Petrogenesis of picrites from the Caribbean Plateau and the North Atlantic magmatic province
Petrogenesis of picrites from the Caribbean Plateau and the North Atlantic magmatic province
复制标题
DOI：
10.1016/s0024-4937(99)00038-9
复制
发表时间：
1999-10
期刊：
影响因子：
3.5
通讯作者：
S. Révillon;N. Arndt;E. Hallot;A. Kerr;J. Tarney
中科院分区：
文献类型：
--
作者：
S. Révillon;N. Arndt;E. Hallot;A. Kerr;J. Tarney
我们研究了来自三个不同地区的苦橄岩的岩相学、矿物学和地球化学：库拉索岛是白垩纪海洋高原的一部分;冰岛是大西洋中脊的一个活跃热点;格陵兰岛海岸外的早第三纪火山边缘，它是在形成大西洋的裂谷过程中形成的。利用橄榄石斑晶成分及MgO与FeO、Al_2 O_3、Ni的关系，估算了各岩石的母液成分及橄榄石富集比例。来自库拉索岛的苦橄岩主要由具有12 wt.% MgO，并且它们含有高达55重量%斑晶形式的过量橄榄石。一小部分富含镁橄榄石的橄榄石颗粒是来自镁源的捕虏晶。来自冰岛的苦橄岩由镁含量稍低的液体形成，但也含有约12重量%的镁。在堆积组合中既含橄榄石又含斜长石。来自格陵兰岛火山边缘的苦橄岩是由一种明显更含镁的液体形成的，氧化镁。在其中一些岩石中，积累的橄榄石比例很小，在这些岩石中，整个岩石的成分大致相当于液体成分。三个地区的苦橄岩形成于不同的条件和不同的熔融过程。库拉索岛苦橄岩来自于相对古老和较厚的海洋岩石圈下中等深度的中等程度熔融形成的汇集液体。另一方面，冰岛苦橄岩是通过地幔的高级部分熔融形成的，这些地幔几乎上升到洋中扩张中心的地壳底部。一个不寻常的组合相对高浓度的不相容的微量元素和高MgO表明，格陵兰苦橄岩形成的相对较低程度的熔融在更深的地幔。
We studied the petrography, mineralogy and geochemistry of picrites from three different regions: the island of Curaçao which forms part of a Cretaceous oceanic plateau; Iceland, an active hot spot on the mid-Atlantic ridge; and the early Tertiary volcanic margin off the coast of Greenland, which formed during the rifting that created the Atlantic ocean. Using the compositions of olivine phenocrysts and relations between MgO and FeO, Al2O3and Ni, we estimated compositions of parental liquids and the proportion of accumulated olivine in each rock. Picrites from Curaçao formed mainly from a liquid with 12 wt.% MgO and they contain up to 55 wt.% excess olivine in the form of phenocrysts. A small proportion of more forsterite-rich olivine grains are xenocrysts from a more magnesian source. Picrites from Iceland formed from a slightly less magnesian liquid but one with also about 12 wt.% MgO and they contain both olivine and plagioclase in the accumulated assemblage. Picrites from the Greenland volcanic margin formed from a liquid that was distinctly more magnesian, with up to 20 wt.% MgO. In some of these rocks the proportion of accumulated olivine was minimal and in these the whole-rock composition is roughly equivalent to the liquid composition. The picrites from the three areas formed under different conditions and through contrasting melting processes. The Curaçao picrites derive from pooled liquids formed through moderate degrees of melting at moderate depths beneath a relatively old and thick oceanic lithosphere. Iceland picrites, on the other hand, formed through advanced fractional melting of mantle that ascended almost to the base of the crust at the mid-ocean spreading center. An unusual combination of relatively high concentrations of incompatible trace elements and high MgO indicates that the Greenland picrites formed by relatively low degrees of melting at greater depths in the mantle.