Helium accumulation in groundwater, III. Limits on helium transfer across the mantle-crust boundary beneath Australia and the magnitude of mantle degassing
Helium accumulation in groundwater, III. Limits on helium transfer across the mantle-crust boundary beneath Australia and the magnitude of mantle degassing
复制标题
地下水中氦气的积累，III。
DOI：
10.1016/0012-821x(87)90098-7
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发表时间：
1987
期刊：
影响因子：
--
通讯作者：
W. B. Clarke
中科院分区：
文献类型：
--
作者：
T. Torgersen;W. B. Clarke
大自流盆地(澳大利亚)的地下水以前被证明积累了地下水年龄<；50KYR的原地生产氦和地下水年龄>；100KYR[1，2]相当于整个地壳生产的外部氦通量。新的氦同位素测量表明，观测到的原位生成氦(3He/4He∼1.6×10−8)与地壳脱气氦通量(3He/4He∼6.6×10−8)在同位素上是不同的。此外，在各种陆相岩石类型中，地壳脱气氦同位素比值略高于整个地壳产率(3He/4He=3.5×10−8)和产率。这表明，在(相对)稳定和“自满”的澳大利亚大陆之下，跨越地幔-地壳边界的挥发性物质输送的上限可以由≲2.6×1064He原子MW−1s−1的“传导-扩散”氦/热通量比Mw−1s−1的“侵入-火山”比在加拉帕戈斯测量的2.9×1084He原子MW−1s−1低两个数量级来表征[16]。这些结果限制了跨地壳4He和40Ar的脱气通量远小于大洋中脊的脱气通量，远小于陆壳的4He和40Ar的脱气通量。因此，地球内部的脱气是由岩浆作用主导的，但进入大气的4He和40Ar的主要通量肯定来自大陆地壳。
The groundwaters of the Great Artesian Basin (Australia) have been previously shown to be accumulating in-situ production helium for groundwaters ages < 50 kyr and an external helium flux equivalent to whole crustal production for groundwater ages > 100 kyr [1,2]. New helium isotope measurements show that the observed in-situ production helium (3He/4He∼ 1.6 × 10−8) is isotopically distinct from the crustal degassing helium flux (3He/4He∼ 6.6 × 10−8). Furthermore, the crustal degassing helium isotope ratio is marginally in excess of the whole crustal production ratio (3He/4He= 3.5 × 10−8) and the production ratio in a variety of continental rock types. This suggests that the upper limit on volatile transport across the mantle-crust boundary beneath the (relatively) stable and “complacent” Australian continent can be characterized by a “conductive-diffusive” helium/heat flux ratio of ≲ 2.6 × 1064He atoms mW−1s−1which is two orders of magnitude less than the “intrusive-volcanic” ratio of 2.9 × 1084He atoms mW−1s−1measured at the Galapagos [16]. These results constrain the transcrustal mantle degassing fluxes of4He and40Ar to be much less than the mid-ocean ridge degassing fluxes; which are much less than the degassing of4He and40Ar from continental crust. Thus, the degassing of the Earth's interior is dominated by magmatic processes but the dominant fluxes of4He and40Ar to the atmosphere must come from the continental crust.