Neoproterozoic I-type granites in the Central Tianshan Block (NW China):geochronology,geochemistry,and tectonic implications

The Central Tianshan Block is one of numerous microcontinental blocks within the Central Asian Orogenic Belt(CAOB)that overlies Precambrian basement rocks.Constraining the evolution of these ancient basement rocks is central to understanding the accretionary and collisional tectonics of the CAOB,and their place within the Rodinia supercontinent.However,to date,the timing and tectonic settings in which the basement rocks in the Central Tianshan Block formed are poorly constrained,with only sparse geochemical and geochronological data from granitic rocks within the northern segment of the block.Here,we present a systematic study combining U-Pb geochronology,whole-rock geochemistry,and the Sr-Nd isotopic compositions of newly-identified granitic gneisses from the Bingdaban area of Central Tianshan Block.The analyzed samples yield a weighted mean Neoproterozoic 206Pb/238U ages of 975-911 Ma.These weakly-peraluminous granitic rocks show a common geochemical I-type granite affinity.The granitic gneisses are calc-alkaline and enriched in large ion lithophile elements(LILEs)and light rare earth elements(LREEs),but they are depleted in high field strength elements(HFSEs);these characteristics are similar to those of typical subduction-related magmatism.All samples show initial(^(87)Sr/^(86)Sr)(t)ratios between 0.705136 and 0.706745.Values forεNd(t)in the granitic gneisses are in the range from-5.7 to-1.2,which correspond to Nd model ages of 2.0-1.7 Ga,indicating a role for Mesoproterozoic to Paleoproterozoic rocks in the generation of the granitic protoliths.The documented geochemical features indicate that the protoliths for the gneisses have a similar petrogenesis and magmatic source,which may reflect partial melting of thickened crust with the addition of small amounts of mantle-derived material.The Central Tianshan Block probably constitute part of an exterior orogen that developed along the margin of the Rodinian supercontinent during the Early Neoproterozoic and underwent a transition from subduction to syn-collision compression at 975-911 Ma.

An engineering classification system for the detached granite blocks distributed on slopes

Gentle slopes with large amounts of granite blocks are widespread in granitic areas with warm and humid climate.These blocks pose a potential risk to the existing and planned infrastructure.The instability type and geometry of these blocks will influence their motility and destructive power to some extent.This study aims at creating a classification system that can indicate both the shape and the instability type of these blocks and then developing a block removal scheme.The classification system was constructed based on the mechanical stability analysis of blocks on an inclined surface.This analysis identified key factors affecting stability,including block shape,block weathering roundness,the existing state of a block on a slope,and the friction between the block and the slope.The achieved work allowed the establishment of a direct correlation between block geometry and their instability types.The availability of this classification system was validated by field data and experimental data in the literature.The proposal to remove blocks identified as the toppling types,such as cylindrical-toppling types,cuboid-toppling types,cube-toppling types,was put forward to avoid the uneconomical problem of a complete clearance.Meanwhile,this classification provides a foundation for further research on the instability probability of each type of block and the development of a more refined blocks’removal scheme.The classification approach adopted in this paper can provide a reference for the classification of other lithological blocks under similar engineering geological conditions.

Two Types of Granites in the Western Yangtze Block and Their Implications for Regional Tectonic Evolution： Constraints from Geochemistry and Isotopic Data

