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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >High-precision Ar-40/Ar-39 dating of Quaternary basalts from Auckland Volcanic Field, New Zealand, with implications for eruption rates and paleomagnetic correlations
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High-precision Ar-40/Ar-39 dating of Quaternary basalts from Auckland Volcanic Field, New Zealand, with implications for eruption rates and paleomagnetic correlations

机译：来自新西兰奥克兰火山田的第四纪玄武岩的高精度Ar-40 / Ar-39年代测定，对喷发率和古磁相关性有影响

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摘要

The Auckland Volcanic Field (AVF), which last erupted ca. 550 years ago, is a late Quaternary monogenetic basaltic volcanic field (ca. 500 km(2)) in the northern North Island of New Zealand. Prior to this study only 12 out of the 53 identified eruptive centres of the AVF had been reliably dated. Careful sample preparation and Ar-40/Ar-39 analysis has increased the number of well-dated centres in the AVF to 35. The high precision of the results is attributed to selection of fresh, non-vesicular, non-glassy samples from lava flow interiors. Sample selection was coupled with separation techniques that targeted only the groundmass of samples with <5% glass and with groundmass feldspars >10 mu m wide, coupled with ten-increment furnace step-heating of large quantities (up to 200 mg) of material. The overall AVF age data indicate an onset at 193.2 +/- 2.8 ka, an apparent six eruption flare-up from 30 to 34 ka, and a <= 10 kyr hiatus between the latest and second-to-latest eruptions. Such non-uniformity shows that averaging the number of eruptions over the life-span of the AVF to yield a mean eruption rate is overly simplistic. Together with large variations in eruption volumes, and the large sizes and unusual chemistry within the latest eruptions (Rangitoto 1 and Rangitoto 2), our results illuminate a complex episodic eruption history. In particular, the rate of volcanism in AVF has increased since 60 ka, suggesting that the field is still in its infancy. Multiple centres with unusual paleomagnetic inclination and declination orientations are confirmed to fit into a number of geomagnetic excursions, with five identified in the Mono Lake, two within the Laschamp, one within the post-Blake or Blake, and two possibly within the Hilina Pali. (C) 2017 Elsevier B.V. All rights reserved.
机译：上一次爆发的奥克兰火山场（AVF） 550年前是新西兰北部北岛的第四纪晚期单生玄武岩火山场（约500 km（2））。在这项研究之前，已确定53个已确定的AVF爆发中心中只有12个是可靠的。精心的样品制备和Ar-40 / Ar-39分析已将AVF中约会良好的中心数量增加到35个。结果的高精度归因于从熔岩中选择新鲜的，非囊泡，非玻璃状的样品内部流动。样品选择与分离技术相结合，分离技术仅针对玻璃含量小于5％的样品和宽长于10微米的磨碎的长石，并结合了十增量的炉子逐步加热大量（最高200 mg）的材料。整个AVF年龄数据表明，发作始于193.2 +/- 2.8 ka，从30 ka到34 ka出现了明显的六次爆发爆发，最近一次至第二次爆发之间的裂隙小于或等于10 kyr。这种不均匀性表明，平均AVF寿命内的喷发次数以产生平均喷发率过于简单。加上喷发量的巨大差异，以及最近喷发（Rangitoto 1和Rangitoto 2）中的大尺寸和不寻常的化学作用，我们的结果阐明了复杂的情节性喷发历史。特别是，自60 ka起，AVF中的火山活动速度有所提高，这表明该领域仍处于起步阶段。多个具有不同古地磁倾角和倾角方向的中心被证实适合许多地磁偏移，其中在莫诺湖中发现了五个，在拉尚（Laschamp）中发现了两个，在布雷克（Blake）或布雷克（Blake）之后发现了一个，在希利纳巴里（Hillina Pali）可能发现了两个。 （C）2017 Elsevier B.V.保留所有权利。

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