Geoscience Frontiers

Geoscience Frontiers

Volume 11, Issue 2, March 2020, Pages 635-650
Geoscience Frontiers

Research Paper
Subduction channel fluid-rock interaction: Indications from rutile-quartz veins within eclogite from the Yuka terrane, North Qaidam orogen

https://doi.org/10.1016/j.gsf.2019.07.009Get rights and content
Under a Creative Commons license
open access

Highlights

  • Aundant rutile-quartz veins are recognized in eclogite from the Yuka terrane.

  • Zircons recorded the abundance of fluids during the early exhumation stage.

  • The rutile-quartz veins were derived from the host eclogite.

Abstract

High-pressure (HP) or ultrahigh-pressure (UHP) rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones. To explore the fluid flow and the associated element mobility during deep subduction and exhumation of the continental crust, we investigated the major and trace elements of Ti-rich minerals. Additionally, U–Pb dating, trace element contents, and Lu–Hf isotopic composition of zircon grains in the UHP eclogite and associated rutile-quartz veins were examined in the North Qaidam UHP metamorphic belt, Yuka terrane. The zircon grains in the rutile-quartz veins have unzoned or weak oscillatory zonings, and show low Th/U ratios, steep chondrite-normalized patterns of heavy rare earth elements (HREEs), and insignificant negative Eu anomalies, indicating their growth in metamorphic fluids. These zircon grains formed in 431 ​± ​3 ​Ma, which is consistent with the 432 ​± ​2 ​Ma age of the host eclogite. As for the zircons in the rutile-quartz veins, they showed steep HREE patterns on one hand, and were different from the zircons present in the host eclogite on the other. This demonstrates that their formation might have been related to the breakdown of the early stage of garnet, which corresponds to the abundance of fluids during the early exhumation stage. The core-rim profile analyses of rutile recorded a two-stage rutile growth across a large rutile grain; the rutile core has higher Nb, Ta, W, and Zr contents and lower Nb/Ta ratios than the rim, indicating that the rutile domains grew in different metamorphic fluids from the core towards the rim. The significant enrichment of high field strength elements (HFSEs) in the rutile core suggests that the peak fluids have high solubility and transportation capacity of these HFSEs. Furthermore, variations in the Nb vs. Cr trends in rutile indicate a connection of rutile to mafic protolith. The zircon grains from both the rutile-quartz veins and the host eclogite have similar Hf isotopic compositions, indicating that the vein-forming fluids are internally derived from the host eclogite. These fluids accumulated in the subduction channel and were triggered by local dehydration of the deeply subducted eclogite during the early exhumation conditions.

Keywords

Quartz-rutile veins
Eclogite
Fluid-rock interaction
Fluid flow
Yuka
North Qaidam

Cited by (0)

Peer-review under responsibility of China University of Geosciences (Beijing).