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。     

In situ zircon U–Pb and Hf–O isotopic results for ca. 73 Ma granite in Hainan Island: Implications for the termination of an Andean-type active continental margin in southeast China

We report in the paper integrated analyses of in situ zircon U–Pb ages, Hf–O isotopes, whole-rock geochemistry and Sr–Nd isotopes for the Longlou granite in northern Hainan Island, southeast China. SIMS zircon U–Pb dating results yield a crystallization age of ∼73 Ma for the Longlou granite, which is the youngest granite recognized in southeast China. The granite rocks are characterized by high SiO₂ and K₂O, weakly peraluminous (A/CNK = 1.04–1.10), depletion in Sr, Ba and high field strength elements (HFSE) and enrichment in LREE and large ion lithophile elements (LILE). Chemical variations of the granite are dominated by fractional crystallization of feldspar, biotite, Ti–Fe oxides and apatite. Their whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios (0.7073–0.7107) and ε_Nd(t) (−4.6 to −6.6) and zircon ε_Hf(t) (−5.0 to 0.8) values are broadly consistent with those of the Late Mesozoic granites in southeast China coast. Zircon δ¹⁸O values of 6.9–8.3‰ suggest insignificant involvement of supracrustal materials in the granites. These granites are likely generated by partial melting of medium- to high-K basaltic rocks in an active continental margin related to subduction of the Pacific plate. The ca. 73 Ma Longlou granite is broadly coeval with the Campanian (ca. 80–70 Ma) granitoid rocks in southwest Japan and South Korea, indicating that they might be formed along a common Andean-type active continental margin of east–southeast Asia. Tectonic transition from the Andean-type to the West Pacific-type continental margin of southeast China likely took place at ca.70 Ma, rather than ca. 90–85 Ma as previously thought.     

滇西芒市地区石板村黑云母二长花岗岩的年代学、地球化学特征及地质意义

滇西芒市地区石板村黑云母二长花岗岩分布于芒市粱河县南部勐养村—芒市石板村一带,主要由黑云母二长花岗岩组成。石板村黑云母二长花岗岩大部分是作者通过1∶5万区域地质填图,从原高黎贡山群中解体出来的。为了限定该地区中生代岩浆事件的准确时间,本文对该黑云母二长花岗岩进行了LA-ICP-MS锆石U-Pb定年。测定结果显示,石板村黑云母二长花岗岩的锆石U-Pb年龄加权平均值为125.60±1.0Ma。表明该花岗岩体的形成时代属于早白垩世。岩石地球化学研究表明,该区早白垩世黑云母二长花岗岩具有高Si02(70.70%~76.14%),高碱(K20+Na20=7.35%~9.00%),中—高钾(K20/Na20=1.12~2.37)的特征。铝饱和指数(A/CNK)为0.67~1.17,岩石属钾玄岩—高钾钙碱性过铝—强过铝S型花岗岩。岩石总体上富集大离子亲石元素Rb、Th、U、Nd、Sm和Pb等,明显亏损高场强元素Nb、Ce、Sr、Eu、Zr、Hf等。稀土元素总量(ΣREE)为80.55×10-6~362.85×10-6,平均为171.97×10-6,稀土元素配分曲线呈右倾型,LaN/YbN介于5.11~18.80之间,δEu=0.28~1.08,显示弱到中等程度的负铕异常,具有较明显的轻稀土富集,重稀土亏损的特征。根据地球化学特征和微量元素构造判别图解判别结果表明,该花岗岩是以含粘土的变质杂砂岩部分熔融形成的,岩浆可能来源于本区中—新元古代高黎贡山群为代表的地壳物质的部分熔融。是一种典型的壳源成因类型,具后碰撞花岗岩特征,形成于板块间从挤压体制向拉张体制转变的后碰撞构造环境。冈底斯—滕冲构造带早白垩世构造岩浆事件与羌塘—保山板块与冈底斯—腾冲板块之间俯冲、碰撞、成弧造山作用密切相关。早白垩世花岗岩体的发现及其形成时代的厘定,为进一步探讨腾冲地块构造演化提供了新证据。     

