The Early Paleozoic Tiefosi syn-collisional granite in the northern Dabie Orogen:Geochronological and geochemical constraints

The Tiefosi granitic pluton is located 5 km northwest of Xinyang City,northern Dabie Orogen,and was emplaced in the Proterozoic Qinling Group. SHRIMP zircon U-Pb dating suggests its crystallization at 436 ± 11 Ma. It is composed of monzogranite and syenogranite containing some amounts of muscovite and few mafic minerals. The rocks are characterized by high and restricted SiO2 content,low FeO,Fe2O3 and MgO contents,high K2O/Na2O ratio,and display high-K calc-alkaline and peraluminous (ACNK>1.1) characteristics. They are generally enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE). They can be divided into three groups in light of rare earth elements (REE) and trace elements. Group I is moderate in ΣREE and characterized by the absence of Eu anom-aly,high (La/Yb)N ratio,and moderate Rb/Sr and Rb/Ba ratios. Group Ⅱ has moderately negative Eu anomaly,low (La/Yb)N ratio and high ΣREE contents,Rb/Sr and Rb/Ba ratios. Group Ⅲ displays positive Eu anomaly,moderate (La/Yb)N ratio,and low ΣREE,Rb/Sr and Rb/Ba ratios. The calculated εNd(440Ma) values of the rocks vary from 8.8 to 9.9 and Nd depleted mantle model ages are about 2.0 Ga,which resemble those of the paragneisses from the Qinling Group. The results indicate that the Tiefosi granite is crust-derived,syn-collisional S-type granite. Generation of Group I was related to low degree melting of the Qinling Group,while Group Ⅱ was formed by fractionational crystallization of plagioclase from Group I magmas,and Group Ⅲ resulted possibly from magma mingling with plagioclase cumulates. The Tiefosi granite was formed within crustal level related to the collision between the North China and South China blocks in the Early Paleozoic time.     

Age and generation of Fogang granite batholith and Wushi diorite-hornblende gabbro body

Fogang granitic batholith, the largest Late Mesozoic batholith in the Nanling region, has an exposure area of ca. 6000 km2. Wushi diorite-hornblende gabbro body is situated at the northeast part of the ba- tholith. Both the granitic batholith main body and the diorite-hornblende gabbro body belong to high-K calc alkaline series. Compared with the granitic main body, the Wushi body has lower Si (49%―55%), higher Fe, Mg, Ca, lower REE, less depletion of Eu, Ba, P, Ti, and obvious depletion of Zr, Hf. Zircon LA-ICP-MS dating and the mineral-whole rock isochron dating reveal that Fogang granitic main body and Wushi body were generated simultaneously at ca. 160 Ma. The Fogang granitic main body has high (87Sr/86Sr)i ratios (0.70871―0.71570) and low εNd(t) values (?5.11―?8.93), suggesting the origins of the granitic rocks from crustal materials. Their Nd two-stage model ages range from 1.37―1.68 Ga. The Sr and Nd isotopic compositions and the Nd model ages of the granitic rocks may suggest that the giant Fogang granitic main body was generated from a heterogeneous source, with participation of mantle component. Wushi diorite-hornblende gabbro is an unusual intermediate-basic magmatic rock series, with high (87Sr/86Sr)i ratios (0.71256―0.71318) and low εNd(t) values (?7.32―?7.92), which was possibly formed through mixing between the mantle-derived juvenile basaltic magma and the magma produced by the dehydration melting of lower crustal basaltic rocks.     

