伊宁地块石炭纪火山岩地球化学特征及岩石成因

发布时间：2018-07-07 22:46

  本文选题：火山岩 + 地球化学特征与成因　； 参考：《长安大学》2017年博士论文

【摘要】：新疆伊宁地块广泛分布石炭纪火山岩系,正确认识和鉴定其构造背景是破解西天山晚古生代洋盆闭合和构造体制转变的关键所在。本研究以区内早石炭世大哈拉军山组和晚石炭世伊什基里克组火山岩为研究对象,在野外调查和查阅各类地质资料的基础上,重编区域地质图,重新划分火山岩地层层序,掌握其时空分布状态、岩石组合、区域变化规律,划分喷发旋回,建立年代格架,总结地球化学特征,并对比两组火山岩在地质特征和地球化学特征方面存在的差异,深入研究其主微量元素地球化学特征、Sr-Nd及Lu-Hf同位素地球化学特征,分析源区性质和成因类型,为探讨西天山晚古生代构造演化提供新的依据。认识如下:1.大哈拉军山组在区内出露面积最广,地层强烈褶皱,主要由玄武岩、安山岩、英安岩、流纹岩及同质火山碎屑岩组成,属钙碱性系列,其中安山岩出露厚度最大,基—中—酸性火山熔岩厚度比为1∶8∶1,主体以爆发相为主,溢流相次之,爆发指数普遍较大,最高可划分为7个喷发旋回;伊什基里克组火山岩在区内呈带状分布,总体呈宽缓的背向斜或单斜产出,熔岩以玄武岩、玄武安山岩和流纹岩为主,缺少或缺失安山岩,具有双峰式火山岩特征,基性、中性、酸性火山岩熔岩厚度比为4∶1∶5,以溢流相为主,爆发相次之,爆发指数偏小,可划分3~5个喷发旋回。2.大哈拉军山组火山岩锆石U-Pb年龄集中在346.3~336.0Ma,表明其地质时代为早石炭世;而伊什基里克组火山岩锆石U-Pb年龄则多为313.4~299.4Ma,形成时代为晚石炭世。3.大哈拉军山组火山岩SiO_2含量45.43%~79.13%,显示从基性到酸性逐渐演化过度趋势,样品普遍富集大离子亲石元素和轻稀土元素(LREE=10.93~348.63×10~(-6)),亏损高场强元素和重稀土元素(HREE=6.62~75.62×10~(-6)),具有明显的Nb(1.02~41.58×10~(-6))、Ta(0.03~4.47×10~(-6))、Ti负异常,部分样品Nb含量较高,具有富Nb岛弧玄武岩特征;该组玄武安山岩样品(87Sr/86Sr)i=0.7041~0.7093,εNd(t)=+0.77~+7.34,安山岩样品(87Sr/86Sr)i=0.7050~0.7079,εNd(t)=+0.87~+3.24,投点较集中,而流纹岩(87Sr/86Sr)i与εNd(t)变化范围较大;176Hf/177Hf=0.282352~0.282768,εHf(t)为-8~+6.9,显示该组火山岩来源于受俯冲流体/熔体交代的地幔楔的部分熔融,且受到不同程度的地壳混染作用;结合构造环境判别图解显示大哈拉军山组火山岩具有陆缘弧火山岩特征。4.伊什基里克组火山岩具有双峰式特征,其中玄武岩SiO_2含量为42.86~53.26%,里特曼指数平均6.43,流纹岩SiO_2含量为70.16~77.72%,碱度率平均6.51,属碱性系列,强烈富集大离子亲石元素和轻稀土元素(LREE=32.7~363.55×10~(-6)),亏损高场强元素和重稀土元素(HREE=3.81~65.55×10~(-6)),流纹岩微量元素特征与A型花岗岩类似;玄武安山岩样品(87Sr/86Sr)i=0.7036~0.7073,εNd(t)=+2.36~+4.89,流纹岩(87Sr/86Sr)i=0.7022~0.7056,εNd(t)变化范围较大(+2.88~+7.43),平均值为4.52;176Hf/177Hf为0.282190~0.283086,εHf(t)=-14.1~+17.4,显示有新元古代陆壳物质的加入,结合地球化学图解我们认为晚石炭世伊宁地块已进入碰撞后伸展阶段。5.大哈拉军山组玄武岩浆源自受消减板片析出的流(熔)体交代的地幔楔部分熔融,安山岩浆来源于受地幔楔影响的地壳根部,酸性岩浆则起源于稳定的下地壳;晚石炭世造山带根部岩石圈发生拆沉作用,导致软流圈地幔物质上涌,上地幔物质部分熔融形成伊什基里克组玄武岩浆,长英质岩浆是玄武岩浆对下地壳的底侵作用形成的。6.伊宁地块早石炭世发育弧前-岛弧-弧后盆地钙碱性火山-沉积建造,是塔里木板块北缘的主要组成部分;而晚石炭世双峰式火山岩则形成于伸展构造环境,是准噶尔板块与塔里木板块缝合后的陆内建造,因而古洋盆的关闭时限是早石炭世晚期。
[Abstract]:The Carboniferous volcanic rock series is widely distributed in the Yining massif of Xinjiang. It is the key to solve the closure and structural transformation of the late Paleozoic oceanic basin in the West Tianshan Mountains. This study is based on the study of the great Hara Jun Mountain formation and the Late Carboniferous I J Kilic group of volcanic rocks in the area. On the basis of various geological data, we reorganize the regional geological map, re divide the stratigraphic sequence of volcanic rocks, grasp the state of space-time distribution, rock assemblage, regional variation law, divide the eruption cycle, establish the age grid, sum up the geochemical characteristics, and compare the differences between the geological characteristics and geochemical characteristics of the two groups of volcanic rocks, and the depth of the geological characteristics and geochemical characteristics of the volcanic rocks. The geochemical characteristics of the main trace elements, the geochemical characteristics of Sr-Nd and Lu-Hf isotopes, the analysis of the nature and genetic types of the source region, provide a new basis for the exploration of the late Paleozoic tectonic evolution of the West Tianshan Mountains. The following are as follows: the 1. Hara Jun Shan formation is the most widely exposed area in the area and the strong fold in the ground layer, mainly from Xuan Wuyan, andesite, and angenite. The rhyolite and homogenous volcanic clastic rocks belong to the calc alkaline series. The thickness of andesite is the largest, the thickness ratio of the base to middle to acid volcanic lava is 1: 8: 1, the main body is the explosive phase, the overflow phase is second, the explosion index is generally large and the highest can be divided into 7 eruption cycles, and the isshilk Formation volcanic rocks are zonal distribution in the area. There is a broad and gentle back syncline or monocline output. The lava is mainly basalt, basaltic andesite and rhyolite, lacking or missing andesite. It has the characteristics of Shuangfeng type volcanic