Fission-track Analysis of Detrital Zircon
Fission-track Analysis of Detrital Zircon
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DOI：
10.2138/rmg.2005.58.8
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发表时间：
2005
影响因子：
--
通讯作者：
M. Bernet;J. Garver
中科院分区：
文献类型：
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作者：
M. Bernet;J. Garver
锆石已成为研究沉积物物源和造山带折返历史的重要矿物之一。之所以如此实用，是因为锆石在许多火成岩、变质岩和沉积岩中很常见，它耐风化和磨蚀，并且可以用具有合理高浓度铀和钍的各种同位素方法进行测年（图1）。用于测定碎屑锆石年代的技术包括U/Pb和（U-Th）/He年代测定，但在本章中，我们只关注裂变径迹（FT）分析。图1.一套碎屑锆石，显示了碎屑样品中遇到的锆石形状和颜色的整个光谱。这个特殊的样品是来自俄罗斯堪察加北方始新世Ukelayet复理石的一个砂岩样品中的一套锆石。有几个端元值得注意（见讨论文本）：非常圆的颗粒可能是多环的;无色，几乎没有损坏和/或低稀土元素;无色和自形;红色系列的颗粒;黄色系列的颗粒。FT分析可以确定单个锆石颗粒的年龄，这些颗粒的冷却年龄可能在几十万年到十亿年或更长时间之间。可定年范围取决于单个锆石颗粒的铀含量和冷却历史。在自然系统中，锆石裂变径迹的有效退火温度约为240 °C ± 30 °C（Hurford 1986;布兰登等人1998;伯内特等人2002）。因此，大多数碎屑锆石在沉积后在典型的沉积盆地中相当耐受热退火，而其他低温热计时器在沉积盆地中常见的较低温度下退火（即，氦定年和磷灰石FT），因此更容易损害物源信息（图2）。因此，碎屑锆石裂变径迹（DZFT）分析的优势在于，该方法提供了源岩的稳定冷却年龄。
Zircon has become one of the most important minerals for studying sediment provenance and the exhumation history of orogenic belts. The reason for this utility is that zircon is common in many igneous, metamorphic, and sedimentary rocks, it is resistant to weathering and abrasion, and it can be dated with various isotopic methods having reasonable high concentrations of uranium and thorium (Fig. 1⇓). Techniques used to date detrital zircon include U/Pb and (U-Th)/He dating, but in this chapter we focus exclusively on fission-track (FT) analysis. Figure 1. Suite of detrital zircon showing the whole spectrum of zircon shapes and colors that encountered in detrital samples. This particular samples is a suite of zircon from a single sandstone sample of the Eocene Ukelayet Flysch, Northern Kamchatka, Russia. Several end members are worth noting (see text for discussion): Very well-rounded grains are likely to be polycyclic; Colorless with little damage and/or low REE; Colorless and euhedral; Grains of the red series; Grains of the yellow series. FT analysis allows age determination of single zircon grains that may have cooling ages between several hundred thousand to a billion years or more. The datable range depends on individual uranium content and cooling history of a zircon grain. Fission tracks in zircon have an effective annealing temperature of ~240 °C ± 30 °C in natural systems (Hurford 1986; Brandon et al. 1998; Bernet et al. 2002). Therefore most detrital zircon are fairly resistant to thermal annealing in typical sedimentary basins after deposition, while the other low-temperature thermochronometers anneal at lower temperatures common in sedimentary basins (i.e., Helium dating and apatite FT) and therefore more readily have compromised provenance information (Fig. 2⇓). Consequently, the strength of detrital zircon fission-track (DZFT) analysis lies in the fact that this method provides robust cooling ages of source …