Major- and trace-element systematics and isotope geochemistry of Cenozoic mafic volcanic rocks from the Vogelsberg (central Germany): Constraints on the origin of continental alkaline and tholeiitic basalts and their mantle sources

The Cenozoic basaltic province of the Vogelsberg area (central Germany) is mainly composed of intercalated olivine to quartz tholeiites and near-primary nephelinites to basanites. The inferred mantle source for the alkaline and tholeiitic rocks is asthenospheric metasomatized garnet peridotite containing some amphibole as the main hydrous phase. Trace element modelling indicates 2 to 3% partial melting for the alkaline rocks and 5 to 7% partial melting for the olivine tholeiites. Incompatible trace element abundances and ratios as well as Nd and Sr radiogenic isotope compositions lie between plume compositions and enriched mantle compositions and are similar to those measured in Ocean Island Basalts (OIB) and the Central European Volcanic Province elsewhere. The mafic olivine tholeiites have similar Ba/Nb, Ba/La and Nd–Sr isotope ratios to the alkaline rocks indicating derivation of both magma types from chemically comparable mantle sources. However, Zr/Nb ratios are slightly higher in olivine tholeiites than in basanites reflecting some fractionation of Zr relative to Nb during partial melting. Quartz tholeiites have higher Ba/Nb, Zr/Nb, La/Nb, but lower Ce/Pb ratios and lower Nd isotope compositions than the alkaline rocks which can be explained by interaction of the basaltic melt with lower (granulite facies) crustal material or partial melts thereof during stagnation within the lower crust. It appears most likely that upwelling of hot, asthenospheric material results in the generation of primitive alkaline rocks at the base of the lithosphere at depths of 75–90 km. Lithospheric extension together with minor plume activity and probably lower lithosphere erosion induced melting of shallower heterogenous upper mantle generating a spectrum of olivine tholeiitic melts. These olivine tholeiitic rocks evolved via crystal fractionation and probably limited contamination to quartz tholeiites.     

Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.     

Sr isotope evolution during chemical weathering of granites —Impact of relative weathering rates of minerals

The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in⁸⁷Sr/⁸⁶Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made⁸⁷Sr/⁸⁶Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the preferential release of Sr from dissolving solid phase and the fluctuation of⁸⁷Sr/⁸⁶Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.     

Early Ordovician strongly peraluminous granite in the middle section of the Yarlung Zangbo junction zone and its geological significance

LA-ICP-MS zircon U-Pb isotopic dating and rock geochemical analysis were done of the Xarru granite in the middle section of the Yarlung Zangbo junction zone.Zircon 206Pb/238U weighted mean ages of 474.9±2.3 and 478.3±1.7 Ma have been obtained for two gneiss granite samples respectively,which represent the formation age of the granite.This is the first discovery of the Early Ordovician magmatism in the Yarlung Zangbo junction zone.The rocks are high-K calcic-alkalic granite,contain tourmaline but not hornblende,with aluminum saturation index(ASI) of A/CNK1.1(1.10–1.20),and are enriched in Rb,Th and U and relatively depleted in Ba,Nb,Sr,Zr,Ti and Eu.They are strongly peraluminous S-type granite,resulting from partial melting of argillaceous components in the crust in a syn-collisional setting.According to previous studies as well as the analysis in this paper,the formation of the Xarru granite is probably related to the Andean-type orogeny in the process of subduction of the Proto-Tethys Ocean towards the Gondwanaland,and it is a product of partial melting of the thickened upper crust as a result of collision between blocks or micro-blocks in the northern margin of the Gondwana supercontinent in the process of oceanic subduction.The Xarru granite is identified as the Early Ordovician granite,indicating that the wall rocks had probably formed in the Cambrian or Precambrian.A crustal basement may exist in the Xarru region.     

