赣南营前岩体的年代学、地球化学、Sr-Nd-Hf同位素组成及其地质意义

赣南营前岩体由早期似斑状花岗闪长岩和晚期细粒黑云母花岗岩组成,在前者中普遍发育暗色基性包体。SHRIMP锆石U-Pb测年显示似斑状花岗闪长岩为172.2±3.1Ma,细粒黑云母花岗岩为168±3Ma,包体为167.6±3.3Ma。所有的岩石均为钙碱性系列,稀土元素显示LREE富集,HREE亏损,Eu负异常并不明显的特征,Nb-Ta负异常显示壳源物质的特征。晚期细粒黑云母花岗岩、早期似斑状花岗闪长岩、暗色包体的(87Sr/86Sr)i和εNd(t)值分别为0.70885～0.70965、0.71058～1.46393、0.70788～0.70923和-6.38～-5.31、-6.51～-5.17、-5.47～-4.31;锆石εHf(t)值分别为-12.4～-5.7、-9.2～-4.2、-9.4～+0.1。结合岩相学、地球化学研究,初步认为营前岩体的两期花岗质岩石源于地壳重熔,地幔底侵导致地壳熔融形成营前岩体,基性岩浆加入到未冷却的酸性岩浆中形成了目前所见到的暗色包体。结合区域上的研究资料,认为中侏罗世期间,沿"十杭"断裂带及与其相平行的一些深断裂发生了板块的撕裂,这些缝合带是岩石圈相对薄弱的地带,有利于幔源物质底侵上升以及壳幔相互作用。     

Neoproterozoic crustal evolution in Southern Chad: Pan-African ocean basin closing, arc accretion and late- to post-orogenic granitic intrusion

In the Lake Léré region, southern Chad, Neoproterozoic terrains are distributed in four lithostructural groups that reveal the geotectonic evolution of a part of the Pan-African orogenic domain. The first group includes basaltic volcanic rocks and fine-grained detrital sedimentary rocks of pre-tectonic basins that were emplaced in an extensional regime, close to a volcanic arc. The second and third groups include calc-alkaline gabbroic intrusions emplaced at an upper crustal level and a midcrustal tonalite, respectively, that are interpreted to be the roots of an active margin volcanic arc. These first three groups experienced WNW to ESE compression, and may belong to a fore-arc basic—volcanic arc—back-arc basin system that was accreted eastward to the Palaeoproterozoic Adamaoua-Yadé Block. The fourth group includes post-tectonic granite plutons invading the older groups. This paper documents the accretion processes in the southern margin of the Saharan Metacraton.     

吉林省北部A型花岗岩的初步认识

分布在吉林省北部的香水、治安一带的正长花岗岩、碱长花岗岩，研究后认为属Ａ型花岗岩。其行征钾长石为微斜长石一条纹长石，斜长石大部分为奥长石Ａｎ＝１３－１７。并有碱性碱物无辉石。     

A型花岗岩的研究进展及意义

A型花岗岩主要形成于伸展的构造背景中,是构造环境识别的重要岩石学标志之一。由于形成于特殊的构造背景和重要的地球动力学意义,A型花岗岩的研究一直得到广泛的关注,但是仍旧有许多问题(如命名、分类和成因等)在争论之中。本文从下面几个方面对A型花岗岩的研究现状进行了较系统的总结:(1)A型花岗岩的概念及特征;(2)A型花岗岩与高分异I、S型花岗岩的区别;(3)A型花岗岩的物质来源及成因模式;(4)A型花岗岩的实验岩石学成果;(5)A型花岗岩的分类;(6)A型花岗岩的构造背景及动力学意义。A型花岗岩在形成过程中斜长石、斜方辉石可能为主要的残留或分离结晶矿物相。除了传统的A1(非造山)、A2(后碰撞)分类外,"还原型"和"氧化型"的分类方案最近也受到广泛关注。     

REE Abundance and REE Minerals in Granitic Rocks in the Nanling Range,Jiangxi Province,Southern China,and Generation of the REE‐rich Weathered Crust Deposits

Studies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.     

