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东秦岭陡岭杂岩中存在新太古代物质组成——SHRIMP锆石U—Pb和Sm—Nd年代学证据 总被引：5，自引：3，他引：5
出露于豫、陕交界处的陡岭杂岩是秦岭造山带中一个不大的构造岩块 ,它可能是在 1.95～ 2 .10Ga期间由于构造作用将不同时代、不同源区的岩石组合叠置在一起而形成的。出露在其西部的透辉变粒岩的 TDM为 2 .6 7～ 2 .76 Ga,残余锆石 SHRIMP年龄为 2 .5～ 2 .6 Ga,表明透辉变粒岩的物质主要来自新太古代 ,基本没有或少有太古宙以后的陆壳物质混合 ,同时也说明透辉变粒岩的原岩形成时在其附近应该有新太古代岩块存在。 相似文献
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《地学前缘(英文版)》2020,11(6):1915-1934
The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane (SW Siberian Craton). Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution. The first stage of regional metamorphism (M1) occurred at high-amphibolite facies conditions at T = 780–800 °C and P = 8–9 kbar. The second stage (M2) belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600–750 °C and pressure 2–4 kbar. Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses. Both of them correspond to the Neoarchean age: the age of M1 falls into the interval of ca. 2489–2496 Ma, the age of M2 – ca. 2446–2456 Ma. The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton. 相似文献
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R-P. Mnot A. Pêcher Y. Rolland J-J. Peucat A. Pelletier G. Duclaux S. Guillot 《Gondwana Research》2005,8(1):1-9
Geological maps of East Commonwealth Bay Unit (ECB), (Terre Adélie and Georges V Land, Antarctica) are presented with a summary of the main structural and metamorphic data for the region. The ECB unit was developed during Neoarchean_Paleoproterozoic event (at 2.5-2.42 Ga), with (i) granulite metamorphism at 9±1.5 kbar and 800±50°C in the lower crust section and amphibolite metamorphism (P=5 kbar, T=750°C) at the upper crustal levels; (ii) the lower crustal granulites were uplifted, and suffered local partial melting and retrogression to the amphibolite facies at 550±50°C_5 kbar. Granulites were extruded in the core of a crustal-scale anticlinal fold, but retrogressed only on the rims of the anticline. Crustal-scale folding, along with other structural features resulted from intense NE-SW shortening that prevailed during the Neoarchean orogenic cycle. Strike-slip and extensional motions were only minor components in that process; (iii) top-to-the-East thrusting and nappe piling had (at least locally) occurred under lower amphibolite to greenschist facies conditions. Finally, it seems that (iv) the Paleoproterozoic 1.7 Ga structural imprint may have only affected the rims of the Archean units. The tectonic context observed in the 1.7 Ga Cape Hunter phyllites features mainly an E-W shortening component and vertical extrusion. The eastern (Mertz) and western (Port Martin) parts of the Archean block were reactivated by localized dextral shearing. 相似文献
