Zircon U-Pb geochronology, Hf isotopes and geochemistry of intrusive rocks in the Simorgh prospecting area, Lut Block, eastern Iran: petrogenesis and geological implications

Abstract

The Simorgh prospecting area is located in the central part of the Lut Block in eastern Iran. The Lut Block, the eastern part of the Central Iranian Microcontinent (CIM), has a complex tectonic evolution and is characterized by extensive magmatic activities with a range of geochemical signatures. The Simorgh intrusions have features typical of calc-alkaline to high-K calc-alkaline rocks, metaluminous to slightly peraluminous and formed in a volcanic arc setting. Mineralization in the area is believed to be related to these intrusions. To better understand the petrogenesis of these intrusions, we report zircon U-Pb dating and Hf isotopes and whole rock geochemistry of two granites and one diorite. Age dating using Zircon U-Pb method on pyroxene diorite porphyry stock and two granite porphyry dikes revealed 24.85 ± 0.51 Ma, 25.37 ± 0.56 Ma and 25.94 ± 0.76 Ma ages respectively (late Oligocene, Chattian). Field observations and U-Pb dating indicate that there are at least two stages of emplacement: pre-mineralization intrusions (diorite porphyry) and syn-mineralization intrusions (granite porphyry, granodiorite porphyry and pyroxene diorite porphyry). Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements (LILE) and light rare earth elements ((La/Yb)N = 9.26–14.48), and depletion in high field strength elements (HFSE) and heavy rare earth elements, as well as negative Eu anomalies (Eu/Eu* = 0.49–0.91). Zircon Hf isotope data from the Simorgh intrusive rocks show largely positive eHf(t) (average = 3.6 ± 2.0). Hf model ages are ranging from 720 to 1320 Ma, indicating its derivation from a relatively juvenile source. The presence of zircon xenocrysts may prove its contamination by older continental crust (Siderian).