西藏冈底斯带侏罗纪岩浆作用的时空分布 及构造环境

在新近完成的1：25万区域地质调查资料和相关研究成果的基础上,初步研究了西藏冈底斯带侏罗纪岩浆作用的分布特点及其年代学,并利用已有的地球化学数据重点分析了早期关注程度较低的侏罗纪花岗岩类岩浆作用的性质。目前在冈底斯弧背断隆带未发现侏罗纪火山岩;在冈底斯东部地区,早侏罗世岩浆活动几乎同时发生于南冈底斯（叶巴组火山岩和鸟郁、尼木花岗岩类）、冈底斯弧背断隆带（宁中、金达、布久花岗岩类）和北冈底斯（聂荣花岗岩类）,中晚侏罗世接奴群和拉贡塘组火山岩断续分布于北冈底斯,晚侏罗世岩浆活动零星分布于沙莫勒一麦拉一洛巴堆～米拉山断裂以北。将冈底斯侏罗纪岩浆活动置于时空框架内分析发现,南冈底斯和北冈底斯在侏罗纪时主要受俯冲作用的影响．而冈底斯弧背断隆带和中冈底斯自早侏罗世以来除了受到俯冲作用的影响外,还受到自东向西逐步扩展的碰撞作用的影响。结合古地磁重建资料和其他新发现．认为冈底斯带侏罗纪这种岩浆活动的特点可用班公湖一怒江洋壳向南、新特提斯洋壳向北的双向剪刀式（剪刀口向西张开）俯冲模式来解释。     

Lermontovskoe Tungsten Skarn Deposit: the Oldest Mineralization in the Sikhote-Alin Orogen, Far East Russia

Abstract. Lermontovskoe tungsten skarn deposit in central Sikhote-Alin is concluded to have formed at 132 Ma in the Early Cretaceous, based on K-Ar age data for muscovite concentrates from high-grade scheelite ore and greisenized granite. Late Paleozoic limestone in Jurassic - early Early Cretaceous accretionary complexes was replaced during hydrothermal activity related to the Lermontovskoe granodiorite stock of reduced type. The ores, characterized by Mo-poor scheelite and Fe^3+- poor mineral assemblages, indicate that this deposit is a reduced-type tungsten skarn (Sato, 1980, 1982), in accordance with the reduced nature of the granodiorite stock.
The Lermontovskoe deposit, the oldest mineralization so far known in the Sikhote-Alin orogen, formed in the initial stage of Early Cretaceous felsic magmatism. The magmatism began shortly after the accretionary tectonics ceased, suggesting an abrupt change of subduction system. Style of the Early Cretaceous magmatism and mineralization is significantly different between central Sikhote-Alin and Northeast Japan; reduced-type and oxidized-type, respectively. The different styles may reflect different tectonic environments; compressional and extensional, respectively. These two areas, which were closer together before the opening of the Japan Sea in the Miocene, may have been juxtaposed under a transpressional tectonic regime after the magmatism.     

内蒙古达茂旗北部奥陶纪花岗岩类特征及其构造意义

研究区奥陶纪花岗岩分布于乌兰布拉格 -哥舍深大断裂 (槽台断裂 )以北 ,岩石类型主要有闪长岩、石英闪长岩、斜长花岗岩和花岗闪长岩。岩石中 Si O2 质量分数为 5 6.76%～ 69.2 4 % ,Al2 O3较高 (多 >1 6% ) ,富 Na2 O贫 K2 O,A/ CNK均 <1 .1 ,为准铝质的钙碱性岩石系列。稀土总量普遍较低 ,为 (63 .4 1～ 1 4 0 .61 )× 1 0 - 6 ,轻重稀土分馏强烈 ,铕异常不明显 (δEu=0 .95～1 .2 2 6)。痕量元素特征与典型的火山弧花岗岩相似。结合区域地质背景 ,认为该套花岗岩类为与洋壳消减有关的岛弧型花岗岩 ,岩浆起源于加厚陆壳的底部。从花岗岩的分布及迁移规律推测 ,华北陆块与其北缘增生带之间的早古生代洋壳可能是由南西向北东的斜向消减     

Temporal variations in magma composition at Merapi Volcano (Central Java, Indonesia): magmatic cycles during the past 2000 years of explosive activity

