Petrology of mafic-ultramafic rocks along North Puruliya Shear zone,West Bengal

The North Puruliya Shear zone (NPSZ) is characterized by occurrence of mafic-ultramafic rocks aligned parallel to the shear zone, intruding the high grade Proterozoic rocks of Chhotanagpur Gneissic Complex. The ultramafic rocks occur as small lenses, pockets, veins, thin dykes and are intimately associated with mafic (gabbro, norite) rocks. Pyroxenites (viz. olivine websterite, websterite, plagioclase websterite) and hornblendite are the two important members of the ultramafic rocks containing clinopyroxene, orthopyroxene, olivine, plagioclase, amphibole, phlogopite and ilmenite. The mafic-ultramafic rocks show evidence of shearing and retrogressive metamorphism. Linear correlation of chemical attributes suggests fractionation-controlled magmatic differentiation. Enrichment of LILE and LREE in the mafic-ultramafic suite suggests an enriched mantle source and pronounced negative Eu-anomalies in all the rock types except hornblendite suggest fractionation of plagioclase under low f_O2 condition. Progressive iron enrichment trend in rocks of the mafic-ultramafic suite also indicate magmatic differentiation under low f_O2 condition. Early fractionation and accumulation of clinopyroxene and plagioclase from a basaltic magma may have given rise to the ultramafic rocks of the area. Little change in the Nb/Zr and Ce/Zr ratios of ultramafic and mafic rocks (except alkali norite) strongly support low crustal contamination. A few samples of norite and gabbro-norites appeared to be variably contaminated by a crustal component or affected by late granitic intrusion resulting in enrichment of alkali in the former.     

Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar,Orissa: Implication for hydrothermal activity in subduction zone setting

The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.     

Petrology,geochemistry and tectonic setting of the Khoy ophiolite,northwest Iran: implications for Tethyan tectonics

The Khoy ophiolite in northwestern Iran represents a remnant of oceanic lithosphere formed in the Mesozoic Neo-Tethys. This northwest–southeast trending ophiolite complex consists from bottom to top (east to west) of a well-defined basal metamorphic zone, peridotites (dunite, harzburgite) and serpentinized peridotite, gabbros, sheeted dikes, pillow and massive lava flows, and pelagic sedimentary rocks, including radiolarian chert. The rocks of the metamorphic zone have an inverse thermal gradient from amphibolite facies to greenschist facies. The high-grade metamorphic rocks are immediately adjacent to the peridotite and the gabbros and the low-grade rocks are in contact with the Precambrian Kahar Formation. Based on mantle-normalized incompatible trace element diagrams there are two distinct types of basalt flows present at the Khoy ophiolite: (1) massive basalts that have patterns virtually identical to E-MORB, and (2) pillow basalts that have more primitive chemical composition whose trace element patterns plot between E-MORB and N-MORB. The chondrite-normalized REE patterns for the pillow basalts are LREE-depleted [(La_N/Sm_N)_ave=0.70], similar to patterns for the mean diabase composition for the Oman ophiolite and LREE-depleted basalts of the Band-e-Zeyarat ophiolite of southern Iran. The REE patterns for the massive basalts are similar in general REE abundances to the pillow basalt patterns, but they are slightly LREE-enriched [(La_N/Sm_N)_ave=1.09] and their patterns cross those of the pillow basalts. The REE patterns for the gabbros and diorites indicates that the crustal-suite rocks were most likely derived by a process of fractional crystallization from a common basaltic melt. This basaltic melt was most likely generated by approx. 20–25% partial melting of a simple lherzolite source and had REE concentrations of roughly 10× chondrite. A comparison between the results from the Khoy ophiolite and the data from other Iranian ophiolites reveals geochemical evidence to suggest a tectonic link between the Khoy ophiolite and the rest of the Iranian ophiolites. Our results suggest that Khoy ophiolite is equivalent to the inner group of Iranian ophiolites (e.g. Nain, Shahr-Babak, Sabzevar, Tchehel Kureh and Band-e-Zeyarat) and was formed as a result of closure of the northwestern branch of a narrow Mesozoic seaway which once surrounded the Central Iranian microcontinent.     

