【作者】 项媛馨；

【导师】 巫建华；

【作者基本信息】 东华理工大学 ， 矿产普查与勘探， 2012， 硕士

【摘要】 华夏古板块和扬子古板块结合带内的广丰盆地和玉山盆地，均以红色碎屑岩和镁铁质火山岩组合为特征。广丰盆地火山-沉积岩系可划分为罗塘、赣州和圭峰三个群级岩石地层单位，火山岩分别产于赣州群上部和圭峰群上部；玉山盆地火山-沉积岩系可归入圭峰群，火山岩产于其上部。SHRIMP锆石U-Pb年代学研究表明，广丰盆地赣州群镁铁质火山岩锆石U-Pb年龄为99±0.7Ma，属晚白垩世最早期的产物；玉山盆地圭峰群镁铁质火山岩锆石U-Pb年龄为93±1Ma，属晚白垩世早期的产物。广丰、玉山盆地圭峰群镁铁质火山岩具有橄榄玄粗岩的矿物学和主元素特征：岩石具斑状结构，斑晶主要以斜长石、辉石为主，并常见橄榄石；辉石斑晶主要为单斜辉石，但常见斜方辉石，斜长石斑晶具有钾长石环边；全岩SiO₂含量范围为49.8%⁵3.6%（平均51.72%），（Na₂O+K₂O）（=5.00⁶.94%，平均6.35%）含量高，在TAS图解上落入碱性系列的范围；（Fe₂O₃+FeO）（=7.10⁹.99%，平均8.26%）、MgO（=2.30⁶.14%，平均4.20%）含量低，Fe₂O₃/FeO（=0.39¹2.87，平均2.84）比值高，在FAM图解上落入钙碱性系列的范围；K₂O（=2.40³.33%，平均2.79%）含量高，K₂O/Na₂O（=0.68¹.08，平均0.79）比值高，在SiO₂-K₂O图解上落入橄榄玄粗岩系列范围，在SiO₂-K₂O/Na₂O图解上落入高钾系列范围；Al2O3（=15.8¹8.4%）含量高且变化大，TiO2（=1.41².07%，平均1.69%）含量相对较低。广丰、玉山盆地橄榄玄粗岩稀土总量较高（ΣREE=239³93×10-6），轻稀土富集明显（（La/Sm）N=3.44⁴.55），无Eu（δEu=0.79⁰.97）、Ce（δCe=0.89¹.06）亏损，微量元素中明显富集亲石元素（Rb、Sr、Ba、Th等），高场强元素Nd、Ti强烈亏损，Nb/Th（=4.3⁸.2）比值和Ti/Yb（3088⁵444）比值较低，显示有地壳物质的加入。广丰、玉山盆地圭峰群橄榄玄粗岩在87Sr/86Sr（t）-SiO₂和εNd（t）-SiO₂图解上没有明显的相关性，在87Sr/86Sr（t）-1/Sr和εNd（t）-1/Nd图解上也没有明显的线性关系，而呈离散分布，这些都说明岩浆上升过程中陆壳混染不明显，地壳物质的加入是地幔源区混合的结果。广丰盆地和玉山盆地北部橄榄玄粗岩（87Sr/86Sr）i值为0.705856⁰.706352，εNd值为-0.07¹.93，n（206Pb）/n（204Pb）值为17.95¹8.08，n（207Pb）/n（204Pb）值为15.46¹5.54，n（208Pb）/n（204Pb）值为38.20³8.38；而玉山盆地东部橄榄玄粗岩（87Sr/86Sr）i值为0.703626⁰.703711， εNd值为3.40³.86， n（206Pb）/n（204Pb）值为17.80¹7.86，n（207Pb）/n（204Pb）值为15.20¹5.24， n（208Pb）/n（204Pb）值为37.82³7.93。在n（87Sr）/n（86Sr）-n（206Pb）/n（204Pb）、n（143Nd）/n（144Nd）-n（206Pb）/n（204Pb）和n（143Nd）/n（144Nd）-n（87Sr）n/（86Sr）图解中，广丰、玉山盆地圭峰群橄榄玄粗岩均位于亏损地幔（DMM）和EMⅡ型富集地幔之间，而且n（87Sr）/n（86Sr）和n（206Pb）/n（204Pb）呈正相关、n（143Nd）/n（144Nd）和n（206Pb）/n（204Pb）呈负相关，意味着两个盆地的橄榄玄粗岩源区中可能均有DMM和EMⅡ型地幔的贡献；玉山盆地东部橄榄玄粗岩更偏向DMM端元指示其DMM端元所占的比例更高。通过微量元素和相关构造环境图解（Ce-Y图解、Zr/Al₂O₃-TiO₂/Al₂O₃图解、Ce/P₂O₅-Zr/TiO₂图解和Zr×3-Nd×50-Ce/P₂O₅图解），显示广丰、玉山盆地圭峰群橄榄玄粗岩产出于后碰撞的构造环境。在早侏罗世或更早古太平洋板块向中国东南大陆发生俯冲，产生的流体交代交代岩石圈地幔使华南形成EMⅡ型富集地幔。晚白垩世早期，古太平洋板块俯冲角度由缓变陡，赣东北地区处于后碰撞的快速拉张环境，使原本加厚的地壳发生拆沉作用，导致软流圈地幔上涌并发生减压部分熔融，软流圈部分熔融产生的熔体进入岩石圈地幔并为后者发生部分熔融提供热量，软流圈部分熔融产生的熔体与岩石圈EMⅡ型富集地幔产生的熔体在源区混合形成橄榄玄粗质岩浆。由于广丰盆地和玉山盆地的分别位于广丰微板块和怀玉坳陷两个不同的次级构造单元之上，来自DMM的组份和EMⅡ型富集地幔的组份的不同比例混合，导致广丰和玉山盆地橄榄玄粗岩的同位素组成存在一定的差别。更多还原

