Geochemistry of lower crustal xenoliths from Neogene Hannuoba basalt, North China craton: implications for petrogenesis and lower crustal composition
Geochemistry of lower crustal xenoliths from Neogene Hannuoba basalt, North China craton: implications for petrogenesis and lower crustal composition
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DOI：
10.1016/s0016-7037(01)00609-3
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发表时间：
2001-08
影响因子：
5
通讯作者：
Yongsheng Liu;Shan Gao;Shuyan Jin;Shenghong Hu;M. Sun;Zu-Bin Zhao;Jiaqing Feng
中科院分区：
文献类型：
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作者：
Yongsheng Liu;Shan Gao;Shuyan Jin;Shenghong Hu;M. Sun;Zu-Bin Zhao;Jiaqing Feng
对华北克拉通新近纪汉诺坝玄武岩中30个麻粒岩和辉石岩捕虏体进行了主量和微量元素分析。麻粒岩的组成范围从镁铁质到长英质，SiO2= 45.7%到73.0%，还含有变质沉积物。镁铁质麻粒岩和中性麻粒岩的成分可以用下地壳岩浆房的分离结晶作用来解释。岩浆麻粒岩捕虏体被解释为玄武质底侵作用和随后的地壳底部分离结晶的产物。温压研究和计算的P波速度与区域地震折射结果的相关性表明，占华北克拉通下地壳2/3的上部（24 ~ 38 km）以中长英质为主。只有最低地壳（38-42公里）具有镁铁质成分。这也支持了丰富的中间和长英质麻粒岩捕虏体，占45%的麻粒岩人口收集。计算出的汉诺坝地区块状下地壳具有中等成分，SiO2= 58%。由于华北其他地区也表现出类似的速度结构，高速层仅限于地壳最低3 - 5 km，因此，汉诺坝地区的结果被认为是代表了整个复活的华北克拉通。
Thirty granulite and pyroxenite xenoliths from the Neogene Hannuoba basalt of the North China craton have been analyzed for major and trace element compositions. The granulites range in composition from mafic to felsic with SiO2= 45.7 to 73.0% and also contain metasediments. The compositions of mafic and intermediate granulites can be explained by fractional crystallization of a magma chamber in the lower crust. The magmatic granulite xenoliths are interpreted as product of basaltic underplating and subsequent fractional crystallization at the base of the crust. Thermobarometric studies and correlation of calculated P-wave velocities with regional seismic refraction results suggest that the upper part of the lower crust, which accounts for two thirds of the entire lower crust in the North China craton at a 24- to 38-km depth, is dominated by intermediate and felsic compositions. Only the lowermost crust (38–42 km) has a mafic composition. This is also supported by the abundance of intermediate and felsic granulite xenoliths, which account for 45% of the granulite population collected. The calculated bulk lower crust in the Hannuoba area has an intermediate composition with SiO2= 58%. Because other parts of North China also show a similar velocity structure, with the high-velocity layer confined to the lowermost 3 to 5 km of crust, the results from the Hannuoba area are considered to be representative of the reactivated North China craton as a whole.