摘要
马槽园群是华南前寒武纪地层中的重要单元,其沉积特征及时代归属对建立和完善扬子北缘地层格架、认识和恢复当时的古地理格局有重要意义。通常认为,扬子北缘马槽园群(下部八里垭组,上部火烧尖组)是一套角度不整合于中元古界神农架群之上的新元古代磨拉石建造。取自该群下部八里垭组上部的同沉积凝灰岩样品的高精度离子探针(SHRIMP)锆石U-Pb年龄为(1165±14)Ma。该年龄数据表明,马槽园群沉积地层的形成时代应为中元古代,而不是新元古代。野外调查与沉积相分析表明,马槽园群沉积地层中滑塌包卷、正粒序等重力流沉积构造发育,主体为一套斜坡相碳酸盐岩重力流沉积,而非磨拉石建造。结合前人研究结果认为,马槽园群无论是在沉积特征还是时代归属上都不能与华南新元古代裂谷系地层进行对比,而应该属于裂谷系之下的基底地层。
The Macaoyuan Group is an important stratigraphic unit of the Precambrian strata in South China, so its sedimentary char- acteristics and ages are of great importance for the stratigraphic division and the correlation and reconstruction of the sedimentary facies and paleogeographic framework of the northern margin of the Yangtze block. It is generally accepted that the Maocaoyuan Group comprising the lower Baliya Formation and the upper Huoshaojian Formation on the northern margin of the Yangtze block consists of a succession of the Neoproterozoic molasse formation unconformably overlying the Mesoproterozoic Shennongjia Group. The SHRIMP U-Pb zircon age of the synsedimentary tuff from the upper part of the Baliya Formation is dated at 1165Ma＋14Ma. This dating result shows that the Macaoyuan Group should be traced back to the Mesoproterozoic rather than previously-considered Neo- proterozoic strata. Field investigation and sedimentary facies analysis demonstrate that there are slump-convolute structures and normal graded bedding formed by the gravity flow in the Maocaoyuan Group, in which the strata are mainly made up of a succession of slope carbonate gravity flow deposits, instead of molasse formation. In combination with previous research results, the authors hold that the Macaoyuan Group is not comparable with the Neoproterozoic rift successions in South China both in sedimentary characteristics and in ages, and the Macaoyuan Group in the Shennongjia area should be assigned to one of the basement strata beneath the Neoprotero- zoic rift succession in South China.
出处
《地质通报》
CAS
CSCD
北大核心
2013年第4期631-638,共8页
Geological Bulletin of China
基金
国家自然科学基金重点项目<华南新元古代"楔状地层"沉积序列及其大地构造属性研究>(批准号:41030315)
国家自然科学基金面上项目<黔东新元古代中期沉积盆地演化与地层划分对比研究>(批准号:41072088)
中国地质调查局计划项目<扬子地块东南缘罗迪尼亚超大陆解体及沉积-成矿响应综合研究>(编号:1212011121111)
<扬子北缘马槽园群沉积充填序列及其沉积大地构造研究>(编号:1212011121109)
关键词
马槽园群
凝灰岩
锆石U—Pb年龄
中元古代
扬子北缘
Maocaoyuan Group
mS SHRIMP U-Pb zircon age
Paleo-Proterozoic
northern margin of the Yangtze block
