Akademik Veri Yönetim Sistemi
TURKIYE JEOLOJI BULTENI-GEOLOGICAL BULLETIN OF TURKEY, sa.1, ss.49-81, 2006 (ESCI)
Mineralogical, petrographical and geochemical features of Liassic, Upper Cretaceom and Eocene volcanic roeks in the Torul region, which aresituatedalongthe transiiion betmen the Northern and Southern Zones of Eastern Pontides, are investigated. Liassic volcanics are mainly basaltic, basattic andesitic and trachy-cindesitic in composuion. Bosalt contains labrador (An(51.63)), olivine and augite, whi.le andesite coniains oligoclase (An(27-2)s), hornblende and annite (Mg# 0.58-0.67). These volcanics has medium-high K contents, and are tholeiiic to calc-alkaline in nature. (La/Lu)N values are between 16.0 and 23.8. SiO2 versus major and irace element variation plots show good correlatiom, suggesting sigmficant role of olivine, clinopyroxene, plagioclase and Fe-Ti oxide fractionation during the evolution. The rocks have high LlLE (BA, Kb, Sr) andLREE (La, Ce) but low Ht'SE (Zr, Y, Ti) contents. Trace element distributions show similarities o/N-type MORB sources. Ba/La ratios are between 3 and 9, and show similarities ofocean island basalt. Ba/Nb, Nb/Th, Th/Y and Nb/Y ratios sha\v similarities ofocean island basalt, while KjRb, K/Ba, Sr/Rb, Zr/Nb, Ba/Th, Ba/La, Zr/Rb and Y/Nb ratios show similarities of N-type MORB. Upper Cretaceous volcanics are bimodal and, are andesite, dacite and rhyolite in composiuon. Andesite contains andesine (An(41-49)), acunoliuc hornblende (Mg# 0.83-0.84), magnesio-hornblende (Mg# 0.79) and biotite: dacite contains oligocla.se, sanidine, auartz andannite (Mg# 0.58-0,62): rhyolite contains andesine-oligoclase (An(27-i4)), guartz, sanidine, biotite and hornblende. (LalLu) N values are between 3.7 and 14.7, Increasing in SiO2 versus K2O, Rb, Th, Ba and Nb contents show positive correlation, suggesting significant plagioclase, hornblende and Fe-Ti oxide fractionation during the evolution of volcanics. These volcanics enrlchedLlLE elements but depleted HFS elenienis at the N-type MORB normalhedira.ee element diagrams. Negaiive Nb and Ti anomalies shows influence of subduction component during the evolution of main magmas. Ba/La ratios are between 15 and 40, and show similarities of typical island are basalt. La/Nb, Ba/Nb, Ba/Th, Rb/Nb, K/Nb, Ba/La, K/Ba, Nb/Th, Zr/Nb and Sm/Nd ratios show similarities of island are calc-alkalinebasalt. Eocene volcanics are andesite in composiiion and contain andesine (An(4i-)44)-oligoclase (An<^>(u) over cap .jg), magnesio-hastingsitic hornblende (Mg# 0.72-0.92), magnesio-hastingsitic (Mgtt 0.84-0.91), tschermakitic hornblende (Mg4 0.70-0.77), augite (Wo43-44), dlopside (Wo46) and biotite. These volcanics are calc-alkaline in character, and has medhim-high K contents. (La/Lu) N values are between 4.6 and 6.9. Fractionation of plagioclase, pyroxene, hornblende and Fe-Ti oxide played an importand role in Eocene volcanic rocks. Rocks have high LlLE and LREE contents and low HFSE contents. Negaiive Nb and Ti anomalies according to the N-type MORB shows influence of subduction component during the evolution of main magmas. Ba/l.a rntioz arebelween 43 and 80, andshow similarUi.es of islandare basalt. Ba/Nb, Ba/Th. Rb/Nb, K/Nb, Ba/La, K/Rb, Zr/Rb, Sm/Nd and Zr/Ba ratios show similarities of island are calc-alkaline basalt. Diseguitibriiim tesiures showing magma mixing such as osculatory zoning, sieve testured and resorbedplagioclase phenoaysts, embayed auartz, breakdown of hornblendes and biotites are commonly observed in these rocks. Reverse zoning such as decreasing of anorlhite contents of plagioclase phenocrysts from rim to core, decreasing of Mg number of hornblende and pyroxene phenocrysts from rim to core, suggesting of magma mbdng in gechemically. In addition, basic enelaves observing in Upper Cretaceous daciles shows signijicant role of magma mingling during the evolution of Torul Volcanics. Assimilation with together fractional crystallisation has signijicant role the evolution of volcanics. High SiO2, La and Ce contents, LlLE enrichment, high K2O/ Na2O ratios andlow Ti/Yb ratios, and low P2O5 concentrations Indlcate interferenceofmain magmas with cruatul materials. Mineralogical, Petrographical andgeochemieal dala indicate that the Torul volcanic rocks evolved hy the fractional crystallizauon and magma mixtng +/- coniamination/assimilauon of a parental magma derived from lower crust and/or metasomatized upper mantle, and the sources of those volcanics are enriched-MORB manile in Liassic, and metasomatised MORB mantle in Upper Cretaceous and Eocene.