High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating
High-reliability zircon separation for hunting the oldest material on Earth: An automatic zircon separator with image-processing/microtweezers-manipulating system and double-step dating
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DOI：
10.1016/j.gsf.2017.04.010
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发表时间：
2018-07-01
影响因子：
8.9
通讯作者：
Maruyama, Shigenori
中科院分区：
文献类型：
--
作者：
Isozaki, Yukio;Yamamoto, Shinji;Maruyama, Shigenori
尽管最近通过 LA-ICPMS 对众多锆石进行放射性测年取得了进展，但矿物分离仍然是一个主要障碍，特别是在寻找地球上最古老的材料方面。为了将锆石分离的效率提高一个数量级，我们设计/开发了一种新机器 - 自动锆石分离器（AZS）。它专为在传统分离程序后从重矿物部分中自动拾取 100 毫米大小的锆石颗粒而设计。 AZS 以三种模式运行：(1) 进行图像处理，从铺在托盘上的所有重矿物中选择目标单个锆石颗粒，(2) 使用微型镊子自动捕获单个锆石颗粒，以及 (3) 将它们一一对齐地放置在接收托盘上。自动捕获的设计/创建是为了在无人值守的情况下连续几个小时进行矿物选择。该软件还可以通过记录数字照片图像、光学（颜色）指数和接收托盘上的坐标来注册每个分离的锆石颗粒以进行约会。我们开发了两种新的约会方法；即 (1) 通过 LA-ICPMS 直接对锆石进行测年，无需传统的树脂镶嵌/抛光，(2) 高速 U-Pb 测年，结合使用带有多离子计数检测器的新设备 (LA-MIC-ICPMS) 的传统样品制备程序。采用第一种方法，从矿物表面获得的 Pb-Pb 年龄在树脂镶嵌/抛光后与同一颗粒的内部进行交叉检查。采用第二种方法，测定一颗锆石颗粒所需的时间约为。 20 秒，并且可以以足够的精度（约 0.5%）实现每小时 > 150 粒的样品吞吐量。我们通过分析西澳大利亚的太古代 Jack Hills 砾岩以及地球上已知最古老的（> 4.3 Ga）锆石，测试了 AZS 的实际效率。初步结果是积极的；我们从大约 194 颗锆石中获得了超过 4.0 Ga 的锆石。检查了 3800 个颗粒，其中 9 个颗粒超过 4300 Ma，最古老的颗粒为 4371 +/- 7 Ma。 AZS 的分离系统与新方法相结合，保证了寻找旧锆石的更高产量。 (C) 2017，中国地质大学（北京）和北京大学。由 Elsevier B.V. 制作和主持
Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine - an automatic zircon separator (AZS). This is designed particularly for automatic pick-up of 100 mm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes: (1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray, (2) automatic capturing of the individual zircon grains with micro-tweezers, and (3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical (color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e. (1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing, (2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors (LA-MIC-ICPMS). With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of > 150 grains per hour can be achieved with sufficient precision (ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest (>4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 +/- 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons. (C) 2017, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.