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首页> 外文期刊>Contributions to Mineralogy and Petrology >Accessory mineral U–Th–Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California
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Accessory mineral U–Th–Pb ages and 40Ar/39Ar eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California

机译：辅助矿物U–Th–Pb年龄和 40 Ar / 39 Ar喷发年代，及其对加利福尼亚更新世科苏火山场流纹岩浆演化的影响

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摘要

We determined Ar/Ar eruption ages of eight extrusions from the Pleistocene Coso volcanic field, a long-lived series of small volume rhyolitic domes in eastern California. Combined with ion-microprobe dating of crystal ages of zircon and allanite from these lavas and from granophyre geothermal well cuttings, we were able to track the range of magma-production rates over the past 650 ka at Coso. In ≤230 ka rhyolites we find no evidence of protracted magma residence or recycled zircon (or allanite) from Pleistocene predecessors. A significant subset of zircon in the ~85 ka rhyolites yielded ages between ~100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an ~200 ka granophyre. The new age constraints imply that magma evolution at Coso can occur rapidly as demonstrated by significant changes in rhyolite composition over short time intervals (≤10’s to 100’s ka). In conjunction with radioisotopic age constraints from other young silicic volcanic fields, dating of Coso rhyolites highlights the fact that at least some (and often the more voluminous) rhyolites are produced relatively rapidly, but that many small-volume rhyolites likely represent separation from long-lived mushy magma bodies. Keywords Coso volcanic field - Magma time scales - Rhyolite - Ar/Ar dating - U–Th–Pb dating - Zircon and allanite Communicated by T.L. Grove.
机译：我们确定了来自更新世的Coso火山场的8次挤压的Ar / Ar喷发年龄，这是加利福尼亚东部的一个长寿命的小体积流纹岩穹顶系列。结合这些熔岩和花岗岩体地热井中切屑中锆石和褐铁矿晶体年龄的离子微探针测年，我们能够追踪到过去650 ka在Coso的岩浆产生速率的范围。在≤230ka的流纹岩中，我们没有证据表明更新世的前辈有长期的岩浆滞留或回收的锆石（或尿石）的迹象。 〜85 ka流纹岩中的大量锆石产生的年龄介于〜100和200 Ma之间，这要求至少生成某些流纹岩涉及中生代基底物质。在约200 ka的粒岩中发现了类似的锆石异晶。新的年龄限制意味着，在短时间内（≤10's至100'ka）流纹岩成分发生了显着变化，证明了Coso处的岩浆演化可以迅速发生。结合其他年轻硅质火山岩田的放射性同位素年龄限制，科索流纹岩的定年凸显了这样一个事实，即至少有一些（而且往往体积更大）流纹岩的生成相对较快，但是许多小体积流纹岩可能代表了与长流纹岩的分离。住着糊状的岩浆体关键词火山火山岩-岩浆时间尺度-流纹岩-Ar / Ar年代-U–Th–Pb年代-锆石和钙铝石树林。

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