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1.
Yuejun Wang Weiming Fan Min Sun Xinquan Liang Yanhua Zhang Touping Peng 《Lithos》2007,96(3-4):475-502
The Indosinian granites in the South China Block (SCB) have important tectonic significance for the evolution of East Asia. Samples collected from Hunan Province can be geochemically classified into two groups. Group 1 is strongly peraluminous (A/CNK > 1.1), similar to S-type granites, and Group 2 has A/CNK = 1.0–1.1, with an affinity to I-type granites. Group 1 has lower FeOt, Al2O3, MgO, CaO, TiO2 and εNd(t) values but higher K2O + Na2O, Rb/Sr, Rb/Ba and 87Sr/86Sr(t) than those of Group 2. Samples of both groups have similar LREE enriched pattern, with (Eu/Eu) = 0.19–0.69, and strongly negative Ba, Sr, Nb, P and Ti anomalies. Geothermobarometry study indicates that the precursor magmas were emplaced at high-level depth with relatively low temperature (734–827 °C). Geochemical data suggest that Group 1 was originated from a source dominated by pelitic composition and Group 2 was from a mixing source of pelitic and basaltic rocks with insignificant addition of newly mantle-derived magma. Eight granitic samples in Hunan Province are dated at the cluster of 243–235 and 218–210 Ma by zircon U–Pb geochronology. Together with recent zircon U–Pb ages for other areas in the SCB, two age-clusters, including 243–228 Ma just after peak-metamorphism ( 246–252 Ma) and 220–206 Ma shortly after magma underplating event (224 Ma), are observed. It is proposed that in-situ radiogenic heating from the over-thickened crust induced dehydrated reaction of muscovite and epidote/zoisite to form the early Indosinian granites in response to the isostatic readjustments of tectonically thickened crust. Conductive heating from the underplating magma in the postcollisional setting triggered the formation of late Indosinian granites. Such a consideration is supported by the results from FLAC numerical simulation. 相似文献
2.
根据全岩K-Ar年龄(287.5~243.6Ma), 辽西朝阳长茂河子辉绿岩墙群形成于晚古生代.这些辉绿岩分为低铁钛辉绿岩和高铁钛辉绿岩2种, 以低铁钛辉绿岩为主.低铁钛辉绿岩以低TiO2(< 2%)、FeOt(12.39%~15.33%)、V(227~335μg/g)、Sc(24~36μg/g) 含量和高的SiO2 (45.61%~47.72%)、Al2O3(12.51%~16.71%)、MgO(6.66%~9.31%)、K2O(0.57%~2.39%)、Cr(107~177μg/g)和Ni(96~235μg/g) 含量, 以及低Ti/Y(327~496)和Ti/Zr (69~114) 比值为特征, 类似于大陆拉斑玄武质岩石; 高铁钛辉绿岩以高的TiO2 (5%~6%)、FeOt(22.13%~22.16%)、V(850~859μg/g)、Sc(51~52μg/g) 含量和低的SiO2 (42.88%~44.90%)、Al2O3(11.53%~11.57%)、MgO (5.15%~5.29%, Mg#=0.32)、K2O (0.48%~0.51%)、Cr(< 2μg/g)和Ni(< 30μg/g) 含量及高的Ti/Y(1046~1106)、Ti/Zr(250~263) 比值为特征, 类似于Skaergaard侵入体.这些辉绿岩相对富集Rb、Th、U、Pb、Ti和轻稀土元素, 而相对亏损Ba、Sr、P和Nb、Ta.εNd(t) (-6.43~-4.12)、εSr(t) (42.94~64.19) 显示Sr-Nd同位素组成较为均匀, 并反映它们源于富集岩石圈地幔.认为长茂河子辉绿岩形成于富集岩石圈地幔的部分熔融, 经历了岩浆结晶分异与地壳混染作用.高铁钛辉绿岩和低高铁钛辉绿岩形成环境不同, 前者形成于相对低氧逸度或相对封闭的结晶环境中. 相似文献
3.
