柴达木盆地北缘小赛什腾山二叠纪花岗岩的发现及其构造意义

赛什腾山位于柴达木地块北缘构造带(柴北缘构造带)与阿尔金走滑断裂带斜交部位,属于柴北缘残山带的一部分,带内零星出露的花岗岩体一直被认为形成于早古生代,属于早古生代洋陆碰撞期的花岗岩。我们对小赛什腾山两个花岗岩体重新进行了LA-ICP-MS锆石U-Pb年代学、Lu-Hf同位素和微量元素分析,结果表明,两个岩体三个花岗岩样品的锆石U-Pb年龄分别为260±3Ma, 268±8Ma和263±8Ma,表明其形成于中二叠世,而非原先认为的早古生代。所有锆石的~(176)Hf/~(177)Hf比值分布在0.28294～0.28320之间,并具有极高的正ε_(Hf)(t)值(11～20),其平均二阶段Hf模式年龄为350Ma,稍高于其U-Pb年龄,反应其源区可能为具有亏损地幔特征的新生镁铁质物质。结合区域地质特征和已有研究成果的分析认为,宗务隆小洋盆向西可能延伸至小赛什腾山地区,中二叠世俯冲的洋壳发生部分熔融形成了具有极高的正ε_(Hf)值的花岗岩。该发现表明柴北缘地区存在二叠纪时期的洋壳俯冲,为深入理解柴北缘晚古生代-中生代的构造演化提供了新的佐证。     

Multistage progressive evolution of rare osumilite‐bearing assemblages preserved in ultrahigh‐temperature granulites from In Ouzzal (Hoggar,Algeria)

Osumilite is reported in Palaeoproterozoic Al–Mg‐rich granulites from the Khanfous area (Tekhamalt, In Ouzzal, Hoggar, Algeria). The main peak assemblages are osumilite + sapphirine + biotite + orthopyroxene + sillimanite and osumilite + orthopyroxene + sillimanite + quartz ± biotite (±K‐feldspar) in silica‐deficient and silica‐saturated granulites respectively. Osumilite coexists with F‐rich biotite (X_F ≈ 0.6). The observed microstructures, the mass balance of metamorphic reactions and P–T pseudosections modelled for bulk‐rock and reaction‐microdomain compositions indicate a clockwise P–T metamorphic evolution at ultrahigh temperatures, without substantial post‐peak deformation. The peak P–T conditions recorded by the osumilite‐bearing assemblages are 8.5–9.0 kbar and 930–980 °C. During retrogression, osumilite was partially or totally replaced by fine‐grained pseudomorphs of cordierite + orthopyroxene + K‐feldspar + quartz at ~7 kbar and ~850 °C. This study confirms that osumilite can occur only in Mg‐rich metamorphic rocks that experienced ultrahigh‐temperature metamorphism under anhydrous conditions. In the presence of a hydrous fluid, it is replaced, even at high temperatures, by cordierite‐bearing assemblages. This important feature explains the rarity of osumilite in granulite facies rocks and its common replacement by cordierite + orthopyroxene + K‐feldspar + quartz pseudomorphs. The peak conditions suggest that a delamination of the lithospheric mantle underneath the In Ouzzal crust brought the asthenosphere close to the Mohorovi?i? discontinuity.     

青海纳日贡玛斑岩钼(铜)矿含矿斑岩矿物学特征及成岩成矿意义

本文侧重于矿物学特征分析对纳日贡玛赋矿斑岩进行了研究,结果表明:斑岩中黑云母斑晶种属为含铁金云母和富镁黑云母,角闪石种属为镁角闪石、透闪石与阳起石。纳日贡玛含矿斑岩属于I型花岗岩类,由幔源岩浆同熔壳源物质而形成;斑岩结晶压力值为1.18×108～1.39×108Pa;闪长玢岩和黑云母花岗斑岩的结晶温度为550℃～650℃,而浅色花岗斑岩则下降为500℃～550℃。斑岩中黑云母的Mg/Fe、Ti、Al、K、Na、Ca及F、Cl等元素含量及比值可以显示纳日贡玛具有良好的含矿性。纳日贡玛结晶压力、温度都较玉龙矿带低,反映纳日贡玛结晶岩浆房更靠近地表。纳日贡玛岩浆源区向壳源区靠近,而玉龙矿带则更靠近幔源区,表明成岩源区中壳幔物质混合比例的不同。     