东准噶尔卡拉麦里断裂以南幔源底侵体、“钉合花岗岩体”的发现及其地质意义

新疆富蕴县滴水泉-畜牧办侵入体出露于卡拉麦里断裂以南,呈北西西向带状分布,以碱长花岗岩体为主,也可见规模较小的角闪辉长岩体。碱长花岗岩体的岩石组合为碱长花岗斑岩+碱长花岗岩,高硅(SiO_2=71.07%~76.71%),富碱(Na_2O+K_2O=7.41%~9.07%)、K_2ONa_2O(平均为1.10),显示出A型花岗岩的特点。角闪辉长岩体涌动侵入于碱长花岗岩体之中,二者接触带附近发育浆混性质的石英闪长岩。辉长岩+花岗岩的双峰式岩石组合、构造判别图解R2-R1及区域地质背景指示滴水泉侵入体形成于陆内伸展环境,且花岗岩体具有"钉合岩体"的作用,穿插了卡拉麦里蛇绿岩带。结合岩体的LA-ICP-MS锆石年龄(碱长花岗岩的206Pb/238U加权平均年龄为321±2Ma,角闪辉长岩的206Pb/238U加权平均年龄为319±3Ma)可知,卡拉麦里洋盆在晚石炭世早期(321Ma)之前已经闭合。同位素及微量元素特征显示,碱长花岗岩为年轻地壳部分熔合融的产物,而角闪辉长岩则来源于亏损的软流圈地幔及俯冲交代的地幔楔物质,代表了同期花岗岩的底侵岩浆演化的产物。辉长岩与花岗岩相似的εNd(t)值及明显的岩浆混合作用表明该区的花岗岩体并非来源于底侵岩浆的高度分异或底侵体的部分熔融,而最可能为底侵体之上的年轻地壳的部分熔融,这一结论与最近一些学者研究的断裂以北的花岗岩体成因机制相同。晚石炭世早期幔源底侵体的发现,为卡拉麦里地区后碰撞花岗岩类的幔源底侵作用提供了可靠的地质依据。     

Geochemical characteristics of the niobium-rich arfvedsonite granites, Younger Granites province of Nigeria

Arfvedsonite granites are most prevalent in the northern sector of the Nigerian anorogenic ring-complex province wherein they form the main granitic rocks at Kudaru and Fagam and are important components of Kila-Warji, Ririwai and Dutsen-Wai ring-complexes. The albitized variety of these rocks hosts pyrochlore to varying extents depending on the degree of albitization and are, therefore, important targets for niobium investigation. Geochemical data of the granites reveal that niobium has a mean concentration of 111 ppm in the arfvedsonite granite, increasing to 168 ppm in the aegirine arfvedsonite granite and reaching 1568 ppm in the albite arfvedsonite granite. Niobium is thus enriched in the albite arfvedsonite granite by a factor of 8-11 relative to its mean value in the aegirine arfvedsonite and arfvedsonite granites, respectively. Uranium contents show a sympathetic trend with niobium, being also enriched in the albite arfvedsonite granite relative to its abundance in both the aegirine arfvedsonite granite and arfvedsonite granite by a factor of 15. The uranium abundance in the albite arfvedsonite granite is more than 48 times higher than the mean background values in low-calcium granite.The REE fractionation patterns in all three arfvedsonite granite varieties are characterized by enrichment of both the light (La-Sm) and heavy (Gd-Lu) rare earth elements and a significant negative Eu anomaly. The albite arfvedsonite granite is, however, preferentially more enriched in the heavy REE relative to the aegirine arfvedsonite and the arfvedsonite granites. A plot of the ∑REE against Na₂O and niobium reveals positive correlation in the arfvedsonite granites. There is also a linear relationship and strongly positive correlation between Nb and Na₂O because the pyrochlore is most abundant in the most extensively albitized variety of the arfvedsonite granites.     

粤西庞西垌-桂东南金山银金成矿带晚燕山期花岗岩的性质与成矿作用

分析了云开地区粤西庞西垌－桂东南金山银金成矿带晚燕山花岗岩的特征与成矿作用的关系。认为晚燕山期英桥花岗岩体属于铝过饱和富钾质的钙碱性花岗岩系列,是同熔型花岗岩。晚燕山期岩浆活动与银金矿床在空间和时间上密切相关,在微量元素、稀土元素、稳定同位素和包体成分等地球化学特征上具有相似性,晚燕山期岩浆活动对银金矿床的形成起着重要的作用。     

