Metallogenic Series Related to Permian Mafic Complex in North Xinjiang:Post-collisional Stage or Mantle Plume Result?

There are four deposit types related to a Permian mafic complex in northern Xinjiang, i.e., copper-nickel sulfide deposit, vanadic titanomagnetite deposit, magnetite （-cobalt） deposit and Cu-Ni- VTiFe composite deposit. The deposits are distributed spanning tectonic units with close and consecutive metallogenic ages. A transitional deposit type can occur among the end-member deposits. Trace elements of host rocks show that they can derive from similar source area. Hence, they constitute a particular metallogenic series related to a mafic-ultramafic complex that is also a symbol series of the post-collisional stage of the Central Asia Metallogenic Province （CAMP）. The metallogenic ages of the series are between 260 Ma and 300 Ma throughout the Permian. Unlike mineralization from a mantle plume, the metallogenic period of this series spans at least 40 Ma. Compared with related deposits of the Emeishan mantle plume, the North Xinjiang series has a similar ore-forming element assemblage but has preferably developed Cu-Ni sulfide deposits rather than vanadic titanomagnetite deposits. In concomitance with this series, North Xinjiang area has developed a set of syntectonic Au-Cu-Mo metallogenic series related to a felsic volcanic-intrusive complex, which might indicate that there is no direct relationship with mantle plume activity. From early to late, i.e., the sequence of copper-nickel sulfide to magnetite （-cobalt） to vanadic titanomagnetite deposit, the host rock series evolves from mafic-ultramafic and tholeiite series to mafic and alkalic series, the ~REE content tends to increase with increasing of REE fractionation, and some of the trace elements （particularly LIL） also show an increasing tendency. The above evolutionary regularity possibly reflects a course where the magma source deepens and thermal interface moves down, energy gradually exhausts, and neo-continental crust forming in the postcollision stage tends to stabilize.

Petrogenesis of the Late Triassic shoshonitic Shadegai pluton from the northern North China Craton: Implications for crust-mantle interaction and post-collisional extension

Latest Permian to Triassic plutons are widespread in the northern North China Craton(NCC); most of them show calc-alkaline, high-K calc-alkaline, or alkaline geochemical features. The Shadegai pluton in the Wulashan area has shoshonitic affinity and I-type character, and is composed of syenogranites containing abundant mafic microgranular enclaves(MMEs). LA-MC-ICP-MS U-Pb data yield weighted mean 206 Pb/238 U ages of 222 ± 1 Ma and 221 ± 1 Ma for the syenogranites and MMEs, respectively, suggesting their coeval formation during the Late Triassic. The syenogranites have high SiO_2(70.42-72.30 wt%),K_2O(4.58-5.22 wt.%) and Na_2O(4.19-4.43 wt.%) contents but lower concentrations of P_2O_5(0.073-0.096 wt.%) and TiO_2(0.27-0.37 wt.%), and are categorized as I-type granites, rather than A-type granites, as previously thought. These syenogranites exhibit lower(^(87)Sr/^(86)Sr)i ratios(0.70532-0.70547) and strongly negative whole-rock εNd(t) values(-12.54 to-11.86) and zircon εHf(t) values(-17.81 to-10.77),as well as old Nd(1962-2017 Ma) and Hf(2023-2092 Ma) model ages, indicating that they were derived from the lower crust.Field and petrological observations reveal that the MMEs within the pluton probably represent magmatic globules commingled with their host magmas. Geochemically, these MMEs have low SiO_2(53.46-55.91 wt.%)but high FeOt(7.27-8.79 wt.%) contents. They are enriched in light rare earth elements(LREEs) and large ion lithophile elements(LILEs), and are depleted in heavy rare earth elements(HREEs) and high field strength elements(HFSEs). They have whole-rock(^(87)Sr/^(86)Sr)i ratios varying from 0.70551 to 0.70564, εNd(t) values of -10.63 to -9.82, and zircon εHf(t) values of -9.89 to 0.19. Their geochemical and isotopic features indicate that they were derived from the subcontinental lithospheric mantle mainly metasomatized by slab-derived fluids, with minor involvement of melts generated from the ascending asthenospheric mantle. Petrology integrated with elemental and isotopic geochemistry suggest that the Shadegai pluton was produced by crust-mantle interactions, i.e., partial melting of the lower continental crust induced by underplating of mantle-derived mafic magmas(including the subcontinental lithospheric mantle and asthenospheric mantle), and subsequent mixing of the mantle-and crust-derived magmas. In combination with existing geological data, it is inferred that the Shadegai pluton formed in a post-collisional extensional regime related to lithospheric delamination following the collision between the NCC and Mongolia arc terranes.

