Cadomian crust of Eastern Iran: evidence from the Tapeh Tagh granitic gneisses

Late Neoproterozoic to Early Cambrian (Cadomian) magmatic rocks are abundant in Iran, but their occurrence in east-central Iran is voluminous. This paper reports, for the first time, on the Cadomian rocks of the eastern Iranian region known as Tapeh Tagh and deals with their geochemistry and uranium-lead (U-Pb) zircon ages. The Tapeh Tagh region contains masses of Cadomian meta-igneous rocks (including various types of granitic gneiss) and overlying meta-sedimentary rocks. The granitic gneisses show tectonic contact with metasedimentary rocks and their connection appears to have been obscured during the younger tectonic movements. The granitic gneisses show mylonitic texture with quartz ribbons and feldspar augen. Laser Ablation Inductively Coupled Plasma Mass Spectrometry U-Pb dating of zircon grains, separated from medium to coarse-grained gneissic rocks, consistently yielded near concordant to discordant pairs of 527 +/- 5 and 522 +/- 10 Ma. Geochemically, these rocks show a felsic composition with SiO2 content varying from 70.30 to 79.63 wt.%, a high content of FeO(t), alkalis, and incompatible trace elements (Zr, Nb), along with high ratios of Ga/Al and FeO(t)/MgO. They have fractionated rare earth element (REE) patterns with La/Yb = 9.1-24.7. Eu shows depletion with Eu/Eu*<1. The highly fractionated granites of the Tapeh Tagh are geochemically classified into the volcanic arc granites (VAG) and within plate granite.The granitic gneisses are geochemically and geochronologically similar to other Cadomian granites and gneisses in other parts of Iran as well as the Cadomian magmatic rocks from Turkey. These widely disseminated Cadomian basement rocks in Iran and Turkey are considered as fragments of Neoproterozoic to Early Cambrian continental arcs that formed the northern active margin of Gondwanaland.

Automated summary

Magmatic rocks from the Late Neoproterozoic to Early Cambrian (Cadomian) period are abundant in Iran, particularly in the east-central region. This paper focuses on the Cadomian rocks found in the Tapeh Tagh area of eastern Iran, providing data on their geochemistry and uranium-lead (U-Pb) zircon ages. The rocks in this region consist of Cadomian meta-igneous rocks, including various types of granitic gneiss, as well as overlying meta-sedimentary rocks. The geochemical and geochronological characteristics of these rocks are similar to those of other Cadomian granites and gneisses in Iran and Turkey.