Fragments of ancient oceanic lithosphere preserved in mountain belts, though volumetrically subordinate, provide essential insights into past geodynamics and formation and destruction of oceanic lithosphere. This contribution shows how the two types of oceanic fragments, blueschists and eclogites, on one hand, and ophiolites on the other, preserve ...
Fragments of former oceans are commonly observed in mountain belts: blueschists and eclogites, on the one hand, and ophiolites, on the other hand, are all that remains of ancient oceanic lithosphere. Though volumetrically subordinate, they provide essential insights into past geodynamics and into the processes involved in the formation and destruct...
Two eclogite samples from the Haut-Allier record a prograde evolution from ~20 kbar, 650 °C to 750 °C, 22-23 kbar followed by heating up to 850-875 °C and partial melting. Incipient decompression in high-pressure granulite facies conditions (19.5 kbar, 875 °C) was followed by exhumation to high-temperature amphibolite facies conditions (
Published in Frontiers in Earth Science
The Changning-Menglian suture zone (CMSZ) in the southeastern Tibetan Plateau is a newly discovered HP-UHP metamorphic zone. The eclogites therein are the key evidence constraining the main suture of the Proto- and Paleo-Tethys Ocean in western Yunnan. Targeting the weakly studied Bangbing eclogites, we developed a comprehensive study on the whole-...
Published in Frontiers in Earth Science
Major and trace element zonation patterns were determined in ultrahigh-pressure eclogite garnets from the Changning-Menglian suture, Bangbing area. Several stages of eclogite metamorphism are recorded by garnet zonation. Cores of garnets are generally darker and inclusion-rich, while rims are brighter and inclusion-poor. Garnets were analyzed for t...
Melting phase relations involving model carbonated basalt with excess silica were studied in experiments over the pressure range of 4–7 GPa in the system CaO-MgO-Al2O3-SiO2-CO2 to determine if there is a sharp decrease in the melting temperatures along the transition from carbon dioxide vapor (vapor) to dolomite. The phase assemblages of clinopyrox...
Published in American Mineralogist
Aluminum-rich and Si-poor calcium amphibole [~3.9 Al atoms per formula unit (apfu) and ~5.5 Si apfu for 23 O] occur in the quartz-bearing eclogites from the Donghai area, Sulu ultrahigh-pressure metamorphic belt, eastern China. Most of the aluminous amphibole phases are retrograde products from the exhumation and hydration stage and are texturally ...
Published in Frontiers in Earth Science
Electrical conductivity of water-rich omphacite and garnet in eclogite was measured at 1 GPa and 200–800°C in a piston cylinder press and by a Solartron-1260 impedance/gain-phase analyzer at 106-1 Hz frequency. The water content of pre-annealed omphacite and garnet was 775–2,000 and 705–1,460 ppm H2O, respectively. Sample chemistry and water conten...
Published in Proceedings of the National Academy of Sciences of the United States of America
SignificanceThe onset time of plate tectonics is highly debated in the Earth sciences. A key indicator of modern-style plate tectonics, with deep subduction of oceanic plates, is the presence of eclogite (oceanic crust metamorphosed at high-pressure and low-temperature) in orogenic belts. Since no orogenic eclogites older than 2.1 billion y are cur...
Eclogites hosted in sillimanite-bearing migmatites in the Montagne Noire dome (French Massif Central) have an oceanic protolith and recorded a prograde P–T path from ~19.5 kbar, 700°C to the pressure peak at ~21 kbar, 750°C (pseudosection modelling), suggesting metamorphism in a subductional setting. Subsequent exhumation to low-pressure high-tempe...