Geodynamic Development of Eurasian Active Margin during Closing of Thetys Ocean, Depending on the Scale of Mantle-Crustal Sources Influence at Pre- and Post-collision Settings, Controlled by Geological and Geochemical Indicators

Phanerozoic geodynamic evolution development of Tethys Ocean,its collision and closing,revealed at the Eurasian active margin in pre-and post-collision stages during convergence of Afro-Arabian and Eurasian continents.Subduction of oceanic slab under continental margin revealed in steady state subduction and steepening of subducting slab provoked the incursion of mantle diapir.The steady state subduction is related with island arc setting whereas steepening provoked incursion of mantle diaper interarc-backarc and minor ocean settings.They are controlled by geological indicators—volcagenic,petrochemical,geochemical,tectonic and metallogenic.Each of them is determined by scale of mantle-crustal influence,controlled by intensity and level of mantle diapir incursion in the crust rising from interarc-backarc to minor oceanic setting.The island arc setting is characterized by blocking,which as others by extension of rifting(interarc-backarc)caused spreading out from zone of volcanic activity and mineralization sialic crusts,whereas minor ocean setting caused by spreading out from zone of volcanic activity and mineralization sialic and basaltic crusts.So mantle crustal influence rising from island arc to minor ocean settings controlled type of volcanism and mineralization in pre-collision development.At the closing of ocean occurred the precollision setting which is transferred in post-collision revealed in orogenesis.It is divided in two stages.The first initial stage occurred in penetration hot fluids from the mantle in sialic crust smelted from in granitoid melt and leached the gold and trace melts Sb,W,Mg and Hg from sialic crust.The latter are geochemical indicators of post-collision setting.The second final stage revealed in shoshonite-basalt volcanism activity occurred with penetrated mantle material into deep volcanic chambers and characterized with increasing of mantle influence than initial stage of post-collision activity.

Geochemistry and Sr,Nd Istopes of Granitoids from the Lac Ifni Area(Sirwa Massif-Anti-Atlas Morocco):A Geodynamic Setting for the Post-collisional Ediacaran Magmatic Chain of the Anti-Atlas

The plutonic rocks of the westernmost part of the Sirwa massif belong to the Ediacaran post-collisional magmatic chain of the Anti-Atlas.The geochemistry of major and trace elements attests that the fractional crystallization cannot account for the variations between the granitoids and the associated MME.They represent two contemporaneous but independent magmatic tendencies.However,Sr and Nd configur data argue for a similar and juvenile material

Geodynamic Development of Eurasian Active Margin at Pre-collision Subduction and at Post-collision Closing of Tethys Ocean

Geodynamic development of Eurasian Active Margin is related to Phanerozoic collision and closure of Tethys Ocean coincided with northvergent movement and stressing of Afro-Arabian continent at the Eurasian margin.The collision coincided with subduction oceanic Slab under margin of continent at pre-collision stage revealed in formation of island arc,inter-arc backarc and minor ocean settings at pre-collision stage.After closure of ocean the subduction is terminated and pre-collision stage transferred in post-collision and orogenesis,caused by stressing Afro-Arabian continent at the Eurasian.Character of subduction determined the settings of pre-collision stage.The island arc setting is related with steady state subduction,interarc-backarc and minor ocean settings are controlled by steepening of subducting slab which caused invasion of mantle diapir extension and spreading the crust revealed in rifting in interarc-backarc and intensive spreading in minor ocean setting,whereas at island arc setting the mantle invasion and spreading did not occur.So,scale of mantle material participation in various settings determined character of volcanism and tectonics.The island arcs are characterized by calc-alkaline rhyo-dacite-andesite-basalt volcanism blocking tectonics,revealed in island uplifting and gold-base metal mineralization.The interarc-backarc settings revealed in tholeiite-olivine basaltic volcanism,rifting and Zn-Cu mineralization the minor ocean setting controlled by ophiolite volcanism ultimatic dunite-peridotite-magmatism and the most intensive spreading of lithosphere and copper-pyrite mineralization confirmed by volcano-petrogenic,metallogenic and tectonic indications and geochemical cryteria.Therefore,type of volcanism,magmatism and mineralization at precollision development are controlled by scale and influence of crustal-mantle participation.The post-collision stage of geodynamic development also is characterized by various scales of crustal mantle influence.Our studied region consists of pre-and post-collision stages,located in Iran,Caucasus,Turkey and Balcan-Carpathian is parth of the Eurasian active margin.At post-collision,as at pre-collision stages the volcanic-magmatic activity,tectonics and mineralization are depended on the crustial-mantle scale of influence and are controlled by volcano-petrogenic,metallogenic,as well as,tectonical and geochemical indicators.

