Gabbroic rocks trapped in the upper mantle at the Mid-Atlantic Ridge
Gabbroic rocks trapped in the upper mantle at the Mid-Atlantic Ridge
复制标题
大西洋中脊上地幔中的辉长岩岩石
DOI：
--
复制
发表时间：
1997
期刊：
影响因子：
--
通讯作者：
G. Ceuleneer
中科院分区：
文献类型：
--
作者：
M. Cannat;F. Chatin;H. Whitechurch;G. Ceuleneer
在920号现场钻探的超镁铁岩被岩脉、岩脉岩和结构、矿物学和化学成分多样的辉长岩的浸渍透镜体侵入。这些岩石约占在920号现场采集的岩芯体积的4%。它们的范围从富镁单斜辉石和钙质斜长石的浸渍透镜体，到富铁单斜辉石和富钠斜长石的含锆岩。在矿物学和化学多样性方面，它们类似于在920号遗址（921-924号遗址）以北几十公里处形成大型露头的辉长岩，以及在735号遗址西南印度洋脊附近钻探的岩石。在920号现场发现的辉长岩的化学多样性反映在橄榄岩的结晶顺序上，最原始的岩石首先结晶，最分离的岩石最后结晶。辉长岩侵入体附近的超镁铁岩的化学改性范围从形成分米厚的纯橄榄岩屏幕的橄榄石Mg#和镍含量，单斜辉石钠含量，尖晶石Mg#和钛含量的隐变量。我们提出了一个模型，在该模型中，辉长岩在站点920回收结晶熔体，经历了不同程度的分化在根的岩石圈地幔下的中大西洋海岭。
The ultramafic rocks drilled at Site 920 are intruded by dikes, dikelets, and impregnation lenses of texturally, mineralogically, and chemically diverse gabbroic rocks. These rocks represent about 4% in volume of the core recovered at Site 920. They range from impregnation lenses with magnesium-rich clinopyroxene and calcic plagioclase, to zircon-bearing dikelets with iron-rich clinopyroxene and sodium-rich plagioclase. In terms of mineralogy and chemical diversity, they are similar to gabbroic rocks that form large outcrops a few tens of kilometers north of Site 920 (Sites 921-924) and to rocks drilled near the Southwest Indian Ridge at Site 735. The chemical diversity of gabbroic rocks recovered at Site 920 is reflected in their order of crystallization in the peridotites, the most primitive rocks crystallizing first, and the most fractionated ones, last. Chemical modifications in the ultramafic rocks near the gabbroic intrusions range from the formation of decimeter-thick dunite screens to cryptic variations in olivine Mg# and nickel content, in clinopyroxene sodium content, and in spinel Mg# and titanium content. We propose a model in which the gabbroic rocks recovered at Site 920 crystallized from melts that had undergone variable degrees of differentiation in a root of lithospheric mantle beneath the Mid-Atlantic Ridge.