摘要
绿岩带记录了早期地球岩浆活动和表生环境的丰富信息,是揭示地质演化历史和规律的重要研究对象。鲁西地区的泰山岩群具有典型的绿岩带组合,其中雁翎关和柳杭岩组的变质玄武岩是新太古代火山岩系的代表,广泛分布于鲁西中部地区,对还原鲁西新太古代的地质演化过程具有重要意义。在七星台地区雁翎关岩组变质玄武岩中存在变安山岩夹层,对其进行锆石SHRIMP U-Pb定年,11颗岩浆锆石的207Pb/206Pb加权平均年龄为2744±12Ma（MSWD=1.6）,表明区域内雁翎关岩组的变质玄武岩系形成于～2.7Ga。地球化学研究显示七星台地区泰山岩群雁翎关岩组的变玄武岩主体属于亚碱性高铁拉斑玄武岩系,它们的Si O2含量为48.2%～51.6%,Mg O介于3.22%～7.66%之间,Ti O2含量为0.63%～1.78%,主量元素Si O2、Ti O2、Al2O3和Fe O与Mg O都没有明显的协变关系。球粒陨石标准化稀土配分模式有两类,多数以轻稀土弱富集为特征,稀土总量为47.5×10-6～143.8×10-6,少数样品的轻稀土弱亏损,配分模式与N-MORB接近。七星台地区雁翎关岩组变玄武岩的主、微量元素组成和演化趋势与区域内柳杭岩组中低Ti和高Ti变质玄武岩都有差别。在Nb/Th与Nb/La、（La/Sm）CN和Ti/Ti＊的协变关系图解中,雁翎关岩组一部分样品与现代和一些新太古代岛弧玄武岩的成份类似,另一部分具有接近原始地幔的Nb/Th、（La/Sm）CN和Ti/Ti＊比值。这些地球化学特征暗示泰山岩群的雁翎关岩组很可能与北美、西澳和印度等新太古代早期形成的绿岩带火山岩系类似,由科马提岩-拉斑玄武岩和拉斑玄武岩、钙碱性玄武岩及安山岩两类火山岩组合复合而成,鲁西在新太古代早期的演化历史比目前的认识更加复杂。
The Archean greenstone belts preserve important information on the magmatism and sedimentary environment in the early earth. The Taishan Group, exposed in the western Shandong Province, is a typical greenstone association in the North China Craton. The meta-basalts from the Yanlingguan and Liuhang formations of the Taishan Group are widespread in the central belt of the western Shandong Province. Geochemical studies on these basahs offer critical constraints on the regional Neoarchean geological and geodynamic processes. We report a weighted mean SHRIMP 207Tpb/206Pb zircon age of 2744 ＋ 12Ma（ MSWD = 1.6）for meta-andesites interlayered with meta-basahs, constraining the timing of the basaltic sequence of the Yanlingguan Formation to be -- 2.7Ga. The basaltic lavas in the Yanlingguan Formation of the Taishan Group display sub-alkaline high-Fe tholeiite geochemical affinities. They show a range of major element composition with 48.2%-- 51.6% SiO2,3.22% -- 7.66% MgO and 0. 63% -- 1.78% TiO2. The MgO vs. SiO2, TiO2, Al2O3 and FeO plots do not show any systematic correlation. Most of the basaltic samples in this study display slight enrichment of LREE on chondrite-normalized diagrams, with total REE contents of 47. 5 × 10-6 ～ 143.8× 10-6 whereas the others show N-MORB-like REE pattern. The geochemical features of the tholeiites from the Yanlingguan Formation in this study distinguish them from both the low-Ti and high-Ti basaltic lavas of the Liuhang Formation. On the Nb/Th vs. Nb/La, （La/Sm）cN and Ti/Ti ＊ diagrams, part of the samples from the Yanlingguan Formation shows composition similar to the Neoarehean and modem island arc basahs whereas the others are characterized by Nb/Th, （La/Sm）CN and Ti/Ti＊ ratios similar to those of the primitive mantle. The geochemical features of all the studied basalts suggest that the protoliths of the Yanlingguan Formation might correspond to komatiite- tholeiite and cal-alkaline sequences.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第10期2959-2973,共15页
Acta Petrologica Sinica
基金
国家自然科学重点基金项目(41430210)
青年基金项目(41302156)
中国地质调查局地质大调查项目(12120114061901)联合资助
关键词
绿岩带
雁翎关岩组
变质玄武岩
地球化学
鲁西
Greenstone belt
Yanlingguan Formation
Meta-basah
Geochemistry
Western Shandong
