On emplacement ages of lamproites in Zhenyuan County, Guizhou Province, China

Emplacement ages of lamproites that comprise lamproite and olivine lamproite in Zhenyuan County, Guizhou Province, China, have been constrained by the whole-rock Sm-Nd and Rb-Sr isochron methods and the whole rock K-Ar method. Intrusive activities of lamproites in the Sinantang area of Zhenyuan County, Guizhou Province, took place during the Late Cambrian, as indicated by the Sm-Nd isochron ages ( t ) = (503 ± 17) (2σ) Ma and by the Rb-Sr isochron ages ( t ) = (501.2 ± 4.6) (2σ) Ma. Intrusive activities of olivine lamproites at the Maping with Ⅱ-type diamond and Xitou in Zhenyuan County, Guizhou Province, took place from the Late Cambrian to the Early Ordovician, as evidenced by the Sm-Nd isochron ages ( t ) = (502 ± 27) (2σ) Ma and by the Rb-Sr isochron age ( t ) = (502 ± 27) (2σ) Ma. This suggests that the upwelling hot materials derived from the deep mantle were emplaced from the Late Cambrian to the Early Ordovician (503-497 Ma), while the time terminal of cooling of the geothermal event of magmatism-tectonism probably was at 442.64-435.54 Ma, as dated by the whole rock K-Ar method.     

大民屯凹陷油气充注史研究

油气充注历史的研究一直是石油地质学和油藏地球化学的重点和难点,而近年来流体定年技术的兴起为人们解决油气充注期次和时间提供了定量分析手段.利用伊利石K-Ar定年技术和流体包裹体均一温度分别研究了大民屯凹陷油气充注史.前者确定出的主充注期略晚于后者的分析结果.结合生烃史模拟资料认为:伊利石K-Ar定年结果可能更精确,但其样品挑选难度大,且只能用于砂岩油藏成藏史分析.而流体包裹体均一温度可用于碎屑岩和非碎屑岩油藏成藏史的分析.大民屯凹陷下第三系和太古界潜山油藏主充注时期为沙一二—东营早期,其中北部安福屯洼陷成藏期(沙一二期)略早于南部荣胜堡洼陷(东营早期).     

伊利石K-Ar测年在确定油气成藏期中的应用

利用伊利石K Ar测年确定油气成藏期 ,能够得出其绝对年龄 ,因而备受人们重视。可是在解释K Ar测年资料时 ,存在一些问题和假设。如果解释者对这些问题和假设没有足够的认识 ,其解释结果就会有误。文中以几个具体实例讨论了利用伊利石K Ar测年确定成藏期时对油气的充注时间和特征进行正确解释的方法     

无稀释剂法K-Ar定年的原理及地质应用

年轻火山物质K-Ar定年中Ar的精确测量一直是地质年代学研究的重要课题。在常规K-Ar定年法中,样品外来氩的⁴⁰Ar/³⁶Ar比值被假定为295.5。但研究表明,这种假定在某些情况下,尤其是在年轻样品的测量中受到了限制。一种无稀释剂的测Ar技术已在近年来得到了发展和应用。该方法的优势在于测氩系统不受³⁸Ar稀释剂的混染,利用标准大气的校准可测得样品中的⁴⁰Ar、³⁸Ar和³⁶Ar。考虑火山岩中大气氩分馏造成的影响,利用测得的³⁸Ar/³⁶Ar比值还可以对所测样品中的外来⁴⁰Ar/³⁶Ar比值进一步加以校正,给出精确的放射性成因⁴⁰Ar^*含量计算和K-Ar定年。目前,无稀释剂的K-Ar定年技术在地质上已有广泛应用,并能取得晚第三纪到第四纪可靠的年龄,对地质事件做出合理地解释和重建岩浆活动历史。对无稀释剂法K-Ar定年原理及地质应用的介绍,将为K-Ar年代学应用于研究晚第三纪以来的年轻火山岩提供一种有力的手段和解决途径。     

