陕北鄂尔多斯盆地埋藏变质作用研究

本文系统地研究了陕北鄂尔多斯盆地的埋藏变质作用。砂岩胶结物在成岩到变质作用转化过程中经历了如下4个阶段:1.粘土胶结阶段;2.压溶长石、石英再生长阶段;3.碳酸盐胶结阶段;4.生成浊沸石阶段。泥岩中粘土矿物组合在埋藏变质过程中出现如下转化:早期蒙皂石、高岭石组合,随埋深的增加转化为伊利石和镁铝蛇纹石混合阶段;进一步埋深出现了伊利石和绿泥石混层阶段;最后转化为分散状的伊利石和绿泥石。     

陕北三叠系延长统浊沸石的成因及形成条件的理论计算

延长统浊沸石是埋藏变质过程中,在没有外来组分加入和带出(H_2O、CO_2除外)的条件下,由砂岩胶结物间或胶结物与碎屑颗粒之间经高岭石+方解石+2石英+H_2O=浊沸石+CO_2或者钙长石+2石英+4H_2O=浊沸石的反应形成,其形成条件为T<250℃,X_(co2)<0.17。     

Pressure-induced migration of zeolitic water in laumontite

A polycrystalline sample of natural laumontite (Pleasant Valley, Connecticut) was studied up to 6.8 (1) GPa at room temperature using monochromatic synchrotron X-ray powder diffraction and a diamond-anvil cell. A methanol: ethanol: water mixture was used as a penetrating pressure-transmitting fluid. A dry sample measured before adding the pressure fluid inside the diamond-anvil cell contained ~12 H₂O per formula unit, consistent with the water content of partially dehydrated laumontite. Upon increasing the pressure to 0.2 (1) GPa, fully hydrated laumontite with 18 H₂O per unit cell formed and the unit-cell volume expanded by 2.6%. Further pressure increase up to 2.4 (1) GPa resulted in a gradual contraction of the unit-cell volume and individual cell lengths. During this process, a successive order–disorder transition of hydrogen-bonded water molecules from their symmetry sites was observed, concomittent with an inflectional behavior of the monoclinic beta angle and the channel ellipticity. Above 3 GPa, a tripling of the b axis was detected. Thereafter, up to 6.8 (1) GPa, the compression behavior was reversed for the c axis length and the monoclinic beta angle which showed a gradual increase and decrease, respectively, without any apparent volume discontinuity. We suspect that different ordering of the water molecules or Ca cations inside the channels along the b axis may be responsible for the observed supercell transition above 3 GPa.