沱沱河盆地是冻土天然气水合物潜在分布区之一,其内发育下—中二叠统开心岭群九十道班组、上二叠统乌丽群那益雄组、上三叠统结扎群巴贡组、中—渐新统雅西措组4套烃源岩以及不同类型的火山岩.研究表明,火山岩岩石类型主要为玄武岩、玄武安山岩、安山岩、玄武质粗面安山岩和粗面安山岩.火山岩主量元素低TiO2,A12O3含量较高,K2O含量较低,K2O＜ Na2O;火山岩的稀土元素配分模式为轻稀土富集型;微量元素配分模式呈锯齿状,Ta、Nb、P2O5、TiO2、Y、Yb以及铁族元素Sc、Cr、Ni亏损,综合判断青海南部沱沱河地区火山岩形成于岛弧环境.结合火山岩的地球化学特征,推断火山活动可以加快烃源岩的热成熟,进而促使有机质裂解,产生热解气,为水合物的生成提供气源条件.同时,火山岩的气孔构造发育,连通性较好,有可能成为水合物的储层.火山热液具有的高压使周围的烃源岩产生裂隙,这些裂隙不仅是水合物气源的运移通道,还可以为水合物提供形成场所和储存空间.

近几年,在祁连山冻土区天然气水合物(以下简称水合物)科学试验钻探过程中,观察到大量与水合物伴生的碳酸盐矿物,为揭示其与水合物的内在成因联系,运用元素地球化学分析方法,研究了伴生碳酸盐岩中主量元素、微量元素、稀土元素的特征,探讨了伴生碳酸盐矿物可能的物质来源与沉积条件.结果表明,伴生碳酸盐岩赋存状态存在以下4种类型:①白色薄层状碳酸盐岩(Ⅰ型);②烟灰色菱形晶簇状方解石集合体(Ⅱ型);③深灰色薄壳状碳酸盐岩(Ⅲ型);④徼细浸染状方解石或碳酸盐岩(Ⅳ型).各类碳酸盐岩元素含量分布较为平行、各自变化幅度不大,并基本能与其他类型区别开来;特别是第Ⅱ类碳酸盐岩,其元素含量总体偏低,个别元素含量和元素比值与其他类型碳酸盐岩明显不同,且出现Sr、Ba、Eu异常和最低化学蚀变指数(CIA),说明黏土矿物对该类碳酸盐岩形成过程贡献最小.结论认为:第Ⅱ类碳酸盐岩中方解石颗粒粗大,含有一定量的文石和草莓状黄铁矿,应为水合物分解后碳酸盐岩化改造形成;第Ⅰ、Ⅲ、Ⅳ类碳酸盐岩可能为湖相碳酸盐与碎屑物质的共沉积作用所形成.

It is a universal phenomenon for gas hydrate associated carbonates in seafloor sediments,but it is rarely reported in the permafrost.Based on microscopic observations and mineral analyses on carbonates associ-ated with gas hydrate,mineral species and occurrence modes of carbonates are determined in the Qilian Moun-tain permafrost.The results show that occurrence modes of carbonates can be divided into four types according to mineral compositions and geological features.Characteristics of C and O isotopes in different occurrence modes of carbonates indicate that the smoky gray rhombic calcite crystals or microcrystalline calcites may be re-lated to gas hydrate decomposition.The variation of C and O isotopic compositions in carbonates with depth sug-gests that there probably exist hydrocarbon seepage activities within a certain depth,namely decomposition of gas hydrate,resulting in carbonate formation.

A method for high-precision measurement of Zn isotope composition has been established,which includes correction of instrumental mass discrimination,assessment of isobaric interferences,investigation of matrix effect,and examination of long-term repeatability.It has been shown that the instrumental mass discrimination can be corrected with the standard-sample-bracketing method.The assessment of isobaric interferences was carried out using three approaches,i.e.,① the direct measurement of the interference signals in the high-resolution mode;② the examination of correlation between Zn isotope ratios of the raw data in a low-resolution mode;③ the investigation of the deviation of the measured Zn isotope values relative to the real value.The matrix effect was examined by using the mixed solution of Fe and Zn relative to pure Zn solution.It is found that the content of Fe has no detectable effect on the measured values of Zn isotope when the Fe/Zn ratio is lower than or equal to 0.2.The repeatability assessed over a period of 7 months is better than 0.06‰(2sd)per amu.The Zn isotope composition of a national standard reference material of sphalerite(GBW 07270)was analyzed with the techniques established,and the results are δ66Zn =6.71‰±0.03‰(2σ),δ67Zn = 10.08‰±0.05‰(2σ),and δ68Zn=13.37‰±0.07‰(2σ).

A method for determining Mg/Ca of stalagmite by LA-MC-ICPMS is studied. 24Mg/44Ca (Mass 22, intensity of 44Ca2+ , collected by ion counting and mass 24, intensity of 24Mg+, collected by Faraday cup) ratios were measured in replace of Mg/Ca ratios. Both diameter of laser sampling spot and laser moving increment were 20 μm. The curve of Mg/Ca vs. distance directly was obtained. The result indicates that relative Mg/Ca ratios changed from 0.5 to 2.0 in this stalagmite and it is enough to reflect environmental factors act.

Through the infrared spectroscopic and electron microprobe analysis of the small_scale 6th rhythmic unit, the content of catios and anions was determined. The result shows that the content of major elements rise and fall indistinctly while F- in the apatite near the bottom of No.3 orebody was replaced by Cl-, forming chlorapatite. This seems one of the reasons for the inversely graded