. It is proposed that the peculiar magma genesis is associated with a relaxation event which followed continental collision and underthrusting of salt rich sediments.

  9. Reconstruction of crustal blocks of California on the basis of initial strontium isotopic compositions of Mesozoic granitic rocks

    USGS Publications Warehouse

    Kistler, Ronald Wayne; Peterman, Zell E.

    1978-01-01

    Initial 87Sr/ 86 Sr was determined for samples of Mesozoic granitic rocks in the vicinity of the Garlock fault zone in California. These data along with similar data from the Sierra Nevada and along the San Andreas fault system permit a reconstruction of basement rocks offset by the Cenozoic lateral faulting along both the San Andreas and Garlock fault systems. The location of the line of initial 87Sr/ 86 Sr = 0.7060 can be related to the edge of the Precambrian continental crust in the western United States. Our model explains the present configuration of the edge of Precambrian continental crust as the result of two stages of rifting that occurred about 1,250 to 800 m.y. ago, during Belt sedimentation, and about 600 to 350 m.y. ago, prior to and during the development of the Cordilleran geosyncline and to left-lateral translation along a locus of disturbance identified in the central Mojave Desert. The variations in Rb, Sr, and initial 87Sr/ 86 Sr of the Mesozoic granitic rocks are interpreted as due to variations in composition and age of the source materials of the granitic rocks. The variations of Rb, Sr, and initial 87Sr/ 86 Sr in Mesozoic granitic rocks, the sedimentation history during the late Precambrian and Paleozoic, and the geographic position of loci of Mesozoic magmatism in the western United States are related to the development of the continental margin and different types of lithosphere during rifting.

  10. Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

    USGS Publications Warehouse

    Ratajeski, K.; Sisson, T.W.; Glazner, A.F.

    2005-01-01

    Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850??C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635-661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486-1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening. ?? Springer-Verlag 2005.

  11. Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps)

    PubMed Central

    Miller, C.; Thöni, M.; Goessler, W.; Tessadri, R.

    2011-01-01

    The northern part of the Karawanken plutonic belt is a gabbro–granite complex located just north of the Periadriatic lineament near the Slovenian–Austrian border. Petrographic and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling. The mafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source. The mafic melts triggered partial melting of the crust and the formation of granite. The granitic rocks are alkalic, metaluminous and have the high Fe/Fe + Mg characteristics of within-plate plutons. Temperature and pressure conditions, derived from amphibole-plagioclase and different amphibole thermobarometers, suggest that the analysed Eisenkappel gabbros crystallized at around 1000 ± 20 °C and 380–470 MPa, whereas the granitic rock crystallized at T ≤ 800 ± 20 °C and ≤ 350 MPa. Mineral-whole rock Sm–Nd analyses of two cumulate gabbros yielded 249 ± 8.4 Ma and 250 ± 26 Ma (εNd: + 3.6), garnet-whole rock Sm–Nd analyses of two silicic samples yielded well-constrained ages of 238.4 ± 1.9 Ma and 242.1 ± 2.1 Ma (εNd: − 2.6). PMID:26525511

  12. Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps).

    PubMed

    Miller, C; Thöni, M; Goessler, W; Tessadri, R

    2011-07-01

    The northern part of the Karawanken plutonic belt is a gabbro-granite complex located just north of the Periadriatic lineament near the Slovenian-Austrian border. Petrographic and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling. The mafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source. The mafic melts triggered partial melting of the crust and the formation of granite. The granitic rocks are alkalic, metaluminous and have the high Fe/Fe + Mg characteristics of within-plate plutons. Temperature and pressure conditions, derived from amphibole-plagioclase and different amphibole thermobarometers, suggest that the analysed Eisenkappel gabbros crystallized at around 1000 ± 20 °C and 380-470 MPa, whereas the granitic rock crystallized at T ≤ 800 ± 20 °C and ≤ 350 MPa. Mineral-whole rock Sm-Nd analyses of two cumulate gabbros yielded 249 ± 8.4 Ma and 250 ± 26 Ma (εNd: + 3.6), garnet-whole rock Sm-Nd analyses of two silicic samples yielded well-constrained ages of 238.4 ± 1.9 Ma and 242.1 ± 2.1 Ma (εNd: - 2.6).

  13. Mantle metasomatism and alkaline magmatism

    SciTech Connect

    Morris, E.M.; Pasteris, J.D.

    1987-01-01

    The 24 papers in this volume were presented at the Symposium on Alkalic Rocks and Kimberlites, held at the Geological Society of America South-Central Section meeting, April 15-16, 1985, in Fayetteville, Arkansas. This two-day symposium included a total of 55 papers dealing with mantle metasomatism and the origin of alkaline magmas, kimberlites and related rocks, alkalic rocks in oceanic settings, and alkalic rocks in continental settings. Papers presented at this symposium heightened the awareness that alkaline magmatism may occur in virtually all tectonic and petrologic settings. Two papers deal specifically with data from California sites. These research papers on aspects of alkaline rock petrology contribute to a better insight into the complex diversity of alkalic systems, the mantle processes which precede and accompany alkaline magmatism, and kimberlitic and oceanic systems. Abstracts of all papers presented at the symposium and not published in full in the volume are included in an appendix to show the broad scope of data presented at the meeting.

  14. Arabian Shield magmatic cycles and their relationship with Gondwana assembly: Insights from zircon U-Pb and Hf isotopes

    NASA Astrophysics Data System (ADS)

    Robinson, F. A.; Foden, J. D.; Collins, A. S.; Payne, J. L.

    2014-12-01

    The Arabian Shield preserves a protracted magmatic record of amalgamated juvenile terranes that host a diverse range of early Neoproterozoic to Cambrian granitoids intruding volcanosedimentary basin assemblages that have corollaries in other parts of the East African Orogen. New zircon U-Pb geochronology of 19 granitoids intruding eight Arabian Shield terranes, define four discrete magmatic events: island arc (∼845 Ma), syncollisional (∼710 Ma), post-tectonic (∼620 Ma) and anorogenic (∼525 Ma). Zircon Lu-Hf isotopic analyses indicate that all studied granitoids are juvenile with typical εHf values of >+5 to +10 and Stenian-Tonian (∼1100-900 Ma) model ages, regardless of their precise intrusive ages or spatial relationship. Subtle changes in isotopic signatures between ∼850 and 600 Ma, suggest the result from changes in granite source materials brought about by; basaltic underplating, limited crustal interaction with Palaeoproterozoic basement and a change to lithospheric delamination/subduction roll-back processes driving juvenile ANS crustal growth. The cycle of granite intrusion reflects accretionary cycles initiated during Mozambique Ocean closure and during Gondwana amalgamation and final assembly. Post-tectonic magmatism is divided into a ∼636-600 Ma phase and post 600 Ma event that reflects first subduction and then within-plate related processes. The identification of magmatism at ∼525 Ma is now the youngest granitoid identified so far in the Saudi Arabian Shield and may change the identified age of the regional, basal Palaeozoic unconformity. This late magmatism may be generated by the Najd Fault reactivation correlating with the Malagasy/Kunnga Orogeny that marked the final stages of Gondwana assembly.

  15. Precise U-Pb Zircon Constraints on the Earliest Magmatic History of the Carolina Terrane.

    PubMed

    Wortman; Samson; Hibbard

    2000-05-01

    The early magmatic and tectonic history of the Carolina terrane and its possible affinities with other Neoproterozoic circum-Atlantic arc terranes have been poorly understood, in large part because of a lack of reliable geochronological data. Precise U-Pb zircon dates for the Virgilina sequence, the oldest exposed part, constrain the timing of the earliest known stage of magmatism in the terrane and of the Virgilina orogeny. A flow-banded rhyolite sampled from a metavolcanic sequence near Chapel Hill, North Carolina, yielded a U-Pb zircon date of 632.9 +2.6/-1.9 Ma. A granitic unit of the Chapel Hill pluton, which intrudes the metavolcanic sequence, yielded a nearly identical U-Pb zircon date of 633 +2/-1.5 Ma, interpreted as its crystallization age. A felsic gneiss and a dacitic tuff from the Hyco Formation yielded U-Pb zircon dates of 619.9 +4.5/-3 Ma and 615.7 +3.7/-1.9 Ma, respectively. Diorite and granite of the Flat River complex have indistinguishable U-Pb upper-intercept dates of 613.9 +1.6/-1.5 Ma and 613.4 +2.8/-2 Ma. The Osmond biotite-granite gneiss, which intruded the Hyco Formation before the Virgilina orogeny, crystallized at 612.4 +5.2/-1.7 Ma. Granite of the Roxboro pluton, an intrusion that postdated the Virgilina orogeny, yielded a U-Pb upper intercept date of 546.5 +3.0/-2.4 Ma, interpreted as the time of its crystallization. These new dates both provide the first reliable estimates of the age of the Virgilina sequence and document that the earliest known stage of magmatism in the Carolina terrane had begun by 633 +2/-1.5 Ma and continued at least until 612.4 +5.2/-1.7 Ma, an interval of approximately 25 m.yr. Timing of the Virgilina orogeny is bracketed between 612.4 +5.2/-1.7 Ma and 586+/-10 Ma (reported age of the upper Uwharrie Formation). The U-Pb systematics of all units studied in the Virgilina sequence are simple and lack any evidence of an older xenocrystic zircon component, which would indicate the presence of a continental

  16. Relationship between monogenetic magmatism and stratovolcanoes in western Mexico: The role of low-pressure magmatic processes

    NASA Astrophysics Data System (ADS)

    Petrone, Chiara M.

