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首页> 外文期刊>Quaternary geochronology >Cosmogenic ~3He exposure ages of basalt flows in the northwestern Payún Matru volcanic field, Mendoza Province, Argentina
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Cosmogenic ~3He exposure ages of basalt flows in the northwestern Payún Matru volcanic field, Mendoza Province, Argentina

机译：宇宙成因〜3He在阿根廷门多萨省西北PayúnMatru火山田中玄武岩流的暴露年龄

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摘要

The Payún Matru volcanic field encompasses more than 12,000 km~2 in the west-central Argentine province of Mendoza. The northwestern part of the field, called Los Volcanes, includes multiple basaltic lava flows and numerous cinder cones and scoria fields. We sampled primary lava flow features (tumuli, pahoehoe and aa flow surfaces) from two different basaltic lava flows and one fluvial strath for cosmogenic ~3He exposure age dating in the Los Volcanes area. Olivines from the sampled basalts have low concentrations of U and Th and a minimal radiogenic ~4He correction. We used the recently established R correction factor to correct our measured ~3He concentrations for magmatic ~3He and ~4He and radiogenic ~4He. Exposure ages for primary lava flow features covering a large area just east of where Route 40 crosses the Río Grande range from 41 to 43 ka with external uncertainties on the order of 7%. A recently published K→Ar age of 26 ± 5 ka was sampled within a few hundred meters of three of our cosmogenic exposure age samples and appears to be from the same basalt flow. Given the large uncertainties associated with dating young lava flows, the K/Ar age and our cosmogenic ages are in reasonable agreement; however, they do not overlap within uncertainties and suggest possible systematic discrepancies between the two methods of up to 20% in this instance. A sample from a bedrock strath carved by the Río Grande into basalt yielded a surface exposure age of 17 ± 1 ka. The toe of a much younger-looking aa flow about 5 km west of the Rt. 40 Río Grande bridge yielded two ages of 0 and 2 ka, and is presumed to be historical.
机译：在阿根廷中西部门多萨省，PayúnMatru火山场覆盖了超过12,000 km〜2。该油田的西北部被称为洛斯火山（Los Volcanes），包括多个玄武岩熔岩流以及众多的煤渣锥和火山灰田。我们在洛斯火山地区从两个不同的玄武岩熔岩流和一个河流层取样了主要的熔岩流特征（肿瘤，泥hoe和aa流动面），这些岩浆具有约3He的成因暴露年龄。采样玄武岩中的橄榄石的U和Th浓度低，放射源〜4He校正最小。我们使用最近建立的R校正因子来校正岩浆〜3He和〜4He和放射源〜4He的测得的〜3He浓度。主要熔岩流特征的暴露年龄覆盖了40号公路穿越格兰德河以东的大片区域，从41到43 ka，外部不确定性约为7％。最近发布的K→Ar年龄为26±5 ka，是在我们三个宇宙成因暴露年龄样本的几百米内采样的，似乎来自同一玄武岩流。鉴于与年轻熔岩流测年有关的巨大不确定性，K / Ar年龄和我们的宇宙成因年龄是合理的;但是，它们不会在不确定性范围内重叠，并且建议这两种方法之间的系统差异在这种情况下可能高达20％。由里奥格兰德（RíoGrande）雕刻成玄武岩的基岩地层样品的表面暴露年龄为17±1 ka。 Rt以西约5公里处，看上去年轻得多的脚趾流。 40RíoGrande桥产生了两个0和2 ka的年龄，并被认为是历史悠久的。

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