Magma mixing/mingling in Salmas granodiorite, NW Iran: evidence from mafic microgranular enclaves

Abstract

The interaction of mafic-intermediate and felsic rocks of the Salmas plutonic rocks produced mixed rocks (granodiorites) which contain mafic microgranular enclaves (MMEs). Enclaves ranging from a few millimeters to centimeters in size, and from ellipsoidal to rounded in shape. Based on both field observation and mineralogical compositions, MMEs are composed of quartz diorite whereas the felsic host rocks comprise mainly granodiorite. MMEs are characterized by a microporphiritic texture and revealed some types of microscopic textures, e.g., prismatic-cellular plagioclase with spike zones and rounded plagioclase megacrysts, bladeshaped biotite and acicular apatite. The host rocks show textures such as oscillatory-and reversely zoned plagioclase with spike zone. Compositions of plagioclases (An 41 to An 48 ) of MMEs are similar to those of host rocks (An 38 to An 45 ) which suggest partial to complete equilibration during maficfelsic magma interactions. The individual petrographic and microstructural textures and mineral chemistry similarities between the MMEs and their host rocks and diorites indicate that the enclaves are of mixed origin and most probably formed by interaction of lower crust magma (granitic melt) and evolved mantle-derived magmas (diorites).

Cogenetic origin of mafic microgranular enclaves in calc-alkaline granitoids: The Permian plutons in the northern North China Block

“…The cognate origin model for crystallization of the MMEs from a coeval magma that gave rise to the host granitoids accounts for similar mineral assemblage and similarities in chemical and isotopic compo- sitions between enclaves and their hosts (e.g., Borodina, 1977, 1991;Dodge and Kistler, 1990;Pin et al, 1990;Dorais et al, 1997;Dahlquist, 2002;Donaire et al, 2005;Ilbeyli and Pearce, 2005;Chen et al, 2007;Shellnutt et al, 2010;Esna-Ashari et al, 2011;Flood and Shaw, 2014). In hybridism or magma mixing and/or mingling model for origin of the MMEs within the granitic pluton, the mineral, chemical, and isotopic similarities between enclaves and their hosts are commonly interpreted in terms of complete thermal and chemical equilibration between coeval, compositionally contrasted magmas in a slowly cooling plutonic body (e.g., Holden et al, 1991;Barbarin and Didier, 1992;van der Laan and Wyllie, 1993;Barbarin, 2005;Kaygusuz and Aydınçakır, 2009;Xiong et al, 2012;Zi et al, 2012;Dan et al, 2015;Ghaffari and Rashidnejad-Omran, 2015). However, others interpreted these similarities as evidence for cognate origin of the MMEs from a coeval magma that gave rise to the host granitoids (e.g., Borodina, 1977, 1991;Dodge and Kistler, 1990;Pin et al, 1990;Dorais et al, 1997;Dahlquist, 2002;Donaire et al, 2005;Ilbeyli and Pearce, 2005;Chen et al, 2007;Shellnutt et al, 2010;Esna-Ashari et al, 2011;Niu et al, 2013;Flood and Shaw, 2014;Huang et al, 2014;…”

Mineral Chemistry and Thermobarometry of the Upper Eocene Volcanic Rocks in NE Tafresh, Iran

“…Eocene volcanic occurrences are the most important volcanic demonstrations In Iran, because it has led to the creation of a volcanic arc which has a length of 1700 km and a width of 100 km [1] [2]. This volcanic arc which is known as the Urmia Dokhtar volcanic arc is widespread from northwest to southeast in Iran and is the most important volcanic zone of Iran [3]- [6]. Eocene volcanic occurrence in almost all regions, except Zagros and Kopet Dagh, took place [7].…”