    2010-10-01

    A large Quaternary monogenetic volcanic field is present in the western part of the Trans-Mexican Volcanic Belt. It is composed by mafic-intermediate scoria cones and silicic domes that are arranged in two NNW-SSE alignments. These mark the north and south borders (Northern Volcanic Chain and Southern Volcanic Chain, SVC) of the San Pedro-Ceboruco graben. The products of this monogenetic volcanic field span a large range of compositions (from basalt to rhyolite) and magma affinities (from sub-alkaline to Na-alkaline), defining different magmatic groups. Mafic and silicic monogenetic centres from the north alignment also coexist with two stratovolcanoes (Ceboruco and Tepetiltic) and sometimes punctuate their flanks. Whole-rock analyses indicate the existence of 4 different types of primitive magmas (Na-alkaline, High-Ti, Low-Ti/SVC and sub-alkaline) which have evolved independently by low-P magmatic processes. Despite the relatively small size and simplicity of the monogenetic magmatism, open-system processes have modified the geochemical and isotope composition of erupted products. The negative correlation between Sr isotope ratios and MgO contents observed for Southern Volcanic Chain and High-Ti groups points to crustal interaction via AFC processes, involving upper granitic crust and mafic lower crust respectively. In contrast, the large variability in Nd-isotopic ratios, combined with low and less variable 87Sr/ 86Sr, shown by the most mafic compositions of the High-Ti group is mostly due to mantle source heterogeneities. Low-Ti and Na-alkaline compositions are only slightly modified by crustal contamination processes and their whole-rock geochemistry reflects the complex nature of the western Mexico sub-arc mantle. It is therefore apparent that a combination of mantle source processes plus crustal assimilation has generated complex geochemical and isotopic characteristics in the western part of the Trans-Mexican Volcanic belt. Despite the presence of

  17. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2017-04-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  18. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2016-09-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  19. Observations and Thermodynamic Models of Water in Silicic Melt Evolution: Implications for Quantifying Water Content in Hydrous and Anhydrous Granites

    NASA Astrophysics Data System (ADS)

    Chen, X.; Lee, C. T.

    2016-12-01

    Water plays a potentially key role in magmatic differentiation because it reduces the freezing point, decreases melt viscosity, and modifies the crystallizing phase assemblage. Here, we explore how magmatic differentiation systems can be used to evaluate the amount of water in the crystallizing system. Of particular interest is the role of water in generating granites and rhyolites. We examined basalt (gabbro) to rhyolite (granite) differentiation series from Phanerozoic arc and intraplate environments, the former thought to derive from hydrous parents and the latter from drier parents. In an Mg# versus SiO2 plot, arc differentiation series start becoming silicic at higher Mg#s than the intraplate series, the former feature often referred to as a calc-alkaline differentiation signature. We also plotted SiO2 as a function of residual melt fraction inferred from the inverse of the enrichment in a perfectly incompatible element, such as Th. This reveals that arc magmas become silicic earlier, that is, at higher melt fractions, than most intraplate magmas. MELTS modeling was used to better understand these observations. Under dry conditions, granite formation is limited to small residual melt fractions (F<0.3) whereas the stability field of granite is greatly expanded at high water contents (F<0.6). The Mg# at which silica rises is controlled by the onset of magnetite crystallization, which in turn is controlled by primarily by oxygen fugacity and to a lesser extent water. High oxygen fugacities and water contents lead to earlier (higher Mg#) silica enrichment. In summary, we show that these major element systematics can be used to quantify the amount of water in the system. In particular, the silica versus residual melt fraction relationship may be used as an approximate hygrometer. Our observations show that most arc magma differentiation series are controlled by high water and oxygen fugacity conditions compared to intraplate differentiation series. Archean

  20. Deep drilling at the Siljan Ring impact structure: oxygen-isotope geochemistry of granite

    USGS Publications Warehouse

    Komor, S.C.; Valley, J.W.

    1990-01-01

    The Siljan Ring is a 362-Ma-old impact structure formed in 1700-Ma-old I-type granites. A 6.8-km-deep borehole provides a vertical profile through granites and isolated horizontal diabase sills. Fluid-inclusion thermometry, and oxygen-isotope compositions of vein quartz, granite, diabase, impact melt, and pseudotachylite, reveal a complex history of fluid activity in the Siljan Ring, much of which can be related to the meteorite impact. In granites from the deep borehole, ??18O values of matrix quartz increase with depth from near 8.0 at the surface to 9.5??? at 5760 m depth. In contrast, feldspar ??18O values decrease with depth from near 10 at the surface to 7.1??? at 5760 m, forming a pattern opposite to the one defined by quartz isotopic compositions. Values of ??18O for surface granites outside the impact structure are distinct from those in near-surface samples from the deep borehole. In the deep borehole, feldspar coloration varies from brick-red at the surface to white at 5760 m, and the abundances of crack-healing calcite and other secondary minerals decrease over the same interval. Superimposed on the overall decrease in alteration intensity with depth are localized fracture zones at 4662, 5415, and 6044 m depth that contain altered granites, and which provided pathways for deep penetration of surface water. The antithetic variation of quartz and feldspar ??18O values, which can be correlated with mineralogical evidence of alteration, provides evidence for interaction between rocks and impact-heated fluids (100-300?? C) in the upper 2 km of the pluton. Penetration of water to depths below 2 km was restricted by a general decrease in impact-fracturing with depth, and by a 60-m-thick diabase sill at 1500 m depth that may have been an aquitard. At depths below 4 km in the pluton, where water/rock ratios were low, oxygen isotopic compositions preserve evidence for limited high-temperature (>500?? C) exchange between alkali feldspar and fluids. The high

  1. Igneous phenocrystic origin of K-feldspar megacrysts in granitic rocks from the Sierra Nevada batholith

    USGS Publications Warehouse

    Moore, J.G.; Sisson, T.W.

    2008-01-01

    Study of four K-feldspar megacrystic granitic plutons and related dikes in the Sierra Nevada composite batholith indicates that the megacrysts are phenocrysts that grew in contact with granitic melt. Growth to megacrystic sizes was due to repeated replenishment of the magma bodies by fresh granitic melt that maintained temperatures above the solidus for extended time periods and that provided components necessary for K-feldspar growth. These intrusions cooled 89-83 Ma, are the youngest in the range, and represent the culminating magmatic phase of the Sierra Nevada batholith. They are the granodiorite of Topaz Lake, the Cathedral Peak Granodiorite, the Mono Creek Granite, the Whitney Granodiorite, the Johnson Granite Porphyry, and the Golden Bear Dike. Megacrysts in these igneous bodies attain 4-10 cm in length. All have sawtooth oscillatory zoning marked by varying concentration of BaO ranging generally from 3.5 to 0.5 wt%. Some of the more pronounced zones begin with resorption and channeling of the underlying zone. Layers of mineral inclusions, principally plagioclase, but also biotite, quartz, hornblende, titanite, and accessory minerals, are parallel to the BaO-delineated zones, are sorted by size along the boundaries, and have their long axes preferentially aligned parallel to the boundaries. These features indicate that the K-feldspar megacrysts grew while surrounded by melt, allowing the inclusion minerals to periodically attach themselves to the faces of the growing crystals. The temperature of growth of titanite included within the K-feldspar megacrysts is estimated by use of a Zr-in-titanite geothermometer. Megacryst-hosted titanite grains all yield temperatures typical of felsic magmas, mainly 735-760 ??C. Titanite grains in the granodiorite hosts marginal to the megacrysts range to lower growth temperatures, in some instances into the subsolidus. The limited range and igneous values of growth temperatures for megacryst-hosted titanite grains support the

  2. Contrasting low- and high-Ca granites in the Archean Barberton Mountain Land, Southern Africa

    NASA Astrophysics Data System (ADS)

    Meyer, F. M.; Robb, L. J.; Reimold, W. U.; de Bruiyn, H.

