当前位置: X-MOL 学术Earth Planet. Sci. Lett. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
3He evidence for fluid transfer and continental hydration above a flat slab
Earth and Planetary Science Letters ( IF 5.3 ) Pub Date : 2020-12-28 , DOI: 10.1016/j.epsl.2020.116722
Coleman D. Hiett , Dennis L. Newell , Micah J. Jessup

The transfer of large volumes of fluid to the overriding lithosphere during flat-slab subduction should drastically alter the physical and chemical properties of continental margins. However, this process is poorly understood and without active magmatism, direct evidence for fluid transfer has remained elusive in modern systems. New helium isotope ratios (3He/4He) and gas species abundances in thermal springs above the Peruvian flat slab in South America demonstrate widespread transit of mantle-derived volatiles through thick (>45 km) continental crust. An unambiguous mantle signature is present in all 52 springs investigated over a 200,000 km2 region, with 3He/4He ratios ranging from 0.26 to 2.52 RC/RA (3He/4He ratio relative to the air ratio, RA, of 1.39×106, corrected for air-derived helium). In the absence of recent magmatism, the observed 3He/4He ratios are best explained by slab-derived fluids mobilizing helium from the subcontinental lithospheric mantle (SCLM). As slab- and mantle-derived volatiles migrate through the continental crust, 3He/4He ratios are reduced from SCLM values (6.1±2.1 RA) by ingrowth of radiogenic 4He and mixing with crustal fluids. The highest 3He/4He ratios in the flat slab region are observed above a probable tear in the Nazca Plate and along the Cordillera Blanca Detachment fault, implying that these features promote faster fluid transport through the crust. Our observations require a persistent flux of slab-derived fluids to move lithospheric-mantle-derived volatiles into and through the continental crust, providing evidence for active continental hydration in a modern flat-slab subduction system. Similar results from springs located in the backarc region to the south of the flat slab indicate that the mantle lithosphere below the northern Altiplano is experiencing dehydration and/or partial melting resulting from a mid-Cenozoic episode of flat-slab subduction.



中文翻译:

3他证明平板上有流体转移和大陆水化

平板俯冲过程中大量流体向上覆岩石圈的转移将极大地改变大陆边缘的物理和化学性质。但是,对该过程了解甚少,并且没有活跃的岩浆作用,在现代系统中,流体转移的直接证据仍然难以捉摸。在南美秘鲁平板上方的温泉中,新的氦同位素比(3 He / 4 He)和气体种类的丰度表明,地幔衍生的挥发物广泛地穿过厚(> 45 km)的大陆壳。在200,000 km 2的区域内调查的所有52个弹簧中均具有明确的地幔特征,其3 He / 4 He比率范围为0.26至2.52 RÇ / R3他/ 4赫相对比的空气比,R,的1.39×10-6,已针对源自空气的氦气进行了校正)。在没有最近的岩浆作用的情况下,观察到的3 He / 4 He比率最好用平板岩溶流体从次大陆岩石圈地幔(SCLM)运出氦来解释。随着板坯和地幔衍生的挥发物在大陆壳中迁移,SCLM值降低了3 He / 4 He的比率(6.1±2.1R A)通过向放射源4 He内生并与地壳流体混合。最高3 He / 4在纳斯卡板块和科迪勒拉布兰卡分离断层的可能撕裂上方观察到了平板区域的氦比率,这表明这些特征促进了流体更快地通过地壳。我们的观测结果需要板状流体的持续流动,才能将岩石圈地幔来源的挥发物运入并穿过大陆壳,从而为现代扁平板俯冲系统中的活跃大陆水化提供了证据。位于平板南部的后弧区域的弹簧的类似结果表明,北高原以下的地幔岩石圈正在经历脱水和/或部分融化,这是由于新生代中期平板俯冲引起的。

更新日期:2020-12-28
down
wechat
bug