In the western Yangtze Block, widespread Mesoproterozoic to Neoproterozoic rocks are the key to understanding the Precambrian tectonic-magmatic evolution of the region. However, their petrogenesis and tectonic setting are still controversial. In this paper, zircon U-Pb ages, Sm-Nd isotopic and whole-rock geochemical data are reported from selected fresh samples in the southern Dechang county, southwestern China, in order to constrain their emplacement age and magma source, as well as their petrogenesis and tectonic setting. They are mainly composed of biotite monzogranite, monzonitic granite, biotite granodiorites, and quartz diorite. Two ages of 1055 ± 43 Ma and 837.6 ± 3.8 Ma were obtained through zircon U-Pb dating by LA-ICP-MS and LA-MC-ICP-MS, respectively. According to their major element compositions, the Grenville-age granites are peraluminous calc-alkaline series calcic S-type granite. In contrast, the mid-Neoproterozoic granites are metaluminous calc-aikaline series alkalic I-type granite. Furthermore, the S-type granites are enriched in LREEs relative to HREEs with （La/Yb）N ratios of 3.85-18.56 and underwent major fractionation with strongly negative Eu anomalies （Eu/Eu＊ = 0.38-0.66）. In the MORB-normalized trace element variation diagram, all the samples are enriched in Ce and large ion lithophile elements such as Rb, Th, and K, and depleted in high field strength elements such as Nb, and Ti, with negative Sr and Ti anomalies. The I-type granites are enriched in LREEs with slight negative Eu anomalies （Eu/Eu＊= 0.83-0.93）. They are characterized by the enrichment of highly incompatible elements （such as K, Rb, Ba, Th） and LREEs, relative to MORB. Neodymium isotopic data show that the S-type granites display 143Nd/144Nd values of 0.51241-0.51256, and have eNa （t = 1055 Ma） values of （-3.29） to （-3.81）. Calculated tDM ages yield values from 1.87 to 1.91 Ga with the tDM.2stg ages of 1.86 to 1.9 Ga. The I-type granites have 143Nd/144Nd ratios between 0.51192 and 0.51195, corresponding to initial eNd （t = 837 Ma） values of 1.22 to 5.63. Calculated tDM ages yield values from 1.0 to 1.38 Ga and the tDM.2stg ages yield values from 0.99 to 1.06 Ga. The S-type granites are distinguished as syn-collision granite, whereas the I-type granites were formed as arc magmas according to the Rb-（Yb＋Ta） and R1-R2 tectonic discrimination diagrams. To conclude, there are two types of spatially associated granite, the Mesoproterozoic S-type granite which were derived from re- melting of upper crustal mudstone and/or clastics and resulted from the convergence of two continental plates, and the mid-Neoproterozoic I-type granite which formed in continental arc and resulted from mantle-derived magma mixed crust material, in the western Yangtze Block. Furthermore, we suggest that collision between the Yangtze and Cathaysia blocks occurred at about 1055 Ma, and caused the S- type granite. The I-type granite related to the subduction of oceanic lithosphere eastward underneath the Yangtze Block in the mid-Neoproterozoic.

Petrogenesis of the Early Cretaceous Tiantangshan A-type Granite in northwestern Guangdong province, SE China and tectonic implications

1 Introduction During the late Mesozoic times,the SE China is characterized by extensive magmatism and mineralization.The widely distributed granitoids with different(I-,S-and A-)types have been inferred to be closely related to the large-scale polymetallic mineralization.The Nanling tungsten-tin polymetallic belt is endowed with considerable

U-Pb zircon geochronology, geochemistry and kinetics of the Huaniushan A-type granite in Northwest China

The Huaniushan granite is located at the Beishan orogenic belt, northwestern China. At the contact zone between the granite and marble, a hydrothermal Pb-Zn and skarn Au deposit is formed. LA-ICP-MS zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 229.5±2.6 Ma (MSDW=0.93) for the Huaniushan granite, imply-ing its Late Triassic intrusion. Geochemistry analyses show that the Huaniushan granite is enriched in Si, K, Na, and REE, and depleted in Mg and Ca, with contents of SiO2 (70.8% to 74.4%), Na2O+K2O (8.8% to 10.2%), CaO (0.93% to 1.44%), and MgO (0.14% to 0.48%). REE is characterized by obvious negative Eu anomaly. Rb, Th, U, K, Pb, Nb, Zr and Hf elements are rich in the granite while Ba, Sr, P, Ti and Eu are deplete. The granite has a high (Zr+Nb+Ce+Y) abundance and 104 Ga/Al ratios. Petrology, major and trace elements data all indicate that the Hua-niushan granite is A-type granite which intruded in a post-collisional extensional tectonic setting. The magma was dominantly sourced from partial melting of crustal intermediate-felsic igneous rocks. Intensive magmatic activities and Au-Cu-Mo mineralization occurred throughout the Beishan orogenic belt during the period from ca. 240 to 220 Ma.