Mafic and felsic magmatism in the Wadi Kalalat area, South Eastern Desert, Egypt: mineralogy, geochemistry and geodynamic evolution during the Neoproterozoic in the Nubian Shield

In the south Eastern Desert of Egypt,two contrasting types of magmatism(mafic and felsic) are recorded in the Wadi Kalalat area,and form the Gabal El Motaghiarat and Gabal Batuga intrusions,respectively.The two intrusions post-dates ophiolitic and arc associations represented by serpentinite and metagabbro-diorite,respectively.The mafic intrusion has a basal ultramafic member represented by fresh peridotite,which is followed upward by olivine gabbro and anorthositic or leucogabbro.This mafic intrusion pertains to the Alaskan-type mafic-ultramafic intrusions in the Arabian-Nubian Shield(ANS)being of tholeiitic nature and emplaced in a typical arc setting.On the other hand,the Gabal Batuga intrusion comprises three varieties of fresh A-type granites of high K-calc alkaline nature,which is peraluminous and garnetbearing in parts.A narrow thermal aureole in the olivine gabbro of the mafic intrusion was developed due to the intrusion of the Batuga granites.This results in the development of a hornfelsic melagabbro variety in which the composition changed from tholeiitic to a calc-alkaline composition due to the addition of S_(i)O_(2),Al_(2)O_(3),alkalis,lithosphile elements(LILEs) such as Rb(70 ppm) and Y(28 ppm) from the felsic intrusion.Outside the thermal aureole,Rb amounts 2-8 ppm and Y lies in the range <2-6ppm.It is believed that the Gabal Batuga felsic intrusion started to emplace during the waning stage of an arc system,with transition from the pre-collisional(i.e.,arc setting) to post-collisional and within plate settings.Magma from which the Gabal Batuga granites were fractionated is high-K calc-alkaline giving rise to a typical post-collisional A-type granite(A_(2)-subtype) indicating an origin from an underplating crustal source.Accordingly,it is stressed here that the younger granites in the ANS are not exclusively post-collisional and within-plate but most likely they started to develop before closure of the arc system.The possible source(s) of mafic magmas that resulted in the formation of the two intrusions are discussed.Mineralogical and geochemical data of the post-intrusion dykes(mafic and felsic) suggest typical active continental rift/within-plate settings.

Post-collisional magmatism in Wuyu basin,central Tibet:evidence for recycling of subducted Tethyan oceanic crust

The trachyte and basaltic trachyte and intruded granite-porphyry of Gazacun formation of Wuyu Group in central Tibet are Neogene shoshonitic rocks. They are rich in LREE, with a weak to significant Eu negative anomalies. The enriched Rb, Th, U, K, negative HFS elements Nb, Ta, Ti and P, and Sr, Nd and Pb isotope geochemistry suggest that the volcanic rocks of Wuyu Group originated from the partial melting of lower crust of the Gangdese belt, with the involvement of the Tethyan oceanic crust. It implies that the north-subducted Tethys ocean crust have arrived to the lower crust of Gangdese belt and recycled in the Neogene magmatism.

SHRIMP U-Pb Zircon Age of the Ka'erjiao Intrusion in the Sawur Region in West Junggar,Xinjiang

Acid intrusions are widespread in the Sawur region, Xinjiang. The Ka＇erjiao intrusion is mainly composed of albite granite porphyry, K-feldspar granite porphyry, ivernlte and granite porphyry. Being a transitional product between magma intrusion and eruption in the Sawur region, the Ka＇erjiao intrusion was formed at the telophase of the late Carboniferous to the begining of early Permian as determined by the SHRIMP U-Pb zircon dating, with an age of 302.6±7.6 Ma （1 σ）. The intrusion consists of alkali-enriched rock, whose REE distribution patterns are of the LREE enrichment type, the δEu value is low and Nd, St, Pb isotopes reflect its mantle source characteristics. The δ^18O value of intrusion is low as a result of isotope exchange with meteoric water. The geochemical characteristics show that it was formed in a post-collisional tectonic setting. Taking combined considerations of current studies of A-type granites and Permian volcanic rocks, we think that in the telophase of the late Carboniferous to the beginning of the early Permian, the Sawur region was within the extension or compressional to extensional period of a post-collisionai stage. The Ka＇erjiao intrusion from mantle sources can confirm the vertical continental crust growth in the late Paleozoic. The Sawur region in west Junggar is consistent with east Junggar in post-collisionai tectonic evolution process.