新疆克拉玛依百口泉蛇绿混杂岩中辉长岩岩石学和地球化学研究

克拉玛依蛇绿混杂岩带百口泉剖面由尖晶石蛇纹岩、辉长岩、玄武岩和硅质岩组成。岩相学研究表明,百口泉辉长岩分为堆晶岩(具堆晶结构)和辉长岩(具辉长结构)两类,且均经历了低-中级变质改造。微量元素地球化学显示其岩浆起源于亏损地幔,强烈的Sr异常和Eu异常表明强烈的斜长石堆晶过程。根据其稀土配分模式推测其源区为尖晶石相的地幔橄榄岩。结合野外地质关系和地球化学特征,白碱滩尖晶石二辉橄榄岩能够代表其源区成分,利用微量元素模拟其岩浆演化过程显示:尖晶石二辉橄榄岩发生2.5%部分熔融所形成的熔体,通过10%～20%分离结晶可以形成堆晶辉长岩,经过80%～90%分离结晶则可以形成具辉长结构的辉长岩。因此,蛇绿混杂岩中零星分布的堆晶岩和辉长岩团块是同源岩浆演化的产物。对分离结晶过程中Nb元素地球化学行为的研究表明,岩浆的结晶分异能够导致辉长岩明显亏损Nb。     

西藏桑日县帕南岩体岩石学、地球化学、地质年代学研究及构造背景探讨

帕南岩体位于西藏桑日县马门地区,主要由二长花岗岩、二长岩组成。本文通过锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素等研究,探讨其构造背景和岩石成因。LA-ICP-MS锆石U-Pb定年表明,帕南岩体的成岩年龄为80.91±0.48Ma,形成时代为晚白垩世。帕南岩体地球化学特征表现为富钠、高钾、高铝、低钛,属准铝质高钾钙碱性-钾玄岩岩石系列。稀土分馏较明显且富集轻稀土（（La/Yb）_N=8.88~11.86）,具负Eu异常,相对富集大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素。Sr-Nd同位素显示,样品具较高的Pb、Sr、Sm、Nd含量,偏低的I_Sr值（0.70442~0.70486）,正εNd（t）值（+1.99~+2.73）。综合帕南岩体的地质、地球化学和年代学特征,认为帕南岩体形成于晚白垩世新特提斯洋向北俯冲背景下的岛弧环境,可能是新特提斯洋俯冲角度变缓进入了平板俯冲阶段之后,由陆壳发生部分熔融产生的正常岛弧岩浆形成,同时也预示着109～80Ma的大规模岩浆活动在该区的落幕。     

Petrology and geochemistry of sandstones in the southern Benue Trough of Nigeria： Implications for provenance and tectonic setting

Petrographic and geochemical analyses of three Cretaceous lithostratigraphic sandstone units were undertaken to constrain their provenance and tectonic setting. Petrographic analysis showed that there are differences in composition between the three sandstone bodies, which can be attributed to differences in provenance relief, transport distance and geology of the terrain. Composition of the three lithostratigraphic sandstone bodies fall within the craton interior field.
Framework mode and chemical features indicated their derivation from basaltic volcanics, source rocks during the early rifting stage, and felsic, intermediate and mafic igneous source rocks located at the southeast basement complex terrain, with minor sedimentary components from the uplifted and folded older Cretaceous strata.
The chemical composition of the sandstones is mainly related to source rocks, chemical weathering conditions and transport agents. The source rocks were derived mainly from the southeastern Precambrian basement of Nigeria. Through examination of the sandstones, the tectonic setting was modeled. The Benue Trough belongs to a continental sedimentary basin of the passive margin type.
The tectonic evolution from Albian to Maastrichtain of the trough is contributed to the difference in framework mode and chemical composition of the sandstones. The evolution of the basin was reconstructed in terms of sandstone petrology and geochemistry. The tectonic evolution can be subdivided into three stages from the petrology and geochemistry data. The first stage covers Albian; the second stage the Turonian-Coniacian, and the third stage the Campanian-Maastrichtain. These are the three mega discontinuities in the sandstone composition among these three stages. These three discontinuities signify the influence of tectonism.     