Two A-type Syenite-Granite Belts in Anhui

There ekist two parallel A-type syenitegranite belts on both banks of the Yangtze River inAnhui Province : one is the Dalongshan- Chengshan- Huangmeijian belt on the north bank and theother is the Huayuangong- Maotan- manshiling belt on the south bank. Both of them consist ofsyenite, quartz-syenite and alkali feldspar granite, which were formed at about 125 Ma ago and areenriched in alkalies and high-field-strength elements but depleted in water, with the total alkali ac-counting for 9- 12%, and H2O+ only for 0.50%’ The Ga x 10-4/Al raho is as high as 2.7 to 3.8for granite. They were formed in the extension stage of ancient riffing. So they are considered to bethe A-type Syenite-granite belts. Granites in the two belts resulted from a syedte magma by an AFCmechanism While the magma was derived from alkali basalt magma through thefractio nal-crystallization-dominated AFC mechanism.

Petrogenesis of I-type granites from Yuqikapa granite pluton of the western Kunlun orogen: Deformation-driven filter-pressing differentiation

1 Introduction The western Kunlun orogen,located in the northwest Tibet Plateau,and is a conjunction between the Pan-Asian and the Tethys tectonic domains.From north to south,the Western Kunlun orogen includes four

Petrogenesis of Late Cretaceous Jiangla＇angzong I-Type Granite in Central Lhasa Terrane, Tibet, China： Constraints from Whole-Rock Geochemistry, Zircon U-Pb Geochronology, and Sr-Nd-Pb-Hf Isotopes

The Jiangla＇angzong granite in the northern part of the Central Lhasa Terrane is composed of syenogranite and adamellite. LA-ICP-MS zircon U-Pb analyses suggest that syenogranite has a weighted mean 2±6pb/23SU age of 86±1 Ma （mean square weighted deviation=0.37）, which is in accordance with the muscovite Ar-Ar age （85±1 Ma） of Cu-Au ore-bearing skarns and the zircon U-Pb age （84±1 Ma） of adamellite. This suggests that the Jiangla＇angzong magmatism and Cu-Au mineralization events took place during the Late Cretaceous. The granite contains hornblende, biotite, and pyroxene, and does not contain Al-bearing minerals, such as muscovite, cordierite, and garnet. It has high contents of SiO2 （65.10 -70.91wt%）, K20 （3.44-5.17wt%）, and total K20＋Na20 （7.13-8.15wt%）, and moderate contents of A12Oa （14.14-16.45wt%） and CaO （2.33-4.11wt%）, with a Reitman index （δ43） of 2.18 to 2.33, and A/ CNK values of 0.88 to 1.02. The P205 contents show a negative correlation with SiO2, whereas Pb contents show a positive correlation with SiO2. Th and Y contents are relatively low and show a negative correlation with the Rb contents. These characteristics suggest that the Jiangla＇angzong granite is a high K calc-alkaline metaluminous I-type granite. It is enriched in light rare earth elements （LREE） and large ion lithofile elements （LILE）, and depleted in heavy rare earth elements （HREE） and high field strength elements （HFSE）, with LREE/HREE ratios of 11.7 to 18.1. The granite has negative Eu anomalies of 0.58 to 0.94 without obvious Ce anomalies （δCe=l.00-1.04）. The relatively low initial a7Sr/a6Sr ratios of 0.7106 to 0.7179, positive ε±nt（t） values of 1.0 to 4.1, and two-stage Hf model ages （TDM2） ranging from 889 Ma to 1082 Ma, These geochemical features indicate that the granite derived from a juvenile crust. The （143Nd/144Nd）t values from the Jiangla＇angzong granite range from 0.5121 to 0.5123, its eNd（t） values range from -10.17 to -6.10, its （^206pb /^204pb）t values range from 18.683 to 18.746, its （^207pb /^204pb）t values range from 15.695 to 15.700, and its （^208pb /^204pb）t values range from 39.012 to 39.071. These data indicate that the granite was formed by melting of the upper crust with the addition of some mantle materials. We propose that the Jiangla＇angzong granite was formed during the post- collision extension of the Qiangtang and Lhasa terranes.

