华北克拉通东部白垩纪中基性火山岩的年代学和地球化学特征

发布时间：2018-05-19 12:46

本文选题：早白垩世 + 中基性火山岩　；参考：《中国科学院研究生院(广州地球化学研究所)》2015年博士论文

【摘要】：华北东部早白垩世火山活动处于华北大规模岩浆活动的高峰期,良好地记录了华北克拉通破坏过程中大陆下岩石圈地幔的热-化学状态。对华北东部早白垩世火山岩的研究能够帮助更好地理解克拉通岩石圈减薄和破坏的时空演化规律及其深部地球动力学背景。本论文以山东和辽东地区早白垩世中基性火山岩为研究对象,通过40Ar-39Ar同位素定年精确厘定火山岩的时空分布特征,通过样品全岩地球化学以及单矿物主量元素分析揭示岩浆源区的性质、矿物组成、水含量以及富集和交代事件,进而探讨克拉通破坏的深部动力学过程。研究结果表明,鲁西地区青山组火山岩的喷发年龄为129~115 Ma,而胶东地区青山组火山岩的喷发时限为126~91 Ma。因此,鲁西青山组火山岩的喷发时间早于胶东地区(约3 Ma),而且持续时间相对较短。辽东抚顺小岭组火山岩的喷发年龄为~110 Ma,明显晚于山东青山组火山岩和辽西义县组火山岩,暗示华北东部早白垩世岩浆活动的时空不均一性。鲁西邹平青山组火山岩以玄武安山岩和安山岩为主,并有少量玄武岩。邹平安山岩的斑晶主要为高钙和低钙普通辉石、钙镁闪石和斜长石。角闪石温压计计算表明对应的初始岩浆熔融温度为916~943°C,与熔体平衡的水的含量(H2Omelt)为4.2~5.9 wt%。全岩样品的Si O2=50.66~58.76 wt%、Mg O=1.68~10.52 wt%,样品富集LILE,亏损HFSE,没有明显的Eu正异常,εNd(t)值变化较大(+0.1~-7.96),而87Sr/86Sr比值较一致(0.7043~0.7060),落在了EM1以及MORB与EM地幔演化趋势线上。结果表明,邹平青山组火山岩可能为软流圈熔体与古老岩石圈地幔相互作用的产物。蒙阴青山组火山岩由玄武岩和安山岩组成。其中玄武岩的斑晶以透辉石和普通辉石为主,伴有斜长石。辉石韵律环带发育,反映了岩浆的反复抽取-再补给过程。蒙阴安山质岩的斑晶主要为钙镁闪石和镁绿钙闪石、普通辉石和斜长石。角闪石温压计计算表明蒙阴安山质岩岩浆熔融温度为880~973°C,与熔体平衡的水含量(H2Omelt)为2.6~5.4 wt%,较邹平安山岩的低。玄武岩样品的Si O2=50.4~51.8 wt%、Mg#=60.3~62.1,其Ti O2、Fe2O3t、Ca O、Mn O和Al2O3含量与方城玄武岩的接近;而安山质岩样品的Si O2=61.2~63.4 wt%、Mg#=50.3~56.1。玄武岩和安山质岩样品的87Sr/86Sr初始值分别为0.7093和0.7110,εNd(t)值分别为-10.5和-14.1,均落在EM2地幔区域内。分析的蒙阴火山岩均富集LILE,亏损HFSE,其可能来源于受到俯冲扬子板片析出流体/熔体改造的富集岩石圈地幔的部分熔融。莱阳青山组火山岩主要由玄武安山岩和安山岩组成,斑晶主要为单斜辉石和斜长石。单斜辉石环带发育,从核部到幔部,一般为正环带,而从幔部到边部则为反环带。核部的Mg#值高达86,暗示了其与原始岩浆是平衡的。完整的正环带-反环带旋回反映了部分熔融过程中岩浆的不断抽取-再补给过程。全岩样品的Si O2=55.47~61.61 wt%,Mg O=3.48~5.74 wt%,富集LILE,亏损HFSE,显示弱的Eu负异常,类似EM2的Sr-Nd组成(εNd(t)=-16.6~-17.6、87Sr/86Sr=0.7087~0.7110)。即墨青山组火山岩主要由玄武岩、玄武安山岩、粗面安山岩和英安岩组成,呈现双峰式特征。分析的英安岩全岩样品Si O2较高(62.49~66.57wt%)、Mg O(1.49~2.99 wt%)较低、Mg#值变化大(37.14~60.95)。样品富集LILE,亏损HFSE,具有弱的Eu负异常,εNd(t)值和87Sr/86Sr初始值分别为-16.7~-17.2和0.70839~0.70843,与莱阳安山岩的接近。结果表明,莱阳和即墨青山组火山岩可能为受俯冲扬子板片析出流体/熔体改造的富集岩石圈地幔部分熔融的产物。辽东小岭组火山岩由玄武岩、安山岩和英安岩组成,主要斑晶为橄榄石、透辉石、Mg-普通辉石、镁绿钙闪石和斜长石。角闪石温压计计算结果表明熔融岩浆温度为902~968°C,与熔体平衡的水含量(H2Omelt)为3.9~6.5 wt%。全岩样品的Si O2=45~62 wt%、Mg O=1.2~9.2 wt%、Ca O=1.8~10 wt%,富集LIL E,亏损HFSE,具有类似EM1的Sr-Nd组成(εNd(t)=-8.7~-16.0、87Sr/86Sr=0.7046~0.7054)。除Ti O2外,样品的主量元素组成与在3~5 GPa实验压力条件下确定的无挥发分类似MORB的榴辉岩熔体的化学组成接近,但明显不同于典型的无水橄榄岩熔体的组成特征,表明其来源于辉石岩源区的部分熔融。橄榄石高的Ni和Fe/Mn比值,及低的Ca含量同样表明其来源于石榴石辉石岩地幔源区的部分熔融。该辉石岩源区可能与晚太古代-古元古代的地幔交代事件有关,通过俯冲再循环地壳物质与周围橄榄岩的固相相互作用形成。华北东部晚三叠世-早白垩世岩浆岩时空分布特征表明岩石圈减薄和克拉通破坏在时空上是不均一的。晚三叠世岩浆活动可能对应于扬子和华北板块陆-陆碰撞造山后的伸展背景,暗示着华北东南缘在晚三叠世开始出现破坏;早-中侏罗世的岩浆活动可能与古太平洋向东亚大陆边缘俯冲挤压作用有关。早白垩世岩浆活动可能与古太平洋板块俯冲方向改变及相应的板片撕裂和后撤有关。华北早白垩世火山岩大量角闪石的出现暗示了太平洋板块俯冲过程中大量的流体加入并交代富集岩石圈地幔。华北早白垩世火山岩的形成表明古太平洋俯冲及其析出流体(水)的交代作用对克拉通的破坏起到了重要作用。
[Abstract]:The early Cretaceous volcanism in eastern North China is in the peak period of large-scale magmatism in North China, which records the thermal and chemical state of the lower lithosphere mantle in the process of failure of the North China Craton. The study of Early Cretaceous volcanic rocks in eastern North China can help better understand the temporal and spatial evolution rules of the reduction and destruction of the cratonic lithosphere. In this paper, the basic volcanic rocks of the early Cretaceous in Shandong and Liaodong were studied in this paper. The characteristics of the space-time distribution of volcanic rocks were determined accurately by 40Ar-39Ar isotope dating, and the properties of the magma source area, mineral composition and water content were revealed by the total geochemistry of the samples and the analysis of