Comparative study of degassing between Mars and Earth bade on noble gases in Martian meteorites

点击翻译按钮获取中文摘要

Noble gas isotopic compositions in atmosphere and interior of the Earth suggest early degassing from interior to form atmosphere. Contrary to this, noble gas distributions of Mars observed from the Viking lander and Martian meteorites are completely different from those in the Earth. To confirm this in detail, we measured many Martian meteorites using high sensitive mass spectrometers and neutron irradiated samples. Some of the results are followings :1. Enriched Ne in Dhofar 378 shergottite shows ^<20>Ne/^<22>Ne ratio of 7.3±0.1 for Martian atmosphere. The value suggests a severe loss of Martian atmosphere.2. NWA2737 chassignite shows much higher ^<40>Ar/^<36>Ar and ^<129>Xe/^<132>Xe than those for Chassigny. This means heterogeneous distribution of noble gas isotopes in the interior of Mars. Uniform degassing might not have occurred from the Martian interior.3. MIL 03346 nakhlite have two phases containing heavily elementally fractionated Martian atmosphere. Weathering products formed on Mars are probable carriers for the fractionated noble gases.4. One of the end components observed for most shergottites is thought to be a Martian interior noble gas as is observed in Chassigny. Our noble gas data for weathering products of olivine and desert sands strongly indicate that the component is not Martian origin but fractionated Earth atmosphere.5. Ar-Ar ages for SaU 060 shergottite are 1.0-1.8 Ga at the temperatures of 700-1400℃ and 3-4 Ga at the higher temperatures. The older age might represent the age of Martian crust.