摘要
白垩纪超静磁带(CNS)是指白垩纪中期约40 Ma内(Aptian Santonian, 121~83 Ma)地球磁场没有出现倒转的异常现象。这一现象引起地球学界的极大关注,原因在于它与白垩纪中期(124~90 Ma)其他一系列事件在时间上非常吻合,包括洋底扩张速率的快速增加和洋底高原、海山链、大型火成岩省等生产速率的快速增加。过去20多年许多研究强调所有这些现象与下地幔对流的联系。近期研究的一个重要的进展在于把地球磁场的变化(反转频率和古强度)与许多重要的地质和地球物理过程结合起来,如周期性地幔对流、地幔柱活动、全球热流、真极移、大型火成岩省的产生和生物群集绝灭。文中回顾了白垩纪地球磁场研究以及与白垩纪中期所发生的全球性的地质事件之间的可能存在的关联,并讨论在这一重要研究领域内未来研究的发展方向。
The mid-Cretaceous(124～90 Ma)was a period of great unrest in geologic history. In the mid-Cretaceous the breakup of the supercontinent Gondwana into separate continents was still underway and the Tethys Ocean was closing. During this time several mountain ranges were formed, such as California's Sierra Nevada, the Rocky mountains in the western USA, the Andes mountains of western South America, and the European Alps. The Gondwana breakup caused South America and Australia-Antarctic-New Zealand to begin advancing into Pacific from east and west, respectively, and slab penetration events began below these margins. Rates of continental drift(i.e. sea-floor spreading rate)were about three times as great as they are now. During the mid-Cretaceous, large scale plutonism occurred in eastern Asia, western Antarctic, New Zealand, the southern Andes, and western North America. This is best documented in western North America where more than 50% of the exposed batholiths are dated between 115 and 85 Ma. The sea levels rose during the mid-Cretaceous, covering about one-third of the land area. Sea levels were up to 250 m higher than present day levels. Geological evidence also points towards an unusually high rate of volcanic activity in the mid-Cretaceous. Large volumes of magmatic material flowed to Earth's surface from the mantle, and not just from the typical seafloor spreading. The “large igneous provinces” or LIPs made a very important contribution to the lithosphere during the mid-Cretaceous. Several LIPs such as the Ontong Java Plateau(120 Ma), the main portion of the Kerguelen Plateau(115～80 Ma), the Madagascar LIP(84～91Ma), the High Arctic LIP(85～95 Ma), and the Caribbean LIP(88～91 Ma)were all formed during this time. Carbon dioxide emissions released by the Cretaceous LIPs may have triggered two to seven oceanic anoxic events(OAEs) and led to a greenhouse effect that raised the Earth's surface temperature by roughly 10 degrees Celsius, reduced temperature gradients from the Equator to the poles,
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2005年第2期199-216,共18页
Earth Science Frontiers
基金
美国自然科学基金资助项目(EAR 0207389
0310309
OCE0327431)
中国国家自然科学基金重点项目(40332020)
关键词
白垩纪中期
地球磁场
超静磁带
地质事件
地幔柱
大火成岩省
mid-Cretaceous
geomagnetic field
secular variation
magnetic reversals
mantle plumes
large igneous province
Ontong Java Plateau
Kerguelen Plateau
superchrons
Gondwana
remagnetization
mantle convection
