Correct nomenclature for the Angadimogar pluton, Kerala, southwestern India

The proper usage of modal composition and geochemical classification of granitoids is discussed for assigning a proper nomenclature for the Angadimogar pluton, Kerala, southwestern India. This discussion is mainly aimed at addressing questions concerning the nomenclature of Angadimogar pluton (syenitevs. granite). Modal composition and whole-rock XRD data clearly show that the pluton exposed near Angadimogar is a quartz-syenite and its geochemistry is typical of a ferroan, metaluminous, alkali (A-type) granitoid     

Oxygen isotopes in the Cretaceous-Paleogene granites of Primorye and some problems of their genesis

The Cretaceous-Paleogene granites of the Eastern Sikhote Alin volcanic belt (ESAVB) and Late Cretaceous granitoids of the Tatibin Series (Central Sikhote Alin) are subdivided into three groups according to their oxygen isotope composition: group I with δ¹⁸O from +5.5 to +6.5‰, group II with δ¹⁸O from +7.6 to +10.2‰, and group III with less than +4.5‰. Group I rocks are similar in oxygen isotope composition to that of oceanic basalts and can be derived by melting of basaltic crust. Group II (rocks of the Tatibin Series) have higher δ¹⁸O, which suggests that their parental melts were contaminated by sedimentary material. The low ¹⁸O composition of group III rocks can be explained by their derivation from ¹⁸O-depleted rocks or by subsolidus isotopic exchange with low-¹⁸O fluid or meteoric waters. The relatively low δ¹⁸O and ⁸⁷Sr/⁸⁶Sr in the granitoids of Primorye suggest their derivation from rocks with a short-lived crustal history and can result from the following: (1) melting of sedimentary rocks enriched in young volcanic material that was accumulated in the trench along the transform continental margin (granites of the Tatibin Series) and (2) melting of a mixture of abyssal sediments, ocean floor basalts, and upper mantle in the lithospheric plate that subsided beneath the continent in the subduction zone (granites of the ESAVB).     

Apatite Composition of Representative Magnetite‐series and Ilmenite‐series Granitoids in Japan

Apatites of representative magnetite‐series and ilmenite‐series granitoids were studied in the Japanese Islands. Concentrations of the volatile components F, Cl and SO₃ are differently distributed in apatites of these granitoid series. Apatites are always fluoroapatite. They have weakly higher F content in the ilmenite series than in the magnetite series. In contrast, Cl and SO₃, are significantly concentrated in apatites of the magnetite series compared to the ilmenite series. These characteristics reflect the original concentrations of these components in the host granitic magmas. A high fO₂ seems most important for the S‐concentration as sulfate in apatite of the magnetite series. REE and Y are only erratically high in the studied apatites.     

浙江花岗岩类地球化学与地壳演化——Ⅱ.元古宙花岗岩类

浙江元古宙花岗岩类包括神功期（1．8－1．9Ga）和晋宁晚期（0．6—0．9Ga）。研究了浙江元古宙花岗岩类的主元素、微量元素、稀土元素和Rb、Sr同位素组成特征及岩石成因，探讨了浙江地壳的演化。浙江地壳形成于太古亩和元古宙，地壳增生的时期为2．6－2．7、0．8-1．1和0.1－0.12Ga。随时间演化浙江地壳组成有变化，但分异演化不明显。沿江-绍断裂分布的晋宁晚期慢源和壳幔混合中酸性岩是普宁期俯冲碰撞的证据。加里乐和印支期是两次规模不大的构造运动。     

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。     

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

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。     

Phase Equilibria of the Lyngdal Granodiorite (Norway): Implications for the Origin of Metaluminous Ferroan Granitoids

