Intershield geochemical differences among Hawaiian volcanoes: implications for source compositions, melting process and magma ascent paths
Intershield geochemical differences among Hawaiian volcanoes: implications for source compositions, melting process and magma ascent paths
复制标题
夏威夷火山之间的地盾间地球化学差异：对源成分、熔化过程和岩浆上升路径的影响
DOI：
10.1098/rsta.1993.0009
复制
发表时间：
1993
期刊：
影响因子：
--
通讯作者：
J. M. Rhodes
中科院分区：
文献类型：
--
作者：
F. Frey;J. M. Rhodes
随着夏威夷火山的发展，其熔岩的Sr，Nd和Pb的成分和同位素比值发生了系统的变化。这些趋势提供了重要的限制，了解羽有关的火山活动作为一个火山迁移远离热点。夏威夷地盾之间也存在着地球化学差异。特别是，来自相邻地盾的熔岩，如夏威夷的基拉韦厄和莫纳罗亚山，以及夏威夷的库劳和怀托，在一些主要和不相容元素的丰度和Sr，Nd和Pb的同位素比值方面有显着差异。一些不相容元素丰度比，如Zr/Nb和Sr/Nb，与Sr和Nd同位素比值的地盾间差异相关，但这些同位素比值与主元素组成的地盾间差异，甚至母/子元素丰度比，如Rb/Sr和Sm/Nd，都不相关。此外，在基拉韦厄和莫纳罗亚山，地盾间的差异显然持续了相对较长的时间，可能有100 ka。这些地盾间的地球化学差异为羽状火山作用提供了重要的制约因素。具体而言，（一）每座火山必须有不同的岩浆上升路径，从熔体分离的区域;（二）25-50公里的距离相邻，但地球化学不同，盾要求源变化在一个类似的规模，并熔体生产区域同样受到限制。熔岩成分和放射性同位素比值之间的相关性的缺乏提供了证据的熔融过程中的显着差异，如每个盾形成不同的平均熔融程度与熔体偏析在不同的平均压力。两种类型的模式是一致的屏蔽间地球化学差异：（i）一个相对较大的半径，约。40公里，羽导管与系统的空间分布的地球化学不均匀性;或（ii）一个小半径，小于20公里，羽导管组成的地球化学不同的底辟。由于垂直范围有限的相对较小半径的底辟太小，无法形成大型夏威夷地盾，因此一种可能的替代方案是含有孤波的连续管道，该管道输送地球化学上不同的物质包。
As Hawaiian volcanoes develop, their lavas systematically change in composition and isotopic ratios of Sr, Nd and Pb. These trends provide important constraints for understanding plume-related volcanism as a volcano migrates away from the hotspot. There are also geochemical differences between Hawaiian shields. In particular, lavas from adjacent shields such as Kilauea and Mauna Loa on Hawaii and Koolau and Waianae on Oahu have significant differences in abundances of some major and incompatible elements and isotopic ratios of Sr, Nd and Pb. Some incompatible element abundance ratios, such as Zr/Nb and Sr/Nb, are correlated with intershield differences in Sr and Nd isotope ratios, but these isotopic ratios are not correlated with intershield differences in major element composition, or even parent/daughter abundance ratios such as Rb/Sr and Sm/Nd. Moreover, at Kilauea and Mauna Loa the intershield differences have apparently persisted for a relatively long time, perhaps 100 ka. These intershield geochemical differences provide important constraints on plume volcanism. Specifically, (i) each volcano must have distinct magma ascent paths from the region of melt segregation; (ii) the 25-50 km distance between adjacent, but geochemically distinct, shields requires that the sources vary on a similar scale, and that the melt production region is similarly restricted. The absence of correlations between lava compositions and radiogenic isotope ratios provides evidence for significant differences in melting process such as each shield forming by a different mean extent of melting with melt segregation at different mean pressures. Two types of models are consistent with the intershield geochemical differences: (i) a relatively large radius, ca. 40 km, plume conduit with a systematic spatial distribution of geochemical heterogeneities; or (ii) a small radius, less than 20 km, plume conduit composed of geochemically distinct diapirs. Because relatively small radius diapirs of limited vertical extent are too small to create the large Hawaiian shields, a possible alternative is a continuous conduit containing solitary waves which transport geochemically distinct packets of material.