排序方式： 共有14条查询结果，搜索用时 15 毫秒
1.
始太古代及形成时代更古老的岩石十分稀少,任何新的发现都是对最早期陆壳形成演化研究的重要贡献。本文首次报道了华北克拉通冀东地区～3.8 Ga TTG岩石的年龄和地球化学组成。样品J2012为花岗闪长质片麻岩,J2013为侵入花岗闪长质片麻岩的花岗闪长岩脉,也遭受变质变形。两者的岩浆锆石年龄分别为3785±8 Ma和3773±6 Ma。尽管岩石的常量元素组成和形成时代类似,但稀土模式明显不同。样品J2012的TREE(稀土总量)和(La/Yb)n比值分别为139.2×10-6和8.44,组成特征与北美4.03 Ga Acasta片麻岩类似,岩浆作用发生在相对低压的条件下,岩浆作用过程中无石榴子石参与而有斜长石存在。样品J2013的TREE和(La/Yb)n比值分别为163.5×10-6和51.16。轻重稀土强烈分异要求花岗闪长岩形成于石榴子石稳定和斜长石不稳定的高压条件下。研究表明,冀东地区在～3.8 Ga时TTG岩浆作用就显示出多样性,支持了古太古代早期—冥古宙陆壳基底广泛存在的认识。根据始太古代岩石... 相似文献
2.
Two Neoarchean alkaline feldspar-rich granites sourced from partially melted granulite-facies granodioritic orthogneiss have been here recognised in the eastern part of the North China Block (NCB). These poorly foliated granites have previously been assumed to be Mesozoic in age and never dated, and so their significance has not been recognised until now. The first granite (AG1) is a porphyritic syenogranite with megacrystic K-feldspar, and the second (AG2) is a quartz syenite with perthitic megacryst. Zircons from the granites yield LA-ICP-MS U-Pb ages of 2499 ± 10 Ma (AG1), and 2492 ± 28 Ma (AG2), which are slightly younger than the granodioritic orthogneiss that they intrude with a crystallisation U-Pb age of 2537 ± 34 Ma. The younger granites have higher assays for SiO2 (71.91% for AG1 and 73.22% for AG2) and K2O (7.52% for AG1 and 8.37% for AG2), and much lower assays for their other major element than the granodioritic orthogneiss. All of the granodioritic orthogneiss and granite samples have similar trace element patterns, with depletion in Th, U, Nb, and Ti and enrichment in Rb, Ba, K, La, Ce, and P. This indicates that the granites are derived from the orthogneiss as partial melts. Although they exhibit a similar REE pattern, the granites have much lower total REE contents (30.97×10−6 for AG1, and 25.93×10−6 for AG2), but pronounced positive Eu anomalies (Eu/Eu* = 8.57 for AG1 and 27.04 for AG2). The granodioritic orthogneiss has an initial 87Sr/86Sr ratio of 0.70144, εNd(t) value of 3.5, and εHf(t) values ranging from −3.2 to +2.9. The orthogneiss is a product of fractional crystallisation from a dioritic magma, which was derived from a mantle source contaminated by melts derived from a felsic slab. By contrast, the AG1 sample has an initial 87Sr/86Sr ratio of 0.6926 that is considered too low in value, εNd(t) value of 0.3, and εHf(t) values between +0.57 and +3.82; whereas the AG2 sample has an initial 87Sr/86Sr ratio of 0.70152, εNd(t) value of 1.3, and εHf(t) values between +0.5 and +14.08. These assays indicate that a Sr-Nd-Hf isotopic disequilibrium exists between the granite and granodioritic orthogneiss. The elevated εHf(t) values of the granites can be explained by the involvement of Hf-bearing minerals, such as orthopyroxene, amphibole, and biotite, in anatectic reactions in the granodioritic orthogneiss. Based on the transitional relationship between the granites and granodioritic orthogneiss and the geochemical characteristics mentioned above, it is concluded that the granites are the product of rapid partial-melting of the granodioritic orthogneiss after granulite-facies metamorphism, and their crystallisation age of about 2500 Ma provides the minimum age of the metamorphism. This about 2500 Ma tectonic-metamorphic event in NCB is similar to the other cratons in India, Antarctica, northern and southern Australia, indicating a possible connection between these cratons during the Neoarchean. 相似文献
3.
