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| Titel |
Thermal history of Yukahe and Xitieshan UHP belts, North Qaidam, western China. |
| VerfasserIn |
Rongguo Hu, Jan Wijbrans, Fraukje Brouwer, Huaning Qiu |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057433
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| Zusammenfassung |
| The North Qaidam Mountains high pressure/ultrahigh pressure metamorphic belt is a recently
discovered HP/UHP metamorphic terrane in western China (Yang et al. 2001). Four HP/UHP
metamorphic units can be distinguished along the North Qaidam Mountains. From East to
West: the Dulan eclogite gneiss unit, the Xitieshan eclogite-gneiss unit, the Luliangshan
garnet Peridotite gneiss unit, and the Yukahe eclogite-gneiss unit. Our research focuses on the
petrology and geochronology of the Xitieshan and the Yukahe units. We have selected quartz,
hornblende and garnet for analysis for 40Ar/39Ar dating by incremental heating and
stepwise crushing in order to shed light on the peak and retrograde metamorphic
history of this area. Stepwise crushing experiments were carried out in an in-house
designed crushing apparatus (Qiu and Wijbrans 2006) which was connected to a
three stage extraction line and a quadrupole mass spectrometer (Schneider et al.
2009).
Ten quartz single mineral samples (8 from Yukahe and 2 from Xitieshan) came
from quartz veins which cross cut eclogite and garnet amphibolite lenses. Eight
hornblende samples (3 from Yukahe and 5 from Xitieshan) were separated from garnet
amphibolite or amphibole mica gneiss. Garnet was separated from two eclogites,
one from Yukahe and one from Xitieshan. Garnet from Yukahe yielded an age by
incremental heating of 506 Ma, whereas hornblende stepwise crushing ages range
from 480 – 450 Ma. Garnet from Xitieshan yielded an age by stepwise crushing
of 234 Ma, whereas hornblende yielded ages in the range 450 – 386 Ma. Quartz
experiments showed a range of apparent ages that point to a dominant excess argon
reservoir. The youngest ages found in quartz experiments, in the range from 217 Ma to
286 Ma, point to overprinting in the late Paleozoic and possibly as young as the
Triassic.
The two sites show distinct differences in their isotopic results with samples from Yukahe
preserving evidence of the 450 – 500 Ma event, whereas the Xitieshan site appears to be
overprinted.
Qiu H.N., and Wijbrans J.R. 2006, Paleozoic ages and excess 40Ar in garnets from the
Bixiling eclogite in Dabieshan, China: New insights from 40Ar/39Ar dating by stepwise
crushing. Geochimica et Cosmochimica Acta 70. pp. 2354 - 2370..
Schneider B., et al. 2009, 40Ar/39Ar geochronology using a quadrupole mass
spectrometer. Quaternary Geochronology 4 (6) 508-516.
Yang, J. et al., 2001. Discovery of coesite in the North Qaidam Early Palaeozoic ultrahigh
pressure (UHP) metamorphic belt, NW China. Comptes Rendus Acad. Sci., Serie II Sci.
Terre Planetes. 333(11): 719-724. |
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