地球化学
地毬化學
지구화학
GEOCHIMICA
2014年
3期
301-316
,共16页
张峰%徐涛%范俊杰%潘爱军%王斌%朝银银
張峰%徐濤%範俊傑%潘愛軍%王斌%朝銀銀
장봉%서도%범준걸%반애군%왕빈%조은은
火山岩%Sm-Nd同位素%弧后盆地%石炭纪%巴塔玛依内山组%东准噶尔
火山巖%Sm-Nd同位素%弧後盆地%石炭紀%巴塔瑪依內山組%東準噶爾
화산암%Sm-Nd동위소%호후분지%석탄기%파탑마의내산조%동준갈이
volcanic rocks%Sm-Nd isochron age%back-arc basin%Carboniferous%Batamayineishan Formation%eastern Junggar
东准噶尔地区石炭系巴塔玛依内山组火山岩分布广泛,规模巨大,目前对其形成时代及构造背景的认识还存在着较大的争议。以火山岩中的玄武岩、玄武安山岩为研究对象,进行了岩石学、岩石地球化学和Sm-Nd同位素地球化学方面的研究。结果表明,该套火山岩属高钾钙碱性火山岩系,微量元素和稀土元素特征相似,(143Nd/144Nd)i变化幅度小,εNd(t)和T2DM近乎相同,具同源岩浆演化特征和良好的封闭条件。利用Sm-Nd等时线定年方法获得的玄武岩全岩等时线年龄为(319.7±5.9) Ma,(143Nd/144Nd)i =0.512414±0.000006, MSWD=0.34,与区域地质构造背景和已有化石证据基本吻合,代表了火山岩的形成时代。准噶尔地区晚古生代区域构造背景复杂。位于西伯利亚板块和哈萨克斯坦-准噶尔板块之间的古亚洲洋存在双向俯冲消减过程。南向俯冲带位于扎河坝-克拉玛依一线,俯冲作用至少延续至(319.7±5.9) Ma。持续的南向俯冲造就了东准噶尔地区扎河坝下泥盆统托让格库都克组火山岩代表的岛弧和卡拉麦里蛇绿岩代表的卡拉麦里不成熟弧后盆地的形成。东准噶尔地区石炭系巴塔玛依内山组火山岩就是该过程中不成熟弧后盆地的产物,成岩过程可能是：古亚洲洋持续南向俯冲,导致卡拉麦里地区幔源物质大量上隆并引起弧后扩张,并在消减沉积物和(或)俯冲洋壳脱水产生的流体作用下发生部分熔融,形成的玄武质岩浆不断底侵至壳幔边界,引起少量主体由古生代残余洋壳和岛弧体系组成的年轻下地壳物质部分熔融生成岩浆,并发生相互较完全的混合,而后随着混合岩浆的不断聚集和构造伸展作用的进一步持续,岩浆沿构造薄弱带快速上升至地表,喷发成岩。319.7~311 Ma 左右的中亚造山带持续南向增生导致了卡拉麦里弧盆北侧古亚洲洋的消亡,并最终迫使卡拉麦里弧盆北向俯冲消减而闭合。
東準噶爾地區石炭繫巴塔瑪依內山組火山巖分佈廣汎,規模巨大,目前對其形成時代及構造揹景的認識還存在著較大的爭議。以火山巖中的玄武巖、玄武安山巖為研究對象,進行瞭巖石學、巖石地毬化學和Sm-Nd同位素地毬化學方麵的研究。結果錶明,該套火山巖屬高鉀鈣堿性火山巖繫,微量元素和稀土元素特徵相似,(143Nd/144Nd)i變化幅度小,εNd(t)和T2DM近乎相同,具同源巖漿縯化特徵和良好的封閉條件。利用Sm-Nd等時線定年方法穫得的玄武巖全巖等時線年齡為(319.7±5.9) Ma,(143Nd/144Nd)i =0.512414±0.000006, MSWD=0.34,與區域地質構造揹景和已有化石證據基本吻閤,代錶瞭火山巖的形成時代。準噶爾地區晚古生代區域構造揹景複雜。位于西伯利亞闆塊和哈薩剋斯坦-準噶爾闆塊之間的古亞洲洋存在雙嚮俯遲消減過程。南嚮俯遲帶位于扎河壩-剋拉瑪依一線,俯遲作用至少延續至(319.7±5.9) Ma。持續的南嚮俯遲造就瞭東準噶爾地區扎河壩下泥盆統託讓格庫都剋組火山巖代錶的島弧和卡拉麥裏蛇綠巖代錶的卡拉麥裏不成熟弧後盆地的形成。東準噶爾地區石炭繫巴塔瑪依內山組火山巖就是該過程中不成熟弧後盆地的產物,成巖過程可能是：古亞洲洋持續南嚮俯遲,導緻卡拉麥裏地區幔源物質大量上隆併引起弧後擴張,併在消減沉積物和(或)俯遲洋殼脫水產生的流體作用下髮生部分鎔融,形成的玄武質巖漿不斷底侵至殼幔邊界,引起少量主體由古生代殘餘洋殼和島弧體繫組成的年輕下地殼物質部分鎔融生成巖漿,併髮生相互較完全的混閤,而後隨著混閤巖漿的不斷聚集和構造伸展作用的進一步持續,巖漿沿構造薄弱帶快速上升至地錶,噴髮成巖。319.7~311 Ma 左右的中亞造山帶持續南嚮增生導緻瞭卡拉麥裏弧盆北側古亞洲洋的消亡,併最終迫使卡拉麥裏弧盆北嚮俯遲消減而閉閤。
동준갈이지구석탄계파탑마의내산조화산암분포엄범,규모거대,목전대기형성시대급구조배경적인식환존재착교대적쟁의。이화산암중적현무암、현무안산암위연구대상,진행료암석학、암석지구화학화Sm-Nd동위소지구화학방면적연구。결과표명,해투화산암속고갑개감성화산암계,미량원소화희토원소특정상사,(143Nd/144Nd)i변화폭도소,εNd(t)화T2DM근호상동,구동원암장연화특정화량호적봉폐조건。이용Sm-Nd등시선정년방법획득적현무암전암등시선년령위(319.7±5.9) Ma,(143Nd/144Nd)i =0.512414±0.000006, MSWD=0.34,여구역지질구조배경화이유화석증거기본문합,대표료화산암적형성시대。준갈이지구만고생대구역구조배경복잡。위우서백리아판괴화합살극사탄-준갈이판괴지간적고아주양존재쌍향부충소감과정。남향부충대위우찰하패-극랍마의일선,부충작용지소연속지(319.7±5.9) Ma。지속적남향부충조취료동준갈이지구찰하패하니분통탁양격고도극조화산암대표적도호화잡랍맥리사록암대표적잡랍맥리불성숙호후분지적형성。동준갈이지구석탄계파탑마의내산조화산암취시해과정중불성숙호후분지적산물,성암과정가능시：고아주양지속남향부충,도치잡랍맥리지구만원물질대량상륭병인기호후확장,병재소감침적물화(혹)부충양각탈수산생적류체작용하발생부분용융,형성적현무질암장불단저침지각만변계,인기소량주체유고생대잔여양각화도호체계조성적년경하지각물질부분용융생성암장,병발생상호교완전적혼합,이후수착혼합암장적불단취집화구조신전작용적진일보지속,암장연구조박약대쾌속상승지지표,분발성암。319.7~311 Ma 좌우적중아조산대지속남향증생도치료잡랍맥리호분북측고아주양적소망,병최종박사잡랍맥리호분북향부충소감이폐합。