Post-collisional strongly peraluminous granites 总被引：181，自引：0，他引：181
Paul J. Sylvester 《Lithos》1998,45(1-4):29-44
Strongly peraluminous (SP) granites have formed as a result of post-collisional processes in various orogens. In ‘high-pressure' collisions such as the European Alps and Himalayas, post-collisional exhumation of overthickened crust (>50 km), heated by radiogenic decay of K, U and Th during syn-collisional thickening, produced small- to moderate-volume, cool (<875°C) SP granite melts with high Al2O3/TiO2 ratios. In ‘high-temperature' collisions such as the Hercynides and Lachlan Fold Belt (LFB), there was less syn-collisional crustal thickening (≤50 km). Crustal anatexis was related to post-collisional lithospheric delamination and upwelling of hot asthenosphere, forming large-volume, hot (≥875°C) SP granite melts with low Al2O3/TiO2 ratios. Both clay-rich, plagioclase-poor (<5%) pelitic rocks and clay-poor, plagioclase-rich (>25%) psammitic rocks have been partially melted in high-pressure and high-temperature collisional orogens, with the pelite-derived SP granites tending to have lower CaO/Na2O ratios (<0.3) than their psammite-derived counterparts. The predominance of pelite-derived SP granites in the Himalayas and psammite-derived SP granites in the LFB suggests that mature continental platforms made up more of the accreted crust in the Himalayan collision than in the LFB. 相似文献
4.
鄂西南利川二叠纪吴家坪组硅质岩成因及沉积环境 总被引：3，自引：1，他引：2
鄂西南利川吴家坪组硅质岩与海相石煤及多层火山粘土岩共生,产海绵骨针及放射虫化石,放射虫组合以泡沫虫类为主,内射球虫类次之,隐管虫类很少,代表外陆棚沉积环境。硅质岩的陆源元素Al、Ti含量较高,热水来源元素Fe、Mn含量较低,Al/(Al+Fe+Mn)值在0.64~0.83之间,平均值0.73。在Al-Fe-Mn三角图中,样品位于或紧邻非热水沉积区,在 SiO2- (K2O+Na2O)、SiO2-Al2O3, (K2O+Na2O)-Al2O3 图解中大多数样品落在火山成因区,少数位于火山成因与生物成因区之间。相对于沉积岩的微量元素丰度,生命元素Mo、V富集,指示热水沉积的特征元素Ba、As、Sc亏损。∑REE较低,∑LREE/∑HREE平均值为3.02,Ce、Eu均轻度负异常（δCe:0.75~0.83,平均值0.79;δEu:0.61~0.95, 平均值0.84）,经北美页岩标准化后稀土元素配分曲线近水平。以上地球化学特征表明研究区硅质岩属火山成因,并伴有生物作用。氧化还原判别指标U/Th、V/(V+Ni)及Ceanom,沉积环境判别指标MnO/TiO2,LaN/YbN 与判别图解100×TFe2O3/SiO2-100 Al2O3/SiO2、TFe2O3/(100-SiO2)-Al2O3/(100-SiO2)、TFe2O3/TiO2-Al2O3/(Al2O3+TFe2O3)、LaN/CeN-Al2O3/(Al2O3+TFe2O3)与∑LREE/∑HREE-100×Eu/∑REE一致表明硅质岩形成于大陆边缘缺氧环境。 相似文献
5.