Geodynamic Background of Intracontinental Cenozoic Alkaline Volcanic Rocks in Laojiezi, Western Yangtze Craton: Constraints from Sr-Nd-Hf-O Isotopes

The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.

Evolution of the Mesozoic Granites in the Xiong'ershan-Waifangshan Region,Western Henan Province,China,and Its Tectonic Implications

Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong＇ershan-Waifangshan region in western Henan Province： high-Ba-Sr I-type granite emplaced in the early stage （-160 Ma）, I-type granite in the middle stage （-130 Ma） and anorogenic A-type granite in the late stage （-115 Ma）. Geochemical characteristics of the high-Ba-Sr I-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New ^40Ar/^39Ar plateau ages of the early-stage Wuzhangshan granite （156.0±1.1 Ma, amphibole） and middle-stage Heyu granite （131.8±0.7 Ma, biotite） are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A- type granite, Taishanmiao pluton, was emplaced at -115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between -160 Ma and -115 Ma. The genesis of the early- and middle-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial ^87Sr/^86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratous.

Permian High Ba-Sr Granitoids:Geochemistry,Age and Tectonic Implications of Erlangshan Pluton,Urad Zhongqi,Inner Mongolia

Erlangshan Pluton from Urad Zhongqi, central Inner Mongolia, is located in the middle segment of the northern margin of the North China Plate. The rocks consist mainly of diorites with gneissic structure. Petrochemical characteristics reveal that the diorites belong to metaluminous, high- potassium calc-alkaline series, with chemical signatures of I-type granites. They are characterized by low SiOz contents (56.63%-58.53%) and A/CNK (0.90-0.96), high Al2O3 contents (17.30%-17.96%) and Na20/K20 ratios (1.20-1.70), enrichment in large ion lithophile elements (LILE, e.g., Ba=556-915 ppm, Sr=463-595 ppm), and relative depletion in high field strength elements (HFSE, e.g., Nb, Ta, Ti) in primitive mantle-normalized spidergram, and right-declined rare earth element patterns with slightly negative Eu anomalies (8Eu=0.72-0.90). They have Sr/Y ratios (20-25) evidently less than Kebu Pluton (49-75) to its east. Sensitive high resolution ion micro-probe U-Pb zircon dating of the diorites has yielded an intrusive age of 270±8 Ma. This leads us to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal-derived magma and minor mantle-derived mafic magma, followed by fractional crystallization, which was trigged by crustal extension and fault activity in post-collisional setting.

Wedge-Shaped Pop-Up Structure in the Eslami Peninsula, Lake Urmia, Northwestern Iran

Ancient subduction zones are characterized by metamorphic and orogenic belts. The Zagros Orogenic Belt comprises almost all sections of an ancient subduction zone along which Neo-Tethyan oceanic crust was subducted beneath central Iran. The Eslami Peninsula, as a part of the Zagros Orogenic Belt in Azerbaijan province, northwestern Iran, is situated between the Lake Urmia fore-arc basin and the Sahand Magmatic Arc. This region contains Eocene leucite dikes, trachyte, tephrite, phenolite, basanite and syenite. Volcanic features related to the Sahand are located in the eastern part of the Eslami Peninsula. In view of its relative age and composition, the Eslami Peninsula proposed as an outer arc of the Sahand Magmatic Arc that formed within the post-collisional setting of the central Iranian and Arabian plates. After subduction and contact of the two plates, a symmetric pop-up structure has been created by thrusting in the Zagros belt as a result of the collision processes. The injesction of dikes in the Eslami Peninsula is also a result of the continent continent collision.

