Ghassem AZIZZADEH, Mostafa RAGHIM, Seyed Jamal SHEIKHZAKARIAEE, Aziz RAHIMI CHAKDEL

Kuzeydoğu İran Ziarat’ta yer alan Gabroik kayaçların jeokimyasal özellikleri

İran’ın kuzeydoğusu, Gürgen’in güneyinde mafi k kayaç mostraları bulunmaktadır. Bu gabroikkayaçlar, Orta-Üst Paleozoyik sedimanter kayaçlar ve kuzey Gondwana bölgesinin bir parçası olanGürgen şistlerinin içerisinde sokulum haldedir. Petrografi k çalışmalar, bu kayaçların orta - iri taneliolduğunu ve ofi tikten intergranülere kadar değişen dokulara sahip olduğunu ortaya koymuştur.Mafi k daykların mineralojik bileşimi baskın olarak klinoprioksen+ortopiroksen+plajiyoklaz vehornblend minerallerinden oluşmaktadır. Gabroik bileşime sahip bu kayaçlar düşük - orta $K_2O$ vedüşük La/Nb içeriğine sahiptir ve hafi f nadir toprak elementler bakımından zenginleşmiştir (La/Yb =21.4) . Gabrolarda gözlenen yüksek HNTE/ANTE (Hafi f Nadir Toprak Element / Ağır NadirToprak Elementler) oranı, beraberinde düşük Y içeriğine karşılık yüksek Ti/Y oranı, bu kayaçlarıngranat içeren bir kaynağın kısmi ergimesi ile oluştuğuna işaret etmektedir Çalışma alanındakigabroların nadir toprak element (NTE) profi lleri ve tektonik ortam ayırtman diyagramları okyanusadası bazaltlarına (OIB) benzerlik göstermekte olup, kayaçların kökeni OIB magması ile aynıdır.

Geochemical characteristics of Gabbroic rocks in Zyarat in North East of Iran

The mafi c rocks outcrops exposed in the South of Gorgan, northeastern of Iran. These gabbroic rocks are intruded into the Middle–Upper Paleozoic sedimentary and Gorgan schist units representing a part of the north Gondwana province. Petrography studies of these rocks show medium to coarse grained sizes and the texture varies from ophitic to intergranular under polarized microscope. The mineralogical composition of mafi c dykes is dominated by large crystals of clinopyroxene + orthopyroxene + plagioclase and hornblende. These rocks can be classifi ed as gabbroic rock. Geochemical studies show that these rocks have low to medium $K_2O$ contents. The trace element data shows low La/Nb ratios and LREE enrichment (La/Yb 10–21.4). The high LREE/HREE ratios and low Y content corresponding high Ti/Y ratios of the gabbros suggest that they could be derived from melt fractions of a garnet stable source. Considering that the REE plot and tectonic diagrams of the region’s gabbro are similar to that of OIB (Ocean island basalt), the former’s origin is the same as that of OIB magmas.

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