Geochemistry and Mineralogy of Two Contrasting Cretaceous Lavas: Implications for Lithospheric Mantle Evolution beneath the Northeastern North China Craton
Geochemistry and Mineralogy of Two Contrasting Cretaceous Lavas: Implications for Lithospheric Mantle Evolution beneath the Northeastern North China Craton
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DOI：
10.2747/0020-6814.50.11.1040
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发表时间：
2008-11
影响因子：
2.6
通讯作者：
G. Shi;R. Zhu;Neng Jiang;Xiuming Jia
中科院分区：
文献类型：
--
作者：
G. Shi;R. Zhu;Neng Jiang;Xiuming Jia
对华北克拉通东北部建国火山岩系进行了地球化学和矿物学的综合研究。该序列包含两种截然不同的岩石类型，下部安山质熔岩和上部玄武质熔岩。下部熔岩由含铬尖晶石（主要是铬铁矿）的安山岩组成，而上部熔岩由含钛磁铁矿（高达59-65摩尔% Usp）的玄武岩组成。40 Ar/39 Ar年龄测定表明建国安山岩和玄武岩的年龄分别为116.8 ± 3.0Ma和105.5 ± 0.5Ma。玄武岩具有大洋中脊玄武岩（MORB）的初始Sr-Nd同位素比值特征，并被解释为来自MORB型软流圈。安山岩，演化Sr-Nd同位素特征和负Ta和Nb异常，被解释为已最终来自MORB型软流圈伴随合并同化和分离结晶。这一建议适用于附近的其他两个同生安山岩的成因。这些地球化学对比表明，华北克拉通东部岩石圈地幔的减薄程度约为1000万年。117 Ma.
A combined geochemical and mineralogical study has been conducted on a volcanic sequence at Jianguo, northeastern North China craton (NCC). This sequence contains two contrasting rock types, the lower andesitic lava and the upper basaltic lava. The lower lava is comprised of Cr-spinel (chromite mostly)-bearing andesites, whereas the upper lava consists of titanomagnetite (up to 59-65 mol% Usp)-bearing basalts. 40Ar/39Ar dating shows that the Jianguo andesites and basalts are 116.8 ± 3.0 Ma and 105.5 ± 0.5 Ma, respectively. The basalts have initial Sr-Nd isotopic ratios characteristic of mid-ocean ridge basalt (MORB) and have been interpreted as derived from MORB-type asthenosphere. The andesites, with evolved Sr-Nd isotope features and negative Ta and Nb anomalies, are interpreted to have been ultimately derived from MORB-type asthenosphere accompanied by combined assimilation and fractional crystallization. This suggestion is applicable to the genesis of two other coeval andesites nearby. These geochemical contrasts imply that the lithospheric mantle beneath the eastern part of NCC was considerably thinned by ca. 117 Ma.