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- MakaleYalnız künye2014Scopus SJRQ1Geochemical fingerprints of Late Triassic calc-alkaline lamprophyres from the Eastern Pontides, NE Turkey: A key to understanding lamprophyre formation in a subduction-related environment
Karsli, Orhan; Dokuz, Abdurrahman; Kaliwoda, Melanie; Uysal, Ibrahim; Aydin, Faruk; Kandemir, Raif; Fehr, Karl-Thomas
The Eastern Pontides in NE Turkey is one of the major orogenic belts in Anatolia. In this paper, we report our new 40Ar/39Ar dating, mineral chemistry, major and trace elements and Sr-Nd-Pb isotopic analyses of the lamprophyre intrusions in this region. The lamprophyres are widely scattered and intrude Late Carboniferous granitoid rocks. The lamprophyres exhibit fine-grained textures and are mineralogically uniform. Hornblende 40Ar/39Ar dating yielded a plateau age of 216.01±10.64Ma. Based on their geochemistry, mineral compositions and paragenesis, the lamprophyres are classified as calc-alkaline lamprophyres in general and spessartites in particular, which are rich in large ion lithophile elements (e.g., Rb, Ba, K) but depleted in Nb and Ti. Our samples exhibit moderate fractionation in LREE patterns approximately 100 times that of chondrite but HREE abundances less than 10 times that of chondrite. These calc-alkaline lamprophyres display a range of ISr (216Ma) values from 0.70619 to 0.71291 and εNd (216Ma) values from -1.4 to 4.1, with TDM=1.11 to 2.20Ga. Their Pb isotopic ratios indicate an enriched mantle source. The enrichment process is related to metasomatism of a subcontinental lithospheric mantle source, which is caused by a large quantity of H2O-rich fluids, rather than sediments released from oceanic crust at depth during the closure of the Paleotethys Ocean in Triassic times. All of the geochemical data and the trace element modeling suggest that the primary magma of the calc-alkaline to high-K calc-alkaline spessartites was generated at depth by a low degree of partial melting (~1-10%) of a previously enriched lithospheric mantle wedge consisting of phlogopite-bearing spinel peridotite. The ascendance of a hot asthenosphere triggered by extensional events caused partial melting of mantle material. The rising melts were accompanied by fractional crystallization and crustal contamination en route to the surface. All of the geochemical features combined with regional data suggest that the Eastern Pontides calc-alkaline lamprophyres originated in an extensional environment along an active continental margin throughout the Late Triassic. Such an extensional event, causing upwelling of hot asthenosphere, led to the opening of the northern branch of the Neotethys as a back-arc basin farther south of the Eastern Pontides.
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İncele - MakaleYalnız künye2012Scopus SJRQ1A-type granitoids from the Eastern Pontides, NE Turkey: Records for generation of hybrid A-type rocks in a subduction-related environment
Karsli, Orhan; Caran, Şemsettin; Dokuz, Abdurrahman; Çoban, Hakan; Chen, Bin; Kandemir, Raif
The Eastern Pontides is characterized by the many of intrusive bodies formed throughout the late Mesozoic-early Cenozoic. Most of these are I-type granitoids, but here, we present for the first time an A-type pluton from the region to assess source characteristics and geodynamic implications. The A-type Pirnalli pluton has a SHRIMP zircon U-Pb age of 81.2±1Ma. It is composed of granite, syenite and quartz monzonite, and its enclaves are monzonitic in composition with elevated Ga/Al ratios and low Mg# (<42). The pluton is dominantly metaluminous (A/CNK=0.88 to 1.00) and belong to shoshonitic and ultra-potassic series. The samples are highly enriched in LREE and show significant negative Eu (Eu/Eu *=0.33 to 0.92), Ba, Nb, Sr and Ti anomalies in the spidergrams. The host rocks and their enclaves posses quite similar Sr-Nd isotopic compositions (I Sr=0.70693 to 0.70736, ε Nd (81Ma)=-2.6 to -2.0, T DM=0.94 to 1.12Ga), pointing to a lower crustal parental magma with a minor contribution of lithospheric mantle. We hypothesize that upwelling of asthenosphere triggered melting of chemically enriched upper mantle and basic magma formed. Melting of lower crust was provided by the underplating of this basic magma. Mixing between lower crust- and mantle-derived melts at depths of lower crust appears to be most reasonable petrogenetic process responsible for generation of the pluton. Sr-Nd isotope modeling suggests mixing of 82-90% of the lower crustal-derived melt with ~10-18% of the mantle-derived melt. Then the hybrid melt ascended to shallower crustal level and underwent a limited fractionation process to generate a variety of rock types. Our data also suggest that the A-type Pirnalli pluton likely formed at an extensional environment of active continental margin throughout the late Cretaceous. Ongoing extension then led to opening of Black Sea as a back-arc basin further north of the Eastern Pontides.
AtıfScopus95WoS91OpenAlex97İncele