Petrogenesis of Hornblendite Enclaves in Jinling Magmatic Complex of Intrusions from the Western Shandong Province

HU Yalu1, LIU Shuwen1,†, JIN Ziliang2, XIE Qiuhong2, WEN Bingbing2, LI Zixi2

1. The Key Laboratory of Orogenic Belt and Crustal Evolution (MOE), School of Earth and Space Sciences, Peking University, Beijing 100871; 2. School of Geosciences and Resources, China University of Geosciences (Beijing), Beijing 100083; † Corresponding author, E-mail: swliu@pku.edu.cn

Abstract In order to determine the genesis of the hornblendite enclaves in the Jinling magmatic complex of intrusions in the Western Shandong Province, petrological, mineralogical and geochemical analyses have been conducted on the hornblendites from the complex. The hornblendites show clearly cumulus structure and are composed of plagioclases and amphiboles. The amphiboles in hornblendite enclaves can be divided into two types. The first type of amphibole shows lower SIO2 but higher AL2O3 contents and is classified as the pargasite with magmatic genesis. The other type of amphibole is composed of actinolite, magnesiohornblende and edenite with higher SIO2 but lower AL2O3, which may be attributed to modifications of the magmatic amphiboles during later tectonothermal events. The crystallization pressure of hornblendite enclaves is estimated to be 0.48 GPA using the hornblende AL2O3 geobarometer. The hornblendite enclaves show similar characters of the REE and trace elements to those of the hosting dioritic rocks, and are characterized by the LREE enrichment but HREE depletion. Together with the mineral crystalline condition of the magmatic hornblende, it is concluded that the hornblendite enclaves and their hosting diorites in the Jinling magmatic complex of intrusions may be produced by fractionation crystallization of cogenetic magmatic evolution, and the hornblendite enclaves crystalized from a lower magmatic chamber in the middle-crust level. Key words Jinling magmatic complex; hornblendite enclaves; the crystallization pressure of amphiboles; magmatic genesis; Western Shandong