The time of eclogite formation in the ultrahigh pressure rocks of the Sulu terrane: Constraints from Lu–Hf garnet geochronology
The time of eclogite formation in the ultrahigh pressure rocks of the Sulu terrane: Constraints from Lu–Hf garnet geochronology
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DOI：
10.1016/j.lithos.2011.04.004
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发表时间：
2011-07
期刊：
影响因子：
3.5
通讯作者：
A. Schmidt;K. Mezger;P. O'Brien
中科院分区：
文献类型：
--
作者：
A. Schmidt;K. Mezger;P. O'Brien
中国大陆科学钻探工程主孔榴辉岩的高精度Lu-Hf石榴石-单斜辉石年龄为216.9 Ma±21.2 Ma(4个样品)和220.5 Ma±22.7 Ma(1个样品)。榴辉岩中稀土元素的空间分布与原生生长带的保存一致，未受扩散的影响，这支持了榴辉岩中主要造岩矿物石榴石的Lu-Hf年龄的解释。尽管变质峰值温度在800-850℃左右，但原生稀土分带的保存表明，Lu-HF计时仪非常适合于测定高品位岩石中石榴石的形成反应。大别-苏鲁超高压榴辉岩的Lu-Hf年龄范围表明，石榴石不是连续生长的，而是幕式生长的，因此在北中国地块与扬子地块的碰撞过程中出现了断续的变质作用。一个榴辉岩样品的锆石U-Pb年龄和Hf同位素系统学表明，榴辉岩前驱体具有漫长的地质历史，始于2 Ma左右，最终形成于220 Ma左右的超高压变质作用。
Eclogites from the main borehole of the Chinese Continental Scientific Drilling project yield highly precise Lu–Hf garnet–clinopyroxene ages of 216.9 ± 1.2 Ma (four samples) and 220.5 ± 2.7 Ma (one sample). The spatial distribution of the rare earth elements in garnet is consistent with the preservation of primary growth zoning, unmodified by diffusion, which supports the interpretation that the Lu–Hf ages date the time of formation of garnet, the major rock forming mineral in the eclogites. The preservation of primary REE-zoning, despite peak metamorphic temperatures around 800–850 °C, indicates that the Lu–Hf chronometer is perfectly suitable to date garnet-forming reactions in high grade rocks. The range of Lu–Hf ages for eclogites in the Dabie–Sulu UHP terrane point to episodic rather than continuous growth of garnets and thus punctuated metamorphism during the collision of the North China Block and the Yangtze Block. The U–Pb ages and Hf-isotope systematics of zircon grains from one eclogite sample imply a protracted geologic history of the eclogite precursors that started around 2 Ga and culminated in the UHP metamorphism around 220 Ma.