CAJ | 학술논문

阿尔泰造山带喀纳斯地区出露一套钾质富镁英安岩,锆石U-Pb定年显示其形成于早泥盆世(411±4 Ma).该套英安岩富SiO_2(64.71～67.77 wt%),MgO(3.28～3.53 wt%)和K_2O(2.12～2.75 wt%),贫Na_2O(1.70～1.85 wt%),K_2O/Na_2O比值介于(1.20～1.53),具较高的Al_2O_3(14.12～15.33 wt%)和较低的CaO(1.12～1.28 wt%),ASI指数＞1.8,显示过铝质钙碱性岩浆系列特征,明显不同于初始的高镁安山质岩浆.样品具有中等的Cr(134×10~(-6)～153×10~(-6))、Co(17.47×10~(-6)～18.65×10~(-6))、Ni(71.64×10~(-6)～80.76×10~(-6))含量,富集大离子亲石元素Rb、K和高场强元素U、Th、Pb及LREE,发育Sr、Ba及"TNT"(Ta、Nb、Ti)负异常,显示俯冲带岩浆岩地球化学特征.其高的Mg~#(51.71～52.47)和低的ε_(Nd)(f)值(-4.6～-4.2)说明该套火山岩可能来自遭受强烈交代作用的地幔楔部分熔融.样品具有较高的Ba/La、Pb/La比值和较低的Th/Yb、Nb/Y比值,显示地幔交代作用以俯冲沉积物熔体的交代作用为主.以上地球化学特征说明,喀纳斯钾质富镁英安岩可能主要是受俯冲沉积物熔体交代的上覆地幔橄榄岩部分熔融的产物,阿尔泰泥盆纪处于俯冲作用相关的活动大陆边缘构造环境.此外,该套火山岩的形成时代制约了其下覆的哈巴河群沉积上限,显示哈巴河群沉积于早泥盆世之前.
아이태조산대객납사지구출로일투갑질부미영안암,고석U-Pb정년현시기형성우조니분세(411±4 Ma).해투영안암부SiO_2(64.71～67.77 wt%),MgO(3.28～3.53 wt%)화K_2O(2.12～2.75 wt%),빈Na_2O(1.70～1.85 wt%),K_2O/Na_2O비치개우(1.20～1.53),구교고적Al_2O_3(14.12～15.33 wt%)화교저적CaO(1.12～1.28 wt%),ASI지수＞1.8,현시과려질개감성암장계렬특정,명현불동우초시적고미안산질암장.양품구유중등적Cr(134×10~(-6)～153×10~(-6))、Co(17.47×10~(-6)～18.65×10~(-6))、Ni(71.64×10~(-6)～80.76×10~(-6))함량,부집대리자친석원소Rb、K화고장강원소U、Th、Pb급LREE,발육Sr、Ba급"TNT"(Ta、Nb、Ti)부이상,현시부충대암장암지구화학특정.기고적Mg~#(51.71～52.47)화저적ε_(Nd)(f)치(-4.6～-4.2)설명해투화산암가능래자조수강렬교대작용적지만설부분용융.양품구유교고적Ba/La、Pb/La비치화교저적Th/Yb、Nb/Y비치,현시지만교대작용이부충침적물용체적교대작용위주.이상지구화학특정설명,객납사갑질부미영안암가능주요시수부충침적물용체교대적상복지만감람암부분용융적산물,아이태니분기처우부충작용상관적활동대륙변연구조배경.차외,해투화산암적형성시대제약료기하복적합파하군침적상한,현시합파하군침적우조니분세지전.
Potassic magnesian-rich dacites occur to the south of the Kanasi,Ahai,northwestern Chinese.U-Pb dating of zircons from these rocks yields an early Devonian age of 411±4 Ma.The dacites are enriched in SiO_2(64.71～67.77 wt%),MgO(3.28～3.53 wt%)and K_2O (2.12～2.75 wt%),and depleted in Na_2O(1.70～1.85 wt%).The rocks have low CaO content(1.12～1.28 wt%),high Al_2O_3 content(14.12～15.33 wt%)and K_2O/Na_2O ratios (1.2～1.6),and ASI indexes larger than 1.8,indicating features of peraluminous potassic calc-alkali igneous rocks,which are clearly different to primitive High-Mg andesites.The dacites possess moderate Cr(134×10~(-6)～153×10~(-6)),Co(17.5×10~(-6)～18.7×10~(-6)),and Ni (72×10~(-6)～81×10~(-6))contents.These rocks are enriched in LREEs,large ion lithophile elements(e.g.Rb,K)and high field strength element(e.g.U、Th、Pb)with moderate Sr,Ba,and"TNT"(Ta,Nb,Ti)negative anomalies,showing geochemical characteristics of igneous rocks in subduction zone.Their high Mg~#(51.7～52.5)and low ε_(Nd)(t)ratios(-4.6～-4.2)imply partial melting of metasomatic peridotites in the mantle wedge.The relative high Ba/La,Pb/La and low Th/Yb,Nb/Y ratios suggest that the metasomatism of mantle peridotites was predominated by the melts of subducted sediments.Therefore,the above geochemistry indicates that the potassic magnesian-rich dacites were originated from the partial melting of metasomatic mantle peridotites mainly altered by the melts of subducted sediments,showing an active continental margin in the Devonian.In addition,the timing of the potassic magnesian-rich dacites provides a good constrain on the minimum depositional age of the underlying Habahe group and suggests the sediments of the group deposited before the early Devonian.