Merapi Volcano (Central Java, Indonesia) has been frequently active during Middle to Late Holocene time producing basalts and basaltic andesites of medium-K composition in earlier stages of activity and high-K magmas from 1900 ¹⁴C yr BP to the present. Radiocarbon dating of pyroclastic deposits indicates an almost continuous activity with periods of high eruption rates alternating with shorter time spans of distinctly reduced eruptive frequency since the first appearance of high-K volcanic rocks. Geochemical data of 28 well-dated, prehistoric pyroclastic flows of the Merapi high-K series indicate systematic cyclic variations. These medium-term compositional variations result from a complex interplay of several magmatic processes, which ultimately control the periodicity and frequency of eruptions at Merapi. Low eruption rates and the absence of new influxes of primitive magma from depth allow the generation of basaltic andesite magma (56–57 wt% SiO₂) in a small-volume magma reservoir through fractional crystallisation from parental mafic magma (52–53 wt% SiO₂) in periods of low eruptive frequency. Magmas of intermediate composition erupted during these stages provide evidence for periodic withdrawal of magma from a steadily fractionating magma chamber. Subsequent periods are characterised by high eruption rates that coincide with shifts of whole-rock compositions from basaltic andesite to basalt. This compositional variation is interpreted to originate from influxes of primitive magma into a continuously active magma chamber, triggering the eruption of evolved magma after periods of low eruptive frequency. Batches of primitive magma eventually mix with residual magma in the magmatic reservoir to decrease whole-rock SiO₂ contents. Supply of primitive magma at Merapi appears to be sufficiently frequent that andesites or more differentiated rock types were not generated during the past 2000 years of activity. Cyclic variations also occurred during the recent eruptive period since AD 1883. The most recent eruptive episode of Merapi is characterised by essentially uniform magma compositions that may imply the existence of a continuously active magma reservoir, maintained in a quasi-steady state by magma recharge. The whole-rock compositions at the upper limit of the total SiO₂ range of the Merapi suite could also indicate the beginning of another period of high eruption rates and shifts towards more mafic compositions.     

北秦岭古聚会带壳幔再循环

以同构造期代表古洋壳残片的蛇绿岩及产于古岛弧的玄武岩为基础，通过Ｎｄ，Ｐｂ同位素与微量元素示踪及岩浆源区分析，揭示出北秦岭元古宙上地幔以强亏损（εＮｄ（ｔ）＋６．３～＋７．３）和高的Ｙｂ／Ｈｆ，Ｎｂ／Ｌａ和Ｔｈ／Ｌａ比值为特征，北秦岭地壳和上地幔明显具有Ｐｂ同位素比值高的特征．北秦岭丹凤群岛弧火山岩、二郎坪群弧后玄武岩以及松树沟蛇绿岩中变拉斑玄武岩εＮｄ（ｔ）、放射成因Ｐｂ同位素、Ｙ／Ｔｂ和Ｔｉ－ＭｇＯ研究表明，本区玄武岩存在两类性质不同的岩浆源．一类与亏损的北秦岭岩石圈上地幔源区有关；另一类与携带海洋沉积物的洋壳板块俯冲参与有关．由此，论证了北秦岭古聚会带壳幔之间物质再循环     

Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning

The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth of “softening”, V_p after “softening” and the percentage of V_p’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km approximately and V_p after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately and V_p after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening” of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting, these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type granitoid.     