Geochronological and Geochemical Constrains on Petrogenesis of the Jietebutiao A-type Granite in West Junggar,Xinjiang

Late Paleozoic post-collisional granitoids are widespread in West Junggar, as well as northern Xinjiang. As a representative of those intrusions, the Jietebutiao granite occurs in the southwestern margin of the West Junggar （northwest China）, and is mainly composed of mid-coarse- grained monzogranite and syenogranite. In the present study, we report the results of high-precision zircon laser-ablation-inductively-coupled plasma mass-spectrometry U-Pb dating on the Jietebutiao granite for the first time, and yield weighted mean 2~~pb/23SU ages of 287 ＋ 9 Ma and 278 ~ 3 Ma for monzogranite and syenogranite, respectively. The Jietebutiao granite has a pronounced A-type affinity; it is metaluminous to slightly peraluminous; has a high-K calc-alkaline composition; high concentrations of Na20 ＋ I（20, varying from 6.8 to 8.5 wt%; high FeOt/MgO; 10 000Ga/AI ratios, a low CaO, MgO, and TiO2 content; enriched in some large ion lithophile elements （LILE, such as Rb and Th） and high field strength elements （HFSE, such as Zr, Hf, and Y）; and depleted in Sr, Ba, and Ti. In addition, the granite has a relatively high rare earth element （REE） content （except for Eu）, with significant negative Eu anomalies （Eu/Eu＊ = 0.01-0.72）, and showing slight tetrad REE patterns and non-charge and radius controlled （CHARAC） trace element behavior. Petrographic, geochemical, and geochronological data suggest that the parental magma of Jietebutiao intrusions are of mixed origin, and are most probably formed by the interaction between the lower crust- and mantle-derived magmas in the Early Permian post-collisional tectonic setting. The basaltic magmas underplated and interacted with the lower crust that was dominated by deeply buried arc （and back-arc basin） series and the oceanic crust formed in the Paleozoic, and then triggered the partial melting of the juvenile lower crust, producing voluminous granitic melts and forming the Jietebutiao A2-type monzogranites, with the lithospheric mantle progressively thinning and rifting to form Al-type granites, such as syenogranites, in the Jietebutiao pluton. This further proves the important contribution of Late Paleozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.

Age and geochemistry of Early Ordovician A-type granites in the Northeastern Songnen Block,NE China

Early Ordovician A-type granites in the northeastern(NE) Songnen Block NE China were studied to better understand the geodynamic settings in this region.This research presents new zircon U–Pb ages and wholerock geochemical data for the Early Ordovician granites in the NE Songnen Block. Zircon U–Pb dating indicates that the granite in the Cuibei, Hongxing, and Meixi areas in the NE Songnen Block formed in the Early Ordovician with ages of 471–479 Ma. The granites show geochemical characteristics of high SiO2 and K2 O compositions and low FeOT, MgO, CaO, and P2 O5 compositions. They belong to a high K calc-alkaline series and display a weak peraluminous featurPe with A/CNK values of 0.98–1.14. The rocks have aREE composition of 249.98–423.94 ppm,and are enriched in LREE with(La/Yb)Nvalues of2.87–9.87, and display obvious Eu anomalies(d Eu =0.01–0.29). Trace elements of the studied granites are characterized by enrichment in Rb, Th, U, Pb, Hf, and Sm,and depletion of Ba, Nb, Ta, and Sr. They display geochemical features of high Zr +Y + Nb+Ce values(324–795 ppm) and Ga/Al ratios consistent with A-type granites. Based on particular geochemical features, such as high Rb/Nb(7.98–24.19) and Y/Nb(1.07–3.43), the studied A-type granites can be further classified as an A2-type subgroup. This research indicates that the Early Ordovician A-type granites were formed by the partial melting of ancient crust in an extensional setting. Lower Sr/Y and(Ho/Yb)Nratios indicate that plagioclase and amphibole are residual in the source, and garnet is absent, implying that the magma was generated at low levels of pressure. By contrast, the contemporaneous granites in the SE Xing'an Block suggest a subduction-related tectonic setting, and its adakitic property indicates a thickened continental crust.We suggest that the Paleo-Asian Ocean plate between the Xing'an and Songnen blocks subducted northward during the Early Ordovician. Meanwhile, the NE Songnen Block was exposed to a passive continental margin tectonic setting.