Significance of K-Ar age of bimodal volcanic rocks at Wangtian’e volcano, Changbaishan area

Wangtian'e volcano, about 30 km south of Tianchi volcano is another large scale volcano center on the south slope of Changbaishan with its nearly 4 000 km2 area of volcanic rocks distributed over the border area of the Chinese side. Based on the field occurrence, petrology and K-Ar age dating of its volcanic rocks, it can be shown that the Wangtian'e volcano had experienced two developing stages of shield forming and cone forming, while its volcanic activities can be divided into three periods: Changbai period (? -2.87 Ma), Wangtian'e period (2.69-2.41 Ma) and Hongtoushan period (2.12 Ma). Its petrographic change goes from trachybasalt→ basaltic trachyandesite, trachyte→ alkalic rhyolite, with a feature of bimodal volcanic rock combination similar to yet a bit different from that of Tianchi volcano, and is a new scene for study of volcanic magma evaluation of Changbaishan volcanoes.     

Influence of olivine grains on K-Ar dating of Late-Cenozoic olivine basalts in eastern China

Five Late-Cenozoic olivine basalt samples, taken from 3 young volcanoes (Keluo, Lianhuashan and Qinglongshan) located in the north of Heilongjian Province, were dated by the conventional K-Ar dating method. The apparent ages of whole rock are (0. 06 ±0. 01) Ma, (0.15 ±0.03) Ma, (0.17 ±0.02) Ma, (21.10 ±0.13) Ma and (24.46 ±0.10) Ma, respectively. In the crushed sample grains (mush number 80–100) olivine (including phynocryst and xenocryst)was picked out under a binocular microscope, then apparent ages obtained are (0.03 ±0.01) Ma, (0.06 ±0.01) Ma, (0.07 ±0.03) Ma, (2.31 ±0.02) Ma and (1.50 ±0.21) Ma, respectively. The apparent ages of the o-livine-picked out sample are come down (younger) 50% to over 90%. There are a lot of the Late-Cenozoic volcanic olivine basalt outcropping in eastern China, probably the age-datings of those basalt samples in which olivine grains are unpicked out are older than the true geological ages. The inference and conclusion drawn from those datings should be renewed.     

Reservoir-forming age and its exploration significance to stratigraphic reservoirs in southern Songliao Basin

Despite many studies concerning the forming age, evolution characteristics and the age of petroleum charging in the Fuxin upheaval of southern Songliao Basin, no consensus has been reached so far. This paper presents the first K-Ar dating of autogenetic illite from stratigraphic petroleum reservoirs in the Fuyu oil layer of the Fuxin upheaval belt. Isotopic test and age calculation were carried out based on the separation and purification of illite mineral, X-diffraction analysis and the detection of scanning electron microscopy. The evolution characteristics of structure, sedimentation, reservoir-forming about the Fuxin upheaval belt were interpreted in terms of the synthetical analysis of "six-type geological history" evolution in southern Songliao Basin. The geologic background of petroleum evolution and reservoir formation are similar in the entire central depression region of southern Songliao Basin. The Changling sag and the Fuxin upheaval belt brought about obvious upheaval-sag separation after the hydrocarbon-generation peak of K2qn1 and the main reservoir-forming period of the Fuyu oil layer, namely reservoir-forming happened before the Fuxin upheaval belt extensively raised. The reservoirs have three characteristics: the hydrocarbon source rock above the reservoir, the oil source in the lo- cality, and the vertical migration. The geological cognition is corrected, that is, oil source came from the Changling sag and migrated from the side direction. The bulk process of petroleum charging in the stratigraphic hydrocarbon reservoirs in the Fuxin upheaval belt of southern Songliao Basin is deter- mined according to the isotopic age of autogenetic illite in combination with the method of fluid inclu- sions. The cognition is helpful to exactly evaluate the resource potential and exploration direction in the Fuxin upheaval belt, Changling sag and their peripheral areas. The present results indicate that the combination of the two methods (the K-Ar dating of autogenetic illite and fluid inclusions) is an effec- tive way to lay bare petroleum charging history and ascertain reservoir age.     

