Melt Inclusions in Zircon (and other accessory minerals)

点击翻译按钮获取中文摘要

EAR-0001168Bodnar/SinhaZircon (ZrSiO4) is a common accessory mineral present in most granitoid rocks. Zircon crystals from granitoid rocks often contain crystallized melt inclusions trapped during crystal growth from a magma. The zircons typically range from 30 to 250 um and the melt inclusions range from 20 to 120 um. Preliminary major and trace element analyses suggest that the melt inclusions preserve magma chemistries and provide information not easily attainable by traditional bulk rock analyses. The chemistry of the melt inclusions will be used to assess chemical evolution of magmas from melting of source rocks (to produce parental magmas) to final crystallization of magmas. This information, in turn, will be used to infer magma histories and the chemical changes that a melt undergoes during crystallization in the earth's crust. During melting and crystallization, some elements have an affinity for the crystalline minerals that form, whereas other elements have an affinity for the melt phase. We will use the melt inclusion and co-existing zircon chemistries to provide new partitioning data for various trace elements which are commonly used to infer petrogenesis of grantitoid rocks. Preliminary results indicate that partitioning data obtained from melt inclusions in refractory minerals, acting as miniature natural autoclaves, may be superior to data obtained in during short-duration laboratory experiments. Preliminary major and trace element data suggests that melt inclusions in zircon preserve original melt compositions. However, these compositions often disagree with magma compositions inferred from bulk rock analyses. Reconciliation of this discrepancy will be a main focus of the proposed research.