http://www.cnr.it/ontology/cnr/individuo/prodotto/ID187688

Exsolution of Garnet and Clinopyroxene from High-Al Pyroxenes in Xugou Peridotite, Eastern China (Articolo in rivista)

Type

Articolo in rivista (Classe)
Prodotto della ricerca (Classe)

Label

Exsolution of Garnet and Clinopyroxene from High-Al Pyroxenes in Xugou Peridotite, Eastern China (Articolo in rivista) (literal)

Anno

2012-01-01T00:00:00+01:00 (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi

10.1093/petrology/egs023 (literal)

Alternative label

Spengler D. 1,2,3; Obata M. 1; Hirajima T. 1; Ottolini L. 4; Ohfuji H. 5; Tamura A. 6; Arai S. 6 (2012)
Exsolution of Garnet and Clinopyroxene from High-Al Pyroxenes in Xugou Peridotite, Eastern China
in Journal of petrology (Print)
(literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori

Spengler D. 1,2,3; Obata M. 1; Hirajima T. 1; Ottolini L. 4; Ohfuji H. 5; Tamura A. 6; Arai S. 6 (literal)

Pagina inizio

1477 (literal)

Pagina fine

1504 (literal)

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53 (literal)

Rivista

Journal of petrology (Rivista)

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7 (literal)

Note

ISI Web of Science (WOS) (literal)

Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni

1. Kyoto Univ, Dept Geol & Mineral, Kyoto 6068502, Japan 2. Ehime Univ, Senior Res Fellow Ctr, Matsuyama, Ehime 7908577, Japan 3. Univ Potsdam, Dept Earth & Environm Sci, D-14476 Potsdam, Germany 4. IGG Sede Pavia, Consiglio Naz Ric, I-27100 Pavia, Italy 5. Ehime Univ, Geodynam Res Ctr, Matsuyama, Ehime 7908577, Japan 6. Kanazawa Univ, Dept Earth Sci, Kanazawa, Ishikawa 9201192, Japan (literal)

Titolo

Exsolution of Garnet and Clinopyroxene from High-Al Pyroxenes in Xugou Peridotite, Eastern China (literal)

Abstract

Abstract: Serpentinized massif peridotite in the Xugou, Su-Lu ultrahigh-pressure (UHP) metamorphic belt, eastern China, preserves texturally old (porphyroclastic) ortho- and clinopyroxene with up to two generations of lamellae of garnet, clinopyroxene and Mg-chromite. Their crystallographic orientation with respect to the host pyroxene is consistent with an origin by solid-state exsolution. Comparison of integrated mineral chemistry with simplified and natural chemical datasets suggests that both aluminous precursor pyroxenes were in equilibrium at a minimum pressure of similar to 4 GPa and within a temperature range of about 1300-1500 degrees C. Steep isopleths of Ca in orthopyroxene imply that exsolution occurred during cooling. Al diffusion modelling suggests growth of widely spaced lamellae in orthopyroxene down to about 900 degrees C. Integrated Al contents between wide lamellae record a minimum of 4 GPa pressure during cooling. Compositionally uniform exsolved minerals were formed at 4 center dot 3 +/- 0 center dot 3 GPa and 730 +/- 30 degrees C and reflect a cratonic geotherm with about 33 mW m(-2) surface heat flow. The peridotite matrix mineral assemblage of olivine + orthopyroxene +/- garnet +/- Mg-chromite +/- clinopyroxene +/- phlogopite records strain-induced recrystallization that partially to completely replaced precursor porphyroclasts. The recrystallized minerals lack lamellar exsolution. Recrystallized orthopyroxene, with Al2O3 at 0 center dot 13 wt %, indicates conditions of 5 center dot 5 +/- 0 center dot 3 GPa and 760 +/- 30 degrees C, which are higher-grade metamorphic conditions than those preserved in the chemically equilibrated exsolution microstructures. Both estimates overlap with the range reported for the Early Mesozoic UHP metamorphism in the region (4 center dot 0-6 center dot 7 GPa and 760-970 degrees C). Major element melt models applied to previously published Xugou peridotite data suggest high degrees of melt extraction (30-35 %) in the garnet peridotite stability field (3-4 center dot 5 GPa) until garnet and clinopyroxene exhaustion. Coincidence in pressure and in the order of temperature of equilibration of precursor pyroxenes and peridotite melting implies that peridotite formation occurred at similar to 135 km depth in the subcontinental lithospheric mantle (SCLM) beneath the Archaean North China Craton. Subsequent refertilization, mineral exsolution and chemical re-equilibration during long-term cooling in the SCLM occurred prior to deformation and incorporation of the mantle fragment into the continental crust during UHP metamorphism at a minimum depth of 170 km. Because the Xugou precursor pyroxenes and peridotite formed at depths greater than the regional SCLM (c. 90 km), we infer that the orogenic peridotite massif formed part of the former hanging wall of the Archaean SCLM, which delaminated after the Late Mesozoic. (literal)

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