华南富氟花岗岩高磷和低磷亚类型对比

根据全岩Ｐ２Ｏ５含量的多寡可将华南富氧花岗岩分为高磷亚类和低磷亚类,它们之间具较大的地球化学差异。高磷亚类以低硅、强过铝和低的ＲＥＥ总量为特征,而低磷亚类则相反。在长石、云母等矿物化学成分上这两亚类花岗岩也有所差异。高磷亚类花岗岩中磷以长石中结构磷和磷铝锂石形式存在,而低磷亚类花夺中的磷则主要存在于磷灰石等磷酸盐矿物中。     

华南前寒武纪花岗岩类的构造演化、成因类型及与成矿的关系

本文根据１：２００万华南花岗岩类地质构造编图工作及资料的研究，对前寒武纪花岗岩岩浆发生的构造动力学机制进行了探讨，从而划分了该区花岗岩的构造环境类型：（１）前造山花岗岩（２）同碰撞造山花岗岩（３）晚碰撞造山花岗岩（４）后碰撞造山花岗岩。论述了华南地区的地质构造演变情况及发展历史。最后讨论了不同构造环境类型花岗岩的演化及其与成矿的关系。     

东昆仑热水钼矿区似斑状黑云母二长花岗岩元素地球化学及年代学研究

热水钼矿区处于东昆仑造山带东段,大地构造位置位于北昆仑岩浆弧,区内侵入岩较发育,其中与热水钼多金属矿密切相关的矿化似斑状黑云母二长花岗岩岩相学及地球化学数据显示,Si O2含量在67.64%~71.09%,铝饱和指数(A/CNK)为0.86~1.11,为准铝质到过铝质,K2O/Na2O值1.35~2.32,里特曼指数为1.73~1.99,属于高钾钙碱性I型花岗岩。岩石总体上富集大离子亲石元素Rb、Th、U、K、Pb等,明显亏损高场强元素Ta、Nb、Ce等,贫P、Ti。稀土元素总量(ΣREE)为94.27×10-6~127.44×10-6,平均为110.92×10-6,稀土元素配分曲线呈右倾型,具有较明显的轻稀土富集、重稀土亏损的特征,弱到中等程度的负铕异常。LA-ICP-MS锆石U-Pb年龄为(230.9±1.4)Ma,形成于印支期,钼多金属矿与这一时期岩浆活动密切相关。综合分析表明,似斑状黑云母二长花岗岩形成构造体制转换阶段,在热水地区具有寻找斑岩型矿床潜力。     

Petrogenesis and Tectonic Significance of CarboniferousGranites on the North Side of the Solonker Suture,CentralSouth Mongolia

The central part of South Mongolia, located to the north of the Solonker Suture, is a key region for studying the late Paleozoic tectonic evolution of the Central Asian Orogenic Belt(CAOB). Voluminous late Paleozoic granitic rocks,especially of Carboniferous age, were intruded in this area. However, these granitoids have not been well studied and there is a lack of precise ages and isotopic data. This has hampered our understanding of the tectonic evolution of southeastern Mongolia, and even the entire CAOB. In this paper, we provide new U-Pb isotopic ages and geochemical analyses for these Carboniferous granites. One granite from the Ulaanbadrakh pluton yielded a zircon U-Pb age of 326 Ma, which indicates emplacement in the Early Carboniferous, and three other granites from the Khatanbulag region gave zircon U-Pb ages of316 Ma, 315 Ma, and 311 Ma, which indicate emplacement in the Late Carboniferous. The Early Carboniferous granite has SiO2 contents of 70.04–70.39 wt% and K2 O + Na2 O contents of 6.48–6.63 wt%, whereas the Late Carboniferous granites have more variable compositions(SiO2 = 65.29–77.91 wt% and K2 O + Na2 O = 5.30–7.27 wt%). All the granites are weakly-peraluminous I-types that are relatively enriched in U, Th, K, Zr, Hf, and LREEs. The whole rock Sr-Nd and zircon in situ Lu-Hf isotope analyses for the Early Carboniferous granite gave positive values of εNd(t)(2.87) and εHf(t)(4.31–12.37) with young Nd(TDM = 860 Ma) and Hf(TDMc = 1367–637 Ma) two-stage model ages, indicating derivation from juvenile crustal material. In contrast, the Late Carboniferous granites had more diverse values of εNd(t)(–4.03 to 2.18) and εHf(t)(–12.69 to5.04) with old Nd(TDM = 1358–1225 Ma) and Hf(TDMc = 2881–1294 Ma) depleted mantle two-stage model ages,suggesting derivation from remelting of Precambrian basement. Based on the existing results, the tectonic setting of the Late Carboniferous granites in the central part of South Mongolia is known for its diversity, and this paper believes that the tectonic background of the carboniferous granite records the tectonic transition from a continental-margin-arc to a postcollisional extensional setting during the Late Carboniferous–Permian.     

