Petrogenesis of Paleoproterozoic Gneissic Granites from JiaoLiaoJi Belt of North China Craton and Their Tectonic Implications(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2015年第05期
- Page:
- 31-51
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Petrogenesis of Paleoproterozoic Gneissic Granites from JiaoLiaoJi Belt of North China Craton and Their Tectonic Implications
- Author(s):
- YANG Ming-chun; CHEN Bin; YAN Cong
- 1. School of Earth and Space Sciences, Peking University, Beijing 100871, China; 2. Key Laboratory of Orogenic Belts and Crustal Evolution of Ministry of Education, Peking University, Beijing 100871, China; 3. China Ocean Press, Beijing 100081, China; 4. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, Anhui, China; 5. Sinochem Petroleum Exploration and Production Co., Ltd., Beijing 100031, China
- Keywords:
- gneissic granite; Paleoproterozoic; petrogenesis; electron microprobe analysis; arc magma; subduction zone; North China Craton; Jiao-Liao-Ji Belt
- PACS:
- P588.12+1
- DOI:
- -
- Abstract:
- Voluminous Paleoproterozoic gneissic granites, which are mainly composed of hornblende or magnetite monzonitic granites, occur in Jiao-Liao-Ji Belt of North China Craton. The typical recognition feature is the orientational melanocratic mineral. The plutons are intruded by diorite dykes, and undergo a late-stage amphibolite facies metamorphism. These gneissic granites are considered as A-type granites and formed in a continental rifting setting. Based on the integrated field, petrographic, geochronological, and geochemical studies on several gneissic granite plutons, the different models for the origin and tectonic setting of these gneissic granites were proposed. LA-ICP-MS zircon U-Pb ages reveal that these gneissic granites emplace at 2 173-2 205 Ma, and the mafic dykes emplace at 2 159 Ma followed by an amphibolite facies metamorphism at 1 907 Ma. The gneissic granites contain basic mafic microgranular enclaves, calcium and mafic hornblendes, and the accessory minerals are zircon, titanite and magnetite. The analysis results of major and trace elements show that the gneissic granites are calc-alkaline magma series, A/CNK values are 0.9-1.2 (mostly less than 1.1), A/NK values are 0.9-1.4, mass fractions of SiO2 are 68.3%-76.9%, and mass fractions of TiO2 are low (<0.3%); large ion lithophile elements such as K, Rb, Sr and Cs are rich, and high field strength elements such as Nb and Ti are depleted. These features suggest that these gneissic granites are I-type granites formed probably in a subduction zone. Because of the high differentiation caused by boron-rich magmatic system, part plutons (such as Dafangshen) have characteristics of A-type-like granites, and the high mass fraction of SiO2 (76.7%-77.1%) is also shown by the high differentiation. The addition of boron causes the decease of solidus temperature, and tends to prolong magma evolution. The large variation of whole-rock εNd(t) values (-8.6-1.5) and zircon εHf(t) values (-1.3-5.6), together with the existence and petrographic features of mafic microgranular enclaves, and oscillatory zoning in plagioclase, suggest that the mixing of lower crust-derived acidic magma with enriched mantle-derived mafic magma might have resulted in the formation of gneissic granites. The existence of Archean inherited zircons with the ages older than 2 500 Ma in the granites together with the arc magma affinity suggests a northward subduction for Jiao-Liao-Ji Belt in Paleoproterozoic.
Last Update: 2015-09-28