Abstract
Sensitive high resolution ion micro-probe (SHRIMP) U-Pb analyses of zoned zircons were performed to constrain the age and geodynamic significance of the Kokchetav ultrahigh-pressure (UHP) metamorphic rocks, which recrystallized at P > 60 kbar and T> 1000°C. Cathodoluminescence images were correlated with micro-assemblages of mineral inclusions in zircons from diamond-bearing gneisses. These revealed UHP mineral-bearing cores and low-pressure mineral-bearing rims, some zircons also retain inherited cores. Our SHRIMP data identified four discrete stages: Middle Proterozoic protolith age, 537 ± 9 Ma for UHP metamorphic conditions, 507 ± 8 Ma for the late-stage amphibolite facies overprint, and 456-461 Ma for post-orogenic thermal events. Thus, we conclude that Middle Proterozoic supracrustal protoliths of the Kokchetav UHP-HP rocks were subducted to mantle depths in the Middle Cambrian, and exhumed to mid-crustal levels in the Late Cambrian. The exhumation rate calculated from the SHRIMP data and relative P-T conditions is approximately 5 km/Ma. The rapid exhumation rate for the massif is in the same range as other UHP metamorphic terranes, and suggests that slab decoupling may be a driving force for exhumation of UHP metamorphic rocks from mantle depths.
| Original language | English |
|---|---|
| Pages (from-to) | 185-198 |
| Number of pages | 14 |
| Journal | Earth and Planetary Science Letters |
| Volume | 188 |
| Issue number | 1-2 |
| DOIs | |
| Publication status | Published - 2001 |
| Externally published | Yes |
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Keywords
- Kokchetav Kazakhstan
- Mineral inclusion
- Polym metamorphism
- Probe
- SHRIMP data
- U/Pb
- Zircon
ASJC Scopus subject areas
- Geochemistry and Petrology
- Geophysics
Cite this
Ion micro-probe U-Pb zircon geochronology of peak and retrograde stages of ultrahigh-pressure metamorphic rocks from the Kokchetav massif, northern Kazakhstan. / Katayama, Ikuo; Maruyama, Shigenori; Parkinson, Christopher D.; Terada, Kentaro; Sano, Yuji.
In: Earth and Planetary Science Letters, Vol. 188, No. 1-2, 2001, p. 185-198.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Ion micro-probe U-Pb zircon geochronology of peak and retrograde stages of ultrahigh-pressure metamorphic rocks from the Kokchetav massif, northern Kazakhstan
AU - Katayama, Ikuo
AU - Maruyama, Shigenori
AU - Parkinson, Christopher D.
AU - Terada, Kentaro
AU - Sano, Yuji
PY - 2001
Y1 - 2001
N2 - Sensitive high resolution ion micro-probe (SHRIMP) U-Pb analyses of zoned zircons were performed to constrain the age and geodynamic significance of the Kokchetav ultrahigh-pressure (UHP) metamorphic rocks, which recrystallized at P > 60 kbar and T> 1000°C. Cathodoluminescence images were correlated with micro-assemblages of mineral inclusions in zircons from diamond-bearing gneisses. These revealed UHP mineral-bearing cores and low-pressure mineral-bearing rims, some zircons also retain inherited cores. Our SHRIMP data identified four discrete stages: Middle Proterozoic protolith age, 537 ± 9 Ma for UHP metamorphic conditions, 507 ± 8 Ma for the late-stage amphibolite facies overprint, and 456-461 Ma for post-orogenic thermal events. Thus, we conclude that Middle Proterozoic supracrustal protoliths of the Kokchetav UHP-HP rocks were subducted to mantle depths in the Middle Cambrian, and exhumed to mid-crustal levels in the Late Cambrian. The exhumation rate calculated from the SHRIMP data and relative P-T conditions is approximately 5 km/Ma. The rapid exhumation rate for the massif is in the same range as other UHP metamorphic terranes, and suggests that slab decoupling may be a driving force for exhumation of UHP metamorphic rocks from mantle depths.
AB - Sensitive high resolution ion micro-probe (SHRIMP) U-Pb analyses of zoned zircons were performed to constrain the age and geodynamic significance of the Kokchetav ultrahigh-pressure (UHP) metamorphic rocks, which recrystallized at P > 60 kbar and T> 1000°C. Cathodoluminescence images were correlated with micro-assemblages of mineral inclusions in zircons from diamond-bearing gneisses. These revealed UHP mineral-bearing cores and low-pressure mineral-bearing rims, some zircons also retain inherited cores. Our SHRIMP data identified four discrete stages: Middle Proterozoic protolith age, 537 ± 9 Ma for UHP metamorphic conditions, 507 ± 8 Ma for the late-stage amphibolite facies overprint, and 456-461 Ma for post-orogenic thermal events. Thus, we conclude that Middle Proterozoic supracrustal protoliths of the Kokchetav UHP-HP rocks were subducted to mantle depths in the Middle Cambrian, and exhumed to mid-crustal levels in the Late Cambrian. The exhumation rate calculated from the SHRIMP data and relative P-T conditions is approximately 5 km/Ma. The rapid exhumation rate for the massif is in the same range as other UHP metamorphic terranes, and suggests that slab decoupling may be a driving force for exhumation of UHP metamorphic rocks from mantle depths.
KW - Kokchetav Kazakhstan
KW - Mineral inclusion
KW - Polym metamorphism
KW - Probe
KW - SHRIMP data
KW - U/Pb
KW - Zircon
UR - http://www.scopus.com/inward/record.url?scp=0034987696&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034987696&partnerID=8YFLogxK
U2 - 10.1016/S0012-821X(01)00319-3
DO - 10.1016/S0012-821X(01)00319-3
M3 - Article
VL - 188
SP - 185
EP - 198
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
IS - 1-2
ER -