    1994-03-01

    or hot-spot related magmatism, with the I-types forming in the time span 2740-2690 Ma along a western array. The putative S-types occurring entirely along an easterly belt were emplaced at 3074 and 2820 Ma. The presence of S-type plutons as old as 3074 Ma implies that sediments (such as the Moodies and Fig Tree Groups, or their equivalents) had been buried to depths of at least 15 km, and that by this time, at least in the Barberton area, granites had evolved beyond the TTG mode that typifies many early Archaean shield areas.

  3. Remelting and Remobilization in a Magmatic Arc: the St Peter Suite, South Australia

    NASA Astrophysics Data System (ADS)

    Symington, N.; Weinberg, R. F.; Hasalova, P.

    2013-12-01

    Thermo-mechanical models of magmatic arcs suggest that intermittent intrusion of magma batches should lead to remelting and remobilization of earlier intrusive rocks as a result of fluctuations in temperature and water content. However, examples of remelting and remobilization of earlier intrusive rocks, formed during arc-building, are surprisingly rare. We investigate the evolution of magmatic rocks of the Palaeoproterozoic St Peter Suite, in the Gawler Craton, South Australia. This suite records multiple intrusions, magma hybridization, and the remelting and remobilization of these intrusions to form migmatites and newly-formed leucocratic magmas. In this paper we detail first how multiple magma batches interact with one another as liquids and mushes during syn-magmatic deformation phases, and then detail the nature of migmatites resulting from anatexis of these same magmatic rocks and the resulting channel ways that allowed for magma remobilization. LA-ICP/MS U/Pb zircon dating yielded crystallization ages of 1647×12 Ma for an early dioritic-to-granitic suite, and 1604×12 Ma for a later magmatic suite of broadly similar composition. Both these suites underwent anatectic events. Titanite from late-formed leucosomes found within D2 shear zones in the older suite, yielded SHRIMP U/Pb age of 1605×7 Ma, within error of the age of the younger suite. We therefore infer that intrusion, crystallization and remelting/remobilization of this younger suite of rocks occurred within 10-15 M.yr. We propose that the St Peter Suite exposures represent a frozen-in record of a continuous, multi-stage, repetitive process, common to the core of arcs where multiple magma intrusions drive multiple hybridization events and fluctuations in temperature and water-content trigger remelting and remobilization of the more fractionated sectors of earlier intrusive. Thus, the St Peter Suite record many of the key processes expected in arcs, including the prediction that early intrusive arc

  4. Remelting and Remobilization in a Magmatic Arc: the St Peter Suite, South Australia

    NASA Astrophysics Data System (ADS)

    Symington, Neil; Weinberg, Roberto; Hasalová, Pavlina

    2014-05-01

    Thermo-mechanical models of magmatic arcs suggest that intermittent intrusion of magma batches should lead to remelting and remobilization of earlier intrusive rocks as a result of fluctuations in temperature and water content. However, examples of remelting and remobilization of earlier intrusive rocks, formed during arc-building, are surprisingly rare. We investigate the evolution of magmatic rocks of the Palaeoproterozoic St Peter Suite, in the Gawler Craton, South Australia. This suite records multiple intrusions, magma hybridization, and the remelting and remobilization of these intrusions to form migmatites and newly-formed leucocratic magmas. In this paper we detail first how multiple magma batches interact with one another as liquids and mushes during syn-magmatic deformation phases, and then detail the nature of migmatites resulting from anatexis of these same magmatic rocks and the resulting channel ways that allowed for magma remobilization. LA-ICP/MS U/Pb zircon dating yielded crystallization ages of 1647±12 Ma for an early diorite-to-granite suite, and 1604±12 Ma for a later magmatic suite of broadly similar composition. Both these suites underwent anatectic events. Titanite from late-formed leucosomes found within D2 shear zones in the older suite, yielded SHRIMP U/Pb age of 1605±7 Ma, within error of the age of the younger suite. We therefore infer that intrusion, crystallization and remelting/remobilization of this younger suite of rocks occurred within 10-15 M.yr. Thus, the St Peter Suite exposures record many of the key processes expected in arcs, including the prediction that early intrusive arc rocks remelt to form younger more fractionated magmas.

  5. Early Mesozoic deep-crust reworking beneath the central Lhasa terrane (South Tibet): Evidence from intermediate gneiss xenoliths in granites

    NASA Astrophysics Data System (ADS)

    Zhou, Xiang; Zheng, Jian-Ping; Xiong, Qing; Yang, Jing-Sui; Wu, Yuan-Bao; Zhao, Jun-Hong; Griffin, William L.; Dai, Hong-Kun

    2017-03-01

    Understanding the rheological behavior of the Tibetan Plateau and its response to geodynamic processes requires a clear knowledge of the composition, evolution and lithological properties of the deep crust. Here we present U-Pb-Hf isotopes of zircons, bulk-rock geochemistry and mineral compositions for seven intermediate gneiss xenoliths and their host Early Mesozoic granites (205 ± 6 Ma) in the central Lhasa terrane to probe the deep crust beneath Southern Tibet. The xenoliths contain plagioclase, amphibole, titanite, allanite, quartz, biotite and muscovite, with accessory Fe-Ti oxides, apatite and zircon. Bulk-rock and mineral geochemistry suggests that these xenoliths have a magmatic origin and experienced deformation and amphibolite-facies metamorphism (equilibration at pressures of 0.46-0.83 GPa and temperatures of 650 °C), before they were captured by the host granite at 205 Ma. Zircons in these xenoliths show complex microstructures, including inherited cores, magmatic or metamorphic bands, and high U-Th hydrothermal rims. Inherited zircon cores record U-Pb ages from 2277 Ma to 517 Ma. Igneous zircons show a range of concordant U-Pb ages, suggesting a protracted magmatism from 236 Ma to 203 Ma. Metamorphic zircon zones record the timing of amphibolite-facies metamorphism from 224 to 192 Ma, while the high U-Th hydrothermal rims show a subsequent fluid activity until 150 Ma. Unradiogenic Hf isotopic compositions of both xenoliths and host granites [xenolith εHf(t) = - 11.2 to 0; host granite εHf(t) = - 17.3 to - 3.3] indicate that the Early Mesozoic deep crust in the central Lhasa terrane originated mainly from ancient (i.e., Proterozoic) crust, with little or no interaction with juvenile magmas. This study suggests a possible continental differentiation mechanism during crustal reworking; progressive melting may initiate from the lower mafic crust (at ca. 236 Ma) and gradually migrate into the sediment-rich upper crust (until ca. 203 Ma). The reworking

  6. Evaluation of a small-diameter sampling method in magnetic susceptibility, AMS and X-ray CT studies and its applications to mafic microgranular enclaves (MMEs) in granite

    NASA Astrophysics Data System (ADS)

    Zhu, Kong-Yang; Li, Ming-Yue; Shentu, Lu-Feng; Shen, Zhong-Yue; Yu, Yi-Hao

    2017-07-01

    This paper reviews the technical details of the small diameter sampling method in a study of anisotropy of magnetic susceptibility (AMS) and X-ray CT (computed tomography) and their applications to studies of MMEs (Mafic Microgranular Enclaves) in granite. The AMS results based on 9 mm diameter cylinder specimens collected from the Cretaceous Tongkengxi mafic dykes in South China were consistent with results using 25 mm diameter specimens. The first case study demonstrated the variation of AMS in the interior of a large MME from South China, which contained a center of strong short-range magnetic lineation. This type of magnetic fabric could be detected only by using sample cores with a small diameter. In the foliation direction, the host granite interacted with the MME more heavily and produced a region with a high magnetite content. The second case study was the investigation of the MMEs in the Early Cretaceous Muchen complex in eastern South China. The MME swarms exhibited relatively uniform magnetic fabrics at the outcrop scale, but the fabrics varied significantly at the intrusion scale. AMS of the MME swarms is coaxial with that of the host granite only at some localities. The disagreement of AMS between MME and host granite either imply different magma flow directions, or different magma flow velocities, or disturbance of the granite fabric by the MME. The MMEs in a mylonitic granite from eastern North China were also studied. The MME specimens show highly variable magnetic susceptibility and lineations. They can be only studied appropriately by a small drill. In the three cases, the three magnetic susceptibility axes of the MMEs are consistent with the volume-weighted maximum eigenvector of long/intermediate/short axes of magnetite. The orientations of the magnetite long axes in the three cases form several modes and the concentration of the modes results in a strong lineation. One implication of this study is that MMEs, with the same magmatic fabrics as

  7. OVERALL VIEW OF QUARRY, FACING NORTH, WITH UNQUARRIED GRANITE OUTCROP ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OVERALL VIEW OF QUARRY, FACING NORTH, WITH UN-QUARRIED GRANITE OUTCROP IN BACKGROUND - Granite Hill Plantation, Quarry No. 3, South side of State Route 16, 1.3 miles northeast east of Sparta, Sparta, Hancock County, GA

