Field and Laboratory Study of Discordant Dunite in Alpine Periodotite Melt-Rock Interaction During Magma Transport in the Shallow Mantle

我们建议研究加州北部和俄勒冈州南部三一橄榄岩和约瑟芬橄榄岩中不协调纯橄榄岩的形成。对自然情况下围岩反应的程度和性质进行量化是至关重要的。如果围岩反应通常具有显著的影响，那么在地幔岩浆的产生中，这一过程可能与熔融和晶体分馏一样重要。我们建议通过测量精选的纯橄榄岩和寄主橄榄岩样品中辉石、橄榄石和尖晶石的主要和微量元素成分来验证我们的假设。我们将使用麻省理工学院和伍兹霍尔的电子和离子微探针分析单个晶体的薄片。利用单个矿物颗粒岩心的主量元素和微量元素数据来估算母体液体成分，以及求解这些元素的一系列质量平衡方程，应该能够定量地估计晶体分馏和围岩反应在不协调纯橄榄岩成因中的相对重要性。

We propose to investigate the formation of discordant dunite in the Trinity and Josephine peridotites, in northern California and southern Oregon. Quantification of the degree and nature of wall rock reaction in natural examples is crucial. If wall rock reaction commonly has a significant effect, then this process may be as important as melting and crystal fractionation in the production of magmas in the mantle. We propose to test our hypothesis by measuring major and trace element compositions of pyroxene, olivine and spinel in carefully selected samples of dunite and host peridotite. We will analyze individual crystals in thin section using the election and ion microprobes at MIT and Woods Hole. Use of major and trace element data on cores of individual mineral grains to estimate parental liquid compositions, and solution of a series of mass balance equations for these elements, should provide a quantitative estimate of the relative importance of crystal fractionation and wall rock reaction in the genesis of discordant dunite.