Geochronology and Geochemistry of the Xingxingxia Triassic A-type Granites in Central Tianshan, NW China: Petrogenesis and Tectonic Implications

The Triassic granitoids in Central Tianshan play a key role in determining the petrogenesis and tectonic evolution on the southern margin of the Central Asian orogenic belt. In this study, we present SHRIMP zircon U-Pb ages, Hf isotopic and geochemical data on the Xingxingxia biotite granite, amazonite granite and granitic pegmatite in Central Tianshan, NW China. Zircon U-Pb dating yielded formation ages of 242 Ma for the biotite granite and 240 Ma for the amazonite granite. These granitoid rocks have high K2O with low MgO and CaO contents. They are enriched in Nb, Ta, Hf and Y, while being depleted in Ba and Sr, showing flat HREE patterns and negative Eu anomalies. They have typical A-type granite geochemical signatures with high Ga/Al (8–13) and TFeO/(TFeO + MgO) ratios, showing an A2 affinity for biotite granite and an A1 affinity for amazonite granite and granitic pegmatite. Zircon εHf(t) values of the granitoids are 0.45–2.66, with Hf model ages of 0.99–1.17 Ga. This suggests that these A-type granites originated from partial melting of the lower crust. We propose that Xingxingxia Triassic A-type granites formed under lithospheric extension from post-orogenic to anorogenic intraplate settings and NE-trending regional strike-slip fault-controlled magma emplacement in the upper crust.     

Multi-mechanism Orogenic Model of the Su-Jiao Orogenic Belt

The Su-Jiao orogenic belt is the eastern part of the Central Mountain System of China. Recent studies on its erogenic system indicate that the Su-Jiao erogenic belt is a complex orogenic belt which suffered at least 3 orogenies of different mechanisms in the Mesoproterozoic, Neoproterozoic and Triassic respectively. The Meso-Neoproterozoic orogenies belong to the Wilson cycle on the plate margins. The belt is a part of the Late Mesoproterozoic supercontinent Rodinia. The Triassic orogeny belongs to the re-orogeny of the non-Wilson cycle. Delamina-tion of mountain roots occurred after both the Wilson and non-Wilson cycles in the Su-Jiao erogenic belt. The large-amplitude isostatic uplift of mountains, magmatic activities and basin-forming and mountain-making in the upper crust, all indicate the general significance of delamination in the development of erogenic belts.     

Syn-collision Biotite Hornblende Granodiorite from the Zedong Area, Tibet: Zircon U–Pb Isotope Chronology, Petro-geochemistry, and Geodynamic Significance

Cu–Au mineralization is rare in the Jurassic–Early Tertiary batholiths related to the India–Asia collision. Geochemical analysis and U–Pb isotope chronology was carried out on Shuangbujiere biotite hornblende granodiorite from the Zedong area. Zircon grains of the biotite hornblende granodiorite show oscillatory growth zonation and have high Th/U ratios of 1.08–2.39, indicating a magmatic origin for the zircons. Geochrological test yielded a LA-ICP-MS U-Pb age of 51.5±1.0 Ma, suggesting that the emplacement age of the biotite hornblende granodiorite is Early Eocene. The Shuangbujiere biotite hornblende granodiorites have geochemical features characteristic of adakite and are associated with a calc–alkaline metaluminous I-type granite enriched in Sr, high in Mg~#(49.6–54.9) and Sr/Y, and depleted in Y and Yb. These results indicate that this intrusion formation may have been associated with crustal thickening caused by the early collision of the Indian and Eurasian Plates. As the process of crustal thickening continued, the heating of the underplated basaltic magma caused the thickened lower crust amphibolite to dehydrate the melt and form a high-K calc–alkaline adakitic melt at about 848°C. Meanwhile, magma mixing of the underplated basaltic melt and high-K calc–alkaline adakitic melt formed a high-Mg# adakite representative of the sys-collisional tectonic setting.     

