Collaborative Research: Argon Retentivity and Closure Temperature in Micas and Amphiboles

EAR-0107054/0106987Foland/DahlPotassium-bearing云母和角闪石被广泛用于40Ar/39Ar年龄研究，以确定热年代学历史，并被认为具有反映温度的年龄，尽管实际的机制(S)和控制既没有很好的理解，也没有很好的记录。本研究将探讨影响慢冷地体中云母和角闪石的Ar保留率和40Ar/39Ar年龄的因素。将研究来自纽约阿迪朗达克低地的标本中的关系。这项研究将测试通常认为的对Ar损失的体积扩散控制，同时也寻求评估影响单个云母和角闪石晶体的Ar保留和年龄的替代机制和因素。这项研究的具体目标是澄清：(1)自然界中Ar损失的机制(S)和体积扩散控制对Ar保留和关闭的控制问题，并具体考察应力和流体(除温度外)的作用；(2)保留的晶体-化学依赖性；(3)微结构和其他因素的作用。这项研究将涉及对单个晶体的一系列现代微观分析技术，包括：40Ar/39Ar和Rb/Sr年代学，包括紫外线激光烧蚀Ar微分析；化学微分析；用于阐明微观结构的透射电子显微镜；X射线衍射测定晶体结构；以及氧和氢同位素分析。这项研究的目标是对这些矿物时代的下一步了解，因此，他们在解释、破译和提炼地壳历史方面的使用。

EAR-0107054/0106987Foland/DahlPotassium-bearing micas and amphiboles are widely used in 40Ar/39Ar age studies to determine thermochronologic histories and are recognized to have ages that reflect temperature, although the actual mechanism(s) and controls are neither well understood nor well documented. This research will investigate the factors governing Ar retention and 40Ar/39Ar ages of mica and amphibole in slowly-cooled terranes. Relationships in specimens from the Adirondack Lowlands of New York will be studied. The research will test the often-assumed volume diffusion control of argon loss, while also seeking to evaluate alternative mechanisms and factors governing argon retention and ages of individual mica and amphibole crystals. Specific objectives of the research are to clarify: (1) the mechanism(s) of argon loss in nature and the question of volume-diffusion control on argon retention and closure, with specific examination of the roles of stress and fluids (in addition to temperature); (2) the crystal-chemical dependence of retention; and (3) the roles of microstructures and other factors. The research will involve an array of modern microanalytical techniques on individual crystals, including: 40Ar/39Ar and Rb/Sr geochronology, featuring UV laser-ablation Ar microanalysis; chemical microanalysis; transmission electron microscopy for elucidation of microtextures; X-ray diffraction determination of crystal structures; and, analyses of O and H isotopes. This research targets the next level of understanding of these mineral ages and, thus, their use in interpreting, deciphering, and refining crustal histories.