鲁西中生代闪长岩中两类幔源捕虏体的岩石学和地球化学  

Petrology and geochemistry of two types of mantle-derived xenoliths in Mesozoic diorite from western Shandong province.

作　　者：许文良[1] 王冬艳[1] 王清海[1] 林景仟[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2003年第4期623-636,共14页Acta Petrologica Sinica

基　　金：教育部高校博士学科点基金(批准号:20010183007);国家自然科学基金(批准号:49733110和40133020)

摘　　要：鲁西铁铜沟岩体辉石闪长岩中黑云母的^(40)Ar/^(39)Ar坪年龄为132.79±0.27Ma。产于辉石闪长岩中深源捕虏体的岩相学、矿物化学、岩石地球化学和野外资料表明,它们可划分成两组。组Ⅰ为具有变质-变形结构的纯橄岩、方辉橄榄岩和尖晶石二辉橄榄岩类。该类捕虏体耗损易熔元素(如Ca、Al)、橄榄石具有较高的Mg~#值和较高的含量表明它们可能为古老岩石圈地幔高度部分熔融的残留体。然而,相对富集轻稀土元素的配分形式、较高的^(87)Sr/^(86)Sr比值以及交代型金云母的存在暗示着该类捕虏体遭受了晚期交代作用的改造;组Ⅱ为具有残留的嵌晶结构、再平衡结构,并叠加有变形结构的纯橄岩、方辉橄榄岩、橄辉岩和二辉石岩类。该类捕虏体具有较低的Mg~#值和^(87)Sr/^(86)Sr比值以及较高的稀土元素丰度表明可能代表了新增生的岩石圈地幔物质。两类幔源捕虏体的共存对认识华北地块东部中生代岩石圈地幔的性质以及揭示中国东部陆下岩石圈地幔的演化历史具有重要意义。The Ar-40/Ar-39 plateau age of biotite in pyroxene-diorite from Tietonggou intrusion of western Shandong is 132.79+/-0. 27 Ma. Petrographic, mineral chemical, petrochemical -geochemical and field data of xenoliths occurred in pyroxene-diorite indicate that they are subdivided into *two groups. Group I is the mantle-derived dunite, harzbergite and spinel-lherzolite with metamorphicdeformation texture. The depletion of fusible elements such as Ca, Al, the high olivine Mg(#)s (ave. Mg-# = 92) and high olivine abundances for Group I xenoliths suggest that they could be the relics of high-degree partial melting of the ancient lithospheric mantle. However, the relative LREE-enrichment REE patterns, high Sr-87/(86) Sr ratios and the existence of secondary phlogopites in Group I xenoliths imply that they could be subjected to a late metasomatism. Group II is the mande-derived dunite, harzbergite, olivinepyroxenite and websterite with relic poikilitic, re-equilibrium and overprinted deformation textures. The relatively lower Mg(#)s and Sr-87/Sr-86 ratios, higher REE abundances for Group II xenoliths indicate that they could be the new accreted lithospheric mantle. The coexistence of two types of the mantle-derived xenoliths is of importance to realize the nature of Mesozoic lithospheric mantle and to reveal the evolutionary history of subcontinental mantle in eastern China.

关 键 词：鲁西 中生代 闪长岩 幔源捕虏体 岩石圈地幔 

分 类 号：P588.125[天文地球—岩石学] P597[天文地球—地质学]