Confirmation and Preliminary Study of Aluminous A-Type Granites in the Wuyi Mountain Area, Eastern Jiangxi Province, China

Widespread in the Wuyi Mountain area of eastern Jiangxi are petrochemically peraluminous granites and they are characterized as being high in silica (SiO\-2>75%) and highly alkaline (ALK=6.9%-7.5%) with K\-2O>Na\-2O and rather high ratios of FeO\+T/MgO (11.3-17.9). The rocks have low contents of CaO, MgO, TiO\-2 and P\-2O\-5 . The granites are enriched in REE (ΣREE=210.3-496.8 μg/g) with remarkable negative Eu anomalies, but depleted in Eu, Ba, Sr, V, Co, and Ni, with 10000×Ga/Al ratios, varying from 6.1 to 9.8. It is clear that these granites are obviously different from the I\| and S\|type granites, but are quite similar to those typical A\|type granites such as aluminous A\|type granites in the coastal areas of Fujian Province.

Chronology and Genesis of S-type Granites in Hetai District, Guangdong Province: Constraints from LA-ICP-MS Zircon U-Pb Dating and Tourmaline Boron Isotope In-situ Analyses

1 Introduction Hetai district,which is a mountainous area,situated on Guangning and Zhaoqing city,west Guangdong Province.Hetai district is generally located on southwest of South China Caledonian fold belt,east margin of Yunkai post-Caledonian uplift.Multiple type granites are widely distributed in Hetai district,including Caledonian,Indosinian and Yanshanian granites.Based on different

An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen,central China:Petrological,mineralogical and geochemical constraints

The Erlangmiao granite intrusion is located in the eastern part of the East Qinling Orogen. The granite contains almost 99 vol.% felsic minerals with accessory garnet, muscovite, biotite, zircon, and Fe-Ti oxide. Garnet is the dominant accessory mineral, shows zoned texture, and is rich in w（FeO） （14.13%--16.09%） and w（MnO） （24.21%--27.44%）. The rocks have high SiO2, alkalis, FeOt/ MgO, TiO2/MgO and low A1203, CaO with w（Na2O）/w（K20）〉 ]. Their Rb, Ga, Ta, Nb, Y, and Yb contents are high and Sr, Ba, Eu, Zr, P, and Ti contents are low. These features indicate that the Erlang- miao granite is a highly evolved metaluminous A-type. Garnet crystallized at the expense of biotite from the MnO-rich evolved melt after fractionation of biotite, plagioclase, K-feldspar, zircon, apatite, and ilmenite. The relatively high initial 878r/S6Sr ratios （0.706--0.708）, low and negative εNd （120 Ma） values （-6.6 to -9.0）, and old Nd model ages （1.5--1.7 Ga） suggest that the rocks were probably formed by partial melting of the Paleoproterozoic granitic gneisses from the basement, with participation of depleted mantle in an extensional setting.

Early Cretaceous I-type granites in the Tengchong terrane:New constraints on the late Mesozoic tectonic evolution of southwestern China

The Early Cretaceous granitoids that are widespread in the Tengchong terrane of Southwest China play a critical role in understanding the tectonic framework associated with the Tethyan oceans. In this study, we present a detailed description of zircon U-Pb ages, whole-rock geochemistry and Hf isotopes for the Laoxiangkeng pluton in the eastern Tengchong terrane and elucidate their petrogenesis and geodynamic implications. Zircon U-Pb dating of the Laoxiangkeng pluton yields ages of 114 ± 1 Ma and 115 ± 1 Ma,which imply an Early Cretaceous magmatic event. The Laoxiangkeng pluton enriched in Si and Na, is calcalkaline and metaluminous, and has the characteristics of highly fractionated I-type granites. Zircons from the pluton have calculated ε_(Hf)(t) values of-12.7 to-3.7 and two-stage model ages of 1327-1974 Ma,respectively, indicating a mixed source of partial melting of Paleo-Neoproterozoic crust-derived compositions with some inputs of mantle-derived magmas. By integrating all available data for the regional tectonic evolution of the eastern Tethys tectonic domain, we conclude that the Early Cretaceous magmatism in the Tengchong terrane was produced by the northeastward subduction of the Meso-Tethyan Bangong-Nujiang Ocean.