大别—苏鲁超高压地体中面理化含榴花岗岩的成因研究 总被引：7，自引：1，他引：6
大别—苏鲁超高压地体中的面理化花岗岩因为常含石榴石而被简称为含榴花岗岩, 其岩石类型主要为二长花岗岩、花岗岩和微斜长石花岗岩, 岩石具有花岗结构和片麻状构造.详细的野外地质研究表明, 超高压片麻岩作为超高压榴辉岩的围岩与含榴花岗岩呈渐变过渡关系, 或在含榴花岗岩中呈与面理平行的残留条带, 体现超高压片麻岩通过构造置换和部分熔融向含榴花岗岩转化.含榴花岗岩在常量元素的总体组成上, w(SiO2)为71.73%~79.15%;A/CNK为0.83~1.09, 平均0.98, 为准铝质; w(K2O+Na2O)为6.15%~9.00%, w(K2O)/w(Na2O)为0.16~1.54(绝大多数集中在0.9~1.1), 具有相对弱富钠-弱富钾特征.从标准矿物组成上看, 大别含榴花岗岩主要相当于奥长花岗岩; 山东含榴花岗岩主要相当于花岗岩; 东海含榴花岗岩主要相当于钾质花岗岩.在微量元素特征上, 含榴花岗岩的∑REE、∑LREE明显富集, δEu具有明显的负异常, 在原始地幔标准化蛛网图上, 相对亏损Nb、Ta、P、Zr、Ti等高场强元素及大离子亲石元素Sr, 富集Ba、La、Nd、Y、K等大离子亲石元素, 结合其贫w(Al)(平均11.6%)富w(Ga)(> 17×10-6)、(Fe/Mg)M(1.087~20.330)等特征, 表明其地球化学特征相当于非造山的A型花岗岩.结合前人超高压变质作用和构造演化等研究成果, 可以推断含榴花岗岩是超高压地体折返到中下地壳, 在底侵、构造体制转换等因素作用下, 由高压片麻岩的部分熔融形成的.含榴花岗岩在大别—苏鲁不同区域上的规律变化, 表明东海含榴花岗岩的出露相对于大别更低位. 相似文献
6.
对姜家屯花岗闪长岩进行的同位素年代学及岩石地球化学研究显示,花岗闪长岩LA-ICP-MS锆石U-Pb加权平均年龄为154.8±1.8 Ma,表明该侵入体是晚侏罗世形成的.岩石学及地球化学数据显示其属于高钾钙碱性系列,具A型花岗岩特征.岩石高硅（SiO2=66.08%~67.80%）、富碱（K2O+Na2O=7.35%~7.97%）、富铝（Al2O3=14.5~15.23）、贫镁（MgO=1.08%~1.62%）、贫钙（CaO=2.05%~3.04%）、低钛（TiO2=0.56%~0.67%）,轻稀土富集,重稀土相对亏损,稀土配分曲线呈右倾型,具明显的负铕异常,轻稀土分馏较好.微量元素亏损Sr、Ba、Ta、Nb,而Th、Zr、Hf、Pb相对富集,在微量元素原始地幔标准化蛛网图上显示明显Sr、Ba、Ti负异常的特征.综合这些特征认为,姜家屯花岗闪长岩是受古太平洋板块俯冲影响,造山后岩石圈伸展剪薄环境下的产物. 相似文献
7.
喀拉昆仑火烧云北火山岩发育在乔尔天山断裂附近,玄武岩体和安山岩体在时空上紧密伴生。主量元素测试结果显示,其中玄武岩和英安岩的Si O2含量分别为48.84%~52.44%和62.22%~65.63%,具有明显的Daly间断面,属于典型的双峰式火山岩。玄武岩Al2O3含量较低,MgO、Ca O、Ti O2含量较高,Sr、Ba、K等微量元素强烈亏损,高场强元素Ta、Nb、Ti、Zr无亏损。英安岩具有相对较高的Al2O3、Na2O、K2O含量,较低的MgO、Ca O、Ti O2含量;微量元素具富集大离子亲石元素(Rb、Th、U、K)、亏损高场强元素(Ta、Nb、Ti),显示典型岛弧环境特征。岩石地球化学特征表明二者同属钙碱系列,形成于弧后盆地,属同源演化,英安岩为玄武岩结晶分异的产物。通过对英安岩进行LA-ICP-MS锆石U-Pb方法测年,获得流纹岩形成年龄为(195.5±1.1)Ma,属于早侏罗世。通过对该区域构造演化进行分析讨论,认为乔尔天山一带盆地整体可能处于弧后盆地的发育阶段,盆地形成过程中岩石圈地幔未被拉断,没有洋壳形成。 相似文献
8.
