Protracted eclogite‐facies metamorphism of the Dulan area, North Qaidam ultrahigh‐pressure terrane: Insights on zircon growth during continental subduction and collision

Abstract

Continental subduction and collision are recorded by ultrahigh-pressure (UHP) terranes; UHP terranes that form at early stages of an orogeny tend to be small and experience short residence at eclogite-facies depths, whereas terranes that form at mature stages of an orogeny tend to be larger and experience longer residence at these depths, but accurately determining eclogitefacies residence time requires a large geochronologic dataset tied to metamorphic conditions (via trace elements and/or inclusions). In the Dulan area, North Qaidam UHP terrane, China, it remains unclear whether the terrane experienced a long residence at eclogite-facies depths, marking the mature stage of an orogeny or two distinct (ultra)high pressure ([U]HP) events (with short residence times), interpreted as the transition from oceanic subduction to continental collision, where one (U)HP event is related to the former and second (U)HP event to the latter. To address this issue, we report new zircon U-Pb ages and trace-element data from eclogite and host paragneiss from the Dulan area and show that this terrane records $42 Myr of eclogite-facies metamorphism at (U)HP conditions, similar to other large UHP terranes. Zircon from 11 eclogite and 2 gneiss samples yields weighted mean ages of 463-425 Ma, flat heavy rare earth element (HREE) patterns without negative Eu anomalies, and eclogitic mineral inclusions, indicating eclogite-facies conditions. Paragneiss metamorphic ages overlap with ages from eclogite but are generally younger, suggesting that a lack of internally generated fluids may have inhibited zircon growth and/or recrystallization until early decompression and white mica consumption in felsic gneiss generated fluids; thus, we interpret that these felsic rocks record the later stages of continental collision. Dataset patterns from all new and previously published analyses for the Dulan area (34 eclogite and 14 gneiss) suggest that metamorphic zircon in eclogite records prograde, peak and possibly early retrograde conditions, in contrast to the prediction from mass balance models that metamorphic zircon should only grow during exhumation and cooling. We reconcile our observations with these model predictions by recognizing that differential solubility can lead to

Sedimentological Evidence for Pre‐Early Permian Continental Subduction in the Dabie Orogen, Central‐East China

“…Wu & Zheng, 2013). Prolonged Early Permian‐Middle Triassic (>55 Myr, c. 290‐235 Ma) continental subduction metamorphism in the Dabie orogen is consistent with the durations for HP‐UHP metamorphism in other major orogens around the world, such as the prolonged continental subduction history of the Alps (>50 Myr, Kylander‐Clark et al., 2012; Lardeaux, 2014; Malusà et al., 2011, 2015), the North Qaidam UHP terrane (>42 Myr, Hernández‐Uribe et al., 2023), the Rogaland terrane of the Sveconorwegian orogen in Norway (>53 Myr, Laurent et al., 2018) and the Himalayas (>35 Myr, O’Brien, 2019). Our results demonstrate that sedimentary basins in proximity to UHP orogenic belts preserve archives that can help decipher the prograde continental subduction process.…”