Origin of trondhjemite and albitite at the expense of A-type granite,Aravalli orogen, India:Evidence from new metasomatic replacement fronts

The A-type Harsora-Dadikar granites in the Alwar complex of northern Aravalli orogen,NW India provide evidence for subsolidus-requilibration of feldspars.They record three new discrete stages of albitisation,producing trondhjemite and albitite sequentially at the expense of original granite.Stage-I metasomatism deanorthised the magmatic oligoclase and transformed the grey least-albitised granite to pinkish grey microcline-oligoclase granite.Stage-II converted the latter to trondhjemite by replacement of microcline to oligoclase.Stage-III metasomatism led to the formation of albitite/albite granite from trondhjemite,where the metasomatically formed oligoclase was replaced by albite.This stage of metasomatism resulted in nearly complete disappearance of amphibole and biotite,producing a monomineralic rock (albitite),which is consistent with Korzhinskii theory of infiltration metasomatism.The reaction fronts delineating the Stage-II and Stage-III are sharp and easily discernible by their prominent color differences in Harsora on the outcrop scale.Chemically,the mineral transformations during three stages are manifested by the differential gains/losses in Na,K,Ca,Rb,Ba,Sr,Fe and Mg.The formation of albite,Cl-rich marialitic scapolite and Cl-rich amphibole in the albitised granites are suggestive of Naand Cl-brines as the metasomatising fluids.The fluid-rock interactions,which can significantly transform the pristine mineralogy of granitoids,should be carefully considered to avoid any misinterpretations about their petrological history.

Mineralogy,M-type tetrad effect and radioactivity of altered granites at the G.Abu Garadi shear zone,central Eastern Desert,Egypt

The G. Abu Garadi area is covered mainly by metasediments, alkali feldspar granites and stream sediments. The alkali feldspar granite is traversed by a major strike-slip fault trending in an N-S direction as well as two subordinate sets of faults trending NW to WNW for the first one and NE for the second one. These faults represent the shear zones affected by magmatic (syngenetic) as well as hydrothermal (epigenetic) activities causing alteration of the granitic rocks. The most common alteration features are albitization, greisenization and koalinitization. The mass balance calculations of the studied altered samples show enrichments in Zr, Y, Ni, U, Th and Ga and depletions in Zn, Sr, Nb, Ba, Pb, Cu and V. Only the greisenized samples exhibit a significant enrichment in Nb, ∑REE budget and pronounced lanthanide tetrad effect (M-type), especially TE1,4, while weakly expressed tetrad effects are for the other albitized and koalinitized samples. Mineralogically, the common accessory minerals in the altered samples include samarskite-(Y), betafite, uranothorite, zircon, fluorite and cassiterite. The greisenized granites contain high eU and eTh than the other altered types, where they are characterized by an assemblage of the radioactive minerals; samarskite-(Y), betafite, uranothorite in addition to zircon. The inter-element relationships between U and Th and also their ratios illustrate that the radioelement distribution in these granites is mainly governed by magmatic processes, in addition to post-magmatic ones. The distribution of chemical elements and the fractionation of some isovalents within the shear zone are largely controlled by the newly formed mineral phases. With respect to uranium mobilization, uranium migrated from the host alkali feldspar granites of G. Abu Garadi, while the shear zones acted as traps for the migrated uranium. Moreover, U migrated in the shear zone during greisenization and albitization, and migrated out during koalinitization.

Petrogenesis and Mineralization of Two-Stage A-Type Granites in Jiuyishan,South China:Constraints from Whole-rock Geochemistry, Mineral Composition and Zircon U-Pb-Hf Isotopes

