Petrography of the dike-gabbro transition at IODP Site 1256 (equatorial Pacific): The evolution of the granoblastic dikes
Petrography of the dike-gabbro transition at IODP Site 1256 (equatorial Pacific): The evolution of the granoblastic dikes
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DOI：
10.1029/2008gc001939
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发表时间：
2008-07-31
影响因子：
3.5
通讯作者：
Yamazaki, S.
中科院分区：
文献类型：
--
作者：
Koepke, J.;Christie, D. M.;Yamazaki, S.
大洋钻探计划（ODP）/综合大洋钻探计划（IODP）在1256号站点的三个航次（第206航次，第309和312航次）首次对快速扩展的洋壳进行了连续原位取样，这些洋壳来自喷出熔岩，穿过席状岩脉，向下进入最上部的辉长岩（科科斯板块;东太平洋隆起;赤道东太平洋）。辉长岩上方的岩脉的最低的类似于60米，通过变质叠印转化为“花岗质岩脉”，其特征在于在麻粒岩相条件下形成的两个辉石域。由双辉石温度计估计的平衡温度范围在930摄氏度和1050摄氏度之间，这意味着花岗变晶带内的条件适合于含水深熔作用，有可能产生奥长花岗岩成分的部分熔体。的花岗岩变晶叠印的井下演化表示的纹理，相组成，和计算的平衡温度的系统变化，符合热变质作用由更深的热源。热模拟表明，在花岗变晶岩脉下面有一个长期的热源，提供了数千年的热能。最有可能的这种来源是一个稳定的状态，高层次的轴向岩浆房（AMC）位于该席状岩墙部分的基础。我们解释的间隔花岗质岩脉的一部分，动态导电边界上覆的AMC。
The Ocean Drilling Program (ODP)/Integrated Ocean Drilling Program (IODP) three-leg campaign at Site 1256 (Leg 206, Expeditions 309 and 312) provides the first continuous in situ sampling of fast spread ocean crust from the extrusive lavas, through the sheeted dikes, and down into the uppermost gabbros (Cocos plate; East Pacific Rise; eastern equatorial Pacific). The lowest similar to 60 m of the dikes above the gabbros were transformed to "granoblastic dikes'' through a metamorphic overprint characterized by two-pyroxene domains formed under granulite-facies conditions. Equilibrium temperatures estimated by the two-pyroxene thermometer range between 930 degrees C and 1050 degrees C, implying that conditions within the granoblastic zone were appropriate for hydrous anatexis, with the potential to generate partial melts of trondhjemitic composition. The downhole evolution of the granoblastic overprint is expressed by systematic changes in texture, phase composition, and calculated equilibrium temperature, consistent with thermal metamorphism by a deeper heat source. Thermal modeling implies a long-lasting heat source located beneath the granoblastic dikes, providing thermal energy over several thousands of years. The most likely such source is a steady state, high-level axial magma chamber (AMC) located at the base of the sheeted dike section. We interpret the interval of granoblastic dikes as part of a dynamic conductive boundary overlying the AMC.