酸性火山岩早成岩期岩矿特征及其地质意义——以新西兰北岛Taupo火山带Waiotapu地热区火山喷口堆积物为例  

Petrological Features and Geological Significance of Acid Volcanic Rock at the Early Diagenesis Stage: A case study of modern volcanic crater deposits in the Waiotapu geothermal area, Taupo Volcanic Zone, North New Zealand

作　　者：杨奕曜 柳益群[1] 周鼎武[2] 焦鑫[1] 岳祯奇 乔江华 YANG YiYao;LIU YiQun;ZHOU DingWu;JIAO Xin;YUE ZhenQi;QIAO JiangHua(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China;College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266510,China)

机构地区：[1]大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]山东科技大学地球科学与工程学院,山东青岛266510

出　　处：《沉积学报》2019年第3期466-476,共11页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41572086,41802120);中国博士后科学基金(2018M633557)~~

摘　　要：新西兰北岛Waiotapu地热区位于Taupo火山带中部,以发育众多的第四纪酸性火山岩而闻名。通过 X衍射、电子探针、扫描电镜、激光拉曼等方法对区内一处于活动间歇期的小型火山口堆积物岩矿特征及特殊结构进行研究。结果表明,火山口堆积物可分为3类:1)球粒流纹岩,矿物组成为:α方石英-PO鳞石英—正长石、奥长石、紫苏辉石—钛铁矿(钛磁铁矿);2)流纹质晶屑熔结凝灰岩,矿物组成为:奥长石晶屑、塑性玻屑;3)硫磺土,矿物组成为:单质硫、长英质细粒岩屑。结合前人实验矿物学结论后认为,球粒流纹岩中的球粒体为富火山玻璃的流纹岩喷出堆积后在热水作用下脱玻化形成的,是酸性火山岩早成岩期表生蚀变阶段的标志;而流纹质熔结凝灰岩则为岩浆喷溢出地表后,在塑性流动中冷凝结晶形成的,是酸性火山岩早成岩期冷凝固结阶段的标志。在此基础上,提出了Waiotapu地热区酸性火山岩的表生蚀变模式,为酸性火山岩冷凝固结—表生蚀变阶段的岩矿特征及蚀变作用研究提供现代对比实例。The Waiotapu geothermal system is located in the centre of the Taupo Volcanic Zone of New Zealand,famous for numerous silicic volcanics. Through X-ray diffraction,electron probe,SEM,and the laser Raman test,we examine the petrological and mineralogical features and the genesis of special structures from acid volcanic rock in the period of condensing consolid-supergene reformation. We determined that there are three types of the deposits in the crater: 1) Spherulite rhyolite,with the following mineral composition:α-cristobalite,po-tridymite,and orthoclase;Plagioclase phenocryst;Hypersthene and titanomagnetite (ilmenite). 2) Rhyolitic ignimbrite: Plagioclase phenocryst;Plastic glass. 3) Sulfur: Powdered sulphur;Felsic fine-grained detrital rock. Comprehensively,spherulite rhyolite is formed by a volcanic glass-rich rhyolite devitrified from volcanic glass under the effect of a hydrotherm,which is a sign of supergene reformation in acidic volcanic rocks. Rhyolitic ignimbrite is formed by the crystallization of rhyolitic magma during the plastic flow process after they reach the surface,which is a sign of cooling until the rock becomes a condensing consolid in acidic volcanic rocks. According to the sedimentary characteristics,a pattern of supergene reformation in acid-volcanic rock has been established,which provides a modern sample for the study of condensing consolid-supergene reformation of acid- volcanic rock.

关 键 词：Waiotapu 酸性火山岩 岩石矿物学特征 冷凝固结-表生蚀变阶段 

分 类 号：P588.14[天文地球—岩石学]