Fe-Ti oxide chronometry: With application to granulite formation
Fe-Ti oxide chronometry: With application to granulite formation
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Fe-Ti 氧化物测年法：应用于麻粒岩形成
DOI：
10.1016/0016-7037(90)90245-g
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发表时间：
1990
影响因子：
5
通讯作者：
R. O’nions
中科院分区：
文献类型：
--
作者：
K. Burton;R. O’nions
斯里兰卡斜长角闪岩和麻粒岩相正片麻岩中的钛铁矿产生精确的U-Pb年龄。麻粒岩相岩石中共存的钛铁矿-磁铁矿表明温度条件为680±60° C，log CO2 =− 17.0±1.2。钛铁矿的U-Pb年龄为498.2± 3.3Ma，与共存硅酸盐矿物的Pb-Pb年龄501±5 Ma无明显区别，表明氧化物-硅酸盐平衡状态得以保存。与此相反，在邻近角闪岩相岩石中的铁钛氧化物显示温度为830±60° C，log δ O 2=− 12.7±0.8，记录的U-Pb年龄为1093.7±7.6 Ma和1095.4±4.2 Ma。这些年龄约600 Ma以上的共存硅酸盐相在同一样品中，或为氧化物和硅酸盐矿物在附近的紫苏花岗岩和有关的花岗岩前体的侵位时间或一些较早的变质情节。这些结果表明，从Fe-Ti氧化物估算的温度、CO_2和流体条件应极其谨慎地解释。
Ilmenites occurring in amphibolite and granulite-facies orthogneisses in Sri Lanka yield precise U-Pb ages. Coexisting ilmenite-magnetite in the granulite-facies rocks indicate temperature conditions of 680±60° C and log ƒO 2=− 17.0±1.2. The U-Pb age of 498.2±3.3 Ma obtained for ilmenite is indistinguishable from the Pb-Pb age of 501±5 Ma derived for coexisting silicate minerals, and suggests that oxide-silicate equilibration has been preserved. In contrast, Fe-Ti oxides in adjacent amphibolitefacies rocks indicate a temperature of 830±60° C and log ƒO 2=− 12.7±0.8 and record U-Pb ages of 1093.7±7.6 Ma and 1095.4±4.2 Ma. These ages are some 600 Ma older than those obtained for coexisting silicate phases in the same sample, or for both oxide and silicate minerals in the nearby charnockite and relate either to the time of emplacement of the granitic precursor or to some earlier metamorphic episode. These results suggest that temperature, ƒO 2 and fluid conditions estimated from Fe-Ti oxides should be interpreted with extreme caution.