Early precambrian trondhjemitic suites in Western Australia and Northwestern Scotland,and the geochemical evolution of shields

Sodium-rich trondhjemites and quartz keratophyres, retained as pebbles in Archaean metaconglomerates, represent some of the oldest components (up to 3 by) of the Kalgoorlie System, Western Australia. New determinations indicate high Si, Na, Na/K, Ba/Rb, Ba/K, Sr/Ca+K, Ni, Ni/Mg, and Cr/Mg, and low K, Rb, Rb/Sr, and Y, in comparison to Taylor's (1965) [1] and other' average granites and to Nockolds and Allen's (1953) [2] acid calc-alkaline rocks. Syngeosynclinal quartz keratophyres (2.6 by) studied by O'Beirne (1968) [3] show similar comparisons. Similarly, high-grade acid and intermediate gneisses of the Lewisian, Scotland, have high Na/K, K/Rb, Ba/Rb, Ba/K, Sr/Ca+K, Ni, Ni/Mg, Cr, Cr/Mg, and low K, Rb, Rb/Sr, Y and Y/Ca. Secular decrease in Na/K, K/Rb and Sr/Rb is shown by granite series in Western Australia, Transvaal, Rhodesia and the Canadian Shield. The earliest members of these series compare with sodic acid plutons of island arcs, in particular Fiji, an archipelago showing a pattern of evolution analogous to that of the proposed model (Glikson, 1971) [4]. Evidence for an origin of Archaean sodic granites from below a basic crust is furnished by the abundance of basic xenoliths, by relationships in agmatite-gneiss terrains in Greenland, Scotland, and India, by K levels lower than those of Archaean metasediments, and by low initial⁸⁷Sr/⁸⁶Sr ratios. The abundance of euhedral quartz phenocrysts in the quartz keratophyres supports origin through partial melting of eclogite [5]. In high-grade belts, the originally low abundances of K and Rb were accentuated by synmetamorphic depletion, with which the formation of late-stage K-granites may have been associated. The correlation of chemical data enables an insight into spatial and temporal relationships between low- and high-grade early Precambrian terrains, and on the geochemical evolution of shields.     

广东南山花岗岩形成时代、地球化学特征与成因

广东南山花岗岩体位于陂头复式岩体西端,锆石的SHRIMP U-Pb年龄为158.1±1.8Ma,是燕山早期岩浆活动的产物。岩石化学特征显示岩体以高硅、富碱、贫Ca和Mg以及高TFeO/MgO、低CaO/Na2O为特征。其K2O/Na2O〉1,A/NK=7.8~11.92,A/CNK=1.33~1.68,属过铝质碱性岩石。在稀土和微量元素组成上,岩石富含稀土元素（除明显的负Eu异常,δEu=0.09~0.16）以及Zr、Y、Th、U、Nb等高场强元素,贫Ba、Sr、Ti等,高10000x Ga/Al（比值大于2.6）。在Zr、Nb、Ce、Y对10000×Ga/Al以及TFeO/MgO-SiO2等A型花岗岩多种判别图上,投影点主要落在A型花岗岩区,而与高分异的I、S型花岗岩明显不同。这些特征均指示,南山岩体具有铝质A型花岗岩的特点。通过Y-Nb-3Ga和Y-Nb-Ce构造环境判别图解将其进一步划分为A2型花岗岩,代表其形成于拉张的构造背景之下。本文在此研究基础上,认为南山花岗质岩浆可能形成于相对挤压的中侏罗世。而在晚侏罗世早期相对拉张的作用下,岩石圈减薄,软流圈地幔上涌,地壳的泥质岩和少量砂质岩受到幔源流体富集后发生部分熔融后上侵形成铝质A型花岗岩,且有较强的结晶分异作用。     

大兴安岭中南段杜尔基地区早白垩世侵入岩岩石地球化学特征及构造环境

杜尔基地区处于大兴安岭中南段,区内中生代侵入岩广泛发育。八个样品K—Ar全岩法测年结果为100．15～120．29Ma,形成于早白垩世。岩石化学分析结果具有高硅、高钾、富碱、过铝、贫铁、镁、钙特征,属于碱性岩系列。稀土元素总量平均值为146．85μg/g,球粒陨石标准化曲线整体平缓右倾,显示富Rb,贫Sr、Ba特征,具有Eu负异常,微量元素具有明显的Sr、Ba、Ti负异常,反映了具有强烈分异的分离结晶作用存在,说明岩石形成于长期较稳定的构造背景,可能形成于非造山板内裂谷或热点地幔柱环境。     