【Abstract】 Guangfeng and Yushan basins are in the juncture between the Yangtze paleoplate andthe Cathaysian paleoplate，which are characterized by the red elastic rocks and maficvolcanic rocks.In Guangfeng basin，the volcanic-sedimentary rocks can divided into3lithostratigraphic units: Luotang group，Ganzhou group and Guifeng group，the volcanicrocks exist in the upper of Ganzhou group and Guifeng group in Yushan basin，thevolcanic-sedimentary rocks can be counted into Guifeng group，and the volcanic rocksexist in the upper group of Guifeng group.According to the SHRIMP U-Pb datingchronology，the zircon U-Pb dating is99±0.7Ma of the mafic volcanic rock of Ganzhougroup in Guangfeng basin，it belongs to the earliest Late Cretaceous. The zircon U-Pbdating is93±1Ma of the mafic volcanic rocks of Guifeng group in Yushan basin， itbelongs to the early Late Cretaceous.In Guangfeng and Yushan basins，the mafic volcanic rocks of Guifeng groupsubordinate to the shoshonite rocks by their the mineralogy and the major elementcharacteristics: they have porphyritic structure，the phenocrysts mainly are plagioclase，pyroxene，and also has olivine；the pyroxene mainly is clinopyroxene，but still hasorthopyroxene，the plagioclase has the K-feldspar shell.The hole rocks span a SiO₂rangeof49.8%⁵3.6%（the average is51.7%）；（Na₂O+K₂O）（=5.00⁶.94%，the average is6.35%）has a high content，and plotted within the field of alkaline series in the TASdiagram；（Fe₂O₃+FeO）（=7.10⁹.99%，the average is8.26%）；low MgO content（=2.30⁶.14%，the average is4.20%）；Fe₂O₃/FeO （=0.39¹2.87，the average is2.84） has a highratio，and belong to calc-alkaline series in the FAM diagram；high K₂O content（=2.40³.33%，the average is2.79%），K₂O/Na₂O （=0.68¹.08，the average is0.79） has a highratio，belonging to the shoshonite series field in SiO₂-K₂O diagram，and within the high-Kseries field in K₂O-Na₂O diagram；Al2O3（=15.8¹8.4%） has a high content and a widerange，TiO2（=1.41².07%，the average is1.69%） is relatively lower. The total amount of rare earth element （ΣREE=239³93×10-6）is relatively higher ofthe shoshonite rocks in Guangfeng and Yushan basins， which show rich LREE（（La/Sm）N=3.44⁴.55） obviously，and with no negative value of Eu （δEu=0.79⁰.97） andCe （δCe=0.89¹.06）.The lithophile element （Rb、Sr、Ba、Th） has enrichment among traceelement， but the Nd、 Ti element loss significantly，Nd/Th （=4.3⁸.2） and Ti/Yb（3088⁵444） has low ratios，which show the earth’s crust were added.There are no evidentcorrelated relationships in87Sr/86Sr（t）-SiO₂，εNd（t）-SiO₂，87Sr/86Sr（t）-1/Sr and εNd（t）-1/Nddiagrams，and all these appearances suggest that the magma has less contamination addedby the crust during rising process，but has the crustal contamination in the mantle sourcearea.The （87Sr/86Sr）ivalue of shoshonite rocks in Guangfeng and north Yushan basins is0.705856⁰.706352，εNd is from-0.07to1.9，n（206Pb）/n（204Pb） is from17.95to18.08，n（207Pb）/n（204Pb） is from15.46to15.54，n（208Pb）/n（204Pb） is from38.20to38.38；But the（87Sr/86Sr）ivalue of shoshonite rocks in east Yushan basin is0.703626⁰.703711，εNd isfrom3.40to3.86，n（206Pb）/n（204Pb） is from17.80to17.86，n（207Pb）/n（204Pb） is from15.20to15.24， n（208Pb）/n（204Pb） is from37.82to37.93.Among n（87Sr）/n（86Sr）-n（206Pb）/n（204Pb）、 n（143Nd）/n（144Nd）-n（206Pb）/n（204Pb） and n（143Nd）/n（144Nd）-n（87Sr）/n（86Sr） diagrams， the points are all between DMM and EM Ⅱ positions， becausen（87Sr）/n（86Sr） and n（206Pb）/n（204Pb） has positive correlation， n（143Nd）/n（144Nd） andn（206Pb）/n（204Pb） has negative correlation，the source mantle of the shoshonite rocksprobably has both DMM and EMⅡ magma，and higher proportion of DMM in the east ofYushan basin.Trace element and tectonic environment diagrams（Ce-Y、Zr/Al₂O₃-TiO₂/Al₂O₃、Ce/P₂O₅-Zr/TiO₂and Zr×3-Nd×50-Ce/P₂O₅）show that the shoshonite rocks generated inrear collision tectonic environment in Guangfeng and Yushan basins. During the EarlyJurassic，because of subduction of the ancient Pacific plate and southeast mainland，themantle enriched by fluid replacement in southern part of China.In Late Cretaceous，thesubduction angle of Pacific plate increased from a very low angle to a median angle，whichcaused delamination of thickened lower crust and asthenosphere upwelling under theextensional background.The shoshonite magama may be produced by the mixing ofmagma from asthenospheric-mantle and enriched lithospheric mantle. The differences ofmixing proportion and area （Guangfeng basin is suited in Guangfeng microplate andYushan basin is located in Huaiyu depression） caused the differences of the shoshoniterocks in Guangfeng and Yushan basin.更多还原