摘要
地质历史上何时何地曾经存在过高原或山脉是人们感兴趣的话题,根据花岗岩的地球化学特征(如Sr和Yb)与其形成压力的关系探讨了这种可能性。花岗岩按照Sr和Yb的含量可以分为5类:①埃达克岩(Sr>400×10-6,Yb<2×10-6)、②喜马拉雅型花岗岩(Sr<400×10-6,Yb<2×10-6)、③广西型花岗岩(Sr>400×10-6,Yb>2×10-6)、④浙闽型花岗岩(Sr<400×10-6,Yb>2×10-6)和⑤南岭型花岗岩(Sr<100×10-6,Yb>2×10-6)。其中除了广西型的含义不清楚以外,其他4类花岗岩的差别可能与其形成的深度有关。埃达克岩与残留相榴辉岩平衡,压力通常大于1.5GPa,相应的地壳厚度超过50km。喜马拉雅型花岗岩与高压麻粒岩平衡,石榴子石和斜长石是主要的残留相,压力通常在0.8～1.5GPa之间,相应的地壳厚度在40～50km之间。浙闽型花岗岩与角闪岩相(斜长石+角闪石)平衡,压力小于0.8GPa,相当于正常地壳的厚度(30～40km)。南岭型花岗岩形成于伸展环境,相当于正常或更薄的地壳厚度(30km或更小)。按照上述标志,根据现有的同位素定年和地球化学资料,在华北北部识别出一个东西向延伸的早中生代的山脉(三叠纪—早侏罗世),称为华北北部山脉。推测该山脉东西长约3000km,南北宽200～500km,高度3000～5000m。山脉大约在早、中三叠世时开始抬升,至晚三叠世达到顶峰,于早侏罗世后垮塌消失,指示西伯利亚板块和华北地块碰撞导致的一次强烈的挤压构造和快速的抬升事件。
Where and when plateaus or mountain ranges ever formed in the geological history is an interesting topic. This possibility is discussed according to the relationship between the geochemistry of granitic rocks and pressures of magma production. Granitic rocks may he divided into five types in terms of their Sr and Yb contents （1） adakites with Sr〉400× 10^-6 and Yb〈2× 10^-6, （2） Himalaya-type granites with Sr〈400×10^-6 and Yb〈2×10^-6, （3） Guangxi-type granites with Sr〉400×10^-6 and Yb〉2×10^-6, （4） Zhe-Min-type granites with Sr〈400×10^-6 and Yb〉2×10^-6, and （5） Nanling-type granites with Sr〈100×10^-6 and Yb〉2×10^-6. Except for the Guangxi type whose connotation is unclear, the differences of the Sr and Yb contents between the other four types of granitic rocks are related to depths of their magma production in the crust. The adakite magma is in equilibrium with the residual phase eclogite at pressures 〉1.5 GPa, which corresponds to a crustal thickness of 〉50 kin. The Himalaya-type granitic magma is in equilibrium with high-pressure granulite with garnet and plagioclase as the main residual phases. It forms at pressures of 0.8-1.5 GPa, which are equivalent to a crustal thickness of 40 to 50 kin. The Zhe-Min-type granitic magma is in equilibrium with amphibolite facies （plagioclase＋amphibole） with a pressure 〈1 GPa, equivalent to a normal crustal thickness （30-40 km）. The Nanling-type granitic magma forms in an extensional environment with a normal or thinner crustal thickness （30 km or less）. According to the above-mentioned criteria and available U-Pb age data and geochemical dataset of granitic rocks, we recognized an Early-Mid Mesozoic （Triassic-Early Jurassic）, E-W-striking mountain range in northern North China, called the northern North China Mountain Range. This mountain range is about 3,000 km in length E-W, 200 to 500 km in width N-S and 3,000 to 5,000 m in height. The range started uplift in the Early and Middle Triassic and the uplift reached the culmination in the Late Triassic. After the Early Jurassic it collapsed and disappeared, indicating a strong compressive tectonic and rapid uplift event in North China due to the collision between the Siberian block and North China block.
出处
《地质通报》
CAS
CSCD
北大核心
2008年第9期1391-1403,共13页
Geological Bulletin of China
基金
国家自然科学基金重大研究计划项目(编号:90714011)资助。
关键词
华北北部山脉
花岗岩
早中生代
埃达克岩
喜马拉雅型
浙闽型
南岭型
northern North China mountain range
granite
Early Mesozoic
adakite
Himalaya-type granite
Zhe-Min-type granite
Nanling-type granite