Ages of the Laocheng Granitoids and Crustal Growth in the South Qinling Tectonic Domain, Central China: Zircon U-Pb and Lu-Hf Isotopic Constraints

The Laocheng granitoid pluton is located in the South Qinling tectonic domain of the Qinling orogenic belt, southern Shaanxi Province, and consists chiefly of quartz diorite, granodiorite and monzogranite. A LA-ICP-MS zircon U-Pb isotopic dating, in conjunction with cathodoluminescence images, reveals that the quartz diorite and granodiorite were emplaced from 220 Ma to 216 Ma, while the monzogranite was emplaced at ~210 Ma. In-situ zircon Hf isotopic analyses show that the εHf(t) values of the quartz diorite and granodiorite range from -8.1 to +1.3, and single-stage Hf model ages from 809 Ma to 1171 Ma, while the εHf(t) values of the monzogranite are -14.5 to +16.7 and single-stage Hf model ages from 189 Ma to 1424 Ma. These Hf isotopic features reveal that the quartz diorite, granodiorite and monzogranite were formed from the mixing of the magmas derived from partial melting of the depleted mantle and the lower continent crustal materials, and there were two stages of continental crust growth during the Neoproterozoic (~800 Ma) and Indosinian (~210 Ma) eras, respectively, in the south Qinling tectonic domain of the Qinling orogrnic belt, Central China.     

Early Neoproterozoic Granite-Gneisses of the Junggar Alataw (Southeastern Kazakhstan): Age, Petrogenesis and Tectonic Implications

The combined petrographic, petrological, geochemical and geochronological study of the Neoproterozoic gneisses of the Sarychabyn and Baskan complexes of the Junggar Alataw of South Kazakhstan elucidate the Precambrian tectonic evolution of the Aktau–Yili terrane. It is one of the largest Precambrian crustal blocks in the western Central Asian orogenic belt. The U-Pb single-grain zircon ages indicate that granite-gneisses formed from the same source and crystallised in the early Neoproterozoic ca. 930–920 Ma. The chemical composition of gneisses corresponds to A2-type granites. The whole-rock Nd isotopic characteristics (εNd(t) = ?4.9 to ?1.0 and TNd(DM-2st) = 1.9 to 1.7 Ga) indicate the involvement of Paleoproterozoic crustal rocks in magma generation. Early Neoproterozoic ca. 930–920 Ma A-type granitoids in the Aktau–Yili terrane of South and Central Kazakhstan might reflect within-plate magmatism adjacent to the collisional belt or a local extension setting in back-arc areas of the continental arc.     

SHRIMP Zircon U-Pb Dating of Gabbro and Granite from the Huashan Ophiolite, Qinling Orogenic Belt, China： Neoproterozoic Suture on the Northern Margin of the Yangtze Craton

The recently identified Huashan ophiolitic melange was considered as the eastern part of the Mianliie suture in the Qinling orogenic belt. SHRIMP zircon U-Pb geochronology on gabbro from the Huashan ophiolite and granite intruding basic volcanic rocks indicates crystallization ages of 947±14 Ma and 876±17 Ma respectively. These ages do not support a recently proposed Hercynian Huashan Ocean, but rather favor that a Neoproterozoic suture assemblage (ophiolite) is incorporated into the younger (Phanerozoic) Qinling orogenic belt.     