The volcanic rocks from Carboniferous Batamayineishan formation in eastern Junggar basin, widely distributed with huge scale, have long been debated on the formation age and tectonic setting. Petrological, petrogeochemical and Sm-Nd isotopic geochemical characteristics indicate that the basalts and basaltic andesites of the formation are of high-K calc-alkaline volcanic series, with similar characteristics of trace elements and REE and similar values of (143Nd/144Nd)i, εNd(t) and T2DM, suggesting that they have homologous magmatic evolution features and good enclosed conditions. The basalt whole rock isochron age by Sm-Nd isochron dating method is (319.7±5.9) Ma, with (143Nd/144Nd)i= 0.512414±0.000006, MSWD = 0.34, which is consistent with the regional tectonic background and the existing fossil evidence. It is represents the volcanic rock formation age. Paleoasian Ocean between the Siberian and Kazakhstan-Junggar plates existed bidirectional subduction process. Southward subduction zone located along Zhaheba-Karamay, the subduction continued until at least (319.7±5.9) Ma. The continued southward subduction created an island arc that represented by Tuoranggekuduoke formation volcanic rocks and the Kalamaili immature back-arc basin that represented by Karameh ophiolite on Lower Devonian of Zhaheba in the East Junggar. The East Junggar Carboniferous Batamayineishan formation volcanic rocks are the products of immature back-arc basin, and the diagenetic mechanism may be that the subduction of the PaleoAsian Ocean trigger the evolvement of a large amount of mantle material in Kalamaili, and dehydration partial melting of subducted sediments and/or oceanic crust, the generated basaltic magmas constantly underplated to the crust-mantle boundary and heated the lower crust and triggered the formation of small amount of magmas by partial melting of young lower crust which was mainly composed of Paleozoic remnant oceanic crust and arc complex. The two types of magma mixed. Thereafter, as the mixed magma continued to gather and tectonic extension in further sustained, part of them removed upward along the structural belt, and erupted. During 319.7-311 Ma, continued southward accretion eventually led to the closure of the Paleoasian in the north side of Karameh back-arc basin, and consequently forced the northward subduction and closure of Karameh back-arc basin.
