Zircon U–Pb Geochronology, Geochemistry, petrogenesis and tectonic significance of the Boroon Igneous Masses (East of Iran)
By: Saied Ansari, Mina Sakhdari
Key Words: Petrogenesis, Magmatic evolution, Boroon, Lut block, Iran.
J. Bio. Env. Sci. 8(1), 52-64, January 2016.
The Boroon igneous masses are Cu bearing porphyries that outcrop in the North part of the Lut Block, about 20 km north-west of Ferdows. These igneous masses occur mainly as dykes and stocks that intrude Eocene volcanics and pyroclastics. Hydrothermal alteration affected these igneous masses, as revealed by the common ocurrence of sericite, chlorite, sphene/leucoxene, epidote and calcite. Chemical classification criteria show that the intrusives may be named as gabbrodiorites, diorites, monzodiorites and tonalites. Major element geochemistry reveals that all the studied lithologies are typically metaluminous (A/CNK ≤ 0.9) and, in addition, trace element patterns normalized to chondrite and primitive mantle are very similar to each other and show enrichments in LREE relative to HREE and in LILE relative to HFSE, as well as negative anomalies of Ta, Nb and Ti. Eu/Eu* ratios vary from 0.88 (in the most mafic composition) to 0.65, showing that plagioclase played a role in magma differentiation. LA-MC-ICP-MS U-Pb zircon data from Tonalite Porphyry yield similar concordia ages of ca. 40.31±1.1 Ma (2σ), which corresponds to the Eocene period. The whole set of geochemical data agree with the emplacement of the studied intrusions in a magmatic belt above a subduction zone. Primitive magmas should have formed by melting of mantle wedge peridotite, and, during magma ascent to crustal levels, both magma differentiations by crystal fractionation and crustal contamination took place. Sulfide mineralizations related to these igneous masses is common and occurs both disseminated and as hydrothermal veins, indicating a high mineralization potential for this area.