Young cumulate complex beneath Veniaminof caldera, Aleutian arc, dated by zircon in erupted plutonic blocks
Young cumulate complex beneath Veniaminof caldera, Aleutian arc, dated by zircon in erupted plutonic blocks
复制标题
阿留申弧韦尼亚米诺夫火山口下方的年轻堆积杂岩，通过喷发的深成岩块中的锆石测年
作者：
C. Bacon;T. Sisson;F. Mazdab
阿拉斯加半岛的维尼亚米诺夫火山提供了将第四纪火山岩与同时代侵入杂岩联系起来的机会。Veniaminof在过去的260 k.y.通过英安岩喷发拉斑玄武岩。辉长岩，闪长岩，晶洞花岗闪长岩块，喷出3700 14 C年B. P.在最近的破火山口形成喷发，是一个浅侵入复杂的堆积物糊状和隔离蒸汽饱和残留熔体的片段。用高分辨率离子探针（SHRIMP）对两个花岗闪长岩和一个闪长岩中的锆石进行了238 U- 230 Th等时线年龄测定，结果分别为17.6 ± 2.7ka、5 + 11/-10ka和10.2 ± 4.0ka（2σ）。两个辉长岩中稀疏锆石的238 U- 230 Th模式年龄分别为36 ± 8 ka和26 ± 7 ka。花岗闪长岩和闪长岩中的锆石是在晚期岩浆水溶液中结晶形成的。虽然历史上的火山爆发已弱爆炸斯特隆波喷泉和小熔岩喷出，年轻的年龄的深成块体，以及晚全新世英安岩浮石，是证据表明，侵入复杂的仍然活跃，并演变成岩浆可以分离在浅层次燃料爆炸性喷发。
Mount Veniaminof volcano, Alaska Peninsula, provides an opportunity to relate Quaternary volcanic rocks to a coeval intrusive complex. Veniaminof erupted tholeiitic basalt through dacite in the past ∼260 k.y. Gabbro, diorite, and miarolitic granodiorite blocks, ejected 3700 14 C yr B.P. in the most recent caldera-forming eruption, are fragments of a shallow intrusive complex of cumulate mush and segregated vapor-saturated residual melts. Sensitive high-resolution ion microprobe (SHRIMP) analyses define 238 U- 230 Th isochron ages of 17.6 ± 2.7 ka, 5 +11/–10 ka, and 10.2 ± 4.0 ka (2σ) for zircon in two granodiorites and a diorite, respectively. Sparse zircons from two gabbros give 238 U- 230 Th model ages of 36 ± 8 ka and 26 ± 7 ka. Zircons from granodiorite and diorite crystallized in the presence of late magmatic aqueous fluid. Although historic eruptions have been weakly explosive Strombolian fountaining and small lava effusions, the young ages of plutonic blocks, as well as late Holocene dacite pumice, are evidence that the intrusive complex remains active and that evolved magmas can segregate at shallow levels to fuel explosive eruptions.