Crustal Accretion and Reworking within the Khanka Massif: Evidence from Zircon Hf Isotopes of Phanerozoic Granitoids

The Central Asian Orogenic Belt(CAOB)is one of the largest Phanerozoic accretionary orogen.(Windley et al.,1990,2007;Jahn et al.,2000a,b,c;Yakubchuk,2002,2004;Xiao et al.,2003,2004).It is the optimal study area for revealing the accretion and reworking processes of the continental crust.The Khanka Massif is located in the most eastern part of the CAOB,and mainly crops out in the territory of Russia,with a small segment in NE China.In addition,a large number of multi-stage granitic rocks are formed in geological evolution in this area,recording amounts of information about crustal accretion and reworking processes(De Paolo et al.,1991;Rudnick,1995;Wu et al.,2011).In view of this,this paper uses the spatial-temporal variations of trace elements and zircon Hf isotopic compositions of phanerozoic granitoids within the Khanka Massif as a case to reveal the crustal accretion and reworking processes of micro continental massifs from the orogenic belt,further to understand the formation and evolution processes and mechanisms of the global continental crust.According to the statistics of zircon U-Pb ages of granitoids in the Khanka Massif,indicate that the granitic magmatisms in the Khanka Massif have eleven peaks:492 Ma,460 Ma,445Ma,430Ma,425Ma,302Ma,287Ma,258Ma,249 Ma,216Ma and 213Ma,it can be divided into eight main stages:Late Cambrian,Middle-Late Ordovician,Middle Silurian,Late Carboniferous,EarlyPermian,Middle-Late Permian—Early Triassic,Late Triassic-Early Jurassic,Early Cretaceous.The Phanerozoic granitoids in Khanka massif are selectedinthispaperasasuiteof granodiorite-monzogranite-syenogranite.TheSi O2contents of the Phanerozoic granitoids exceed 65%,and has high Al2O3,low Mg#,TFe2O3,Cr,Co and Ni contents.This suggests that mixture with mantle-derived magma did not occur,and it should be a typical crustal source(Lu and Xu,2011).Combined with evident characteristics of light rare-earth elements(LREEs)and large ion lithophile elements(LILEs)enrichment,and heavy rare-earth elements(HREEs)and high field-strength elements(HFSEs)loss,we suggest that the primary magma was derived by partial melting of lower crustal material(Xu et al.,2009),and geochemical properties of the Phanerozoic granitoids essentially reflect the nature of the magmatic source region.According to the temporal variation of zircon Hf isotopic data of Phanerozoic granitioids,zircon Hf isotopic compositions of Phanerozoic granitoids have a obvious correlation with age.With the decrease of formation time ofthePhanerozoicgranitoids(Late Cambrian~Middle-LateOrdovician~Middle Silurian~EarlyPermian~Middle-LatePermian–Early Triassic~Late Triassic-Early Jurassic),εHf(t)values of zircons gradually increase,whereas their TDM2 ages gradually decrease(Paleoproterozoic–Neoproterozoic),suggesting that the generation of granitic magmas from the Khanka Massif could have experienced the change from the melting of the ancient crust to the juvenile crust during Paleozoic to Mesozoic.According to the sample location,it can be found thatεHf(t)values of Phanerozoic granitoids have the tendency to decrease with latitude increase,showing that components of the ancient continental crust gradually increase from south to north.However,at the same latitude range,theεHf(t)values of Phanerozoic granitoids also inconsistent.Taken together,these differences reveal the horizontal and vertical heterogeneity of the lower continental crust within the Khanka Massif.According to the relative probability of two-stage model(TDM2)ages of zircon Hf isotope from Phanerozoic granitoids within the Khanka massif,it could be divided into three stages:(1)Late Paleoproterozoic(2)Mesoproterozoic(3)Neoproterozoic.It reveals that the main part of the continental crust within the Khanka MassifwereformedinLate Paleoproterozoic–Neoproterozoic.The Phanerozoic granitoids in the Khanka Massif reworked from the source rockswithdifferent ages(Paleoproterozoic–Mesoproterozoic–Neoproterozoic).     

Neoproterozoic(750–711 Ma) Tectonics of the South Qinling Belt,Central China: New Insights from Geochemical,Zircon U-Pb Geochronological,and Sr-Nd Isotopic Data from the Niushan Complex

The Xiejiaba and Fuqiangbei plutons form part of the newly identified Neoproterozoic Niushan complex, which is located in the southern South Qinling belt(SQB). The plutons are compositionally similar, were emplaced at 750–711Ma, and provide insights into Neoproterozoic tectonism within the South Qinling belt. The Xiejiaba pluton contains diorite,quartz diorite, granodiorite, and granite phases, all of which are sub-alkaline and have variable major element compositions with negative correlations ...     

