Contact metamorphism and crystal size distribution studies in the Shivar aureole,NW Iran |
| |
| Authors: | M Moazzen M Modjarrad |
| |
| Abstract: | The Shivar pluton, a large granodiorite–monzonite intrusion in NW Iran, was intruded into Cretaceous sedimentary rocks during the Oligo‐Miocene. Its thermal aureole contains a variety of pelitic, basic and calc‐silicate hornfelses. Mineral parageneses in the pelitic and calc‐silicate hornfelses are studied here and mineralogical zones are determined. The maximum pressure of contact metamorphism is estimated to have been about 2.2 kbar on the basis of mineral parageneses in the pelitic rocks, indicating that the intrusion was emplaced no deeper than 8 km in the crust. Crystal size distribution (CSD) studies in the calc‐silicate hornfelses indicate that the degree of overstepping was high near the igneous contact. Secondary solid phases (SSP) inhibited growth of calcite grains in the calc‐silicate rocks and impure marbles. Garnet had a greater inhibitory effect as a SSP than tremolite or clinopyroxene. The time required for coarsening of calcite is calculated for two samples collected at different distances from the igneous contact. The time required for calcite coarsening is about 33 000 years for the sample 800 m from the contact and about 226 000 years for the sample 120 m from the contact. Copyright © 2005 John Wiley & Sons, Ltd. |
| |
| Keywords: | metapelites calc‐silicate rocks calcite coarsening secondary solid phases crystal size distribution Shivar aureole Iran |
|
|
