Abstract
The Pliocene-Quaternary volcanic rocks which outcrop between Qorveh and Bijar are part of post-collisional within-plate volcanic activity in northern Iran. These mafic alkaline rocks form part of the northern arm of the Sanandaj-Sirjan (Hamedan-Tabriz) zone. Thermobarometry on equilibrium clinopyroxene - whole-rock pairs yields pressures and temperatures of 4-6 (±1.8) kbar and 1182-1213 (±27) °C, respectively; olivine - whole-rock (melt) equilibrium thermometry yields crystallization temperatures of 1212-1264 (±27) °C. Field relationships, including the presence of pyroxenitic xenoliths, and geochemical evidence (e.g. high FeO/MnO, and low CaO compared to lavas derived from peridotite sources) suggest a pyroxenitic mantle source for the studied rocks. Variation of trace elements and isotopic ratios (i.e. Ce/Pb, Ba/La, 87Sr/86Sr) indicate that this pyroxenite mantle source was generated by interaction between melted sediments of the subducted Neo-Tethys slab with ambient peridotitic lithospheric mantle. The resulting metasomatized lithosphere is denser and has a lower viscosity than the peridotitic mantle, and tectonic disturbance can cause it to fall into the depths of the mantle. The descending volatile-rich material starts to melt with increasing temperature. Modelling of rare earth element (REE) abundances suggests that <1 % partial melting of the descending pyroxenite could create the Plio-Quaternary alkali basaltic magma of the Qorveh-Bijar. The geochemical evidence for lithospheric foundering, and hence drip magmatism, in the Qorveh-Bijar volcanic belt is supported by seismographic studies indicating thinned lithosphere beneath the study area.
Original language | English (US) |
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Pages (from-to) | 888-904 |
Number of pages | 17 |
Journal | Geological Magazine |
Volume | 160 |
Issue number | 5 |
DOIs | |
State | Published - May 1 2023 |
All Science Journal Classification (ASJC) codes
- Geology