Abstract

The composition of chevkinite-group minerals from the Late Permian Woshui pluton is presented. The Woshui pluton is one of the few mantle-derived metaluminous syenitic intrusions within the Emeishan large igneous province of SW China and contains four times less ∑REE (∑REE = 0.05 wt.%) than the spatially and temporally associated Baima peralkaline syenitic pluton (∑REE = 0.2 wt.%). The chevkinite-group minerals are relatively uniform in composition and observed chemical trends are consistent with substitution between major cationic sites defined as:  
CaA2++TiC4+REEA3++MC3+,2+

The chevkinite-group minerals from the Woshui syenites are unique in that they display positive chondrite-normalized Eu-anomalies (i.e. Eu/Eu* = 2.3 to 23) which may be related to the conditions that produced the parental magma. The magmatic conditions of Woshui pluton were likely to be low pressure (i.e. ≤ 1 kbar), moderate temperature (i.e. 700–800°C) and relatively oxidizing (fO2 ≥ FMQ > 0). In comparison to chevkinite-group minerals reported from peralkaline rocks, those from metaluminous rocks tend to have higher SiO2, Al2O3, CaO and ZrO and lower FeO*, Nb2O5 and Ce2O3. The compositional differences are attributed to parental magma composition and possible magmatic origin (i.e. partial melting vs. crystal fractionation).

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