167-4 The long-lived eclogite-facies metamorphism of an orogenic belt revealed by zircon petrochronology and whole-rock geochemistry.

Session: Integrating Geochronology and Geochemistry to Decipher the Tectonic Evolution of Orogenic Belts

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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 eclogite-facies 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. 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. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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