The petrology and geochemistry of volcanic rocks from the Northern Harşit river area, Pontid Volcanic Province, Northeast Turkey

摘要: Abstract Two volcanic cycles can be distinguished, in the Pontid magmatic arc. They comprise an Upper Cretaceous, Lower Volcanic Cycle of which only waning stage contains abundant pyroclastic rocks. The latter show spatial association to fault pattern and are closely related mineralisation. overlying, early Tertiary, shows evidence explosive vulcanicity Basic Series. Dacites rhyodacites locally developed again with faulting. Comparison major minor element chemistries two demonstrates clear separation into a lower tholeiitic upper calc-alkaline cycle. rocks similar chemistry suites from island arcs other areas. origin magma is ascribed melting “dry” amphibolite during subduction Tethyan ocean floor beneath “Pontian Land”. This resulted low K abundances K/Rb ratios, some Fe enrichment basalts. thought derived later process when amphibole was joined by biotite or phlogopite. thus enriched no due probable higher water content. Cr Ni contents Cycle, together K, may imply lherzolite overlying subducted slab.