A-type Granites Research Articles

Geochronology and petrogenesis of the Late Triassic A-type granitoids in the Yeongnam Massif and its implication for Late Triassic geodynamics of northeast Asia

The Late Triassic A-type granitoids along the continental margins of East Asia are important for deciphering the crust-mantle interactions, transformation of tectonic regime, and termination of the Indosinian Orogeny (known as the Songrim Orogeny in South Korea). The newly identified Wangdong plutons are distributed in the southwestern part of Yeongnam Massif, South Korea. U–Pb dating of zircons from the Wangdong plutons has established its date of emplacement at ca. 226–221 Ma, similar to the emplacement ages of the Daegang and Ian alkali granites. Geochemical data have shown that the Wangdong granitoid samples are magnesian to ferroan in composition and can be further classified in the range from alkalic to calc-alkalic. They have a high zircon saturation temperature (~ 850 °C), K2O/Na2O and, Ga/Al ratios, and are enriched with high field strength elements (e.g., Zr and Y), indicating an A-type granite affinity. Their classification into A2-type granites based on the A-type subdivision diagrams suggest that they formed in an extension-related tectonic setting. Moreover, the Wangdong A-type granitoids have high (La/Nb)N and (Th/Nb)N ratios with peraluminous characteristics (value of aluminum saturation index >1.0). In addition, magmatic zircons from the Wangdong granitoids have negative ɛHf(t) values (−6.6 to −15.5) with a Paleoproterozoic to Mesoproterozoic two-stage Hf model ages (from 1.99 to 1.49 Ga). This suggests that the Wangdong granitoids were derived from ancient crustal materials with compositions similar to metagraywackes. Based on geochemical, isotopic, and geochronological studies, we concluded that the lithospheric mantle delamination induced by slab roll-back of the subducted Paleo-Pacific plate is the main trigger in the production of Late Triassic magmatism in Yeongnam Massif, South Korea.

Compositional Variability of Monazite–Cheralite–Huttonite Solid Solutions, Xenotime, and Uraninite in Geochemically Distinct Granites with Special Emphasis to the Strongly Fractionated Peraluminous Li–F–P-Rich Podlesí Granite System (Erzgebirge/Krušné Hory Mts., Central Europe)

A comprehensive study of monazite–cheralite–huttonite solid solutions (s.s.) and xenotime from the highly evolved, strongly peraluminous P–F–Li-rich Podlesí granite stock in the Krušné Hory Mts., Czech Republic, indicates that, with the increasing degree of magmatic and high-T early post-magmatic evolution, the content of the cheralite component in monazite increases and the relative dominance of middle rare earth elements (MREE) in xenotime becomes larger. Considering the overall compositional signatures of these two accessory minerals in the late Variscan granites of the Erzgebirge/Krušné Hory Mts., three types of granites can be distinguished: (i) chemically less evolved F-poor S(I)- and A-type granites contain monazite with a smooth, mostly symmetric chondrite-normalized (CN) rare-earth elements (REE) pattern gradually declining from La to Gd; associated xenotime is Y-rich (˃0.8 apfu Y) with a flat MREE–HREE (heavy rare earth elements) pattern; (ii) fractionated A-type granites typically contain La-depleted monazite with Th accommodated as the huttonite component, combined with usually Y-poor (0.4–0.6 apfu Y) xenotime characterized by a smoothly inclining, Yb–Lu-dominant CN-REE pattern; (iii) fractionated peraluminous Li-mica granites host monazite with a flat, asymmetric (kinked at La and Nd) CN-LREE pattern, with associated xenotime distinctly MREE (Gd–Tb–Dy)-dominant. Monazite and xenotime account for the bulk of the REE budgets in all types of granite. In peraluminous S(I)-type granites, which do not bear thorite, almost all Th is accommodated in monazite–cheralite s.s. In contrast, Th budgets in A-type granites are accounted for by monazite–huttonite s.s. together with thorite. The largest portion of U is accommodated in uraninite, if present.

