阴山东部固阳地区晚石炭世碱性火山岩的发现及其地质意义  

Discovery of the Late Carboniferous alkaline volcanic rocks in the Guyang area,eastern Yinshan Block,and its geological implications

作　　者：朱伟鹏 田伟[1] 魏春景[1] ZHU WeiPeng;TIAN Wei;WEI ChunJing(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871

出　　处：《岩石学报》2023年第3期670-688,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42030304、42202047);国家重点研发计划课题(2017YFC0601302)联合资助。

摘　　要：在华北克拉通北缘阴山地块东部固阳地区发现了假白榴石粗面玄武岩和钾质粗面岩两种高钾准铝质碱性火山岩。地质年代学数据显示,假白榴石粗面玄武岩的磷灰石U-Pb年龄为322±14Ma,钾质粗面岩的锆石U-Pb年龄为315.6±7.5Ma,说明其形成时代均为晚石炭世。岩石地球化学特征显示,二者均富Al、Fe,贫Mg;富集大离子亲石元素(如Rb、Ba和K),相对亏损高场强元素(如Ta、Nb和Ti),轻重稀土分异明显,富集轻稀土,相对亏损重稀土,Eu异常不明显;高(87Sr/86Sr)i比值(0.710028~0.714745),低εNd(t)值(-9.0~-17.2),表现出相似的交代岩石圈地幔源区和地壳混染特征。将该碱性火山岩与兴蒙造山带晚石炭世-早二叠世中基性火山岩和阴山地块白垩纪中基性火山岩进行岩石类型对比,发现华北克拉通北缘产出的火山岩多为高钾碱性系列,而兴蒙造山带中产出的火山岩则多为钙碱性系列;与兴蒙造山带晚石炭世-早二叠世中基性火山岩进行岩石成因对比,发现它们的岩浆源区和混染程度并不相同,即固阳地区碱性火山岩为受到早古生代俯冲沉积物交代的岩石圈地幔部分熔融所形成的岩浆在上升过程中混染华北克拉通TTG片麻岩后喷发的产物,而兴蒙造山带中火山岩的产出则多为亏损地幔部分熔融所形成的岩浆在上升过程中轻度混染地壳物质后喷发的结果。在固阳地区发现晚石炭世碱性火山岩,代表着古亚洲洋在该时期的后造山伸展作用范围已延伸至华北克拉通北缘。Two types of high-potassium metaluminous alkaline volcanic rocks, pseudoleucite trachybasalt and potassium trachyte, have been found in the Guyang area, eastern Yinshan Block, and northern margin of North China Craton(NCC). Geochronology data show that the apatite U-Pb age of pseudoleucite trachybasalt is 322±14 Ma and the zircon U-Pb age of potassium trachyte is 315.6±7.5 Ma respectively, indicating that these alkaline volcanic rocks were formed in the Late Carboniferous. Geochemical analyses show that both of the two type rocks have high Al, Fe, and low Mg, enriched in large ion lithophile elements(such as Rb, Ba and K), and relatively depleted in high field-strength elements(such as Ta, Nb and Ti). The rare earth elements of them are obviously differentiated, i.e., they are enriched in light rare earth elements and relatively depleted in heavy rare earth elements, without obvious Eu anomaly. Furthermore, they have high(87Sr/86Sr)iratios(0.710028~0.714745), low εNd(t) values(-9.0~-17.2). All these characteristics show that the alkaline volcanic rocks are derived from a same metasomatic lithospheric mantle source and have experienced a similar crustal contamination. Comparing the alkaline volcanic rocks with the Late Carboniferous-Early Permian intermediate-basic volcanic rocks exposed in Xing’an-Mongolia Orogenic Belt(XMOB) and the Cretaceous intermediate-basic volcanic rocks exposed in Yinshan Block, it is found that the volcanic rocks produced in the northern margin of NCC are mostly high-potassium alkaline series, while most of the volcanic rocks produced in XMOB are calc-alkaline series. Comparing the alkaline volcanic rocks with the Late Carboniferous-Early Permian intermediate-basic volcanic rocks exposed in XMOB, it is found that their magma sources and contamination levels are different: the alkaline volcanic rocks in the Guyang area are the products of magma formed by the partial melting of lithospheric mantle metasomatized by the Early Paleozoic subduction sediments, which erupted after mixing wi

关 键 词：华北克拉通北缘 固阳地区 碱性火山岩 晚石炭世 部分熔融 古亚洲洋 后造山伸展作用 

分 类 号：P588.143[天文地球—岩石学] P597.3[天文地球—地质学]