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Two Neoarchean supercontinents? Evidence from the Paleoproterozoic 总被引：10，自引：0，他引：10
An unresolved question in Precambrian geology is the relationship between Archean crustal fragments that are now separated by younger orogens: were they once contiguous? Williams et al. (1991) proposed the name ‘Kenorland' for a speculative Neoarchean supercontinent comprising the Archean provinces in North America. Recently, a large number of ca. 2.5–2.0 Ga magmatic, metamorphic, detrital and xenocrystic ages have been reported from North America. We interpret that the wide geographic distribution and temporal spread of these ages may signify long-lived, regional-scale mantle upwelling, and anorogenic magmatic and metamorphic processes related to the protracted breakup of Kenorland. Breakup may have extended from ca. 2.5 to 2.1 Ga, culminating with dispersion of continental fragments at ca. 2.1–2.0 Ga. In North America, ca. 2.5–2.1 Ga intracratonic basin successions (e.g. Hurwitz Group) formed in the interior of Kenorland before dispersion, and passive margin sequences flanking the Superior Province (e.g. Huronian Supergroup) and the Wyoming Province (e.g. Snowy Pass Supergroup) defined the edges of Kenorland. Earliest Paleoproterozoic magmatic and sedimentary rocks, which include voluminous quartz arenites and glacigenic deposits, are consistent with a high-standing supercontinent and a mantle superplume. The Paleoproterozoic record from the Baltic and Siberian shields is similar to that of North America, suggesting inclusion in Kenorland. A slightly different record from the southern continents suggests a second, coexisting supercontinent that included the Zimbabwe, Kaapvaal, and Pilbara cratons, (‘Zimvaalbara' of I.G. Stanistreet), the São Francisco Craton, and possibly, cratonic blocks in India. Attenuation of this second supercontinent started earlier than in Kenorland (ca. 2.65 Ga) and was accompanied by high sea level and deposition of vast Lake Superior-type iron formations. Immediately thereafter, both supercontinents became emergent and were subject to global cooling and glaciation. 相似文献