Identification of two-phased late Paleoproterozoic magmatism in the Wuyishan Domain (SE China): Implications for the tectonic evolution of the Cathaysia Block

The Cathaysia Block amalgamated with the Yangtze Block along the Jiangnan orogenic belt to form the South China Craton during early Neoproterozoic time. However, the origin of the Cathaysia Block and its position in the Nuna supercontinent remain controversial. This paper synthesizes geochronological, geochemical and isotopic data from late Paleoproterozoic igneous rocks in the Wuyishan Domain of the Cathaysia Block (SE China). Two-phases of late Paleoproterozoic A- and S-type granitoids were identified and dated at 1925–1848 Ma and 1816–1750 Ma. The A-type granites in the Wuyishan Domain were likely derived from partial melting of mafic lower crust with a tonalitic to granodioritic geochemical composition, and the S-type granites were derived from partial melting of a meta-sedimentary source. These late Paleoproterozoic granitoids were emplaced in a continental arc/back-arc setting and the two-phased arc/back-arc magmatism was related to the assembly of the Paleoproterozoic Nuna supercontinent. Combining our results with previous late Paleoproterozoic geochemical and age data, we suggest that the Cathaysia Block was located close to northern India Shield during Proterozoic time until the breakup of the Rodinia Supercontinent in the late Neoproterozoic.

Early Permian Granitic Magmatism in Middle Part of the Northern Margin of the North China Craton: Petrogenesis, Source, and Tectonic Setting

The late Palaeozoic was an important period of tectonic evolution for the northern margin of the North China Craton (NCC). The source(s) and tectonic setting of early Permian granitoid rocks emplaced along the northern margin of the NCC are still unclear. These granitoids formed between ~295.4–276.1 Ma (uncertainties ranging from ±1.5 to ±7.8 Ma) according to zircon laser ablation inductively coupled mass spectrometry (LA-ICP-MS) and sensitive high-resolution ion microprobe (SHRIMP) U-Pb data. The Dadongou (DDG) pluton is an A1-type granite and the Dananfangzi (DNFZ) pluton is an A2-type granite. The Erdaowa (EDW), Lisicun (LSC), Wuhai (WH) and Gehuasitai (GHST) plutons are I-type granites. The Yuanbaoshan (YBS) dykes are diorite and syenodiorite. All the granitoids are enriched in large ion lithophile elements and light rare earth elements, depleted in high field strength elements and have negative εNd(t) and εHf(t) values. The A1-type granite was formed by the melting of the mafic crust. The A2-type granite was derived from partial melting of tonalite gneiss from the NCC crust and mantle materials. The EDW, LSC, WH and GHST granites mainly originated from partially melted granulite, with some mantle input. The YBS dykes are formed by the magma mixing of hot mantle melt and the relatively cold crustal magma. The northern margin of the NCC experienced anorogenic and collision tectonic stages, and the structural setting started to transform to post-collision at the later period of early Permian.

High-temperature melting of different crustal levels in the inner zone of the Emeishan large igneous province: Constraints from the Permian ferrosyenite and granite from the Panxi region

The Late-Permian Emeishan mantle plume event caused large-scale flood basalts and related mafic-ultramafic layered mafic intrusions in the inner zone of the Emeishan large igneous province (ELIP). However, the related crustal magma response of this mantle plume event in the inner zone of the ELIP remains poorly understood. In this contribution, we report contemporaneous (~259 Ma) ferrosyenite and A-type granite in the inner zone of the ELIP, and their chronological and geochemical data suggest simultaneous crustal melting at different depths. The ferrosyenites display moderate SiO2 (60.14 to 63.58 wt%), high Fe2O3T (4.28 to 8.52 wt%) and alkaline (Na2O + K2O = 10.91 to 12.75 wt%) contents. In combination with their positive zircon εHf(t) values (+1.5 to +12.9), we propose that the ferrosyenites were formed by high temperature melting of Fe-rich refractory juvenile lower crust at H2O-poor condition, which was induced by underplating of the high-temperature mantle plume. Rhyolite–MELTS modeling results show that ~7% melting of ferrodiorite-like source at ~1120 °C and 8 kbar can produce similar compositions with least evolved ferrosyenite under a relatively dry condition. The Baima granites have high SiO2 (70.58 to 74.26 wt%) contents and 10000*Ga/Al ratios (3.00 to 3.28), indicating the affinity to A-type granites. Their evolved zircon εHf(t) values (−8.1 to −0.6) indicate an evolved crustal source region. Rcrust modeling indicates that ~9% partial melting of ancient granodiorite-like crustal material under low pressure condition (4 kbar) can produce the observed granitic compositions. Considering the close spatial and temporal relationship between ferrosyenites and A-type granites, we propose that the emplacement of ferrosyenitic magma resulted in low-degree partial melting at a relatively shallow crustal level, responsible for the formation of the A-type granites. In summary, this study highlights the significant impact on crustal magma response to the high-temperature mantle plume event in the inner zone of ELIP.