Neoproterozoic–Early Paleozoic Tectonic Evolution of the South China Craton: New Insights from the Polyphase Deformation in the Southwestern Jiangnan Orogen

A >1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton (SCC) consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen (JO) and experienced at least two phases deformation. Combined with new (detrital) zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed <800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica 40Ar/30Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.     

Late Cretaceous Adakitic Granites of the Southeastern Tibetan Plateau: Garnet Fractional Crystallization of Arc‐Like Magmas at the Thickened Neo‐Tethyan Continental Margin

The tectonic setting of Cretaceous granitoids in the southeastern Tibet Plateau, east of the Eastern Himalaya Syntax, is debated. Exploration and mining of the Laba Mo–Cu porphyry-type deposit in the area has revealed Late Cretaceous granites. New and previously published zircon U–Pb dating indicate that the Laba granite crystallized at 89–85 Ma. Bulk-rock geochemistry, Sr–Nd isotopic data and in situ zircon Hf isotopic data indicate that the granite is adakitic and was formed by partial melting of thickened lower crust. The Ca, Fe, and Al contents decrease with increasing SiO2 content.These and other geochemical characteristics indicate that fractional crystallization of garnet under high-pressure conditions resulted in the adakitic nature of the Laba granite. Cretaceous granitoids are widespread throughout the Tibetan Plateau including its southeastern area, forming an intact curved belt along the southern margin of Eurasia. This belt is curved due to indenting by the Indian continent during Cenozoic, but strikes parallel to both the Indus–Yarlung suture zone and the Main Frontal Thrust belt. It is therefore likely that Cretaceous granitoids in both the Gangdese and southeastern Tibetan Plateau areas resulted from subduction of Neo-Tethyan lithosphere.     

南阿尔金陆块科克萨依新元古代花岗岩成因及地质意义

南阿尔金陆块是阿尔金造山带的重要组成部分.大量新元古代花岗岩出露于南阿尔金亚干布阳-帕夏拉依裆-科克萨依一带.这些花岗岩记录了与Rodinia超大陆汇聚有关的动力学信息,因此对其进行研究有利于对阿尔金造山带演化历史的认识和理解.选取了科克萨依花岗岩岩体进行了岩相学、地球化学、锆石U-Pb年代学和Hf同位素组成的研究.研究结果表明:（1）科克萨依二长花岗岩的主要矿物有:石英、钾长石、斜长石、黑云母和白云母;花岗岩的锆石U-Pb年龄为947~945 Ma.（2）地球化学特征显示,岩石具有高SiO₂（71.54%~74.69%）、高Na₂O+K₂O（6.33%~7.40%）,低CaO（1.59%~2.00%）,低MgO（0.43%~0.61%）和TiO₂（0.25%~0.37%）的特征,相对富钾,K₂O/Na₂O比值为1.02~1.71,A/CNK在1.10~1.14之间,属高钾钙碱性系列的过铝质花岗岩.富集Rb、Th、K、La等元素,亏损Nb、Ta、P、Ti等元素;轻稀土富集而重稀土亏损,具有明显的负Eu异常.（3）锆石ε_Hf（t）为-4.09~+3.87之间,二阶段模式年龄t_DM2为1.6~2.0 Ga.这些特征表明科克萨依二长花岗岩是古老地壳富长石贫黏土的（变）杂砂岩部分熔融形成的S型花岗岩.结合相邻地区新元古代花岗岩类的地球化学、同位素特征及阿尔金区域构造资料,认为科克萨依二长花岗岩形成于新元古代时期,是碰撞造山环境下的产物,是Rodinia超大陆汇聚碰撞过程的响应.      

