摘要
花岗质岩石地球化学组成可以为研究下地壳物质组成提供有效的信息。本文报道出露于华北克拉通中部带南部地区的蚕坊花岗闪长岩体和孤峰山花岗闪长岩体同位素年代学和地球化学组成,限定研究地区下地壳地球化学特征。锆石U-Pb分析结果表明,蚕坊岩体形成于130Ma左右,与孤峰山岩体的形成时间相当。蚕坊岩体和孤峰山岩体具有高硅、低镁、富钠的主量元素特征,富集大离子亲石元素K、Rb、Ba、Sr等,Sr/Y值高,亏损高场强元素Nb、Ta和Ti,显示明显Pb正异常。蚕坊岩体和孤峰山岩体具有相似的Sr-Nd-Pb同位素组成特征,前者初始87Sr/86Sr比值0.7071~0.7075,初始εNd值-18.2^-15.7;后者为0.7069~0.7074和-16.5^-15.6;Pb同位素组成特征显示岩浆源区与下地壳存在亲缘性。结合地质背景和同位素混合模拟计算表明,太古代下地壳和古元古代新生的玄武质下地壳可能是岩浆源区的主要物质组成,并推断早白垩世华北克拉通太行山以西地区壳-幔相互作用主要表现为软流圈地幔上涌,导致区域热异常,引发下地壳部分熔融和成岩浆作用。
Geochemical composition of granitoid rock can provide virtual information for study of compositional characteristics of the lower crust. This study here reports isotopic geochronology and geochemistry of the Canfang and Gufengshan granodiorite plutons exposed in the southern area of the central North China craton,in order to constrain geochemical feature of the lower crust beneath the study area. Analytical results of the zircon U-Pb dating yield an age of ca. 130 Ma for the formation time of the Canfang pluton,similar with that of the Gufengshan pluton. Both the Canfang and Gufengshan plutons have similar geochemical composition of major elements,such as high Si O_2- and Na2O-contents and low Mg O-content,enriched in large ion lithospheric elements of K,Rb,Ba and Sr,high Sr/Y ratios,depleted in high field strength elements of Nb,Ta and Ti,significantly positive Pb-anomalies. Two plutons bear similar feature in Sr-Nd-Pb isotopic composition,i. e.,initial87 Sr/86 Sr ratios of 0. 7071 to 0. 7075 and initial εNdvalues of- 18. 2 to- 15. 7for the Canfang samples,0. 7069 to 0. 7074 and- 16. 5 to- 15. 6 for the Gufengshan samples. Pb isotopic composition of the samples from both plutons shows an affinity with lower crust for magma source（ s）. Combining geological evolution of the North China craton,simulation calculation using Sr-Nd isotopic composition and mixing model indicates that Archean lower crust and basaltic rocks newly forming in Paleoproterozoic mainly contributed material to the magma source（ s） of the Early Cretaceous plutons. It can be deduced that interaction between the mantle and the crust beneath the North China craton west to the Taihangshan Mountains in Early Cretaceous,was characterized mainly by up-welling of asthenosphere,resulting high thermal anomaly and subsequently partial melting of lower crust and magmatism.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第7期2015-2028,共14页
Acta Petrologica Sinica
基金
国家基础科学人才培养基金(XDCX09-06)
国家自然科学基金项目(40973042)联合资助