对东海陆架西湖凹陷区SFK-1孔的岩性、粒度、常量元素以及测年数据的综合分析表明:元素地球化学信息对于地层的划分有良好的指示意义。 SFK-1孔沉积物常量元素质量分数平均值分别为SiO2 65.35%、Al2O3 12.12%、FeO 1.75%、CaO 3.88%、MgO 2.04%、K2O 2.63%、 Na2O 2.04%、 TiO2 0.66%、 P2O5 0.12%、 MnO 0.065%、TFe2O3 4.74%、CaCO3 5.38%,标准差系数较小,反映SFK-1孔常量元素离散程度较小。SFK-1孔沉积物CaCO3/TiO2、CaO/TiO2和P2O5/TiO2反映了化学风化程度的强弱;TiO2/Al2O3可以作为古水流能量的指标,反映当时河流水动力条件的影响强度;而SiO2/TiO2、Na2O/TiO2可以用来反映沉积水动力的强度。依据常量元素质量分数垂直变化特征划分的8个层段分别与沉积物粒度、气候变化地层划分界线吻合。研究区自91 ka BP以来沉积环境经历了剧烈变化,它们分别反映了末次间冰期( 暖期) 晚期以来东海陆架区沉积环境的变化。 相似文献
9.
Daniel Harlov Peter Tropper Wolfgang Seifert Timo Nijland Hans-Jürgen Frster 《Lithos》2006,88(1-4):72-84
Reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite-facies metapelites and amphibolites namely the Tamil Nadu area, southern India; the Val Strona area of the Ivrea-Verbano Zone, northern Italy, the Bamble Sector, southern Norway, and the northwestern Austroalpine Ötztal Complex. The titanite rims, and hence the stability of titanite (CaTiSiO4O) and Al–OH titanite, i.e. vuaganatite (hypothetical end-member CaAlSiO4OH), are discussed in the light of fH2O- and fO2-buffered equilibria involving clinopyroxene, amphibole, biotite, ilmenite, magnetite, and quartz in the systems CaO–FeO/Fe2O3–TiO2–SiO2–H2O–O2 (CFTSH) and CaO–FeO/Fe2O3–Al2O3–SiO2–H2O–O2 (CFASH) present in each of the examples. Textural evidence suggests that titanite reaction rims on ilmenite in rocks from Tamil Nadu, Val Strona, and the Bamble Sector originated most likely due to hydration reactions such as clinopyroxene + ilmenite + quartz + H2O = amphibole + titanite and oxidation reactions such as amphibole + ilmenite + O2 = titanite + magnetite + quartz + H2O during amphibolite-facies metamorphism, or, as in the case of the Ötztal Complex, during a subsequent greenschist-facies overprint. Overstepping of these reactions requires fH2O and fO2 to be high for titanite formation, which is also in accordance with equilibria involving Al–OH titanite. This study shows that, in addition to P, T, bulk–rock composition and composition of the coexisting fluid, fO2 and fH2O also play an important role in the formation of Al-bearing titanite during amphibolite- and greenschist-facies metamorphism. 相似文献
10.
长江源区新生代火山岩的系列及成因 总被引：2，自引：0，他引：2
长江源区的新生代火山岩系包括高钾钙碱性系列和钾玄岩系列.高钾钙碱性火山岩形成于始新世, 钾玄岩系列火山岩形成于中、上新世.总体而言, 该区火山岩富碱高钾, 富集大离子亲石元素, 稀土元素含量高且轻稀土相对富集.相对而言, 高钾钙碱性火山岩富集SiO2、Al2O3, 无负Eu异常, 属于壳源岩浆系列, 其原始岩浆由加厚陆壳的榴辉岩质下地壳经部分熔融产生.钾玄岩系列火山岩富集K2 O、TiO2、P2 O5、MgO、FeO, ∑REE、HFSE、ISr值均较高, 弱负Eu异常, 属于幔源岩浆系列, 其原始岩浆由EMⅡ型富集地幔的部分熔融生成.2个系列的火山岩均是大陆碰撞造山后期岩浆作用的产物.始新世以来, 随着该区由碰撞、挤压作用发展到出现走滑, 应力环境由挤压转变为张性, 导致依次喷发高钾钙碱性火山岩和钾玄岩系列火山岩. 相似文献
11.