  8. Tracing an Early Jurassic magmatic arc from South to East China Seas

    NASA Astrophysics Data System (ADS)

    Xu, Changhai; Zhang, Lu; Shi, Hesheng; Brix, Manfred R.; Huhma, Hannu; Chen, Lihui; Zhang, Minqiang; Zhou, Zuyi

    2017-03-01

    Drilling has revealed suites of magnesian granite and diorite emplaced in Early Jurassic time (198-195 Ma) and an arc-related low-temperature (678 to 696°C) magmatism in NE South China Sea. These rocks have 87Sr/86Sri (0.705494 to 0.706623) and ɛNdt (-0.9 to +2.2) as evidence of evolved mantle-derived magmas, coupled with enriched fluid-mobile elements Cs to K and Pb implying involvement of subduction-zone fluids. Another Early Jurassic granodiorite (zircon U-Pb 187 Ma) drilled from the SW East China Sea, a magnesian high-K calc alkaline, is comparably confined to a range of low-temperature ( 675°C) arc-related granite, characterized by enrichment of fluid-mobile elements and Nb-Ta depletion. Its Sr-Nd isotopes (87Sr/86Sri = 0.705200, ɛNdt = 1.1) suggest a product of evolved mantle-derived melts. Together with detrital igneous zircons from Paleocene sequences, these observations reveal an Early Jurassic arc-related low-temperature (600 to 740°C) magmatism in the SW East China Sea. These arc-related granitoids, along with those from SE Taiwan, could define an Early Jurassic NE-SW trending Dongsha-Talun-Yandang magmatic arc zone along the East Asian continental margin paired with Jurassic accretionary complexes from SW Japan, East Taiwan to the West Philippines. This arc-subduction complex assembly was associated with oblique subduction of the paleo-Pacific slab beneath Eurasia, presumably responsible for Early Jurassic lithospheric extension in south China block.

  9. Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr-Nd-Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil

    NASA Astrophysics Data System (ADS)

    Florisbal, Luana Moreira; Bitencourt, Maria de Fátima; Janasi, Valdecir de Assis; Nardi, Lauro Valentim Stoll; Heaman, Larry M.

    2012-11-01

    The Neoproterozoic post-collisional period in southern Brazil (650-580 Ma) is characterized by substantial volumes of magma emplaced along the active shear zones that compose the Southern Brazilian Shear Belt. The early-phase syntectonic magmatism (630-610 Ma) is represented by the porphyritic, high-K, metaluminous to peraluminous Quatro Ilhas Granitoids and the younger heterogranular, slightly peraluminous Mariscal Granite. Quatro Ilhas Granitoids include three main petrographic varieties (muscovite-biotite granodiorite — mbg; biotite monzogranite — bmz; and leucogranite — lcg) that, although sharing some significant geochemical characteristics, are not strictly comagmatic, as shown by chemical and Sr-Nd-Pb isotope data. The most primitive muscovite-biotite granodiorite was produced by contamination of more mafic melts (possibly with some mantle component) with peraluminous crustal melts; the biotite monzogranite, although more felsic, has higher Ca, MgO, TiO2 and Ba, and lower K2O, FeOt, Sr and Rb contents, possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity; the leucogranite may be derived from pure crustal melts. The Mariscal Granite is formed by two main granite types which occur intimately associated in the same pluton, one with higher K (5-6.5 wt.% K2O) high Rb and lower CaO, Na2O, Ba and Zr as compared to the other (3-5 wt.% of K2O). The two Mariscal Granite varieties have compositional correspondence with fine-grained granites (fgg) that occur as tabular bodies which intruded the Quatro Ilhas Granoitoids before they were fully crystallized, and are inferred to correspond to the Mariscal Granite feeders, an interpretation that is reinforced by similar U-Pb zircon crystallization ages. The initial evolution of the post-collisional magmatism, marked by the emplacement of the Quatro Ilhas Granitoids varieties, activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat-lying and

  10. Platinum metals magmatic sulfide ores.

    PubMed

    Naldrett, A J; Duke, J M

    1980-06-27

    Platinum-group elements (PGE) are mined predominantly from deposits that have formed by the segregation of molten iron-nickel-copper sulfides from silicate magmas. The absolute concentrations of PGE in sulfides from different deposits vary over a range of five orders of magnitude, whereas those of other chalcophile elements vary by factors of only 2 to 100. However, the relative proportions of the different PGE in a given deposit are systematically related to the nature of the parent magma. The absolute and relative concentrations of PGE in magmatic sulfides are explained in terms of the degree of partial melting of mantle peridotite required to produce the parent magma and the processes of batch equilibration and fractional segregation of sulfides. The Republic of South Africa and the U.S.S.R. together possess more than 97 percent of the world PGE reserves, but significant undeveloped resources occur in North America. The Stillwater complex in Montana is perhaps the most important example.

  11. The Colima volcano magmatic system

    NASA Astrophysics Data System (ADS)

    Spica, Z.; Perton, M.; Legrand, D.

    2016-12-01

    We show how and where magmas are produced and stored at Colima volcano, Mexico, by performing an ambient noise tomography inverting jointly the Rayleigh and Love wave dispersion curves for both phase and group velocities. We obtain shear wave velocity and radial anisotropy models. The shear wave velocity model shows a deep, large and well-delineated elliptic-shape magmatic reservoir below the Colima volcano complex at a depth of about 15 km. The radial anisotropy model shows an important negative feature rooting up to ≥35 km depth until the roof of the magma reservoir, suggesting the presence of vertical fractures where fluids migrate upward and accumulate in the magma reservoir. The convergence of both a low velocity zone and a negative anisotropy suggests that the magma is mainly stored in conduits or inter-fingered dykes as opposed to horizontally stratified magma reservoir.

  12. 7. Photocopied August 1971 from Photo 13729, Granite Station Special ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Photocopied August 1971 from Photo 13729, Granite Station Special Folder, Engineering Department, Utah Power and Light Co., Salt Lake City, Utah. GRANITE HYDRO-ELECTRIC PLANT (1500KW) STATION. PENSTOCK AND SPILWAY, NOVEMBER 1914. - Utah Power Company, Granite Hydroelectric Plant, Holladay, Salt Lake County, UT

  13. 9. Photocopied August 1971 from Photo 13730, Granite Folder #1, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    9. Photocopied August 1971 from Photo 13730, Granite Folder #1, Engineering Department, Utah Power and Light Co., Salt Lake City, Utah. GRANITE STATION: WESTINGHOUSE 750 K.V.A., 2- PHASE GENERATORS AND SWITCHBOARD, MAY 24, 1915. - Utah Power Company, Granite Hydroelectric Plant, Holladay, Salt Lake County, UT

  14. 8. Photocopied August 1971 from Photo 11479, Granite Station Special ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Photocopied August 1971 from Photo 11479, Granite Station Special Folder, Engineering Department, Utah Power and Light Co., Salt Lake City, Utah. GRANITE HYDRO-ELECTRIC PLANT (1500 KW) STATION. PENSTOCK AND SPILWAY, NOVEMBER 1914. - Utah Power Company, Granite Hydroelectric Plant, Holladay, Salt Lake County, UT

  15. Geochronology, petrogenesis and tectonic settings of pre- and syn-ore granites from the W-Mo deposits (East Kounrad, Zhanet and Akshatau), Central Kazakhstan

    NASA Astrophysics Data System (ADS)

    Li, GuangMing; Cao, MingJian; Qin, KeZhang; Evans, Noreen J.; Hollings, Pete; Seitmuratova, Eleonora Yusupovha

    2016-05-01

    There is significant debate regarding the mineralization ages of the East Kounrad, Zhanet and Akshatau W-Mo deposits of Central Kazakhstan, and the petrogenesis and tectono-magmatic evolution of the granites associated with these deposits. To address these issues, we present molybdenite Re-Os dating, zircon U-Pb dating, whole rock geochemistry as well as Sr-Nd-Pb and zircon O-Hf isotopic analyses on the pre-mineralization and ore-forming granites. U-Pb dating of zircons from pre-mineralization granitic rocks yield Late Carboniferous ages of 320-309 Ma, whereas ore-forming granites have Early Permian ages of 298-285 Ma. Molybdenite Re-Os isotopic data indicate a mineralization age of ~ 296 Ma at East Kounrad, ~ 294 Ma at Akshatau and ~ 285 Ma at Zhanet. The pre-ore and ore-forming granites are high-K calc-alkaline, metaluminous to slightly peraluminous I-type granites. The pre-mineralization granites are relatively unfractionated, whereas the ore-forming granites are highly fractionated. The fractionating mineral phases are probably K-feldspar, apatite, Ti-bearing phases and minor plagioclase. The pre-mineralization and ore-forming rocks are characterized by similar Sr-Nd-Pb-Hf-O isotopic compositions ((87Sr/86Sr)i = 0.70308-0.70501, εNd (t) = - 0.5 to + 2.8, 207Pb/204Pb = 15.60-15.82, zircon εHf (t) = + 1.2 to + 15.6 and δ18O = + 4.6 to + 10.3‰), whole rock TDMC (Nd) (840-1120 Ma) and zircon TDMC (Hf) (320-1240 Ma). The isotopic characteristics are consistent with a hybrid magma source caused by 10-30% assimilation of ancient crust by juvenile lower crust. The geochronology and geochemistry of these granites show that the Late Carboniferous pre-mineralization granitic rocks formed during subduction, whereas the Early Permian ore-forming, highly fractionated granite probably underwent significant fractionation with a restite assemblage of K-feldspar, apatite, Ti-bearing phases and minor plagioclase and developed during collision between the Yili and Kazakhstan

  16. Zircon Geochemistry of Granitic Rocks from Ong Valley and Moraine Canyon in the Central Transantarctic Mountains, Antarctica

    NASA Astrophysics Data System (ADS)

    Liu, J.; Morgan, D. J.; Claiborne, L. L.; Padilla, A. J.; Edwards, K. L.; Putkonen, J.; Bibby, T.; Cribb, J. W.

