PETROGRAPHY AND IDENTIFICATION OF THE ATYPICAL OPHITIC DIABASES IN EASTERN CENTRAL ASIAN OROGENIC BELT

Hornblende metamorphic diabase is found in the eastern tectonic zone of Central Asian Orogenic Belt. Its petrographical features present atypical ophitic texture, as blastodiabasic texture and blastophitic poikilitic texture, with major minerals of plagioclase and hornblende and minor clinopyroxene and actinolite. The whole rock petrochemical analysis results show that the chemical compositions in the samples include SiO₂ (49.15%-52.96%), Na₂O+K₂O (2.71%-5.07%), CaO (7.07%-10.40%), Al₂O₃ (14.77%-17.31%), TFeO (8.80%-12.27%), and MgO (6.45%-9.57%). The data fall into the basalt area in the volcanic rock TAS classification diagram, belonging to basic rock, which confirms the naming of the hornblende metamorphic diabase with atypical ophitic texture. The hornblende metamorphic diabase underwent retrometamorphism with the basic plagioclase (labradorite) turned to intermediate plagioclase (andesine) and further to albite or sodium oligoclase, while the clinopyroxene is metamorphosed to hornblende, and then to actinolite.