Partial melting of deeply subducted eclogite from the Sulu orogen in China

Abstract

We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust.

Polygenetic titanite records the composition of metamorphic fluids during the exhumation of ultrahigh‐pressure metagranite in the Sulu orogen

“…After excluding such zircon data from sample 00BH17a, the zircon rims in the other two samples give 206 Pb/ 238 U ages of 223 ± 4 to 219 ± 2 Ma (Fig. ), consistent with previous dates for anatectic zircon from the Sulu orogen (Liu et al ., , ; Chen et al ., ,b,c; Li et al ., ; Wang et al ., ). Therefore, the zircon rims grew from hydrous melts due to partial melting of the UHP metagranites during the continental subduction‐zone metamorphism.…”

“…Recent studies indicate that such a temperature can be as high as ~800 °C for a grain size of 200 μ m and a cooling rate of 10–100 °C Ma −1 , typical of regional metamorphism (Kohn & Corrie, ; Gao et al ., ; Spencer et al ., ). In this study, the samples experienced peak metamorphic temperatures of 740–850 °C at 3.0–4.0 GPa in the Donghai outcrop (Zhang et al ., , ), and 830–890 °C at 3.5–4.5 GPa in the Yangkou outcrop (Wang et al ., ). The highest Si number (apfu) of 3.35–3.43 in phengite (Table ) comparable to the UHP metagranites in Dabie‐Sulu orogen and finding of coesite in anatectic zircon of the metagranites from the adjacent outcrop in Donghai area suggest such samples probably experienced UHP metamorphism (Carswell et al ., ; Chen et al ., ).…”

“…Wang et al . () found petrographic evidence for syn‐exhumation partial melting of eclogites and small‐scale melt migration in this area. Two metagranite samples (102SL10 & 102SL11) were selected from the Yangkou outcrop for this study, with a distance of ~1 m between them.…”

“…Some UHP rocks experienced granulite facies and/or amphibolite facies overprinting during exhumation. Partial melting during exhumation has been documented in the UHP rocks by the occurrence of multiphase solid inclusions and anatectic products in migmatitic veins/veinlets (Wallis et al ., ; Zeng et al ., , , ; Zhao et al ., ; Liu et al ., , ; Zong et al ., ; Zheng et al ., ; Chen et al ., ,b; Wang et al ., ).…”

Distinct zircon U–Pb and O–Hf–Nd–Sr isotopic behaviour during fluid flow in UHP metamorphic rocks: evidence from metamorphic veins and their host eclogite in the Sulu Orogen, China

“…Subsequently, different amounts of melt would be incorporated into the fluid flow due to the dehydrated melting of phengite (Fig. ) (Gao et al ., , ; Chen et al ., , , ; Wang et al ., ). In this study, both the veins contain minerals that grew from fluid under eclogite facies conditions (Rubatto & Hermann, ; Wu et al ., ).…”