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《China Geology》2021,4(2):215-229
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
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经构造—岩性—事件法的详细填图,将五台山花岗绿岩带划分为庄旺—银厂、太平沟—岩头、高凡和北台—朱家坊四个构造岩片。通过对各岩片的构造岩石组合、岩石地球化学、变形变质作用和同位素年龄的综合研究,认为五台山地区新太古代碰撞造山带具有洋壳俯冲、陆—陆碰撞造山的特点。新太古代晚期的地质事件序列为:(1)2600～2560Ma:首先在恒山、阜平两侧的大陆活动边缘沉积了富铝泥砂质岩;主伸展期形成了庄旺—银厂和北台—朱家坊岩片中的金岗库岩组大洋拉斑玄武岩;(2)2560～2530Ma:大洋消减转化为岛弧环境,形成以太平沟—岩头岩片为主体的岛弧钙碱性玄武岩,石佛、北台、光明寺等钠质花岗岩体侵位,高凡浊积岩形成;(3)2530～2510Ma:主碰撞造山事件产生一系列紧闭褶皱、冲断构造,导致各岩片相互叠置、陆—陆碰撞,峨口、王家会钙碱性花岗岩侵位,绿片岩相—角闪岩相变质;(4)2510～2500Ma:碰撞造山后纵向伸展作用,各岩片抬升,高凡浊积岩整体向南滑移,形成高凡岩片。 相似文献
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胶东谭格庄地区奥长花岗质片麻岩和斜长角闪岩的野外地质和锆石SHRIMP定年 总被引：10，自引：9，他引：1
对胶东谭格庄地区一地质剖面进行了详细野外观察和锆石SHRIMP年代学研究.剖面主要是由奥长花岗质片麻岩和斜长角闪岩组成,两者互层产出并一起发生褶皱变形,在强变形域两者完全平行化.所以,在强变形地区,不同成分岩性的薄层状互层产出不能作为变质沉积岩的识别标志.奥长花岗质片麻岩(S1105)形成于2496±10Ma,遭受了古元古代早期和晚期变质.两个斜长角闪岩样品(S1238和S0812)都只发育变质锆石,年龄分别为1842±3Ma和1833±13Ma.该剖面岩石记录的两期变质作用在胶东地区具有普遍意义.结合前人研究,作者指出该地区太古宙末存在区域性变质深熔作用,早期地壳受到了强烈的再造;古元古代末的变质作用具有带状分布特点,与造山作用有关. 相似文献
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Mingda Huang Guangming Ren Jinwei Guo Fei Ren Weihua Pang 《International Geology Review》2020,62(6):649-664
ABSTRACTWe report the oldest I-type granites in the Lengshui Complex of the Yangtze Craton, providing new insights for its tectonic evolution during the Neoarchean. An approach-combined study of zircon U-Pb dating and Lu-Hf isotopes, as well as whole-rock element geochemistry and Nd isotopes, were employed. LA-ICP-MS zircon U-Pb dating for the monzogranite sample LSG03 and LSG16 yielded ages of 2732 ± 13 Ma and 2738 ± 25 Ma, respectively. The more precise age of 2732 ± 13 Ma for the sample LSG03 was taken as the crystallization age of the monzogranite. These rocks have high SiO2 (73.11–74.01 wt%), K2O (3.93–5.48 wt%), Na2O (3.93–4.86 wt%) and low CaO (0.30–0.69 wt%), MgO (0.17–0.30 wt%), TiO2 (0.14–0.17 wt%), P2O5 (0.01–0.06 wt%), Al2O3 (14.11–14.37 wt%) content with weakly peraluminous affinity (A/CNK = 1.04–1.11). Geochemically, they belong to I-type granites, indicating partial melting of a thickened lower crust. Their relatively high Nb/Ta (15.2–34.8) ratios further suggest they formed under eclogite-facies conditions. The consistent whole-rock Nd and zircon Hf isotopic compositions indicate a homogeneous source. According to their εHf(t) values (?2.0 to 0.8), two-stage Hf model ages (3.1 to 3.2 Ga) and positive εNd(t) (1.4 