东昆仑中泥盆世A型花岗岩的确定及其构造意义 总被引：5，自引：0，他引：5
东昆仑中泥盆世冰沟正长花岗岩具有高硅(SiO2含量为71.85%~72.77%)和高碱(K2O+Na2O值为8.39~8.58)、相对富铝(A/CNK为0.93~1.03)、高FeOt/MgO(6.24~7.86)和104 Ga/Al值(3.04~3.60)、富集轻稀土、明显的Eu负异常、相对原始地幔明显富集Zr、Ga、Y和Hf等高场强元素并强烈亏损Ba、Sr、P和Ti元素的特征, 这些特征与A型花岗岩类的地球化学特征一致.采用锆石LA-ICP-MS U-Pb法获得206Pb/238U值加权平均年龄为391±3 Ma(MSWD值为2.36), 表明该岩体为中泥盆世岩浆活动的产物.综合全岩Sr-Nd同位素、地球化学及实验岩石学等资料, 可以判断该岩石为造山后伸展阶段长英质地壳物质(变杂砂岩)在低压高温氧化条件下发生部分熔融的产物.冰沟正长花岗岩是目前东昆仑地区报道的时代最晚的古生代A型花岗岩, 它的出现可能标志着中泥盆世时期东昆仑始特提斯构造演化的彻底终结和古特提斯构造演化的崭新开始. 相似文献
12.
寒武系第四阶是生命演化史上重要的时间节点.渝东地区寒武系第四阶龙王庙组以碳酸盐岩为主要岩石类型,地层中、下部混积岩发育,生物化石发育程度低.∑（CaO+MgO+LOI）含量分布范围广（74.64%~99.18%）,Na2O、K2O、Fe2O3与MnO含量较高（平均值分别为0.20%、0.27%、0.27%和0.014%）,∑（SiO2+Al2O3+Fe2O3+P2O5+TiO2）在地层中下部具较高含量（最大值24.00%）;Sr元素含量较低（135×10-6~407×10-6）,∑REE+Y在地层中部含量较高,∑LREE/∑HREE分布在2~4,具显著正铈异常（δCe=5.6~6.2）,配分曲线为平缓右倾模式.全岩与方解石的δ13C值分别为-1.5‰~1.1‰ VPDB、-3.4‰ ~+0.5‰ VPDB,δ18O值分别为-9.7‰ ~-3.5‰ VPDB、-9.8‰~-5.0‰ VPDB;垂向上,两者的δ13C值在地层中下部均以负值为主,中上部多为正值.依据δ13C、δ18O、MgO/CaO（0.03%~0.12%）、100×MgO/Al2O3（93.1~4 715.4）、B校（278.7~1 494.2）、Sr/Ba（4.05~58.25）、1 000×Sr/Ca（5.41~14.43）、V/（V+Ni）（0.61~0.78）及U/Th（0.21~1.45）等与沉积环境的关系,推断龙王庙期水体温度在17~25℃,属半咸水-咸水环境;水体深度在早-中期波动频繁;以贫氧-缺氧环境为主,在早-中期、末期为阶段性富氧环境.整体上龙王庙组沉积早-中期受河流注入影响较为明显、陆源碎屑供给充足,具海陆过渡环境特征,沉积中后期为稳定的海相环境.咸水、缺氧的条件及海平面波动频繁并伴有大量陆源碎屑注入所产生的环境压力,是引发渝东地区寒武系第四阶生物消亡的主要环境因素. 相似文献
13.
