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Determining the Depositional Age of Precambrian Clastic Sedimentary Rocks: Diagenetic Authigenic Xenotime Dating(PDF)

《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]

Issue:
2017年第06期
Page:
711-720
Research Field:
基础地质与矿产地质
Publishing date:

Info

Title:
Determining the Depositional Age of Precambrian Clastic Sedimentary Rocks: Diagenetic Authigenic Xenotime Dating
Author(s):
ZHANG Yan-bin LI Qiu-li
1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 2. College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Keywords:
Precambrian authigenic xenotime in-situ micro U-Pb dating clastic sedimentary rock ion probe depositional age Changcheng System
PACS:
P597
DOI:
-
Abstract:
Sedimentary rocks are important material to investigate paleoenvironment, paleogeography and tectonic evolution history. Biostratigraphy and volcanic rocks dating are two most commonly used and accurate methods to limit the depositional age. However, it is rather difficult to constrain the depositional age of Precambrian sedimentary rocks without volcanic interlayers, as the stratigraphical paleontology methods are hardly applicable for these rocks. Consequently, in-situ U-Th-Pb dating on authigenic xenotime is a powerful tool to constrain the depositional age of such kinds of rocks. Shortly after burial in siliciclastic sediments, the authigenic xenotime grows within tens of meters of the sediment-water interface, where Y, REE and phosphate are supplied sufficiently. Therefore, the forming age of authigenic xenotime is close to that of the sedimentary rock. In most cases, the authigenic xenotime occurs as pyramidal to irregular overgrowths on detrital zircon grains, because the crystal structure of xenotime is the same as that of zircon. Due to the indistinguishable petrography of hydrothermal xenotime and diagenetic xenotime, the age of xenotime shows multiple interpretations in sedimentary rocks. Taking the xenotime from the Changcheng System as an example, the characteristics and discrimination of authigenic xenotime, and the methods to search, locate, analyze authigenic xenotime, as well as to process the data were summarized. The results show that the xenotime in coarse-grained sandstone of the lowermost Changzhougou Formation is hydrothermal origin, while the xenotime in medium-fine sandstone of the Chuanlinggou Formation is diagenetic origin; the oldest age of (1 716±3)Ma is interpreted as the minimum depositional age of the Changcheng System.

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Last Update: 2017-12-15