Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: Origin and evolution of garnet exsolution in clinopyroxene

A perspective view on ultrahigh-pressure metamorphism and continental collision in the Dabie-Sulu orogenic belt

“…This suggests that the Yangkou eclogite originated at even greater pressures, implying subduction depths greater than ~200 km. Zhang and Liou [117] found such exsolution of hypothesized majoritic garnet in coarse clinopyroxene grains from garnet clinopyroxenite at Rizhao in the Sulu orogen, which contains up to 25 vol% exsolved garnet, 4 vol% ilmenite and minor amphibole. Liu et al [20] discovered clinoenstatite exsolution lamellae in clinopyroxene grains of garnet peridotite at Bixiling in the Dabie orogen, suggesting a possible pressure of ~9 GPa for precipitation and thus extending the depth of continental subduction to ~300 km.…”

Exsolution microstructures in ultrahigh-pressure rocks: Progress, controversies and challenges

“…This type of 'water' is possibly the dominant water reservoir in the deep subduction zones with the absence of hydrous minerals. Recently, many exsolution microstructures of hydrous mineral in nominally anhydrous mineral have been reported in ultrahigh pressure rocks, such as the phlogopite + coesite exsolution in clinopyroxene from the Kokcheav diamond-bearing REVIEW GEOCHEMISTRY marbles of Kazakstan [50] , the soda amphibilite + rutile + apatite exsolution in garnet from the garnet peridotites of the north margin of Chaidam basin [88,89] , and K-bearing pargasite (KCa 2 (Mg, Fe) 4 AlSi 6 Al 2 O 22 (OH,F) 2 ) exsolution in clinopyroxene from the garnet lherzolites of Sulu [23,90] . These discoveries provide important evidences that 'water' coupled with incompatible elements (such as Na, K, P) can be transported into the deep mantle by continental deep subduction and released during exhumation.…”

Ultradeep Rocks and Diamonds in the Light of Advanced Scientific Technologies

“…Liou et al (2007) have suggested that the Rizhao clinopyroxene containing ∼25 vol.% of exsolved garnet and ∼4 vol.% of exsolved ilmenite originated from the former majoritic garnet. They assume that the following cations substitution has occurred during such majoritic breakdowns: Ca 2+ Ti 4+ → 2Al 3+ , Mg 2+ Si 4+ → 2Al 3+ , and Na 1+ Ti 4+ → Ca 2+ Al 3+ in octahedral sites (e.g., Zhang and Liou, 2003). These authors also hypothesized that a pure clinopyroxene could be a precursor for such a "lamellar" clinopyroxene-garnet assembly.…”