云南永平卓潘碱性杂岩体岩石学和地球化学特征及成因研究

卓潘碱性杂岩体为"三江"地区富碱(高钾)侵入岩的重要组成部分,位于哀牢山-金沙江缝合带的中部,侵位于兰坪盆地南部的白垩系砂岩中,主要由碱性辉长岩、辉石正长岩和霞石正长岩组成。对卓潘碱性杂岩体的岩相学、岩石学、主元素和稀土微量及同位素地球化学特征的系统研究表明,该杂岩体主量元素显示低硅、富钾、高碱(K2O+Na2O为6.92%~13.43%)、低TiO 2(0.31%~1.20%)的特征,属钾质碱性系列岩石;杂岩体的各种岩石均富集Rb、Sr、Ba、Th等大离子亲石元素、亏损Nb、Ta、Ti等高场强元素,并具有轻稀土富集的右倾型稀土元素分布模式、具较高的87Sr/86Sr、206Pb/204Pb、207Pb/204Pb、208Pb/204Pb及较低的143Nd/144Nd等特征,表明源区具有较明显的EMⅡ型富集地幔特征,源区明显受到壳源物质的混染。卓潘岩体形成于印度-欧亚大陆后碰撞的剪切和拉张的构造环境,古扬子板片向西俯冲,诱发了经过陆壳交代混染了的岩石圈地幔的部分熔融。由于兰坪走滑拉分盆地东缘断裂拉伸强度大,岩浆起源的深度大,以及岩浆源区成分(特别是CO2含量)与其它部位不同,因此在卓潘地区形成一套与金沙江-哀牢山-红河断裂带其它新生代富碱斑岩完全不同的过碱性的岩石。     

南天山川乌鲁碱性杂岩体的岩石学和地球化学特征及其岩石成因

位于中国南天山西侧阔克萨彦岭一带的川乌鲁碱性杂岩体,与该区川乌鲁铜金多金属矿床有着直接的成因联系,该杂岩体由早期的辉长岩—闪长岩岩、主期的二长岩—正长岩和晚期的正长花岗斑岩脉组成,各期岩石在矿物组成和化学成分上有明显的变化。从早到晚,SiO2含量增加,变化范围是50.52%～70.64%;全碱含量先增后减,在SiO2含量小于61.69%时,随SiO2含量增加而增加,而当SiO2含量大于61.69%时,与SiO2含量负相关。在AR-SiO2图解上,大多样品落入碱性区间,在A/CNK-A/NK图解上表现出由准铝质向过碱性演化的趋势。微量元素表现为大离子亲石元素相对高场强元素富集,Rb、Ba、Th、Sr等元素的相对富集和Nb、Ta、P、Ti等元素的负异常。稀土元素表现为轻稀土相对富集的特征,其(La/Yb)N为14.13～25.09,具有Eu的正异常或极微弱的Eu负异常。一些元素比值的线性关系暗示了该杂岩体为岩浆混合成因,基性岩浆的源区为富水的岩石圈地幔,而酸性岩浆是中下地壳中性火成岩在含饱和水条件下部分熔融的产物。这些性质指示川乌鲁杂岩体是在后碰撞拉张环境中由岩石圈地幔熔融的基性岩浆的底侵作用导致地壳的熔融以及后期的岩浆混合作用有关。     

胶东西涝口金矿深部110Ma角闪辉长岩脉及其对成矿时代的约束

西涝口金矿是胶莱盆地北东缘新近取得找矿突破的蚀变岩型金矿,金矿体主要赋存于古元古界荆山群与牧牛山二长花岗岩之间的构造破碎带中。前期在其深部新发现的角闪辉长岩脉中,通过人工重砂分选,获得了自然金。为探索其与金成矿的关系,文章对其进行了主量、微量元素、锆石U-Pb年代学以及Hf同位素研究。主量、微量元素分析结果表明,角闪辉长岩属钾玄岩岩石系列,全碱、Ba、Sr、轻稀土元素含量高,Rb、P和重稀土元素含量相对较低,无铕异常或有轻微的正铕异常,明显亏损Nb、Zr、Hf等高场强元素,具有富集大离子亲石元素与轻稀土元素、亏损高场强元素与重稀土元素的地球化学特征,类似于富闪深成岩。锆石Hf同位素结果显示,其岩浆锆石的ε_Hf（t）为-14.0~-11.8,暗示其来源于富集地幔源区或存在源区混染的可能性。锆石LA-ICP-MS U-Pb定年结果显示,角闪辉长岩年龄为（108.4±2.2）Ma,属早白垩世晚期,明显晚于郭家岭、伟德山序列岩体。综上,笔者认为西涝口金矿角闪辉长岩形成于俯冲板片脱水而导致上覆地幔楔部分熔融,其成因可能与古太平洋板块向华北板块俯冲所形成的火山弧有关,其与该区金成矿过程密切相关,极有可能在成矿过程中直接提供了金的来源。西涝口金矿的形成时代应当在110 Ma左右,胶东东部应该存在110 Ma的金成矿事件。     

