Accessory mineral U-Th-Pb ages and Ar-40/Ar-39 eruption chronology, and their bearing on rhyolitic magma evolution in the Pleistocene Coso volcanic field, California

作者：Simon Justin I^*; Vazquez Jorge A; Renne Paul R; Schmitt Axel K; Bacon Charles R; Reid Mary R

来源：Contributions to Mineralogy and Petrology, 2009, 158(4): 421-446.

DOI：10.1007/s00410-009-0390-9

• Coso volcanic field
• Magma time scales
• Rhyolite
• Ar/Ar dating
• U-Th-Pb dating
• Zircon and allanite

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 similar to 85 ka rhyolites yielded ages between similar to 100 and 200 Ma, requiring that generation of at least some rhyolites involves material from Mesozoic basement. Similar zircon xenocrysts are found in an similar to 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.

• 出版日期2009-10