Two episodic Nb-Ta mineralization events and genesis of the Zhaojinggou rare-metal deposit, north margin of the North China Craton

The Zhaojinggou rare-metal deposit is located in the Wulashan-Daqingshan region, central north margin of the North China Craton. Nb-Ta mineralizations are mainly hosted in the biotite alkali-feldspar granite (BAG) and albite granite (AG), with subordinate mineralization in the alkali-feldspar aplite dyke (AFA), the amazonite granitic pegmatite dyke (AGP), and the greisen (black + white colored greisen). In this paper, we present a systematic work of geochronology (CGM U-Pb combined with cassiterite U-Pb, monazite U-Th-Pb, and muscovite 40Ar-39Ar dating), whole-rock geochemistry, and Sr-Nd isotopes to understanding the timing of mineralization, petrogenesis, geodynamic setting, and ore-forming processes. Our geochronological data reveal two episodic Nb-Ta mineralization events in the Zhaojinggou deposit during the Early Cretaceous. The first and major ore-forming episode occurred at ~130 Ma, forming a sequence of ore-bearing rocks of the BAG-AG-greisen-AFA. The second but subordinate ore-forming episode occurred at ~114 Ma, forming the ore-bearing AGP. The whole-rock geochemistry indicates the granitic rocks (the BAG-AG-AFA and AGP) from the two episodes are highly evolved with analogous trace element and REE patterns, and have A-type affinity. The whole-rock εNd(t) values of these granitic rocks are relative similar, ranging from −9.6 to −7.6, with corresponding T2DM ages of 1490–1713 Ma. These features suggest that these A-type granites from the two discrete episodes are derived from the same magma reservoir by high-temperature partial melting of the Middle Proterozoic basement in an infracrustal extensional environment. These A-type granites experienced extremely fractional crystallization during emplacement. The whole-rock REE tetrad effects, element ratios (Nb/Ta, Zr/Hf and K/Rb), and Nb-Ta fractionation modeling indicate that both magmatic and hydrothermal processes are involved to form the two episodic Nb-Ta mineralizations. High degree of factional crystallization and magmatic-hydrothermal processes after high-temperature anataxis are crucial to form the Zhaojinggou rare-metal deposit. Moreover, these highly-evolved A-type granites (the BAG-AG-AFA and AGP) formed during the Early Cretaceous (at ~ 130 Ma and ~ 114 Ma respectively) are the important targets for rare-metals prospecting in the central north margin of the NCC.

Oblique continental collision and the formation of syn-collisional A-type granites: insights from the Early Jurassic Baoji granite suite in the Qinling orogenic belt, central China

ABSTRACT A-type granites are conventionally interpreted to be formed in late post-collisional or anorogenic settings. However, we firstly identified an Early Jurassic syn-collisional A-type granite suite in the Qinling orogenic belt: the Baoji granite suite. A comprehensive investigation into its mineralogical, petrological, geochronological, and geochemical characteristics can shed light on the genesis of syn-collisional A-type granites and geodynamic evolution of collisional orogeny. The Baoji granite suite contains two types of rocks: (1) A-type granites including biotite syenite, coarse-grained, porphyritic, and fine-grained syenogranites, and alkali-feldspar granite, and (2) magnesian monzodiorite; both types are coeval, with zircon U–Pb ages of ca. 190 Ma. The A-type granites yield A1-type trace element signatures and large variations in trace element contents, with Ba contents of 16.9–762 ppm, Sr of 11.0–211 ppm, Rb of 193–645 ppm, and Eu of 0.08–1.24 ppm. Their radiogenic isotope compositions (87Sr/86Sri = 0.70631–0.70637; εNd = −5.18 to −3.84; εHf = −5.01 to +2.76) are similar, and overlap those of Neoproterozoic OIB-like basic volcanics from the South Qinling belt. These characteristics show that the A-type granites originated from the anatexis of OIB-like lower crust and underwent fractional crystallization in a silicic magma reservoir. The monzodiorite has low SiO2 contents (49.82–53.29 wt.%) and enriched radiogenic isotopic compositions (87Sr/86Sri = 0.70554–0.70638; εNd = −11.0 to −5.28) contains abundant hornblende and biotite (~40%), and exhibits evidence of magma mingling. It also contains two groups of zircon: pristine and unzoned zircon that yields negative Hf isotope compositions (εHf = −9.42 to −3.14), and xenocrystic zircon that yields similar Hf isotope compositions (εHf = −3.54 to +1.85) to the A-type granites. These characteristics demonstrate that the monzodiorite was derived from the differentiation of basaltic partial melts of an enriched mantle source, and mingled with the A-type granitic magma during its ascent and emplacement into a silicic magma reservoir. Along with regional records of the Early Jurassic magmatism, deformation, metamorphism, and sedimentation, the genetic models for the Baoji A-type granites and monzodiorite suggest that the Middle Triassic to Early Jurassic oblique continental collision (ca. 230–190 Ma) produced coupled EW-trending strike-slip and NE-trending extensional faults at crustal levels and Rayleigh–Taylor (gravitational) convective instabilities at mantle depths in the Qinling orogenic belt, which controlled the production of the syn-collisional A-type granite suite. Our work also indicates that the A-type granites can be formed in syn-collisional setting in response to oblique continental collision and the resultant slow foundering of a high-density lithospheric root; therefore, we suggest that the syn-collisional A-type granites are evidence for oblique continental collision.

