Title

Uncovering the tectonic relationship between eclogites and granulites in the Dulan UHP belt, North Qaidam Mountains, China

Presenter Information

Megan Regel
Chris Mattinson

Document Type

Oral Presentation

Location

SURC Ballroom C/D

Start Date

16-5-2013

End Date

16-5-2013

Abstract

In the Dulan ultrahigh-pressure (UHP) terrane, eclogites and granulites outcrop in the east and west, respectively, but their pressure-temperature relationship is not well understood. Previous Fe2+-Mg exchange thermometry suggests ~620–800°C temperatures and 27-32 kbar pressures for eclogites and 750-950°C temperatures and ~14 kbar pressures for granulites; these large temperature ranges prevented understanding of P-T histories and exhumation paths. Zirconium-in-Rutile thermometry of 5 representative eclogites yields ~670-710±10°C, which suggests a westward-increasing thermal gradient of 3-5°C/km. Rutile inclusions from two samples show temperatures ~40-50°C lower than the matrix rutile, suggesting increasing temperatures during prograde and peak metamorphism. Rutiles from one representative granulite show two much higher temperature populations: 1) ~775±10°C and 2) ~740±10°C. The lower temperature population likely records exhumation conditions. The higher granulite temperatures are likely underestimated; current pseudosection and past P-T work suggests peak temperatures of ~810-870°C. Zircon U-Pb geochronology of the 5 eclogites give ages of 432.6±4.0 Ma, 433.9±2.5 Ma, 436±3.0 Ma and 432.4±2.4 Ma, which are consistent within error and record eclogite facies metamorphism. These data show that temperatures are a snapshot of the P-T conditions rather than an artifact of crystallization times. The temperature discontinuity between eclogites and granulites supports the presence of an unmapped fault, which could suggest tectonic juxtaposition after peak metamorphism, followed by concurrent amphibolite facies retrogression.

Poster Number

62

Faculty Mentor(s)

Chris Mattinson

Additional Mentoring Department

Geological Sciences

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Uncovering the tectonic relationship between eclogites and granulites in the Dulan UHP belt, North Qaidam Mountains, China

SURC Ballroom C/D

In the Dulan ultrahigh-pressure (UHP) terrane, eclogites and granulites outcrop in the east and west, respectively, but their pressure-temperature relationship is not well understood. Previous Fe2+-Mg exchange thermometry suggests ~620–800°C temperatures and 27-32 kbar pressures for eclogites and 750-950°C temperatures and ~14 kbar pressures for granulites; these large temperature ranges prevented understanding of P-T histories and exhumation paths. Zirconium-in-Rutile thermometry of 5 representative eclogites yields ~670-710±10°C, which suggests a westward-increasing thermal gradient of 3-5°C/km. Rutile inclusions from two samples show temperatures ~40-50°C lower than the matrix rutile, suggesting increasing temperatures during prograde and peak metamorphism. Rutiles from one representative granulite show two much higher temperature populations: 1) ~775±10°C and 2) ~740±10°C. The lower temperature population likely records exhumation conditions. The higher granulite temperatures are likely underestimated; current pseudosection and past P-T work suggests peak temperatures of ~810-870°C. Zircon U-Pb geochronology of the 5 eclogites give ages of 432.6±4.0 Ma, 433.9±2.5 Ma, 436±3.0 Ma and 432.4±2.4 Ma, which are consistent within error and record eclogite facies metamorphism. These data show that temperatures are a snapshot of the P-T conditions rather than an artifact of crystallization times. The temperature discontinuity between eclogites and granulites supports the presence of an unmapped fault, which could suggest tectonic juxtaposition after peak metamorphism, followed by concurrent amphibolite facies retrogression.