美国犹他州州立大学Dennis L. Newell小组报道了通过阿拉斯加德纳里断层岩石圈尺度的地幔-地表挥发性通量。该项研究成果发表在2023年4月13日出版的《地质学》上。

研究显示，位于2002年7.9级德纳里断层，地震破裂以西的主链上的温泉的³He / ⁴He 高达2.4 R_C / R_A (空气校正³He / ⁴He相对于空气的比率)，表明地幔He含量约为 30%。相应的δ¹³C值为-9.1‰到-7.8‰(相当于Vienna Peedee箭石)，表明这些西部泉的二氧化碳部分来自地幔。在2002年底破裂的东端，Totschunda断层泉有0.65-0.99 R_C / R_A (约 8%- 12%的地幔He)的³He / ⁴He，和来自碳酸盐的δ¹³C值(约 0‰)。

结果证实德纳里断层系统具有利用地幔挥发物的岩石圈尺度的特征。沿着2002年断裂的泉水产生了类似空气的³He / ⁴He，其比值为1 R / R_A和 δ¹³C值为-9.2‰ 到-3.4‰，被解释为没有地幔作用影响，且代表了通过页岩、碳酸盐的浅层地下水循环。

平行与断裂带的逆冲展曲具有类似空气的³He / ⁴He，而沿走向的高角度正常展曲产生了1.3 R_C / R_A 的³He / ⁴He(地幔He含量约为16%)，这意味着沿着断裂带的流动路径在断层带的上部10km处被中断。因为德纳里断层是一个岩石圈规模的，横贯北美和独立运动的阿拉斯加南部的构造，研究人员认为它具有转换边界的特征。研究结果与相似构造环境下氦同位素值的相似性表明，在没有岩浆作用影响的情况下，通过大陆走滑断层的地幔流体流量最大。

据研究人员介绍，沿德纳里断层系统（美国阿拉斯加州）400km区段的12个泉的氦和碳同位素数据，揭示了这一神秘结构的地幔-地表联系。

附：英文原文

Title: Roadblocks and speed limits: Mantle-to-surface volatile flux through the lithospheric-scale Denali fault, Alaska

Author: Dennis L. Newell, Jeff A. Benowitz, Sean P. Regan, Coleman D. Hiett

Issue&Volume: 2023-04-13

Abstract: Helium and carbon isotopic data from 12 springs along a ～400 km segment of the Denali fault system (Alaska, USA), inform mantle-to-surface connections of this enigmatic structure. Warm springs on the main strand, west of the 2002 M7.9 Denali fault earthquake rupture, have ³He / ⁴He as high as 2.4 R_C / R_A (air-corrected ³He / ⁴He relative to air ratio) indicating ～30% mantle He. Corresponding δ¹³C values are -9.1‰ to -7.8‰ (relative to Vienna Peedee belemnite), suggesting that the CO₂ at these western springs is partially mantle derived. At the eastern end of the 2002 rupture, Totschunda fault springs have ³He / ⁴He of 0.650.99 R_C / R_A (～8%-12% mantle He), with δ¹³C values (～0‰) from carbonates. Results confirm the Denali fault system is a lithospheric-scale feature tapping mantle volatiles. Springs along the 2002 rupture yield air-like ³He / ⁴He of 1 R / R_A and δ¹³C values from -9.2‰ to -3.4‰, interpreted as representing shallow groundwater circulation through shales and carbonates without mantle contributions. A thrust splay parallel to the rupture zone has air-like ³He / ⁴He, whereas an along-strike high-angle normal splay yields ³He / ⁴He of 1.3 R_C / R_A (～16% mantle He), implying that flow paths along the ruptured strand are disrupted in the upper 10 km of the fault zone. Because the Denali fault is a lithospheric-scale, transcurrent structure separating North America from independently moving southern Alaska, we suggest that it has characteristics of a transform boundary. The similarity of our results to helium isotope values at analogous tectonic settings suggest that without magmatism influence, there is a maximum mantle fluid flux through continental strike-slip faults.

DOI: 10.1130/G51068.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G51068.1/622204/Roadblocks-and-speed-limits-Mantle-to-surface