Journals / Turkish Journal of Earth Sciences / 2004 / Cilt: 13 - Sayı: 3
Magma Interaction Recorded in Plagioclase Zoning in Granitoid Systems, Zigana Granitoid, Eastern Pontides, Turkey
- Pages
- 287–306
- DOI
- —
Abstract
Plagioclase crystals characterized by compositional zoning are typical of the Zigana Granitoid (ZG), NE Turkey. The zoned crystals, which show textural equilibrium with the assemblage quartz + plagioclase + K-feldspar + hornblende + biotite + pyroxene + magnetite + ilmenite, exhibit oscillatory zoning. The zoned plagioclase crystals, ranging in size from 3 to 6 mm, are oval and larger than normal lath-shaped crystals. The zoned crystals are divided petrographically into two main types: (i) crystals zones only at their rims, with spongy cores; and (ii) completely zoned ones. Composition of the zoned crystals ranges from An23 (oligoclase) to An70 (labradorite). Plagioclase crystals with oscillatory zoning are governed by strong substitution mechanisms of Ca2+ Na+, Al3+ Si4+ and weak substitution of Fe3+ for Si4+. The Fe2O3(t) (wt %) contents of the subject plagioclases increase with increasing An content. The petrographic and compositional changes from rim to rim (oscillatory zoning), and positive correlation between Fe2O3(t) (wt %) and An (mol %) contents of the zoned plagioclases, suggest recurrent mafic magma injection into a felsic magma chamber, and thus magma interaction as a dominant magmatic process during the evolution of the Zigana Granitoid (ZG).
Özet
Bileflimsel zonlanma ile karakterize olan plajiyoklaz kristalleri Zigana Granitoyidi’nde (ZG), KD-Türkiye tipik olarak gözlenmektedir. Kuvars + plajiyoklaz + K-feldspat + hornblend + biyotit + piroksen + magnetit + ilmenit denge kristaleflmesi sunan zonlu plajiyoklaz kristalleri sal›n›ml› (oscillatory) zonlanma gösterirler. Kristal boylar› 3 ile 6 mm aras›nda de¤iflen zonlu plajiyoklaz kristalleri çoklukla oval biçimli olup, normal lata biçimlilerden daha büyüktürler. Zonlu plajiyoklazlar petrografik olarak, tamamen zonlu ve merkezi süngerimsi kenar› zonlu kristaller olmak üzere iki ana grupta toplanm›fllard›r. Zonlu kristallerin bileflimleri An23 (oligoklaz) ile An70 (labradorit) aras›ndad›r. Sal›n›ml› zonlu plajiyoklaz kristalleri kuvvetli Ca2+ ⇔ Na+, Al3+ ⇔ Si4+ ve zay›f Fe3+ ⇔ Si4+ sübsitüsyon mekanizmas› ile kontrol edilirler. Plajiyoklazlar›n Fe2O3 top (% a¤.) konsantrasyonu, An içeri¤i ile art›fl sunar. Zonlu kristallerin petrografik, kenardan kenara kimyasal de¤iflimleri ve mol % An içerikleri ile Fe2O3 top konsantrasyonlar› aras›ndaki pozitif iliflki, Zigana Granitoyidi’nin (ZG) oluflumu s›ras›nda felsik magma odas›na sürekli bir mafik injeksiyonun varl›¤›na ve dolay›s›yla magma etkilefliminin a¤›rl›kl› magmatik olay olabilece¤ini yans›tmaktad›r.