Remnants of premetamorphic fluid and oxygen isotopic signatures in eclogites and garnet clinopyroxenite from the Dabie-Sulu terranes, eastern China
Fu, B., Touret, J.L.R., and Zheng, Y.-F. (2003) Remnants of premetamorphic fluid and oxygen isotopic signatures in eclogites and garnet clinopyroxenite from the Dabie-Sulu terranes, eastern China. Journal of Metamorphic Geology, 21 (6). pp. 561-578.
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A combined oxygen-isotope and fluid-inclusion study has been carried out on high- and ultrahigh-pressure metamorphic (HP/UHPM) eclogites and garnet clinopyroxenite from the Dabie-Sulu terranes in eastern China. Coesite-bearing eclogites/garnet clinopyroxenite and quartz eclogites have a wide range in whole-rock δ18OVSMOW, from 0 to 11‰. The high-T oxygen-isotope fractionations preserved between quartz and garnet preclude significant retrograde isotope exchange during exhumation, and the wide range in whole-rock oxygen-isotope composition is thought to be a presubduction signature of the precursors. Aqueous fluids with variable salinities and gas species (N2-, CO2-, or CH4-rich), are trapped as primary inclusions in garnet, omphacite and epidote, and in quartz blebs enclosed within eclogitic minerals. In high-δ18O HP/UHPM rocks from Hujialin and Shima, high-salinity brine and/or N2 inclusions occur in garnet porphyroblasts, which also contain inclusions of coesite, Cl-rich blue amphibole and dolomite. In contrast, in low-δ18O eclogites from Qinglongshan and Huangzhen, the Cl concentrations in amphibole are very low, < 0.2 wt.%, and low-salinity aqueous inclusions occur in quartz inclusions in epidote porphyroblasts and in epidote cores. These low-salinity fluid inclusions are believed to be remnants of meteoric water, although the fluid composition was modified during pre- and syn-peak HP/UHPM. Eclogites at Houshuichegou and Hetang contain CH4-rich fluid inclusions, coexisting with high-salinity brine inclusions. Methane was probably formed under the influence of CO2-rich aqueous fluids during serpentinisation of mantle-derived peridotites prior to or during plate subduction. Remnants of premetamorphic low- to high-salinity aqueous fluid with minor N2 and/or other gas species preserved in the Dabie-Sulu HP/UHPM eclogites and garnet clinopyroxenite indicate a great diversity of initial fluid composition in the precursors, implying very limited fluid–rock interaction during syn- and post-peak HP/UHPM.
|Item Type:||Article (Refereed Research - C1)|
|Keywords:||eclogite; fluid inclusions; garnet clinopyroxenite; oxygen isotopes; ultrahigh-pressure metamorphism (UHPM)|
|FoR Codes:||04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 100%|
|SEO Codes:||97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%|
|Deposited On:||13 Dec 2010 08:48|
|Last Modified:||29 Jul 2013 01:02|
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