在1.5GPa,950℃,恒温101h条件下对华北北缘太古宙地体中的斜长角闪岩块状样品进行了脱水部分熔融实验,实验产物组合为Hb+Cpx+Gt+Gl,获得的熔体为花岗闪长质成分。利用LA-ICP-MS测试了矿物和熔体的微量元素,获得该体系内各矿物/熔体的微量元素分配系数。角闪石、单斜辉石和石榴石的分配系数与前人在类似条件下的实验结果基本一致。这说明无论实验的初始物质是粉末状还是块状,对元素的分配没有太大的影响。各矿物的REE分配系数对离子半径的拟合曲线很好地符合晶格应变弹性模型。整体特征上,角闪石、单斜辉石和石榴石的LILE,LREE分配系数较低,而HREE的分配系数较高,石榴石具有强烈富集HREE的特征。由此,造成实验熔体表现出LILE、LREE富集而HREE亏损的特征。残留相中无金红石,使得熔体中没有明显的Nb、Ta负异常。熔体的主-微量元素特征符合华北北缘中生代埃达克质岩石的基本特征,进一步支持了该类岩石"可能起源于古老下地壳的部分熔融"的成因模式。 相似文献
4.
为更深入了解西准噶尔晚古生代岩浆活动和构造背景,对位于西准噶尔中部的别鲁阿嘎希岩体开展了年代学、地球化学以及Sr-Nd同位素研究,讨论了岩石成因、源区性质和构造背景.别鲁阿嘎希花岗闪长岩为钙碱性系列岩石,岩浆锆石结晶年龄为318.7±3.3 Ma.其具相对高的MgO(Mg#=49~59)、Ni、Cr含量,富集大离子亲石元素(如K、Rb、Sr和Ba)、亏损高强场元素(如Nb、Ta、Ti),轻重稀土元素分异不明显.Sr-Nd同位素特征显示,其有较低的初始Sr比值(0.704 297~0.704 399),较高的εNd(t)值(5.8~6.5).通过综合分析,认为在晚石炭世早期,达尔布特洋壳(板片)俯冲至地幔楔下部,俯冲洋壳板片脱水所产生的流体在上升过程中与地幔楔共同作用,底侵加热由亏损地幔形成不久的年轻地壳(由洋壳和岛弧组成),使其部分熔融形成了别鲁阿嘎希分异I型花岗岩. 相似文献
5.
大别山北部漫水河灰色片麻岩的锆石UPb年龄及其地质意义 总被引：13，自引：2，他引：11
北大别杂岩主要由灰色片麻岩和斜长解闪岩组成。通过对大别山北部霍山漫水河花岗闪长片麻岩的锆石U-Pb年龄测定,得到中元古代、早三叠世和晚侏罗世3组年龄数据。中元古代的年龄老于灰色片麻岩集中在新元古代的锆石U-Pb上交点年龄,指示漫水河北部片麻岩中有古老锆石捕掳晶;早三叠世年龄指示该片麻岩中有印支期变质作用形成的锆石;晚侏罗世年龄表明灰色片麻岩中有燕山早期形成的岩浆锆石。根据北大别杂岩的构造背景、变质作用及地球化学特征,认为北大别杂岩中的部分灰色片麻岩形成于燕山早期的花岗闪长岩,它们可能源自或混染了经过早三叠世变质作用的扬子陆块俯冲基底。本文的结果表明,北大别杂岩既不是形成于白垩纪的岩浆杂岩,也不完全是形成于新元古代的TTG岩系,其中的部分灰色片麻岩为形成于燕山早期的花岗闪长岩,即在白垩纪大规模岩浆作用前的燕山早期,北大别曾有过一次岩浆作用。 相似文献
6.
