Collaborative Research: Petrologic and Geochemical Studies of a Layered Peridotite, Horoman, Japan: Implications for Melt Segregation and Migration in Arc-Related...

8 × 10 Km的Horoman橄榄岩（日本北海道）是一层状上地幔橄榄岩，包含熔体分离、迁移和反应过程的记录，产生了相当大的地球化学非均质性。在与日本同事的合作下，F. Frey （MIT）、研究生E. Takazawa （MIT）和N. Shimizu （WHOI）正在确定霍罗曼岩石及其组成斜辉石的地球化学特征。这些数据表明：(a)主要的岩石类型斜长石斜辉橄榄岩是洋中脊玄武岩的合适烃源岩；(b)相对缺乏CaO和Al2O3的无斜长石斜辉橄榄岩和斜长石斜辉橄榄岩与不相容的富元素熔体发生反应。这种不相容元素的富集，表现为高轻稀土/重稀土丰度比，通常被称为“地幔交代”。通过对熔体-橄榄岩反应的空间范围的三维研究（这是研究地幔捕虏体无法达到的目标），确定了这一过程的机理和规模。这项研究的结果将确定在弧和海洋构造背景下形成非均质上地幔的事件和过程序列。

9406914 Shimizu The 8 x 10 Km Horoman Peridotite (Hokkaido, Japan) is a layered upper mantle peridotite that contains a record of melt segregation, migration and reaction processes that have created considerable geochemical heterogeneity. In a collaborative effort with Japanese colleagues, F. Frey (MIT), graduate student E. Takazawa (MIT) and N. Shimizu (WHOI) are determining the geochemical characteristics of Horoman rocks and their constituent clinopyroxene. These data have been used to establish that: (a) the main rock type, plagioclase lherzolite, is a suitable source rock for mid-ocean ridge basalts but that (b) the plagioclase-free lherzolites and harzburgites which are relatively depleted in CaO and Al2O3 have reacted with an incompatible element-rich melt. This enrichment of incompatible elements, expressed by high light REE/heavy REE abundance ratios, is commonly known as "mantle metasomatism". By studying the spatial extent of the melt- peridotite reaction in three dimensions (an objective that cannot be attained by studying mantle xenoliths), the mechanism and scale of this process is being determined. The results of this study will identify the sequences of events and processes that create heterogeneous upper mantle in an arc and oceanic tectonic settings.