to 2.1), we argue that they were probably generated by partial melting of a juvenile lower crust with little ancient materials. Monzogranites formed in a late-orogenic or collisional compressive tectonic regime, whereas subsequent ca. 2.73 Ga and 2.67–2.62 Ga A-type granites in the Zhongxiang Uplift (including the Lengshui Complex) may represent a prolonged extensional setting. Thus, Archean subduction (probably unlike modern subduction) likely occurred prior to ca. 2.73 Ga. Similar magmatism in the Kongling Complex implies that the Zhongxiang Uplift may have accrete to the Kongling Complex during the early Neoarchean. The transition from I-type to A-type magmatism may have resulted from a change in the geodynamic regime from the late-orogenic or collisional compressive environment to an extensional environment caused by the subsequent lithospheric collapse and mantle upwelling, suggesting an early Neoarchean orogenic event in the eastern Yangtze Craton. 相似文献
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河南嵩山地区新太古代TTG质片麻岩的成因及其地质意义：来自岩石学、地球化学及同位素年代学的制约 总被引：15，自引：10，他引：5
河南嵩山地区位于华北克拉通南缘,是我国记录前寒武纪地质的典型地区之一。该区广泛出露新太古代TTG质片麻岩套,主要以英云闪长岩类为主,闪长岩类次之,测得的锆石SHRIMP年龄在2600~2500Ma。该套TTG质片麻岩富Na2O(3%~7%)、SiO2(>67%)、贫铁、镁,高的Na2O/K2O比值（多在1.5~5.2）,Al2O3=13.72%~16.37%,A/CNK=0.97~1.21,属英云闪长岩-奥长花岗岩系列,显示新太古代富铝型TTG岩石特征。岩石富Sr (平均433×10-6),Rb/Sr比值(<0.5) 较低,Sr/Y比值高(平均165),Nb、Ta和Ti负异常,∑REE偏低,强烈分异((La/Yb) N=27~150),基本无Eu异常,低的Nb/Ta(14左右)、La/Nb (平均约为7)比值及其它微量元素特征表明其与岛弧或大陆边缘弧玄武质岩石特征相似。全岩Nd同位素和锆石Hf同位素数据显示岩石源区是来自亏损地幔的约2.66Ga的初生地壳;Mg#值变化较大反映存在地幔楔不同程度的混染。地球化学特征指示该岩浆是在较高温度和压力(约700~1000℃,>1.5Gpa)下由俯冲的含水玄武质洋壳部分熔融形成,残留相中有石榴石和角闪石而不含斜长石。嵩山地区TTG片麻岩的这种成因机制表明当时陆壳以水平方式增生,也说明在随后的2.5Ga左右微陆块碰撞拼合事件之前不同陆块之间很可能被一个古大洋所分隔。 相似文献
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白云鄂博位于华北克拉通北缘,是阴山地块的重要组成部分。本文对该区变质基底的5个花岗质岩石样品进行了锆石SHRIMP U-Pb定年,获得了2.63Ga和1.89~2.20Ga的岩浆锆石年龄以及2.47~2.51Ga和1.86~1.94Ga的变质锆石年龄。新太古代早期片麻状英云闪长岩的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为3.57~8.36和2.59~2.88Ga,古元古代中晚期花岗质岩石的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为-17.20~8.58和2.11~3.70Ga。变质锆石与岩浆锆石具有类似的Hf同位素组成。结合前人研究成果,表明:白云鄂博地区存在新太古代早期到古元古代晚期岩浆作用;在每一岩浆作用过程中,地幔添加和壳内再循环都起了重要作用;白云鄂博地区变质基底经历了新太古代晚期-古元古代早期和古元古代晚期构造热事件;阴山地块与南侧孔兹岩带具有类似的早前寒武纪地质演化历史。 相似文献
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胶北新太古代两类片麻岩的岩石地球化学特征和成因指示 总被引：1，自引：1，他引：0
