藏南康马地区石炭系及其下伏变质构造地层序列

Metamorphic Structural Sequence of Carboniferous and Its Underlying Strata in Kangmar Region of Southern Tibet

西藏康马地区位于拉轨岗日构造带南缘中部。前人对该地区的康马穹窿及周围地层进行了大量研究,但长期以来对该区石炭系及以下变质构造地层的层序及时代认识不清,致使拉轨岗日构造带前石炭纪的地质演化史成为空白。根据1∶25万江孜县幅、亚东县幅区域地质调查工作取得的地层学资料及古生物、岩石组合特征,对康马附近石炭系及其以下地层进行了重新厘定。厘定后的地层单元分别为前奥陶系郎巴群(POl)、奥陶系则果群(Oz)、下石炭统雇孜组(C1g)。下石炭统雇孜组(C1g)与上覆早二叠世破林浦组(P1p)之间为伸展不整合接触,与奥陶系则果群(Oz)之间为伸展拆离断层接触,前奥陶系郎巴组(POl)与奥陶系则果群(Oz)之间为伸展不整合接触,与下伏康马岩体为伸展拆离断层接触。

The Kangmar region is located in the central southern Lhagoi Kangri tectonic belt of the Kangmar- Lhunze stratigraphic area. Large amount of work has been done at the formation of Kangmar dome, but the sequence of Carboniferous and underlying strata is still obscure. It causes the geological history of Lhagoi Kangri tectonic belt before Carboniferous being missing. Based on great deal of data on paleontology, stratigraphy, and rock assemblages obtained during the 1：250,000 geological survey in Gyangze-Yadong region, the present authors restudied the Carboniferous and underneath strata in this region, and a new stratigraphic sequence has been set up. It is in ascending order, the Ordovician Langba Group （POl）, Ordovician Zeguo Group （Oz）and Lower Carboniferous Guzi Formation（C1g）. The Lower Carboniferous Guzi Formation（C1g）is underlying unconformably the Early Permian Polinpu Formation （ PiP ） by extensional unconformity contact, and overlying the Ordovician Zeguo Group（Oz） by a detachment fault. Pre-Ordovician Langba Group （ POl ） contacts Ordovician Zeguo Group （Oz）by extensional unconformity, and separates the underlying Kangmar rock mass by a detachment fault.