| 冀北窟窿山复式岩体年代学、地球化学特征及岩石成因 |
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| 引用本文： | 郭佳磊,巫建华,牛子良,张韶华,吴仁贵,刘帅.冀北窟窿山复式岩体年代学、地球化学特征及岩石成因[J].高校地质学报,2019,25(1):33. |
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| 作者姓名： | 郭佳磊 巫建华 牛子良 张韶华 吴仁贵 刘帅 |
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| 作者单位： | 东华理工大学核资源与环境国家重点实验室培育基地,南昌330013;东华理工大学地球科学学院,南昌330013;核工业243地质大队,赤峰,024006;东华理工大学地球科学学院,南昌,330013;东华理工大学核资源与环境国家重点实验室培育基地,南昌,330013 |
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| 基金项目： | 国家自然科学基金;中国核工业集团公司项目 |
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| 摘 要： | 窟窿山复式岩体位于赤峰-开原断裂以南、尚义-平泉断裂带以北的华北克拉通北缘隆起带和沽源-红山子铀成矿带
的西南段，由外侧的中粗粒碱长花岗岩和内侧的中细粒碱长花岗岩组成，两者呈侵入接触，出露面积约120 km2。SHRIMP
锆石U-Pb年龄表明，中粗粒碱长花岗岩和中细粒碱长花岗岩锆石的206Pb/238U年龄分别为129.4±1.5 Ma （MSWD=1.2） 和
134.0±1.7 Ma（MSWD=1.8），分别形成于早白垩世晚期和早白垩世早期。窟窿山花岗岩具有高硅，富钾、钠，高FeOT/MgO
比值，贫铝、镁、钙、磷的高分异特征，属准铝质-弱过铝质高钾钙碱性系列岩石。在SiO2 vs (Na2O+K2O)-CaO和SiO2 vs
FeOT/(FeOT+MgO)图解中落于A型花岗岩区。ΣREE含量较低，Eu负异常明显，具燕式轻稀土富集型稀土配分曲线特征。富
集Rb，Th，U，Nb，Ta，Zr，Hf，Y等元素，亏损Sr，Ba，P，Ti等元素，10000Ga/Al=4.63~5.66(＞2.6)，Zr+Nb+Ce+Y=402×
10-6~713×10-6(＞350×10-6)，显示A型花岗岩微量元素的特征。具有异常的Sr初始比值((87Sr/86Sr)i =0.750562~0.839814)，较低
的Nd初始比值(εNd(t)= -14.3~-13.2)和相对较年轻的Nd模式年龄(TDM2=2084~1996 Ma)及较低的Pb同位素组成：(206Pb/204Pb)t=
16.797~17.010, (207Pb/204Pb)t=15.406~15.434, (208Pb/204Pb)t=37.477~37.540。中粗粒碱长花岗岩和中细粒碱长花岗岩的δ18OV-SMOW分
别为5.3‰~6.2‰和0.1‰~3.1‰，后者低于正常花岗岩的δ18OV-SMOW 值（6‰~10‰） 和正常地幔的δ18OV-SMOW （5.7‰±0.3‰）
值，在铅同位素图解中窟窿山花岗岩同时带有下地壳物质和富集地幔印记，构造环境判别图解显示窟窿山花岗岩属于板内
后造山花岗岩，形成于板内伸展拉张构造背景。通过与区域上同时代A型花岗岩的对比，表明窟窿山花岗岩是华北克拉通
北缘早白垩世与岩石圈减薄相关的伸展构造体制下的产物，这种构造体制可能与太平洋板块的俯冲作用有关。综上所述，
窟窿山花岗岩的成因为古元古代源于EMI富集地幔的岩浆混有少量古老下地壳物质形成年轻下地壳，可能还与俯冲的经历
了高温热液蚀变的洋壳有关，但由于源区混染不均一导致花岗岩的氧同位素值存在差异，至早白垩世板内拉张构造环境下
发生部分熔融产生的岩浆在上侵过程中形成窟窿山花岗岩。
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| 关 键 词： | 花岗岩成因 地球化学 Sr-Nd-Pb-O同位素 早白垩世 窟窿山 |
Petrogenesis of the Kulongshan Complex Pluton in Northern Hebei:Chronologic and Geochemical Constraints |
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| GUOJialei,WUJianhua,NIU Ziliang,ZHANG Shaohua,WURengui,LIU Shuai.Petrogenesis of the Kulongshan Complex Pluton in Northern Hebei:Chronologic and Geochemical Constraints[J].Geological Journal of China Universities,2019,25(1):33. |
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| Authors: | GUOJialei WUJianhua NIU Ziliang ZHANG Shaohua WURengui LIU Shuai |
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| Abstract: | The Kulongshan complex pluton is situated in the northern margin uplift belt of North China Craton and Southwest section of
the Guyuan-Honshanzi uranium belts, which occur between the Chifeng-Kaiyuan fault zone and Shangyi-Pinquan fault zone. The
Kulongshan complex pluton consists of medium-fine alkali-feldspar granite in the middle and medium-coarse alkali-feldspar granite in
the rim, both displaying intrusive contacts and a exposed area of 120 km2. SHRIMP zircon U-Pb dating indicates that the zircon 206Pb/