Geochemistry and Zircon U-Pb Geochronology of Early Paleozoic S-type Granites in the Eastern Qilian Block,Northwest China

The Qilian Block(QB)is a Precambrian micro-continent located in the northeastern Qinghai–Tibet Plateau.Prevalent Lower Paleozoic granitic magmatic rocks crop out in the QB.A new integrated study of zircon U-Pb ages and systematic whole-rock geochemical data for the Xindian,Dongjiazhuang and Xiaogaoling granites in the eastern segment of the QB constrains their emplacement ages,petrogenesis,and regional evolutionary history.U-Pb dating reveals that the Xindian granite was emplaced 454 Ma,and both the Dongjiazhuang and Xiaogaoling granites were emplaced ca.440 Ma.Geochemical study shows that all granites belong to the high-K calc-alkaline to shoshonitic series and are S-type granites formed by partial melting of continental crust,mainly metagraywacke.We infer that these ca.454–445 Ma granites formed in a syn-collisional setting during the continental collisional between the Qaidam and Qilian blocks.

Paleoproterozoic Granitoids on Liaodong Peninsula, North China Craton

Paleoproterozoic granitoids are an important constituent of the Jiao-Liao-Ji Belt(JLJB). The spatial-temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre-tectonic(~2.15 Ga;peak age=2.18 Ga) and post-tectonic(~1.85 Ga) granitoids. The pre-tectonic granitoids are magnetite and hornblende-biotite monzogranites and granodiorites. Pre-tectonic monzogranites are widespread in the JLJB and have A2-type affinities. In contrast, pretectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post-tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I-, S-, and A2-type granitoids. The assemblage of pre-tectonic A2-type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back-arc basin. The assemblage of post-tectonic adakitic rocks and I-, S-, and A2-type granitoids indicates a post-collisional setting. The 2.20-2.15 Ga A2-type granitoids and adakitic rocks were associated with the initial stage of back-arc extension, and the peak of back-arc extension is inferred from the subsequent(2.15-2.10 Ga) mafic intrusive activity. The ~1.90 Ga adakitic rocks mark the beginning of the postcollisional stage, which was followed by the intrusion of low-temperature S-and I-type granitoids. High-to low-pressure granitoids(S-type) were generated during the peak of post-collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.

Petrogenesis and Tectonic Implications of A-type Granites in Zhaheba in the East Junggar Region of Xinjiang,China:Evidence from Geochronology,Geochemistry and Sr-Nd Isotopic Compositions

The magma source,petrogenesis,tectonic setting and geochronology of the late Paleozoic A-type granites widely exposed in the Zhaheba area,East Junggar,have thus far not been well-constrained.A better understanding of these issues will help to reveal the magmatic processes and continental growth of Central Asia.The A-type granites in Zhaheba include the Ashutasi alkaline granites and the Yuyitasi syenogranites,which were emplaced at 321.5±4.8 Ma and 321.7±0.6 Ma,respectively.The major rock-forming minerals are orthoclase,perthite,arfvedsonite and quartz,which exhibit the following principal geochemical characteristics of A2-type granites.(1)Their REE distribution curves each exhibit a‘V’-shaped pattern and a marked depletion in Eu.They are rich in large-ion lithophile elements Rb,Th and U as well as high-field-strength elements Nb,Ta,Zr and Hf,but significantly depleted in Ba,Sr,P and Ti.(2)Their(^(87)Sr/^(86)Sr)i values(0.7021-0.7041),εNd(t)values(4.57-5.16)and REE distribution patterns are in basic agreement with those of the Kalamaili A-type granite belt in East Junggar.The T DM2 values of the alkaline granites and syenogranites range from 661 to 709 Ma.The A-type granites may be the products of upwelling asthenosphere-triggered partial melting of immature lower crust.The alkaline granites were late-stage products of crystallization and differentiation.Compared to the syenogranites,the alkaline granites are significantly lower in K_(2)O,Na_(2)O,Al_(2)O 3,FeO,MgO and CaO,but significantly higher in incompatible elements(e.g.,SiO_(2),Rb,and Sr).The magmatic crystallization temperatures of the syenogranites and alkaline granites are 874℃ and 819℃,respectively.As their age gradually decreases(peak ages:322 Ma and 307 Ma,respectively),there is a gradual decrease in the T_(DM2)of the A-type granites and a gradual increase in theεNd(t)value from the Ulungur belt to the Kalamaili belt in East Junggar.The study of A-type granites is therefore one of the keys to understanding the laws and mechanisms of crustal accretion during the Phanerozoic period,as well as also being of great significance for understanding the Paleozoic accretion.

