摘要
详细的地球化学分析表明,普朗复式岩体侵入岩的SiO2含量为60.87%~65.86%,岩石富铝(Al2O3为12.57%~15.59%)、富碱(K2O+Na2O为4.66%~8.47%,K2O/Na2O=0.25~2.85,平均为1.27),具准铝质(A/CNK=0.76~0.98)的特点。富集大离子亲石元素(K、Rb、Ba、Sr),亏损高场强元素(Nb、Hf、P、Ti),稀土总量中等(REE=(115.62~212.85)×10-6),无明显的δEu、δCe异常。这些岩石学特征表明,岩石属高钾钙碱性系列和准铝质的I型花岗岩。锆石LA-ICP-MS定年结果显示,石英闪长玢岩侵位于(220.5±3.2)^(220.8±4.1)Ma;石英二长斑岩侵位于(214.8±1.4)^(215.9±3.1)Ma,其锆石的εHf(t)值分别为-8.27^-3.1(平均为-5.58)和-6.64^-4.07(平均为-5.24),对应的二阶段模式年龄为1 107~1 409 Ma和1 175~1 319Ma。在εHf(t)-U-Pb年龄图解中,所有样品均落入球粒陨石线以下,距同时期亏损的地幔演化线距离较远。岩石地球化学特征及Hf同位素组成表明,普朗复式斑岩体的形成不可能单纯源于中元古代时期基底变质岩的部分熔融,也有基性岩浆岩的部分熔融,这表明岩石的成岩过程有幔源组分的参与。
Geochemical researches indicate that the porphyries from Pulang composite intrusion having SiO2 60. 87%- 65.86%, are enriched in alumina（Al2O3 12.57%- 15.59%）with high alkaline（K2O＋Na2O 4. 66%- 8.47%, K2O/Na2O=0.25 -2.85, average of 1.27）and are metaluminous（A/CNK=0. 76 -0. 98）. The rocks are moderate in REE concentration （REE = （ 115. 62 - 212. 85） × 10^-6 ） and without obvious 8Eu and 8Ce anomaly, showing relatively enriched in large ion lithophile elements （K, Rb, Ba, Sr）, and relatively depleted in high-field strength elements （Nb, Hf, P, Ti）, suggesting the nature of high-K calc alkaline series and metaluminous I-type granite. Zircon LA-ICP-MS dating shows that the quartz diorite porphyrite emplaced at （220. 5±3. 2）-（220. 8±4. 1） Ma, and quartz monzonite porphyry emplaced at （214. 8±1.4）-（215.9±3. 1） Ma. The zircon εHf（t） values range from -8. 27 to -3. 1（average of 5. 58） and 6. 64 to -4. 07（average of -5.24）, with corresponding two stage model ages ranging from 1107 to 1409 Ma and 1175 to 1319 Ma. In the plot of εHf （t） values versus U-Pb ages, all samples are plotted in the region below the chondrite evolution line with a distance from the depleted mantle evolution line of the same period. Geochemical characteristics and Hf isotopic composition show that the formation of Pulang compound porphyry may be not simply due to the partial melting of basement metamorphic rock in the Middle Proterozoic period, but also due to the partial melting of preexisting basic magmatic rocks, which indicates that the petrogenic process of the rocks may be involved with the participation of mantle components.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2013年第5期57-74,共18页
Earth Science Frontiers
基金
国家重点基础研究发展计划'973'项目(2009CB421007)
中央高校基本科研业务费专项资金资助项目(2011PY0154)
中国地质调查局项目'滇西北地区斑岩成矿系统研究与靶区优选'
