摘要
对采自苏北-胶南构造混杂岩带中的15个矿物样品进行了国内首次系统的多重扩散域^(40)Ar-^(39)Ar年龄谱研究,其中七个样品的冷却历史表明,这一地区存在着两个明显的快速冷却事件:172～196Ma(10～40℃/Ma)和105～123Ma(4～10℃/Ma)。采自南缘的样品给出的这一地区最早抬升事件的时间大约为260Ma。这些结果表明苏北-胶南碰撞带的剥蚀历史可能与秦岭-大别山造山带相一致。应用多重扩散域新理论可以从单一长石样品揭示较完整的热历史。
The tectonic melange zone of North Jiangsu and South Shandong has recently been interpreted as a part of the collision zone between the North China and Yangtze plates.To better understand the response of the lithosphere following collision, ^(40)Ar-^(39)Ar age spectrum analyses were made on minerals from fifteen samples taken throughout the melange zone.
These data indicate that a K-feldspar can reveal a continuous thermal history in the temperature rang 150～350℃(or 150～500℃ if co-existing hornblende is also analyzed) using a multiple diffusion domain model. Four Kfeldspars from samples MH89-11,MH89-13,MH89-12-1 and MH89-26 yield an excellent fit to the observed age spectra, log(r/r_0) plots and cooling histories, respectively. Unusual pattern of ^(40)Ar-^(39)Ar age spectra, like a saddle, was obtained on four samples. These spectra are characterized by excess argon at the low temperature steps, but sensible apparent ages were obtained at temperature steps after 30% ^(39)Ar released. Three samples (except MH89-15) also yield useful cooling histories.
There are two clear episodes of relatively rapid cooling, 172～196Ma(10～40℃/Ma) and 105～123Ma (4～10℃/Ma) form the seven cooling histories obtained. Three of four hornblendes yield the ages ranging from 195 to 220Ma. Our results show that the denudation history in the northern Jiangsu and eastern Shangdong collision zone between North China and Yangtze plates was at about 220Ma ago. Our results also show that the denudation history in the northern Jiangsu and southern Shandong collision zone probably correspond wifh the Qinling-Dabie orogeny. The earliest uplift episode was at about 260Ma ago obtained from MH89-7 K-feldspar at southern boundary of the collision zone. The rapid uplift events are determined to be in a range from 172 to 196Ma.
Subsequent rapid cooling events(105～123Ma) are consistent with the latest movement along the Tancheng-Lujiang fault, a major fault zone in East China. Fault gouge from this fault yield Rb-Sr and K-Ar ages between 90 and 110Ma. While this is a little younger than coming, perhaps this reflects the formation of new illite.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1992年第1期1-17,共17页
Acta Petrologica Sinica
基金
国家自然科学基金
地震联合基金
关键词
混杂岩带
扩散域
同位素
年代学
Multiple diffusion domain
^(40)Ar/^(39)Ar
Thermal geochronology
