KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 西天山伊犁地块北部前寒武纪基底属性及古生代构造演化 | |
| Alternative Title | The Precambrian basement nature and Plaleozoic tectonic evolution of the northwest Chinese Tianshan |
| 孙敏佳 | |
| Subtype | 博士 |
| Thesis Advisor | 蔡克大 |
| 2020-06-30 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 工学博士 |
| Keyword | 中亚造山带 伊犁地块 温泉群 花岗岩 哈萨克斯坦山弯构造 The Central Asian Orogenic Belt The Yili Block Wenquan group granitoids Kazakhstan Orocline |
| Abstract | 中亚造山带（CAOB） 是显生宙形成的巨型增生型造山带之一。 其中， 哈萨克斯坦拼贴系统代表了 CAOB 内最大、最复杂的超级构造单元，是解密亚洲大陆早期形成历史的关键区域。 概括来讲， 它由一系列岛弧及微陆块在早古生代经连续的增生拼贴形成， 而后经历了晚古生代的山弯构造，形成现今的地质格局。然而， 具体而言， 哈萨克斯坦拼贴体系中微陆块的起源， 岛弧的时代和性质， 以及它们之间的拼合过程， 甚至哈萨克斯坦山弯构造形成的动力学机制等诸多问题仍需要具体工作予以回答。 伊犁地块位于哈萨克斯坦拼贴体系的东南缘，其具有前寒武纪的结晶基底并在其基础上发育古生代岛弧，对前寒武纪基底属性的探讨和古生代构造演化历史的厘定对于破解中亚造山带甚至古亚洲的形成具有重要意义。花岗岩是大陆地壳的重要组成部分，记录了陆壳物质的增生与分异，是大陆形成和演化的关键物质载体。 伊犁地块北部二云花岗片麻岩侵位于 851.5±3.2Ma，并记录了 913.8±3.7 Ma 区域混合岩化事件。岩石具有高硅（≥70 wt.%）、富碱（K2O+Na2O=6.43-9.07 wt.%）， 高的 A/CNK 值（1.13-1.25） 特征， 与典型的 S 型花岗岩地球化学特征相类似。 绝大多数正的锆石 εHf(t)值（-5.67~+0.83），以及老的 Hf 二阶段模式年龄（TDM2=1.69-2.12 Ga），表明二云花岗片麻岩可能是地壳增厚环境下古元古代地壳再造的产物。 晚震旦世（558.6±9.1 Ma） 二长花岗岩， 为 I 型花岗岩，具有高硅（≥70%）、 富碱（K2O+Na2O=7.98-8.65 wt.%），高的 Na2O（4.20-5.53 wt.%） 含量的特征。 正的锆石 εHf(t)值（+1.98~+8.39），以及高的 Mg#值（35-42），表明源区有新生幔源物质的加入。 二长花岗岩显示出 Nb、Ta、 P 和 Ti 的相对亏损和 LILEs（如 K、 Ba）的富集，与俯冲构造环境中形成的弧岩浆相似， 推测其为 Rodinia 超大陆裂解后形成的大洋板片俯冲的产物。对温泉岩群变沉积碎屑锆石研究表明， 其沉积于中元古代晚期至新元古代早期， 锆石 U-Pb 年龄主要分布在 850-950 Ma 及 1100-1450 Ma。 其中 850-950 Ma的锆石可能是对区域混合岩化作用的记录，大概 80%该时期的碎屑锆石具有富集的 εHf(t)同位素的特征，表明主要以古老地壳的改造为主。 1100-1450 Ma 的碎屑锆石来自伊犁地块本源地或近源地的碎屑物质， 70%的该时期锆石具有亏损的εHf(t)同位素的特征，表明物质源区以地壳生长为主。 通过对比研究，伊犁地块南部与北部在新元古代无显著差异， 在该时期伊犁地块与中天山地块具有亲缘性。伊犁地块北部奥陶纪（~456 Ma） 变质辉长岩和志留纪（~420 Ma）花岗岩类，记录了研究区早古生代的岩浆事件，反映了古亚洲洋早期的构造演化历史。变质辉长岩具有高的 MgO 含量（4.91-9.89 wt.%）和亏损的 εHf(t)值（-0.95~+4.96），以及相对富集的 LREEs 元素， 其原岩地球化学特征类似于受俯冲板块流体交代的亏损地幔楔体的部分熔融产生的玄武质岩浆。含石榴子石花岗岩为过铝质（A/CNK=1.06-1.10）岩石，具高的(87Sr/86Sr)i 值（0.715）， 负的全岩 εNd(t)值（-0.4），并且包含大量的继承锆石， 以及富集的锆石 εHf(t)值（-4.11 至-1.99）， 表明它是 S型花岗岩， 可能产生于碰撞造山作用导致的增厚的地壳沉积岩的重熔。黑云母花岗岩具有较高的 SiO2含量，低的 MgO 含量， 高的 Sr 含量（453-628 ppm），高的 Sr/Y 比值（31-97），以及亏损的 HREEs 元素，具有埃达克质岩石的地球化学特征。结合其较高的全岩初始锶同位素（0.7092-0.7098）和变化范围大的 εNd(t)值（-3.3-5.0），表明其来源于新生下地壳和古老基底的混合源区在深部地壳水平的部分熔融。 上述岩浆岩主要发育在阿克套-准噶尔地块南段， 该地块向西延伸处与楚伊犁地块间存在一条蛇绿混杂带。 俯冲相关的镁铁质岩浆作用向碰撞相关的酸性岩浆作用的转变，可能与阿克套-准噶尔块体与楚伊犁块体在早古生代的汇聚作用有关。 这一认识不仅能够解释上述 S 型和埃达克质黑云母花岗岩的成因，还能阐释志留系地层与早泥盆世砾岩之间的不整合。伊犁地块北部完成微陆块的拼贴之后，经历了晚古生代强烈的岩浆活动， 并形成了显著的山弯构造变形。为理解板块构造-岩浆活动-山弯变形之间的关系，本论文对伊犁地块北部泥盆纪岩浆岩进行了锆石 U-Pb 定年、 锆石 Hf 同位素分析、全岩地球化学和 Nd-Sr 同位素研究。锆石 U-Pb 定年结果表明， 存在 390.6±1.8 Ma 和 371.2±2.4 Ma 两期岩浆事件。岩石为二长花岗岩， 具高的 SiO2 含量（75.9-77.9 wt.%和 74.1 wt.%），中-高 K2O 含量（2.06-3.85 wt.%和 3.81-4.82 wt.%），显示钙碱性和过铝质特征（A/CNK=1.02-1.03 和 1.03-1.09）。它们具 Ba、 Nb、 Ta、P 和 Ti 相对于 LREEs、 Rb 和 Th 的明显亏损， 显示出俯冲相关岩浆的显著特征。锆石 εHf(t)值的变化（两个样品分别为-0.60 至+5.53 和+2.12 至+8.39）表明，古老的地壳岩石和幔源新生组分之间存在广泛的相互作用。因此，中-晚泥盆世岩浆活动可与哈萨克斯坦拼贴体系泥盆纪火山带（DVB） 相联系， 它是准噶尔洋洋壳的俯冲形成的岩浆带。 伊犁地块北部早泥盆世-早石炭世弧相关岩浆活动的稳态分布和长期地球化学变化化趋势，使我们推断哈萨克斯坦山弯构造南缘岩浆岩带未发生明显后撤。 因此， 山弯构造西部及北翼快速后撤 vs.伊犁地块北部正常俯冲，支持用非对称俯冲板片后撤模式来解释哈萨克斯坦拼贴体系第一阶段的弯曲。 |