Zircon U--Pb ages of Au-bearing host rocks in Northwest Iran as evidence for gold mineralization in the Carboniferous, not Cenozoic time!

A few gold deposits occur in northwest Iran which are hosted by mylonitic granitoids and phyllonite. New U--Pb ages yield ages of 350–311 Ma for the mylonitic granitoid and 354–348 Ma for the phyllonite, which indicate Carboniferous magmatic activity in northwest Iran. The host granitoid and phyllonite have high contents of Zr (212, 246 ppm) and Y (26.8, 38.7 ppm). High 10,000 × Ga/Al ratios (2.1–5.1) and fractionation of the rare earth elements (REEs) pattern with depletion of Eu, Sr, and P may infer an A-type (anorogenic) granite affinity for the host rocks. Correspondingly, these rocks are characterized by high contents of Nb (33.1 to 39.2 ppm), Ta (1.68 to 2.40 ppm), Tb (0.84 to 1.17 ppm), and Th/Yb ratios with some similarity to OIB-like rocks. Whole rock compositions of these host rocks are consistent with both A1 and A2 type granites, which infer magmatic activity in an extensional tectonic regime. Perhaps the extension may have occurred during rifting of Neo-Tethys in northern Gondwana. Upwelling of the hot OIB-like melts during the opening of Neo-Tethys ocean was the main mechanism of this extension. The OIB signatures of the A-type granitoids controlled the gold mineralization during this process. Accordingly, we classify the gold mineralization in NW Iran as intrusion-related gold deposits. These mantle-derived magmas from the asthenosphere may support a source of both sulfur and gold. These elements were concentrated in hydrothermal fluids in the late stages of magma crystallization. Also, hot magma injection increased the geothermal gradient and caused extensive dehydration of the sedimentary rocks inin the roof of the magma chamber. Circulation of these hot fluids with injection into the hot crystallizing magmatic rocks and mixing with late-stage magmatic-hydrothermal fluids and meteoric water (?) seem to all have essential roles for transporting the gold and precipitating it within fractures in the semi-brittle to brittle zone. The gold precipitated as native or nanoparticles in pyrite in the inner part of the shear zone. This research reveals that mineralization occurred in the Late Paleozoic in an extensional tectonic regime and not above the subduction zone or collision zone which had been suggested before.

Intracontinental extension and geodynamic evolution of the Paleoproterozoic Jiao-Liao-Ji belt, North China craton: Insights from coeval A-type granitic and mafic magmatism in eastern Liaoning Province

