桐柏—大别造山带内与脆性-韧性剪切带共生的假玄武玻璃的发现及意义

Pseudotachylytes Generated in the Dahezhen Brittle-ductile Shear Zone in the Tongbei-Dabie Orogenic Belt, China and Their Significance for Seismo-tectonics

在桐柏—大别造山带大河镇剪切带中首次发现与碎裂岩和糜棱岩共生的两种不同类型的假玄武玻璃。野外产状及显微结构的研究表明与碎裂岩共生的假玄武玻璃产出于以脆性破裂为主的断层浅部(<15km),而与糜棱岩共生的假玄武玻璃则产出于以韧性变形为主的断层深部(>15 km)。这两种类型的假玄武玻璃均含有熔解起源的自形微晶体,圆形或港湾状的碎片,流动结构和部分玻璃质基质。假玄武玻璃与碎裂岩和糜棱岩共生的现象说明在桐柏—大别造山带形成和隆起过程中同一断层剪切带内大地震重复发生。大河镇假玄武玻璃的研究可对大陆型大地震的发震机制及地壳浅部的脆性变形领域到深部的塑性变形领域的地震断层的破裂过程和力学性质的研究提供重要信息。

Two types of pseudotachylytes are observed in the Dahezhen ductile shear zone of the Tongbei-Dabie oro-genic belt, southwest Henan Province of China, one associated with the cataclasite cuts the foliation of mylonite and the other is interlayered and associated with the mylonite. The occurrences and microstructures suggest that the former type formed in the brittle regime (<15 km), and the latter was generated in the semi-ductile regime (15-25 km). Both pseudotachylytes display textures attesting of a melting origin: microlites, rounded and embayed clast, flow structures and glassy matrix. The coeval presence of the two types of pseudotachylytes indicates that cyclic seismic slips occurred in the same shear zone from brittle to semi-ductile regimes in the Tongbei-Dabie collisional erogenic belt.