新疆西南天山霍什布拉克碱长花岗岩体岩石学及地球化学特征——岩石成因及其构造与成矿意义

位于中国西南天山南缘的霍什布拉克岩体,由碱长花岗岩和碱长花岗斑岩组成。岩石化学成分比较均一,具有富SiO2、Al2O3,贫Fe2O3T、MgO、TiO2、P2O5等特点。AR-SiO2图解中,样品均落入碱性区间,在A/CNK-A/NK图解中,样品主要为准铝质。微量元素总体表现为高场强元素(HFSE)相对于大离子亲石元素的富集以及高场强元素P、Ti和大离子亲石元素Sr、Ba的明显亏损。稀土元素中轻稀土元素相对于重稀土元素富集,Eu的负异常十分明显。岩体含副矿物萤石,并具有高FeOT/MgO、低CaO等特征,10000Ga/Al的比值和Zr+Ni+Sr+Y的含量亦较高,岩石学和地球化学特征表明它为典型的A1型花岗岩,是铁镁质下地壳在低压条件下部分熔融的产物。岩体具有极低的Ti含量是由于源区部分熔融过程中大量磁铁矿的残留所致,而较高的Nb-Ta含量则与岩浆中富含F有关。岩体产出于板内环境,在构造岩体的形成上受到塔里木板块内部裂谷体系的影响。岩体对霍什布拉克铅锌矿成矿意义不大,但具有Sn元素的成矿潜力。     

西天山小哈拉军山富钛磁铁矿辉长岩的岩石成因及其构造环境

天山造山带晚古生代构造争议部分源于对晚古生代岩浆岩的岩石成因及其构造环境认识不足。本文对西天山小哈拉军山辉长岩进行了系统的矿物学、岩石学、地球化学和年代学研究,以探讨其岩石成因、地幔源区特征及其形成的构造背景。锆石U-Pb定年分析结果显示小哈拉军山辉长岩形成于早二叠世早期（295±3Ma）。该辉长岩富含钛磁铁矿（含量高达8vol%以上）,并且主要造岩矿物如斜长石、单斜辉石、角闪石均显示出富Fe-Ti的特征,表明其形成于富Fe-Ti的岩浆体系。岩相学特征显示,小哈拉军山辉长岩的斜长石结晶早于单斜辉石和角闪石,由角闪石成分估算的岩浆水含量相对较低,暗示了相对干的初始岩浆体系,并且单斜辉石的Al-Ti含量关系显示出板内岩浆的特征,均表明该辉长岩并非岛弧岩浆产物,应形成于拉张构造环境,因此西天山地区在早二叠世早期已处于碰撞后伸展阶段。另外,该辉长岩的全岩富集大离子亲石元素和轻稀土元素,相对亏损重稀土和高场强元素,全岩ε_Nd（t）略亏损（2.34~3.30）,Sr同位素比值变化较大（⁸⁷Sr/⁸⁶Sr=0.7045~0.7067）,表明岩浆来源于富集的地幔源区,可能与造山带形成之前的俯冲板片组分的交代富集相关。由于西天山地区在早二叠世已处于造山后的伸展阶段,是塔里木大火成岩省范围内地幔柱活动最易于表现的地区,而小哈拉军山辉长岩与相邻的哈拉达拉富V-Ti磁铁矿层状辉长岩具有相似的岩浆源区和矿化特征,并具有密切的时空关系,很可能都为塔里木早二叠世地幔柱活动的产物。

     

Geochronology and geochemistry of the Huilvshan gabbro in west Junggar (NW China): Implications for magma process and tectonic regime

Mineralogy and Petrology - Gabbro plutons, consisting of clinopyroxene and plagioclase with trace amounts of magnetite, titanite, and apatite, intruded into Early Carboniferous volcanic-sedimentary...     

