Geochemistry of a long in-situ section of intrusive slow-spread oceanic lithosphere: Results from IODP Site U1309 (Atlantis Massif, 30°N Mid-Atlantic-Ridge)
Geochemistry of a long in-situ section of intrusive slow-spread oceanic lithosphere: Results from IODP Site U1309 (Atlantis Massif, 30°N Mid-Atlantic-Ridge)
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DOI：
10.1016/j.epsl.2008.12.034
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发表时间：
2009-03
影响因子：
5.3
通讯作者：
M. Godard;S. Awaji;H. Hansen;E. Hellebrand;D. Brunelli;K. Johnson;T. Yamasaki;J. Maeda;M. Abratis;D. Christie;Y. Kato;C. Mariet;M. Rosner
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文献类型：
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作者：
M. Godard;S. Awaji;H. Hansen;E. Hellebrand;D. Brunelli;K. Johnson;T. Yamasaki;J. Maeda;M. Abratis;D. Christie;Y. Kato;C. Mariet;M. Rosner
IODP站点U1309是在大西洋中脊(MAR)北纬30°的大洋核心杂岩Atlantis Massif钻探的。我们介绍了在该地区采集的228个代表不同岩性的样品的块状岩石地球化学研究(常量元素和微量元素)的结果。U1309D井96%以上为辉长岩。辉绿岩和玄武岩横切剖面上部，它们具有类似于3月30°N取样的玄武岩的亏损的MORB成分，在浅层发现了地幔的遗迹。地幔橄榄岩显示了广泛的熔岩-岩石相互作用的岩石学和地球化学证据。辉长岩包括：富橄榄橄榄岩(>；70%状态橄榄石)和高镁#(82-89)、高镍(高达2300ppm)和贫微量元素(Yb0.06-0.8ppm)的橄榄辉长岩和辉长岩(包括辉长岩)，镁#60-86，微量元素含量低(Yb 0.125-2.5ppm)；低镁#(<；50)、低镍(∼65ppm)和高微量元素含量(Yb高达26ppm)的氧化辉长岩和淡色岩墙。榴辉岩和辉长岩是最原始和最枯竭的大洋辉长岩之一。U1309点辉长岩的主要地球化学特征与普通母质MORB熔体之后的累积序列地层一致，尽管井下变化(缺乏系统的)表明辉长岩系列是由多次岩浆注入形成的。具体地说，富含橄榄石的闪长岩和辉长闪长岩的结构和地球化学变化表明存在化学作用(同化作用？)在母体熔体和侵入的岩石圈之间。U1309点辉长岩并不代表30°N火山岩的互补岩浆产物，尽管它们采集了相同的地幔来源。U1309点辉长岩的整体微量元素组成与原始的MORB熔体组成相似，表明该辉长岩段没有大规模的熔体搬运。如此大的岩浆序列的出现表明，高岩浆活动与亚特兰蒂斯地块的形成有关。我们的结果表明，几乎所有供给这个岩浆系统的熔体都被困在侵入的岩石圈中。
IODP Site U1309 was drilled at Atlantis Massif, an oceanic core complex, at 30°N on the Mid-Atlantic Ridge (MAR). We present the results of a bulk rock geochemical study (major and trace elements) carried out on 228 samples representative of the different lithologies sampled at this location. Over 96% of Hole U1309D is made up of gabbroic rocks. Diabases and basalts cross-cut the upper part of the section; they have depleted MORB compositions similar to basalts sampled at MAR 30°N. Relics of mantle were recovered at shallow depth. Mantle peridotites show petrographic and geochemical evidence of extensive melt–rock interactions. Gabbroic rocks comprise: olivine-rich troctolites (>70% modal olivine) and troctolites having high Mg# (82–89), high Ni (up to 2300 ppm) and depleted trace element compositions (Yb 0.06–0.8 ppm); olivine gabbros and gabbros (including gabbronorites) with Mg# of 60–86 and low trace element contents (Yb 0.125–2.5 ppm); and oxide gabbros and leucocratic dykes with low Mg# (<50), low Ni (∼65 ppm) and high trace element contents (Yb up to 26 ppm). Troctolites and gabbros are amongst the most primitive and depleted oceanic gabbroic rocks. The main geochemical characteristics of Site U1309 gabbroic rocks are consistent with a formation as a cumulate sequence after a common parental MORB melt, although (lack of systematic) downhole variations indicate that the gabbroic series were built by multiple magma injections. In detail, textural and geochemical variations in olivine-rich troctolites and gabbronorites suggest chemical interaction (assimilation?) between the parental melt and the intruded lithosphere. Site U1309 gabbroic rocks do not represent the complementary magmatic product of 30°N volcanics, although they sample the same mantle source. The bulk trace element composition of Site U1309 gabbroic rocks is similar to primitive MORB melt compositions; this implies that there was no large scale removal of melts from this gabbro section. The occurrence of such a large magmatic sequence implies that a high magmatic activity is associated with the formation of Atlantis Massif. Our results suggest that almost all melts feeding this magmatic system stays trapped into the intruded lithosphere.