新疆塔里木北缘新元古代最晚期岩浆事件

报道了塔里木库鲁克塔格地区新元古代晚期花岗闪长岩和钾长花岗岩的锆石U-Pb年龄和Hf同位素组成。花岗闪长岩锆石U-Pb谐和年龄为630.1±1.3Ma,钾长花岗岩锆石U-Pb谐和年龄为630.6±1.3Ma。Hf同位素组成表明,这2种岩石主要来自古老（中）基性地壳的重熔,可能有部分地幔物质的加入。结合已有的研究表明,650~615Ma期间的岩浆活动代表了塔里木地块新元古代最晚期的岩浆活动,是Rodinia超大陆解体过程中的产物,与泛非造山事件无关。塔里木地块自新元古代中期到早寒武世,持续接受了被动大陆边缘沉积,表明在这一时期塔里木为冈瓦那大陆之外独立的大陆块体,或是位于冈瓦那大陆最边缘的稳定大陆块体。     

新疆东准噶尔北部扎河坝富碱花岗质岩石矿物学特征及物理化学条件

新疆东准噶尔北部扎河坝富碱花岗质岩石分布于乌伦古大断裂与额尔齐斯-玛因鄂博大断裂之间。富碱花岗岩类有石英碱性正长岩、碱性长石花岗岩、石英二长斑岩及碱性长石正长岩等岩石类型。在详细的显微镜观察基础上,全岩分析和电子探针分析结果表明,富碱花岗质岩中的矿物组合是碱性长石 石英 钠铁闪石 霓辉石,以出现高硅、富碱、贫铝、低钙、低镁、高铁、高锰、贫水为特征。铁钛氧化物温度计估算出的富碱花岗岩体结晶温度在650℃~755℃之间,氧逸度为10-17.17Pa~10-14.39Pa,结合钠铁闪石的特征,碱性岩浆演化后期存在着明显的水-岩作用,扎河坝富碱花岗质岩石形成于低压、高氧逸度、中高温环境,反映了相对开放、浅成的形成环境。     

秦祁结合部位宝鸡地区早泥盆世香泉A型正长花岗岩年龄、地球化学特征及其构造意义

对秦祁结合部位宝鸡地区香泉正长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究。结果显示,锆石~(206)Pb/~(238)Pb年龄加权平均值为410±5Ma(MSWD=0.20,n=18),限定该岩体的形成时代为早泥盆世。香泉正长花岗岩具有高硅(SiO_2=69.63%~73.94%)、富钾(K_2O=4.24%~4.88%,K_2O/Na_2O=1.23~1.44)、富铁(TFe_2O_3=2.10%~3.70%,TFe_2O_3/MgO=3.88~6.84)、低镁(MgO=0.31%~0.94%)、低磷(P_2O_5=0.08%~0.21%)的特征,属准铝质、高钾钙碱性系列。香泉正长花岗岩稀土元素含量较高(318×10~(-6)~499×10~(-6)),表现出明显的负Eu异常(δ Eu=0.37~0.46),富集Rb、Th、Zr、Sm、Ga(10000×Ga/Al=2.59~2.93)等微量元素,贫Ba、Nb、Ta、Sr,整体表现出A型花岗岩特征。结合区域资料认为,香泉正长花岗岩形成于造山后环境,为低压环境下长英质地壳物质部分熔融成因。     

Mineralogical,geochemical and Sr-Nd isotopes characteristics of fluorite-bearing granites in the Northern Arabian-Nubian Shield,Egypt: Constraints on petrogenesis and evolution of their associated rare metal mineralization