赣东北蛇绿岩形成时代及构造环境——樟树墩辉长岩锆石U_Pb年龄、Hf同位素和地球化学约束

赣东北蛇绿岩是华南最重要的前寒武纪蛇绿岩之一,本文对其中的樟树墩辉长岩进行了年代学、岩石地球化学及锆石Hf同位素研究。LA_ICP_MS锆石U_Pb测年结果显示樟树墩辉长岩结晶年龄为1 061±44 Ma,代表了洋盆扩张的年龄,也即赣东北蛇绿岩的形成年龄。单颗粒锆石原位Hf同位素分析得到樟树墩辉长岩εHf(t)=6.22~9.94,平均值为8.10,略低于结晶时亏损地幔值;单阶段亏损地幔Hf模式年龄tDM1为1.21~1.41 Ga,平均为1.28Ga,明显大于成岩年龄1 061 Ma。地球化学及锆石Hf同位素结果显示赣东北蛇绿岩地幔具有E-MORB的特点,表明这些辉长岩起源于未发生大规模熔融的初始地幔,推测赣东北蛇绿岩可能形成于古洋盆初始裂解阶段的洋脊环境,赣东北蛇绿岩为MOR型蛇绿岩。     

西藏八宿花岗岩岩石学、地球化学特征及其构造意义

西藏八宿地区大地构造位置为冈底斯-念青唐古拉板块北东缘,紧邻班公湖-怒江结合带。区内出露有花岗岩体,包括花岗闪长岩和黑云母二长花岗岩,侵位于朱村组火山岩中。区域主要完成了1:25万区域地质调查,研究程度相对较低,有关花岗岩的报道较少。本次工作在详细野外调研的基础上,研究了花岗岩类的岩石学,地球化学和年代学特征来确定岩体的构造意义。在该地区获得花岗闪长岩和石英闪长岩LA-ICP-MS锆石U-Pb年龄分别为119.7±1.2Ma和120.6±1.8Ma。岩体锆石ε_Hf(t)值为-10.42~-7.00,对应的地壳模式年龄为1624~1841Ma。地球化学特征反映壳源部分熔融成因,有地幔物质及热流参与,形成于板块俯冲构造环境。岩体北东侧的朱村组火山岩所获得的角闪英安岩锆石SHRIMP U-Pb年龄为128±2Ma,较岩体早9Myr,属于同一岩浆事件产物,因此,八宿花岗岩与火山岩一样,属于伯舒拉岭火山岩浆弧的一部分,形成于怒江洋壳向冈底斯-念青唐古拉板块俯冲、消减的火山弧环境。八宿岩体很可能是在班公湖-怒江洋岩石圈向南俯冲的地球动力学背景下形成的。     

Compositions and petrogenetic significance of the eudialyte group minerals from Sushina,Purulia, West Bengal

The eudialyte-group of minerals (EGM) is one of the most important index minerals of the peralkaline (agpaitic) nepheline syenites. They crystallize in varied physico-chemical conditions ranging from the early-magmatic (orthomagmatic) to late-magmatic and even in the post-magmatic (hydrothermal) stage. In India, the only agpaitic nepheline syenite gneisses of the Sushina Hill region contain both late-magmatic as well as hydrothermal eudialytes. Compositionally these are Mn-Nb-Ca rich eudialytes and are comparable to the other EGM occurrences such as Ilímaussaq (Greenland), Tamazeght (Morocco), Mont-Saint Hilaire (Canada) and Pilansberg (South Africa). High Mn content (>6.5 wt.%) for both varieties of the Sushina EGM indicates that they are highly evolved in nature. In terms of the calculated site occupancy, particularly the [M(3)] and [M(2)], the Sushina eudialytes mimic some Pilansberg eudialytes. In addition to the eudialyte, the host nepheline syenite gneiss also contains an unknown Na-Zr-silicate (NZS) which is often found to be replacing both types of eudialytes. Compositionally these NZS can be tentatively represented as Na₂Zr₂S₆O₁₇. These NZS are characterized by much higher Zr, but lower Mn and Nb concentrations compared to the associated eudialytes. Two distinct varieties of eudialyte and NZS indicate subtle changes in the alkalinity during their formations. The formation of the late-magmatic as well as hydrothermal eudialyte essentially took place at somewhat elevated pH conditions. The replacement or alteration of eudialytes by NZS indicates a decreasing pH condition. In terms of the chemical composition the late-magmatic eudialytes can be represented as a solid-solution series between the kentbrooksite-taseqite-aqualite while the hydrothermal eudialyte represents solid-solution between kentbrooksitetaseqite -Ce-zirsilite.     