Petrogenesis and Geochemical Characterization of the Granitoids of the Magba Shear Zone West Cameroon Central Africa

Magba granitoids are made up of granites, orthogneiss, migmatites, metagabbro, mafic dykes and mylonites with respectively porphyritic, porphyroblastic, grano-lepido-porphyroblastic, and cataclastic texture. Mafic dykes and metagabbro occur as intrusives into the mylonitic and granitic rocks. Magba rocks were subjected to whole rock geochemistry analyses and results show that those rocks have the chemical composition of gabbro, monzodiorite, monzonite syenite, quartz-monzonite, granodiorite and diorite. The rocks are metaluminous, display high-K, calc-alkaline to shoshonitic affinities and plot on the field of volcanic arc granites and are formed by differentiation of I-type magma. They are largely situated within the syn-collision to within plate fields, show a subduction—to collision-related magmatism, and suggest their emplacement during the syn—to post-collisional phase of the Pan-African orogeny.

Dalongshan A-type Granite:Petrology,Mineralogy,Geochemistry and Its Geological Significance

The Dalongshan A-type granite belongs to the Anlu (Anqing,Zongyang and Lujiang)A-type granite belt, the rocks of Dalongshan granite are mainly quartz syenite,syenite and alkaline-feldspar granite. Mineralogy,petrology and geochemistry features of this granite support the argument that Anlu A-type granites and Luzong shoshonite volcanic rocks belong to the same magma evolution series.And A-type granites do not represent ultrapotassic rocks.Compared to Luzong volcanic rocks,the A-type granites are the end of the shoshonitic magma association.

Petrogenesis of the Early Jurassic Longtang and Menglong Peraluminous Granites in Tengchong Terrane,and their Tectonic Implication

A comprehensive study of zircon U-Pb geochronology,in situ Hf isotopes,whole-rock major and trace element geochemistry,and Nd isotopes was carried out for two Early Jurassic two-mica granites(Longtang and Menglong)in the southern part of the Tengchong terrane,which is in the northern part of the larger Sibumasu terrane.We assess the origin of the granites and explore their possible genetic relationship to the Paleo-Tethyan regime.LA-ICP-MS zircon U-Pb dating shows that they were simultaneously emplaced in the Early Jurassic(ca.199 Ma).They have SiO2 contents of 69.7–75.1 wt%and are mainly strongly peraluminous with alumina saturation index(ASI)values ranging from 1.06 to 1.46.They show similar Mg#(0.29–0.42)to experimental partial melts of metasedimentary rocks under continental pressuretemperature(P-T)conditions.They are enriched in light rare earth elements(LREEs)relative to heavy rare earth elements(HREEs),with moderately negative Eu anomalies and flat HREEs patterns.They show negativeεNd(t)values(−9.0 to–12.4)andεHf(t)values(−8.0 to−9.1).Elemental and isotopic data suggest that they most likely to formed by muscovitedehydration melting of a metapelitic source at lower temperatures in the range of 700℃to 750℃.The granites might represent a post-collisional tectonic setting response to Paleo-Tethyan regime.

Genesis of A-type Granites in the East Junggar, Xinjiang and Growth of Continental Crust——Evidence from Geochronological and Sr-Nd Isotopic Compositions

The magma source,petrogenesis,tectonic setting and its geochronology of the Late Paleozoic A-type granites,which widely exposed in Zhaheba area,East Junggar,have not been well constrained so far(Fig.1 a,b).A better understanding of above issues will help us to reveal the magmatic processes and the continental growth of Central Asia(Xiao et al.,2009).

Geology and Geochemistry of Iroko-Granites Southwestern Nigeria:Implication on Provenance

The geology,geochemistry of Iroko-granites have been studied and reported in this paper.The study area has been described as of Archaean-Early Proterozoic terrain underlain by migmatite-gneiss-quartzite complex with supracustal rocks.Large number of granites which outcrops in Iroko-Ekiti represent a typical occurrence of granitoids sporadically distributed in the basement and are known to belong to the Older Granite suites,which are attributable to the Pan-African Orogeny(750±150Ma).The rocks occur,mostly as flat and low lying within sparse vegetation.Structures common on and around the outcrops include quartz vein,veinlets,pegmatite dykes which trend North-south,discrete exfoliated surfaces and xenoliths of older rocks.This study reveals that the granites belong to calc-alkalic suites,demonstrate metaluminous nature,and exhibit characteristics of I-type granites.The granite is a distinctive type in that it is relatively highly potassic,has high FeO/(FeO+MgO)ratio,and high average Zr(299.75ppm)concentration with other high field strength elements.The trace elements study implicates pronounced fractional crystallization during evolution of the granites and thus petrogenetically discriminates as Syn-collision provenance.