Neoproterozoic granites of the Lajeado intrusive suite,north-center Brazil: A late Ediacaran remelting of a Paleoproterozoic crust     

《Journal of South American Earth Sciences》2013

In north-central Brazil, a number of granite plutons, which intrude Paleoproterozoic gneiss-granulite terrains of the Goiás Massif, crop out along a thermal axis parallel to the Transbrasiliano Lineament. Single zircon lead evaporation ages from three granitic bodies span between 552 and 545 Ma. Sm–Nd model ages (T_DM) vary between 2.1 and 1.7 Ga and negative εNd_{(0.55 Ga)} values between −10 and −13 show that Paleoproterozoic crust was involved in the genesis of these granites. These plutons, which form the Lajeado Intrusive Suite are part of an important Ediacaran magmatic event in central-northern of the Tocantins Tectonic Province, composed of metaluminous to slightly peraluminous granites with geochemical characteristics similar to A-type granites, whose crystallization occurred under low water activity during magmatic emplacement. The granitic intrusive bodies are related to a crustal extensional/transtensional tectonic event at the end of the Neoproterozoic. They may have connection with the granitic plutons of similar age (0.56–0.52 Ga) in northwestern Ceará state, on the other side of the Paleozoic Parnaíba Basin in northwest of Borborema Province, along the Transbrasiliano Lineament.  相似文献   

内蒙古道郎呼都格地区A型花岗岩年代学、地球化学及地质意义   总被引：5，自引：3，他引：2  

解洪晶  武广  朱明田  刘军  张连昌 《岩石学报》2012,28(2):483-494

道郎呼都格钾长花岗岩体位于华北克拉通北缘白乃庙构造带。SHRIMP锆石U-Pb定年获得139.6±1.7Ma岩体侵位年龄。岩体富硅(SiO₂=75.79%~78.07%)、富碱(K₂O+Na₂O=7.39%~8.29%)、贫钙(CaO=0.22%~0.59%);稀土配分曲线呈现"海鸥式"分布特征,显示强烈的Eu负异常(δEu =0.03~0.12);微量元素特征显示具有较高Ga(21.2×10^-6~26.6×10^-6)、Zr(173×10^-6~417×10^-6)、Nb(32.3×10^-6~42.4×10^-6)和Y(24.6×10^-6~53.9×10^-6)含量,较低的Sr(14×10^-6~44×10^-6)、Ba(18×10^-6~211×10^-6)含量,在微量元素原始地幔标准化蛛网图上显示明显的Ba、Sr、P、Eu和Ti的负异常。以上特征表明道郎呼都格钾长花岗岩为A型花岗岩,为高温低压下长英质地壳的部分熔融及其后长石、榍石等的分离结晶作用的产物。结合区域构造演化,本文认为该区钾长花岗岩形成于板内伸展背景。在晚中生代期间,华北板块北缘的构造体制经历了重要的转变,由挤压体制转变为岩石圈减薄和地壳伸展,在伸展体制下,软流圈地幔上涌对上覆长英质地壳的直接加热作用促使其部分熔融形成该区A型花岗岩。  相似文献   

大兴安岭中部柴河地区钾长花岗岩的成因及构造背景:岩石地球化学、锆石U-Pb同位素年代学的制约   总被引：6，自引：3，他引：3  

王兴安  徐仲元  刘正宏  朱凯 《岩石学报》2012,28(8):2647-2655

对大兴安岭中部柴河林场地区钾长花岗岩进行了系统的地球化学及锆石U-Pb同位素年代学研究,并对其岩石成因及构造意义进行讨论.研究结果表明,柴河林场地区钾长花岗岩中锆石具有典型的岩浆振荡生长环带和较高的Th/U比值(0.44 ～ 1.42),反映了岩浆成因特征.LA-ICP-MS锆石U-Pb定年结果为133±3Ma.岩石具有富硅、稀土元素含量较高、相对富集轻稀土元素亏损重稀土元素的特征,Eu负异常较为明显,稀土元素配分图解具有右斜“V”字型的特征,并相对富集高场强元素和大离子亲石元素.以上特征表明,柴河林场地区钾长花岗岩为铝质A型花岗岩,是地壳岩石部分熔融的产物,具有典型A1型(裂谷或板内)花岗岩的特征,代表了伸展的构造环境.  相似文献   

A型花岗岩的实质是什么？   总被引：39，自引：0，他引：39  

张旗  冉白皋  李承东 《岩石矿物学杂志》2012,31(4):621-626

A型花岗岩是富碱、贫水的花岗岩类,地球化学上以贫Al、Sr、Eu、Ba、Ti、P为特征,形成于低压高温条件下,对源岩没有选择。A型花岗岩的实质为:在低压下部分熔融形成的花岗岩类,大多产于地壳伸展减薄的构造背景中。  相似文献   

Zircon ages and Hf isotopic compositions of Permian and Triassic A-type granites from central Inner Mongolia and their significance for late Palaeozoic and early Mesozoic evolution of the Central Asian Orogenic Belt     

《International Geology Review》2012,54(8):967-982

ABSTRACT

This work presents zircon ages and Hf-in-zircon isotopic data for Permian and Triassic A-type granitoids and reviews the evolution of central Inner Mongolia, China, during the early Permian and Late Triassic. SHRIMP U–Pb dating of zircons of peralkaline granites yielded ²⁰⁶Pb/²³⁸U ages of 294 ± 4 Ma and 293 ± 9 Ma that reflect the time of Permian magmatism. Zircon ages were also obtained for Late Triassic granites (226 ± 4 Ma, 224 ± 4 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia.