南祁连北缘东段晚奥陶世构造演化:多藏角闪辉长岩U-Pb年代学、岩石地球化学和矿物化学证据

为约束多藏角闪辉长岩的岩石成因和南祁连北缘东段晚奥陶世的构造演化,对多藏角闪辉长岩进行了LA-ICP-MS锆石U-Pb年代学、岩石地球化学和矿物化学分析。结果表明,角闪辉长岩中锆石具条痕状吸收和高的Th/U比值(0.37~1.16),暗示其岩浆成因。岩浆锆石的206Pb/238 U定年结果为(444±3)Ma,表明多藏角闪辉长岩形成于晚奥陶世,两组捕获锆石的年龄为520 Ma和484 Ma,代表早期的岩浆事件。多藏岩体具相对低的SiO_2含量(51.68%~55.66%)和高的MgO(4.48%~7.37%)、TiO_2(1.01%~1.24%)、FeO~T(7.99%~8.72%)含量以及高的Mg#值(53~63);LREEs相对富集、HREEs相对亏损,(La/Yb)N=4.03~7.89,具有弱的Eu异常(δEu=0.78~1.16),富集LILEs(Rb、Ba、K)、亏损HFSEs(Nb、Ta),具Sr、P、Ti元素的亏损。结合矿物化学分析表明,南祁连北缘东段多藏角闪辉长岩起源于受俯冲流体交代的富集岩石圈地幔物质的部分熔融,形成于洋-洋汇聚向洋-陆碰撞转换背景下俯冲大洋板片断离后的伸展构造环境。     

Epithermal deposits in South China: Geology,geochemistry, geochronology and tectonic setting

South China Block (SCB) is the broad area including the Yangtze Craton in the northwest and Huanan Orogen in the southeast. It is an important epithermal metallogenic province in China, containing at least 1 high-sulfidation (HS) and 42 low-sulfidation (LS) Au-Ag ± Cu ± Pb-Zn ± Sb epithermal deposits. Porphyry-type mineralization was recognized in four of the LS deposits, and thus they were regarded as LS–P type. These 43 deposits are mainly located in: (1) the Lower Yangtze River Belt and (2) the Northeastern Jiangnan Orogenic Belt in the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt and (4) the Southeast Coastal Volcanic Belt in the Huanan Orogen. They are mostly located in Mesozoic volcanic basins, especially where the regional faults and their subsidiaries occurred. The host rocks include Jurassic–Cretaceous volcanic-sedimentary rocks, coeval or slightly older subvolcanic, granitoids and breccias, and metamorphic basement rocks. The alteration of the HS epithermal deposit (Zijinshan Cu-Au) zoned from silicic (vuggy quartz), through alunite, to dickite and phyllic alteration zones, from the ore veins outwards. The alteration of the LS deposits is zoned from adularia-chalcedony-bladed calcite (or quartz pseudomorphs after bladed calcite) in ore veins to distal illite-sericite-chlorite-kaolinite assemblages. For those LS–P systems, besides the dominated LS alteration assemblages, phyllic and potassium silicate alteration related to porphyry mineralization were identified. Acid leaching textures and vein, stockwork and breccia structures are common in HS deposit, while the LS epithermal deposits are characterized by open-space filling, crustifications, colloform banding and comb structures. The ore-forming fluids are low-temperature, low-salinity meteoric water-dominated in most epithermal deposits in SCB, with variable input of magmatic water. The ore components were derived from both the deep magma and host rocks, and transported upwards or laterally and precipitated in the fracture systems by fluid boiling, mixing and cooling. Most of the epithermal deposits are formed at depth of < 1.5 km and < 300 °C, with few exceptions containing porphyry-type mineralization, such as the Zhilingtou, Yinshan and Longtoushan deposits. Deep drilling is suggested in these deposits as more epithermal and/or porphyry mineralization could be expected. The mineral systems were formed in Early Yanshanian (180–130 Ma) and Late Yanshanian (120–90 Ma) periods. The Early Yanshanian epithermal ore systems are mainly located in a series of E–W-trending metallogenic belts to the west of the Lishui–Haifeng Fault, which were formed in a syn- or post-collision tectonic setting by the collision between the SCB and its surrounding plates. The Late Yanshanian epithermal deposits are mainly located in Southeast Coastal Volcanic Belt, genetically related to the westward subduction of the paleo-Pacific plate.     

