新疆东准噶尔早古生代蛇绿岩SHRIMP U-Pb定年、成因类型及其构造环境

发布时间：2018-07-09 10:28

本文选题：东准噶尔 + 早古生代蛇绿岩　；参考：《中国地质大学》2016年博士论文

【摘要】：东准噶尔造山带是中亚造山带的重要组成部分,位于中亚造山带中部,是研究中亚造山带古生代构造演化的关键区域,扎河坝-阿尔曼泰-北塔山蛇绿岩带为该造山带中早古生代形成的蛇绿岩,本文针对该蛇绿岩带进行了较为详细的研究,结合前人已有研究资料,对该蛇绿岩带的SHRIMP U-Pb年龄、锆石氧同位素特征、成因类型以及构造环境进行了探讨。该蛇绿岩带的研究为确定东准噶尔造山带的构造演化历史提供了可靠依据及新的认识。扎河坝-阿尔曼泰-北塔山蛇绿岩带由于受到强烈的构造作用而发生强烈肢解,沿断裂带主要出露于扎河坝、阿尔曼泰以及北塔山地区,而每个区段蛇绿岩出露规模及出露的岩性存在差异,但整体上该蛇绿岩带出露蛇绿岩单元岩性较为齐全：(1)超基性岩类：方辉橄榄岩,及少量纯橄岩；(2)镁铁质堆晶岩类：二辉岩、辉长岩；(3)浅色岩类：奥长花岗岩、钠长岩、钠长花岗岩；(4)火山熔岩单元：玄武岩；(5)上覆岩性：玄武岩、辉绿岩、闪长岩、闪长斑岩等。扎河坝蛇绿岩中辉长岩的SHRIMP U-Pb年龄为488±, Ma(n=19; χ2=1.05)和481±4 Ma(n=9,χ2=0.89),与年龄对应的锆石δ18O的加权平均值为5.0±0.2‰(1σ)和5.1±0.3‰(1σ),与幔源锆石氧同位素值(δ18O幔源=5.3±0.3‰)完全一致,该年龄代表了辉长岩的结晶年龄；扎河坝蛇绿岩中奥长花岗岩的SHRIMP U-Pb年龄为485±3Ma (n=11,χ2=0.98),与年龄对应的锆石δ18O的加权平均值为5.2±0.2‰(1σ),与幔源锆石氧同位素值(δ18O 幔源=5.3±0.3‰)完全一致,该年龄代表了奥长花岗岩的结晶年龄,进而基本确定了扎河坝蛇绿岩的形成时代为488～481Ma,而相应岩石单元(辉长岩及奥长花岗岩)的地球化学特征揭示了该蛇绿岩带形成过程中可能受到一定程度俯冲消减带影响。阿尔曼泰蛇绿岩带的堆晶辉长岩中锆石SHR/MP U-Pb年龄分别为506± Ma (n=16,χ2=0.94)、515±3 Ma (n=17,χ2=0.30)及516±4 Ma (n=17, χ2=0.07)。与年龄值对应的锆石的δ18O加权平均值分别为5.5±0.1‰(1σ),5.1±0.1‰(1σ),5.2±0.2‰(1σ),与幔源锆石氧同位素值一致(δ18O 幔源=5.3±0.3‰),该年龄代表了辉长岩的结晶年龄,可以基本确定其代表了阿尔曼泰蛇绿岩的形成时代。辉长岩的地球化学特征揭示了阿尔曼泰蛇绿岩带形成过程中没有或者只是受到微弱的俯冲消减的影响。北塔山蛇绿岩辉长岩的SHRIM0PU.Pb年龄分别为494±3 Ma(χ2=1.16).495 ±2 Ma(n=20,χ2=0.07)以及497±3 Ma(n=15,χ2=0.37),其对应锆石的818O加权平均值分别为5.2士0.3%。(1σ)、5.2士0.1%o(1σ)以及5.1士0.1%o(1σ),与幔源锆石氧同位素值(δ18O馘=5.3士0.3%。)完全一致,该年龄代表了辉长岩的结晶年龄,亦代表了北塔山蛇绿岩的形成时代。辉长岩的地球化学特征表现为轻稀土亏损,重稀土略富集的左倾配分模式,大离子亲石元素相对富集,存在一定Nb的负异常,揭示了北塔山蛇绿岩形成过程可能受到一定程度的俯冲消减的影响。北塔山蛇绿岩中出露的花岗斑岩的锆石SHRIMPU-Pb年龄407士2 Ma,代表了花岗斑岩的形成年龄,对应锆石δ18O值为6.1士0.2%。(1σ),反映了其岩浆物质来源以下伏玄武质洋壳为主。通过地球化学特征分析并结合前人的研究成果,表明了其可能为岛弧区地壳增厚、下伏洋壳物质部分熔融的岩浆演化产物。与此同时,北塔山蛇绿岩和扎河坝蛇绿岩中存在的一组年轻锆石年龄,其与花岗斑岩形成年龄基本一致,其均可能形成于扎河坝-阿尔曼泰-北塔山洋盆汇聚闭合过程中,为限定该洋盆闭合时限提供了新的依据。结合前人研究成果,发现阿尔曼泰蛇绿岩带中出露一类玄武岩,其地球化学数据表现出SSZ型蛇绿岩的特征,表现为(1)似N-MORB轻稀土亏损REE配分模式；(2)(略)低于N-MORB的Ti/V比；(3)流体活动、大离子亲石元素富集；(4)没有、或只有微弱深部消减的地球化学显示。与马里亚纳弧前玄武相似,基本确定该类玄武岩属于弧前玄武岩,其是弧前SSZ型蛇绿岩的鉴别性岩石,进而揭示了扎河坝-阿阿尔曼泰-北塔山蛇绿岩带可能为SSZ型弧前蛇绿岩,形成于弧前环境,反映了阿尔曼泰洋初始消减的开始。与此同时,扎河坝-阿尔曼泰-北塔山蛇绿岩带不同区段出露有岛弧火山岩,地球化学特征显示了强烈的深部消减信号,指示了消减板片-地幔楔格架建立、消减组分因而卷入岩浆活动。
[Abstract]:The eastern Junggar orogenic belt is an important part of the Central Asian orogenic belt. It is located in the middle of the Central Asian orogenic belt. It is the key area to study the Paleozoic tectonic evolution of the Central Asian orogenic belt. The Zhan he Tai - Bei taashan ophiolite belt is the early Paleozoic ophiolite formed in the middle Paleozoic of the orogenic belt. This paper has carried out a more detailed study of the ophiolite belt. In the light of the previous research data, the SHRIMP U-Pb age of the ophiolite belt, the oxygen isotope characteristics of zircon, the genetic type and the tectonic environment are discussed. The study of the ophiolite belt provides a reliable basis for determining the tectonic evolution