    2015-12-01

    A number of granitic rocks exposed throughout the Central Transantarctic Mountains (CTAM) are thought to have been generated during and following the Ross Orogeny (late Cambrian to early Ordovician). Understanding the origin of these rocks can help improve our understanding of the tectonic events responsible for the suturing of Gondwana. In this study, we use zircon as a tool to investigate the magmatic origins and evolution of CTAM granites. Zircon has a low solubility in almost all melt and fluid compositions, is stable and resistant to alteration at Earth's surface, and is physically durable during transport. These features enable it to survive many crustal processes during which most other minerals are destroyed, thus preserving an important geochemical record of its crystallizing environments. We collected granitic samples from two sites in the CTAM: Ong Valley (157.5°E, 83.25°S), where the Hope Granite is exposed intruded into pre-Cambrian gneisses, and Moraine Canyon (157.55°W, 86.1°S), where bedrock exposure is dominated by a silicic porphyry of the Wyatt Formation. Our zircon U-Pb data, collected in-situ by laser ablation (LA) ICP-MS, suggests that the Hope Granite has a mean weighted crystallization age of 582 ± 23 Ma (2σ; n=26), older than the published age (510 ± 9 Ma, 1σ; whole-rock Rb-Sr isochrons; Faure & Mensing, 2010). The spread in individual zircon ages is consistent with previous estimates for the duration of intrusion (~20 Myr) of the Hope Granite. Published ages for Wyatt Fm rocks range from ~525 to ~800 Ma, but their origin is uncertain. We will analyze zircons from the Wyatt porphyry for U-Pb isotopes (by LA-ICP-MS) to better constrain its age. In addition, we will obtain trace element compositions of zircons from both intrusions to investigate their magmatic origins. This will allow us to explore potential geochemical connections between the intrusions, and may yield additional insight into the tectonic events involved in the Ross

  17. Hydrogen and oxygen isotope geochemistry of Ascension Island lavas and granites: variation with crystal fractionation and interaction with sea water

    NASA Astrophysics Data System (ADS)

    Sheppard, Simon M. F.; Harris, Chris

    1985-09-01

    Lavas and pyroclastics on Ascension Island contain plutonic blocks that include fluid-inclusion-bearing peralkaline-granite. 18O/16O ratios, F and Cl have been analysed on whole rocks and/or minerals for lavas and granites, and D/H ratios and H2O+ for comenditic obsidians and granites. Whole rock 18O/16O ratios of fresh alkali-basalt, hawaiite, trachyandesite, trachyte and comendite range from 6.0 to 6.9‰ with 18O tending to increase with increase in SiO2. The δ 18O values of the granites are from 0.0 to 0.3‰ depleted in 18O relative to the comendites. Comenditic obsidians have δD= -80±4‰ and H2O+ ˜0.3 wt.% while amphiboles from the granites have δD= -56±2‰ The O-isotope trend of the lavas is consistent with a crystal fractionation model. Fresh igneous rocks with δ 18O values greater than 7‰ involve processes in addition to crystal fractionation of a basaltic magma. The D/H ratios and Cl contents (˜ 3,000 ppm) of the H2O-poor comenditic obsidians represent undegassed primary magmatic values. The H-isotope compositions and low H2O and Cl (167 ppm) contents of the granites are consistent with the major degassing (loss of >90% of initial H2O) of an H2Osaturated magma derived from the interaction of sea (or possibly meteoric) water with the H2O-undersaturated comenditic melt. It is proposed that, associated with caldera subsidence and stoping, water was sucked in around the residual magma before the system had time to be sealed up. The H2O-undersaturated magma consumed this H2O with possibly some minor partial dehydration and dewatering of the hydrated volcanic roof blocks, at a pressure of about 1.5 kb. The granites are the plutonic equivalents of rhyolitic pyroclastics and not directly of the comendites. Granites from oceanic islands may, in general, be a result of generating an H2O-saturated acid melt by such direct or indirect crustal water-magma interaction processes.

  18. The Early Jurassic Bokan Mountain peralkaline granitic complex (southeastern Alaska): geochemistry, petrogenesis and rare-metal mineralization

    USGS Publications Warehouse

    Dostal, Jaroslav; Kontak, Daniel J.; Karl, Susan M.

    2014-01-01

    magmatic mineralization. Mineralization is mostly composed of new minerals. Fluorine complexing played a role during the transportation of REE and HFSE in hydrothermal fluids and oxygen isotopes in the granites and quartz veins negate the significant incursion of an external fluid and support a dominantly orthomagmatic hydrothermal system. Many other REE-HFSE deposits hosted by peralkaline felsic rocks (nepheline syenites, peralkaline granites and peralkaline trachytes) were formed by a similar two stage process.

  19. Temporal evolution of granitic magmas in the Luanchuan metallogenic belt, east Qinling Orogen, central China: Implications for Mo metallogenesis

    NASA Astrophysics Data System (ADS)

    Li, Dong; Han, Jiangwei; Zhang, Shouting; Yan, Changhai; Cao, Huawen; Song, Yaowu

    2015-11-01

    The Luanchuan metallogenic belt, located within the eastern part of the Qinling Orogen, central China, hosts a number of world-class Mo deposits that are closely related to small late Mesozoic granitic plutons. Zircon U-Pb dating of distinct plutons in the Luanchuan metallogenic belt has yielded ages of 153 ± 1, 154 ± 2, 152 ± 2, and 148 ± 1 Ma. Molybdenite Re-Os isotopic compositions of Yuku ore district in the southern part of Luanchuan metallogenic belt has yielded an isochron age of 146 ± 1 Ma, which is consistent with the large-scale mineralization ages in the northern part of the Luanchuan metallogenic belt. A combination of previous studies and new geochronological and isotopic data show a concordant temporal and genetic link between granitic magmatism and Mo mineralization in the Luanchuan metallogenic belt, suggesting that this mineralization episode formed the most extensive Mo mineralization belt in the east Qinling Orogen. Zircon grains from Mo-related granitic plutons show similar trace element distributions. High-precision Multi Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS) Pb isotope analysis of K-feldspar megacrysts from mineralization-related granites suggest that they were derived from the lower crust. Similarly, the Pb isotopic compositions of pyrite coprecipitated with molybdenite also suggest that the metals were derived form the lower crust, with probably minor mantle contribution. A continuum mineralization model that describes the sourcing of Mo from an evolving granitic magma over successive differentiation events, possibly in separate but connected magma chambers, could explain the remarkable Mo enrichment in the Luanchuan metallogenic belt. The volatile- and Mo-bearing granitic magmas ascended as diapirs from the deep crust, and were emplaced as dikes in the upper crust. Lithological differences between these Mo-bearing granites may relate to different stages in the evolution of individual magmas. Finally, ore

  20. Landslides and the weathering of granitic rocks

    Treesearch

    Philip B. Durgin

    1977-01-01

    Abstract - Granitic batholiths around the Pacific Ocean basin provide examples of landslide types that characterize progressive stages of weathering. The stages include (1) fresh rock, (2) corestones, (3) decomposed granitoid, and (4) saprolite. Fresh granitoid is subject to rockfalls, rockslides, and block glides. They are all controlled by factors related to...

  1. The origin of granites and related rocks

    USGS Publications Warehouse

    Brown, Michael; Piccoli, Philip M.

    1995-01-01

    This Circular is a compilation of abstracts for posters and oral presentations given at the third Hutton symposium on the Origin of granites and related rocks. The symposium was co-sponsored by the Department of Geology, University of Maryland at College Park; the U.S. Geological Survey, Reston, Virginia; and the Department of Terrestrial Magnetism and Geophysical Laboratory, Carnegie Institution of Washington.

