PRELIMINARY DATA ON THE PINETO GABBROIC MASSIF AND NEBBIO BASALTS: PROGRESS TOWARD THE GEOCHEMICAL CHARACTERIZATION OF ALPINE CORSICA OPHIOLITES
PRELIMINARY DATA ON THE PINETO GABBROIC MASSIF AND NEBBIO BASALTS: PROGRESS TOWARD THE GEOCHEMICAL CHARACTERIZATION OF ALPINE CORSICA OPHIOLITES
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DOI：
10.4454/ofioliti.v25i2.116
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发表时间：
2000-01
期刊：
影响因子：
1.3
通讯作者：
E. Saccani;Elisa Padoa;R. Tassinari
中科院分区：
文献类型：
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作者：
E. Saccani;Elisa Padoa;R. Tassinari
Pineto Massif和Nebbio蛇绿岩序列代表了科西嘉蛇绿岩的两个主要例子，与著名的Balagne推覆岩类似，它们没有经历高压-低温高山变质作用。由于这个原因，这些序列到目前为止被称为巴拉格尼型蛇。Pineto地块由堆积侵入序列组成，该侵入序列由层状的橄榄岩、纯橄榄岩、辉长岩和斜长岩组成，并被玄武岩岩墙横切。堆晶岩和岩墙的化学成分显示出大洋拉斑玄武岩的相似性。特别是，Pineto地块玄武岩岩墙的稀土元素模式类似的N-MORB轻微轻稀土/重稀土贫化，也证明了低的CeN/YbN（0.9-1.2）的比例。内比奥蛇绿岩序列由枕状和块状熔岩流玄武岩组成，其上覆盖着硅质岩、Calpionella石灰岩和白垩纪硅质岩地层。内比奥玄武岩的化学成分与海底玄武岩相似。它们的特征是轻稀土相对于重稀土富集，如CeN/YbN（1.2-1.9）比值所证明的。它们的稀土配分模式与T-MORB相似。地球化学数据表明，Pineto Massif蛇绿岩与Balagne推覆体T-MOR玄武岩不同，这表明Pineto Massif蛇绿岩与Balagne推覆体之间的任何相关性都应该被排除。相比之下，他们强调密切的相似性之间的Pineto地块和内Ligurides蛇从北方亚平宁山脉，这表明这两个蛇代表皮埃蒙特-利古里亚海洋岩石圈的片段位于一个内部的海洋位置，相对远离大陆边缘。相反，内比奥玄武岩显示出惊人的地球化学相似性的巴拉涅，进一步支持的假设，即巴拉涅和内比奥蛇绿岩可以代表在皮埃蒙特-利古里亚盆地海洋化的早期阶段产生的洋壳碎片。
The Pineto Massif and Nebbio ophiolitic sequences represent two main examples of Corsican ophiolites that, similarly to the well-known Balagne Nappe, have not undergone high pressure-low temperature alpine metamorphism. For this reason these sequences have been so far referred to the Balagne-type ophiolites. The Pineto Massif is composed of a cumulitic intrusive sequence consisting of layered troctolites, dunites, gabbros, and anorthosites cross cut by basaltic dykes. The chemical composition of both cumulates and dykes reveal an oceanic tholeiitic affinity. In particular, the Pineto Massif basaltic dykes have REE patterns similar to those of N-MORBs with slight LREE/HREE depletion, as also evidenced by low CeN/YbN (0.9-1.2) ratios. The Nebbio ophiolitic sequence consists of pillow and massive lava flow basalts capped by cherts, Calpionella limestones, and Cretaceous siliciclastic formations. Chemically, the Nebbio basalts are similar to ocean-floor basalts. They are characterized by LREE enrichment with respect to HREE, as evidenced by the CeN/YbN (1.2-1.9) ratios. Their REE patterns are similar to those shown by T-MORBs. Geochemical data show that the Pineto Massif ophiolites are different from the Balagne Nappe T-MOR basalts, suggesting that any correlation between the Pineto Massif ophiolites and the Balagne Nappe should be ruled out. By contrast, they highlight close analogies between the Pineto Massif and the Internal Ligurides ophiolites from the Northern Apennine, suggesting that both these ophiolites represent fragments of the Piedmont-Ligurian oceanic lithosphere located in an internal oceanic position, relatively far from the continental margins. Conversely, the Nebbio basalts show striking geochemical similarities to those of the Balagne, further supporting the hypothesis that both the Balagne and Nebbio ophiolites could represent fragments of oceanic crust generated in the early stages of the Piedmont-Ligurian basin oceanization.