the main elements of the single mineral elements. The results show that the eruption age of the Qingshan Formation volcanic rocks in the western Shandong Province is 129~115 Ma, and the eruption time of the Qingshan group volcanic rocks in Jiaodong area is 126~91 Ma., and the eruption time of the volcanic rocks in the Luxi Qingshan Formation is earlier than that of the Jiaodong region (about 3 Ma), and the eruption time of the volcanic rocks in the Western Qingshan Formation is earlier than that of the region (about 3 Ma). The eruption age of the volcanic rocks in the Fushun Xiaoling formation of Liaodong is ~110 Ma, which is obviously later than the volcanic rocks of the Qingshan group in Shandong and the volcanic rocks of the Yixian Formation in the west of Liaoning Province, suggesting that the magmatism of the early Cretaceous in the eastern part of North China is inhomogeneous. The volcanic rocks of the Zouping Qingshan Formation in the west of Luxi are mainly basaltic andesite and andesite, with a small amount of basalt. The speckles of rock. Zou Ping rocks are mainly high calcium and low calcium common pyroxene, calcite and plagioclase. The corresponding initial melting temperature of the hornblende indicates that the corresponding initial melting temperature of the magma is 916~943 C, and the content of the water in the equilibrium with the melt (H2Omelt) is Si O2=50.66 ~58.76 wt%, Mg O=1.68~10.52 wt%, and the sample is enriched. The loss of HFSE, there is no obvious Eu anomaly, and the value of the Nd (T) change is larger (+0.1~-7.96), and the 87Sr/86Sr ratio is consistent (0.7043~0.7060), which falls on the evolution trend of EM1 and MORB and EM mantle. The result shows that the volcanic rocks in the Qingshan Formation of Zouping may be the product of the interaction between the asthenosphere melt and the old lithospheric mantle. The volcanic rocks of the Qingshan Formation in Mengyin The basalts and andesite are composed of diopside and common pyroxene, accompanied by plagioclase and pyroxene rhythmic belt, which reflects the repeated recharge of the magma. The speckles of the Anshan rock in Mengyin are mainly calcite and magnesium calcite, ordinary pyroxene and plagioclase. The magma melting temperature of Yanshan rock is 880~973 C, and the water content (H2Omelt) is 2.6~5.4 wt% and lower than Zou Ping mountain. The Si O2=50.4~51.8 wt% of the basalt samples, Mg#=60.3~62.1, Ti O2, Fe2O3t, and the proximity of the square city basalt. The initial 87Sr/86Sr values of the basalt and Anshan rock samples are 0.7093 and 0.7110 respectively, and the values of the epsilon Nd (T) are -10.5 and -14.1 respectively in the EM2 mantle region. The analysis of the Mengyin volcanic rocks enriched LILE and lost HFSE, which may originate from the partial melting of the enriched lithosphere mantle transformed by the precipitated fluid / melt from the subducted Yangtze plate. The volcanic rocks of the Yang Qingshan Formation, mainly composed of basaltic andesite and andesite, are mainly monoclinopyroxene and plagioclase. The monoclinopyroxene belt is developed, from the nucleus to the mantle, which is generally a positive ring, but from the mantle to the edge. The Mg# value of the nucleus is up to 86, suggesting that it is balanced with the original magma. It reflects the continuous extraction and recharge