  2. Subsurface drainage erodes forested granitic terrane

    Treesearch

    Philip Durgin

    1984-01-01

    Abstract - Solution and landsliding, the dominant erosion processes in undisturbed forested mountainous watersheds, are both influenced by subsurface drainage. Biological processes that generate organic acids accelerate loss of dissolved solids by promoting the dissolution of primary minerals in granitic rock. These organic acids can also disperse the secondary...

  3. The global age distribution of granitic pegmatites

    USGS Publications Warehouse

    McCauley, Andrew; Bradley, Dwight C.

    2014-01-01

    An updated global compilation of 377 new and previously published ages indicates that granitic pegmatites range in age from Mesoarchean to Neogene and have a semi-periodic age distribution. Undivided granitic pegmatites show twelve age maxima: 2913, 2687, 2501, 1853, 1379, 1174, 988, 525, 483, 391, 319, and 72 Ma. These peaks correspond broadly with various proxy records of supercontinent assembly, including the age distributions of granites, detrital zircon grains, and passive margins. Lithium-cesium-tantalum (LCT) pegmatites have a similar age distribution to the undivided granitic pegmatites, with maxima at 2638, 1800, 962, 529, 485, 371, 309, and 274 Ma. Lithium and Ta resources in LCT pegmatites are concentrated in the Archean and Phanerozoic. While there are some Li resources from the Proterozoic, the dominantly bimodal distribution of resources is particularly evident for Ta. This distribution is similar to that of orogenic gold deposits, and has been interpreted to reflect the preservation potential of the orogenic belts where these deposits are formed. Niobium-yttrium-fluorine (NYF) pegmatites show similar age distributions to LCT pegmatites, but with a strong maximum at ca. 1000 Ma.

  4. Granite School District First Grade Reading Study.

    ERIC Educational Resources Information Center

    Castner, Myra H.; And Others

    A comparative study of first-grade reading instructional methods was undertaken with the support of the Granite School District Exemplary Center for Reading Instruction. This study was conducted in 19 schools of the district and involved approximately 1,295 students. Nine hypotheses concerning the various approaches used in reading instruction…

  5. From Mesoproterozoic magmatism to collisional Cretaceous anatexis: Tectonomagmatic history of the Pelagonian Zone, Greece

    NASA Astrophysics Data System (ADS)

    Schenker, Filippo Luca; Burg, Jean-Pierre; Kostopoulos, Dimitrios; Moulas, Evangelos; Larionov, Alexander; Quadt, Albrecht

    2014-08-01

    The magmatic history of the Pelagonian Zone, in northern Greece, is constrained with secondary ion mass spectrometer (SIMS) U-Pb dating on zircons of various granitoids whose structural positions were defined with respect to the regional main foliation. Ages pertain to four groups: (i) Mesoproterozoic (circa 1430 Ma) crystallization of granites inferred from inherited magmatic zircon cores that have been partially molten during the (ii) Neoproterozoic at circa 685 Ma (metamorphic zircon rims) and subsequently intruded by a Neoproterozoic leucogranite (circa 600 Ma). (iii) Late- or post-Variscan calc-alkaline granitoids (315-301 Ma) were in turn intruded by a subvolcanic dike at about 280 Ma. In the Early Permian the ɛNd(t) in magmas decreased from -7.3 to -1.3, hinting to mantle-derived melts produced during extension. Rifting is further heralded by two acidic and one mafic dike containing Lower-Middle Triassic zircons (246-242 Ma). (iv) Early Cretaceous anatectic melts at 117 ± 8 Ma formed during regional metamorphism. This age is the first report of in situ anatexis in the Pelagonian Zone. Cretaceous anatexis developed during the Mesozoic collision of Pelagonia with the Eurasian margin. Major- and trace-element geochemistry of amphibolites further attests for the complex pre-Alpine tectonic history with Neoproterozoic calc-alkaline and back-arc geochemical signature and Triassic alkali-magmatism.

  6. Paleoproterozoic magmatic and metamorphic events link Yangtze to northwest Laurentia in the Nuna supercontinent

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Cawood, Peter A.; Zhou, Mei-Fu; Zhao, Jun-Hong

    2016-01-01

    Zircons from granitic gneisses in North Vietnam have magmatic cores dated at 2.28-2.19 Ga, and constitute the first reported evidence of continental crust with these ages in the Yangtze Block of the South China Craton. Overgrowths on zircon rims indicate two periods of metamorphism at 1.97-1.95 Ga and ∼1.83 Ga. These events, along with a previously reported ∼2.36 Ga metamorphic overgrowth on ∼2.9 Ga crystallized zircons from the same region, suggest a sequence of events similar to that recorded for the northwestern region of Laurentia and possibly Siberia, which are associated with assembly of the Nuna supercontinent. These include the 2.4-2.3 Ga Arrowsmith Orogen and a range of events in the interval 2.32-1.80 Ga, including accretionary magmatism in northwestern Laurentia and Siberia (2.32-2.07 Ga), the Thelon orogeny (2.02-1.96 Ga) and the 1.85-1.80 Ga collision between the Superior and Hearne-Rae cratons during the Trans-Hudson Orogen in Laurentia, and the Akitkan Orogen in Siberia (2.03-1.86 Ga). Subsequent attempted breakup of Nuna may be represented by ca. 1.80 to 1.59 Ga consanguineous extension related sedimentation and magmatism in the southwestern Yangtze Block and northwestern Laurentia. These correlations favor location of the Yangtze Block adjacent to northwest Laurentia, and possibly Siberia, within the Nuna supercontinent.

  7. Generation of Late Mesozoic Qianlishan A2-type granite in Nanling Range, South China: Implications for Shizhuyuan W-Sn mineralization and tectonic evolution

    NASA Astrophysics Data System (ADS)

    Chen, Yuxiao; Li, He; Sun, Weidong; Ireland, Trevor; Tian, Xufeng; Hu, Yongbin; Yang, Wubin; Chen, Chen; Xu, Deru

    2016-12-01

    The Late Mesozoic Qianlishan granitic complex in the western Nanling Range, South China is associated with the Shizhuyuan giant W-Sn-Mo-Bi polymetallic deposit. It mainly consists of three phases of intrusions, P-1 porphyritic biotite granite, P-2 equigranular biotite granite and P-3 granite porphyry. All three phases of granite contain quartz, plagioclase, K-feldspar and Fe-rich biotite. They have geochemical affinities of A-type granites, e.g., high FeOT/(FeOT + MgO) ratios (0.84-0.99), total alkali (Na2O + K2O, 7.50-9.04 wt.%), high Ga/Al ratios (10,000*Ga/Al > 2.6) and high Zr + Nb + Y + Ce concentrations (> 350 ppm). High Y/Nb ratios (> 1.2) suggest that the Qianlishan complex belongs to A2-type granite. Zircon U-Pb ages indicate a short age interval decreasing from 158-157 Ma, to 158-155 Ma and to 154 Ma for the P-1, P-2 and P-3 granites, respectively. These ages are similar to the mineralization age of the Shizhuyuan tungsten polymetallic deposit, within error. The Qianlishan granites were generated at low oxygen fugacity conditions based on the low values of zircon Ce4 +/Ce3 + ratios (1.53-198) and significantly negative Eu anomalies (EuN/EuN*, 0.03-0.13) in apatite. New zircon εHf(t) values for the P-3 granite range from - 13.0 to - 4.4, similar to those previously obtained for the P-1 and P-2 granites. Both the granite and apatite grains therein are characterized by high F but low Cl concentrations, suggesting the influx of a high F/Cl component. The P-2 granites especially contain higher F contents (1840-8690 ppm) and W (7-158 ppm) and Sn (6-51 ppm) concentrations and with stronger evolution features. Positive trends between F and W and Sn of Qianlishan complex indicate that high F source is crucial for mineralization of W and Sn. We consider that the lithospheric mantle source may have been metasomatized by subduction fluids in the far end of subduction zones to produce the A2 feature of the Qianlishan granite and the fluorine was introduced through

  8. The Blaník Gneiss in the southern Bohemian Massif (Czech Republic): a rare rock composition among the early palaeozoic granites of Variscan Central Europe

    NASA Astrophysics Data System (ADS)

    René, Miloš; Finger, Fritz

    2016-08-01

    Metamorphosed and deformed tourmaline-bearing leucogranites with a Cambro-Ordovician formation age are widespread in the Monotonous Group of the Variscan southern Bohemian Massif, Czech Republic. The rocks, known locally as Blaník gneiss, are strongly peraluminous and classify as phosphorus-rich low-T, S-type granite. The magma formed from a metapelitic source, most likely through muscovite dehydration melting. With respect to its low-T origin and the abundance of tourmaline, the Blaník gneiss is exotic within the spectrum of Early Palaeozoic granites of the Variscan fold belt of Central Europe. Coeval granitic gneisses in the neighbouring Gföhl unit of the Bohemian Massif can be classified as higher T S-type granites and were probably generated through biotite dehydration melting. The geochemical differences between the Early Palaeozoic granitic magmatism in the Gföhl unit and the Monotonous Group support models claiming that these two geological units belonged to independent peri-Gondwana terranes before the Variscan collision. It is suggested here, that the Gföhl unit and the Monotonous Group represent zones of higher and lower heat flow within the Early Palaeozoic northern Gondwana margin, respectively. The geochemical data presented in this study could be helpful for terrane correlations and palaeogeographic reconstructions.

