Petrogenesis of Maobei rutile eclogites from the southern Sulu ultrahigh-pressure metamorphic belt, eastern China

The Maobei complex in the southern Sulu ultrahigh-pressure (UHP) metamorphic belt, eastern China, mainly consists of layered eclogites, garnet peridotites and orthogneisses. Based on the modal mineral and whole-rock compositions, eclogites from the Maobei complex are divided into quartz eclogite, quartz-rich eclogite, rutile eclogite, rutile-rich eclogite and eclogite. The distinct spatial changes in the lithology and related chemical compositions indicate that this complex includes 10 rhythmic layers. The rutile eclogites have high TiO2 (2.4-5.9 wt%), commonly coupled with high P2O5 (up to 4.1 wt%) contents; most show fractionated REE patterns with slight positive Eu anomalies. The rutile-rich eclogites have very high TiO2 (3.3-5.7 wt%), FeOT (17.5-25.3 wt%), V (126-1163 ppm) and Co (14-132 ppm), and very low SiO2 (38.0-42.3 wt%), Zr (24-85 ppm), Nb (0.3-6.9 ppm), Ta (< 0.1-0.6 ppm) and total REE (10.7-334.0 ppm) contents, variable degree of LREE depletion, and positive Eu anomalies (Eu/Eu* = 1.1-2.9), and the Ti is decoupled from other high-field-strength elements. These characteristics are consistent with Fe-Ti gabbros of typical layered intrusions, implying a cumulate of plagioclase, clinopyroxene and abundant accessory magnetite in an evolved basaltic magmatic chamber. Based on a normal stratigraphic sequence, the Maobei complex shows an iron-enrichment trend, followed by alkaline enrichment with increasing fractionated crystallization and stratigraphic height. These facts, together with SHRIMP U-Pb zircon ages of 773.7 +/- 8.0 Ma, indicate that the protolith of the Maobei complex is a Neoproterozoic layered intrusion consisting of a base of peridogabbro, a main body of gabbro and minor granodiorite. Unusually high Ti, V and P contents in three rutile eclogite layers suggest that they are potential economic ore deposits.