238U age of medium-coarse alkali-feldspar granite is 129.4±1.5 Ma (MSWD=1.2), and medium-fine alkali-feldspar granite is 134.0±1.7 Ma
(MSWD=1.8). These ages suggest that the granites were formed in the late stage of Early Cretaceous and in the early stage of Early
Cretaceous. Kulonghsan granites show high differentiation features of enrichment in Si, K, Na and high ratios of FeOT/MgO, low
contents of Al, Mg, Ca, P, belonging to the peraluminous-weak high potassium calcium alkaline series rocks. In the SiO2 vs (Na2O +
K2O)-CaO and SiO2 vs FeOT/(FeOT +MgO) diagrams, allthese rocks fall into the Atype granite area. They have low rare earth elements
(REE) contents and display swallow type chondrite-normalized distribution patterns with a distinct negative Eu anomaly. These rocks are
enriched in Rb, Th, U, Nb, Ta, Zr, Hf, Y, and other elements, and are depleted in Sr, Ba, P, Ti, and other elements. These rocks also
display 10000 Ga/Al ratios of 4.63~5.66(＞2.6) and Zr+Nb+Ce+Y values of 402×10-6~713×10-6(＞350×10-6), showing trace element
features of A- type granite. The Kulongshna granites with abnormal initial ratios of Sr: (87Sr/86Sr)i=0.750562~0.839814, relatively low
Nd: εNd(t) =-14.3~-13.2 and young Nd mode age: TDM2=2084~1996 Ma, they exhibit low radiogenic Pb isotopic compositions: (206Pb/
204Pb)t=16.797~17.010, (207Pb/204Pb)t=15.406~15.434, (208Pb/204Pb)t=37.477~37.540. δ18OV-SMOW in medium-coarse alkali-feldspar granites
and medium-fine alkali-feldspar granites were 5.3‰~6.2‰ and 0.1‰~3.1‰, the latter is lower than the normal values of granite (6‰~
10‰) and mantle (5.7‰±0.3‰). The Kulongshan granites have fingerprint of lower crust and enriched mantle in Pb isotope diagrams.
In the tectonic setting discrimination diagrams, the Kulongshan granites belong to the intraplate post orogenic granites, which were
formed in the extensional tectonic setting. Compared with the A type granite of the same age, the Kulongsahn granites were likely the
product of an extensional tectonic system related to the Early Cretaceous and craton destruction in the northern margin of the North
China Craton. This tectonic setting may be related to the subduction of the Pacific Plate. In conclusion, petrogenesis of the Kulongshan
granites can be explained by EM I enriched mantle magma mixed with a small amount of younger crust that were fractionated from
ancient crust material in the Palaeoproterozoic. The genesis of these granites was also likely related to the subducted oceanic slab which
experienced high temperature hydrothermal alteration. However, because the source area was mixed unevenly leading to different
oxygen isotope values of granites, by the Early Cretaceous, the magma formed by partial melting intruded in an intraplate extensional
environment, producing the Kulongshan granites. |
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| Keywords: | granite petrogenesis geochemistry Sr-Nd-Pb-O istopes Early Cretaceous Kulongshan |
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