A zircon petrochronologic view on granitoids and continental evolution
A zircon petrochronologic view on granitoids and continental evolution
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DOI：
10.1016/j.epsl.2019.116005
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发表时间：
2020-02-01
影响因子：
5.3
通讯作者：
Petrescu, L.
中科院分区：
文献类型：
--
作者：
Balica, C.;Ducea, M. N.;Petrescu, L.
花岗岩化学和测温的时间趋势限制了大陆岩浆活动、构造活动或地壳厚度的重大全球变化。我们的研究依赖于四种新碎屑岩（两种现代沉积物和两种太古代变沉积岩）的锆石地质年代学和微量元素地球化学，以及对已发表的单个锆石碎屑年代学和从 5587 个颗粒获取的微量化学数据的全球汇编。从 4.4 Ga 至今的所有年龄的锆石都存在于该档案中。锆石钛测温表明，超过 98% 的具有一致 U-Pb 年龄的颗粒是在超过 650 摄氏度的温度下形成的。这些锆石中的绝大多数是在 650-850 摄氏度范围内形成的，与中硅质岩浆的生长一致。在地球历史的前 1.2 Ga 中，岩浆温度随着时间的推移而增加，之后保持恒定，然后在最近的过去下降。绝大多数颗粒的 U/Th < 5 值与岩浆起源一致。 La/Yb、Sm/Yb 和 Eu/Eu* 值在整个地球历史中相对恒定，表明大多数花岗岩形成于或演化自位于 35-45 公里深度的岩浆库，存在角闪石、石榴石和有限的斜长石。如今，这种储层在一些较厚的岛弧和沿俯冲带的所有大陆弧下方的炎热深部地壳环境中很常见。现代俯冲以外的过程可能促成了早期地球花岗岩类的形成，但由角闪石的存在所决定的温度、深度和水的存在是相似的。这些结果还表明，在锆石档案覆盖的 4.4 Ga 时期，产生花岗岩的地区大陆地壳的厚度与今天的全球平均厚度相似。随着时间的推移，锆石的化学性质与超大陆的聚集之间没有相关性。 (C) 2019 Elsevier B.V. 保留所有权利。
Temporal trends in granitoid chemistry and thermometry constrain major global changes in magmatism, tectonism or crustal thickness in the continents. Our study relies on zircon geochronology and trace element geochemistry on four new detrital rocks (two modern sediments and two Archean metasedimentary rocks) and a global compilation of published single zircon detrital chronology and trace chemistry data acquired on 5587 individual grains. Zircons of all ages from 4.4 Ga to present exist in this archive. Ti-in-zircon thermometry indicates that more than 98% of the grains with concordant U-Pb ages formed at temperatures exceeding 650 degrees C. The great majority of these zircons formed in the 650-850 degrees C range consistent with growth in intermediate to silicic magmas. Magmatic temperatures increased over time for the first 1.2 Ga of Earth's history after which they stayed constant before decreasing during the more recent past. U/Th < 5 values in the overwhelming majority of grains are consistent with a magmatic origin. La/Yb, Sm/Yb and Eu/Eu* values are relatively constant throughout the history of the Earth suggesting that most granitoids formed at, or evolved from magmatic reservoirs located at depths of 35-45 km in the presence of amphibole, garnet and limited plagioclase. Such reservoirs are common today in hot deep crustal environments beneath some of the thicker island arcs and all continental arcs along subduction zones. Processes other than modern day style subduction may have contributed to the formation of granitoids in the early Earth but temperatures, depths and the presence of water arbitrated by the presence of amphibole were similar. These results also suggest that the thickness of continental crust in areas that produced granitoids was similar to today's global average throughout the 4.4 Ga time period covered by the zircon archive. There is no correlation between zircon chemistry over time and the assembly of supercontinents. (C) 2019 Elsevier B.V. All rights reserved.