Eruptive history and petrology of Mount Drum volcano,Wrangell Mountains,Alaska

Mount Drum is one of the youngest volcanoes in the subduction-related Wrangell volcanic field (80×200 km) of southcentral Alaska. It lies at the northwest end of a series of large, andesite-dominated shield volcanoes that show a northwesterly progression of age from 26 Ma near the Alaska-Yukon border to about 0.2 Ma at Mount Drum. The volcano was constructed between 750 and 250 ka during at least two cycles of cone building and ring-dome emplacement and was partially destroyed by violent explosive activity probably after 250 ka. Cone lavas range from basaltic andesite to dacite in composition; ring-domes are dacite to rhyolite. The last constructional activity occurred in the vicinity of Snider Peak, on the south flank of the volcano, where extensive dacite flows and a dacite dome erupted at about 250 ka. The climactic explosive eruption, that destroyed the top and a part of the south flank of the volcano, produced more than 7 km³ of proximal hot and cold avalanche deposits and distal mudflows. The Mount Drum rocks have medium-K, calc-alkaline affinities and are generally plagioclase phyric. Silica contents range from 55.8 to 74.0 wt%, with a compositional gap between 66.8 and 72.8 wt%. All the rocks are enriched in alkali elements and depleted in Ta relative to the LREE, typical of volcanic arc rocks, but have higher MgO contents at a given SiO₂, than typical orogenic medium-K andesites. Strontium-isotope ratios vary from 0.70292 to 0.70353. The compositional range of Mount Drum lavas is best explained by a combination of diverse parental magmas, magma mixing, and fractionation. The small, but significant, range in ⁸⁷Sr/⁸⁶Sr ratios in the basaltic andesites and the wide range of incompatible-element ratios exhibited by the basaltic andesites and andesites suggests the presence of compositionally diverse parent magmas. The lavas show abundant petrographic evidence of magma mixing, such as bimodal phenocryst size, resorbed phenocrysts, reaction rims, and disequilibrium mineral assemblages. In addition, some dacites and andesites contain Mg and Ni-rich olivines and/or have high MgO, Cr, Ni, Co, and Sc contents that are not in equilibrium with the host rock and indicate mixing between basalt or cumulate material and more evolved magmas. Incompatible element variations suggest that fractionation is responsible for some of the compositional range between basaltic andesite and dacite, but the rhyolites have K, Ba, Th, and Rb contents that are too low for the magmas to be generated by fractionation of the intermediate rocks. Limited Sr-isotope data support the possibility that the rhyolites may be partial melts of underlying volcanic rocks. Received March 13, 1993/Accepted September 10, 1993     

Petrology and geochemistry of potassic rocks in the Gölcük area (Isparta, SW Turkey): genesis of enriched alkaline magmas

The Lower Pliocene volcanic rocks occurring in the Gölcük area of SW Turkey exhibit alkaline major element trends with a general potassic character. The development of volcanism can be divided into 2 major stages such as trachytic ancient lavas/domes and tephriphonolitic, trachyandesitic to trachytic Gölcük eruptions (ignimbrites, lava/dome extrusions, phreatomagmatic deposits, and finally, young domes). Volcanic rocks consist primarily of plagioclase, clinopyroxene (which ranges in composition from diopside to augite and are commonly zoned), biotite, and phlogopite. Amphibole phenocrysts are restricted to the pyroclastic deposits. Pseudoleucites are also seen only in the lava/dome extrusions. Oxides and apatites are common accessory phenocryst phases. As would be expected from their potassic–alkaline nature, the volcanic rocks of the Gölcük area contain high amounts of LILE (Ba, Sr, Rb and K), LREE, and Zr. Concentrations of compatible elements such as Cr, Ni and V are very low, possibly indicating fractionation of olivine and clinopyroxene. Correlation of SiO₂, Rb/Sr and MgO with ⁸⁷Sr/⁸⁶Sr (0.703506–0.704142) exhibit an increasing trend in the direction of crustal contamination. However, the isotopic compositions of Sr are not as high to indicate a high level of crustal contamination. Geochemical data are consistent with the derivation of Gölcük volcanic rocks from a metasomatized and/or enriched lithospheric mantle source during crustal extension in the area. This metasomatism was probably occurred by fluids released from the northward subduction between African and Eurasian plates during Tertiary, as the Gölcük volcanic rocks display features of island-arc magmas with having high Ba/Nb (>28) ratios, and Nb and Ti depletions. Lower Pliocene volcanism in the Gölcük was response to extensional tectonics.     

