Abstract
Garnet clinopyroxenite at Rizhao occurs as a lens 100 × 225 m2 within a serpentinized peridotite body, in fault contact with felsic gneiss. Minor dunite also occurs within the same peridotite. The clinopyroxenite consists of porphyroblastic Grt-bearing (type 1), megacrystic Grt-bearing (type 2), porphyroblastic Cpx-bearing (type 3), and equigranular (type 4) garnet clinopyroxenite. Lamellaerich, coarse-grained Cpx occurs as inclusions in megacrystic Grt from type 2 clinopyroxenite, and as porphyroblasts in a matrix of Cpx + Grt + Ilm from type 3 clinopyroxenite; these clinopyroxenes contain abundant exsolution lamellae of Grt (PrP16-19Grs62 Alm19-21SpS1) + Ilm± Mag ± Amp (Mg#: 0.88-0.98; Na2O: 0.5-3.3 wt%; K2O: 0.7-1.0 wt%; TiO2: 0.1-0.2 wt%). Megacrystic and porphyroblastic garnet (Prp35-42Grs34-45Alm19-24 SpS1) also occurs in a matrix of fine-grained Cpx + Grt + Ilm; spinel (Mg#: 0.60-0.62) is present as inclusions in both porphyroblastic Grt and lamellae-rich Cpx. Petrochemical data support a mantle origin involving crystallization of majoritic garnet. We propose that the protolith of the Rizhao clinopyroxenite initially was a spinel clinopyroxenite, and was convected to great depths (>450 km) to form a majoritic garnet that contains high CaO and considerable amounts of FeO and TiO2. During later decompression, the majoritic garnet broke down to form intergrowths of Cpx + Grt + Ilm ± Mag ± Amp at T = 700-300°C, P ≤ 3 GPa. It was then emplaced into a subduction zone and experienced UHP metamorphism at 620-880°C, 3 GPa during Triassic continental collision. Megacrystic /porphyroblastic garnet formed during this stage, and lamellae-rich Cpx recrystallized to the matrix assemblage of Cpx + Grt + Ilm subsequently. The clinopyroxenite also experienced later retrogression during exhumation. Zircon U-Pb geochronology yields 215 ± 2 Ma for the Rizhao garnet clinopyroxenite, occurrence of garnet and clinopyroxene inclusions in zircon suggests that this age reflects the UHP metamorphism.
| Original language | English |
|---|---|
| Pages (from-to) | 732-752 |
| Number of pages | 21 |
| Journal | International Geology Review |
| Volume | 49 |
| Issue number | 8 |
| DOIs | |
| Publication status | Published - Aug 2007 |
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Petrology and U-Pb SHRIMP Geochronology of a Garnet Peridotite, Sulu UHP Terrane, East-Central China. / Zhao, Ruixuan; Liou, Juhn G.; Tsujimori, Tatsuki; Zhang, Ru Y.
In: International Geology Review, Vol. 49, No. 8, 08.2007, p. 732-752.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Petrology and U-Pb SHRIMP Geochronology of a Garnet Peridotite, Sulu UHP Terrane, East-Central China
AU - Zhao, Ruixuan
AU - Liou, Juhn G.
AU - Tsujimori, Tatsuki
AU - Zhang, Ru Y.
