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31.
Seamount accretion is one of the most significant accretionary orogenic processes in the Central Asian Orogenic Belt, but there are few paleo-seamounts reported from and debate on the tectonic evolution of the Junggar Ocean still exists. In this study, we present geochronological, mineralogical, geochemical and isotopic data for basalts from the Chagantaolegai ophiolitic mélanges in Junggar. Zircon U-Pb dating on one basalt yielded a weighted mean 206 Pb/238 U age of 469 ± 7 Ma, which suggests that it formed in the Middle Ordovician. All rock samples belong to alkaline basalt and show similar geochemical characteristics, displaying high TiO2(～3 wt%),(La/Yb)N(17.6–19.0), ΣREE(232–289 ppm) and enrichment in Nb and Ta, which implies an ocean island basalt(OIB) affinity. Based upon positive εN d(t)(+4.16 to +4.23), ΔNb(0.20–0.22) and low initial 87 Sr/86 Sr(0.70425 to 0.70452) and Zr/Nb(3.35–3.57), we suggest that the Chagantaolegai OIB samples were likely derived from a fertile mantle source related to plume. The OIB rock assemblage, chert and marble in the southern part of the Chagantaolegai ophiolitic mélange indicates that a Middle Ordovician seamount was accreted to the Boshchekul-Chingiz arc due to the northward subduction of the Junggar-Balkhash Ocean. 相似文献
32.
中亚造山带东段南缘早志留世岩体锆石U-Pb定年、地球化学特征及其地质意义 总被引：6，自引：4，他引：2
本文报道了分布于中亚造山带南缘苏尼特右旗太古生庙地区太古生庙岩体和库伦哈达岩体的岩相学、地球化学和年代学特征,以讨论该岩体的形成时代、岩石成因及其构造环境。锆石U-Pb定年结果显示,太古生庙英云闪长岩结晶年龄为442.6±2.4Ma,库伦哈达石英闪长岩结晶年龄为434.2±2.2Ma,说明太古生庙地区早古生代存在岩浆活动。其中太古生庙岩体地球化学特征类似于典型的埃达克岩,其Si O2含量56%(70.02%~70.51%),Al2O3含量≥15%(15.99%~16.37%),Mg O3%(0.56%~0.83%),Na2O3%(4.33%~4.66%),K2O/Na2O比值0.5(0.3~0.4);在微量元素特征方面,Sr400×10-6(681×10-6~783×10-6),Yb1.9×10-6(0.6×10-6~0.9×10-6),Y18×10-6(5.4×10-6~9.3×10-6),无明显的Eu异常。库伦哈达岩体与太古生庙岩体相比,Si O2含量较低(57.92%~66.78%),Al2O3为相当(14.91%~18.26%),MgO含量为1.17%~2.31%,Na2O含量为3.29%~4.36%,K2O含量为1.43%~3.09%;在微量元素判别图解中,库伦哈达岩体的岩石样品投图位于埃达克岩和典型的岛弧型火山岩的叠加区域,而太古生庙岩体样品全部落入埃达克岩区域内,太古生庙岩体可能是洋壳部分熔融的产物,而库伦哈达岩体可能是早期俯冲的洋壳部分熔融的产物混染了部分熔融的地幔楔之后形成了这种具有正常岛弧岩浆特征的岩石,其形成的环境为岛弧环境。 相似文献
33.
新疆准噶尔北缘早石炭世金-铜-钼成矿事件:年代学证据 总被引：2，自引：0，他引：2
新疆准噶尔北缘地区已发现多处大中型内生金属矿床,它们主要形成于2个构造-岩浆活动期,即泥盆纪洋陆俯冲期的岛弧型斑岩铜(金)矿,二叠纪后碰撞造山期的铜镍硫化物型矿床和造山型(或剪切带型)Au矿。作者近年来在对该区地质构造和矿床研究中获得了一批早石炭世成岩成矿年代学数据:除已发表的希勒库都克斑岩铜钼矿床流纹斑岩(329Ma)和辉钼矿(327Ma)年龄外,本文工作新近获得201金矿闪长岩年龄为324Ma、科克森套地区花岗闪长斑岩年龄为328Ma、库尔吐班套地区花岗岩年龄为323Ma、阿克塔斯Au矿区花岗闪长岩年龄为327Ma,这些年龄数据集中在323~328Ma,即早石炭世(主要在维宪阶和谢尔普霍夫阶)。综合分析认为,该区在早石炭世洋盆已经闭合进入碰撞造山阶段,该阶段岩浆活动以出露小规模中酸性岩脉、岩株为特征,构造活动和壳幔相互作用强烈,主要成矿类型有斑岩型Cu Mo矿、浅成低温热液型Au矿、脉岩-构造蚀变岩型Au矿,构成一独特的与浅成岩有关的早石炭世金-铜-钼成矿带。 相似文献
34.
