Abstract:

The Jiaohe mantle rock fragment was brought to the surface by magmatic alkali olivine basalt, of which, 40-55% (in some parts 60%) are mantle fragments of different tile sizes, generally from 4×5×8 cm to 2×3×4 cm, with the largest measuring 20×22×35 cm and so named mantle rock agglomerate lava. The main mantle rock fragments are spinel iherzolite and clinopyroxene. The cement is alkali olivine basalt. Abundant melt microzones with different compositions and shapes have been found. These microzones can be divided according to shape into drop, fan, ball, irregular short vein and ringed edge. The new minerals can be divided into OL, K, Na+Chl, PL, Chl and SP+Chl+Ser types. The structure of the melt zone is the hidden or radial structure between glass bases, with minerals in skeletal crystal or hollow glass forms. The residual glass is devitrified, forming a small number of acicular and black opaque primary crystallites. The morphology, structure and material composition and mineral crystallization of the melt microzones have the characteristics of residual mantle crystalline rocks. The mantle rock underwent an explosion caused by strong volcanic eruption, resulting in the melting of fusible components such as K, Na and Ca and releasing of volatile components such as H₂O and CO₂, creating a rapid crystallization and quenching environment. These melts preferentially occupy mineral gaps, fissures, dislocation or crystal defect sites and gather and fuse nearby metasomatic minerals, continuously expanding space and forming microzone blobs. The melts have different chemical compositions and crystallization characteristics due to different degrees of melting. They represent different initial magmas, including ultrabasic, alkaline basaltic or lamprophyre magmas. Our data indicate that the Jiaohe mantle xenoliths are residue mantle from extracted melts, i.e., lithospheric mantle.

Key words: Jiaohe of Jilin, mantle agglomerate lava, melting zone, metasomatic texture of mantle, melt pocket