含水矿物在真空下的释Ar机制:Ar-Ar热年代学面临的新问题

ARGON RELEASE MECHANISMS OF HYDROUS-BEARING MINERALS IN VACUO:THE NEW PROBLEM FACED BY AR-AR THERMOCHRONOLOGY

地质体的实际情况、激光显微探针束研究、XRD和SEM观测以及真空加热下Ar的释放特征都表明体积扩散不是含水矿物在真空加热中释放Ar的唯一机制。在低温下 ,Ar的释放主要受由缺陷引起的短程扩散和体积扩散共同作用的多途径扩散机制制约 ;而在高温下 ,由于含水矿物在真空中不够稳定 ,Ar的释放受到脱羟基、脱氢、氧化反应、分层作用等造成的晶体结构改变的强烈影响。含水矿物在高温下的氧化分解会导致矿物中原始Ar浓度梯度的均一化 ,因而无法得到真实的Ar分布剖面 ,也无法据此计算矿物的封闭温度 ,并进而可能影响到ArAr年龄坪的地质意义。

The histories of geological terranes, the laser microprobe, XRD and SEM studies and the characters of argon release in vacuo all indicate that volume diffusion is not the only mechanism of Ar release from hydrous\|bearing minerals in vacuo. At low temperature, Ar release is mainly controlled by multipath diffusion which is the combined action of volume diffusion and short\|circuit diffusion. At high temperature, Ar release is influenced strongly by structural change, because hydrous\|bearing minerals are unstable in vacuo. The decomposition process initiated by Fe oxidation and dehydroxylation of the minerals in high temperature will tend to homogenize any Ar spatial gradient that originally exists in the mineral. So the original Ar distribution and closure temperature can not be inferred from 40 Ar/ 39 Ar incremental heating technique. And the accurate interpretation of geologic history from 40 Ar/ 39 Ar age plateau should be derived more cautiously.