北秦岭瓦穴子—乔端断裂带的构造特征及形成温度—压力条件探讨

瓦乔(瓦穴子—乔端)断裂带是北秦岭尤为重要的断裂带之一,该带经历了长期的变质变形作用,记录了二郎坪弧后盆地向华北板块南缘俯冲消亡的信息。本文运用多种方法,对瓦乔断裂带几何学、运动学及形成温压条件进行研究和探讨,得出以下几点认识:①瓦乔断裂带产状基本倾向NNE,带内线理发育,表现为由N向S逆冲的运动学特征,且存在左旋剪切的分量;②瓦乔断裂带变形岩石显微构造特征明显,反映了挤压应力下塑性流变的特征;③运用角闪石全铝压力计,得到瓦乔断裂带形成压力为0.64GPa。越靠近瓦乔断裂带中心,压力逐渐变大,位于断裂带中心压力达到0.68GPa,已达到中压相系环境;④运用角闪石—斜长石地质温压计算得瓦乔断裂带形成温度范围500～550℃,属中温环境。     

Genesis of the Mamut Porphyry Copper Deposit, Sabah, East Malaysia

Abstract: The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu‐Au deposit genetically related to a quartz monzonite (“adamellite”) porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore– and alteration–petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post‐ore “granodiorite” porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Sub‐dendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomor‐phic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher X_Mg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor. Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu‐Fe sul–fides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE‐trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2%) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks.     

Differential uplift between Beihuaiyang and Dabie orogenic belt

Isotope dating, hornblende geobarometer, fission-track analysis and fluid inclusion homogeneous temperature analysis have been applied to Caledonian, Variscan and Yenshan plutons in Bei Huaiyang (BHY) and Dabie orogenic belt (DOB), and the emplaced depths and ages of these plutons have been obtained in order to obtain differential uplift time and uplift heights between BHY and DOB since late Paleozoic era. BHY had experienced three stages of uplift (C1-C2, T-J2, J3-K1) and its total uplift height is about 10 km, but, DOB had only experienced two stages of uplift (T-J2, J3-K1) and its maximum uplift height is more than 15 km. BHY uplift occurred mainly before the mid-Jurassic (about 150 Ma), but DOB uplift took place after the mid-Jurassic (about 150 Ma).     

阿尔泰造山带南缘昆格依特岩体LA-ICP-MS锆石U-Pb年代学、岩石成因及其地质意义

昆格依特岩体出露于阿尔泰造山带南缘青河县大青格里河昆格依特一带,主要为角闪黑云英云闪长岩。LA-ICP-MS锆石U-Pb定年结果显示,锆石的²⁰⁶Pb/²³⁸U年龄加权平均值为(403.4±7.4)Ma,表明该岩体形成于早泥盆世。岩体的SiO₂含量介于52.39%~71.89%之间,里特曼指数为0.68~1.53,A/CNK 值为0.76~1.06,属中钾、钙碱性、准铝质-弱过铝质岩石。具有富集Cs、Rb、Th、U等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、Hf、Ti等高场强元素和重稀土元素,弱的负Eu异常(δEu=0.56~0.86)的岛弧岩浆岩特征。结合区域地质资料,认为阿尔泰造山带南缘早泥盆世昆格依特岩体形成于活动大陆边缘的陆缘弧构造环境,是古亚洲洋俯冲过程中幔源的基性岩浆底侵下地壳使之熔融,并发生了岩浆混合和分异作用的产物。     

Experimental Petrology of the 1991-1995 Unzen Dacite, Japan. Part II: Cl/OH Partitioning between Hornblende and Melt and its Implications for the Origin of Oscillatory Zoning of Hornblende Phenocrysts

High-temperature–pressure experiments were carried outto determine the chlorine–hydroxyl exchange partitioncoefficient between hornblende and melt in the 1992 Unzen dacite.Cl in hornblende and melt was analyzed by electron microprobe,whereas OH in hornblende and melt was calculated assuming anionstoichiometry of hornblende and utilizing the dissociation reactionconstant for H₂O + O = 2(OH) in water-saturated melt, respectively.The partition coefficient strongly depends on the Mg/(Mg + Fe)ratio of hornblende, and is expressed as ln K₁ = (Cl/OH)_hb/(Cl/OH)_melt= 2·37 – 4·6[Mg/(Mg + Fe)]_hb at 2–3kbar and 800–850°C. The twofold variation in Cl contentin the oscillatory zoned cores of hornblende phenocrysts inthe 1991–1995 dacite cannot be explained by the dependenceof the Cl/OH partition coefficient on the Mg/(Mg + Fe)_hb ratio,and requires c. 80% variation of the Cl/OH ratio of the coexistingmelt. Available experimental data at 200 MPa on Cl/OH fractionationbetween fluid and melt suggest that c. 1·2–1·8wt % degassing of water from the magma can explain the required80% variation in the Cl/OH ratio of the melt. The negative correlationbetween Al content and Mg/(Mg + Fe) ratio in the oscillatoryzoned cores of the hornblende phenocrysts is consistent withrepeated influx and convective degassing of the fluid phasein the magma chamber. KEY WORDS: chlorine; element partitioning; hornblende; oscillatory zoning; Unzen volcano     