A complex of gabbro (with metamorphic pyroxenite xenoliths)–gabbroic diorite–granodiorite was recently discovered in Tongxunlian, Xilinhot city, Inner Mongolia. Zircon U–Pb isotopic dating showed that the gabbro and the granodiorite were formed ca. 319 ± 1 Ma and ca. 318 ± 1 Ma respectively, indicating that emplacement of the composite rocks occurred in the late Carboniferous. Positive εHf(t) values of +12.0 to +14.1 and two‐stage model ages (TDM2) of 418 to 537 Ma of these rocks are similar to the age of formation of metamorphic pyroxenite (560 Ma, based on Sm–Nd isochron dating) and suggest that the rocks were derived from depleted lithospheric mantle (metamorphic pyroxenite). Our findings revealed that all of these calc‐alkaline and metaluminous intrusive rocks formed from the fractional crystallization of comagmatic evolution in an island‐arc setting. Moreover, the gabbro–gabbroic diorite in the study region was characterized by a low TiO2 content, a slight deficit of Nb, a surplus of Ta, and relatively low LREE/HREE ratios. Along with a relatively high Zr/Y ratio (4.0 to 5.6), these characteristics indicate that the rocks may have been formed by melting of the mantle wedge via metasomatism. Combination with other features of the rocks indicates a two‐episode tectonic model: we conclude that first, the fluid and Si‐rich melt metasomatism caused partial melting of the enriched lithospheric mantle, and these influences were then stored in the mantle; and second, slab breakoff resulted in upwelling of the upper mantle's soft fluid (stratum), which melted the enriched mantle of the lithosphere and formed the basaltic magma of the gabbro–gabbroic diorite. This study provides new geological evidence to support the Neoproterozoic subduction between the Paleo‐Asian Ocean plate and the Xilinhot microcontinent. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
35.
《地学前缘(英文版)》2020,11(4):1415-1429
As the southernmost segment of the Central Asian Orogenic Belt (CAOB), the northern Alxa orogenic belt (NAOB) connects the southeastern and southwestern segments of the CAOB. The NAOB amalgamated with the closure of the Paleo-Asian Ocean; however, the closure time of the Paleo-Asian Ocean is still on great debate. In this study, we reported new detrital zircon U–Pb geochronology and Hf–O isotopes for the Permo–Carboniferous sediments in the northern Alxa to constrain the provenance and its tectonic implications. The Permo–Carbonifereous Amushan Formation is composed of volcanic-carbonite-clastic rocks and was deposited in a shallow marine environment. Based on the zircon U–Pb geochronology, the Amushan Formation was deposited in the late Carboniferous to early Permian, but some outcrops of volcanic and clastic rocks in the Quaganqulu area were likely formed in the middle to late Permian. The integrated zircon age spectrum for the clastic rocks shows a wide range from late Archean to Paleoproterozoic, Mesoproterozoic (with a peak age at 1458 Ma), early Neoproterozoic (with peak ages of 988 Ma and 929 Ma), early Paleozoic (with a peak age at 447 Ma) and late Paleozoic (with a peak age at 294 Ma). Combined with the zircon Hf–O isotopes, the provenance was considered to be the Alxa Block, the Shalazhashan terrane and the Zhusileng–Hangwula block (and the southern Beishan orogenic belt). The multiple source regions to the south and north of the Paleo-Asian Ocean indicate the closure of this ocean before the late Carboniferous. The absence or small proportion of depositional age-approximated zircons in most samples makes their age spectra similar to extensional basins. Combined with the intra-plate volcanism, the deposits were considered to be formed in extensional settings. Accordingly, after the closure of the Paleo-Asian Ocean, the NAOB stepped into an extensional stage. 相似文献
36.
Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: Implications for petrogenesis and tectonic evolution 总被引：4，自引：0，他引：4
Keda Cai Min Sun Chao Yuan Guochun Zhao Wenjiao Xiao Xiaoping Long Fuyuan Wu 《Gondwana Research》2010,18(4):638-652
Fifteen zircons separated from a mafic dyke in the Chinese Altai give a concordant age population with a weighted mean 206Pb/238U age of 375.5 ± 4.8 Ma, suggesting a Devonian emplacement. On the basis of their mineralogical compositions and textures, the coeval dykes can be divided into gabbroic and doleritic types. They are both sub-alkaline, tholeiitic, characterized by similarly low SiO2 contents (45.2–52.7 wt.%) and total alkaline (K2O + Na2O = 0.99–4.93 wt.%). Rare earth element patterns of the gabbroic dykes are similar to N-MORB (La/YbN = 0.86–1.1), together with their high εNd(t) values (+ 7.6 to + 8.1), indicating that their precursor magma was mainly derived from a N-MORB-type depleted asthenospheric mantle. While the REE patterns of the doleritic dykes resemble that of E-MORB (La/YbN = 1.12–2.28), enriched in LILEs and strongly depleted in HFSEs, with relative low εNd(t) values (+ 3.4 to + 5.4) and high initial 87Sr/86Sr ratios (0.7057–0.7060). The zircon Hf isotopic analysis of the doleritic dykes give εHf(t) values from + 10.7 to + 13.8. These signatures suggest that a depleted mantle wedge metasomatized by slab-derived fluids and/or melts was possibly involved in the generation of the doleritic magma. The refractory peridotite may have been melted with variable degrees caused by upwelling of the hot asthenosphere. The petrogenesis of the mafic dykes suggest a high heat flux as a result of upwelling of the hot asthenosphere and the contrast geochemical signatures can be interpreted by a ridge subduction, which could be an important tectonic control in the accretionary process of the Chinese Altai. 相似文献
37.
塔里木和中亚造山带西段二叠纪大火成岩省的两类地幔源区 总被引：7，自引：2，他引：5
对塔里木和中亚造山带西段二叠纪玄武质岩石地质、年龄、元素地球化学、同位素组成的系统总结表明,二叠纪火成岩在分布面积、岩石类型(以玄武岩占绝对优势)、活动时间(以275Ma左右为峰期)等方面均与世界典型的大火成岩省一致,将其命名为巴楚大火成岩省(Bachu LIP)。元素和同位素地球化学特征表明,塔里木玄武岩来自长期富集的岩石圈地幔,来源深度为60～80km。塔里木基性岩墙和超镁铁-镁铁杂岩的原始岩浆可能来自软流圈地幔(OIB)部分熔融。中亚造山带西段的玄武岩、基性岩墙和超镁铁-镁铁杂岩主要来自被俯冲带熔体交代的强烈亏损的岩石圈地幔,其中部分地区可能有软流圈物质的加入,如东天山和阿勒泰南缘高Ti系列的玄武质岩石。根据元素和同位素地球化学资料,将巴楚大火成岩省分为2个地幔省(mantledomain),即塔里木省和中亚省。这2个不同地幔省的成矿系列也有显著的差异,塔里木省为钒-钛磁铁矿矿床,而中亚则以铜-镍-(铂族金属)硫化物矿床为主,成矿作用的差异和岩浆地幔源区的差异是完全对应的。综合地质、地球化学和成矿作用,认为巴楚大火成岩省的形成和二叠纪地幔柱密切相关。 相似文献
38.