Geochemical approach to magmatic evolution of Mt. Erciyes stratovolcano Central Anatolia, Turkey

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During its evolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these products are calc-alkaline in character and they constitute Kocdag and Erciyes sequences by repeated activities. Alkaline activity is mainly observed in the first stages of Kocdag and approximately first-middle stages of Erciyes sequences. Generally, Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyolite (48.4–70.5 wt.% SiO₂). Calc-alkaline rocks are represented mostly by andesites and dacites. Some compositional differences between alkaline basaltic, basaltic and andesitic rocks were found; while the composition of dacites remain unchanged. All these volcanics are generally enriched in LIL and HFS elements relative to the orogenic values except Rb, Ba, Nb depleted alkaline basalt. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopic composition of the volcanics range between 0.703344–0.703964, 0.512920–0.512780 for alkaline basalts and change between 0.704322–0.705088, 0.512731–0.512630 for alkaline basaltic rocks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic ratios (0.703434–0.705468, 0.512942–0.512600). Low Rb, Ba, Nb content with high Zr/Nb, low Ba/Nb, La/Yb ratio and low Sr isotopic composition suggest an depleted source component, while high Ba, Rb, Nb content with high La/Yb, Ba/Nb, low Zr/Nb and low ⁸⁷Sr/⁸⁶Sr ratios indicate an OIB-like mantle source for the generation of Erciyes alkaline magma. These elemental and ratio variations also indicate that the different mantle sources have undergone different degree of partial melting episodes. The depletion in Ba, Rb, Nb content may be explained by the removal of these elements from the source by slab-derived fluids which were released from pre-collisional subduction, modified the asthenospheric mantle. The chemically different mantle sources interacted with crustal materials to produce calc-alkaline magma. The Ba/Nb increase of calc-alkaline samples indicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevated LIL and HFS element content imply that calc-alkaline magma may be derived from mixing of an OIB-like mantle melts with a subduction-modified asthenospheric mantle and involvement of crustal materials in intraplate environments.     

Zircon U-Pb and geochemical analyses for leucocratic intrusive rocks in pillow lavas in the Danfeng Group,north Qinling Mountains,China

Field observation showed that there are many irregular leucocratic intrusive rocks in pillow lavas in the Danfeng Group in the Xiaowangjian area, north Qinling orogenic belt. Photomicrographs indicated that the protoliths of those altered leucocratic intrusive rocks are dioritic rocks. Geochemical analyses showed that pillow lavas have a range of SiO2 from 47.35% to 51.20%, low abundance of TiO2 from 0.97% to 1.72%, and percentages of MgO (MgO#=41―49). Chondrite-normalized REE patterns of pillow lavas are even, indicative of a weak differentiation between LREE and HREE (La/YbN=1.52―0.99). N-MORB-normalized trace element abundances showed that pillow lavas are enriched in incompatible elements (e.g., K, Rb, and Ba). Leucocratic intrusive rocks in pillow lavas have a wide range of SiO2 from 53.85%―67.20%, low abundances of TiO2 from 0.51%―1.10%, and MgO (MgO#=40―51), and higher percentages of Al2O3 (13.32%―16.62%) and concentration of Sr (342-539 μg/g), ratios of Na2O/K2O (2―7) and Sr/Y (17―28). Chondrite-normalized REE patterns of leucocratic intrusive rocks showed highly differentiation between LREE and HREE (La/YbN=12.26―19.41). N-MORB-normalized trace element abundances showed that leucocratic intrusive rocks are enriched in incompatible elements (e.g., K, Rb, and Ba), and significantly depleted in HFSE (e.g., Nb, Ta, Zr and Ti), indicative of a relationship to subduction. Isotopically, leucocratic intrusive rocks have a similar εNd(t) ( 7.45― 13.14) to that of MORB ( 8.8― 9.7), which indicates that those leucocratic intrusive rocks sourced from depleted mantle most likely. SHRIMP U-Pb analyses for zircon showed that those leucocratic intrusive rocks were formed at 442±7 Ma, yielding an age of subduction in the early Paleozoic in the north Qinling orogenic belt.     