process of the magma during partial melting. The Si O2=55.47~61.61 wt%, Mg O=3.48~5.74 wt% of the whole rock sample, the enrichment of LILE, the loss of HFSE, the weak negative Eu anomaly, the Sr-Nd composition of the EM2, which is mainly composed of Xuan Wuyan and Xuanwu mountain. Rock, rough andesite and anganite are characterized by Shuangfeng style. The analysis of Si O2 is higher (62.49~66.57wt%), Mg O (1.49~2.99 wt%) is lower, Mg# value is larger (37.14~60.95). Sample enrichment LILE, loss HFSE, weak Eu negative anomalies, epsilon values and initial values respectively The close of Laiyang andesite shows that the volcanic rocks in Laiyang and Jimo Qingshan Formation may be the product of partial melting of the enriched lithosphere mantle transformed by fluid / melt from the subducted Yangtze plate. The Liaodong Xiaoling formation is composed of Xuan Wuyan, andesite and anganite, and the main speckles are olivine, diopside, Mg- ordinary pyroxene, magnesium green calcium. The calculation results of the amphibole and plagioclase show that the molten magma temperature is 902~968 C, and the water content of the melts (H2Omelt) is Si O2=45~62 wt% of the whole rock samples of 3.9~6.5 wt%., Mg O=1.2~9.2 wt%. In addition to Ti O2, the composition of the main elements of the sample is close to the chemical composition of the eclogite melts without volatile components similar to MORB determined under the 3~5 GPa experimental pressure, but obviously different from the typical composition characteristics of the peridotite melts, indicating that they are derived from the partial melting of the pyroxene source region, the Ni and Fe/Mn ratios of olivine high, and the low C. The content of a also indicates that it originated from the partial melting of the mantle source area of the garnet pyroxenite. The pyroxene source area may be related to the late Archean Paleoproterozoic mantle metasomatism, and formed by the solid interaction of the subduction recirculating crustal substance and peridotite. The late three fold Early Cretaceous magmatic rocks in eastern North China were distributed in time and space. The sign indicates that the lithosphere thinning and cratonic failure are uneven in time and space. The late three superposition of the magmatism may correspond to the extension background of the Yangtze and North China plate continental collision orogenic orogeny, suggesting that the southeast margin of the North China began to occur at the beginning of the late three fold, and the early Middle Jurassic may be from the palaeopacific to the edge of the East Asia continent. The early Cretaceous magmatic activity may be related to the change of the subduction direction of the paleo Pacific plate and the corresponding plate tear and withdrawal. The emergence of a large number of hornblende in the early Cretaceous volcanic rocks in North China suggests a large number of fluids in the subduction of the Pacific plate and the metasomatism of the enrichment of the lithosphere mantle. The formation of the mountain rocks indicates that the subduction of the paleo Pacific Ocean and the metasomatism of the precipitation fluid (water) played an important role in the destruction of the craton.
【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P588.14;P597.3

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