Visible/near-infrared spectra of experimentally shocked plagioclase feldspars -: art. no. 5120
Visible/near-infrared spectra of experimentally shocked plagioclase feldspars -: art. no. 5120
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DOI：
10.1029/2003je002127
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发表时间：
2003-11-15
影响因子：
4.8
通讯作者：
Hörz, F
中科院分区：
文献类型：
--
作者：
Johnson, JR;Hörz, F
[1]高冲击压力会导致斜长石的结构变化，如亚微米级的机械断裂和晶格解聚，形成闪长玻璃(硅铝榴石)，以及真正的熔融。过去对受冲击长石的可见光/近红外光谱的研究表明，除了1250-1300 nm附近吸收特征的深度减小和反射率总体下降外，光谱随压力变化很小。新的可见光/近红外光谱(400-2500 nm)显示出相似的趋势，包括1410、1930、2250和2350 nm附近的少量水化矿物带的丢失。然而，最有趣的新观测是在中等压力下反射率增加，随后在较高压力下反射率下降。内部散射量和样品总反射率由冲击变质过程中形成的微裂缝、亚微米颗粒、闪辉玻璃和熔体的相对比例控制。我们解释说，在中等压力下观察到的反射率增加是由于亚微米长石颗粒和闪辉玻璃所占比例逐渐增大所致。随后反射率的下降发生在重熔玻璃形成完成后，真正的熔融包裹体比例增加。这些反射率变化发生的压力模式在钠长石和钙长石之间不同，这与这些样品的热红外光谱和以前对受冲击的长石的研究一致。在对行星和小行星表面的可见光/近红外遥感光谱进行解释和建模时，应考虑到与不同峰值冲击压力有关的这些类型的光谱变化。
[1] High shock pressures cause structural changes in plagioclase feldspars such as mechanical fracturing and disaggregation of the crystal lattice at submicron scales, the formation of diaplectic glass (maskelynite), and genuine melting. Past studies of visible/ near-infrared spectra of shocked feldspars demonstrated few spectral variations with pressure except for a decrease in the depth of the absorption feature near 1250 - 1300 nm and an overall decrease in reflectance. New visible/ near - infrared spectra ( 400 - 2500 nm) of experimentally shocked (17 - 56 GPa) albite- and anorthite-rich rock powders demonstrate similar trends, including the loss of minor hydrated mineral bands near 1410, 1930, 2250, and 2350 nm. However, the most interesting new observations are increases in reflectance at intermediate pressures, followed by subsequent decreases in reflectance at higher pressures. The amount of internal scattering and overall sample reflectance is controlled by the relative proportions of micro-fractures, submicron grains, diaplectic glass, and melts formed during shock metamorphism. We interpret the observed reflectance increases at intermediate pressures to result from progressively larger proportions of submicron feldspar grains and diaplectic glass. The ensuing decreases in reflectance occur after diaplectic glass formation is complete and the proportion of genuine melt inclusions increases. The pressure regimes over which these reflectance variations occur differ between albite and anorthite, consistent with thermal infrared spectra of these samples and previous studies of shocked feldspars. These types of spectral variations associated with different peak shock pressures should be considered during interpretation and modeling of visible/ near-infrared remotely sensed spectra of planetary and asteroidal surfaces.