Accretion and oxidation of a superfast-spread axial melt lens: TIMS and SIMS zircon analyses of the IODP Hole 1256D gabbros
Accretion and oxidation of a superfast-spread axial melt lens: TIMS and SIMS zircon analyses of the IODP Hole 1256D gabbros
复制标题
DOI：
10.1016/j.lithos.2019.105184
复制
发表时间：
2019-12-01
期刊：
影响因子：
3.5
通讯作者：
Schmitz, Mark
中科院分区：
文献类型：
--
作者：
Hayman, Nicholas W.;Rioux, Matthew;Schmitz, Mark
IODP孔1256D以高达220毫米/年的全速穿过从东太平洋隆起延伸出来的整个洋壳。本文利用同位素稀释-热电离质谱(ID-TIMS)和二次离子质谱仪(SIMS)研究了1256D井辉长岩中的锆石U-Pb值。三个辉长岩样品经Th校正的加权平均Pb-206/U-238 SIMS年龄分别为15.03±0.14 Ma、15.13±0.35 Ma和15.23±0.12 Ma。三个样品中第一个样品的ID-TIMS Th校正的加权平均Pb206/U-238值为15.191+/-0.040 Ma，为岩浆活动的时间提供了验证和精确化。U-Pb年龄与根据海洋磁异常预测的地壳年龄一致，表明辉长岩最有可能是在山脊轴线或附近侵入和结晶形成的。其中两个样品的锆石具有异常高的Th/U比值，可能反映了锆石结晶之前或结晶过程中U的氧化。轴向熔融透镜中晚期熔体的fo(2)升高可能与递进结晶、水热蚀变的席状岩脉和辉长岩的同化作用和/或来自海水的盐水对熔融透镜的污染有关。(C)2019爱思唯尔B.V.保留所有权利。
IODP Hole 1256D penetrates a complete section of upper oceanic crust spread from the East Pacific Rise at a full rate of up to 220 mm/yr. Here we present U-Pb zircon data from Hole 1256D gabbroic rocks using isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and secondary ion mass spectrometry (SIMS). Three gabbro samples yielded Th-corrected weighted mean Pb-206/U-238 SIMS dates of 15.03 +/- 0.14 Ma, 15.13 +/- 0.35 Ma, and 15.23 +/- 0.12 Ma. An ID-TIMS Th-corrected weighted mean Pb-206/U-238 date of 15.191 +/- 0.040 Ma from the first of the three samples provides verification and refinement of the timing of magmatism. The U-Pb dates agree with the predicted age of the crust based on marine magnetic anomalies, suggesting the gabbros most likely formed by intrusion and crystallization at or near the ridge axis. Zircons from two of the studied samples have anomalously high Th/U ratios, likely reflecting oxidation of U prior to or during zircon crystallization. The elevated fO(2) of late stage melts in the axial melt lens may be related to progressive crystallization, assimilation of hydrothermally altered sheeted dikes and gabbros, and/or contamination of the melt lens by seawater derived saline brines. (C) 2019 Elsevier B.V. All rights reserved.