CAJ | 학술논문

通过对塔里木盆地中、北部地区寒武系-奥陶系碳酸盐岩的研究,发现鞍形白云石胶结物发育比较普遍,常见于孔洞或裂缝之中,乳白色,晶体粗大,晶面弯曲或呈阶梯状,镜下波状消光,晶体内部常见微裂缝,常与热液矿物共生.本文对28个鞍形白云石样品进行了碳、氧、锶同位素测试,结果显示鞍形白云石的δ~(13)C和δ~(18)O值分别介于-2.446‰～0.686‰和-9.101‰～-5.117‰之间,~(87)Sr/~(86)Sr值介于0.708 6～0.710 2之间;流体包裹体测温分析表明,鞍形白云石中气-液两相包裹体的均一温度(T_h)介于121～159.5℃之间,但集中分布在135～145℃之间;根据最后冰融点温度(T_m)求得的白云岩化流体盐度介于21.3%～23.1%之间.这些数据表明,该类型白云石形成于热卤水(盐度是海水的5～8倍)之中.塔里木盆地鞍形白云石与世界范围内其它盆地的鞍形白云石的碳、氧同位素特征基本相似,但其~(87)Sr/~(86)Sr值相对偏低.导致这一现象的原因可能是鞍形白云石形成于来自深部的岩浆热液流体之中,这些流体伴随岩浆侵位或通过切穿基底的深大断裂及其与之相连的次级断裂系统从深部直接进入碳酸盐岩地层中,未经过碎屑岩输导层的长时间运移,所以导致其中形成的鞍形白云石~(87)Sr/~(86)Sr值偏低.
통과대탑리목분지중、북부지구한무계-오도계탄산염암적연구,발현안형백운석효결물발육비교보편,상견우공동혹렬봉지중,유백색,정체조대,정면만곡혹정계제상,경하파상소광,정체내부상견미렬봉,상여열액광물공생.본문대28개안형백운석양품진행료탄、양、송동위소측시,결과현시안형백운석적δ~(13)C화δ~(18)O치분별개우-2.446‰～0.686‰화-9.101‰～-5.117‰지간,~(87)Sr/~(86)Sr치개우0.708 6～0.710 2지간;류체포과체측온분석표명,안형백운석중기-액량상포과체적균일온도(T_h)개우121～159.5℃지간,단집중분포재135～145℃지간;근거최후빙융점온도(T_m)구득적백운암화류체염도개우21.3%～23.1%지간.저사수거표명,해류형백운석형성우열서수(염도시해수적5～8배)지중.탑리목분지안형백운석여세계범위내기타분지적안형백운석적탄、양동위소특정기본상사,단기~(87)Sr/~(86)Sr치상대편저.도치저일현상적원인가능시안형백운석형성우래자심부적암장열액류체지중,저사류체반수암장침위혹통과절천기저적심대단렬급기여지상련적차급단렬계통종심부직접진입탄산염암지층중,미경과쇄설암수도층적장시간운이,소이도치기중형성적안형백운석~(87)Sr/~(86)Sr치편저.
Detailed researches of Cambrian-Ordovician dolostones in Tabei and Tazhong areas of Tarim Basin demonstrated widespread presence of saddle dolomite cements,which commonly occur as cements(or infilling)in vugs and/or fractures. These dolomite crystals,generally 500 μm up to 6 mm in size,are creamy white non-planar crystals with curved or lobate or stepped crystal faces. They are gappy and sweeping extinction under microscope,commonly associated with other hydrothermal minerals. The saddle dolomites have δ~(13)C values from -2.446‰ to 0.686‰ PDB,and δ~(18) O values from -9.101‰ to -5.117‰ PDB,and ~(87)Sr/~(86)Sr ratios from 0.708 6 to 0.710 2. Fluid inclusion micro thermometry data of the saddle dolomites cements indicates homogenization temperatures(T_h) of gas-liquid inclusions is about 121～159.5℃ and salinities of dolomitization fluids is about 18.7% ～23.1%(wt% NaCl equivalent)from which the saddle dolomites precipitated. These data suggest that the saddle dolomites could have formed in thermal brine. Compared with saddle dolomites of other basins all over the world,the saddle dolomites of Tarim Basin have similar δ~(13)C and δ~(18) O values,but lower ~(87)Sr/~(86)Sr ratios. The reason could be that the saddle dolomites were formed in magmatic hydrothermal,which was mantle-derived and reached carbonate formation accompanying igneous intrusion or through discordogenic faults without going through siliciclastic sediments. Thus the saddle dolomites formed from the magmatic hydrothermal have lower ~(87)Sr/~(86)Sr ratios than others.