阿尔金造山带青白口纪片麻状花岗岩的厘定及对Rodinia超大陆汇聚时限的制约

阿尔金造山带新元古代花岗岩的研究对探讨该地区Rodinia超大陆汇聚阶段构造演化过程具有重要意义。本文对在亚干布阳一带新厘定的青白口纪片麻状花岗岩开展了详细的岩石学、年代学和岩石地球化学研究。锆石LA-ICP-MS U-Pb年代学证据显示片麻状花岗岩结晶年龄分别为(883.0±3.3)Ma和(883.1±3.3)Ma,说明其侵位于青白口纪。地球化学结果显示,常量元素具有富硅、铝、钾和低钠、镁、钙和钛的特点,具钙碱性-高钾钙碱性、过铝质花岗岩特征。岩石轻稀土分馏较强而重稀土分馏较弱,具有明显的负Eu异常,总体呈右倾的"V"型稀土分配模式。岩石富集Rb、Th、LREE等大离子亲石元素,中等亏损Ba,强烈亏损Nb、Sr、P、Hf、Ti等高场强元素,总体特征显示了典型的壳源花岗岩的特征,其源于地壳变质砂岩部分熔融,形成于同碰撞晚期构造环境,属Rodinia超大陆汇聚阶段的产物。综合研究表明,阿尔金地区新元古代早期同碰撞型岩体的形成时代集中在871～945 Ma,限定了Rodinia超大陆汇聚时限,且在空间上构成了一条重要的岩浆岩带,是对Rodinia超大陆碰撞汇聚作用的响应。     

阿尔金山北缘早古生代岩浆活动的构造环境

阿尔金山北缘地处塔里木盆地和柴达木盆地之间的阿尔金断裂的西北,是青藏高原北部边界地区。该区花岗岩类主要形成于早古生代以来,为钙碱性岩系(碱性程度不高),发育Ⅰ型和A型两种花岗岩类,缺少S型花岗岩。早古生代与蛇绿岩伴生的双峰式火山岩系属于亚碱性系列,其中的玄武岩主要为拉斑系列,流纹岩属钙碱系列。花岗岩类构造环境分析和判别结果表明,阿尔金山北缘早古生代处在破坏性活动板块边缘,构造环境可能经历了早古生代活动陆缘的(火山)岛弧、中生代大陆造陆抬升以至新生代的后造山作用演化过程。火山岩类的构造环境分析结果表明,玄武岩类可能具有洋脊区、岛弧区和板内区各种构造环境,流纹岩类则主要处在板内区。以上分析说明早古生代"阿尔金洋"的存在。      

GRANITOIDS,VOLCANIC ROCKS AND CHERTS FROM NORTH ALTYN TAGH,NW CHINA: IMPLICATION FOR THE TECTONIC ENVIRONMENT DISCRIMINATION

GRANITOIDS,VOLCANIC ROCKS AND CHERTS FROM NORTH ALTYN TAGH,NW CHINA: IMPLICATION FOR THE TECTONIC ENVIRONMENT DISCRIMINATIONtheNationalKeyProjectforBasicResearch (G19980 4 0 80 0 )andtheYoungGeologistsFoundationofthe MGMR(No.Qn979812 )     

桂北新元古代两类过铝花岗岩的地球化学研究

广西北部新元古代花岗岩类岩石包括黑云母花岗闪长岩和黑云母花岗岩。地球化学特征表明，黑云母花岗闪长岩与含堇青石的过铝花岗岩（CPG）相当，而黑云母花岗岩则类似于白云母二长花岗岩（MPG）。黑云母花岗岩类是成熟地宙岩石部分熔融作用的产物，而黑云母花岗闪长岩类的形成与地幔柱起源的镁铁质岩浆和地壳起源的过铝质黑云母花岗岩浆之间的混合作用有关。这两类新元古代过铝花岗岩的形成与碰撞造山导致地壳加厚的挤压性构造无关，而与导致Rodinia超大陆裂解的地幔柱上升诱发岩石圈伸展的张性构造相联系。     