The Permian peralkaline granites show typical geochemical features of A-type granites, which also have highly positive zircon ε_Hf(t) values (+4.9 – +17.1), indicating a significant contribution of an isotopically depleted source, likely formed from mantle-derived magmas. Late Triassic A-type granitoids, however, in central Inner Mongolia show large variations and mostly positive in zircon ε_Hf(t) values (?1.3 – +13.5), suggesting derivation from a mixture of crust and mantle or metasomatized lithospheric mantle with crustal contamination. The geochemical characteristics of the Permian peralkaline granites and Late Triassic A-type granitoids are consistent with a post-collisional setting and were likely related to asthenosphere upwelling during the evolution of the Northern Block and Central Asian Orogenic Belt (CAOB).  相似文献   

U-Pb zircon geochronology, geochemistry and kinetics of the Huaniushan A-type granite in Northwest China   总被引：1，自引：0，他引：1  

Jiang Zhu  Xinbiao Lü  Xiaofeng Cao  Yalong Mo  Chao Chen 《中国地球化学学报》2012,31(1):85-94

The Huaniushan granite is located at the Beishan orogenic belt, northwestern China. At the contact zone between the granite and marble, a hydrothermal Pb-Zn and skarn Au deposit is formed. LA-ICP-MS zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 229.5±2.6 Ma (MSDW=0.93) for the Huaniushan granite, imply-ing its Late Triassic intrusion. Geochemistry analyses show that the Huaniushan granite is enriched in Si, K, Na, and REE, and depleted in Mg and Ca, with contents of SiO2 (70.8% to 74.4%), Na2O+K2O (8.8% to 10.2%), CaO (0.93% to 1.44%), and MgO (0.14% to 0.48%). REE is characterized by obvious negative Eu anomaly. Rb, Th, U, K, Pb, Nb, Zr and Hf elements are rich in the granite while Ba, Sr, P, Ti and Eu are deplete. The granite has a high (Zr+Nb+Ce+Y) abundance and 104 Ga/Al ratios. Petrology, major and trace elements data all indicate that the Hua-niushan granite is A-type granite which intruded in a post-collisional extensional tectonic setting. The magma was dominantly sourced from partial melting of crustal intermediate-felsic igneous rocks. Intensive magmatic activities and Au-Cu-Mo mineralization occurred throughout the Beishan orogenic belt during the period from ca. 240 to 220 Ma.  相似文献   

黄沙坪矿区花岗岩岩石地球化学、U-Pb年代学及Hf同位素制约   总被引：1，自引：0，他引：1  

全铁军  孔华  王高  费利东  郭碧莹  赵志强 《大地构造与成矿学》2012,36(4)

湘南坪宝地区地处南岭中段,黄沙坪铅锌多金属矿床位于坪宝成矿带南部,304岩体是未来深部找矿的远景地区,岩石地球化学特征显示其具有A型花岗岩的特点,与区域上的千里山岩体相似。根据微量元素判别图解进一步划分为A1型,反映为非造山板内拉张背景;岩石稀土配分型式具有特征的四分组效应(tetrad effect),这是岩浆高度演化晚期熔体与流体相互作用的结果。采用LA-ICPMS方法对花斑岩中锆石进行了微区U-Pb同位素及Hf同位素测试,结果显示成岩年龄为179.9±1.3Ma(MSWD=1.9),属于燕山早期第一阶段岩浆侵入产物,成岩时代早于301岩体。Hf同位素显示地壳模式年龄为2220～2459Ma,平均为2353Ma,反映源区物质为新太古代至古元古代地壳物质。  相似文献   

西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束   总被引：20，自引：0，他引：20  

曲晓明  辛洪波  杜德道  陈华 《地球化学》2012,(1):1-14

近年来地质调查在班公湖-怒江缝合带中段发现了一批A型花岗岩,岩体呈面积不大(＜1 km2)的岩株产出,岩性上分为钾长花岗岩和花岗闪长斑岩两种,侵入白垩系地层中.岩石化学上这些A型花岗岩相对富硅,SiO2含量在68.62％～75.36％之间,全碱含量(K2O+Na2O=8.03％ ～ 9.37％)和全铁含量(FeO(T)...  相似文献   

小兴安岭石林林场A型花岗岩地球化学特征及构造环境     

李超  孙国胜  杨乃峰  孙珍军  杜美艳  敖东 《世界地质》2013,32(1):1-7

根据岩石学及地球化学等特征,对小兴安岭北部石林林场A型花岗岩进行了构造环境研究。石林林场A型花岗岩为高钾钙碱性系列、过铝质岩石,富集大离子亲石元素Rb、Th、U、La、Ce和轻稀土元素。岩石化学成分特点及Na2O--K2O图解表明,花岗岩为铝质A型花岗岩。通过对Nb--Y构造环境判别图解、R1--10 000 Ga/Al判别图解及构造环境讨论表明,石林林场花岗岩形成于陆内拉张环境。  相似文献   

关于A型花岗岩判别过程中若干问题的讨论   总被引：1，自引：0，他引：1  

李小伟  莫宣学  赵志丹  朱弟成 《地质通报》2010,29(2)

自A型花岗岩提出(1979年)30年来,其内涵和外延相对于原始定义而言已发生了很大的变化.主要针对A型花岗岩的各种判别方法(尤其是判别图解)的有效性和局限性进行了讨论.这些判别方法对于A型花岗岩的判定并不总是奏效,所以在实践过程中不能过于依赖判别图解,否则就很容易得出错误的结论.实际上,A型花岗岩最本质的特征很可能在于它是一种高温花岗岩(相时于I型争S型花岗岩),因此较高地温梯度下的各种地球动力学背景均有利于这一类型花岗岩的发育.  相似文献