Deep structure and lithospheric shear faults in the East Kunlun-Qiangtang region,northern Tibetan Plateau

The Cenozoic magmatic rocks of shoshonitic series in the eastern Qinghai-Tibet Plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Analytical results show that these different lithological rocks are extremely similar in Sr, Nd and Pb isotopic compositions with the range of 0.705 187– 0.707 254 for⁸⁷Sr/⁸⁶Sr, 0.512 305–0.512 630 for¹⁴³Nd/¹⁴⁴Nd, 18.53–18.97 for²⁰⁶Pb/²⁰⁴Pb, 15.51–15.72 for²⁰⁷Pb/²⁰⁴Pb and 38.38–39.24 for²⁰⁸Pb/²⁰⁴Pb. They are isotopically similar to the EMII end-member. This indicates that mantle metasomatism must have taken place in their source region. The formation of these particular rocks is related to crustal thinning and mantle upwelling in a large-scale strike-slip and pull-apart fault zone at about 40 Ma in northern and eastern Qinghai-Tibet Plateau     

Rhyolitic ignimbrites in the region of Afyon (Central Anatolia)

Occurrence and field relations of an extensive ignimbrite sheet near Afyon in Central Anatolia are described. These rhyolitic ignimbrites are part of the important Neogene volcanic activity in Turkey and belong to the alignment of volcanic complexes along the inner border of the Taurian ranges. In close stratigraphical connection and in the same tectonic position as the rhyolites there occurs an assemblage of high-potassic, intermediate to basic volcanic rocks (alkali trachytes, mela-trachytes, latites and leucite-bearing rocks). Petrological and magmatological considerations led to the conclusion that the rhyolites and the potassic series, in spite of the close geological connection, are not related by processes of magmatic differentiation. Arguments in favour of an anatectic origin of the rhyolitic melt are presented. The occurrence of garnet and allanite as accessory minerals and as inclusions in the salic minerals of the ignimbrite are interpreted as relictic witnesses of a sialic parent rock. However, the trace elements, especially high Rb connected with low Sr, Ba and Zr and K/Rb ratios below 100 give a pattern generally explained by strong fractionation processes.     

Origin of Li-F-rich granite: Evidence from high P-T experiments

In South China and some regions around the world, there is a special type of rocks. These rocks are usually ultra-acidic, peraluminous, rich in Na and volatile components, such as H2O, F, B and P, and with higher concentrations of lithophile rare metal elements, including Li, Rb, Cs, Be, Ta, Nb, Sn, W, etc. Rocks of this type are commonly called Li-F-rich, rare-metal bearing granitic rocks, or Li-F granites for short[1]. The economic importance and distinct forma-tion mechanism of Li-…     

Calc-alkaline and shoshonitic lavas from five Andean volcanoes (between latitudes 21° 45′ and 24°30′S) and the distribution of the Plio-Quaternary volcanism of the south-central and southern Andes

