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天山北部石炭纪埃达克岩-高镁安山岩-富Nb岛弧玄武质岩：对中亚造山带显生宙地壳增生与铜金成矿的意义 总被引：28，自引：30，他引：28
新疆天山北部地区存在有石炭纪的埃达克岩-高镁安山岩-富Nb玄武质岩组合，并且其中许多岩石与铜（金）矿床伴生（如达巴特、阿希、土屋-延东、赤湖，等等）。埃达克岩富钠、高Sr但亏损Y与Yb，无明显Eu-正Eu异常以及正Sr异常与Nb、Ti亏损。高镁安山（闪长）岩是本次研究首次报道的，这些岩石无明显Eu-正Eu异常以及Nb、Ti亏损，普遍具有高的MgO和Cr、Ni含量，其中阿希金矿区一些样品类似于日本西南新生代Setouchi弧火山岩带中的赞岐岩类。富Nb玄武质岩富钠贫钾，具有微弱负．正Ba、Nb和Ti异常以及高的Nb／La比值，不同于大多数正常岛弧玄武岩。天山北部地区石炭纪埃达克岩具有高的8Nd（t）（＋3．4-＋9．0）和低的（^87Sr／^86Sr）i（0．7032—0．7043）。富Nb玄武质岩具有变化的εNd（t）（＋3．6-＋11．6）和（^87Sr／^86Sr）；（0．7007—0．7067）。我们的研究表明，天山北部地区石炭纪埃达克岩-高镁安山岩-富Nb玄武质岩组合可能是“埃达克岩交代的岛弧岩浆岩系列”。埃达克岩最有可能由石炭纪北天山洋的年轻洋壳在俯冲过程中熔融形成。另外，俯冲板片产生的熔体以及所释放的少量流体在上升过程中可能交代地幔楔橄榄岩或与其发生反应：一方面，触发地幔楔橄榄岩发生熔融形成富Nb岛弧玄武质岩；另一方面，地幔组分迅速进入到板片熔体中，导致其地幔组分增加，乃至形成高镁安山岩。因此，天山北部地区石炭纪埃达克岩-高镁安山岩-富Nb玄武质岩组合表明：（1）天山北部地区石炭纪可能为岛弧环境而非裂谷环境；（2）天山地区石炭纪的地壳生长可能以侧向增生为主；（3）除了亏损地幔之外，俯冲洋壳的熔融可能也在地壳的生长中发挥了重要的作用；（4）俯冲板片产生的埃达克质岩浆具有高的氧逸度，而其与地幔楔橄榄岩的强烈相互作用将导致地幔中的金属硫化物分解，成矿金属元素进入到岩浆中。这可能是新疆北部铜金矿化与一些埃达克岩、高镁安山（闪长）岩或富Nb岛弧玄武质岩密切共生的基本原因。 相似文献
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Gan-Yu Li Xuan-Ce Wang Gao-Xue Yang Ran Wang Kun-Peng Xiang 《International Geology Review》2017,59(9):1116-1130
ABSTRACTVolcanic rocks in the Hala’alate and Aladeyikesai formations, which are composed of basaltic andesite and pyroxene andesite, are widespread in Hala’alate Mountain, West Junggar, Northwest China. These rocks (plagioclase + clinopyroxene/olivine) formed in the late Carboniferous and show a remarkable geochemical affinity with typical sanukitoids with oversaturated SiO2 (52.9–56.9 wt.%) and high MgO (3.47–6.88 wt.%, Mg# >48) contents. They also exhibit a narrow range of Sr-Nd-Pb isotopes within (87Sr/86Sr)i = 0.7037–0.7041, εNd(t) = 4.4–6.2, 206Pb/204Pb = 18.22–18.41, 207Pb/204Pb = 15.48–15.52, 208Pb/204Pb = 37.99–38.30. Hala’alate Formation volcanic rocks are similar to the sanukitoids of Karamay, with high Sr (633.5–970.1 ppm), Ba (268.7–796.3 ppm), and Sr/Y (61.34–84.28), formed by partial melting of the mantle metasomatized by slab-derived adakitic melts. In contrast, Aladeyikesai Formation volcanic rocks show some affinity with sanukitoids of the Hatu area and the Setouchi Volcanic Belt, with low Sr (442.2–508.7 ppm), Ba (199.2–485.1 ppm), and Sr/Y (25.03–30.28), generated by the partial melting of subducting sediments. Identification of late Carboniferous sanukitoids in Hala’alate Mountain provides important constraints on the closing time of the remnant ocean basin in West Junggar, and implies that multi-stage subduction–accretionary orogeny plays a crucial role in the evolution and growth of the continental crust in the Central Asian Orogenic Belt. 相似文献
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The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(avg.La_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 to-5.4.These chemical features of the HSG are akin to potassic granitoids found elsewhere. In this backdrop, we propose that the HSG suite of the Mangalwar Complex was derived from re-melting(partial) of an older crust(TTG?) occurring within the BGC-Ⅱ. 相似文献
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对羌塘地块东北缘甘孜-理塘缝合带南侧日啊日曲石英闪长岩进行了系统的锆石U-Pb年龄、主量-微量元素及Sr-Nd同位素分析, 以探讨其岩石成因及地球动力学意义.LA-ICP-MS锆石U-Pb定年结果表明, 石英闪长岩侵位年龄为218±1 Ma, 为晚三叠世岩浆活动的产物.岩石SiO2含量介于53.02%~62.06%之间, 富Al2O3(15.84%~17.00%)和CaO(6.71%~8.94%), 贫TiO2(0.49%~1.01%)和P2O5(0.04%~0.12%), 具有较高的MgO(3.31%~5.66%)和Mg#(50~62), 属准铝质钙碱性系列; 岩体稀土元素总量较低(38.05×10-6~61.58×10-6), 轻重稀土分馏不明显, LILE富集, HFSE亏损, 具有含量较高的Cr(33.45×10-6~176.64×10-6)和Ni(13.34×10-6~43.62×10-6).全岩(87Sr/86Sr)i比值较为一致(0.706 8~0.707 9), εNd(t)变化于-5.5~-1.6.主微量元素及同位素结果表明日啊日曲石英闪长岩具有高镁闪长岩的特征, 与赞岐岩地球化学特征类似, 为俯冲沉积物来源的熔体交代岩石圈地幔形成的尖晶石相金云母二辉橄榄岩低度(10%~15%)部分熔融的产物, 岩浆演化过程中经历了辉石、角闪石等矿物的分离结晶.微量元素构造判别图解表明岩石为俯冲环境下的弧岩浆岩, 结合区内蛇绿岩、研究区南部陆缘弧火山岩和义敦岛弧埃达克岩的发现, 认为古特提斯洋在晚三叠世时期可能仍处于消减状态, 日啊日曲高镁石英闪长岩形成于甘孜-理塘洋南西向俯冲过程中. 相似文献
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