| 1. |
- Marks, M. A. W., et al.
(författare)
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Sodic pyroxene and sodic amphibole as potential reference materials for in situ lithium isotope determinations by SIMS
- 2008
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Ingår i: Geostandards and Geoanalytical Research. - 1639-4488. ; 32:3, s. 295-310
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Tidskriftsartikel (refereegranskat)abstract
- Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilimaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro-drilled material analysed by MC-ICP-MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 +/- 51 mu g g(-1) (2s, n = 69, MC-ICP-MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 +/- 3.6 mu g g(-1) (2s, n = 33) as determined by SIMS. The seven micro-drilled regions measured by solution MC-ICP-MS returned slightly lower concentrations (41-46 mu g g(-1)), but still overlap with the SIMS data within uncertainty. Based on MC-ICP-MS and SIMS analyses, the variation in delta(7)Li was about 1 parts per thousand in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC-ICP-MS and SIMS. The latter deviated from the MC-ICP-MS results by -6.0 +/- 1.9 parts per thousand (2s) for the amphibole and by -3.9 +/- 1.9 parts per thousand (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC-ICP-MS results, mean delta(7)Li values of +0.7 +/- 1.2 parts per thousand (2s, n = 10) for the arfvedsonite crystal and of -3.7 +/- 1.2 parts per thousand (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request.
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| 3. |
- Topuz, G., et al.
(författare)
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Carboniferous high-potassium I-type granitoid magmatism in the Eastern Pontides: The Gumushane pluton (NE Turkey)
- 2010
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Ingår i: Lithos. - 0024-4937. ; 116:1-2, s. 92-110
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Tidskriftsartikel (refereegranskat)abstract
- The Gumushane pluton, a high-K calc-alkaline I-type granodionte/granite complex, forms an important component of the pre-Liassic basement of the Eastern Pontides (NE Turkey) In its eastern part, the pluton shows a compositional zonation ranging from biotite-hornblende granodiorite in the NW through biotite-hornblende granite to leucogranite/granophyre in the SE Numerous mafic microgranular enclaves (up to similar to 40 cm in diameter) suggest the former presence of globules of mafic melt during crystallization Emplacement of the pluton occurred during the latest Early Carboniferous, as shown by the 320 +/- 4 Ma (40)Ar-(39)Ar bionte/homblende and 324 +/- 6 Ma LA-ICP-MS U-Pb zircon ages. In Harker diagrams, samples of the different rock types exhibit well-defined data trends. With increasing SiO(2), the abundances of TiO(2), Al(2)O(3), Fe(2)O(3)(tot), MnO, MgO, CaO, P(2)O(5) and Sc decrease, but those of K(2)O and Rb increase However, the variations of Sr, Ba, (La/Yb)(cn) Sr/Y and Sigma REEs vs SiO(2) form distinctive groupings, which cannot be explained by a simple fractional crystallization Chondrite-normalized (cn) REE patterns of granodionte/granite samples show concave-upward shapes with (La/Yb)(cn) ranging from 5.2 to 124 and Eu/Eu* from 084 to 0.47, while there is almost no fractionation of the middle REE relative to the heavy REE In primitive mantle-normalized element concentration diagrams, all rocks display marked negative anomalies in Ba, Nb/Ta, Sr, P and Ti. but positive anomalies in K and Pb. These geochemical features imply a fractionating mineral assemblage of clinopyroxene, amphibole and plagioclase without significant involvement of garnet. The granophyres are, on the other hand, characterized by higher K(2)O/Na(2)O and Rb/Sr ratios, lower (La/Yb)(cn), ratios (1 3 to 4 8) and more pronounced negative anomalies in Ba, Nb/Ta, Sr, Eu, P and Ti Initial epsilon(Nd) values range from -3 78 to -5.30 and Nd model ages from 1 38 to 163 Ga The magmas of the granite/granodiorite portion were probably generated by partial melting of high-potassic amphibolitic rocks, and those of the granophyres by a relatively felsic micaceous crustal source. The Gumushane pluton was emplaced at the wake of the lowpressure-high-temperature metamorphism, and is regarded as a late phase of Hercynian orogeny in the Eastern Pontides (C) 2010 Elsevier B.V All rights reserved
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| 4. |
- Topuz, G., et al.