Abstract To better understand the origin and tectonic evolution of the Paleoproterozoic Jiao-Liao-Ji belt, North China craton, which have long been debated, we have conducted whole-rock geochemical and zircon U-Pb and Hf isotope analyses on Paleoproterozoic monzo(syeno)granitic gneisses and metamafic rocks from eastern Liaoning Province. The results indicate that these monzo(syeno)granitic gneisses and metamafic rocks formed concurrently at ca. 2.2–2.1 Ga. The monzo(syeno)granitic gneisses show geochemical features of A-type granites and were derived from dehydration melting of Archean tonalite-trondhjemite-granodiorite (TTG) with minor involvement of coeval mantle-derived magma in an extensional setting. The metamafic rocks are geochemically similar to mid-ocean-ridge basalt; they were generated by partial melting of isotope-depleted asthenospheric mantle in an intracontinental extensional setting and experienced crustal and continental lithospheric mantle contamination and fractional crystallization. Based on this study and published geological evidence, we propose the following tectonic model for the origin and geodynamic evolution of the Jiao-Liao-Ji belt: (1) Generation of high-density eclogitized lower crust accompanied by formation of voluminous Archean TTGs in the Eastern block; (2) intracontinental extension driven by upwelling of an asthenospheric hotspot along the Jiao-Liao-Ji belt in period of 2.20–2.0 Ga; (3) convergent orogenic processes between the Longgang block and Nangrim block governed by gravity-driven subduction of high-density eclogitized lower crust at ca. 1.95–1.85 Ga; and (4) postorogenic extension caused by delamination of the orogenic root and subsequent hot asthenospheric upwelling. This tectonic model can well explain the origin and geodynamic evolution of the Paleoproterozoic Jiao-Liao-Ji belt.

Genesis of Late Cretaceous granite and its related Nb–Ta–W mineralization in Shangbao, Nanling Range: Insights from geochemistry of whole-rock and Nb–Ta minerals

The Shangbao mining district, located in Nanling Range, South China, includes a series of middle-large scale granite-related W–Sn–Nb–Ta deposits. The genesis for W-Sn-Nb–Ta mineralization in this region is in fact ambiguous. In addition, the research of the latest mineralized granites in Nanling Range may be contributed to further understand the mineralization mechanism. In this study, we report the geochronological, geochemical and isotopic compositions of the Shangbao granite, together with the texture and element of Nb–Ta bearing minerals. LA-MC-ICP-MS U–Pb dating of zircon and columbite in granite from Shangbao Nb–Ta deposit yields weighted mean 206Pb/238U age of 87.3 ± 0.9 Ma and 86.83 ± 0.8 Ma, respectively, revealing the emplacement of the granites and their mineralization during Late Cretaceous. The major elements of these granites show high contents of K2O + Na2O, Fe2O3, SiO2 and F, low contents of P2O5, CaO, TiO2 and MgO, suggesting high-K calc-alkaline series with slightly peraluminous signature. Besides, they exhibit flat REE pattern and high content of Zr + Nb + Ce + Y, revealing the Shangbao granite affinity of highly fractionated A-type granite. Lu–Hf and Sr–Nd isotopes indicate that the Nb–Ta bearing magma was formed by the mixing crust-mantle materials. Combined with the previous studies, emplacement of Shangbao granite is linked to an expansional geodynamic setting, likely caused by the roll-back of the paleo-Pacific plate subduction.The principal economic Nb–Ta oxides of Shangbao granite are columbite group minerals (CGM). Three major groups are identified given textural and chemical characteristics of CGM, i.e., (i) Group I displays systematic core-rim evolution from columbite to tantalite, and eventually to columbite; (ii) Group II shows that the columbite and tantalite have undergone metasomatism through the wolframoixiolite, and numerous REE-mineral were contained; (iii) Group III is anhedral columbite crystallized together with rutile. As revealed from geochemical characteristics of these three groups, the formation of Nb–Ta oxides within Shangbao granite display three generating stages, supporting the magmatic-hydrothermal origin. The high-degree fractional crystallization of Shangbao granitic magma is the main factor leading to the enrichment of Nb to allow saturation of columbite.

The First Evidence for Late Devonian Granitoid Magmatism in the Northeastern Flank of the South Mongolia–Khingan Orogenic Belt

This paper reports the geochemical, U–Pb geochronological, and Sm-Nd isotopic–geochemical data on granites of the Medvedka Massif in the northern part of the Nora–Sukhotino terrane. It has been found that these granites have an age of 378 ± 3 Ma. They contain ferruginous silicates, have high iron index (FeO*/(FeO*+MgO)), low concentrations of Al2O3, CaO, MgO, high contents of Nb, Ga, Y, a deficiency of Sr and Eu, positive values of eNd(t) (+3.0…+4.1), and a high Y/Nb ratio. All these data indicate that the granites of the Medvedka massif are A2-type granites. The Late Devonian hastingsite–biotite granites of the Medvedka massif most likely reflect a transform continental margin setting in the evolution of the South Mongolian–Khingan orogenic belt.

