وﯾﮋﮔﯽ ﻫﺎي زﻣﯿﻦ ﺷﯿﻤﯽ، ﻣﺤﯿﻂ ژﺋﻮدﯾﻨﺎﻣﯿﮑﯽ و ﻓﺮاﯾﻨﺪﻫﺎي ﭘﺘﺮوﻟﻮژﯾﮑﯽ ﺳﻨﮓ ﻫﺎي دﯾﻮرﯾﺖ ﺗﺎ ﮔﺎﺑﺮوﯾﯽ ﮐﻤﭙﻠﮑﺲ ﻧﻄﻨﺰ

Geochemistry, Geodynamic Setting and Petrological processes of Diorite to Gabbro Igneous Rocks in the Natanz Intrusive Complex

ﻣﺠﻤﻮﻋﻪ ﻧﻔﻮذي ﻧﻄﻨﺰ )NIC(در ﺑﺎﺧﺘﺮ ﺷﻬﺮﺳﺘﺎن ﻧﻄﻨﺰ و درﻧﻮار ﻣﺎﮔﻤﺎﯾﯽ اروﻣﯿﻪ دﺧﺘﺮ واﻗﻊ ﺷﺪه اﺳﺖ. ﺳﻨﮓ ﻫﺎي آذرﯾﻦ ﻣﺎﻓﯿﮏ اﯾﻦ ﻣﺠﻤﻮﻋﻪ را ﮔﺎﺑﺮو و دﯾﻮرﯾﺖ ﺗﺸﮑﯿﻞ ﻣﯽ دﻫﻨﺪ. ﺳﻨﮓ ﻫﺎي ﻧﻔﻮذي ﮔﺎﺑﺮو ﻗﺪﯾﻤﯽ ﺗﺮﯾﻦ واﺣﺪ ﻣﺤﺴﻮب ﻣﯽ ﺷﻮﻧﺪ، زﯾﺮا ﺗﻮﺳﻂ ﮔﺮاﻧﯿﺘﻮﺋﯿﺪﻫﺎ ﻗﻄﻊ ﺷﺪه اﻧﺪ. ﺳﻨﮓ ﻫﺎي ﻧﻔﻮذي ﻣﻨﻄﻘﻪ ﻫﻤﮕﯽ ﻣﺘﻌﻠﻖ ﺑﻪ ﯾﮏ ﻣﺎﮔﻤﺎي ﻣﺸﺘﺮك ﻫﺴﺘﻨﺪ ﮐﻪ اﯾﻦ ﻣﺎﮔﻤﺎ در آﺷﯿﺎﻧﻪ ﻣﺎﮔﻤﺎﯾﯽ ﺧﻮد ﭘﺲ از اوﻟﯿﻦ ﺟﺎﯾﮕﺰﯾﻨﯽ دﭼﺎر ﺗﻔﺮﯾﻖ ﺷﺪه اﺳﺖ. ﭘﺮاﮐﻨﺪﮔﯽ و اﻟﮕﻮي ﻋﻨﺎﺻﺮ ﮐﻤﯿﺎب ﻧﺎدر ﺧﺎﮐﯽ در ﺳﻨﮓﻫﺎي ﻣﺨﺘﻠﻒ ﺗﻘﺮﯾﺒﺎً ﺑـﺎ ﯾﮑﺪﯾﮕﺮ ﻣﺸﺎﺑﻪ و از ﻋﻨﺎﺻﺮ ﻧﺎدر ﺧﺎﮐﯽ ﺳـﺒﮏ )LREE (ﻏﻨـﯽ ﺷـﺪه اﻧـﺪ. ﺗﻄـﺎﺑﻖ اﻟﮕـﻮي ﺗﻐﯿﯿـﺮات ﻋﻨﺎﺻــﺮ ﻧـﺎدر ﺧــﺎﮐﯽ ﻣـﯽﺗﻮاﻧــﺪ ﻧﺸـﺎﻧﻪ ﺧﺎﺳــﺘﮕﺎه ﻣﺸﺘﺮك اﯾﻦ ﺳﻨﮓ ﻫﺎ ﺑﺎﺷﺪ. ﺑﺮ اﺳﺎس ﻣﻄﺎﻟﻌﺎت ژﺋﻮﺷﯿﻤﯿﺎﯾﯽ و ژﺋﻮدﯾﻨﺎﻣﯿﮑﯽ ﺻﻮرت ﮔﺮﻓﺘﻪ ﺑﺮ ﺳﻨﮓ ﻫﺎي دﯾﻮرﯾﺘﯽ ﺗﺎ ﮔﺎﺑﺮوﯾﯽ ﻣﺤﺪوه ﻣﻮرد ﻣﻄﺎﻟﻌﻪ، ﺗﻮده ﻫﺎي ﻣﺰﺑﻮر ﻣﺎﻫﯿﺖ ﺳﺎب آﻟﮑﺎﻟﻦ ، ﮐﺎﻟﮑﻮآﻟﮑﺎﻟﻦ و ﻣﺘﺎآﻟﻮﻣﯿﻦ ﺗﺎ ﭘﺮآﻟﻮﻣﯿﻦ را ﻧﺸﺎن ﻣﯽ دﻫﻨﺪ. ﺑﺎ ﻣﻘﺎﯾﺴﻪ ﻣﯿﺰان H2O و ﻓﺸﺎر ﺗﺨﻤﯿﻦ زده ﺷﺪه، ﻓﺎز ﻟﯿﮑﻮﺋﯿﺪ ﺑﺮاي ﺗﺒﻠﻮر ﮐﺎﻧﯽ ﻫﺎ در ﺳﻨﮓ ﻫﺎي ﺣﺪواﺳﻂ ﻧﻔﻮذي ﻧﻄﻨﺰ ﺑﺎﯾﺪ ﺑﯿﻦ 950 ﺗﺎ 1000 درﺟﻪ ﺳﺎﻧﺘﯿﮕﺮاد ﺑﺎﺷﺪ. درﺟﻪ ﺣﺮارت ﺑﯿﺶ ﺗﺮ ﺑﺮاي ﻓﺎز ﻟﯿﮑﻮﺋﯿﺪي ﻣﯽ ﺗﻮاﻧﺪ ﺑﻪ ﻋﻠﺖ ﻣﺤﺘﻮاي ﺑﯿﺶ ﺗﺮ ﮐﻠﺴﯿﻢ ﺑﺎﺷﺪ. رﻓﺘﺎر ﻋﻨﺎﺻﺮ اﺻﻠﯽ و ﻓﺮﻋﯽ ﺗﺒﻠﻮر ﺗﻔﺮﯾﻘﯽ را ﺑﻪ ﻋﻨﻮان ﻋﻤﺪه ﺗﺮﯾﻦ ﻓﺮاﯾﻨﺪ ﻣﺴﺌﻮل در ﺗﮑﺎﻣﻞ ﻣﺎﮔﻤﺎﯾﯽ ﻧﻔﻮذي ﻫﺎي ﻧﻄﻨﺰ ﭘﯿﺸﻨﻬﺎد ﻣﯽ ﻧﻤﺎﯾﺪ. وﺿﻌﯿﺖ ﻋﻨﺎﺻﺮ ﻧﺎﺳﺎزﮔﺎر ﺑﺎ ﻓﺮوراﻧﺶ ﻫﻤﺎﻫﻨﮕﯽ ﺑﯿﺶ ﺗﺮي دارد. ﻣﻘﺪار ﺑﺎﻻي ﭘﻼژﯾﻮﮐﻼز در ﮔﺎﺑﺮوﻫﺎ ﻧﺸﺎن ﻣﯽ دﻫﺪ ﮐﻪ ﺗﻔﺮﯾﻖ در ﻓﺸﺎر ﻧﺴﺒﺘﺎً ﺑﺎﻻ اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﺷﻮاﻫﺪ ﭘﺘﺮوﻟﻮژﯾﮑﯽ ﺣﺎﮐﯽ از ﺷﮑﻞ ﮔﯿﺮي ﺗﻮده ﻫﺎ در ﻣﺤﯿﻂ ﻗﻮس ﻫﺎي آﺗﺸﻔﺸﺎﻧﯽ اﺳﺖ.

