幔源包体和中国东部现代弧后地热标志

利用矿物学、岩石学、组构,显微构造和红外光谱的综合分析方法,研究了福建省明溪石榴石和尖晶石-石榴石二辉橄榄岩包体。根据Bertrand和Mecier温度计、Nickel和Green压力计方法,利用TEMPEST最新程序分别计算了包体平衡温度和压力,其变化范围为:1300K,1.9GPa(60km)至1500K 2.6GPa(80km)。由包体温压资料推断的明溪地区地热与实测地表热流量(70mW/m~2)一致。地热特征、包体矿物显微构造和优选方位与现代伸展弧后环境的岩石圈减薄作用是一致的。     

激光剥蚀多接收杯电感耦合等离子体质谱仪原位分析硫化物铅同位素组成

采用193 nm准分子激光与MC-ICP-MS质谱仪探讨了原位微区分析过程中物质基体效应对铅同位素测定的影响,指出选择基体匹配标准物质对测定硫化物铅同位素具有重要意义.通过模拟计算发现准确测定Tl与Hg的分馏因子关系,可以在204Hg/204 Pb＜2的范围内有效校对204Hg对204 Pb的干扰.研究表明,束斑直径(24～160μm)和剥蚀频率(2～20 Hz)并不影响铅同位素组成测试.改变激光剥蚀参数可以解决MC-ICP-MS信号检测范围较窄的问题.针对目前硫化物固体标准物质缺乏的现状,采用压片法和快速熔融法制备硫化物标准物质.压片样品铅同位素组成表现出较好的均一性,而不同批次快速熔融法样品存在铅同位素分馏,仅单次制造的熔融样品内部铅同位素组成具有均匀性.结果表明,虽然快速熔融法还存在一定缺陷,但这两种方法都有望成为硫化物标准样品制作方法的备选方案.利用本方法对天然硫化物样品(黄铁矿和闪锌矿)及人工合成硫化物样品的铅同位素组成进行了准确测定,测定值与溶液值在误差范围内一致.     

Mantle-derived Xenoliths and the Token of a Modern Back-Arc Geotherm Beneath Eastern China

Xenoliths of garnet and spinel-garnet 1herzolite from Mingxi, Eastern China have been studied in terms of comprehensive methods of mineralogy, petrology, fabrics, mierostructures and infrared spectrum. The temperature and pressure equilibration of the xenolith have been calculated using the TEMPEST program with the two-pyroxene geothermometer of Bertrand and Mercier (1985) combined with the geobarometer of Nickel and Green (1985). The temperature and pressure of xenoliths range from~1300 K at 1. 9 GPa (60 km) to ~1500 K at 2. 6 GPa (80 km). The geotherm inferred from xenolith is excellently consistent with the measured surface heat flow (70 mW/m2) in Mingxi. A character of geothermal curve and conductive type suggest that these xenoliths are from the lithosphere, not from the asthenosphere. The geotherm and mierostructures and preferred orientations of minerals in the xenolith are consistent with tecon-ic thinning of the lithosphere in the present-day extensional back-arc environment.