台湾利吉蛇纹岩角砾碎屑岩地球化学特征及其指示意义

马里亚纳海沟弧前广泛发育来源于深部地幔楔、由泥火山作用形成的碎屑蛇纹岩,并且在泥火山顶部海底有非生物成因甲烷渗漏和无光合作用的自养生物群,是地球科学界的研究热点。在弧陆碰撞形成的台湾利吉混杂岩带发育有蛇纹岩角砾碎屑岩,一直有构造成因、沉积成因与构造沉积复合成因的争议。本次研究对台湾利吉蛇纹岩角砾碎屑岩的岩石学和地球化学进行了研究,蛇纹岩角砾碎屑岩呈层状或巨砾发育于台东利吉村附近的混杂岩泥质基质中,蛇纹岩角砾碎屑岩的角砾和粉砂质-泥质基质均由蛇纹岩组成,角砾呈次棱角状至次圆状,显示沉积成因特征。蛇纹岩角砾碎屑岩的Al₂O₃-MgO-CaO位于与蛇绿岩套有关的变质橄榄岩范围内,且偏低的Al₂O₃和CaO含量表明,其来源于活动大陆边缘俯冲带上盘的弧前环境。此外,蛇纹岩角砾富集As、Sb和Pb元素,暗示具有俯冲带上驮板块地幔楔蛇纹岩的特征,并富集来自俯冲板片的中低温流体。因此,利吉蛇纹岩角砾碎屑岩很可能来自俯冲带上盘地幔楔,由北吕宋火山岛弧弧前基底形成的蛇纹岩通过泥火山作用喷出海底,最后经弧陆碰撞进入台湾利...

Geochemical characteristics and their indicative significance of serpentine breccia clasolites in Lichi,Taiwan,China

Clastic serpentines derived from deep mantle wedges formed by mud volcanism are extensively developed in front of the Mariana trench;abiogenic methane leakage and autotr ophic biota without photosynthesis are found in the seabed at the top of a mud volcano,which is a research hotspot in the field of geosciences.Serpentine breccia clasolites are developed in the Lichi Mélange of Taiwan formed by arc-continent collision and their genesis has been controversial for tectonic origin,sedimentary origin,and tectonic-sedimentary origin.The petrology and geochemistry of serpentine breccia clasolites in the Lichi Mélange of Taiwan are studied in this paper.Serpentine breccia clasolites are stratified boulders developed in the mudstone matri x of the Mélange near Lichi village in eastern Taiwan.Both breccias and the silty-mudstone matrix are composed of serpentine.The breccias are subangular to subcircular,showing the characteristics of sedimentary genesis.Al2O3-MgO-CaO of the serpentine breccia clasolite is located in the range of metamorphic peridotite related to the ophiolite suite and its content of Al2O3 and CaO is low.This indicates that it has originated from the forearc environment of the upper plate of the subduction zone on the active continental margin.Furthermore,serpentine breccia enriches As,Sb,and Pb,suggesting that it has the characteristics of the mantle wedge serpentine of the piggyback plate in the subduction zone and enriches medium-low temperature fluids from the subduction plate.Therefore,the serpentine breccia clasolites of Lichi probably originated from the mantle wedge in the upper wall of the subduction zone.The serpentine probably formed in the basement of the arc front of North Luzon volcanic island and er upted into the seafloor by mud volcanism,to finally collide into Lichi Mélange by arc-continent collision.