滇西昌宁─孟连带南部地层地质问题

滇西孟连以南，整合于南段组浊积岩之上的拉巴群硅质岩含晚二叠世早期放射虫化石，南段组时代不仅限于石炭纪，可能延入二叠纪。二者为晚古生代思茅地块的外陆坡沉积。其西面的南基河杂岩（新名）由层序混乱的晚古生代硅质岩、泥岩和少量砂岩、玄武岩构成。放射虫化石证据表明，硅质岩时代不仅限于晚泥盆世－早二叠世，还延入晚二叠世，而有的砂岩时代为早石炭世，它们是经过强烈构造变动的古特提斯洋的沉积记录。昌宁－孟连带向南可能延至泰国北部的清迈带，而非东北部的难河带。

A discussion on some problems concerning stratigraphic geology of southern part of the Changning Menglian Belt, Western Yunnan

The field investigation along the highways to the south of Menglian reveals that the early late permian radiolarian-bearing Laba Group lies comformably on the turbidites of the Nanduan Formation. So the age of Nanduan Pormation may well extend into the Permian. Both are the Late Paleozoic outer continental slope deposits of the Simao block. Westward the Nanjihe (Nanji River) Complex is composed of chaotic late paleozoic chens, mudstones and subordinate sandstones and basalts. The evidences from radiolarian fossils indicate that the ages of cherts in the complex range not only from Late Devonian to Early Permian, but also extend to Late Permian, and some sandstones are Early Carboniferous in age. They are strongly deformed sedimentary records of the Paleo-Tethyjn Ocean.To the south of the study area, the Nan River Belt in Thailand has been correlated with the Changning-Menglian Belt by many researchers. The SW-NE stretching Nan River Belt, in fact, extends northeastward to meet the Ailaoshan-Red River Belt. The Chiang Mat Belt in Northern Thailand, in our opinion, seems most likely to be the southern extension of the Changning-Menglian Belt (Fig.4).