history of the eastern Junggar orogenic belt and the new understanding. The band is strongly dismembered because of strong tectonic action. Along the fault zone, it is mainly exposed in the Chaina dam, Arman Tai and the North Tashan area, and the Ophiolites in each section are different in the exposure scale and exposed lithology, but on the whole, the ophiolite with the ophiolitic Dan Yuanyan property is more complete: (1) the ultrabasic rock: olives Rock and a small amount of pure rite; (2) mafic heap rocks: two pyroxenite, gabbro; (3) light color rocks: oldite, sodium long rock, sodium feldspar; (4) volcanic lava unit: basalt; (5) lithology: basalt, diabase, diorite, diorite and so on. The SHRIMP U-Pb age of gabbro in the zhheba ophiolite is 488 +, Ma ( N=19, X 2=1.05) and 481 + 4 Ma (n=9, Chi 2=0.89), the weighted average value of zircon Delta 18O with age is 5 + 0.2% (1 sigma) and 5.1 + 0.3 per thousand (1 sigma), which is exactly the same as that of the mantle derived zircon oxygen isotopes (delta 18O mantle derived =5.3 + 0.3%). This age represents the age of the crystalline gabbro and the SHRIMP U-Pb age of the ordovite in the zhhe Ba ophiolite. With 485 + 3Ma (n=11, X 2=0.98), the weighted average value of zircon Delta 18O corresponding to age is 5.2 + 0.2 per 1000 (1 sigma), which is exactly the same as that of the mantle derived zircon oxygen isotope (delta 18O mantle source =5.3 + 0.3%). This age represents the age of the Ordovician granitic granite, and then basically determines the formation age of the Zha he Ba ophiolite from 488 to 481Ma, and the corresponding rock. The geochemical characteristics of the unit (gabbro and orogranite) reveal that the formation of the ophiolite may be affected by a certain degree subduction subduction zone. The zircon SHR/MP U-Pb ages in the heap gabbro of the Arman Thailand belt are 506 + Ma (n=16, Chi 2=0.94), 515 + 3 Ma (n=17, Chi 2=0.30) and 516 + 4 Ma (n=17, Chi 2=0.07). The mean values of delta 18O weighted zircon with age value are 5.5 + 0.1% (1 sigma), 5.1 + 0.1% (1 sigma) and 5.2 + 0.2 per 1000 (1 sigma), consistent with the oxygen isotope values of the mantle derived zircons (delta 18O mantle source =5.3 + 0.3 per 1000). This age represents the age of crystalline gabbro, and it can be basically determined that it represents the formation age of Arman Thailand ophiolite. The chemical characteristics of the sphere reveal that the formation process of the Arman Thailand ophiolite belt has no or only weak subduction. The SHRIM0PU.Pb age of the ophiolitic gabbro of the North Tashan ophiolite is 494 + 3 Ma (x 2=1.16).495 + 2 Ma (n=20, Chi 2=0.07) and 497 + 3 Ma (n=15, Chi 2=0.37), and the 818O weighted average of the corresponding zircon is 5.2, respectively. 