滇西哀牢山镇沅煌斑岩~(40)Ar-~(39)Ar年代学和地球化学特征   总被引：4，自引：4，他引：0  

陈福川  王庆飞  李龚健  赵岩 《岩石学报》2015,31(11):3203-3216

滇西镇沅煌斑岩呈岩脉状产出于金沙江-哀牢山富碱斑岩带南段。不同脉体的矿物组合特征相似,均为云煌岩。煌斑岩黑云母40Ar-39Ar坪年龄结果为35.69±0.40Ma和36.21±0.43Ma,与区域富碱斑岩年代一致。煌斑岩Si O2含量为43.26%~47.66%,K2O+Na2O含量为6.39%~8.22%,K2O/Na2O比值为3.68~5.55,属于碱性、高钾钙碱性系列。岩石富集大离子亲石元素(Rb、Ba、K、Sr)和轻稀土元素(LREE);相对亏损高场强元素(Nb、Ta、Ti、Zr)和重稀土元素(HREE);LREE/HREE为6.32~7.44,δEu为0.80~0.91;Nb/U值为1.15~2.18,接近俯冲带含水流体的Nb/U比值(Nb/U≈0.22)。La/Sm比值与La值具有弱的正相关趋势。岩石学和地球化学特征显示,哀牢山古特提斯洋壳俯冲交代作用形成的富集地幔,在新生代三江地区岩石圈地幔拆沉-软流圈上涌形成的伸展背景下经过部分熔融,上升侵位形成煌斑岩脉。  相似文献   

The carbonate fraction in carbonatitic Italian lamprophyres   总被引：1，自引：0，他引：1  

Giada Vichi  Francesco Stoppa  Frances Wall 《Lithos》2005,85(1-4):154-170

Alkaline and ultramafic lamprophyres represent the majority of pre-Pleistocene alkaline mafic magmatic activity in Italy and have been described from several localities. The age of magmatism ranges from Triassic to Lower Oligocene. Some contain appreciable amounts of carbonate. The primary carbonate of the Italian carbonatitic lamprophyres is mainly Sr- or Mn-rich calcite that occurs mostly as immiscible ocelli or as groundmass. Its textural occurrence, composition, and relationship with co-precipitating silicate phases is taken as evidence of an igneous origin. Low BaO and REE contents in the carbonate are explained by early crystallization of essential mica and subordinate apatite. Whole rock analyses and isotopic data (Rukhlov, A.S., Bell, K., Vichi, G., Stoppa, F., submitted for publication. The heterogeneous deep mantle: the Sr, Pb and Nd isotopic evidence from Early Cretaceous alkaline lamprophyres of Southern Tuscany, Italy. Lithos.) suggest a mantle origin for these rocks and rule out contamination in either high or low pressure regimes. The bulk compositions of the carbonatitic lamprophyres have high HFSE / LILE and LREE / HREE ratios and although the abundances of these elements are generally lower than for carbonatites s.s., they are comparable with the abundances in other ‘carbonate-free’ Italian lamprophyres and Italian carbonatites, suggesting similar mantle sources. Moreover, the age of the Italian lamprophyres, ranging from Middle Triassic to Lower Oligocene, is much greater than the Pleistocene age of Italian carbonatites and indicates that the source remained similar over a long time span.  相似文献   

Origin of early Cretaceous calc-alkaline lamprophyres from the Sulu orogen in eastern China: implications for enrichment processes beneath continental collisional belt   总被引：13，自引：0，他引：13  

Feng Guo  Weiming Fan  Ming Zhang 《Lithos》2004,78(3):291-305

K-Ar dating, major- and trace-element and Sr-Nd isotopic analyses were carried out for early Cretaceous (122-127 Ma) lamprophyres from the Sulu orogen in eastern China. The results show strong fractionation in rare-earth elements with (LREE) >100 times chondrite, but HREE <10 times chondrite, indicating the presence of residual garnet in the melting source. These rocks are characterized by significant LILE and LREE enrichment but Nb and Ta depletion with moderate Zr/Hf (39.8-50.8 with regard to 36 for primitive mantle) and Nb/Ta (17.8-23.0, compared with 17.5 for primitive mantle) fractionations, probably as a consequence of carbonate- and rutile-rich melt metasomatism induced by dehydration and/or melting of subducted continental slab at mantle depths. Age-correlated Sr-Nd isotope ratios show moderate ranges of ⁸⁷Sr/⁸⁶Sr(i) from 0.70787 to 0.70934 and −17.2 to −11.6 of ε_Nd(t). The lamprophyres from the Sulu orogen were derived from decompression melting of such a metasomatized lithospheric mantle that was mainly composed of phlogophite garnet peridotites and experienced crystal fractionation of a mineral assemblage of olivine+clinopyroxene±plagioclase en route to the surface. Such geochemical and isotopic signatures are also prevalent in the contemporaneous basaltic lavas in the Dabie-Sulu belt, suggesting predominant enrichment processes by carbonate- and rutile-rich metasomatic assemblage beneath the continental collisional belt.  相似文献   

滇西北衙煌斑岩的岩石成因及动力学背景:年代学、地球化学及Sr-Nd-Pb-Hf同位素约束   总被引：11，自引：7，他引：4  

和文言  莫宣学  喻学惠  董国臣  和中华  黄雄飞  李小伟  姜丽莉 《岩石学报》2014,30(11):3287-3300

北衙地区出露有多条煌斑岩脉,锆石LA-ICP-MS定年表明岩脉的侵位时间为34.96±0.66Ma,与滇西地区新生代岩浆活动的高峰期一致.岩石地球化学分析表明北衙煌斑岩具有高钾(K₂O/Na₂O为1.03~10.38)、富碱((K₂O+Na₂O)(平均7.55%)、高Mg^#(30~73),富集大离子亲石元素(LILE)(K、Rb、Ba)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土元素的特征.同位素以高(⁸⁷Sr/⁸⁶Sr)_i(0.70615~0.70825),低ε_Nd(t)(-5.3~-1.3),富集放射性Pb(²⁰⁸Pb/²⁰⁴Pb=38.542~38.856,²⁰⁷Pb/²⁰⁴Pb=15.553~15.617,²⁰⁶Pb/²⁰⁴Pb=18.482~18.612)为特征,¹⁷⁶Hf/¹⁷⁷Hf为0.282631~0.282882,ε_Hf(t)为-4.2~1.8.岩石地球化学和同位素特征表明该煌斑岩源自经俯冲板片交代富集了的岩石圈地幔,推测源区可能为含金云母的尖晶石相橄榄岩地幔与石榴石相橄榄岩地幔的过渡区,起源深度大致在75~85km,明显高于同区富碱斑岩的起源深度.构造和地球动力学背景分析表明,该煌斑岩以及滇西地区新生代岩浆作用都是对印度-欧亚大陆强烈碰撞的响应,都产在强烈伸展的动力学背景下,为岩石圈减薄的产物.  相似文献