The Heig-utian intrusion is a small-scaled gabbroic intrusion containing Ti-V-magnetite oxides and is located in the central part of the Emeishan large igneous province. In contrast to other typical large layered intrusions characterized by several cyclic units in a petrographic zone, the Heigutian intrusion is subdivided into a lower zone and an upper zone. The lower zone consists of olivine pyroxenite, magnetite gabbro, apatite gabbro and medium-grained gabbro from the base upward, whereas the upper zone consists of primarily fine-grained gabbro, and demonstrates a sharp contact between these two zones. The zircon SHRIMP U-Pb age dating result displays that the Heigutian intrusion was intruded at 263 +/- 5Ma, and may be the product of the main stage of plume-related magmatism at similar to 260Ma. The Heigutian intrusion shows a close genetic relationship to the Emeishan high-Ti basalts, evidenced consistently by the mineral assemblages (mainly by clinopyroxene, plagioclase, magnetite, and small amounts of olivine, apatite), geochemical features (enriched in Fe2O3, TiO2, and P2O5, high Sm/Yb and low La/Sm ratios), and low initial Sr-87/Sr-86 ratios as well as high epsilon(Nd) (t) values in the mafic rocks. The accumulation sequences and geochemical features reveal the lower zone was resulted from accumulation of olivine, clinopyroxene, magnetite, apatite and plagioclase crystallized from a single pulse of Fe-Ti-enrich magma, whereas the upper zone was generated by slightly rapid cooling consolidation of a new influx of magma. However, both the lower and upper zones were originated from the same parental magma genetically related to the Emeishan mantle plume. The lower zone has lower initial Sr-87/Sr-86 (0. 7041 similar to 0.7051) and higher epsilon(Nd) (t) values (2. 1 similar to 4. 4) than the upper zone (0.7050 similar to 0. 7056, and 0. 6 similar to 1. 3, respectively), suggesting the later had experienced slightly more extensive crustal contamination relative to the former. Only the olivine pyroxenite and gabbro occur in the lower zone but absence of granites and synenites. The thick stratiform Fe-Ti oxide layers are located at the concave part of the base of the Heigutian intrusion. These observations imply that the Heigutian intrusion occurred in a magma plumbing system, and the Fe-Ti oxide layers resulted from coupling of gravity settling and sorting of the crystallized Fe-Ti oxides from Fe-Tienriched magmas. The discovery of the Heigutian Fe-Ti oxide bearing intrusion indicates that the small-scaled intrusions can also be very significant targets to host Fe-Ti oxide deposit and should not be ignored during exploration.
| Publication name | ACTA PETROLOGICA SINICA, 30 (5):1415-1431; MAY 2014 |
| Author(s) | Chen LieMeng; Yi JunNian; Song XieYan; Yu SongYue; She YuWei; Xie Wei; Luan Yan; Xiang JianXin |
| Corresponding author | CHEN Liemeng
chenliemeng@vip.gyig.ac.cn
Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Peoples R China. |
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