摘要
利用电子、离子探针技术对吉林汪清－尖晶石方辉橄榄岩包体的原生和地幔交代矿物进行了详细分析。结果表明：（１）原生矿物强烈亏损玄武质组分，斜方辉石残斑具强烈的成分分带。地质温度计计算结果暗示该地区上地幔经历了一个由大于１２００℃到８５０℃的抬升历史；（２）该包体经历了多期交代作用，交代介质均与寄主玄武岩浆无关。较早一期为隐型交代，交代介质富轻稀土、贫重稀土；较晚一期的交代主要反映在各种交代组合的出现，仅发生在寄主玄武岩喷发之前，交代介质的稀土含量明显高于前一期，这可能与碳酸盐交代作用有关。
A spinel harzburgite(WQ91-28) from Wangqing, northeastern China contains large exsolved orthopyroxene(Opx) porphyroclasts (>1cm) and metasomatic assemblages around primary orthopyroxene and spinels. In order to investigate the themial history experienced by this sample and to determine the nature of metasomatism, we have analysed its constituent minerals using electron microprobe for major elements and ion microprobe for trace elements (Sr, Ti, Zr, Y and REE). The primary minerals are strongly depleted in basaltic components, consistent with its petrographic characteristics. The Opx popohyroclasts are chemically zoned with Cr, Al, and Ca decreasing from core to rim. Opx neoblasts have compositions similar to porphyroclast rim. Themiometric calculation indicates that the uppermantle beneath Wangqing experienced a cooling process from > 1200 to 850℃ . A possible tectonic phenomenon connected to this proeess is a diapiric uplift. Major element and trace element abundances in primary and metasomatic clinopyroxenes(Cpx) suggest that the WQ91-28 recorded at least two episodes of metasomatism. The first metasomatism is cryptic in nature and the metasomatic agent is characterised by high LREE and low HREE contents. The second episode of metasomatism happened shortly before the basaltic eruption. The metasomatic agent which is responsible for development of Opx epolacement rim and Cpx-Ol-feldspar-glass assemblage around spinel cannot be the host basalts, but is related to carbonatite melts.
出处
《地球化学》
CSCD
北大核心
1996年第5期481-493,T001,共13页
Geochimica
关键词
橄榄岩包体
热历史
尖晶石
矿物
化学成分
peridotite xenolith
electron and ion probe analyse
thermal history
metasomatism.