The Proterozoic (950 Ma) Lyngdal granodiorite of southern Norwaybelongs to a series of hornblende–biotite metaluminousferroan granitoids (HBG suite) coeval with the post-collisionalRogaland Anorthosite–Mangerite–Charnockite (AMC)suite. This granitoid massif shares many geochemical characteristicswith rapakivi granitoids, yet granodiorites dominate over granites.To constrain both crystallization (P, T, fO₂, H₂O in melt) andmagma generation conditions, we performed crystallization experimentson two samples of the Lyngdal granodiorite (with 60 and 65 wt% SiO₂) at 4–2 kbar, mainly at fO₂ of NNO (nickel–nickeloxide) to NNO + 1, and under fluid-saturated conditions withvarious H₂O–CO₂ ratios for each temperature. Comparisonbetween experimental phase equilibria and the mineral assemblagein the Lyngdal granodiorite indicates that it crystallized between4 and 2 kbar, from a magma with 5–6 wt % H₂O at an fO₂of NNO to NNO + 1. These oxidized and wet conditions sharplycontrast with the dry and reduced conditions inferred for thepetrogenesis of the AMC suite and many other rapakivi granitesworldwide. The high liquidus temperature and H₂O content ofthe Lyngdal granodiorite imply that it is not a primary magmaproduced by the partial melting of the crust but is derivedby the fractionation of a mafic magma. Lyngdal-type magmas appearto have volcanic equivalents in the geological record. In particular,our results show that oxidized high-silica rhyolites, such asthe Bishop Tuff, could be derived via fractionation of oxidizedintermediate magmas and do not necessarily represent primarycrustal melts. This study underlines the great variability ofcrystallization conditions (from anhydrous to hydrous and reducedto oxidized) and petrogenetic processes among the metaluminousferroan magmas of intermediate compositions (granodiorites,quartz mangerites, quartz latites), suggesting that there isnot a single model to explain these rocks. KEY WORDS: ferroan granitoids; crystallization conditions; experiments; Norway; Sveconorwegian; Bishop Tuff     

Paleozoic granitoid magmatism of the eastern part of the Central Asian Fold Belt and formation of large ore deposits

Evidence on the Paleozoic granitoids of the eastern part of the Central Asian Fold Belt (CAFB) was analyzed. A tectonic chart of orogenic belts was compiled. Sketch maps were constructed for the geodynamic settings of the formation of Paleozoic granitoids and the extensiveness of their occurrence. Two types of deep controlling structures were distinguished: zones of lithospheric faults and plumes, including the newly recognized Jiamusi-Bureya plume. It was sown that the distribution of large and superlarge Paleozoic ore deposits is related to these structures, primarily to plumes. Sites promising for large and superlarge deposits related to the Paleozoic granitoid magmatism were determined in the Russian Far East.     

阿拉善地块南缘古生代花岗岩类研究进展

阿拉善地块处于华北克拉通,塔里木克拉通和祁连造山带的交汇处,其南缘古生代花岗岩广泛分布。结合近年来阿拉善南缘古生代花岗岩研究成果,从锆石U-Pb年代学和地球化学等方面进行分析总结,认为阿拉善南缘早古生代花岗岩主要受控于祁连造山带的构造演化,其岩浆活动可分为两期,中奥陶世—早志留世和中志留世—早泥盆世,前者处于俯冲环境,后者为后碰撞伸展环境;晚古生代花岗岩仅零星出露于龙首山地区,岩石地球化学特征与宗乃山—沙拉扎山构造带花岗岩相似,与中亚造山带的构造演化相关。并对目前研究中存在的问题和未来研究的方向提出了建议。     

再论南岭侏罗纪“铝质”A型花岗岩的成因及其对古地温线的制约

对南岭地区侏罗纪4个典型"铝质"A型花岗岩岩基——柯树北、寨背、西山和南昆山的成因分析表明:柯树北、寨背岩基中的低分异花岗岩SiO2≈70%,A/CNK<1.1,CaO≥1%,高Zr、Ba含量,是下地壳部分熔融产物;而SiO2含量较高者由低分异花岗岩岩浆通过分离结晶演化而来。西山花岗质火山-侵入杂岩也是下地壳部分熔融产物。南昆山花岗岩为高硅花岗岩,贫Zr、低Ba、Sr和Eu/Eu*值,但具有高的Nb、Ga、REE含量和Ga/Al比值,在Whalen等(1987)图解中地球化学参数落在A型花岗岩区域内。碱性玄武岩浆分离结晶的成岩模式无法解释南昆山岩基较大的体积、均一的成分和低的Nb/Ta比值。详细的成岩分析表明,南昆山花岗岩可能是先期侵入的(幔源)碱性正长岩在富水和相对低温低压条件下发生部分熔融的产物。由这些"铝质"A型花岗岩的熔融温压条件估算得出热流值达到80~95mWm-2的南岭地区侏罗纪古地温线。由古地温线推算出的岩石圈厚度45~75km。南岭侏罗纪高热流背景及其对应的花岗质岩浆活动可能与后碰撞造山阶段岩石圈地幔拆沉或被"热侵蚀"有关,但并不一定意味着岩石圈伸展的大地构造环境。