PY - 2007/8
Y1 - 2007/8
N2 - Garnet clinopyroxenite at Rizhao occurs as a lens 100 × 225 m2 within a serpentinized peridotite body, in fault contact with felsic gneiss. Minor dunite also occurs within the same peridotite. The clinopyroxenite consists of porphyroblastic Grt-bearing (type 1), megacrystic Grt-bearing (type 2), porphyroblastic Cpx-bearing (type 3), and equigranular (type 4) garnet clinopyroxenite. Lamellaerich, coarse-grained Cpx occurs as inclusions in megacrystic Grt from type 2 clinopyroxenite, and as porphyroblasts in a matrix of Cpx + Grt + Ilm from type 3 clinopyroxenite; these clinopyroxenes contain abundant exsolution lamellae of Grt (PrP16-19Grs62 Alm19-21SpS1) + Ilm± Mag ± Amp (Mg#: 0.88-0.98; Na2O: 0.5-3.3 wt%; K2O: 0.7-1.0 wt%; TiO2: 0.1-0.2 wt%). Megacrystic and porphyroblastic garnet (Prp35-42Grs34-45Alm19-24 SpS1) also occurs in a matrix of fine-grained Cpx + Grt + Ilm; spinel (Mg#: 0.60-0.62) is present as inclusions in both porphyroblastic Grt and lamellae-rich Cpx. Petrochemical data support a mantle origin involving crystallization of majoritic garnet. We propose that the protolith of the Rizhao clinopyroxenite initially was a spinel clinopyroxenite, and was convected to great depths (>450 km) to form a majoritic garnet that contains high CaO and considerable amounts of FeO and TiO2. During later decompression, the majoritic garnet broke down to form intergrowths of Cpx + Grt + Ilm ± Mag ± Amp at T = 700-300°C, P ≤ 3 GPa. It was then emplaced into a subduction zone and experienced UHP metamorphism at 620-880°C, 3 GPa during Triassic continental collision. Megacrystic /porphyroblastic garnet formed during this stage, and lamellae-rich Cpx recrystallized to the matrix assemblage of Cpx + Grt + Ilm subsequently. The clinopyroxenite also experienced later retrogression during exhumation. Zircon U-Pb geochronology yields 215 ± 2 Ma for the Rizhao garnet clinopyroxenite, occurrence of garnet and clinopyroxene inclusions in zircon suggests that this age reflects the UHP metamorphism.
AB - Garnet clinopyroxenite at Rizhao occurs as a lens 100 × 225 m2 within a serpentinized peridotite body, in fault contact with felsic gneiss. Minor dunite also occurs within the same peridotite. The clinopyroxenite consists of porphyroblastic Grt-bearing (type 1), megacrystic Grt-bearing (type 2), porphyroblastic Cpx-bearing (type 3), and equigranular (type 4) garnet clinopyroxenite. Lamellaerich, coarse-grained Cpx occurs as inclusions in megacrystic Grt from type 2 clinopyroxenite, and as porphyroblasts in a matrix of Cpx + Grt + Ilm from type 3 clinopyroxenite; these clinopyroxenes contain abundant exsolution lamellae of Grt (PrP16-19Grs62 Alm19-21SpS1) + Ilm± Mag ± Amp (Mg#: 0.88-0.98; Na2O: 0.5-3.3 wt%; K2O: 0.7-1.0 wt%; TiO2: 0.1-0.2 wt%). Megacrystic and porphyroblastic garnet (Prp35-42Grs34-45Alm19-24 SpS1) also occurs in a matrix of fine-grained Cpx + Grt + Ilm; spinel (Mg#: 0.60-0.62) is present as inclusions in both porphyroblastic Grt and lamellae-rich Cpx. Petrochemical data support a mantle origin involving crystallization of majoritic garnet. We propose that the protolith of the Rizhao clinopyroxenite initially was a spinel clinopyroxenite, and was convected to great depths (>450 km) to form a majoritic garnet that contains high CaO and considerable amounts of FeO and TiO2. During later decompression, the majoritic garnet broke down to form intergrowths of Cpx + Grt + Ilm ± Mag ± Amp at T = 700-300°C, P ≤ 3 GPa. It was then emplaced into a subduction zone and experienced UHP metamorphism at 620-880°C, 3 GPa during Triassic continental collision. Megacrystic /porphyroblastic garnet formed during this stage, and lamellae-rich Cpx recrystallized to the matrix assemblage of Cpx + Grt + Ilm subsequently. The clinopyroxenite also experienced later retrogression during exhumation. Zircon U-Pb geochronology yields 215 ± 2 Ma for the Rizhao garnet clinopyroxenite, occurrence of garnet and clinopyroxene inclusions in zircon suggests that this age reflects the UHP metamorphism.
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UR - http://www.scopus.com/inward/citedby.url?scp=34548204862&partnerID=8YFLogxK
U2 - 10.2747/0020-6814.49.8.732
DO - 10.2747/0020-6814.49.8.732
M3 - Article
AN - SCOPUS:34548204862
VL - 49
SP - 732
EP - 752
JO - International Geology Review
JF - International Geology Review
SN - 0020-6814
IS - 8
ER -