The Natanz intrusive complex (NIC) is located in the West of Natanz city and in the Orumieh -Dokhtar magmatic belt. Natanz complex is composed of two types of mafic igneous rocks, including gabbro and diorite. The gabbroic unit was cut by granitoid rocks, so gabbro is the oldest igneous rock units in the area. The geological study of the intrusion of diorite to gabbro igneous rocks has been done by petrology and geochemical studies.The intrusive rocks of the area all belong to a common magma, which has been subdivided in its magma chamber after the first replacement. The distribution and pattern of the rare earth elements (REE) are the same and these igneous rocks are enriched in LREE. The similarity of the REE patterns in these rocks, is an evidence that they have common origin. According geochemical and geodynamical studies on diorite to gabbroic rocks in the area, these igneous rocks show sub alkaline, calk alkaline and meta aluminous to per aluminous natures. Because amount of H2O and evaluated pressure, the crystallization liquid phase had 950 – 1000 °C for intermediate intrusive rocks in Natanz complex. This is because of more calcium content. The behavior of major and trace elements especial in silicate minerals suggested that fractional crystallization of magma was the main role in the magmatic evolution of these rocks. The position of incompatible elements is more in harmony with subduction. The high amount of plagioclasein gabbros show that crystallization of magma happened in high pressure. The petrological evidences indicate that the igneous rocks were formed in volcanic arc environment.