U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications 总被引：12，自引：0，他引：12
The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization
in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from
Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans
a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some
of the zircon grains give an upper intercept age of about 1753 Ma and 207Pb/206Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement
in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas
were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components
during the melting process. 相似文献
7.
湖南宝山花岗闪长质隐爆角砾岩的岩石学、地球化学特征及锆石SHRIMP定年 总被引：24，自引：6，他引：24
通过湖南宝山地区花岗闪长质隐爆角砾岩体的岩石学、地球化学特征的研究,表明岩体中的角砾与基质岩石的特征大致相近,均为高钾钙碱性准铝质花岗质岩石,其成因为壳-幔同熔型。锆石SHRIMP U-Pb定年研究表明,隐爆角砾岩中花岗闪长斑岩的角砾岩石年龄为（164.1±1.9）Ma,基质岩石年龄为（162.2±1.6）Ma,表明两者的形成时间相近,是燕山期构造岩浆作用的产物。隐爆角砾岩体的岩石学、地球化学特征又与其共生的含矿花岗闪长斑岩体相似,岩体中的角砾与基质岩石中的W、Mo、Cu、Pb、Zn成矿元素丰度都很高,其周围有利部位也有矿化,说明隐爆角砾岩体同样可为成矿母岩,这对该区岩体成因及其多金属矿成矿作用的研究具有重要的意义。 相似文献
8.
天山东段1.4Ga花岗闪长质片麻岩SHRIMP锆石U-Pb年龄及其地质意义 总被引：7，自引：0，他引：7
天山最东段星星峡地区出露的片麻岩、混合岩和斜长角闪岩等,一直被看作是东天山最老的地层星星峡群,实际上是中—新元古代变质杂岩体。用SHRIMP锆石U-Pb定年技术分析了星星峡花岗闪长质片麻岩中19颗锆石,由其中谐和性较好的14个锆石的分析结果得到206Pb/238U和207Pb/206Pb加权平均年龄分别为(1436±13)Ma(2σ)和(1405.2±7.8)Ma(2σ),为天山东段星星峡花岗闪长岩的形成年龄,从而确定了天山造山带中元古代基底岩浆岩形成的时间,与北美及欧洲大陆广泛存在的1.4Ga岩浆活动具有同时性,对进一步思考天山造山带中1.4Ga岩浆活动形成的古陆块在前Rodinia大陆时期的归属有重要意义。主元素和微量元素研究结果显示星星峡1.4Ga花岗闪长岩具有岛弧岩浆岩特征,与北美中部大陆和欧洲大陆Fennoscandia的中元古代非造山作用形成的岩浆岩有所不同。另外,片麻岩中有的锆石具有新的生长边,并给出年轻化和较大的不一致年龄,说明1.4Ga片麻岩不同程度地受到新元古代(0.9～1.1Ga)变质作用和岩浆活动的改造,同时形成一些混合岩和花岗片麻岩。19颗锆石分析数据中有1个锆石的207Pb/206Pb比值年龄为(1845±23)Ma,与该片麻岩的Nd模式年龄相一致,可能代表更古老地壳物质中的残留锆石。 相似文献
9.
在东昆仑那陵格勒河地区发现新元古代变质侵入体,侵位于古元古代金水口岩群及中-新元古代万宝沟岩群中,岩性为花岗闪长质片麻岩和二长花岗质片麻岩。通过对花岗闪长质片麻岩的LA-ICP-MS锆石U-Pb测年,获得岩体形成的年龄为（840±2）Ma。岩石地球化学显示强过铝质-高钾钙碱性系列岩石特征,属S型花岗岩,形成于大陆碰撞造山环境,为同碰撞环境下岩浆作用产物。该岩体与东昆仑地区已报道的新元古代变质侵入岩（体）为同一性质,表明东昆仑地区存在一条新元古代花岗岩深成侵入岩带。整个东昆仑可能曾响应了全球罗迪尼亚超大陆的汇聚事件。 相似文献
10.