Petrochemistry of Granitoids Along the Loei Fold Belt,Northeastern Thailand

Petrochemical characteristics of Permo‐Triassic granitoids from five regions (i) Mung Loei, (ii) Phu Thap Fah – Phu Thep, (iii) Phetchabun, (iv) Nakon Sawan – Lobburi, and (v) Rayong – Chantaburi along the Loei Fold Belt (LFB), northeastern Thailand were studied. The LFB is a north–south trending 800 km fold belt that hosts several gold and base‐metal deposits. The granitoids consist of monzogranite, granodiorite, monzodiorite, tonalite, quartz‐syenite, and quartz‐rich granitoids. These are composed of quartz, plagioclase, and K‐feldspar with mafic minerals such as hornblende and biotite. Accessory minerals, such as titanite, zircon, magnetite, ilmenite, apatite, garnet, rutile, and allanite are also present. Magnetic susceptibilities in the SI unit of granitoids vary from 6.5 × 10⁻³ to 15.2 × 10⁻³ in Muang Loei, from 0.1 × 10⁻³ to 29.4 × 10⁻³ in Phu Thap Fah – Phu Thep, from 2.7 × 10⁻³ to 34.6 × 10⁻³ in Petchabun, from 2.4 × 10⁻³ to 14.1 × 10⁻³ in Nakon Sawan – Lobburi, and from 0.03 × 10⁻³ to 2.8 × 10⁻³ in Rayong – Chantaburi. Concentration of major elements suggests that these intermediate to felsic plutonic rocks have calc‐alkaline affinities. Concentration of REE of the granitoids normalized to chondrite displays moderately elevated light REE (LREE) and relatively flat heavy (HREE) patterns, with distinct depletion of Eu. Rb versus Y/Nb and Nb/Y tectonic discrimination diagrams illustrate that the granitoids from Muang Loei, Phu Thap Fah – Phu Thep, Phetchabun, Nakon Sawan – Lobburi, and Rayong – Chantaburi formed in continental volcanic‐arc setting. New age data from radiometric K‐Ar dating on K‐feldspar from granodiorite in Loei and Nakhon Sawan areas yielded 171 ± 3 and 221 ± 5 Ma, respectively. K‐Ar dating on hornblende separated from diorite in Lobburi yielded 219 ± 8 Ma. These ages suggest that magmatism of Muang Loei occurred in the Middle Jurassic, and Nakon Sawan – Lobburi occurred in Late Triassic. Both Nb versus Y and Rb versus (Y + Nb) diagrams and age data indicate that Nakon Sawan – Lobburi granitoids intruded in Late Triassic at Nong Bua, Nakon Sawan province and Khao Wong Phra Jun, Lobburi province in volcanic arc setting. Muang Loei granitoids at the Loei province formed later in Middle Jurassic also in volcanic arc setting. The negative δ³⁴S_CDT values of ore minerals from the skarn deposit suggest that the I‐type magma has been influenced by light biogenic sulfur from local country rocks. The Au‐Cu‐Fe‐Sb deposits correlate with the magnetite‐series granitoids in Phetchabun, Nakon Sawan – Lobburi and Rayong – Chantaburi areas. Metallogeny of the Au and Cu‐Au skarn deposits and the epithermal Au deposit is related to adakitic rocks of magnetite‐series granitoids from Phetchabun and Nakon Sawan areas. All mineralizations along the LFB are generated in the volcanic arc related to the subduction of Paleo‐Tethys. The total Al (^TAl) content of biotite of granitoids increases in the following order: granitoids associated with Fe and Au deposit < with Cu deposit < barren granitoids. X_Mg of biotite in granitoids in Muang Loei indicates the crystallization of biotite in magnetite‐series granitoids under high oxygen fugacity conditions. On the other hand, low X_Mg (<0.4) of biotite in magnetite‐series granitoids in Phu Thap Fah – Phu Thep and Rayong – Chantaburi indicates a reduced environment and low oxygen fugacity, associated with Au skarn deposit (Phu Thap Fah) and Sb‐Au deposit (Bo Thong), respectively. The magnetite‐series granitoids at Phu Thap Fah having low magnetic susceptibilities and low X_Mg of biotite were formed by reduction of initially oxidizing magnetite‐series granitic magma by interaction with reducing sedimentary country rocks as suggested by negative δ³⁴S_CDT values.     

内蒙古北山地区阿民乌素公婆泉组变质火山岩年代学、地球化学特征及地质意义

内蒙古北山地区阿民乌素一带公婆泉组变质火山岩主要由钠长阳起岩、斜长阳起岩和斜长阳起片岩组成.三者主量元素显示相对高钠w(Na2O)=0.32％～2.46％,低钾w(K2O)=0.08％～0.38％、钛w(TiO2)=0.93％～1.03％,略富镁 w(MgO)=9.61％～12.04％、钙 w(CaO)=9.96％～1...     

Trace‐element signatures of apatites in granitoids from the Mt Isa Inlier,northwestern Queensland

The concentrations of trace elements in apatite from granitoid rocks of the Mt Isa Inlier have been investigated using the laser‐ablation inductively coupled plasma‐mass spectrometry (ICP‐MS) microprobe. The results indicate that the distribution of trace elements (especially rare‐earth elements (REE), Sr, Y, Mn and Th) in apatite strongly reflects the chemical characteristics of the parental rock. The variations in the trace‐element concentrations of apatite are correlated with parameters such as the SiO₂ content, oxidation state of iron, total alkalis and the aluminium saturation index (ASI). The relative enrichment of Y, HREE and Mn and the relative depletion of Sr in the apatites studied reflect the degree of fractionation of the host granite. Apatites from strongly oxidised plutons tend to have higher concentrations of LREE relative to MREE. Manganese concentrations are higher in apatite from reduced granitoids because Mn²⁺substitutes directly for Ca²⁺. The La/Ce ratio of apatite is well‐correlated with the whole‐rock K²O and Na²O contents, as well as with the oxidation state and ASI. Because apatite trace‐element composition reflects the chemistry of the whole rock, it can be a useful indicator mineral for the recognition of mineralised granite suites, where particular mineralisation styles are associated with granitoids that have specific geochemical fingerprints.     

陕西金堆城花岗岩类主要造岩矿物特征及其岩石学意义

本文依据大量测试数据,对金堆城地区花岗岩类主要造岩矿物学特征同钼迁移富集成矿关系进行了探讨。研究结果表明:异常晶胞条纹长石和正长石以及富重稀土和具明显负铕异常的黑云母是含钼花岗岩类标型矿物,并且可作为花岗岩类岩石发育地区寻找隐伏钼矿体的指示性矿物。钾钠长石和斜长石的结构状态和成分不仅可以提供有关花岗岩类成因演化的信息,其矿物本身亦可成为钼的载体矿物。岩浆期后,强烈的热液蚀变作用可造成钾钠长石和斜长石分解,并且引起钼的释放,从而形成高品位钼矿石。