In situ U‐Pb measurements on zircons of the Ries impact crater are presented for three samples from the quarry at Polsingen. The U‐Pb data of most zircons plot along a discordia line, leading to an upper intercept of Carboniferous age (331 ± 32 Ma [2σ]). Four zircons define a concordia age of 313.2 ± 4.4 Ma (2σ). This age most probably represents the age of a granite from the basement target rocks. From granular textured zircon grains (including baddeleyite and anatase/Fe‐rich phases, first identified in the Ries crater), most probably recrystallized after impact (13 analyses, 4 grains), a concordia age of 14.89 ± 0.34 Ma (2σ) and an error weighted mean ²⁰⁶Pb*/²³⁸U age of Ma 14.63 ± 0.43 (2σ) is derived. Including the youngest concordant ages of five porous textured zircon grains (24 spot analyses), a concordia age of 14.75 ± 0.22 Ma (2σ) and a mean ²⁰⁶Pb*/²³⁸U age of 14.71 ± 0.26 Ma (2σ) can be calculated. These results are consistent with previously published ⁴⁰Ar/³⁹Ar ages of impact glasses and feldspar. Our results demonstrate that even for relatively young impact craters, reliable U‐Pb ages can be obtained using in situ zircon dating by SIMS. Frequently the texture of impact shocked zircon grains is explained by decomposition at high temperatures and recrystallization to a granular texture. This is most probably the case for the observed granular zircon grains having baddeleyite/anatase/Fe‐rich phases. We also observe non‐baddeleyite/anatase/Fe‐rich phase bearing zircons. For these domains, reset to crater age is more frequently for high U,Th contents. We tentatively explain the higher susceptibility to impact resetting of high U,Th domains by enhanced Pb loss and mobilization due to higher diffusivity within former metamict domains that were impact metamorphosed more easily into porous as well as granular textures during decomposition and recrystallization, possibly supported by Pb loss during postimpact cooling and/or hydrothermal activity.

中文翻译：

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NördlingerRies陨石坑撞击融化后的锆石的U‐Pb年代

针对波辛根采石场的三个样本，对里斯撞击坑的锆石进行了原位U-Pb测量。大多数锆石的U-Pb数据沿着一条迪斯科球线绘制，导致石炭纪年龄（331±32 Ma [2σ]）的上截距。四个锆石定义的共生年龄为313.2±4.4 Ma（2σ）。这个年龄很可能代表了从地下目标岩石到花岗岩的年龄。从粒状带纹理的锆石晶粒（包括首先在Ries陨石坑中鉴定出的锆石和锐钛矿/富铁相）中，最有可能在撞击后重结晶（13个分析，4个晶粒），协合年龄14.89±0.34 Ma（2σ）和误差加权平均值²⁰⁶ Pb * / ²³⁸得出U年龄为14.63±0.43（2σ）。可以算出五个多孔质锆石晶粒的最小最小一致年龄（24个点分析），一个协和年龄14.75±0.22 Ma（2σ）和²⁰⁶ Pb * / ²³⁸ U平均年龄14.71±0.26 Ma（2σ）。这些结果与先前发表的⁴⁰ Ar / ^39一致冲击玻璃和长石的年龄。我们的结果表明，即使对于相对年轻的撞击坑，也可以使用SIMS现场锆石测年获得可靠的U-Pb年龄。通常，通过在高温下分解并重结晶为颗粒状纹理来解释冲击冲击锆石晶粒的结构。对于观察到的具有锆石/锐钛矿/富铁相的粒状锆石，最可能是这种情况。我们还观察到了含非铅锌矿/锐钛矿/富铁相锆石。对于这些域，较高的U，Th含量更经常重置为火山口年龄。我们试探性地解释高U影响重新设定的敏感性，