The South Kitakami Belt in the northeast Japan is unique in presence of a thick Paleozoic–Mesozoic sedimentary rocks. The Permian sedimentary succession in the Maiya area of this belt is divided into the Nishikori, Tenjinnoki, and Toyoma formations, in ascending stratigraphic order. The Tenjinnoki Formation includes the Yamazaki Conglomerate Member containing granitic clasts. We performed U–Pb dating for detrital zircon of one sample of tuffaceous sandstone from the Nishikori Formation, six samples of sandstone from the Tenjinnoki and Toyoma formations, and five granitic clasts from the Yamazaki Conglomerate using laser ablation-inductively coupled plasma-mass spectrometry. Our dating results show that the tuffaceous sandstone sample has two age peaks at 287 and 301 Ma for the Nishikori Formation, three age peaks at 320–300, 290, and 270 Ma for the Tenjinnoki and Toyoma Formation, and ages of 311, 300, and 270 Ma from granitic clasts of the Yamazaki Conglomerate. In addition, older ages of 452–435 and 380 Ma were obtained from some zircon grains of the sandstone and granitic clasts. Our results suggest igneous activity in these periods. The South Kitakami Belt's origin with respect to continental blocks has been discussed in regard of the margin of North China Block or South China Block. Based on the stratigraphic ages and timing of igneous activity, we conclude that during the Permian the South Kitakami Belt was located at the margin of the South Central Asian Orogenic Belt, near the Solonker-Xra Moron-Changchun suture and the North China Block in East Asia. 相似文献
39.
内蒙古西乌旗大石寨组火山岩年代学和地球化学特征及地质意义 总被引：1，自引：0，他引：1
中亚造山带南缘二叠纪火山岩的成因及形成环境一直存在争议。本文以内蒙古西乌旗罕乌拉地区发育的大石寨组火山岩为研究对象,对其开展了野外地质、岩石学、锆石U-Pb同位素年代学、地球化学研究。大石寨组火山岩为一套中酸性火山熔岩-碎屑岩组合,岩性以流纹岩为主。锆石LA-ICP-MS U-Pb同位素定年结果显示,2件流纹岩样品的~(206)Pb/~(238)U年龄加权平均值分别为276±0.81Ma(MSWD=1.3)和280±0.76Ma(MSWD=0.69),说明大石寨组流纹岩喷发于早二叠世,反映了早二叠世的构造岩浆作用事件。岩石地球化学研究表明,大石寨组火山岩为一套中酸性火山岩,以高硅、富碱为特征,Ti、Mg、Fe、Ca等元素含量较低;微量元素总体含量较高,具有一致的配分曲线,Rb、Th、U、K、LREE等大离子亲石元素相对于Nb、Ta、HREE等高场强元素明显富集;稀土元素总量偏高,具一致的右倾"海鸥式"配分型式。在微量元素原始地幔标准化蛛网图上显示明显的Ba、Sr、P、Eu和Ti的负异常。10000Ga/Al平均值3.6。地球化学特征显示该套火山岩具有岛弧火山岩的属性,类似A型花岗岩的地球化学特征,为高温低压下长英质地壳部分熔融的产物。结合地球化学特征及区域地质资料,大石寨组火山岩最可能形成于弧后扩张环境,是早二叠世古亚洲洋闭合前洋壳俯冲消减作用的产物。 相似文献
40.
The Wulungu Depression is the northernmost first-order tectonic unit in the Junggar Basin.It can be divided into three sub-units:the Hongyan step-fault zone,the Suosuoquan sag and the Wulungu south slope.The Cenozoic strata in the basin are intact and Mesozoic—Cenozoic deformation can be observed in the Wulungu step-fault zone,so this is an ideal place to study the Mesozoic—Cenozoic deformation.By integration of fault-related folding theories,regional geology and drilling data,the strata of the Cretaceous—Paleogene systems are divided into small layers which are selected as the subjects of this research.The combination of the developing unconformity with existing growth strata makes it conceivable that faults on the step-fault zone have experienced different degrees of reactivation of movement since the Cretaceous.Evolutionary analyses of the small layers using 2D-Move software showed certain differences in the reactivation of different segments of the Wulungu Depression such as the timing of reactivation of thrusting,for which the reactivity time of the eastern segment was late compared with those of the western and middle segments.In addition the resurrection strength was similarly slightly different,with the shortening rate being higher in the western segment than in the other segments.Moreover,the thrust fault mechanism is basement-involved combined with triangle shear fold,for which a forward evolution model was proposed. 相似文献