中国南北构造带北部中生代地质事件及其演化序列

Mesozoic Geological Events and Its Evolution Sequence of the Northern North—South Tectonic Belt,China

南北构造带是中国大陆中部地表系统、地质构造及地球物理场的重要分界线,也是一条强震多发地带,长期以来被诸多学者所关注。但目前对该带中生代期间所经历的重要地质事件及其演化序列的研究较为薄弱,限制了对该带演化过程的认识。本文以南北构造带北部(宁南—六盘山地区)为研究对象,收集整理了大量低温热年代学数据、火山事件、构造事件及其它事件沉积的时空分布,分析和探讨了南北构造带北部中生代构造事件的演化序列。裂变径迹年龄统计结果表明,南北构造带北部中生代期间经历了晚三叠世—早侏罗世(220~180 Ma)、晚侏罗世—早白垩世早期(160~135 Ma)和晚白垩世—古新世中期(100~60 Ma)等多期的构造抬升事件。这些构造抬升事件在研究区均具有明显的地质响应,且其形成与中生代期间研究区及周邻的地球动力学环境变迁密切相关。而在构造变动的间歇期内,研究区大量接受沉积,并伴随着区域气候的变化,发生了诸多事件沉积,这一时期也往往是研究区油、气、煤、膏岩等能源矿产的富集时期。

Objectives： The North—South Tectonic Belt is a significant boundary between the east and west parts of Chinese continent in geological structure,geophysical field and surface system,and is also one of the major regions of strong earthquakes in the continental interior. However,the inner link of the geological events during the Mesozoic is still ambiguous. This paper is aimed to discuss the geological events and tectonic evolution of the northern North—South Tectonic Belt.Methods： Based on a large amount of low temperature thermochronology data,magmatic events,tectonic events and other depositional events,analysis the distribution sequence,depositional response and the inherent coupling relationship of these Mesozoic tectonic events.Results： Fission track ages indicate that the study area underwent four cooling events which occurred in the Late Triassic—Early Jurassic（ 220 ～ 180 Ma）,Late Jurassic—Early Cretaceous（ 160 ～ 135 Ma）,and late Early Cretaceous—Paleocene（ 110 ～ 60 Ma）. Futhermore, the north segment of the North—South Tectonic Belt experienced a serious of volcanic eruptions,tuff deposition and other depositional events during the Mesozoic.Conclusion： The north segment of the North—South Tectonic Belt experienced multi-phase tectonic evolution.It triggered a series of significant geological events that were closely related with each other from the aspects of temporal and spatial distribution.