The Plio-Quaternary volcanic rocks of the south-central Andes (southward from latitude 18°S) contain two associations: calc-alkaline and shoshonitic which coincide with seismic belts as geographically distinct zones aligned parallel to the oceanic trench. There is a continuous gradation from calc-alkaline to shoshonitic associations. The shoshonitic association appears to the north of latitude 26°S; southwards, the calc-alkaline association directly abuts against the continental (Argentinian) alkaline association.Thirty-one lavas from the Plio-Quaternary calc-alkaline Socompa, Lascar, Sairecabur and Tocorpuri and shoshonitic Sierra de Lipez volcanoes were studied. The lavas are porphyric with abundant glass. The distribution and the nature of the phenocrysts vary according to the chemistry of the calc-alkaline lavas. Petrographic evidence for crystal fractionation has been observed. Occasional phenocrysts of alkali feldspars occur in the shoshonitic lavas. The K₂O and SiO₂ contents increase from calc-alkaline to shoshonitic lavas with distance away from the oceanic trench. In lavas from Socompa, Lascar, Sairecabur and Tocorpuri calc-alkaline volcanoes, K₂O, Li and Rb increase and K/Rb and Sr decrease with increasing SiO₂; Ba increases with decreasing Sr, probably as a result of plagioclase fractionation. In lavas from Sierra de Lípez shoshonitic volcano, SiO₂ is high, K₂O is high and rather constant and Li, Rb, Ba and Sr increase with increasing SiO₂. Bolivian shoshonitic lavas appear to be genetically related to the calc-alkaline suite.The calc-alkaline lavas may be derived by crystal fractionation from a parental magma of andesitic nature that originated in or above the subjacent Benioff zone.     

Cretaceous volcanic-intrusive magmatism in western Guangdong and its geological significance

The Nanling Mountains lying in the southern part of South China are an economically important gran-ite-related multi-metallogenic province. The Nanling Mountains granites can be described as: temporally spanning from Caledonian to Yanshanian and spatially distributed as three EW trending zones: the north one in Zhuguangshan-Qingzhangshan, the middle one in Dadongshan-Guidong, and the south one in Fogang-Xinfengjiang with two neighboring zones’ midline having an interval of ca. latitude …     

Distribution of trace elements in spinel and garnet peridotites

The distribution of trace elements in the upper mantle has been discussed on the basis of the trace element abundances in bulk rocks and constituent minerals of two spinel and garnet facies peridotite xenoliths in alkali basalts from eastern China. The data presented are consistent with the suggestion that highly incompatible elements (Rb, Ba, Th, U, Sr, Nb, Ta) mainly reside in intergranular components, and to a lesser extent in fluid inclusions in minerals. The LILE composition in olivine and orthopyroxene can be seriously affected by the presence of fluid inclusions. Consequently the subsolidus partitioning of the LILE cannot be used to infer the olivine-melt and orthopyroxene-melt partition coefficients for these elements. There is a significant difference in (Opx/Cpx)_HREE ratios for spinel and garnet peridotites, suggesting a P-T control on equilibrium partition coefficients.     

Strontium isotope geochemistry of the Lemachang independent silver ore deposit, northeastern Yunnan, China

Sr isotope geochemical studies (the 87Sr/86Sr and ?18O-87Sr/86Sr systems) on the wall rocks and ores from the Lemachang independent Ag deposit in northeastern Yunnan provide strong evidence that the ore-forming fluids had flown through radiogenetically Sr-enriched rocks or strata prior to their entry into the locus of ore precipitation, and water-rock interaction is the main mechanism of Ag ore precipitation. The radiogenetically Sr-enriched source region may be the Proterozoic basement (the Kunyang and Hekou groups). Moreover, the theoretical modeling of the Sr isotopic system indicates that the ore-forming fluids contain as much as 3×10?6 Sr with isotopic composition of Sr being 0.750 and that of oxygen 7.0‰. The ore-forming temperatures were estimated at 150-250℃ for the carbonate rock-type ores and at 200-260℃ for the clastic rock-type.