“黔中隆起”和贵州晚古生代古地理演化及其对铝土矿的控矿作用*

早古生代的区域隆升形成的古地貌和晚古生代海平面变化明显控制了贵州晚古生代古地理与古地貌的演化,“黔中隆起”表现尤为明显。然而对“黔中隆起”的形成时间及演化存在较大争议,限制了对贵州铝土矿的沉积古地理与古地理演化史的认识。通过野外踏勘、资料收集和整理,建立了贵州晚寒武世至二叠纪数个重要地质历史时期的古地理图,对“黔中”隆起的形成时间、演化等进行了再认识,揭示其与贵州铝土矿成矿的耦合关系。寒武纪至早志留世早—中期,“黔中隆起”北缘缺失与之相关的古陆边缘相沉积,黔中地区大规模的隆起时间应以下志留统韩家店组潮坪相沉积的出现作为开始。在“黔中隆起”的显著影响下,黔中和遵义地区经历长期而强烈的风化剥蚀,于早石炭世分别形成喀斯特洼地和漏斗、峡谷地貌,为九架炉组含铝岩系的形成提供了物质条件和成矿场所,并在晚古生代冰盖消长带来的海平面和气候变化的影响下,通过强烈的淋滤作用形成铝土矿。黔北务正道地区经历了长期的风化剥蚀后,在海平面高频变化下形成有利于下二叠统大竹园组铝土矿形成的滨岸湿地环境和洼地地貌。贵州早二叠世的铝土矿与晚古生代冰期具有更明显的耦合关系。

‘Qianzhong Uplift’ and evolution of the Late Paleozoic palaeogeography and its control on formation of bauxite in Guizhou Province

The Early Paleozoic regional uplift(e.g.,the Qianzhong Uplift)and sea-level changes had obviously controlled the evolution of the Late Paleozoic palaeogeography and paleogeomorphology in Guizhou Province. However,the formation time and evolution of the Qianzhong Uplift is still in debate,which limits the understanding of the Permo-Carboniferous paleogeographic and paleogeomorphologic evolution that formed bauxite in Guizhou. In this paper,based on field surveys and data collection,we established the palaeogeography of several important geological periods from the Late Cambrian to Permian in Guizhou,and re-recognized the formation time and evolution of the Qianzhong Uplift,and revealed the coupling relationship between the Qianzhong Uplift and Guizhou bauxite formation. During the Cambrian to early-middle Early Silurian,the continent-marine transitional facies were missed in the northern margin of the Qianzhong Uplift,central Guizhou Province,such as Bijie,Jinsha and Zunyi. The large-scale uplift of the central Guizhou Province should begin with the tidal flat deposits of the Hanchiatien Formation in the Early Silurian. Because of the Qianzhong Uplift,the central Guizhou and Zunyi areas experienced long-lasting and intense weathering and erosion,forming karst depressions,funnels,and canyons in the Early Carboniferous. The karst landform provided material conditions and location for the formation of bauxite deposits in the Early Carboniferous. The bauxite ore formed under intense chemical wreathing and leaching induced by the glacio-eustasy and paleoclimate fluctuations. The early long-lasting and intense weathering and erosion occurred in the northern Guizhou along with the Permo-Carboniferous glacio-eustasy,had leaded to the formation of coastal wetland and depressions,which were favorable places for the Early Permian bauxite formation. The Early Permian bauxite ores in Guizhou Province have an obvious coupling relationship with the Late Paleozoic Ice Age.