K-Ar dating of late Mesozoic volcanism and geochemistry of volcanic gravels in the North Huaiyang Belt, Dabie orogen: Constraints on the stratigraphic framework and exhumation of the northern Dabie orthogneiss complex

Two eruption episodes are identified through systematic field investigations and K-Ar dating of the lateMesozoic volcanic rocks in the North Huaiyang belt (NHB),Dabie orogenic belt, of which the earlier volcanic suitetermed Maotanchang Fm. (Fm.) occurring at Jinzhai,Xianhualing and Maotanchang, etc., was erupted from 149Ma to 138 Ma. The other named Xiaotian Fm. mainly dis-tributed at Xiaotian, Shucheng, etc., was formed between132 Ma and 116 Ma. During the eruption gap of the two vol-canic suites deposited a volcano-sedimentary conglomeratelayer, which are composed of the multi-compositional gravels, including the North Dabie orthogneiss complex (NDOC),volcanic gravels, etc. These volcanic gravels in the con-glomerate layer show identical geochemical and isotopic compositions (87Sr/86Sr(t) =0.7084-0.7092, (Nd (t) = 21.8-24.4) to the Maotanchang Fm. volcanic rocks (87Sr/86Sr = 0.7086-0.7102, (Nd = 19.2-24.4), but significantly distinct from those of Xiaotian Fm. (87Sr/86Sr = 0.7076-0.7084, (Nd = 17.2 - 19.2). K-Ar dating results of its underlying andoverlying volcanic sequences indicate that the conglomerate layers were deposite d at ~135 Ma. This suggests that the NDOC was rapidly exhumed to the surface dur ing or shortly before ~135 Ma and became the important provenance of the late Me sozoic volcano-sedimentary basins in the NHB. In combination with the regional v olcano-sedimentary correlation, we divided the Mesozoic stratigraphic sequence i n the NHB from base to top into Fanghushan Fm. (>160 Ma), Yuantongshan Fm. (/mid dle- lower segment of Sanjianpu Fm.) (160-149 Ma), Maotanchang Fm. (/Zhougongsh an Fm./upper segment of Sanjianpu Fm./Fenghuangtai Fm.) (149-135 Ma) and Xiaoti an Fm. (/Baidafan Fm./Heshidu Fm.) (135-116 Ma).     

黑龙江科洛晚新生代火山岩K—Ar定年和地球化学

对采自8个火山锥和其它产状的15个火山岩样品和一个幔源包体样品进行了系统的岩石薄片观察,常量元素、微量元素和稀土元素的化学分析,K-Ar定年及氧、锶和钕同位素测定。显微镜下首次发现了贵橄榄石的贯穿双晶,包括四角星状和六角星状双晶。化学分析表明这是一套SiO_2不饱和、高K、Mg而贫Ca,同时特别富集LREE、不相容元素和地幔元素的岩浆。全岩的δ~(18)O值略高于初始地幔,Sr和Nd同位素组成在~(87)Sr/~(86)Sr-~(143)Nd/~(144)Nd图解上,落在第Ⅳ象限地幔排布的延长线上,并且靠近坐标原点,显示初始地幔的特征,K-Ar表现年龄值域在0.03Ma和2.98Ma之间,大多数落在晚更新世。地幔包体表现年龄约为70Ma,中生代的玄武岩年龄在93.3Ma和95.5Ma之间。趋势分析表明年青火山仍有喷发的可能性、显微镜下挑除橄榄石捕虏晶后的对比定年实验给出了有益的提示:我国东北和东部大面积分布的晚新生代橄榄玄武岩过去的定年可能都偏老了。