晚古生代伊犁地块北缘岩浆岩的成因及地质意义
文献类型：学位论文
| 作者 | 王祥松 |
| 答辩日期 | 2017-05-01 |
| 文献子类 | 硕士 |
| 授予单位 | 中国科学院大学 |
| 授予地点 | 新疆乌鲁木齐 |
| 导师 | 蔡克大 |
| 关键词 | 伊犁地块 中亚造山带 块体聚合 前进式造山 后撤式造山 陆壳生长 Yili Block Central Asian Orogenic Belt terrane assembly advancing orogeny retreating orogeny continental crust growth |
| 学位专业 | 工程硕士 |
| 英文摘要 | The Central Asian Orogenic Belt is one of the typical accretionary orogens on theEarth, and represents the major site of the continental crust growth during the Phanerozoic.The Central Asian Orogenic Belt can be devided into three collage systems, i.g., Siberiaarctive continental margin collage systems, Tarim and North China cratons collage systems,and Kazakhstan collage system. The Kazakhstan collage system is located at thecombinative region between the other two collage systems, and is characterized by thetypical oroclinal bending structure. The northern Yili Block is situated inboard in thesouthern limb of Kazakhstan collage system with numerous igneous rocks and ore deposits,and thus retains a record of the bending processes of the Kazakhstan Orocline and theassociated evolution of the Junggar Ocean in the late Paleozoic. However, the latePaleozoic evolution of Junggar ocean, the terrane assembly process and continental crustgrowth in the northern Yili Block have been poorly constrained. This thesis focuses on theLate Paleozoic igneous rocks from the Borohoro and Alataw area in the northern YiliBlock. Detailed geological field investigations combined with petrology, mineralogy,geochronlogy, major and trace element, Sr-Nd-Hf-O isotope data are reported in this study,for the sake of investigating the petrogensis of these rocks, their temporal-spatialdistribution and associated geodynamic processes, identify the tectonic evolution andimplication for continental crust growth and formation of ore deposits. The majorconclusions are summarized as follow:（1）These granitoids are mainly monzogranite, K-feldspar granite and granodiorite.On the basis of the chronological study, these samples are subdivided into Group 1 with theage of the Late Devonian (374-369 Ma) and Group 2 with the age of the LateCarboniferous (ca.304 Ma). They have similar major and trace elements contents, butdistinct Sr-Nd-Hf isotopic compositions. Most of these granitoids show high-Kcalc-alkaline and metalumious affinities, and enriched in large ion lithophile elements(LILE) and depleted in high field strength elements (HFSE), and contain low Sr/Y(3.4-20.7) and Sr (96-431 ppm) values, indicating typical arc geochemical affinities. They have variable SiO2 (62.6-72.9 wt.%) and Fe2O3T (2.54-5.21 wt.%) contents, and Mg#(33-51) values. The Group 1 samples display slightly higher initial 87Sr/86Sr ratios(0.7075-0.7089) but lower εNd(t) (+0.3 to +0.9) values than those of Group 2 samples(87Sr/86Sr(i)= 0.7060-0.7066 and εNd(t)= +1.7 to +2.0). The Group 1 samples show the lowerεHf(t) (-3.62 to +6.79) values and older TCDM (0.90-1.61 Ga) than those of Group 2 samples(εHf(t) of +1.21 to +11.3 and TCDM of 0.56 to 1.25 Ga). These features suggest that thegranitoids were derived from a hybridized source of a juvenile materials (includecrust-derived and mantle-derived magmas) and an old metamorphic component, while theGroup 2 samples have greater contribution of juvenile materials.（2）The Nd-Hf isotopic compositions of granitic rocks from northern Yili Blockshow comparable zircon εHf(t)-time and whole-rock εNd(t)-time patterns with an abruptchange at ca. 360 Ma. During ca. 400-360 Ma igneous isotopic features are characterizedby a large spread of zircon εHf(t) values (-12 to +10) and whole-rock εNd(t) values (-5 to+5), and an overall decreasing trend with time, whereas ca.360-300 Ma igneous isotopicfeatures have mostly positive zircon εHf(t) values (+2 to +12) and whole-rock εNd(t) values(-2 to +8) and gradually increasing with time, suggesting a subduction tectonic switch froman advancing subduction of the Junggar oceanic plate to the retreating subduction wasidentified occurred at ca.360 Ma.（3）Combing the data from this study and published in the study area, showing thatgranitic rocks have high whole-rock εNd(t) and zircon εHf(t) values with the affinity ofdepleted source, which indicate the continental crust growth event. In the Hf isotopesystem, the modeling results show that during the 400-300 Ma, about 15-100 % juvenilematerials with varying degrees involved in the formation of granitic rocks, while in the Ndisotope system, the modeling results show that about 5-60 % juvenile materials withvarying degrees involved in the formation of granitic rocks during the 400-300 Ma.（4）For the ca. 300 Ma volcanism, the ignimbrites have low SiO2 (65.8-71.5 wt.%)and Mg# (6-13) values, and exhibit arc affinity with significantly enrichment of large ionlithophile elements (LILE) and depletement of high field strength elements (HFSE) such as Nb, Ta and Ti. The whole-rock εNd(t) and zircon εHf(t) values range from +6.9 to +7.0 and+9.9 to +14.1 respectively, indicating a juvenile basaltic lower crustal origin. Rhyoliteshave slightly high SiO2 (72.7-74.0 wt.%) and K2O (3.86-4.53 wt.%) contents, high zirconδ18O (11.67-13.23‰) values, and low whole-rock εNd(t) (+2.9 to +3.8) and zircon εHf(t)(+2.8 to +10.0) values, which may suggest sediment involvements during magmageneration. In contrast, for the ca. 288 Ma plutonism, the biotite granites have obviouslyhigher SiO2 (74.7-75.5 wt.%) contents and whole-rock εNd(t) (+7.7 to +8.8), zircon εHf(t)(+9.8 to +12.7), and lower zircon δ18O (5.99-6.84‰) values, than those of the ca. 300 Mavolcanic rocks, which are consistent with signatures of juvenile magma source.（5）The ca.300 Ma ignimbrites and rhyolites have high zircon whole-rock saturationtemperature (888-938℃ and 815-832℃), and high εHf(t) values, indicating an hightemperature magmatic event at ca. 300 Ma, we interpret this magmatic episode having alink with arc-continent collision/amalgamation of the West Junggar Terrane and Yili Block,which intrigued the asthenospheric upwelling through slab break-off. The ca.288 Mabiotite granites have low zircon whole-rock saturation temperature (723-735℃), withresidual amphibole in the source. Thus, we infer the subsequent strike-slipping of NorthTianshan Fault that facilitated introduction of water-fluxes triggering hydrous partialmelting of juvenile lower crust. |
| 学科主题 | 测绘工程 |
| 语种 | 中文 |
| 源URL | [http://ir.xjlas.org/handle/365004/14901]  |
| 专题 | 新疆生态与地理研究所_研究系统_荒漠环境研究室 |
| 作者单位 | 中国科学院新疆生态与地理研究所 |
| 推荐引用方式 GB/T 7714 | 王祥松. 晚古生代伊犁地块北缘岩浆岩的成因及地质意义[D]. 新疆乌鲁木齐. 中国科学院大学. 2017. |
入库方式： OAI收割
来源：新疆生态与地理研究所
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