在胶北三口探矿深钻中识别出两类新太古代片麻岩,一种是TTG片麻岩,数量较多;另一类是石榴黑云斜长片麻岩,数量相对较少,以夹层状发育于TTG片麻岩中.已有年代学资料显示,两种片麻岩原岩均形成于～2.5Ga.TTG片麻岩SiO2含量为53.95％ ～ 75.56％,Na2O为1.51％～5.94％,Na2O/K2O＞1;贫Fe2O3T(2.22％～9.54％)和MgO (0.53％ ～4.87％),Al2O3多大于15％(10.45％ ～ 17.64％),A/CNK=1.18～1.75,说明其属于高铝TTG岩系.富集大离子亲石元素(如Rb、Ba、Sr),亏损高场强元素(如Nb、Ta、Zr、Hf),Sr含量高(204×10-6～2906×10-6),Sr/Y比值高(7.30～355).∑REE含量(40.4×10-6～ 512×10-6)相对较高,轻重稀土强烈分异((La/Yb)N=11.5 ～ 121),Eu无异常或弱正异常(δEu=0.79～1.89).以上地球化学性质表明,胶北TTG片麻岩是含水玄武质岩石高压下部分熔融形成的,残留相主要是石榴石、角闪石和含Ti矿物,没有斜长石.全岩Nd和锆石Hf同位素数据显示其模式年龄与形成年龄相近,表明岩石源区可能是来源于亏损地幔的2.57～2.64Ga的初生玄武质地壳.另外,胶北TTG片麻岩高的Mg#值(40 ～67)和Cr(147×10-6～371×10-6)、Ni(6.68×10-6～ 156 × 10-6)含量,表示与地幔楔发生了反应,结合Nb、Ta负异常以及源区为初生的玄武质地壳等特征,说明研究区TTG形成于与俯冲有关的岛弧环境,而非加厚的下地壳.DF值和K-A关系图显示,石榴黑云斜长片麻岩原岩是泥质-粉砂质沉积岩.Cr/Zr比值(0.90 ～1.99,平均为1.62)和Th/Sc比值(平均为0.30)与太古宙沉积岩相应值相近(分别为1.44和0.4),稀土配分型式与太古宙沉积岩类似,表明源区物质以长英质为主.绝大多数样品显示轻稀土富集、重稀土平坦的特征,总稀土含量平均为176×10-6,(La/Yb)N比值平均为14.7,LREE/HREE平均为3.3,Eu无异常或微弱的负异常(δEu=0.69～0.92,平均为0.84),这些特征值表明原岩形成的大地构造背景为岛弧或主动大陆边缘.Grt-Bi地质温度计得到的变质温度为549 ～663℃,其中黑云母化学成分与角闪岩相中黑云母特征相同,共同指示变质程度为角闪岩相,可能代表了～2.5Ga麻粒岩相-高角闪岩相变质作用的退变质阶段.石榴黑云斜长片麻岩原岩与TTG属同一时代(～2.5Ga)的产物,形成的构造背景类似(岛弧或主动大陆边缘),说明当时该区有俯冲过程发生;TTG岩浆事件和～2.5Ga的变质事件大体同时,但变质事件较岩浆事件稍晚,可以用俯冲后的碰撞来解释.因此,研究区在～2.5Ga可能发生过一次重要的俯冲-碰撞拼合事件:TTG和石榴黑云斜长片麻岩原岩形成于俯冲阶段,后期发生碰撞引发麻粒岩相-高角闪岩相的区域变质作用. 相似文献
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鲁西沂山地区高级深熔混合岩中存在丰富的不同时代、不同类型的岩石包体。在详细野外地质工作基础上,本文对高级深熔混合岩中的包体进行了锆石SHRIMP U-Pb定年和Hf同位素分析及全岩地球化学研究,以期探讨沂山地区高级深熔混合岩的源区性质。英云闪长质片麻岩形成时代为~2.7Ga,存在2.69Ga和2.53~2.51Ga两期基性岩浆作用,并记录了2.52~2.50Ga变质作用。角闪斜长片麻岩与黑云角闪变粒岩互层产出,它们可能为变质火山岩,其岩浆锆石年龄为2.51Ga。变质基性岩的岩浆锆石ε_(Hf)(t)为0~+8.1,一阶段Hf模式年龄为2.83~2.54Ga;变质火山岩的岩浆锆石ε_(Hf)(t)为-1.2~+5.8,一阶段Hf模式年龄为2.89~2.71Ga。结合前人研究,这套高级深熔混合岩的源区组成包括了新太古代早期的英云闪长质片麻岩和变质辉长岩,新太古代晚期的石英闪长质片麻岩、变质火山岩及斜长角闪岩等岩石类型。~2.5Ga基性岩浆作用在鲁西地区发育广泛,为新太古代晚期深熔作用及高级深熔混合岩和壳源花岗岩的形成提供了热源。 相似文献
16.
Magmatic Event at the End of the Archean in Eastern Hebei Province and Its Geological Implication 总被引：20，自引：0，他引：20
GENG Yuansheng LIU Fulai YANG Chonghui Institute of Geology Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》2006,80(6):819-833
1 Introduction With a wide distribution of the early Precambrian rocks, eastern Hebei Province is one of the classical regions for early Precambrian study of China. From the 1960s up to now, a great deal of geological surveys and researches have been undertaken in the region. The region was well-known among geologists of the world for the first report of the isotopic age of c. 3500 Ma (Rb-Sr Group, Laboratory of Isotopic Geology and Composite Research Group, Institute of Geology, Academ… 相似文献
17.
