Abstract
Clinoenstatite exsolution lamellae have been discovered in clinopyroxene grains of garnet peridotite from the Bixiling massif of the ultrahigh-pressure metamorphic (UHPM) terrane in the Dabie Mountains, China. Using transmission electron microscopy, we show here that although the lamellae are low clinoenstatite (Lclen) with P21/c space-group symmetry, they contain nanometer-scale antiphase domains indicating that the originally precipitating phase had C2/c space-group symmetry. The lamellae are oriented parallel to [010] and ~18° to [001] of the host.approximately parallel to (401). Both the very cold exhumation path of the Dabie UHPM terrane and the orientation of the lamellae preclude the possibility that the originally precipitating phase could have been high-temperature clinoenstatite (HTclen). We conclude that the lamellae precipitated as high-pressure clinoenstatite (HPclen) and subsequently inverted to Lclen. Analysis of the incomplete high-pressure crystallographic data available for compositions approximating those of the lamellae and host suggests a minimum pressure of precipitation of ~9 GPa for Dabie and about 12 GPa for similar exsolution previously observed in the Alpe Arami peridotite, Switzerland. The Bixiling complex is a crustal cumulate, hence this result extends the minimum depth of subduction of continental rocks in the Dabie/SuLu orogen to ~300 km (P > 9 GPa).
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- New constraints on metamorphic history of Adirondack diopsides (New York, U.S.A.): Al and δ18O profiles
- Hammadah al Hamra 193: The first amphibole-bearing winonaite
- Crystal chemistry of trioctahedral micas in alkaline and subalkaline volcanic rocks: A case study from Mt. Sassetto (Tolfa district, Latium, central Italy)
- Magnetic excitations and heat capacity of fayalite, Fe2SiO4
- The barometer tremolite + tschermakite + 2 albite = 2 pargasite + 8 quartz: Constraints from experimental data at unit silica activity, with application to garnet-free natural assemblages
- In-situ measurement of dissolution of anorthite in Na-Cl-OH solutions at 22 °C using phase-shift interferometry
- Experimental investigation of the breakdown of dolomite in rock cores at 100 MPa, 650-750 °C
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- Co2+-Cu2+ substitution in bieberite solid-solution series, (Co1-xCux)SO4·7H2O, 0.00 ≤ x ≤ 0.46: Synthesis, single-crystal structure analysis, and optical spectroscopy
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- Heat-pulse calorimetry measurements on natural chlorite-group minerals
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- The effect of valence state and site geometry on Ti L3,2 and O K electron energy-loss spectra of TixOy phases
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