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“Grenville”时代碎屑锆石物源与LaurentiaR西南部新元古代至早古生代演化碎屑锆石U-Pb年龄测定已经成为研究硅质碎屑沉积物源的主要工具，部分原因是由于从单个锆石颗粒中获得同位素数据的快速原位方法的出现。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感兴趣的是评估在沉积物源方面，特定碎屑锆石年龄群的年龄分布和相对峰高变化的意义。他们的方法是通过结合原位锆石U-Pb和Hf同位素分析，使用激光烧蚀-多收集器ICPMS技术获得数据。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，但碎屑锆石Hf同位素数据很少。现有的U-Pb年龄谱显示，这些岩石中的碎屑锆石有相当一部分来自1.0 Ga ~ 1.3 Ga（“Grenville”）基底源。该年龄范围内的碎屑锆石所描述的宽度和相对峰高在不同的沉积序列中具有较大的时空差异。许多样品以~1.1 Ga的碎屑锆石为主，单从它们的U-Pb年龄推断，这些锆石均来自同一中元古代基底源。然而，PIs对“Grenville”碎屑锆石的Hf同位素试验研究表明，~1.1 Ga颗粒相差超过15个epsilonHf(0)单位，表明这些锆石并非都具有相同的物源。这一事实不能仅从U-Pb年龄谱中识别出来。在此基础上，建议利用U-Pb和Hf同位素组合数据来探讨碎屑锆石年龄谱中“Grenville”峰特征的变化如何反映这些碎屑颗粒最终基岩源的变化。更好地了解中元古代碎屑锆石的基底物源，可以用来完善北美前寒武纪到早古生代构造和古地理演化的模型。PIs将在阿巴拉契亚山脉中南部的Grenville造山带、德克萨斯州的Llano隆起的1.0 Ga至1.3 Ga火成岩中，以及分布在美国西南部和墨西哥北部古元古代地壳的~1.1 Ga火成岩中，对“Grenville”锆石的潜在来源进行U-Pb和Hf同位素组成的广泛调查。他们将利用这些信息，连同对尚未获得此类数据的样品进行的全岩Nd同位素分析，来评估死亡谷地区和索诺拉州中部卡博卡地区的硅质沉积岩中的“Grenville”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).