CAJ | 학술논문

东准噶尔地区石炭纪巴塔玛依内山组火山岩分布广泛,规模巨大。对其岩石学、元素地球化学及同位素地球化学研究表明：1)该套火山岩岩石类型复杂,具玄武岩-安山岩-英安岩-流纹岩组合特征,属高钾钙碱性火山岩系,并富集大离子亲石元素(Sr、K、Rb、Ba、Th)和轻稀土元素,亏损高场强元素(Nb、Ta、Ti)和重稀土元素,87Sr/86Sr和143Nd/144Nd初始值分别为0.70385~0.71312,0.152378~0.512998,εNd(t)多介于3.0~6.2之间,显示了与俯冲消减作用相关的不成熟弧后盆地火山岩地球化学特征。2)火山岩物质来源以亏损地幔源为主,并混有少量主体由古生代残余洋壳、岛弧体系组成的年轻下地壳物质。其中,基性熔岩以亏损地幔源为主,并在岩浆源区与少量新生地壳物质发生了近乎完全的壳-幔岩浆混合和Sm-Nd同位素体系均一化,其形成很可能与俯冲沉积物和(或)俯冲洋壳变质脱水产生的流体引起上覆地幔楔物质的部分熔融有关；而酸性熔岩与基性熔岩存在明显的不同,酸性熔岩是少量幔源岩浆经强烈结晶分异和经历较多壳源物质混染的结果。3)玄武岩全岩 Sm-Nd等时线年龄为319.7±5.9 Ma,与区域地质构造背景和已有化石证据基本一致,代表了火山岩的形成时代。综合研究表明,东准噶尔地区320 Ma左右依旧存在古亚洲洋的俯冲消减作用,准噶尔古洋盆最终闭合时间应介于320~311 Ma之间。在此过程中,火山岩浆作用强烈,蕴含成矿物质丰富,东准噶尔地区找矿前景值得期待。
동준갈이지구석탄기파탑마의내산조화산암분포엄범,규모거대。대기암석학、원소지구화학급동위소지구화학연구표명：1)해투화산암암석류형복잡,구현무암-안산암-영안암-류문암조합특정,속고갑개감성화산암계,병부집대리자친석원소(Sr、K、Rb、Ba、Th)화경희토원소,우손고장강원소(Nb、Ta、Ti)화중희토원소,87Sr/86Sr화143Nd/144Nd초시치분별위0.70385~0.71312,0.152378~0.512998,εNd(t)다개우3.0~6.2지간,현시료여부충소감작용상관적불성숙호후분지화산암지구화학특정。2)화산암물질래원이우손지만원위주,병혼유소량주체유고생대잔여양각、도호체계조성적년경하지각물질。기중,기성용암이우손지만원위주,병재암장원구여소량신생지각물질발생료근호완전적각-만암장혼합화Sm-Nd동위소체계균일화,기형성흔가능여부충침적물화(혹)부충양각변질탈수산생적류체인기상복지만설물질적부분용융유관；이산성용암여기성용암존재명현적불동,산성용암시소량만원암장경강렬결정분이화경력교다각원물질혼염적결과。3)현무암전암 Sm-Nd등시선년령위319.7±5.9 Ma,여구역지질구조배경화이유화석증거기본일치,대표료화산암적형성시대。종합연구표명,동준갈이지구320 Ma좌우의구존재고아주양적부충소감작용,준갈이고양분최종폐합시간응개우320~311 Ma지간。재차과정중,화산암장작용강렬,온함성광물질봉부,동준갈이지구조광전경치득기대。
The volcanic rocks from the Carboniferous Batamayineishan Formation are widely distributed in eastern Junggar. Petrology, geochemistry and isotope geochemistry of the rocks indicate that:1) They have widely varied rock types including basalt-andesite-dacite-rhyolite rocks and are of high-K calc-alkaline, enriched in large ion lithophile elements (LILE) (Sr, K, Rb, Ba, Th) and LREE and depleted in high field strength elements (HFSE) (Nb, Ta, Ti)and HREE. Besides, the initial values of 87Sr/86Sr and 143Nd/144Nd are low and the εNd(t) values generally vary in range of 3.0~6.2. All these features suggest that they are immature back-arc basin volcanics related to subduction;2) The parent magma of the volcanic rocks mainly derived from the depleted mantle with involvement of minor juvenile lower crust comprised of remnants of Paleozoic oceanic crust and island arc system. The genesis of basic lavas may be attributed to a mixing process by hybridization of depleted mantle-derived magma and a small amount of juvenile crust-derived magma, which was related to partial melting of mantle wedge induced by fluid and sediments of subducted oceanic crust. Distinguished from the basic ones, the acid lavas originated from mantle-derived magma, coupled with strong fractional crystallization and crust contamination. 3) Consistent with regional geological background and discovered fossils, the Sm-Nd isochron age of 319.7±5.9 Ma can represent the time of eruption of the volcanic rocks. Based on comprehensive analysis, it is inferred that subduction of the Paleo-Asian Ocean was still underway at the time of 320 Ma and the final closure of the ancient Junggar ocean basin occurred in the period 320 to 311 Ma. Enriched in ore-forming substances, the intensified magmatism during this process made the eastern Junggar region of great prospecting potential.