The Oetmoed Granite–Migmatite Complex (OGMC), Central Damara Orogen, Namibia, consists mainly of 526 to 516 Ma garnet- and cordierite-bearing granite and subordinate 488 to 494 Ma hornblende- and titanite-bearing granite in the form of planar sheets and dykes. Additionally, a slightly elongated granite body occurs in the center of the complex. The garnet- and cordierite-bearing granite has major- and trace-element characteristics of S-type granite but the hornblende- and titanite-bearing granite has higher HFSE and REE contents similar to A-type granite. Whereas the garnet- and cordierite-bearing granite contains numerous restitic xenoliths, the hornblende- and titanite-bearing granite is xenolith-free. The country rocks are cordierite–sillimanite–K-feldspar–garnet-bearing metasedimentary rocks and migmatite. Cordierite- and garnet-rich xenoliths in the S-type granite do not represent primary restite, their depleted chemical composition is best explained by varying and large degrees of partial melting of incorporated country rocks. Most chemical variations among the garnet- and cordierite-bearing granite can be explained by processes linked with fractional crystallization of plagioclase, biotite and accessory phases, mostly monazite and zircon. Major and trace element data and high δ 18O values suggest that the least evolved members of the garnet- and cordierite-bearing granite were derived from metapelitic rocks at ca. 800°C as inferred from monazite and apatite dissolution thermometry. Higher CaO and Na2O but lower SiO2 contents and lower Rb/Sr ratios as well as lower δ 18O values of the hornblende- and titanite-bearing granite suggest that they are more likely generated by partial melting of non-pelitic sources (metagranitoids?) at temperatures in excess of 900°C. Decreasing TiO2, Na2O, FeOtot., MgO, CaO, total REE content but increasing Al2O3 and K2O indicate fractionation of mainly hornblende and titanite in the case of the hornblende- and titanite-bearing granite. The differing compositions of the garnet- and cordierite-bearing granite and the hornblende- and titanite-bearing granite are attributed to different source rocks (metapelite instead of metagranitoid) and different temperatures during melting as inferred from accessory phase dissolution thermometry. Furthermore, significant entrainment of country rock in some samples played a major role during petrogenesis of the garnet- and cordierite-bearing granite but was not important during the evolution of the hornblende- and titanite-bearing granite. Intrusion of such hot, felsic magmas close to the inferred peak of metamorphism has probably caused, in part, the high temperature metamorphism and anatexis of the country rocks at relatively low pressures. 相似文献
14.
The origin of medium-K ankaramitic arc magmas from Lombok (Sunda arc, Indonesia): Mineral and melt inclusion evidence 总被引：2，自引：0，他引：2
High-calcium, nepheline-normative ankaramitic basalts (MgO > 10 wt.%, CaO/Al2O3 > 1) from Rinjani volcano, Lombok (Sunda arc, Indonesia) contain phenocrysts of clinopyroxene and olivine (Fo85–92) with inclusions of spinel (Cr# 58–77) and crystallised melt. Olivine crystals have variable but on average low NiO (0.10–0.23 wt.%) and high CaO (0.22–0.35 wt.%) contents for their forsterite number. The CaO content of Fo89–91 olivine is negatively correlated with the Al2O3 content of enclosed spinel (9–15 wt.%) and positively correlated with the CaO/Al2O3 ratios of melt inclusions (0.9–1.5). Major and trace element patterns of melt inclusions are similar to that of the host rock, indicating that the magma could have formed by accumulation of small batches of melt, with compositions similar to the melt inclusions. The liquidus temperature of the magma was 1275 °C, and its oxygen fugacity ≤ FMQ + 2.5. Correlations between K2O, Zr, Th and LREE in the melt inclusions are interpreted to reflect variable degrees of melting of the source; correlations between Al2O3, Na2O, Y and HREE are influenced by variations in the mineralogy of the source. The melts probably formed from a water-poor, clinopyroxene-rich mantle source. 相似文献
15.