内蒙古狼山地区早石炭世角闪辉长岩、花岗闪长岩的岩石成因及构造意义

内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,时代集中在早石炭世—晚二叠世,早石炭世角闪辉长岩、花岗闪长岩体出露于潮格温都尔镇西侧。角闪辉长岩体呈岩滴状产出,被花岗闪长岩体侵入,LA-ICP-MS锆石U-Pb年龄显示,角闪辉长岩的~(206)Pb/~(238)U加权平均年龄为329.0±2.3 Ma,花岗闪长岩的~(206)Pb/~(238)U加权平均年龄为331.1±0.9 Ma~330.0±4.2 Ma。花岗闪长岩暗色矿物以角闪石为主,富钠(Na2O=3.48%~4.46%),高钠钾比值(Na2O/K2O=1.03~2.39),钙碱性系列,P2O5-SiO_2之间存在较好的负相关性,岩石地球化学特征具Ⅰ型花岗岩的特点。Hf同位素及元素地球化学特征指示了角闪辉长岩及花岗闪长岩均来自于受地壳混染的亏损地幔,为同源岩浆演化的产物。角闪辉长岩及花岗闪长岩稀土元素配分型式一致,均为轻稀土元素富集,重稀土元素亏损,具弱的负Eu异常;角闪辉长岩富集Ba、Sr,亏损Nb、Ta、Zr、Hf;花岗闪长岩富集大离子亲石元素Rb、K、Pb、Sr,不同程度地亏损高场强元素Nb、Ta、P、Ti,总体反映了岩浆弧的地球化学特征。结合区域地质背景,早石炭世狼山地区侵入岩岩石组合为角闪辉长岩(闪长岩)+石英闪长岩+花岗闪长岩,认为狼山地区早石炭世处于大陆边缘弧构造背景。     

四川盐边基性—超基性杂岩体中角闪石矿物学研究

本文采用光学法、探针分析法、红外光谱法、单晶X射线衍射法对杂岩体中角闪石进行了详细的研究,总结了各期岩体中角闪石的特征。从早期到晚期,角闪石光性呈递变关系,2V由(-)76.7→(+)84.2;化学成分呈规律性变化,Si、Fe含量减少,Al、Mg、Na含量增加,矿物种属明显地呈浅闪石质角闪石→含铁韭闪石→韭闪石的变化规律,因而首次在该区确定了含铁韭闪石、韭闪石矿物的存在;红外光谱随T类阳离子Al~(Ⅳ)/Si值,C类阳离子Fe/Mg值呈规律性变化;晶胞参数也显示规律性变化,a由9.838—9.866A,b由18.047—17.980A,c由5.308—5.295A,V由910.73—906.55A~3。清楚地反映了该区角闪石各期演化上的“血缘”关系和差异。同时,探讨了各期角闪石的结晶温度(770—1114℃);成因类型为基性及超基性岩浆型,岩浆来源于上地幔;超基性岩具有地幔交代成因特征。     

横断山区花岗岩类中角闪石的标型特征及其成因意义

本文研究了横断山区不同成因类型花岗岩中角闪石的化学成分、微量元素、稀土元素、晶胞参数和物理性质等特征。按化学成分对角闪石作了晶体化学成因分类。在三种不同成因类型角闪石中，其M值[M=Mg/(Mg Fe^2 )]各不相同；幔型M＞0．7，壳幔型M＝0．7－0．5，壳型M<0．5。     

A thermodynamic model for Ca–Na clinoamphiboles in Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O for petrological calculations

A calibration is presented for an activity–composition model for amphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O (NCFMASHO), formulated in terms of an independent set of six end‐members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing‐on‐sites for the ideal‐mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks, formed over 400–600 °C and 2–18 kbar. The model parameters are calibrated by combining these geometric constraints with qualitative consideration of parameter relationships, given that the data are insufficient to allow all the model parameters to be determined from a regression of the data. Use of coexisting amphiboles means that amphibole activity–composition relationships are calibrated independently of the thermodynamic properties of the end‐members. For practical applications, in geothermobarometry and the calculation of phase diagrams, the amphibole activity–composition relationships are placed in the context of the stability of other minerals by evaluating the properties of the end‐members in the independent set that are in internally consistent data sets. This has been performed using an extended natural data set for hornblende–garnet–plagioclase–quartz, giving the small adjustments necessary to the enthalpies of formation of tschermakite, pargasite and glaucophane for working with the Holland and Powell data set.     

Geochemistry and origin of hornblende‐bearing xenoliths in the I‐type Petford Granite,North‐East Queensland

Hornblende‐bearing xenoliths in the I‐type Petford Granite, north‐east Queensland, show an abundance pattern suggesting redistribution in a convecting magma system and were probably carried up with the host magma. The Petford Granite and xenoliths are chemically cognate, but quartz monzodiorite‐granodiorite bodies (a potential source for the xenoliths) in the adjacent country rocks belong to an independent magma suite. The xenoliths are chemically similar to andesite lavas and dykes 90 km to the NW. They represent fragments of the parental andesite (diorite) of a calcalkaline suite, which fractionated to yield the Petford Granite. They are not source rocks for the granite melt, melt residua, or early cumulates. The fractionated granite melt broke through the earlier envelope of diorite and rose into the upper crust, carrying dioritic fragments with it. Interaction between magma and xenoliths was generally minimal.