The noble gas contents and helium and argon isotopic compositions in the cobalt-rich crusts from the Magellan Seamounts
| 作者: |
Ye, X.R., et al. |
| 期刊名称: |
Acta Petrologica Sinica |
| 发表年度: |
2008 |
| 卷: |
24 |
| 期: |
1 |
| 联系作者: |
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| 页码: |
185-192 |
| 摘要: |
The noble gas contents and isotopic compositions in the cobalt-rich crusts and basement rocks from the Magellan Seamounts had been measured using MM5400 mass spectrometry to trace the ocean condition. The abundance patterns of the noble gases in the crusts were consistent with the one of air-saturated water (ASW). It indicated that the fluid formed crusts was balanceable with surrounding seawater. All of the F, fractionation factor of the crusts were higher 2 similar to 3 magnitude degree than one of ASW, this suggested that the crusts were rich in He-3 relative to ASW. The patterns of crusts, which were depleted in He-3 and rich in Kr and Xe, were completely different with the one of interplanetary dust particles (IDP), which were strongly rich in 3 He and depleted in Kr and Xe. The fact implied that the noble gases budgets of the crusts were not essentially dominated by extraterrestrial matters as IDP. The fact that the higher R (R = He-3/He-4 in a sample) values even in excess of 8R(a) (R-a = He-3/He-4 in air), a typical value of MORB, were found in the crusts revealed the contributions from mantle fluid to the Western Pacific seawater. The R values between each and every layer in a layered crust were clearly different. The value much higher as 15.60Ra was found in the middle layer of the crust, and it further suggested that the fluid included into the crusts was derived from a plume-type hydrothermal. The R values of the basaltic basement rocks were less than Ra. A possible reason was that basaltic magmas had been contaminated by the earth's crust-derived matter, and also, this result showed the materials formed the crusts was not directly originated from the basement rocks. The Ar-40/Ar-36 values of the crusts were closed to the one of ASW, and it suggeted the exchange between the ore-formed fluids and surrounding seawater was sufficient.
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