大兴安岭中部乌兰浩特地区中生代花岗岩的成因——地球化学及Sr-Nd-Hf同位素制约

大兴安岭中部中生代花岗岩成因和构造背景的确定对讨论该地区及东北地区中生代构造-岩浆演化具有重要意义。乌兰浩特地区中生代花岗岩详细的岩石地球化学及Hf、Nd同位素的研究表明:研究区中晚三叠世查干岩体是A2型花岗岩;早中侏罗世景阳岩体为I型花岗岩,而大石寨岩体是具有特殊稀土元素四分组效应的花岗岩;早白垩世花岗岩体可根据其Sr含量划分为高Sr和低Sr两类,它们具有相同或相似的源岩组成,但其起源深度不同。其中高Sr型花岗岩类似于C型埃达克质花岗岩,起源于压力较高的下地壳,而低Sr型及永和屯花岗岩则是起源于压力较低的中地壳的高分异Ⅰ型花岗岩。全岩Nd和锆石Hf同位素特征及前人的研究结果显示,乌兰浩特地区花岗岩类岩石的源区主要为显生宙新增生的年轻地壳物质,并有老的地壳物质的贡献,并且随着花岗岩侵位时间的逐渐变新,锆石的εHf(t)值逐渐减小,认为地幔上涌导致岩浆底侵以及老地壳物质的折返是造成下地壳源岩组成复杂的原因。     

Formation and geodynamic implication of the Early Yanshanian granites associated with W–Sn mineralization in the Nanling range,South China: an overview

ABSTRACT

The Nanling range (Nanling) is characterized by intense and widespread Mesozoic magmatism related large-scale W–Sn mineralization. A summary of geochemistry, geochronology, and petrogenesis for the W–Sn-bearing granites has been carried out in this study. A series of rock- and ore-forming ages in Nanling indicate that the W–Sn mineralization is closely related to the Early Yanshanian granitic magmatism both in temporal and spatial dimensions (165–150 Ma). Geochemical features show that both of the W- and Sn-bearing granites, which mainly belong to highly fractionated I-type granites with a few A-type granites, are characterized by high contents of SiO₂, Al₂O₃, Na₂O, and K₂O; enrichment in Rb, Th, U, Zr, Hf, and REE; depletion in Sr, Ba, P, and Ti; and high ratios of A/CNK. Furthermore, the different Sr–Nd–Hf isotopic compositions indicate that they are mainly originated from the partial melting of the Precambrian basement rocks of the Cathaysia Block at low oxygen fugacity, and the estimated temperatures for the tungsten-bearing and tin-bearing granites are ca. 700°C and ca. 800°C, respectively. The model of the mantle–crust interaction exhibits that different percentages of mantle-derived magma were likely involved in the generation of the tin-bearing granites and tungsten-bearing granites. In combination with previous studies, we propose that these granites in Nanling were emplaced in an extensional setting, as a response to the break-off and roll-back of the subducted Palaeo-Pacific Plate during 175–150 Ma.     

攀西茨达和太和层状岩体时代

由于对攀西层状岩体中的同一岩体采用不同的定年方法获得的年龄结果有较大差异,导致对层状岩体的成岩时代产生争议。对攀西古裂谷带内茨达和太和两个层状辉长岩体进行了黑云母^40Ar/^39Ar法和锆石ELA-ICP-MS法定年研究,结果表明：茨达不含矿层状辉长岩中黑云母^40Ar/^39Ar坪年龄为256Ma,太和含矿层状辉长岩中锆石U-Pb年龄为215Ma,其年龄范围在256-215Ma,相当于晚二叠世—晚三叠世,属于海西晚期—印支期,而且不含矿层状辉长岩侵位时间在前,含矿层状岩体侵位时间在后。此外,根据此次层状岩体同位素地质年龄测定,表明其早期侵位时间并非在裂谷张裂之前的成穹阶段,而是和峨眉山玄武岩在晚二叠世—晚三叠世张裂阶段的喷溢具有同步性,亦显示层状辉长岩的岩浆作用与地幔柱活动,以及断裂构造的密切关系。