The Jiuyishan complex massif,located in the northern section of the Nanling region,is a combination of five plutons,namely,the Xuehuading,Jinjiling,Pangxiemu,Shaziling and Xishan plutons.Whole-rock geochemistry,Imineral electron microprobe analysis,zircon U-Pb dating and Hf isotope analysis were carried out for the Jinjiling and Pangxiemu plutons.The zircon U-Pb dating yields weighted mean ages of 152.9±0.9 Ma for the Jinjiling pluton and 151.7±1.5 Ma for the Pangxiemu pluton,with a narrow gap between them.The Jinjiling and Pangxiemu plutons both have geochemical characteristics of high SiO2,Al2 O3,Na2 O,K2 O and low TiO2,MgO,CaO,P2 O5 contents,with intense depletions in Sr,Ba,Ti,Eu and enrichments in Ga,FeoOT and HFSE,and these characteristics reflect an A-type affinity.From the Jinjiling to the Pangxiemu plutons,the mineral composition of mica changes from lepidomelane to zinnwaldite,with increases in F,Li2 O and Rb2 O contents.The mineral composition of zircon changes from low Zr/Hf to high Zr/Hf,with increasing HfO2,P2 O5 and UO2+ThO2+Y2 O3 contents.The mineral compositions of feldspar indicate that the Pangxiemu pluton contains more alkali feldspar than the Jinjiling pluton.The whole-rock geochemistry and mineral compositions reveal a higher degree of differentiation for the Pangxiemu pluton.The nearly uniformεHf(t)indicates the same source region for the two plutons:both were derived from partial melting of the lower crust,with small contributions of mantle materials.In addition,higher F,lower Nb/Ta and Zr/Hf ratios in the Pangxiemu Pluton suggest a closer relationship with the rare metal mineralization than for the Jinjiling pluton.

Geochronology and Geochemistry of the Early Permian A-Type Granite in the Hongol Area, Central Inner Mongolia:Petrogenesis and Tectonic Implications

We performed geochronological and geochemical analyses of the A-type granite in the Hongol area, central Inner Mongolia, to determine its age, petrogenesis and tectonic setting, which are significant for clarifying the Late Paleozoic tectonic evolution of the Xing’an Mongolian Orogenic Belt(XMOB). The rock type of the A-type granite in the Hongol area is alkali-feldspar granite, and it constitutes a western part of the Baiyinwula-Dongujimqin A-type granite belt. Zircon U-Pb geochronology yieldsPb/U ages ranging from 293 to 286 Ma for the alkali-feldspar granite, indicating this granitic pluton formed in the Early Permian. The alkali-feldspar granite is high in silica(SiO=75.13 wt%-80.17 wt%), aluminum(AlO=10.59 wt%-13.17 wt%) and alkali(NaO+KO=7.33 wt%-9.11 wt%), and low in MgO(0.08 wt%-0.39 wt%) and CaO(0.19 wt%-0.70 wt%). It is obviously enriched in LILEs such as Rb, Th and K,depleted in HFSEs such as Nb, Ti, La and Ce, with pronounced negative anomalies of Nb, Ti, P, Eu, Sr and Ba. Its Sr-Nd-Pb isotopic compositions show positive ε(t)(+0.72-+3.08), low T(805-997 Ma),and high radioactive Pb with(Pb/Pb)of 18.710-19.304,(Pb/Pb)of 15.557-15.604 and(Pb/Pb)of 37.887-38.330. Petrological characteristics and geochemical data suggest that the alkalifeldspar granite in the Hongol area belongs to aluminous A-type granite. This A-type granite formed in a post-collisional extensional setting and was generated by the partial melting of felsic rocks in the middlelower crust resulting from post-collisional slab breakoff. It is suggested that the Paleo-Asian Ocean was closed before the Permian in central Inner Mongolia.

The Late Triassic I-Type Granites from the Longmu Co-Shuanghu Suture Zone in the interior of Tibetan Plateau, China： Petrogenesis and Implication for Slab Break-Off

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between POand SiO, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO, MgO, FeOt, MnO, CaO) and SiO. Almost all ε(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low NaO/KO ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.

Characterization of a Post Orogenic A-Type Granite, Gabal El Atawi, Central Eastern Desert, Egypt: Geochemical and Radioactive Perspectives

The alkali feldspar granite of Gabal El Atawi is post orogenic granite originated from subalkaline magma in extensional suite. It is developed within plate tectonic setting and has A2-type character which generated from apparent crustal source. The petrographic, geochemical and radioactive characteristics of El Atawi granite meet and fulfill the requirements of being fertile granite and it can be considered as promising uraniferous granite. Fluid inclusion studies of the altered granite elucidated two different solutions acting on the host granitic pluton. The first is NaCl-CaCl low temperature fluid with a wide range of salinity. The second is high temperature and salinity Fe-Mg-Na chloride solution. Different fractures in the granite acted as good channels for the hydrothermal fluids that leached uranium from its bearing minerals disseminated all over the host granite and redeposited it in the alteration zones.