COLLABORATIVE RESEARCH: Petrogenesis of the Laramie Anorthosite Complex

斜长岩的成因及伴生碱 岩石仍然是一个重要的问题。 为了确定我们对 拉勒米斜长岩杂岩是少数几个未变质的 近年来，斜长岩杂岩的研究已成为国内外学者关注的焦点。 演化的岩石：红山、西比尔和 马卢因牧场 我们已经发现了分化的证据， 在这些机构的可变污染，并在马卢因有 确定了一个额外的过程，在这个过程中， 辉长岩岩浆与分异岩浆混合。 我们 初步的Sr和Nd同位素数据表明， 洛杉矶是简单的耗尽的地幔驱动的熔融物，但这一切 即使是斜长岩也曾与地壳发生过相互作用 ℃下 此外，每个演化的岩体都具有独特的Sr和Nd 同位素特征表明，尽管它们的矿物 化学研究表明它们是通过类似的过程进化的， 独立进化，吸收地壳物质， 不同程度的 我们迄今为止的工作使我们能够确定几个重要的 目标：（1）研制出石油化工的新产品， 综合大楼内的验证过程，特别侧重于 斜长岩中的同位素和化学趋势 由过渡接触面上的围岩污染产生 斜长岩和二长岩之间，辉长岩上 它们的演化过程中几乎没有与乡村岩石的相互作用。 (2)我们必须确定分层和非分层的范围- 在现场，确定分层的原因，并评估是否 这些斜长岩中的任何一种或全部是作为底辟侵位的。 （三） 我们将确定氧逸度和二氧化硅的变化 活动与地壳污染有关。 (4)我们将 研究复合岩脉，以确定基性岩部分是否 与斜长岩单元的残余岩浆有关。(5)我们 将继续确定各单位的绝对年龄。 (6)最后，我们将尝试确定 形成复合体的岩浆

The origin of massif anorthosites and associated alkaline rocks remains an important problem. To date our studies of the Laramie Anorthosite Complex, one of the few unmetamorphosed massif anorthosite complexes in the world, have focussed on the evolved rocks: the monozosyenites of Red Mountain, Sybille, and Maloin Ranch. We have found evidence for differentiation and variable contamination in these bodies, and in the Maloin have identified an additional process in which less evolved biotite gabbro magma has mixed with differentiated magma. Our preliminary Sr and Nd isotopic data indicate that no units of the L.A.C. are simple depleted mantle-drived melts, but that all-- even the anorthosites--have interacted with the crust to some degree. Moreover, the evolved plutons each have unique Sr and Nd isotope characteristics indicating that, although their mineral chemistries suggests that they evolved by similar processes, they evolved independently and assimilated crustal materials to different degrees. Our work to date allows us to identify several important goals: (1) We must produce petrochemical models of the differen- tiation processes within the Complex, focussing in particular on the isotopic and chemical trends within the anorthosites that are produced by country rock contamination on transitional contacts between the anorthosite and monzosyenites, and on the gabbroic bodies that have evolved with little country rock interaction. (2) We must determine the extent of layered and unlayered anor- thosite, determine the cause of the layering, and assess whether any or all of these anorthosites was emplaced as a diapir. (3) We will determine whether changes in oxygen fugacity and silica activity are correlated to crustal contamination. (4) We will study composite dikes to determine whether the mafic portions are related to residual magmas from the anorthosite units. (5) We will continue to determine the absolute age of the various units. (6) Finally, we will attempt to determine the origin(s) of the magmas that produced the Complex.