  9. FROGS (Friends of Granite) Report Winter 1989

    NASA Astrophysics Data System (ADS)

    The purpose of FROGS reports is to disseminate information and stimulate thinking about felsic magmatism granitoids in particular. We publish semiannually, as part of VGP News, brief updates from investigators whose current research concerns felsic magmatism, information about events and publications that are relevant to granitoids, and commentaries on new and controversial themes. FROGS Reports is critically dependent on response from people interested in these topics. Please keep me (Calvin Miller, 6028B, Vanderbilt University, Nashville, TN 37235) informed about upcoming or recent conferences, major publications, and your own research. Also, please send me your suggestions for topics for pertinent commentaries for FROGS reports (or volunteer to write one yourself!).

  10. Fractal patterns of fractures in granites

    USGS Publications Warehouse

    Velde, B.; Dubois, J.; Moore, D.; Touchard, G.

    1991-01-01

    Fractal measurements using the Cantor's dust method in a linear one-dimensional analysis mode were made on the fracture patterns revealed on two-dimensional, planar surfaces in four granites. This method allows one to conclude that: 1. (1)|The fracture systems seen on two-dimensional surfaces in granites are consistent with the part of fractal theory that predicts a repetition of patterns on different scales of observation, self similarity. Fractal analysis gives essentially the same values of D on the scale of kilometres, metres and centimetres (five orders of magnitude) using mapped, surface fracture patterns in a Sierra Nevada granite batholith (Mt. Abbot quadrangle, Calif.). 2. (2)|Fractures show the same fractal values at different depths in a given batholith. Mapped fractures (main stage ore veins) at three mining levels (over a 700 m depth interval) of the Boulder batholith, Butte, Mont. show the same fractal values although the fracture disposition appears to be different at different levels. 3. (3)|Different sets of fracture planes in a granite batholith, Central France, and in experimental deformation can have different fractal values. In these examples shear and tension modes have the same fractal values while compressional fractures follow a different fractal mode of failure. The composite fracture patterns are also fractal but with a different, median, fractal value compared to the individual values for the fracture plane sets. These observations indicate that the fractal method can possibly be used to distinguish fractures of different origins in a complex system. It is concluded that granites fracture in a fractal manner which can be followed at many scales. It appears that fracture planes of different origins can be characterized using linear fractal analysis. ?? 1991.

  11. Riftogenic magmatism of western part of the Early Mesozoic Mongolian-Transbaikalian igneous province: Results of geochronological studies

    NASA Astrophysics Data System (ADS)

    Yarmolyuk, V. V.; Kozlovsky, A. M.; Salnikova, E. B.; Travin, A. V.; Kudryashova, E. A.

    2017-08-01

    Geochronological studies of rocks from a bimodal high-alkali volcanic-plutonic complex collected in the area of Kharkhorin zone of the Early Mesozoic Mongolian-Transbaikalian igneous province (MTIP) are made. The age of alkali granites from Olziit sum is 211 ± 1 Ma (U-Pb ID-TIMS on zircon) to 209 ± 2 and 217 ± 4 Ma (40Ar/39Ar on alkali amphibole); the age of alkali granite-porphyries from the area of Sant sum is 206 ± 1 Ma (U-Pb ID-TIMS on zircon). These rock series formed syncronously to the analogous magmatism episode in the Northern Gobi and Western Transbaikalian rift zones of the MTIP. The similarity of the age and composition of igneous associations of the MTIP suggests a common mechanism of its formation related to the effect of a mantle plume on the continental lithosphere at the base of the entire igneous zone having a zonal structure.

  12. The geology and petrogenesis of the southern closepet granite

    NASA Technical Reports Server (NTRS)

    Jayananda, M.; Mahabaleswar, B.; Oak, K. A.; Friend, C. R. L.

    1988-01-01

    The Archaean Closepet Granite is a polyphase body intruding the Peninsular Gneiss Complex and the associated supracrustal rocks. The granite out-crop runs for nearly 500 km with an approximate width of 20 to 25 km and cut across the regional metamorphic structure passing from granulite facies in the South and green schist facies in the north. In the amphibolite-granulite facies transition zone the granite is intimately mixed with migmatites and charnockite. Field observations suggests that anatexis of Peninsular gneisses led to the formation of granite melt, and there is a space relationship between migmatite formation, charnockite development and production and emplacement of granite magma. Based on texture and cross cutting relationships four major granite phases are recognized: (1) Pyroxene bearing dark grey granite; (2) Porphyritec granite; (3) Equigranular grey granite; and (4) Equigranular pink granite. The granite is medium to coarse grained and exhibit hypidiomorphic granular to porphyritic texture. The modal composition varies from granite granodiorite to quartz monzonite. Geochemical variation of the granite suite is consistent with either fractional crystallization or partial melting, but in both the cases biotite plus feldspar must be involved as fractionating or residual phases during melting to account trace element chemistry. The trace element data has been plotted on discriminant diagrams, where majority of samples plot in volcanic arc and within plate, tectonic environments. The granite show distinct REE patterns with variable total REE content. The REE patterns and overall abundances suggests that the granite suite represents a product of partial melting of crustal source in which fractional crystallization operated in a limited number of cases.

  13. Magmatic epidote and its petrologic significance

    SciTech Connect

    Zen, A.; Hammarstrom, J.M.

    1984-09-01

    Epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the Mesozoic accreted terranes between northern California and southeastern Alaska. Textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase. The observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure. Plutonic rocks bearing magmatic epidote must have formed under moderately high pressures, corresponding to lower crustal depths, under fairly oxidizing conditions. 23 references, 3 figures, 1 table.

  14. Zircon U-Pb age and geochemistry of the late ordovician monzonitic granite in the Xiaoxilin from the lesser Khingan

    NASA Astrophysics Data System (ADS)

    Zhao, Feifei; Sun, Fengyue; Li, Liang; Wang, Jian

    2017-04-01

    In this paper, we present new U-Pb zircon ages and major and trace elements for the Late Ordovician monzonitic granite rocks in Xiaoxilin area in the Eastern lesser khingan of Northeast China to elucidate the westward subduction of the Oceanic plate in Late Ordovician. U-Pb zircon dating results demonstrate that the monzonitic granites formed at 451±5Ma, belonging to the Late Ordovician. These monzonitic granites are characterized have SiO2 of 66.45%~72.93%, Na2O of 2.41%~3.93%, K2O of 3.09%~5.58%, CaO of 2.02%∼3.76%, ALK of 6.56%∼7.99% and A/CNK=0.97~1.02, belonging to the high-K calc-alkaline series. The monzonitic granites is characterized by the enrichment of LILEs (e.g., Rb and K) and incompatible elements (e.g., Th and U), and depletion of HFSEs (e.g., Nb, Ta, Sr, P and Ti), as well as very lesser Eu anomalies (Eu/Eu*=0.49~1.06). The rock falls into the zone of Pre-Plate collision with the characteristics of active continental margin before the collision. Combine the mineral assemblage and geochemical characteristics, it is believed that the monzonitic granite in Xiaoxilin area was formed in the environment of oceanic crust subduction, which indicates that there was an westward subduction oceanic plate between Jiamusi Massif and Songnen-Zhangguangcailing Massif. The melt/fluid precipitated from the subducting oceanic plate confessed the overlying mantle wedge and caused the partial melting of it, which resulted in the arc magmatism. The Jiamusi Massif and Songnen-Zhangguangcailing Massif had not yet joined in the Late Ordovician.

