Collaborative Research: The provenance of "Grenville" age detrital zircon in western North America and the Neoproterozoic to early Paleozoic evolution of southwestern Laurentia

合作研究：北美西部格伦维尔时代碎屑锆石的起源和劳伦蒂亚西南部新元古代至早古生代的演化。Lang Farmer，科罗拉多大学，EAR-1251851克里斯托弗·费多，田纳西大学，EAR-1251869 EAR-1251859 EAR-1251851田纳西大学克里斯托弗·费多(Christopher Fedo)-EAR-1251869 EAR-1251859 EAR-1251851田纳西大学克里斯托弗·费多(Christopher Fedo)-EAR-1251869 EAR-1251869然而，收集这些数据的能力超出了我们对使用U-Pb年龄谱解释大陆构造和古地理的局限性的理解。在这项研究中，PI感兴趣的是评估特定碎屑锆石年龄组在硅屑沉积序列中的年龄分布和相对峰高的变化在沉积物来源方面的意义。他们的方法是结合现场锆石U-Pb和Hf同位素分析，数据将使用激光烧蚀-多收集器ICPMS技术获得。PIS将以美国西南部和墨西哥北部的中元古代至寒武纪沉积序列为目标，这些岩石已被广泛用于U-Pb碎屑锆石研究，但几乎没有碎屑锆石Hf同位素数据。现有的U-Pb年龄谱表明，这些岩石中的碎屑锆石有很大一部分来自1.0Ga到1.3Ga(“格伦维尔”)的基底源。在这些沉积序列中，碎屑锆石在这个年龄范围内描述的宽度和相对峰高在时间和空间上都有很大的变化。许多样品以~1.1Ga碎屑锆石为主，仅根据其U-Pb年龄就表明这些锆石都来自相同的中元古代基底来源。然而，对“格伦维尔”碎屑状锆石的PIS先导Hf同位素研究表明，~1.1Ga颗粒的Hf(0)单位相差超过15epsilon，并揭示了这些锆石并不都具有相同的来源。这一事实不能仅从U-Pb年龄谱中识别出来。基于这一观察结果，建议结合U-Pb和Hf同位素数据来探索碎屑锆石年龄谱中“格伦维尔”峰特征的变化如何反映这些碎屑颗粒的最终基岩来源的变化。更好地了解中元古代碎屑锆石的基底来源，反过来可以用来完善北美前寒武纪至早古生代的构造和古地理演化模式。PIS将对阿巴拉契亚山脉中部和南部格伦维尔造山带内1.0Ga至1.3Ga火成岩、德克萨斯州拉诺隆起以及分布在美国西南部和墨西哥北部整个古元古代地壳的~1.1Ga火成岩中“格伦维尔”锆石潜在来源的U-Pb和Hf同位素组成进行广泛调查。他们将应用这些信息，以及对尚未获得此类数据的样品进行全岩ND同位素分析，以评估死亡谷地区和索诺拉中部(MX)卡博卡地区硅质碎屑沉积岩中“格伦维尔”碎屑锆石的来源。

Collaborative Research: The provenance of "Grenville" age detrital zircon in western North America and the Neoproterozoic to early Paleozoic evolution of southwestern LaurentiaR. Lang Farmer, University of Colorado, EAR-1251851Christopher Fedo, University of Tennessee, EAR-1251869ABSTRACTDetrital zircon U-Pb age determinations have become a primary tool in siliciclastic sedimentary provenance studies due in part to the advent of rapid, in situ methods of obtaining isotopic data from individual zircon grains. However, the ability to collect such data is outstripping our understanding of the limitations of using U-Pb age spectra in interpreting continental tectonics and paleogeography. In this study, PIs are interested in assessing the significance, in terms of the sediment provenance, of variations in the age spread and relative peak height of specific detrital zircon age populations in siliciclastic sedimentary successions. Their approach is through combined in situ zircon U-Pb and Hf isotope analyses, data to be obtained using the laser ablation-multicollector ICPMS technique. PIs will target Mesoproterozoic to Cambrian sedimentary successions in the SW United States and northern Mexico, rocks that have been extensively used for U-Pb detrital zircon studies, but for which there is little detrital zircon Hf isotope data. Existing U-Pb age spectra reveal that a significant fraction of the detrital zircons in these rocks were derived from 1.0 Ga to 1.3 Ga ("Grenville") basement sources. The width and relative peak heights described by detrital zircon in this age range vary considerably both temporally and spatially within these sedimentary successions. Many samples are dominated by ~1.1 Ga detrital zircon, which on the basis of their U-Pb ages alone implies that these zircon were all derived from the same Mesoproterozoic basement source. However, PIs pilot Hf isotopic studies of "Grenville" detrital zircon show that the ~1.1 Ga grains vary by over 15 epsilonHf(0) units and reveal that these zircons do not all share the same provenance. This fact is not recognizable from the U-Pb age spectra alone. Based on this observation, it is suggested that combined U-Pb and Hf isotopic data can be used to explore how changes in the characteristics of the "Grenville" peaks in detrital zircon age spectra reflect changes in the ultimate bedrock source of these detrital grains. A better understanding of the basement provenance for Mesoproterozoic detrital zircons can, in turn, be used terms to refine models for the Precambrian to early Paleozoic tectonic and paleogeographic evolution of North America. PIs will conduct a broad survey of the U-Pb and Hf isotopic compositions of potential sources of "Grenville" zircon amongst 1.0 Ga to 1.3 Ga igneous rocks within the Grenville Orogen in the central and southern Appalachians, in the Llano Uplift in Texas, and among the ~1.1 Ga igneous rocks distributed throughout Paleoproterozoic crust of the SW U.S. and northern Mexico. They will apply this information, along with whole-rock Nd isotopic analyses on samples for which such data not already available, to assess the provenance of "Grenville" detrital zircon in siliciclastic sedimentary rocks in the Death Valley region and in the Caborca area of central Sonora (MX).