2.5 Ga gabbro-anorthosites in the Belomorian Province,Fennoscandian Shield: Petrology and tectonic setting

The Vorochistoozersky, Nizhnepopovsky, and Severo-Pezhostrovsky gabbro-anorthosite massifs have been studied in the central part of the Belomorian Province, Fennoscandian Shield. The similarity of geological setting and rock composition of these massifs suggests their affiliation to a single complex. The age of the gabbro-anorthosites was determined by U-Pb (SHRIMP II) zircon dating of gabbro-pegmatites from the Vorochistoozersky massif at 2505 ± 8 Ma. The studied massifs were overprinted by the high-pressure amphibolite facies metamorphism. Relicts of magmatic layering and primary magmatic assemblages preserved in the largest bodies. The massifs consist mainly of leucocratic gabbros but also contain rocks of the layered series varying in composition from olivinite to anorthosite. The presence of troctolites in the layered series indicates the stability of the olivine–plagioclase liquidus assemblage and, respectively, shallow depths of melt crystallization. Despite the composition differences between gabbro-anorthosites of the Belomorian and peridotite–gabbronorite intrusions Kola provinces, these simultaneously formed massifs presumably mark a single great igneous event. It also includes the gabbronorite dikes in the Vodlozero terrane of the Karelian province, the Mistassini swarm in the Superior province, and the Kaminak swarm in the Hearne Craton, Canadian Shield. The large igneous province of age ~2500 Ma reflects the oldest stage of within-plate magmatism after a consolidation of the Neoarchean crust of the Kenorland Supercontinent (Superia supercraton).     

东昆仑阿克楚克塞地区辉长岩地球化学特征、锆石U-Pb年龄及其构造意义

东昆仑地区基性-超基性岩石的研究较薄弱,缺乏对东昆仑幔源岩浆活动及岩浆演化的整体认识。对阿克楚克塞辉长岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究,结果显示,该岩石形成于晚三叠世早期(219.3±1.1Ma,MSWD=0.80);岩石SiO2含量为49.03%~57.26%,Mg#值为49~57,属于钙碱性系列岩石;稀土元素配分曲线为轻稀土元素富集的右倾型,富集大离子亲石元素Rb、Ba、K,相对亏损高场强元素Nb、Ta、Ti;εHf(t)=-1.81~3.25,锆石Hf模式年龄大于锆石结晶年龄。地球化学特征显示,阿克楚克塞辉长岩岩浆源区应为受俯冲板片流体交代的岩石圈地幔。结合区域构造背景分析,阿克楚克塞辉长岩形成于印支期造山后伸展的构造环境,继承了早期板片俯冲改造的地幔源区特征。     

新疆西准噶尔罕哲尕能Cu-Au矿床的锆石U-Pb年代学和岩石地球化学特征:对源区和成矿构造背景的指示

位于准噶尔西北缘萨吾尔地区的罕哲尕能Cu-Au矿床是新近发现的斑岩型矿床,具有很好的找矿前景。矿区岩浆活动早期以闪长岩为主,晚期以花岗闪长岩和二长花岗斑岩为主。钻孔中所见似斑状石英二长岩LA-ICP-MS锆石U-Pb年龄为343.6±5.7Ma~345.3±8.3Ma;二长花岗斑岩锆石U-Pb年龄为334.9±7.3Ma~336.4±7.5Ma,表明西准萨吾尔地区早石炭世存在一期重要的岩浆-热液Cu-Au成矿事件。花岗闪长岩、石英二长岩、闪长玢岩、闪长岩和二长花岗斑岩的主量元素具有一致的演化趋势,表明它们可能是同一岩浆演化的产物。富集大离子亲石元素(LILE:如Rb、Ba、K、Sr)和活泼的不相容元素(如:U、Th),相对亏损高场强元素(HFSE:如Nb、Ta、Ti),显示具有岛弧岩浆的地球化学特征。87Sr/86Sri比值在0.7033~0.7037之间,143Nd/144Nd比值在0.512538~0.512579之间,εNd(t)在+6.7~+7.5之间,显示源区具有类似亏损地幔的特征;而且具有年轻的Nd两阶段模式年龄为488~553Ma,这些特征表明罕哲尕能矿区岩石的岩浆源区可能来源于亏损地幔分异的新生玄武质下地壳。罕哲尕能Cu-Au矿床的形成时代明显早于该区域A型花岗岩的形成时代(290~300Ma左右),结合岩石微量元素特征反映其形成于岛弧构造背景,萨吾尔山具有寻找斑岩Cu-Au矿的成矿条件。