华南二叠系栖霞组菊花状天青石锶同位素特征及其地质意义

菊花状天青石是华南地区栖霞组内一种特殊的矿物集合体，形成于早期成岩作用阶段。在研究其成因过程中，系统分析了湖北黄石和湖南浏阳栖霞组内菊花状天青石的Sr同位素组成以及湖南浏阳、湖北黄石、江西永丰和广西来宾四处天青石假象、天青石围岩（泥晶灰岩）和围岩中方解石脉的Sr同位素组成。Sr同位素分析结果表明，天青石中的87Sr/ 86Sr最高值为0.707525，最低值为0.706981，平均值为0.707215。与天青石相比，天青石假象、天青石围岩和方解石脉的87Sr/ 86Sr值整体相对富含87Sr。由于天青石假象和方解石脉明显为晚期成岩作用成因，它们相对富含87Sr的锶同位素特征应是晚期成岩作用叠加的结果，与其类似的泥晶灰岩的87Sr/ 86Sr值也可能同样受到了晚期成岩作用的影响。栖霞组菊花状天青石比同组泥晶灰岩更好地记录了栖霞期海水的Sr同位素组成。

Strontium isotope and its geological implications of chrysanthemum-shaped celestite of the Qixia Formation of Permian in South China

Nodular celestite(Chrysanthemum stone),a specific celestite cluster in the Qixia Formation (Middle Permian) of South China, formed in the early diagenesis In a course deciphering its origin,33 samples were analyzed for strontium isotope These samples include nodular celestites from Liuyang,Hunan Province and Huangshi,Hubei Province,and include replacement calcites,host rock (micrites) and vein calcites from Liuyang (Hunan Province),Yongfeng (Jiangxi Province),Huangshi (Hubei Province) and Laibin (Guangxi Autonomous Region) The 87 Sr/ 86 Sr ratios determined from the celestites range from 0 706981 to 0 707525 with a mean value of 0 707215,coincide with those of seawater of the late Artinskian to Roadian stages The 87 Sr/ 86 Sr ratios from replacement calcite,host rock and vein calcite are richer than those of celestite Because the genesis of the replacement calcite and vein calcite is obviously later diagenetic,their relative riching of 87 Sr isotopic characteristics must have originated from the overprint of later diagenesis Analogously,the 87 Sr/ 86 Sr values of micrite also include contributions of late diagenesis Based on geological context on the evolution of the celestite cluster,it is proposed that the Qixia nodular celestite reflects the 87 Sr/ 86 Sr value of the Qixia seawater more reliably than Qixia micrites do, and that the differences of Sr isotopic values between celestites and micrites may be of significance in evaluations of Sr isotopic data from micrites