| Other Abstract | The Central Asian Orogenic Belt (CAOB) is one of the world’s largestaccretionary orogens since the Phanerozoic. The Kazakstan collage system representsone of the largest and most complex domains within the CAOB and is a key area forunderstanding the tectonic history of the entire belt. It was expanded mainly bymultiple amalgamations of several continental fragments in the early Paleozoic bycontinuous accretion and collage, and then experienced the bend in the late Paleozoic,forming the current pattern. However, there are still many controversies on the originof the continental fragments, the age and nature of the island arc, timing and processof these accretionary or amalgamation events, and the dynamic mechanism of theformation of the Kazakhstan Orocline, etc. Yili block is located in the southeastmargin of the college system. It has a Precambrian basement and Paleozoic island arcs.The study of Precambrian basement properties and Paleozoic tectonic evolution is ofgreat significance to solve the above problems.Granitoids are the main component of the continental crust, recording theaccretion and differentiation of continental crust materials, and is the key materialcarrier of continental formation and evolution. In the North Yili block, the two-micagranitic gneiss intruded at 851.5 ± 3.2 Ma, and the migmatization represent animportant anatexis at the age 913.8 ± 3.7 Ma. The rocks are characterized by highsilicon (≥ 70% wt.%), alkali rich (K2O + Na2O = 6.43-9.07 wt.%), high A/CNK value(1.13-1.25), similar to typical S-type granite. Abundant positive zircon εHf(t) values(-5.67 to +0.83) and the old Hf two-stage model age (TDM2 = 1.69-2.12 Ga) indicatethat the two-mica granitic gneiss may be the product of Paleoproterozoic crustalreconstruction in the context of crustal thickening. The late Sinian (558.6 ± 9.1 Ma)monzogranite is I-type granite, which is characterized by high silicon (≥ 70% wt.%),alkali rich (K2O + Na2O = 7.98-8.65 wt.%), and high Na2O (4.20-5.53 wt.%) content.The depleted zircon εHf(t) value (+1.98 to +8.39) and the high Mg# value (35-42)indicate the addition of mantle-derived material in the source area. The monzograniteshows the relative depletion of Nb, Ta, P, and Ti and the enrichment of LILEs (eg. K,Ba), which is consistent with the arc magma formed in the subduction related tectonicenvironment, and may be the product of the subduction of oceanic crust formed by thebreakup of Rodinia supercontinent.The study of detrital zircons from the metasedimentary in Wenquan group showsthat it was deposited from the late Mesoproterozoic to the early Neoproterozoic. Theages of zircons are mainly in 850-950 Ma and 1100-1450 Ma. Zircons of 850-950 Mamay have recorded the regional migmatization. About 80% of the zircons in thisperiod have enriched εHf(t) isotopes, indicating that crustal reworking was the mainprocess. Zircons aged 1100-1450 Ma were originated from the Yili Block or anothernear source. 70% of the zircons in this period are characterized by depleted εHf(t)isotopes, indicating that the source area is dominated by crustal growth. Throughregional comparison, there was no significant difference between the South and theNorth Yili block in Neoproterozoic, and they may have a close tectonic affinity with theChinese Central Tianshan block in this period.This paper reports Ordovician (ca. 456 Ma) amphibolites and Silurian (ca. 420Ma) granites in the North Yili block record the early Paleozoic magmatic events in thestudy area and reflect the early tectonic evolution history of the paleo Asian Ocean.The amphibolites are characterized by high MgO (4.91-9.89 wt.