  15. Geochemical evidence concerning the nature of the source region to the Middle Proterozoic Granite-Rhyolite Province

    SciTech Connect

    Shuster, R.D. . Dept. Geography Mueller, P.A.; Heatherington, A.L. . Dept. Geology)

    1992-01-01

    The mostly buried 1.5--1.3 Ga old Granite-Rhyolite Province of the midcontinent of North America, is characterized by extensive, undeformed silicic volcanic rocks and related epizonal granitic plutons. Thirty-three previously dated samples from a wide geographic range (Michigan to Colorado) have been analyzed to determine their chemical and Nd and Pb isotopic compositions in order to constrain source regions and processes involved in the formation of these rocks. Major and trace element analyses of these rocks indicate their anorogenic nature, with relatively high Ce/Nb and Y/Nb ratios, as well as relatively high Ga/Al ratios. Geochemically, these rocks are similar to the A2 granites of Eby (1992), which are thought to be generated from the melting of crust which has experienced at least one cycle of subduction-related magmatism. Rare earth element and Pb isotopic data suggest melting at middle to shallow depths. The isotopic data (Nd and Pb) indicate little to no contribution of Archean crust to the source of these rocks. Initial Pb isotopic ratios (208Pb/204Pb) suggest a low Th/U ratio in the source, which contrasts strongly with high Th/U ratios of the Wyoming Province. The Pb isotopic ratios for these rocks are variable, but cluster about the orogene plumbotectonics curve. The variability in the data suggest sources which are variable in their U/Pb ratios and/or ages. The isotopic data are consistent with the existence of a proposed lithospheric boundary which trend NE-SW through the Granite-Rhyolite Province and separates 1.65 Ga old lithosphere (to the NW) from 1.5 Ga old lithosphere (to the SE). Samples analyzed from either side of this boundary have different isotopic signatures. Many of the samples appear to be derived from sources which are only slightly older than the crystallization ages of the granites themselves.

  16. Identification of granite varieties from colour spectrum data.

    PubMed

    Araújo, María; Martínez, Javier; Ordóñez, Celestino; Vilán, José Antonio

    2010-01-01

    The granite processing sector of the northwest of Spain handles many varieties of granite with specific technical and aesthetic properties that command different prices in the natural stone market. Hence, correct granite identification and classification from the outset of processing to the end-product stage optimizes the management and control of stocks of granite slabs and tiles and facilitates the operation of traceability systems. We describe a methodology for automatically identifying granite varieties by processing spectral information captured by a spectrophotometer at various stages of processing using functional machine learning techniques.

  17. Identification of Granite Varieties from Colour Spectrum Data

    PubMed Central

    Araújo, María; Martínez, Javier; Ordóñez, Celestino; Vilán, José Antonio

    2010-01-01

    The granite processing sector of the northwest of Spain handles many varieties of granite with specific technical and aesthetic properties that command different prices in the natural stone market. Hence, correct granite identification and classification from the outset of processing to the end-product stage optimizes the management and control of stocks of granite slabs and tiles and facilitates the operation of traceability systems. We describe a methodology for automatically identifying granite varieties by processing spectral information captured by a spectrophotometer at various stages of processing using functional machine learning techniques. PMID:22163673

  18. The origin of radiogenic isotope variability in granites: intracrustal recycling and/or juvenile crust production?

    NASA Astrophysics Data System (ADS)

    Farina, Federico

    2014-05-01

    Radiogenic isotope data determined at the crystal and sub-crystal scale has led to the recognition that isotope variability is commonplace in igneous rocks of intermediate to acidic composition. This evidence has often been considered as the smoking gun supporting the involvement of mantle-derived magmas in the genesis of many granites; with the implication that crustal growth is reflected in the genesis of felsic rocks exhibiting inter- and intra-crystalline isotopic diversity. Such interpretations overlook two important realities. Firstly, that granites and rhyolites, tap source rock volumes that are very unlikely to have been isotopically homogeneous. Therefore, some aspects of the isotopic variability recorded in granites may represent mixing between magmas produced by partial melting of isotopically diverse domains of the source. Secondly, typical source rocks also exhibit isotopic diversity at the mineral-scale that either may homogenize during the pre-anatectic metamorphic event, melting and magma extraction, or be transferred to the granite. The isotopic variability of the source may be a primary feature, such as in the case of ɛHf diversity among detrital zircons in metasediments, or be acquired by the source through time, as the result of isotopic ingrowth. When isotopic equilibrium between melt and crustal residue is not attained, the composition of the melt will be dependent on the isotopic compositions of the reactant phases, the stoichiometry of the melting reaction as well as on the amount of accessory phases that dissolve into the melt. In such situations, an individual source is able generating melts with different isotopic composition. Here, I report two case studies. In the first one, the ɛHf range recorded by magmatic and inherited zircon in the S-type Peninsula pluton (South Africa) is investigated as a function of sample size. At all scales, the ɛHf variability in the magmatic zircon fraction (ca. 8 ɛHf units) matches well that portrayed

  19. Magmatic intrusions and hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Gulick, Virginia Claire

    1993-01-01

    This dissertation investigates the possible role of hydrothermally driven ground-water outflow in the formation of fluvial valleys on Mars. Although these landforms have often been cited as evidence for a past warmer climate and denser atmosphere, recent theoretical modeling precludes such climatic conditions on early Mars when most fluvial valleys formed. Because fluvial valleys continued to form throughout Mars' geological history and the most Earth-like stream valleys on Mars formed well after the decline of the early putative Earth-like climate, it may be unnecessary to invoke drastically different climatic conditions for the formation of the earliest stream valleys. The morphology of most Martian fluvial valleys indicates formation by ground-water sapping which is consistent with a subsurface origin. Additionally, many Martian fluvial valleys formed on volcanoes, impact craters, near fractures, or adjacent to terrains interpreted as igneous intrusions; all are possible locales of vigorous, geologically long-lived hydrothermal circulation. Comparison of Martian valley morphology to similar features on Earth constrains valley genesis scenarios. Volumes of measured Martian fluvial valleys range from 1010 to 1013 m3. Based on terrestrial analogs, total water volumes required to erode these valleys range from approximately 1010 to 1015 m3. The clustered distribution of Martian valleys within a given terrain type, the sapping dominated morphology, and the general lack of associated runoff valleys all indicate the importance of localized ground-water outflow in the formation of these fluvial systems. An analytic model of a conductively cooling cylindrical intrusion is coupled with the U.S. Geological Survey's numerical ground-water computer code SUTRA to evaluate the magnitude of ground-water outflow expected from magmatically-driven hydrothermal systems on Mars. Results indicate that magmatic intrusions of several 102 km3 or larger can provide sufficient ground

  20. Mantle hydrous-fluid interaction with Archaean granite.

    NASA Astrophysics Data System (ADS)

    Słaby, E.; Martin, H.; Hamada, M.; Śmigielski, M.; Domonik, A.; Götze, J.; Hoefs, J.; Hałas, S.; Simon, K.; Devidal, J.-L.; Moyen, J.-F.; Jayananda, M.

    2012-04-01

    ähle et al., 1987).The previously published data as well as the new ones point to volatile elements from both mantle and crust playing a prominent role in the petrogenesis of magmatic rocks during the Archaean. Their composition differs significantly in regard to water and CO2 activity. The present contribution gives an evidence of hydrous mantle-derived fluids. Taking under consideration two-end members model proposed for Archaean mantle, the contribution favours wet-mantle model. The work has been done within the framework of IGCP-SIDA 599 and has been funded by IGSci PASci 'Hybrid' and IGSci PASci-CNRS-UMR 6524-LMV project: 'Equilibration and re-equilibration processes in Archaean granites'. Klein-BenDavid, O., Izraeli, E.S., Hauri, E. & Navon, O. (2007). Fluid inclusions in diamonds from the Diavik mine, Canada and the evolution of diamond-forming fluids. Geochimica et Cosmochimica Acta 71, 723-744. Słaby, E., Martin, H., Hamada, M., Śmigielski, M., Domonik, A., Götze, J., Hoefs, J., Hałas, S., Simon, K., Devidal, J-L., Moyen, J-F., Jayananda, M. (2011) Evidence in Archaean alkali-feldspar megacrysts for high-temperature interaction with mantle fluids. Journal of Petrology (on line). doi:10.1093/petrology/egr056. Stähle, H.J., Raith, M., Hoernes, S. & Delfs, A. (1987). Element mobility during incipient granulite formation at Kabbaldurga, Southern India. Journal of Petrology 28, 803-834.

  1. Assessment of radiological hazard of commercial granites from Extremadura (Spain).

    PubMed

    Guillén, J; Tejado, J J; Baeza, A; Corbacho, J A; Muñoz, J G

    2014-06-01

    The term "commercial granite" comprises different natural stones with different mineralogical components. In Extremadura, western Spain, "commercial granites" can be classified in three types: granite s.s. (sensus stricti), granodiorite, and diorite. The content of naturally occurring radionuclides depended of the mineralogy. Thus, the (40)K content increased as the relative content of alkaline feldspar increased but decreased as the plagioclase content increased. The radioactive content decreased in the following order: granite s.s. > granodiorite > diorite. In this work, the radiological hazard of these granites as building material was analyzed in terms of external irradiation and radon exposure. External irradiation was estimated based on the "I" index, ranged b