古特提斯洋俯冲碰撞在南羌塘的岩浆岩证据:西藏荣玛乡冈塘错花岗岩

西藏荣玛乡冈塘错花岗岩岩体分布于南羌塘地块中,由中粗粒巨斑状黑云母二长花岗岩和中细粒含电气石二云母二长花岗岩组成。中粗粒花岗岩的锆石测年结果为214.4±4.0Ma,中细粒花岗岩锆石测年结果为222.2±6.6Ma,均为晚三叠世。中粗粒花岗岩A/CNK为1.00~1.09,刚玉标准分子的百分含量均大于1%(1.84~3.04%),Al2O3的含量均大于14%,属于含白云母过铝质花岗岩。中细粒花岗岩的A/CNK1.1,刚玉标准分子的百分含量均大于1%(2.40~3.42%),Al2O3的含量均大于14%,属于强过铝质S型花岗岩。虽主量元素特征相近,但两类花岗岩的微量元素特征差异较大。根据锆石饱和温度计得出中粗粒花岗岩为高温类型的花岗岩,中细粒花岗岩为低温类型的花岗岩。结合区域地质背景推断中细粒花岗岩形成可能与三叠纪俯冲碰撞作用有关,而中粗粒花岗岩为碰撞后拆沉岩浆底侵的结果。冈塘错岩体中两种成因类型不同的花岗岩的形成时代对古特提斯洋的演化以及缝合带增生杂岩的形成具有时代约束意义。     

Pan-African Magmatism, and Sedimentation in the NW Himalaya

Correlation of early Palaeozoic, Pan-African (500 ± 50 Ma) granites that intruded the Chail, Salkhala, Haimanta Formations in the Lesser Himalaya, Zanskar crystallines, and Lower Taglang La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic setting, mineralogical, and geochemical characteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical, and geochemical character. The mineralogical composition of the granites is quite similar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, muscovite, garnet, tourmaline, ± cordierite, andalusite, and sillimanite fibrolite. The granite which are massive, and inequigranular in the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having high A/CNK value (> 1). Presence of normative corundum, rounded shape of zircon, and high initial Sr ratio suggest crustal source of the granites. Mantle normalized spider-diagram exhibits similar characters for all these granitoids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic. The sudden break in sedimentation towards the terminal phases of the Lower Cambrian has been observed in almost all parts in Lesser as well as the Tethys Himalaya. Occurrences of large number of plutons along different tectonic belts of northwestern Himalaya are indicative of widespread tectono-thermal event during early Palaeozoic (500 ± 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian, and the intrusion of granites around 500 ± 50 Ma, is considered to be the result of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.     

Petrogenesis of the Palaeoproterozoic Xishankou pluton,northern Tarim block,northwest China: implications for assembly of the supercontinent Columbia

The Tarim block, one of the largest cratons in China, records an important part of the Proterozoic crustal evolution of the Earth. Many previous studies have focused on the Neoproterozoic magmatism and tectonic evolution of this block in relation to the break-up of Rodinia, although relatively little is known about its earlier tectono-magmatic history. In this article, we present detailed petrographic, geochronologic, whole-rock geochemical, and in situ zircon Hf isotope data for the pre-Neoproterozoic Xishankou granitoid pluton (XBP), one of several blue quartz-bearing granitoid intrusions well exposed in the Quruqtagh area, and discuss these intrusions in terms of their tectonic environment. Zircon LA-ICP-MS dating indicates that gneissic quartz diorite and granodiorite of the XBP crystallized at 1934 ± 13 and 1944 ± 19 Ma, respectively. Both underwent metamorphism essentially coeval with emplacement, a time that is compatible with the globally distributed 2.1–1.8 Ga crustal amalgamation during formation of the supercontinent Columbia. Petrographic and geochemical evidence suggest that the XBP is a continental-arc-type granite and may have been generated by the partial melting of Archaean thickened lower crust; this would suggest that the northern Tarim block was a continental-type arc at ca. 1940 Ma. Our new data, together with previous regional geological studies, indicate that a series of Palaeoproterozoic (ca. 2.0–1.8 Ga) tectono-magmatic events occurred in the northern Tarim attending the assembly of Columbia.     

骑田岭花岗岩体的地球化学特征及其对成矿的制约

骑田岭花岗岩体位于湖南省南部 ,在其东北部接触带有骑田岭大型夕卡岩型锡矿 ,南部接触带有新探明的芙蓉超大型锡多金属矿床。本文采用ICP_AES和ICP_MS分析了骑田岭花岗岩全岩的主量、微量和稀土元素含量。其主量元素特征表明 ,骑田岭花岗岩具有富硅富碱富铝、贫镁铁的特点 ,经历了较大程度的结晶分异。稀土元素总量较高 ,轻稀土元素富集 ,重稀土元素亏损。岩石富集大离子亲石元素 ,特别是富集Rb、Th ,推测源岩可能来源于陆壳物质。与相邻的千里山花岗岩比较 ,虽然没有显著的四分组效应 ,但它们的地球化学性质具有很大的相似性。另对岩体的成因、形成时代和成矿作用进行了讨论 ,认为骑田岭花岗岩超大型锡多金属矿床的形成是侏罗纪岩石圈在伸展环境下引起地幔物质上涌使地壳物质发生重熔 ,同时在热液作用参与下金属元素重新富集的结果