A-type granites induced by a breaking-off and delamination of the subducted Junggar oceanic plate, West Junggar, Northwest China

The A-type granites with highly positive εNd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic sourceq and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon εHf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (high SiO2 and K2O contents, enriched LILEs (except Sr), depleted Sr, Ta and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (315–305 Ma) and moderate 18O enrichments (δ18Ozircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (305–301 Ma) with higher 18O enrichments (δ18Ozircon=+8.72‰–+9.89‰). The authors deduce that the elevated 18O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere’s counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.©2022 China Geology Editorial Office.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.

The 1.88 Ga Uatumã Magmatism in the Serra dos Magalhães region: petrology and implications to the extension of the south-eastern edge of the Amazonian Craton

The Amazonian Craton (AC) is a Pre-Cambrian tectonic segment that extends over 4.3 × 105 km2 at the northern portion of the South American Platform. Phanerozoic sedimentary basins cover most of the edges of the AC and sparse occurrences of Precambrian rocks may aid the definition of its extension. One of these occurrences is the volcano-plutonic rocks that outcrop in the Serra dos Magalhães region, which relates to the Uatumã Magmatism, an expressive Orosirian magmatic event that constitutes a Siliceous Large Igneous Province. Effusive rhyodacites and rhyolites comprise the volcanic unit and the plutonic counterpart consists of epizonal monzogranites. Whole-rock geochemistry indicates an A2-type granite affinity to all magmatic rocks. Contrasting signatures suggest a magmatic evolution from a single stratified magma chamber. U-Pb zircon crystallization ages are 1870 ± 11 Ma for the rhyodacites, 1879 ± 5 Ma for the monzogranites, and a slightly younger age of 1863 ± 14 Ma for the rhyolites. Interpretation of satellite and geophysical images allows the recognition of regional lineaments in the Parecis and Bananal basins that suggest the extension of the AC up to the Tucurui Fault in the eastern portion (Bananal Basin) and up to the Brasnorte High in the southern part (Parecis Basin).

ПЕРВЫЕ СВИДЕТЕЛЬСТВА ПОЗДНЕДЕВОНСКОГО ГРАНИТОИДНОГО МАГМАТИЗМА В ИСТОРИИ ФОРМИРОВАНИЯ СЕВЕРО-ВОСТОЧНОГО ФЛАНГА ЮЖНО-МОНГОЛЬСКО–ХИНГАНСКОГО ОРОГЕННОГО ПОЯСА

The results of geochemical, U-Pb geochronological, Sm-Nd isotopic-geochemical studies of granites of the Medvedka Massif in the northern part of the Nora–Sukhotino terrane are presented. It has been found that these granites are of 378 ± 3 Ma in age. It was shown that these granites are characterized by the presence of ferruginous silicates, high iron index (FeO*/(FeO*+MgO)), low concentrations of Al2O3, CaO, MgO, high contents of Nb, Ga, Y, deficiency of Sr, Eu, positive values of εNd(t) (+3.0...+4.1), and high values of the ratio Y/Nb. In total, this indicates that the granites of the Medvedka massif are related to A2-type granites. The Late Devonian hastingsite-biotite granites of the Medvedka Massif most likely reflect evidence of the transform continental margin setting in the history of the formation of the South Mongolian – Khingan orogenic belt.

Petrogenesis of late-Paleoproterozoic A-type granites in the Tarim Craton and implications for the Columbia assembly and break-up

