Abstract

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Title:: Petrogenesis of Laoniushan Granitoid Complex in the Southern Margin of North China Block: Information from Biotite

Author(s):: QI Qiu-ju; WANG Xiao-xia; KE Chang-hui; LI Jin-bao; 1. Institute of Resource Survey and Assessment, East China Mineral Exploration and Development Bureau for Non-ferrous Metals, Nanjing 210007, Jiangsu, China; 2. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China; 3. School of Earth Science and Resources, Chang’an University, Xi’an 710054, Shaanxi, China

Keywords:: granitoid complex; biotite; crystallization temperature; crystallization pressure; emplacement depth; syntexis type granitoid; crust-mantle interaction; North China Block

Abstract:: Laoniushan granitoid complex is located in the southern margin of North China Block, and consists of Late Triassic (Indosinian) and Late Jurassic (Yanshanian) granitoids. Based on the field geological and petrographic observation, the systematic chemical compositions of biotites were carried out. The results show that the compositions of biotites have a little change with high Mg, Ti, Al and K contents; these biotites are mainly Mg-biotites; the compositions of biotites for granitoids have certain change rule from Indosinian to Yanshanian, and mainly the contents of TiO₂, FeO^T and Al₂O₃ increase, and the contents of MgO gradually decrease; biotites from Indosinian granites crystallize under temperature of 600 ℃-700 ℃, and pressure of 0.98-1.95 kbar, and the corresponding emplacement depth is 3.72-7.38 km; biotites from Yanshanian granitoids crystallize under temperature of 650 ℃-700 ℃, and pressure of 1.47-2.01 kbar, and the corresponding emplacement depth is 5.55-7.61 km; Laoniushan granitoid complex belongs to syntexis type (I-type) granitoid, and derives from a crust-mantle mixing source, while the diagenetic material sources of Indosinian and Yanshanian granitoids are slightly different, manifested as the mantle source material could be more in Indosinian granitoids.