阿尔金断裂带东段古生代花岗岩浆作用及其大陆动力学意义

造山带花岗岩浆作用一直是地学的重要研究方向, 它记录了地球动力学深部过程的信息, 开展深入的研究工作可以更好的了解板块汇聚环境的陆壳生长和再造以及壳幔之间的相互作用。北祁连造山带是一典型的早古生代造山带, 先后经历了洋盆的打开到闭合, 敦煌地块则是主要由前寒武纪TTG片麻岩和变质表壳岩组成。北祁连造山带和敦煌地块分别位于阿尔金断裂带东段的东南侧和西北侧, 且均出露有大面积的古生代花岗岩体。本文以阿尔金主断裂两侧产出的花岗岩类为研究对象, 涉及北祁连造山带中的赵家庄二长花岗岩, 石包城复式岩体(花岗岩、正长花岗岩和花岗闪长岩)和红柳河花岗岩, 敦煌地块中的党河水库花岗闪长岩、沙枣园二长花岗岩、安盆沟复式岩体(正长花岗岩和花岗岩)以及小草湖似斑状花岗岩。通过对上述花岗岩体的岩相学、锆石U-Pb年代学、地球化学和锆石Hf同位素的研究, 取得了新的认识:     

塔里木盆地东南缘(阿尔金山)"变质基底"记录的多期构造热事件:锆石U-Pb年代学的制约

塔里木盆地东南缘的阿尔金山被认为是塔里木克拉通变质基底的主要出露地区之一。 本文通过阿尔金山北坡不整合在太古代-古元古代变质基底之上的安南坝群中的碎屑岩和中南阿尔金中深变质岩石(原定为阿尔金岩群)的锆石U-Pb年代学研究,来确定塔里木盆地东南缘变质基底的性质及所经历的多期构造热历史。研究结果显示,塔里木盆地东南缘的安南坝群中含砾砂岩的碎屑锆石年龄集中在1.92Ga左右,少量在2.0~2.4Ga,表明其碎屑物质主要来源于下伏的太古代-早元古代米兰岩群和相关的深成侵入体。在中阿尔金地块和南阿尔金俯冲碰撞杂岩带的深变质岩石中,锆石U-Pb年代学数据表明其记录有新元古代早期(920~940Ma)、新元古代晚期(760Ma左右)和早古生代(450~500Ma)三期构造热事件,新元古代早期的构造热事件与塔里木(或晋宁)造山作用有关,它普遍存在于塔里木盆地周缘的和南中国地块(扬子克拉通)的变质基底岩石中,与Rodinia超级大陆汇聚相关;新元古代晚期的构造热事件也同样广泛存在于塔里木盆地周缘和扬子克拉通之中,被认为与Rodinia超大陆的裂解作用有关。因此,在新元古代时期,阿尔金的地质演化历史与扬子克拉通非常相似,而与华北则有很大的不同,锆石U-Pb测定还表明中南阿尔金的深变质岩石普遍遭受了早古生代的变质作用的改造,显示它们普遍卷入了早古生代的碰撞造山事件之中,成为早古生代碰撞造山带的组成部分。     

The Grenvillian orogeny in the Altun–Qilian–North Qaidam mountain belts of northern Tibet Plateau: Constraints from geochemical and zircon U–Pb age and Hf isotopic study of magmatic rocks

Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have ε_Hf (0.9 Ga) values and t_DM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO₂, K₂O, and low P₂O₅; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian orogeny (950–900 Ma).     