0.3%. (1 sigma), 5.2 man 0.1%o (1 sigma) and 5.1 0.1%o (1 sigma) are exactly the same as the oxygen isotope of the mantle derived zircons (delta 18O =5.3 0.3%.). This age represents the age of the crystalline gabbro and represents the age of the formation of the ophiolite in the North Tashan. The geochemical characteristics of the gabbro are characterized by the loss of light rare earth and the left leaning partition of heavy rare-earth elements. The relative enrichment of the large ion stone elements and the negative anomaly of a certain Nb reveal that the formation process of the ophiolite may be affected by a certain degree of subduction. The zircon SHRIMPU-Pb age of the granite porphyry in the North Tashan ophiolite is 407 and 2 Ma, representing the formation age of the granite porphyry, and the corresponding zircon Delta 18O value of 6.1 SZ 0.. 2%. (1 sigma) reflects the main basaltic oceanic crust below the source of its magma material. Through the analysis of geochemical characteristics and the results of previous studies, it shows that it may be the crust thickening of the island arc region and the partial melting of the lower oceanic crust material. At the same time, a group of years in the northern Tashan ophiolite and the Zhanhe ophiolite. The age of light zircon is basically consistent with the formation age of granite porphyry, which may be formed in the process of convergence and closure of the Arman Tai - Bei Tashan oceanic basin, which provides a new basis for limiting the closed time limit of the ocean basin. In combination with the previous research results, it is found that a class of basalt is exposed in the Arman Thailand ophiolite belt, and its geochemical data is shown. The characteristics of SSZ ophiolite are (1) similar to N-MORB light rare-earth loss REE distribution pattern; (2) (slightly) lower than Ti/V ratio of N-MORB; (3) fluid activity, large ion stone element enrichment; (4) no, or only weak deep subtractive geochemical display. Similar to the pre arc basalt of maryyana arc, basically ascertain that this kind of basalt belongs to prearc basalt The rock, which is the differential rock of the pre arc SSZ ophiolite, reveals that the Zha he Tai - Arman Tai - Bei Tashan ophiolite belt may be SSZ - type pre arc ophiolite, which is formed in the pre arc environment and reflects the beginning of the initial reduction of the Arman Thailand. At the same time, the island arc fire is revealed in the different sections of the Zhaba - Arman Taibei Tashan ophiolite belt. The rock and geochemical characteristics show strong deep subduction signals, indicating the establishment of the subduction plate mantle wedge, and the subduction components are involved in the magmatic activity.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P597.3;P588

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