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Different Parental Magma Compositions of the Hongge and Panzhihua Magmatic Fe‐Ti‐V Oxide Deposits, Emeishan Large Igneous Province, SW China
Author(s) -
BAI Zhongjie,
ZHONG Hong,
LI Chusi,
ZHU Weiguang,
HE Defeng,
QI Liang
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12371_1
Subject(s) - chinese academy of sciences , geochemistry , china , geology , biogeosciences , magma , large igneous province , earth science , archaeology , geography , tectonics , volcano , magmatism , paleontology
Panzhihua, Hongge, Baima and Taihe, in the Emeishan Large Igneous Province (ELIP), SW China, host worldclass Fe-Ti-V oxide ore deposits. Massive oxide ore layers (up to ~60 m-thick in the Panzhihua, ~84 m-thick and ~70 m-thick in the Hongge and Baima intrusions, respectively; Zhong et al., 2002, 2005; Pang et al., 2009, 2010) occur in the lower or middle parts of the intrusions. The origins of oxide ores in these intrusions are hotly debated. Regardless of mechanism, the variations of parental magma compositions for these deposits are poorly constrained. The Hongge and Panzhihua intrusions show differences in lithology and mineral chemistry. The most important orebodies in the Hongge intrusion occur as concordant layers in the middle part of the intrusion, closely associated with clinopyroxenites. Titanomagnetite and Mg-rich ilmenite are the major ore minerals of the Hongge deposit (Zhong et al., 2002; Pang et al., 2008a; Bai et al., 2012). Coexisting clinopyroxene contains >1.7 wt % TiO2. These data indicate high Ti parental magma for the Hongge ore-bearing clinopyroxenites. In the Panzhihua intrusion, the most important orebodies also occur as concordant layers but in its lower part instead of middle part. In contrast with the Hongge deposit, the most important host rocks of the Panzhihua deposit are gabbros, not clinopyroxenites. In addition, ilmenite is rare and titanomagnetite is predominant in the Panzhihua deposit (Pang et al., 2008a, b). Coexisting clinopyroxene in the Panzhihua deposit contains <1.6 wt % TiO2. The contrasting lithologic and mineral compositions indicate that the parental magma for the Hongge deposit has higher TiO2 than that for the Panzhihua deposit. The compositions of clinopyroxene from the Panzhihua and Hongge deposits indicate that their parental magmas are also different in MgO/FeO and trace element ratios as well. Calculations using average experimental Mg-Fe exchange coefficient and trace element partition coefficients between clinopyroxene and magma show that the Hongge parental magma has higher MgO/FeO ratios and more fractionated mantle-normalized trace element patterns than the Panzhihua parental magma. The estimated compositions of the parental magmas for the Hongge and Panzhihua orebearing lithologies resemble the average compositions of the Longzhoushan-type high Ti basalts and Ertan-type intermediate Ti basalts in the Emeishan large igneous province, respectively. The new trace element data from this study, together with available Sr-Nd isotope data for the ore-bearing intrusions from literature, support a new petrogenetic model involving selective assimilation of newly subducted, stagnant oceanic gabbroic slab above the deepseated Emeishan mantle plume. This process and subsequent contamination with the upper crust played an important role in the variation of parental magma compositions between the Hongge and Panzhihua magmatic oxide ore deposits. Abundant Fe-Ti oxide ore deposits associated with less evolved basaltic magma in the Emeishan large igneous province than elsewhere in the world are attributed to selective assimilation of newly subducted, stagnant oceanic lithospheric slab by the ascending mantle plume-derived picritic magma that was originally undersaturated with Fe-Ti oxides.