Petrogenesis of the Palaeoproterozoic Xishankou pluton,northern Tarim block,northwest China: implications for assembly of the supercontinent Columbia

The Tarim block, one of the largest cratons in China, records an important part of the Proterozoic crustal evolution of the Earth. Many previous studies have focused on the Neoproterozoic magmatism and tectonic evolution of this block in relation to the break-up of Rodinia, although relatively little is known about its earlier tectono-magmatic history. In this article, we present detailed petrographic, geochronologic, whole-rock geochemical, and in situ zircon Hf isotope data for the pre-Neoproterozoic Xishankou granitoid pluton (XBP), one of several blue quartz-bearing granitoid intrusions well exposed in the Quruqtagh area, and discuss these intrusions in terms of their tectonic environment. Zircon LA-ICP-MS dating indicates that gneissic quartz diorite and granodiorite of the XBP crystallized at 1934 ± 13 and 1944 ± 19 Ma, respectively. Both underwent metamorphism essentially coeval with emplacement, a time that is compatible with the globally distributed 2.1–1.8 Ga crustal amalgamation during formation of the supercontinent Columbia. Petrographic and geochemical evidence suggest that the XBP is a continental-arc-type granite and may have been generated by the partial melting of Archaean thickened lower crust; this would suggest that the northern Tarim block was a continental-type arc at ca. 1940 Ma. Our new data, together with previous regional geological studies, indicate that a series of Palaeoproterozoic (ca. 2.0–1.8 Ga) tectono-magmatic events occurred in the northern Tarim attending the assembly of Columbia.     

Field, geochemistry and Sr-Nd isotopes of the Pan-African granitoids from the Tifnoute Valley (Sirwa, Anti-Atlas, Morocco): a post-collisional event in a metacratonic setting

In the Tifnoute Valley, three plutonic units have been defined: the Askaoun intrusion, the Imourkhssen intrusion and the Ougougane group of small intrusions. They are made of quartz diorite, granodiorite and granite and all contain abundant mafic microgranular enclaves (MME). The Askaoun granodiorite and the Imourkhssen granite have been dated by LA-ICP-MS on zircon at 558?±?2 Ma and 561?±?3 Ma, respectively. These granitic intrusions are subcontemporaneous to the widespread volcanic and volcano-detrital rocks from the Ouarzazate Group (580–545 Ma), marking the post-collisional transtensional period in the Anti-Atlas and which evolved towards alkaline and tholeiitic lavas in minor volume at the beginning of the Cambrian anorogenic intraplate extensional period. Geochemically, the Tifnoute Valley granitoids belong to an alkali-calcic series (high-K calc-alkaline) with typical Nb-Ta negative anomalies and no alkaline affinities. Granitoids and enclaves display positive ε_Nd-560Ma (+0.8 to +3.5) with young Nd-T_DM between 800 and 1200 Ma and relatively low ⁸⁷Sr/⁸⁶Sr initial ratios (Sr_i: 0.7034 and 0.7065). These values indicate a mainly juvenile source corresponding to a Pan-African metasomatized lithospheric mantle partly mixed with an old crustal component from the underlying West African Craton (WAC). Preservation in the Anti-Atlas of pre-Pan-African lithologies (c. 2.03 Ga basement, c. 800 Ma passive margin greenschist-facies sediments, allochthonous 750–700 Ma ophiolitic sequences) indicates that the Anti-Atlas lithosphere has not been thickened and was never an active margin during the Neoproterozoic. After a transpressive period, the late Ediacaran period (580–545 Ma) is marked by movement on near vertical transtensional faults, synchronous with the emplacement of the huge Ouarzazate Group and the Tifnoute Valley granitoids. We propose here a geodynamical model where the Tifnoute Valley granitoids as well as the Ouarzazate Group were generated during the post-collisional metacratonic evolution of the northern boundary of the West African craton. The convergence with the peri-Gondwanan active margin produced brittle fracturing of the cratonic boundary without thickening, allowing rising of magmas. The Tifnoute Valley granitoids display a metasomatized lithospheric mantle source mixed with a minor ancient (2 Ga) continental crust component from the underlying WAC.