重庆石柱二叠纪栖霞组地球化学特征及其环境意义 总被引：5，自引：1，他引：4
在对重庆市石柱县二叠纪栖霞组地层野外露头沉积特征研究的基础上,结合室内薄片观察,根据碳酸盐岩样品的元素含量、比值及相关性,探讨了栖霞组沉积地球化学特征与古环境意义.用于古环境分析的10件栖霞组样品SiO2、MgO含量低,且两者具有较好的正相关性,Sr含量高,平均为1 751×10-6,Mn/Sr<0.1,Fe/Sr<1,δ18OPDB>-10‰,表明成岩过程中样品几乎不受硅化及白云岩化作用的影响,未发生化学性质上的改变,可作为古环境分析的可靠对象.栖霞组碳酸盐岩CaO含量高,平均为53.81%,接近纯灰岩的理论化学组成,陆源元素Al2O3、TiO2含量很低,平均值分别为0.17%与0.012%,表明其形成于陆源碎屑影响微弱的稳定古海洋环境.古气候指标MgO/CaO比值极低,平均为0.026,古盐度指标100×(MgO/Al2O3)比值高,平均为1 241,古水深判别指标Sr/Ba、1000×(Sr/Ca)比值高,平均值分别为286和4.54,指示了栖霞组碳酸盐岩为潮湿气候下的陆表海(远岸)沉积.古氧相地球化学指标U/Al、V/Al、Mo/Al、Cr/Al、Co/Al、V/(V+Ni)和U/Th特征一致表明栖霞组碳酸盐岩沉积于贫氧—缺氧环境.垂向上,陆源元素∑(Al2O3+TiO2)含量逐渐降低,古水深指标Sr/Ba、1000×(Sr/Ca)比值逐渐增大,表明栖霞组沉积过程中离岸渐远、陆源供给逐步减少、水体持续加深. 相似文献
16.
黄河三角洲ZK5钻孔沉积物地球化学特征及其沉积环境 总被引：3，自引：2，他引：1
本文根据36件沉积物样品的微量元素和常量元素的相关性、组分含量及某些元素的比值特征,探讨了黄河三角洲ZK5钻孔的元素地球化学特征与古环境意义。应用历史地理学和沉积地质学综合分析方法确定钻孔岩芯沉积年代,将ZK5岩芯沉积物自下而上大致划分为7个层序。元素地球化学特征的研究表明:K2O、Fe2O3、Al2O3、TiO2、Cr、V、Rb元素相互间呈明显的正相关关系;SiO2与其他元素呈明显的负相关,与P2O5呈弱负相关关系;Sr与CaO呈弱负相关关系;P2O5与Al2O3、Fe2O3、K2O、TiO2、CaO呈弱的正相关。据V/Cr值分析,ZK5钻孔从下往上水体有逐渐加深的趋势,与相关性分析结果相符。根据锶钡比值（Sr/Ba）和镁铝比值102（MgO/Al2O3）分析得出,ZK5孔沉积环境的水体盐度从下往上变化相差不大,属于海相沉积环境,同时有黄河水的注入。通过古气候指示剂Rb/Sr值和MgO/CaO值的分析:ZK5孔从NQ1到NQ7层序沉积时期的气候变化不大,气候相对潮湿。总之,地球化学特征所反映的沉积环境与沉积相分析的结果相一致,说明元素地球化学与沉积环境关系密切,可作为沉积相判别的标志。 相似文献
17.
青海玉树县南洞卡组粗面安山岩的SiO2含量为55.92%～57.85%,高Na2O、MgO和Al2O3,低K2O、TiO2和 P2O5,铝饱和指数A/CNK=0.98～1.08,具有准铝-弱过铝质的特点。岩石K2O含量低,Na2O/K2O=12.60～15.97,显示出钠质粗面安山岩特征。SiO2-K2O图解和里特曼指数(2.89～3.25),说明岩石属于钙碱性系列。稀土配分模式为轻稀土弱富集右倾型,铕弱负异常(σEu=0.90～0.96)。微量元素蛛网图显示,岩石富集Rb、Th和U等元素,亏损高场强元素Nb、Ta和大离子亲石元素Ba,样品Ce/Pb、Nb/U 并未随着MgO含量的升高而升高,样品的La/Nb、Zr/Nb、Ba/Nb比值均表现出良好的稳定性,表明岩浆在上升过程中遭受地壳物质混染的可能性不大,可能是其源区特征的反映。研究表明岩浆经历了橄榄石和单斜辉石的结晶分异,且受到俯冲板片熔体对源区的改造作用。结合234 Ma的形成年龄,说明该粗面安山岩是金沙江洋盆向西俯冲消减和斜向碰撞的地质记录,其形成时代和地球化学特征也为江达-维西火山弧的形成演化及成矿作用研究提供依据。 相似文献
18.