(författare)
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Carboniferous mafic-ultramafic intrusions in the Eastern Pontides (Pulur Complex): Implications for the source of coeval voluminous granites
- 2023
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 436-437
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with the age and petrogenesis of mafic-ultramafic intrusions ranging in size from a few meters to 10 km within the Early Carboniferous high-grade gneisses of the Pulur Complex in the Eastern Pontides. The intrusions comprise dunite, wehrlite, gabbronorite, leucogabbro, anorthosite and ilmenite-bearing gabbronorite of cumulus origin, and are crosscut by dikes of ilmenite-bearing gabbronorite, leucogranite and microdiorite. U–Pb dating on zircons from gabbronorite, anorthosite and leucogranite yielded igneous crystallization ages of 322–326 Ma, indicating that the intrusions were emplaced ca. 5–7 Ma after the peak of high-grade metamorphism, and form part of the Late Carboniferous high-volume magmatism in the region. In most cumulate rocks, Cr–Al spinel, olivine and plagioclase were early crystallizing phases, followed by orthopyroxene, clinopyroxene and hornblende. Whole rock geochemical data suggest that wehrlite, gabbronorite, leucogabbro and anorthosite stem from a common magma, and ilmenite-bearing gabbronorite and dikes of leucogranite and microdiorite from different magmas. Application of mineral/melt partition coefficients to trace element compositions of clinopyroxene and hornblende in cumulate rocks suggests that the main cumulate body was derived from middle- to high-K calc-alkaline basic melts, and relatively late ilmenite-bearing gabbronorites from hypersthene-normative Ca-rich melts. All the rock types display radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios, which are indistinguishable from those of the coeval voluminous high-K calc-alkaline I-type granites in the region; the isotopic ratios are probably related to the metasomatism of the lithospheric mantle by sediment-derived melts. We suggest that the parental melts of the mafic-ultramafic intrusions and those of the high-K calc-alkaline granites were genetically related, and melts of the high-K calc-alkaline granites were probably derived from the melting of newly underplated calc-alkaline basic material at lower crustal depths, that were compositionally comparable to the parental magmas of the mafic-ultramafic intrusions.
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| 5. |
- Topuz, G., et al.
(författare)
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Post-collisional adakite-like magmatism in the Agvanis Massif and implications for the evolution of the Eocene magmatism in the Eastern Pontides (NE Turkey)
- 2011
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Ingår i: Lithos. - 0024-4937. ; 125:1-2, s. 131-150
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Tidskriftsartikel (refereegranskat)abstract
- In the Anatolia, the Caucasus and northwest Iran, the Eocene epoch is characterized by widespread basic to acidic magmatism, whose temporal and spatial evolutions and origin are poorly understood. In this paper, we provide geochronological and geochemical data on a suite of Early Eocene intrusions from northeast Turkey and discuss their origin within a regional tectonic framework. Post to late-collisional, moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude Permo-Triassic low-grade metamorphic rocks in the southern part of the Eastern Pontides very close to the Neo-Tethyan Izmir-Ankara-Erzincan suture. In places, the intrusives display well-developed subsolidus foliations, indicating ongoing penetrative deformation during and shortly after emplacement. Different emplacement depths were inferred based on the contact metamorphic mineral assemblages. Al-in-hornblende barometry and igneous textures (quartz diorite similar to 14-16 km vs dacitic porphyries <= 7 km). Biotite and hornblende Ar-Ar and zircon U-Pb data indicate that the compositionally and texturally different intrusives were emplaced at similar to 51 Ma (Ypresian). Three lines of evidence indicate that the Early Eocene represents a tectonically active time with high exhumation rates (>= 0.6 cm a(-1)): (i) the quartz diorite and dacitic porphyries were emplaced at different crustal depths, (ii) the emplacement ages of these texturally distinct intrusive rocks are geochronologically undistinguishable, and (iii) intrusive rocks locally show a well-developed foliation. The intrusive rocks display high abundances of Al2O3, Sr, Ba. LREEs and low abundances of Y, Sc and HREEs, and are similar to high-silica adakites from supra-subduction zone settings. The geochemical features imply a residual and/or fractionating assemblage rich in hornblende, garnet, pyroxene, and poor in plagioclase. All rock types display similar Sr-Nd isotopic characteristics with initial epsilon(Nd) and Sr-87/Sr-86 values ranging from 1.0 to -1.1 and from 0.70421 to 0.70494, respectively. These three coeval rock groups (quartz diorite. leucogranodiorite and dacite porphyries) were generated from a similar source by variable degrees of partial melting and fractionation. These data together with those from the literature clearly reveal that the adakitic signature is common in Paleocene to Early Eocene igneous rocks in northern Turkey on both sides of the Izmir-Ankara-Erzincan suture, but disappears towards the Middle Eocene. Regional geological constraints indicate that the continental collision between the Pontides and the Anatolide-Tauride block occurred in the Paleocene and that the Middle Eocene represents a period of major extension, characterized by a marine transgression. We therefore suggest that the Early Eocene adakitic magmatism in northern Turkey resulted from the presence of a thickened continental crust following the continental collision along the Neo-Tethyan Izmir-Ankara-Erzincan suture whereas the voluminous Middle Eocene magmatism was related to extensional collapse of a thickened orogen. (C) 2011 Elsevier B.V. All rights reserved.
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