THE TECTONIC ASPECT OF MINGLING-LIKE PROCESS (EXAMPLE FROM THE TASTAU VOLCANO-PLUTONIC STRUCTURE, CHARA SHEAR ZONE, EASTERN KAZAKHSTAN)

The Tastau volcano-plutonic structure disposes within Chara shear zone (Eastern Kazakhstan). It has elliptic form and is composed of the ring dike system and several separate bodies. In the center of the structure there is a granitic shoot and a number of subvolcanic dikes having north-eastern and submeridional streching. With distance from the shoot number of dikes decreases. Host rocks (Low-Carboniferous siltsandstone and sandstone) have undergone shear deformations, associated with evolution of the Chara shear zone. It was established, that injection of subvolcanic felsitic dikes was synkinematic. Unique mingling-like structures were discovered during the mapping of the volcano-plutonic structure. In the cataclastic sedimentary rocks felsites form oval enclaves and separate bodies varying in size from 2-3 cm to 30-40 cm. The boundaries with host rocks are festoon, drop-shaped and flame-shaped. Quenched contact zones are observed. We propose the following model of ningling-like structures formation. The main idea of this model is the high velocity of shear deformation which occurred during the formation of Tastau volcano-plutonic structure. Structural analysis shows, that at the moment of felsitic melt injection the deformation of sedimentary rocks changed from ductile to ductile-brittle and brittle. The melt injection phase and rheology transition stage were very short. It is proved by undeformed contact zones around small felsite nodules. On this stage mechanical integrity of host rocks was lost on a short-time, and their rheological characteristics became lesser then viscosity of the silicate melt being injected. Favorable conditions for mechanical interaction between melt and sedimentary rocks were established during the continued shear flow. We suggest that structural characteristics of this processes were the same with the classic magmatic mingling. We gratefully acknowledge the financial support of the Russian Foundation for Fundamental Research (Grants N00-05-65308, 99-05-64727).