%) contents, positivezircon εHf(t) values (-0.95 to +4.96), and enriched LREEs relative to HFSEs,resembling the chemical signatures of basaltic magmas that originate from partialmelting of a depleted mantle wedge metasomatized by slab-derived fluids throughsubduction process. The garnet-bearing granites have peraluminous A/CNK ratios(1.06-1.10), and high (87Sr/86Sr) i value (0.715), demonstrating that they are S-typegranites via anatexis of sedimentary rocks by crustal thickening of orogenic collision,which is compatible with their abundant zircon inheritances and negative whole-rockεNd(t) value (-0.4) and zircon εHf(t) values (-4.11 to -1.99). The adakitic biotitegranites have high SiO2, low MgO contents, high Sr (453-628 ppm), Sr/Y ratios(31-97), and depleted HREEs. Combined with the high initial Sr isotopic(0.7092-0.7098), and a wide range of εNd(t) values (-3.3 to 5.0), indicate generation bythe partial melting of a mixing source of juvenile mafic lower crust and ancientbasement at a deep crustal level. Those two episodes of intrusion emplaced in thesouthern domain of the Aktau-Junggar block, westward extension of which has anoutcrop of ophiolitic mélange separating itself from Chu-Yili block. The sequentialtransition from subduction-related mafic magmatism to collision-associated felsicplutonism can be interpreted by convergence between the Aktau-Junggar block andChu-Yili block in Early Paleozoic. Accordingly, the proposed orogenic scenario likelytriggered S-type and adakitic magmatism, terminated marine sedimentation, and caused unconformity between Silurian strata and early Devonian conglomerates.After the amalgamation of the continental fragments in the North Yili block, itexperienced strong magmatism and the process of oroclinal bending in the latePaleozoic. To understand the relationship between plate tectonics-magmatism-bendingdeformation, we conducted zircon U-Pb dating and Hf isotopic analyzing as well aswhole-rock geochemical and Nd-Sr study for the Devonian magmatic rocks in theNorth Yili block. Zircon U-Pb dating results showed two phases of magmatism of390.6 ± 1.8 Ma and 371.2 ± 2.4 Ma, respectively. These rocks have monzogranitecompositions, with high SiO2 (75.9-77.9 wt.% and 74.1 wt.%), medium-high K2O(2.06-3.85 wt.% and 3.81-4.82 wt.%) concentrations, showing calc-alkaline andperaluminous characteristics (A/CNK = 1.02-1.03 and 1.03-1.09). They also displayevident depletions in Ba, Nb, Ta, P, and Ti relative to LREEs, Rb, and Th, showingstriking features of subduction-related magma. The variations of zircon εHf(t) values(-0.60 to +5.53 and +2.12 to +8.39 for two samples) may suggest an extensiveinteraction between old crustal rocks and mantle-derived juvenile components.Therefore, the Middle-Late Devonian magmatism can be correlated with DevonianVolcanic Belt in Kazakhstan, which constituted a magmatic belt generated by thesubduction of Junggar-Ocean plate. The steady-state distributions and long-termgeochemical variations of Early Devonian-Early Carboniferous arc-relatedmagmatism in the North Yili block allow us to conclude the lack of retreat ofmagmatic belts in the southern limb of the Kazakhstan Orocline. Accordingly, rapidretreat in the west and north limbs of orocline vs. normal subduction in theNorthwestern Chinese Tianshan, supports the asymmetric retreat model interpretingthe first stage of bending of Kazkhstan collage system. |
| Subject Area | 地球探测与信息技术 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/15476 |
| Collection | 中国科学院新疆生态与地理研究所 研究系统 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 孙敏佳. 西天山伊犁地块北部前寒武纪基底属性及古生代构造演化[D]. 北京. 中国科学院大学,2020. |
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