Geochemistry, mineralogy and petrogenesis of the northeast Niğde volcanics, central Anatolia, Turkey

Abstract

The volcanics exposed in the northeast Nigde area are characterized by pumiceous pyroclastic rocks present as ash flows and fall deposits and by compositions ranging from dacite to rhyolite. Xenoliths found in the volcanics are basaltic andesite, andesite and dacite in composition. These rocks exhibit linear chemical variations between end-member compositions and a continuity of trace element behaviour exists through the basaltic andesite-andesite-dacite-rhyolite compositional range. This is consistent with the fractionation of ferromagnesian minerals and plagioclase from a basaltic andesite or andesite parent. These rocks are peraluminous and show typical high-K calc-alkaline differentiation trends with total iron content decreasing progressively with increasing silica content. Bulk rock and mineral compositional trends and petrographic data suggest that crustal material was added to the magmas by subducted oceanic crust and is a likely contaminant of the source zone of the Nigde magmas.The chemical variations in these volcanics indicate that crystal liquid fractionation has been a dominant process in controlling the chemistry of the northeast Nigde volcanics. It is also clear, from the petrographic and chemical features, that magma mixing with disequilibrium played a significant role in the evolution of the Nigde volcanic rocks. This is shown by normal and reverse zoning in plagioclase and resorption of most of the observed minerals. The xenoliths found in the Nigde volcanics represent the deeper part of the magma reservoir which equilibrated at the higher pressures.

Review of post-collisional volcanism in the Central Anatolian Volcanic Province (Turkey), with special reference to the Tepekoy Volcanic Complex

“…The Nigde ignimbrites are rhyolitic-rhyodacitic-dacitic in composition, while the lithic fragments within the ignimbrites are basaltic andesites, andesites, and dacites, dacites being much more common than the others (Yurtmen and Rowbotham 2002). Yurtmen and Rowbotham (2002) also identified disequilibrium textures within the xenoliths, and gave mineral chemistry data as an evidence for magma mixing. Based on these points, Aydin (2008) suggested basaltic andesite and dacite fragments within the ignimbrites of Yurtmen and Rowbotham (2002) display comparable mineral compositions to MPv.…”

“…Yurtmen and Rowbotham (2002) also identified disequilibrium textures within the xenoliths, and gave mineral chemistry data as an evidence for magma mixing. Based on these points, Aydin (2008) suggested basaltic andesite and dacite fragments within the ignimbrites of Yurtmen and Rowbotham (2002) display comparable mineral compositions to MPv. However, MPv volcanics are not spatially and temporally comparable to the lithic fragments sampled by the Nigde ignimbrites, and there are no age and isotope constraints on the lithic clasts to make such correlation.…”

“…Despite having dacite and basaltic andesite compositions in the MPv data set, Aydin (2008) quoted the lithic xenoliths within the ''volcanics'' (ignimbrites, more precisely) in northeast Nigde region (Yurtmen and Rowbotham 2002) for end members to use in magma mixing modelling. The Nigde ignimbrites are rhyolitic-rhyodacitic-dacitic in composition, while the lithic fragments within the ignimbrites are basaltic andesites, andesites, and dacites, dacites being much more common than the others (Yurtmen and Rowbotham 2002). Yurtmen and Rowbotham (2002) also identified disequilibrium textures within the xenoliths, and gave mineral chemistry data as an evidence for magma mixing.…”

Gümüşler-Aktaş (Ni̇ğde) Bölgesi̇ni̇n Genel Jeoloji̇si̇ Ve Yapi Malzemesi̇ Potansi̇yeli̇

“…İnceleme alanı ve yakın çevresinde Niğde Grubuna ait alttan üste doğru farklı gnays çeşitleri içeren Gümüşler Formasyonu, gnays, amfibolit ve karbonat ardalanmasından oluşan Kaleboynu Formasyonu ve masif karbonatlardan oluşan Aşıgediği Formasyonu yayılım sunmaktadır [2][3][4][5][6]. Bölgenin jeolojik, tektonik, metamorfizma ve maden potansiyeline yönelik olarak birçok çalışma yapılmıştır [7][8][9][10][11][12][13][14][15][16][17][18]. Bölgede Orta Anadolu Kristal Kompleksi olarak bilinen bu kayaçlar, Neojen öncesi temel kayaçlarıdır [8,9].…”

“…Bu kompleks Üst Kratase-Paleosen dönemine ait granitoyidler tarafından kesilmekte ve benzer stratigrafik dizilimler sunmaktadır [3,7]. Bölgede gözlenen piroklastikler riyolitik ve dasitik bileşime sahiptir [18]. Gümüşler ve Aktaş yöresi kayaçlarının mühendislik ve malzeme özelliğine yönelik çalışmalar ise oldukça az sayıdadır [19][20][21][22][23].…”