滇东南'新寨岩组'与变质花岗质岩的接触关系及其地质意义

摘要

越北地块位于中国滇桂交界和越南北部地区,是研究扬子、华夏、印支等陆块之间相互作用的重要地区.通过对越北地块北缘马关-麻栗坡地区"新寨岩组"与花岗质岩石接触关系的研究发现,两者之间应为三种接触关系(沉积接触、侵入接触、过渡接触),而不是前人划定的剥离断层接触.沉积接触关系反映出震旦纪-寒武纪时越北地块北缘地区从南西向北东的逐渐超覆过程,也揭示了本区还存在新元古代花岗岩.侵入接触和过渡接触关系表明,奥陶纪末-志留纪时伴随广西运动的构造-热事件,成就了越北地区的都龙-Song Chay花岗岩底辟-片麻岩穹窿构造.前人划分的新元古界"新寨岩组"实际包含了晚震旦纪末-中寒武世的多组地层在内.前人划分的古元古代"南捞片麻岩"当属志留纪构造-热事件的产物,而原志留纪花岗岩乃是新元古代和志留纪两期花岗岩搅合未解体片麻状花岗杂岩.%North Vietnam Block is situated in Yunnan－Guangxi boundary, China, and northern Vietnam, is a key area for studying the interactions between Yangtze, Cathaysia and Indochina blocks. We investigated the contact relationships between “Xinzhai Formation-complex” and metamorphic granitic rocks located in north margin of North Vietnam Block. We suggest that the contact relationships should be three new relationships (sedimentary contact, intrusive contact, transitional contact), instead of prior detachment fault contact. The sedimentary contact indicates the Sinian－ Cambrian overlap (Southwest toward northeast) in north margin of North Vietnam Block. Intrusive contact and transitional contact reflect the emplacement of Caledonian granites in this area, which result in the forming of Dulong－Song Chay dome. The prior “Xinzhai Formation-complex” includes Late Sinian － Cambrian System. The prior Palaeoproterozoic granitic gneisses should be Silurian tectonic－magmatic thermal event. The previous Silurian granites should be re-divided into Neoproterozoic and Silurian granites.