The Study of Metamorphic Rocks, Zonation and Isogrades in Garnet Rocks in the Hamadan Area

ZAHRA HOSSEIN MIRZAEI BENI, ZOHREH HOSSEIN MIRZAEI BENI
2012 Current World Environment  
INTRODUCTION Garnet crystallizes in cubic system and mostly in dodecahedron (rhomb-dodecahedron) and trapezohedron (tetragon-trioctahedron) crystal forms. General chemical formula of this mineral is: R 3 R' 2 (SiO 4 ) 3 , which bivaliant cations (i.e. Mg 2+ , Fe 2+ , Mn 2+ , Ca 2+ ) lie in R site and trivaliant cations (i.e. Al 3+ , Cr 3+ , Fe 3+ ) in R' site. Commonly, more than one cation lies in R and R' sites and therefore garnet crystals give rise to isomorphous (solid solution) series of
more » ... olution) series of minerals. If Al 3+ is located in R' site, the pyralspite group [( Fe 2+ ,Mg 2+ ,Mn 2+ ) 3 Al 2 (SiO 4 ) 3 ] with almandine [(Fe 2+ ) 3 Al 2 (SiO 4 ) 3 ], pyrope [(Mg 2+ ) 3 Al 2 (SiO 4 ) 3 ] and spessartine [(Mn 2+ ) 3 Al 2 (SiO 4 ) 3 ] end members will form. If Ca 2+ is located in R site, the ugrandite group [(Ca 2+ ) 3 (Al 3+ ,Fe 3+ ,Cr 3+ ) 2 (SiO 4 ) 3 ] with grossularite[Ca 3 Al 2 (SiO 4 ) 3 ], andradite [Ca 3 (Fe 3+ ) 2 (SiO 4 ) 3 ] and uvarovite [Ca 3 (Cr 3+ ) 2 (SiO 4 ) 3 ] end members will form. Some other cations may also be emplaced in R and R' sites [1, 2] . The garnet ABSTRACT The study area is a part of the Sanandaj-Sirjan metamorphic belt. We can divide Hamadan metamorphic rocks in three groups: regional metamorphic rocks, contact metamorphic rocks and migmatites. In this area we can't completely divide zonation of contact and regional metamorphic. In some places that contact metamorphic has influenced to low degree regional metamorphic rocks, contact metamorphic zonations are clearly appear, but when contact and regional metamorphic have a same degree or regional metamorphic has high degree than contact metamorphic, we can't distinguish them easily. In Hamadan area regional metamorphic zones are Chlorite± Biotite zone (we haven't garnet rocks in this zone), Biotite± Garnet zone (divided in two sub zone, Biotite and Garnet zone), Andalusite zone, Staurolite zone, Staurolite± Andalusite zone, Sillimanite-Muscovite zone and Sillimanite-Potassium feldspar± Cordierite zone, also contact metamorphic zones are Cordierite zone and Cordierite-Potassium feldspar zone. minerals chemistry in the study area are rich in almandine. Geological Setting The study area is a part of the Sanandaj-Sirjan metamorphic belt. The Alvand plutonic complex is the most important plutonic body that regional and contact metamorphic rocks with low to high grade are located around it. The metamorphic sequence comprises pelitic, psammitic, basic, calc-pelitic and calc-silicate rocks. Pelitic rocks are the most abundant lithologies. Pelitic sequence is mostly made up of slates, phillites, micaschists, garnet schists, garnet andalusite (± sillimanite, ± kyanite) schists, garnet staurolite schists, mica hornfelses, garnet hornfelses, garnet andalusite (± fibrolite) hornfelses, cordierite (± andalusite) hornfelses, cordierite K-feldspar hornfelses and sillimanite Kfeldspar hornfelses. Major plutonic rocks of this area are granitoids, diorites and gabbroids, which
doi:10.12944/cwe.7.1.10 fatcat:b27thcw34fgejlhbxxuy2l4raq