Major regional deformation and metamorphic events in the Godthåbsfjord region, southern West Greenland, occurred at 3650 and 2820–2720 Ma (e.g. Precambrian Res. 78 (1996) 1). New geochronological constraints (U–Pb zircon, Sensitive High Resolution Ion Microprobe [SHRIMP] and thermal ionisation mass spectrometry [TIMS]) have been obtained from a stack of mylonitic, crystalline thrust-nappes in the footwall of the western part of the Paleoarchean (3.8–3.7 Ga) Isua Greenstone Belt, Isukasia. A mylonitic tonalite sheet, interpreted to have intruded synkinematically with respect to mylonitisation, yields a magmatic crystallisation age of 3640±3 Ma. A cross-cutting pegmatite and a post-kinematic tonalite pluton yield magmatic crystallisation ages of 2948±8 and 2991±2 Ma, respectively. Accordingly, we interpret the thrust-nappe stack to have formed during the Paleoarchean (3640 Ma), making it the oldest example known on Earth. The similarity of this structural regime to that of modern mountain belts suggests that Paleoarchean and modern continental crust were comparable in terms of mechanical strength and constitution.Southern West Greenland has been interpreted in terms of Neoarchean accretion, comparable with modern plate tectonics (e.g. Earth Planet. Sci. Lett. 142 (1996) 353). Isukasia lies just east of a purported Neoarchean accretionary boundary between the Akia terrane to the Northwest and the Akulleq terrane to the Southeast. The Akia terrane was previously considered to overthrust the Akulleq terrane at 2820–2720 Ma. Our geochronological and geological data indicate (i) that the two “terranes”, as presently defined, were stitched at 2991±2 Ma and (ii) that thrusting across the boundary was directed toward the Akia terrane. Therefore, we suggest that the Akia–Akulleq interface was not a fundamental tectonic structure during the Neoarchean, and we question its identification as an accretionary boundary. 相似文献
18.
以崆岭杂岩中新太古代花岗片麻岩为研究对象,系统研究了其锆石U-Pb年代学和全岩地球化学特征,并对其岩石成因和扬子陆核～3.0～2.6Ga构造演化过程进行了初步探讨.锆石LA-ICP-MS U-Pb同位素测年结果表明,花岗片麻岩形成年龄为2 673±39Ma,且遭受了古元古代(2 042±27Ma)的高压麻粒岩相变质作用.地球化学研究表明,该套花岗片麻岩富Si,贫Mg、Cr、Ni,具有Eu、Sr和高场强元素的负异常.花岗片麻岩的εNd(t)值在-1.9～-0.1之间变化,对应两阶段Nd同位素模式年龄为3.15～3.01Ga,锆石饱和温度为789～825℃,显示岩体可能形成于初生长英质地壳物质在后碰撞伸展构造背景高温条件下部分熔融.结合前人已有的研究成果,认为以崆岭杂岩为代表的扬子陆核可能完整记录了～2.9～2.6Ga板块俯冲-碰撞-后碰撞与造山作用相关的完整过程. 相似文献
19.
徂徕山是鲁西新太古代岩石的重要出露区。在野外地质基础上,本文对3个岩石样品进行了锆石SHRIMP U-Pb定年研究。英云闪长质片麻岩遭受一定重结晶影响的岩浆锆石年龄为(2711±11)Ma,变质作用时代可能为~2.6 Ga。变质石英闪长岩遭受强烈重结晶影响的岩浆锆石年龄为2.51 Ga,被解释为更接近构造热事件的时代,而岩浆锆石年龄可能在2.53~2.55 Ga之间。二长花岗岩锆石普遍存在强烈铅丢失,根据数据点在谐和线上的分布特征,二长花岗岩的形成时代应为~2.5 Ga。结合地球化学研究和前人工作,确定了徂徕山地区新太古代地质演化历史及新太古代早期古老岩石带(B带)和新太古代晚期新生岩石带(C带)之间的界线。 相似文献
20.
通过区域地质调查研究,在湘东北文家市涧溪冲村原中元古代冷家溪群新发现一套基本无序的变质沉积-火山岩系。根据岩石矿物学、岩石地球化学研究表明,涧溪冲变质沉积-火山岩系为变质火山岩夹变质粘土质沉积岩,属绿片岩—高绿片岩相。变质火山岩的原岩为大洋拉张环境下形成的以低钾拉斑玄武岩为主,低钾玄武安山岩次之的火山-次火山岩系,其物源为亏损地幔。变火山岩Sm-Nd全岩等时线年龄为(2594±48)Ma,其形成时代可能是新太古代。因此,与传统的中元古代冷家溪群的岩石组合、形成环境、形成时代、变质变形都具有明显不同的特征,原冷家溪群应予以解体。 相似文献