Tourmaline and rutile geochemistry in the Early–Middle Devonian sandstones of the Padeha Formation, Alborz Range, Northern Iran

Abstract

The provenance of Devonian sandstones of the Padeha Formation (Fm.), Eastern Alborz in Iran, has been investigated by standard heavy‐mineral analysis and tourmaline and rutile geochemistry. Heavy‐mineral assemblage is dominated by the ultra‐stable tourmaline, zircon, and rutile, while unstable species are completely absent. The Padeha Fm. sandstones show a very high value of zircon‐tourmaline‐rutile index signalizing either strong weathering in source area(s) or their recycled origin in older Early Palaeozoic formations. Detrital tourmaline shows predominantly dravitic, lesser Mg‐foititic, and uvitic compositions and metasedimentary origin. Metapelitic source is also indicated by rutile geochemistry. Temperature estimates according to Zr‐in‐rutile thermometry show a wide range from 519 to 872°C and indicate the presence of low‐ to upper‐amphibolite and granulite facies metapelitic rocks. Based on chemical composition of detrital tourmaline and rutile, we inferred that the crystalline basement rocks of the Arabian–Nubian Shield were potential primary sources for the Padeha Fm. deposits. Shape of tourmaline and rutile as well as their microtexture surface features indicate long‐distance transport, storage, and recycled history.