The Central Eastern Desert (CED) of Egypt, a part of Neoproterozoic Arabian Nubian Shield (ANS), embraces a multiplicity of rare metal bearing granitoids. Gabal El-Ineigi represents one of these granitic plutons and is a good example of the fluorite-bearing rare metal granites in the ANS. It is a composite pluton consisting of a porphyritic syenogranite (SG; normal granite) and coarse- to medium-grained highly evolved alkali-feldspar granite (AFG; fluorite and rare metal bearing granite) intruded into older granodiorite and metagabbro-diorite rocks. The rock-forming minerals are quartz, K-feldspar (Or_94-99), plagioclase (An_0-6) and biotite (protolithonite-siderophyllite) in both granitic types, with subordinate muscovite (Li-phengite) and fluorite in the AFG. Columbite-(Fe), fergusonite-(Y), rutile, zircon and thorite are the main accessory phases in the AFG while allanite-(Ce) and epidote are exclusively encountered in the SG. Texture and chemistry of minerals, especially fluorite, columbite and fergusonite, support their magmatic origin. Both granitic types are metaluminous to weakly peraluminous (A/CNK = 0.95–1.01) and belong to the post-collisional A2-type granites, indicating melting of underplated mafic lower crust. The late phase AFG has distinctive geochemical features typical of rare metal bearing granites; it is highly fractionated calc-alkaline characterized by high Rb, Nb, Y, U and many other HFSE and HREE contents, and by extremely low Sr and Ba. Moreover, the REE patterns show pronounced negative Eu anomalies (Eu/Eu¹ = 0.03 and 0.06) and tetrad effect (TE_1,3 = 1.13 and 1.27), implying extensive open system fractionation via fluid–rock interactions that characterize the late magmatic stage differentiation. The SG is remarkably enriched in Sr, Ba and invariably shows a relative enrichment in light rare-earth elements (LREEs). The SG rocks (569 ± 15 Ma) are characterized by relatively low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7034–0.7035) that suggest their derivation from the mantle, with little contamination from the older continental crust. By contrast, the AFG has very high ⁸⁷Rb/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr ratios that reflect the disturbance of the Rb-Sr isotopic system and may give an indication for the high temperature magma-fluid interaction. The positive εNd(t) values of AFG (+7.40) and SG (+5.17), corresponding to young Nd-T_DM2 ages ranging from 707 to 893 Ma, clearly reflect the juvenile crustal nature of Gabal El-Ineigi granitoids and preclude the occurrence of pre-Neoproterozoic continental crust in the ANS. The field relationships, chemical, petrological and isotopic characteristics of El-Ineigi SG and AFG prove that they are genetically not associated to each other and indicate a complex origin involving two compositionally distinct parental magmas that were both modified during magmatic fractionation processes. We argue that the SG was formed by partial melting of a mid-crustal source with subsequent fractional crystallization. In contrast, the AFG was generated by partial melting and fractionation of Nb- and Ta-rich amphibole (or biotite) of the lower crust. The appreciable amounts of fluorine in the magma appears to be responsible for the formation of rare metal element complexes (e.g., Nb, Ta, Sn and REEs), and could account for the rare metal mineralization in the El-Ineigi AFG.     

滇东北东川下田坝A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

通过对滇东北东川下田坝地区黑云母二长花岗岩和似斑状钾长花岗岩2种岩体的地球化学分析及对黑云母二长花岗岩的U-Pb同位素测试,得到如下认识：黑云母二长花岗岩和似斑状钾长花岗岩总体地球化学特征相似,主量元素表现出高SiO2（平均71.7%）、过铝质（A/CNK指数在1.03～1.52）的特征,过碱指数在0.95～1.37之间,总体属于钙碱系列;稀土元素总量较高（ΣREE平均313×10-6）,（Ce/Yb）N均值为8.85,（La/Yb）N均值为9.54,呈现轻稀土元素（LREE）富集,仅Eu亏损（δEu均值0.31）的海鸥型右倾模式;大离子亲石元素Rb、Th、U、K等相对富集,高场强元素Nb、Ta、Sr、Ti等呈明显负异常,说明岩浆源岩以陆壳成分为主;Ga/Al均值为2.69,(Zr+Nb+Ce+Y)均值为383;微量元素Sr、Eu低,富集Nb、Zr等元素,反映其源区存在斜长石的残留;锆石饱和温度为724～786℃,表明初始岩浆温度较高。上述特征说明,下田坝花岗岩为典型的A型花岗岩,形成于中上地壳的板内伸展背景。黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为801.1±6.6Ma,同时受到762.1±6.2Ma热事件的影响,与新元古代Rodinia超大陆裂解事件在时间上一致,亦与东川铜矿成矿时代相符,说明新元古代裂谷环境的岩浆事件范围可扩大至滇东北东川,并可能引发热液成矿作用。