滇东-川西下二叠统白云岩的形成机理--玄武岩淋滤白云化

在滇东－ 川西地区的下二叠统中,白云岩发育,并可分两种类型:块状白云岩和斑状白云岩。块状白云岩呈浅灰色、灰色,主要由细晶或中晶白云岩石组成。白云岩的δ13C为+0.8‰～+3.5‰, 平均+2.7‰; δ18O为 -6.8‰～-9.1‰, 平均 -7.8‰。 Sr 为 25×10-6～52×10-6, 平均 39×10-6; Na 为 52×10-6～74×10-6, 平均 64×10-6。斑状白云岩呈灰色,由白云岩斑块和交代残余的石灰岩斑块组成,其中白云岩斑块含量大于50 %。白云岩斑块呈云朵状,大小多为几厘米至二十几厘米。白云岩斑块由细晶和中晶白云石组成。白云石呈自形或半自形,含量60% ～ 90%。白云石的δ13C为+0.8‰～+3.5‰, 平均+2.7‰; δ18O为 -6.8‰～-9.1‰, 平均 -7.8‰。 Sr 为 25×10-6～52×10-6, 平均 39×10-6; Na 为 52×10-6～74×10-6, 平均 64×10-6。各种资料表明,块状白云岩和斑状白云岩成因相同,只是白云化程度不同。白云岩是在埋藏环境中较高温度条件下形成的。白云化水来自淋滤峨嵋山玄武岩的大气

Origin of Dolostones of the Lower Permian in East Yunnan--West Sichuan--Dolomitization through Leaching of Basalts

In the East Yunnan-West Sichuan area,dolostones are well developed and can be divided into two types:massive dolostones and patchy dolostones. Massive dolostones are light gray and gray,and mainly consist of fine or medium dolomites.The δ13C is +0.8‰～+3.5‰(PDB) and averages +2.7‰;δ18O is -6.8‰～-9.1‰(PDB) and averages -7.8‰.Sr is 25×10-6～52×10-6 and averages 39×10-6;Na is 52×10-6～74×10-6 and averages 64×10-6.Patchy dolostones are gray and consist of dolomite patches and calcite patches,with dolomite patches over 50%.The dolomite patches are several centimeters to over 20 cm in size and consist of fine to medium dolomite crystals.The dolomite crystals are euhedral or subhedral and are commonly 60%～90%.The δ13C is +3.1‰～+4.0‰ and averages +3.6‰;δ18O is -6.4‰～-8.1‰ and averages -7.8‰.Sr is 46×10-6～68×10-6 and averages 55×10-6;Na is 60×10-6～89×10-6 and averages 74×10-6. Various data show that massive dolostones and patchy dolostones are the same in origin and different only in dolomitization degree.These dolostones were formed under burial conditions,and the dolomitizing water was fresh meteoric water leaching basalts.The Mg2+ for dolomitization came from weathering and dissolution of basalts.Very thick basalts formed high mountains.which formed great relief of landform and large water head and made the meteoric water leaching basalts flow deep into underground.Such water resulted in large scale dolomitization of limestones.Thus,the dolomitization mechanism in this area may be called "dolomitization through leaching of basalts”.