Detrital zircon and rutile geochronology, geochemistry and provenance of Cambrian sandstones of Iranian Azerbaijan: implications for the Neoproterozoic-Cambrian evolution of the northern Gondwana margin

Abstract

Within the Tethyan belt, the NW-Iranian block is bound by two sutures, the Sevan-Akera suture in the north, and the Zagros suture in the south, where the pre-Cambrian geology is poorly constrained. Lower-Middle Cambrian sandstone in NW Iran is represented by quartz and feldspar dominated sub-arkose and sub-litharenite with well-developed cross bedding structures. They are interlayered with shale and limestone and overlain unconformably by Middle Cambrian dolomite. Here we describe and present U–Pb ages of the detrital zircon and rutile together with in-situ ε-Hf data from Lower to Middle Cambrian sandstones. Some zircons are characterized by oscillatory zoning and Th/U ratios of 0.3 to 2.0, pointing to an igneous provenance. Ages of the detrital zircons range from 481 to 2762 Ma, whereby the majority of zircons have ages between 524 and 1000 Ma (Neoproterozoic), and small peaks at 1800–2000 and 2400–2600 Ma. Late Paleoproterozoic to Mesoproterozoic zircons (1100–1750 Ma) are absent in the detrital record which is a distinctive feature of Gondwana-related detrital zircons. Detrital rutile has elevated Cr contents and variable Zr content (88 to 1087 ppm), suggesting derivation mainly from amphibolite-facies meta-basic rocks. U–Pb rutile ages range from 561 to 1253 Ma. Initial ε-Hf values of the Neo-Proterozoic zircons range from -10 to 20, suggesting an association of highly depleted mantle and crustal magmas. Thus, the Lower-Middle Cambrian sandstones in Iranian Azerbaijan were supplied from a Neoproterozoic igneous and metamorphic provenance. Sandstone whole-rock major and trace elements are in accordance with a detrital material provenance from continental granitoids and Precambrian recycled sediments. These results support the hypothesis that Iranian Azerbaijan Cambrian detritus was supplied from repetitive recycling of the crystalline basement and related sedimentary cover of the Saharides and the Arabian-Nubian Shield and deposited in a passive-margin setting in northern Gondwana land. Our results show a close geological tie between Iranian Azerbaijan, Sanandaj-Sirjan, Zagros, Alborz, and other Gondwana-Land-derived units in terms of Early Paleozoic detritus sources. Northwest Iranian Block was probably a passive continental margin in Late Ediacaran-Cambrian after the so-called Cadomian orogeny.

Graphical Abstract