Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2021-04-16 , DOI: 10.1016/j.gca.2021.04.008 Timmons M. Erickson , Christopher L. Kirkland , Fred Jourdan , Martin Schmieder , Michael I.H. Hartnady , Morgan A. Cox , Nicholas E. Timms
The Haughton Dome located on Devon Island, in the Canadian Archipelago represents a well-preserved, moderate-sized, complex impact crater. Previous age constraints for the 24 km-diameter impact structure have ranged from ca. 21 Ma to ca. 39 Ma. Herein, we present a coordinated microstructural and in situ U-Pb study of zircon and monazite coupled with 40Ar/39Ar laser step heating of shock-melted K-feldspar clasts from shock metamorphosed gneissic fragments collected from the allochthonous impact breccia at Haughton. Moderately shocked zircon and monazite grains yield an age distribution consistent with an Archean protolith metamorphosed at ca. 1.9 Ga, whereas shock recrystallized zircon and monazite yield a lower intercept age of 31.8 ± 1.7 Ma (n = 48, MSWD = 0.58, P = 0.99). Four inverse isochron 40Ar/39Ar ages of shocked feldspar clasts yield a weighted mean age of 31.04 ± 0.37 Ma (MSWD = 0.98, P = 0.40), within uncertainty of the U-Pb lower concordia intercept. Ar diffusion modelling supports the interpretation of the impact age and helps resolve impact-driven age resetting. These results highlight the power of coupling multiple geochronologic techniques for determining impact ages, especially from targets with complex geologic histories. Furthermore, they resolve previous discrepancies in the age of the Haughton Dome and the interpretation of the post impact stratigraphy of the crater fill.
中文翻译:
利用40 Ar / 39 Ar和U-Pb地球年代学方法解析Haughton撞击结构的年龄
位于加拿大群岛德文郡岛上的霍顿巨蛋代表着保存完好的中等大小,复杂的撞击坑。对于24 km直径的冲击结构,以前的年龄限制范围大约为。约21 Ma至 39毫。在这里,我们提出了锆石和独居石结合40 Ar / 39的微观组织和原位U-Pb协调研究Ar激光分步加热来自赫顿(Haughton)外来撞击角砾岩的激增变质片麻岩碎片中的激熔的钾长石碎片。中度冲击的锆石和独居石晶粒产生的年龄分布与大约在2000年变质的太古宙原生质一致。1.9 Ga,而冲击重结晶的锆石和独居石的截距年龄较低,为31.8±1.7 Ma(n = 48,MSWD = 0.58,P = 0.99)。四个反向等时40 Ar / 39受到冲击的长石碎屑的Ar年龄产生的加权平均年龄为31.04±0.37 Ma(MSWD = 0.98,P = 0.40),处于U-Pb下共生体截距的不确定性范围内。Ar扩散建模支持对影响年龄的解释,并有助于解决由影响驱动的年龄重置。这些结果突出了结合多种地质年代学技术来确定影响年龄的力量,特别是来自具有复杂地质历史的目标的影响年龄。此外,他们解决了以前在霍顿巨蛋时代的差异以及对火山口填充物的撞击后地层的解释。