rocks, basic and neutral, the thickness ratio of the acid volcanic lava is 4: 1: 5, the overflow phase is the main, the eruption index is small, and the 3~5 eruption cycle.2. Da HA can be divided. The zircon U-Pb age of the lava of the La Jun Mountain Group is concentrated in 346.3~336.0Ma, indicating that the geological age is early Carboniferous, while the U-Pb age of the zircon from the iskiskic group is mostly 313.4~299.4Ma, and the formation age is the SiO_2 content 45.43%~79.13% of the Late Carboniferous.3. great Hara Jun Mountain volcanic rocks, indicating the gradual evolution from the base to the acid. The samples are generally enriched with large ion stone and light rare-earth elements (LREE=10.93~348.63 x 10~ (-6)), high field strong elements and heavy rare earth elements (HREE=6.62~75.62 x 10~ (-6)), which have obvious Nb (1.02~41.58 * 10~ (-6)), Ta (0.03~4.47 x), negative anomaly, high content of some samples, and characterized by rich island arc basalt; this group of basalt The andesite samples (87Sr/86Sr) i=0.7041~0.7093, epsilon Nd (T) =+0.77~+7.34, andesite samples (87Sr/86Sr) i=0.7050~0.7079, and Nd (T) =+0.87~+3.24, are concentrated, while the rhyolite (87Sr/86Sr) I and epsilon has a larger range. 0.282768, epsilon is regarded as the origin of the group of volcanic rocks from subduction fluid / melt metasomatism The partial melting of the mantle wedge is affected by different degrees of crustal contamination, and it shows that the volcanic rocks of the great Hara Jun Mountain volcanic rocks have the characteristics of Shuangfeng type of the.4. iskolk formation, including the SiO_2 content of the basalt, the average 6.43 of the RRT man index, and the rhyolite SiO_2. The content is 70.16~77.72%, the average alkalinity rate is 6.51, which belongs to the alkaline series, which strongly enriches the large ion stone elements and the light rare earth elements (LREE=32.7~363.55 x 10~ (-6)), the high field and strong elements and the heavy rare earth elements (HREE=3.81~65.55 * 10~ (-6)). The characteristics of the trace elements in the rhyolite are similar to those of the A type granite, and the basalt andesite samples (87Sr/86Sr) i=0.7036~0.707 (87Sr/86Sr) i=0.7036~0.707. 3, epsilon Nd (T) =+2.36~+4.89, rhyolite (87Sr/86Sr) i=0.7022~0.7056, epsilon Nd (T) with a larger range (+2.88~+7.43) with an average value of 4.52, 176Hf/177Hf for 0.282190~0.283086, and Hf (T), showing the addition of the Neoproterozoic continental crust material, and combined with the geochemical diagram of the earth ball, we think that the Late Carboniferous Yining massif has entered the post collision extension stage. The basaltic magma of the.5. great Hara Jun Shan formation originated from the partial melting of the mantle wedge, which was precipitated by subtractive plates. The magma of Anshan magma originated from the crust root of the mantle influenced by the mantle wedge, and the acid magma originated from the stable lower crust, and the lithosphere in the roots of the Late Carboniferous orogenic belt resulted in the upwelling of the mantle material in the asthenosphere and the upper mantle. The partial melting of mantle material forms the basalic magma in the isshelic formation, and the felsic magma is the calc alkaline volcano sedimentary formation of the Early Carboniferous arc - arc basin of the Early Carboniferous arc - arc basin of the.6. Yining massif and the main component of the northern margin of the Tarim plate, while the Late Carboniferous Shuangfeng type volcanic rocks were formed by the formation of the basaltic magma undergression of the lower crust. In the extensional tectonic setting, it is an intracontinental construction after the Junggar plate and the Tarim plate are sutured. Therefore, the closing time of the paleoceanic basin is in the late Early Carboniferous.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.14
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本文编号：2106525