塔里木克拉通保存有古元古代晚期与哥伦比亚超大陆演化相关的岩浆和构造记录。本文综述了塔里木克拉通周缘的古元古代晚期A型花岗岩，识别出两期（1.95Ga和1.85~1.73Ga）具不同地球化学特征的A型花岗岩。两期花岗岩均来源于具英云闪长岩和花岗闪长岩成分特征的地壳的部分熔融。~1.95Ga花岗岩具有相对较高的SiO₂和Sr含量、Y/Nb和Ce/Nb比值、较低的ε_Hf（t）值（-13~-5.2），为A2型花岗岩，形成于活动大陆边缘或弧后伸展等构造环境；而1.85~1.73Ga花岗岩具有相对较低的SiO₂和Sr含量、Y/Nb和Ce/Nb比值、和较高的ε_Hf（t）（-5.9~+8.7）和ε_Nd（t）（-6.2~-2.5）值，为A2向A1过渡类型，形成于碰撞后伸展或者陆内伸展背景。笔者综述还发现塔里木克拉通内部元古代晚期岩浆和变质也可以明显的分为两期，岩浆岩峰值分别为1.93Ga和1.85Ga，变质年龄峰值为1.96Ga和1.84Ga，说明塔里木克拉通内部存在两期不同的古元古代晚期构造-岩浆事件。这两期构造-岩浆事件对应于俯冲型造山和碰撞造山后伸展环境，可能分别记录了哥伦比亚超大陆聚合和裂解过程，也就是说哥伦比亚超大陆可能在1.85Ga左右已经开始部分裂解。;Lots of late-Paleoproterozoic magmatic and tectonic records, which are commonly interpreted as products of the Columbia assembly and break-up, were preserved in the Tarim Craton. In this study, we summarized the late-Paleoproterozoic A-type granitoids at the periphery of the Tarim Craton, and identified two A-type granitoid flare-ups at 1.95Ga and 1.85~1.73Ga. All these A-type granitoids are derived from partial melting of the crustal materials with tonalitic to granodioritic compositions. The ca. 1.95Ga granites show high SiO₂ and Sr contents, high Y/Nb and Ce/Nb ratios, low ε_Hf(t) values (-13~-5.2), and could be classified as A2 subtype granitoid. They were formed in continental arc or back-arc settings. The 1.85~1.73Ga granites show relatively low SiO₂ and Sr contents, low Y/Nb and Ce/Nb ratios, high ε_Hf(t) (-5.9~+8.7) and ε_Nd(t) (-6.2~-2.5) values, and could be classified as A2 to A1 transitional subtype. They were formed in post-collisional or intracontinental extension settings. Besides, magmatism and metamorphism ages in the Tarim Craton also show two peaks at 1.93Ga and 1.85Ga, 1.95Ga and 1.84Ga, respectively. These age data suggest that the Tarim Craton may have experienced two significant tectono-magmatic events at about 1.93Ga and 1.85Ga. These two events may record the subduction related orogeny and collisional orogeny, and are related to the Columbia assembly and break-up, respectively. We believed that the Columbia supercontinent may have broken up at 1.85Ga.

New data concerning the age and composition of intrusion complexes of the northern part of Balygychan-Sugoi rift depression (North-Eastern Russia)

The Balagychan-Sugoi (Omsukchan) riftogeneous depression is described by different authors both as a part of Okhotsk-Chukotka volcanic belt (OCVB) and as a separate structure. The unique Dukat gold and silver deposit and a lot of others ore deposits including rare-metal, such as Arylah, Lunnoe, Askold, Mechta, Tidid, Krasin, are associated with this structure. All mentioned objects are located in the south part of the depression and from this point of view are connected with OCVB structure. Evolution of the Balygychan-Sugoi depression is closely related to the stages of magmatic evolution of the region. In the article, these stages are characterized based on the data form intrusion bodies located in the northern part (Naygain depression). This part is the most outlying from the OCVB and less investigated. For the first time, the U-Pb zircon and baddeleyite dating and the description of petrographic and geochemical composition have been carried out for Mandychan gabbro-diorite and Nayahan gabbro leucogranite intrusion complexes from the northern part of the depression and for Omsukchan leucogranite complex. The Late Jurassic – Early Cretaceous intrusions of the Mandychansk complex dated as 143-139 Ma mark the beginning of the rift depression formation. Intrusion of granitoids of the Nayahan and Omsukchan complexes dated as 84-85 Ma and 81-82 Ma correspondently is related with new stage of magmatic activity, synchronous to OCVB formation. The petrographic and geochemical compositions of these granitoids indicate their belonging to the I-type granites, which are typical for extension environments, whereas leucogranites of the Omsukchan complex have some features corresponding to the A-type granites.

Integration of remote-sensing, structural, and geochemical data for characterizing granitoid rocks in Um Naggat pluton, Central Eastern Desert, Egypt

