Stratigraphy of volcanic rocks in the Changning–Menglian Belt in southwestern Yunnan, China

Abstract

The Changning–Menglian Belt is regarded as an important geosuture of the Paleotethyan Ocean in southwest China. Volcanic rocks occur extensively in this belt and are critical for understanding its tectonic evolution. However, the lithostratigraphic division, age and correlation of these volcanic rocks remain contentious. In this paper, the sequences in two lithostratigraphic units in the Manxin area, which include volcanic rocks, the Pingzhang and Huoju formations, have been determined. This is a key area for interpreting the Changning–Menglian Belt, using systematic biostratigraphy and information from the recently published 1:50,000 geological map. The Huoju Formation is assigned to the Middle Permian. Five sections in the Pingzhang Formation from different parts of the Changning–Menglian Belt are correlated, on the basis of their biostratigraphy. This correlation suggests that the top of the Pingzhang Formation becomes progressively younger, from Visean to early Late Carboniferous, from north to south. Recent progress on the Late Permian Laochang Formation is also reviewed. It is concluded that most of the volcanic rocks were formed in seamount/oceanic island settings, and that the Changning–Menglian Belt represents a late Devonian to Late Permian Paleotethyan Ocean Basin.