天宫山花岗岩体成因的研究对闽西南地区岩浆演化及动力学过程有重要意义.天宫山岩体岩性主要为正长花岗岩.前人于天宫山岩体中利用K-Ar法测得年龄值为146~149 Ma,天宫山正长花岗岩中测得锆石LA-ICP-MS U-Pb年龄为233±2.0 Ma、230±2.8 Ma,为晚三叠世,属印支期.该岩体富硅,富碱,σ=1.21~2.55,A/CNK=0.97~1.73,属钙碱性系列,准铝质到过铝质范畴.岩石ΣREE较高,LREE相对富集,贫Al2O3和Sr,富Y和Yb,发育有明显的显微文象结构,具有较强的铕负异常,中等铈负异常到弱正异常;亏损大离子亲石元素,富集高场强元素.Ga/Al值高,具有A型花岗岩特征.w（P2O5）平均值为0.02%,低于高分异S型花岗岩;w（Na2O）平均值为2.93%,高于高分异S型花岗岩;全铁含量w（TFeO）平均值为1.15%,高于高分异I型花岗岩.锆石饱和温度平均值为729.8℃.εHf（t）全部为负值（-5.29~-10.69）,表明其物质起源可能主要为古元古代下地壳物质.参与成岩作用的岩浆来源于地壳物质的部分熔融,为同碰撞环境下形成的壳源型铝质A型花岗岩.在印支期碰撞-挤压为主的造山运动背景下,岩体在高温环境中经历了古元古代下地壳物质的初步熔融,经印支期运动伸展,部分地幔物质参与了经底侵作用. 相似文献
19.
末次冰期以来鄱阳湖东北缘下蜀黄土常量元素地球化学特征及其物源指示 总被引：5，自引：1，他引：4
长江中游、鄱阳湖东北缘,末次冰期以来发育区域性风沙-风尘堆积体系。沿现代冬季风方向自北而南选取了10个剖面(通称D-D断面)采集下蜀黄土样品,并用湿筛法提取<20 μm粒级颗粒进行XRF元素分析,结果揭示:①自北而南,元素含量具有系统性变化特征,SrO、Na2O、CaO、K2O、MnO、CaO呈负对数函数关系,SiO2、ZrO2、Al2O3、TiO2及化学蚀变指数(CIA)呈正对数变化;在距离长江河谷5~20 km的范围内,变化最为剧烈,随后趋于平稳。稳定元素-稳定元素、次稳定元素-稳定元素、活动元素-稳定元素对散点图同样具有系统的变化特点,显示D-D断面具有高度同源性。这些特征进一步揭示D-D断面属同一粉尘堆积体系。②现代长江河漫滩沉积物、渭南黄土、南京下蜀黄土与D-D断面上北端剖面稳定元素组成极其相似,与南端剖面则差异较大。这揭示了长江碎屑物质和风尘堆积一样具有广泛的来源及高度混合性,利用常量元素地球化学方法进行粉尘物源示踪需要谨慎。 相似文献
20.
黑龙江省东部那丹哈达增生杂岩主要由晚三叠世-中侏罗世含放射虫硅质岩组成,并夹有镁铁-超镁铁质杂岩和晚古生代浅海沉积岩.对黑龙江省东部石场、勤得利和胜利农场地区硅质岩分析显示,样品Al2O3、TiO2、CaO、Al2O3/（Al2O3+TFe2O3）及ΣREE整体上偏低,具有较高的SiO2含量,为纯硅质岩.结合Al-Fe-Mn三角图和K2O/Na2O值,表明该地区硅质岩的形成过程与海底热液作用无关.元素判别图解及地球化学特征揭示,黑龙江东部三个地区的硅质岩形成于大陆坡及边缘海环境. 相似文献