Zircons from Syros, Cyclades, Greece—Recrystallization and Mobilization of Zircon During High-Pressure Metamorphism
Zircons from Syros, Cyclades, Greece—Recrystallization and Mobilization of Zircon During High-Pressure Metamorphism
复制标题
DOI：
10.1093/petrology/egg067
复制
发表时间：
2003-11
影响因子：
3.9
通讯作者：
F. Tomaschek;A. Kennedy;I. Villa;M. Lagos;C. Ballhaus
中科院分区：
文献类型：
--
作者：
F. Tomaschek;A. Kennedy;I. Villa;M. Lagos;C. Ballhaus
锆石研究高压/低温变质变质火成岩岩石从锡罗斯。这些岩石携带有几代锆石，它们通过溶解-再沉淀过程相互关联。第一代是原始锆石，显示出生长环带，三价阳离子含量相对较高，Th/U比值较高。另一端员是一个骨架锆石代可以忽略不计的三价阳离子含量和低Th/U比（0 - 1）。从结构上看，在这两者之间，有一系列锆石晶体，具有复杂的Y-HREE-Th相包裹体和流体包裹体，显示出不同的置换-重结晶过程。这两个端员产生不同的灵敏度高分辨率离子探针（SHRIMP）U-Pb年龄。变质辉长岩的原始世代年龄为80 2 16 Ma，变质斜长花岗岩脉的原始世代年龄为76 4 2 1 Ma。骨骼状、低Th/U锆石世代的年龄为52408 Ma。较老的晚白垩世锆石被解释为岩浆原岩在一小部分洋壳中的侵位。年轻，始新世，年龄，但是，日期的锆石重结晶事件，这可能与高溶解度和流动性的高场强元素在高压含水流体相一致。锆石与峰变质石榴石之间的共生关系以及同一样品的U-Pb年龄与白色云母Ar-Ar年龄的良好一致性支持始新世是锡罗斯高压变质作用的真实年龄的结论。
Zircons were studied from high-pressure/low-temperature metamorphosed meta-igneous lithologies from Syros. These rocks carry several zircon generations related to each other by dissolution---reprecipitation processes. One generation is pristine zircon that shows growth zoning, relatively elevated contents of trivalent cations and high Th/U ratios. The other end-member is a skeletal zircon generation with negligible trivalent cation contents and low Th/U ratios ( 0 1). Texturally between these two, there is a range of zircon crystals with complex inclusion populations of Y---HREE---Th phases and fluid inclusions, showing variable progress of replacement--recrystallization. Both end-members yield distinct sensitive high-resolution ion microprobe (SHRIMP) U---Pb ages. The pristine generation has an age of 80 2 1 6Ma from a metagabbro, and 76 4 2 1Ma from a meta-plagiogranite dyke. The skeletal, low-Th/U zircon generation yields an age of 52 4 0 8Ma. The older, Late Cretaceous, zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust. The younger, Eocene, age, however, dates a zircon recrystallization event, which possibly coincides with high solubility and mobility of high field strength elements in a high-pressure aqueous fluid phase. Intergrowth relations between zircon and peak-metamorphic garnet, and excellent agreement of the U---Pb ages with white mica Ar---Ar ages for the same samples support the conclusion that Eocene is the true age of high-pressure metamorphism on Syros.