Geochemical characteristics of volcanic rocks from Ningwu area, and its significance.

	Geochemical characteristics of volcanic rocks from Ningwu area, and its significance.
	Wang, YL; Zhang, Q; Wang, Y
刊名	ACTA PETROLOGICA SINICA
	2001-10-01
卷号	17 期号:4 页码:565-575
关键词	Nanjing-Wuhu area early Cretaceous volcanic rocks Shoshonitic series adakite-like rocks geochemistry
ISSN号	1000-0569
文献子类	Article
英文摘要	The early Cretaceous volcanic rocks in Ningwu area are composed of basic to intermediate volcanic rocks. Compared with alkaline basalts, Ningwu volcanic rocks are poor in Ti, Fe and enriched in K and LREE, with Na(2)O/K(2)O ratios near to 1. Plotting in the shoshonite field in SiO(2) - K(2)O diagram, all samples from Longwangshan Formation and most of samples from Dawangshan Formation are considered to be the products of partial melting of LILE- and fluid-rich mantle. Since the volcanic rocks in Ningwu area are formed in the interplate environment, the potassium-rich magma is probably generated by upwelling of asthenospheric mantle and the extension-thinning process of the Lithosphere or rifting. Ningwu volcanic rocks are enrichment of LILE and depletion of HFSE with negative Ti, Nb (Ta) anomaly. At the same time, the volcanic rocks of Longwangshan Formation and Dawangshan Formation in the bottom of Ningwu volcanic rocks show different geochemical characters from that of Ningwu volcanic rocks. The volcanic rocks of Longwangshan Formation have higher contents of Rb, Ba, K and poorer LREE (La, Ce, Nd), Eu, Sr and higher ISr ratios and lower epsilon (Nd) (t) values than that of the volcanic rocks of Dawangshan Formation. This cannot be interpreted as a crystallization process because the Dawangshan Formation lies higher than the Longwangshan Formation in stratigraphic sequence. The only explanation for this is that in the early stage of volcanic exploration (Longwangshan Formation) the magmas undergo contamination with continental crust during upwelling and absorb abundant LILE such as K, Rb, Ba from the country rocks, which result in relatively high ISr ratios and low epsilon (Nd)(t) values of the volcanic rocks of Longwangshan Formation. Poor correlation between SiO(2) and K(2)O in the volcanic rocks of Longwangshan Formation also argues the contamination of the continental crust. But in the strongest exploration stage (Dawangshan Formation) the isotopic composition of the volcanic rocks are close to that of primative magmas due to the decrease of contamination between magmas and country rocks. Recent studies show that a large amount of adakite-like rocks of late-Mesozoic period crop out in the middle-lower reaches of Changiiang River. The adakite-like rocks are assumed to be derived from the lowest part of the thickened continental crust and to be generated by partial melting of the basic lower crust under very high temperature. Widespread eruption of the volcanic rocks in Ningwu area demonstrates that the mantle of the region was active during the early Cretaceous period, resulting in large amount of shoshonitic magma underplating beneath the lower crust, and the lower crust melting to form adakite-like magma finally.
WOS关键词	CALC-ALKALINE ; CHINA ; PETROGENESIS ; MAGMAS ; LITHOSPHERE ; POTASSIUM ; PROVINCE ; ORIGIN ; ISLAND
WOS研究方向	Geology
语种	英语
出版者	SCIENCE PRESS
WOS记录号	WOS:000172356500007
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/76475]
专题	中国科学院地质与地球物理研究所
通讯作者	Wang, YL
作者单位	Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China
推荐引用方式 GB/T 7714	Wang, YL,Zhang, Q,Wang, Y. Geochemical characteristics of volcanic rocks from Ningwu area, and its significance.[J]. ACTA PETROLOGICA SINICA,2001,17(4):565-575.
APA	Wang, YL,Zhang, Q,&Wang, Y.(2001).Geochemical characteristics of volcanic rocks from Ningwu area, and its significance..ACTA PETROLOGICA SINICA,17(4),565-575.
MLA	Wang, YL,et al."Geochemical characteristics of volcanic rocks from Ningwu area, and its significance.".ACTA PETROLOGICA SINICA 17.4(2001):565-575.