Integration of remotely-sensed data, field work in addition to geochemical and mineral chemistry analyses, indicates that the Um Naggat granite pluton (UNP) has distinctive lithologic and structural characteristics. Image transformation techniques of using Landsat-8 Operational Land Imager (OLI) data successfully discriminated lithologic characteristics and highlighted hydrothermally altered areas. Shuttle Radar Topography Mission (SRTM) and OLI data allowed highlighting the structural contacts and revealed that the dominant structural trends are NW-SE, NE-SW, and N-S. Petrographic examination, field, and structural survey results revealed that the (UNP) pluton consists of biotite alkali feldspar granite (BAFG) and alkali granite (AG) in addition to a hybrid granite zone (HGZ). The BAFG phase is dominated by an alkaline suite with composition ranging from granite to alkali feldspar granite and pertains to post-orogenic granite (POG) and within-plate granites (WPG). The AG represents the youngest alkali granite phase of magmatism in the studied pluton. Various enclaves from diorites and microgranites have been recorded within the HGZ. Field relationships confirmed with quantitative analysis of magmatic fabric measurements indicate that the AG granitic phase was emplaced as subparallel-elongated sheets or dike-like masses trending E-W and associated with an extensional regime overprinted by the right-lateral strike-slip regime. This phase of “within plate” hypersolvus granite has excessive of large-ion lithophile (LIL) and high field strength (HFS) elements such as Zr, Nb, and Ga that belongs to A-type granites, being depicted by elevated alkali composition and high Fe2O3t/(Fe2O3t +MgO) ratios, and excessive amount of Zr, Y, Nb, and Ga. Microprobe analysis reveals that the compositions of amphibole mineral in the HGZ extent from magnesio-hornblende to actinolite and the temperature of the plagioclase range from 900 to 1050 °C, while the plagioclase of the BAFG is extremely pure albite in composition.

Age and petrogenesis of the beryl-bearing granitic magmatism of the Velasco Pegmatite District, Pampeana Province, NW Argentina

Two porphyritic granitoids (Huaco and Sanagasta) in the Velasco district of the Pampeana Pegmatite Province in Northwestern Argentina are recognized. They are considered the fertile granites of the beryl-bearing pegmatites and can be described as post-orogenic and peraluminous A-type granites formed in an intraplate tectonic setting during an extensive regime, whose magma source is predominantly of cortical origin and to a lesser extent, mantle-derived. The pegmatites are classified as Rare Elements of the beryl type and beryl-columbite-phosphate subtype, while the entire district shows characteristics related to the NYF (Nb-Y-F) petrogenetic family. From rocks and cogenetic minerals of an individual ‘Ismiango’ pegmatite of the Velasco district, two Rb/Sr isochrons have been constructed. They define an age of 330.3 ± 8.3 and 331.7 ± 2.3 Ma and fall in the Lower Carboniferous period, consistent with the age of the parental and host-rock, the Huaco granite. As the Ismiango pegmatite has a similar composition and structure to the other beryl mineralized pegmatites of the Velasco district, the obtained age is attributed extensively for the entire district. According to the initial 87Sr/86Sr value obtained of 0.713, the pegmatite-magmatism of the Velasco District might be mainly derived from the crust with some minor participation of mantle materials.

Amazonite Li–F Granites with REE–Nb–Zr–Th–U Specialization: Geochemistry, Mineralogy, and Isotope Geochronology of the Turga Massif, Eastern Transbaikalia

The paper reports major relations and trends determined in the distributions of trace elements and the Sr and Nd isotope composition of leucogranites of the Turga massif in Eastern Transbaikalia. Three varieties of the leucogranites are distinguished: porphyritic biotite granites, equigranular granites with Li-siderophyllite, and amazonite granites that make up small stocks and dikes. All of the rocks define a single Rb–Sr isochron that corresponds to an age of 134 ± 1 Ma at IR(Sr) = 0.71768 ± 22 and MSWD = 1.2, i.e., all of these rocks crystallized within a narrow age span. The porphyritic biotite granites, which are thought to be parental for the leucogranites, crystallized at lower temperatures (710–740°C) than the younger granites with Li-siderophyllite (810–850°C). Moreover, the granites with Li-siderophyllite have elevated Fe concentrations, which is reflected in that their micas are Fe-rich. The leucogranites are enriched in HFSE (270 ± 59 ppm Zr, 337 ± 93 ppm REE, 72 ± 31 ppm Th, and 16 ± 6 ppm U), which is atypical of amazonite granites in the study area. Considered together with very low Sr and low Ti and P concentrations, these compositional features are distinguishing features of A-type granites. The rare-metal granites of the Turga massif are unique in composition: being similar to amazonite granites in mineralized massifs, these rocks carry accessory minerals typical of peralkaline rocks. They contain LREE fluorides and fluorcarbonates (fluocerite, bastnaesite, and parisite), minerals of the pyrochlore and samarskite groups, and minerals of the isostructural group of REE–Y–Zr–Th–U silicate-phosphates. Our data provide grounds for classifying the rare-metal granites of the Turga massif with an unusual transitional geochemical subtype: peraluminous columbite-bearing amazonite granites of elevated alkalinity with peralkaline REE–Nb–Zr–Th–U mineralization.