藏南冈底斯岩基弧期

IF 2.1 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Xuxuan Ma , Snir Attia , Tarryn Cawood , Wenrong Cao , Zhiqin Xu , Haibing Li
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引用次数: 8

摘要

弧的特征随时间而变化,岩浆活动的数量和时空格局有显著的时间波动。然而,这种情节行为的驱动机制需要更多约束。本文结合藏南冈底斯断裂带新锆石U-Pb定年、Hf同位素及深成岩全岩地球化学资料,探讨冈底斯断裂带幕式弧活动的特征、潜在驱动因素及其构造意义。综合整理了冈底斯带火成岩、沟填层序沉积岩、弧前盆地和前陆盆地以及现代河流砂的锆石U-Pb年龄和Lu-Hf同位素分析结果表明:(1)冈底斯弧活动在晚白垩世至中始新世期间是幕式的,表现为两次岩浆爆发(约100-80和65-45 Ma)和一次岩浆间歇(约80-65 Ma);(2)两次岩浆爆发的εHf(t)值均为正(+5 ~ +15),表明岩浆源为幼年岩浆,主要来自枯竭地幔。相比之下,这两次岩浆爆发之间的岩浆平静可能是由拉萨地体南缘下的新特提斯板块的平坦俯冲引起的。这些爆发可能对冈底斯带的地壳增厚起到了很大的作用。古海拔和地壳厚度的地球化学指标表明,~100 ~ 80 Ma的耀斑发生在厚弧根的形成过程中,而~65 ~ 45 Ma的耀斑发生在较薄的地壳中,没有弧根。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Arc tempos of the Gangdese batholith, southern Tibet

Arc tempos of the Gangdese batholith, southern Tibet

The character of arcs varies over time with significant temporal fluctuations in the quantity and spatiotemporal patterns of magmatism. However, the driving mechanisms for this episodic behavior of arcs need more constraints. This paper analyzed the published data along with our new zircon U-Pb dating and Hf isotopic and whole-rock geochemical data of plutonic rocks in the Gangdese belt in southern Tibet to explore the features, potential drivers, and tectonic implications of episodic arc activity in the Gangdese arc. A comprehensive compilation of U-Pb ages and Lu-Hf isotopic analyses of zircon grains from igneous rocks in the Gangdese belt, sedimentary rocks in trench fill sequences, forearc basins and foreland basins, and sands from modern river reveals that: 1) Gangdese arc activity was episodic during Late Cretaceous to Middle Eocene, displaying two magmatic flare-ups (ca. 100–80 and 65–45 Ma) and one magmatic lull (ca. 80–65 Ma), and 2) both flare-up magmas show relatively positive εHf(t) values (+5 ~ +15) indicative of juvenile sources suggesting these magmas are dominated by contributions from the depleted mantle. In contrast, the magmatic lull between these two magmatic flare-ups could be caused by flat subduction of the Neotethyan slab beneath the southern margin of the Lhasa terrane. These flare-ups likely contributed greatly to the crustal thickening of the Gangdese belt. Constraints from paleo-elevation and geochemical proxies for crustal thickness showed that the ~100–80 Ma flare-up was accompanied by the formation of a thick arc root while the ~65–45 Ma flare-up likely developed in a thinner crust without an arc root.

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来源期刊
Journal of Geodynamics
Journal of Geodynamics 地学-地球化学与地球物理
CiteScore
4.60
自引率
0.00%
发文量
21
审稿时长
6-12 weeks
期刊介绍: The Journal of Geodynamics is an international and interdisciplinary forum for the publication of results and discussions of solid earth research in geodetic, geophysical, geological and geochemical geodynamics, with special emphasis on the large scale processes involved.
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