【摘要】 在华北克拉通陆续发现有大量的古元古代末-中元古代早期A-型花岗岩,它们具有独特的地球化学特征和特定的形成条件,可为进一步了解A-型花岗岩的岩石成因以及华北克拉通由结晶基底的形成向稳定盖层发育时期构造环境的转折提供重要依据。本文对华北克拉通南缘产出的垣头花岗岩体进行了岩石学、锆石U-Pb年代学、元素地球化学和Nd-Hf-O同位素研究。结果表明,垣头岩体岩石类型主要为正长花岗岩,形成时代为1841±4Ma;全岩样品具有较高的铁（FeO^T/（FeO^T+MgO）=0. 75～0. 86）、富碱（K₂O+Na₂O=8. 11%～9. 13%,K₂O/Na₂O> 1）、低MgO （0. 28%～0. 56%）、P₂O₅（0. 04%～0. 08%）和MnO（0. 03%～0. 04%）,富含大离子亲石元素（如Rb、Th、U、K）、亏损高场强元素（Nb、Ta、Zr、Hf）,具有Eu、Sr负异常,高10,000Ga/Al比值（> 2. 76）、准铝质-弱过铝质且不含碱性暗色矿物,属于铝质A-型花岗岩;全岩εNd（t）=-4. 68、tC DM=2. 70Ga,锆石εHf（t）=-12. 0～-4. 71、tC8DM=3. 22～2. 78Ga,锆石δ1O=5. 4‰～6. 5‰（加权平均值为6. 1‰）,指示它们是古老基底物质部分熔融的产物。结合区域上的地质特征和研究资料,我们认为垣头A-型花岗岩体形成于碰撞后的伸展环境,标志着华北克拉通1. 85Ga前后的造山运动的结束。更多还原

【Abstract】 The North China Craton（ NCC） has been successively recognized many Late Paleoproterozoic to Early Mesoproterozoic Atype granites,showing unique geochemistry characteristics and particular formation environment,which would provide further important insights into their petrogenesis and tectonic transition from the formation of crystalline basement to the deposition of stable sedimentary cover in NCC. Here we report systematic investigation on petrology,geochronology,elemental geochemistry,and Nd-Hf-O isotopic characteristics of the Yuantou pluton in the southern margin of the NCC. The results show that the Yuantou pluton mainly consists of syenogranite,which was emplaced at 1841 ± 4 Ma. All rocks are rich in ferroan（ FeO T/（ FeO T+ MgO） = 0. 75 ～ 0. 86） and alkaline（ K₂O + Na₂O = 8. 11% ～ 9. 13%,K₂O/Na₂O > 1）,but poor in MgO（ 0. 28% ～ 0. 56%）,P₂O₅（ 0. 04% ～ 0. 08%） and MnO（ 0. 03% ～ 0. 04%）. Additionally,they show enrichment of LILEs（ Rb,Th,U,K）,depletion of HFSEs（ Nb,Ta,Zr,Hf） with negative Eu and Sr anomalies. Their high 10,000 Ga/Al ratios（ > 2. 76） with metaluminous to peraluminous characteristics,containing biotite without alkali mafic minerals,show an affinity to aluminous A-type granite. The Late Paleoproterozoic A-type granite displays low whole-rock εNd（ t） value（-4. 68） with two-stage Nd model age of 2. 70 Ga,low zircon εHf（ t） values（-12. 0 ～-4. 71） with zircon two-stage Hf model ages of 3. 22 ～ 2. 78 Ga,and high zircon δ¹⁸O values（ 5. 4‰ to 6. 5‰,weighted mean = 6. 1‰）,indicating that the Yuantou A-type granite was derived predominantly from partial melting of the ancient continental crust. Combined with above results and regional geological data,the Yuantou A-type granite was related to the underplating of mafic magmas in a post-collisional regime,marking the end of ～ 1. 85 Ga orogenic movement in the NCC.更多还原