K-rich lamellar exsolution in clinopyroxene： Constraint on the depth of peridotite source at Zhimafang

The oriented lamellar K-rich exsolutions within clinopyroxene host were recognized in garnet peridotite massif at Zhimafang in the Sulu ultrahigh pressure metamorphic terrane, eastern China. EMP and TEM analyses revealed that the composition and the index of electron diffraction for this exsolution are corresponding with phlogopite, and the shape is the lamellae with 1 μm in width and 5 to 30 μm in length. Moreover, the topotaxy is that the (001) of K-rich exsolution parallels to (I00) of the clinopyroxene host. The electron diffraction analyzing shows the exsolution is of a 1M polymorphism. The high-resolution lattice fringe image displays the stack features along 001], which only a layer mineral shows. We conclude that the clinopyroxene with IM and K-rich exsolution was probably derived from mantle depths over 240 km, thus resulting from decompressional exsolution in the initial stage of slab exhumation.

K-rich lamellar exsolution in clinopyroxene: Constraint on the depth of peridotite source at Zhimafang

The oriented lamellar K-rich exsolutions within clinopyroxene host were recognized in garnet peridotite mas-sif at Zhimafang in the Sulu ultrahigh pressure metamorphic terrane, eastern China. EMP and TEM analyses revealedthat the composition and the index of electron diffraction for this exsolution are corresponding with phlogopite, and theshape is the lamellae with 1 mm in width and 5 to 30 mm inlength. Moreover, the topotaxy is that the (001) of K-rich exsolution parallels to (100) of the clinopyroxene host. Theelectron diffraction analyzing shows the exsolution is of a 1M polymorphism. The high-resolution lattice fringe image dis-plays the stack features along 001], which only a layer min-eral shows. We conclude that the clinopyroxene with 1M and K-rich exsolution was probably derived from mantle depthsover 240 km, thus resulting from decompressional exsolution in the initial stage of slab exhumation.