Geochronology and geochemistry of gneissic metagranites in eastern Dabie Mountains:Implications for the Neoproterozoic tectono-magmatism along the northeastern margin of the Yangtze Block

The gneissic metagranites with Neoproterozoic protolith ages are widely exposed along the eastern margin of the Dabie ultra-high-pressure(UHP) metamorphic belt.In this paper,five representative plutons,including Huangzhen,Daba,Shima,Shuanghe,and Sanzusi,were selected for a detailed chronological and geochemical study aiming to identify the nature of the protoliths and to reveal their implications for the Neoproterozoic tectono-magmatic evolution along the northeastern margin of the Yangtze Block.These gneissic metagranites consist mainly of quartz,albite(oligoclase) and K-feldspar,and minor amphibole and biotite,as well as some metamorphic minerals due to the UHP metamorphism,such as phengite,epidote and minor kyanite and garnet.Mafic alkaline minerals(e.g.,aegirine or aegirine-augite) have been observed in some of these plutons.Zircon LA-ICP-MS U-Pb dating results indicate that the protoliths of the gneissic metagranites have been generated in Mid-Neoproterozoic(770-780 Ma),and suffered both ultrahigh-pressure metamorphism in Early Mesozoic and subsequently high-pressure eclogite-facies recrystallization at about 215 Ma.Although the gneissic metagranites generally have high SiO2 contents(70.23%-77.23%) and show metaluminous-weakly peraluminous signatures(ASI=0.90-1.05),there are still some geochemical variances between different plutons.Compared with the Sanzusi pluton,the metagranites from the Huangzhen,Daba,Shima,and Shuanghe have high K2O+Na2O contents(7.76%-9.45%),FeOtotal/(FeOtotal+MgO) ratios(0.82-0.96),HFSEs and Ga concentrations with an average 104×Ga/Al ratio up to 3.07.Combined with the features that the four plutons commonly contain aegirine-augite and have high zircon saturation temperatures(816-918°C),it is suggested that their proto-liths belong to peralkaline A-type granites.The Sanzusi pluton generally contains biotite and epidote generated from metamorphic reaction of amphibole,and is chemically enriched in calcium and depleted in potassium with K2O/Na2O ratios ranging from 0.42 to 0.54,suggesting their protoliths should be ascribed to calc-alkaline granitoids(I-type).The gneissic metagranites in the eastern margin of Dabie Mountains show both arc-and rift-like geochemical signatures,and their protoliths likely have been generated by reworking of the preexisting arc-related crust under an extensional setting,suggesting that the northeastern margin of the Yangtze Block during the Middle Neoproterozoic likely have been under the initial stage of a passive rifting rather than in an active rifting setting typically induced by the upwelling of a mantle plume.

Alkaline Prophyries in the Chenghai-Binchuan Tectono-Magmatic Belt,Western Yunnan Province,SW China

1 Introduction Sanjiang tectonic-magma belt is one of the most potential resources’metallogenic belts in China.Cenozoic alkali-rich porphyry-type gold polymetallic mineralization system is a significant characteristic of thisbelt.Chenghai-Binchuan tectonic belt,located in the western margin of the Yangtze block,is an important part

Geochronology and geochemistry of Cretaceous-Eocene granites,Tengchong Block(SW China):Petrogenesis and implications for Mesozoic-Cenozoic tectonic evolution of Eastern Tethys

The Early Cretaceous-Early Eocene granitoids in the Tengchong Block record the evolutionary history of the Mesozoic-Cenozoic tectono-magmatic evolution of Eastern Tethys.(a)The Early Cretaceous granitoids with relatively low(^(87)Sr/^(86)Sr)iratios of 0.7090-0.7169 andε_(Nd)(t)values of-9.8 to-7.8 display metaluminous,calc-alkaline dominated by I-type granite affinity and hybrid mantle-crust geochemical signatures.They may have been derived from melting of the subducted Meso-Tethyan BangongNujiang oceanic crust with terrigenous sediments in an arc-continent collisional setting.(b)The Late Cretaceous-Paleocene granitoids with relatively high(^(87)Sr/^(86)Sr)iratios of 0.7109-0.7627,andε_(Nd)(t)values of-12.1 to-7.9 exhibit metaluminous to peraluminous,calc-alkaline dominated by S-type granite affinity and hybrid Lower-Upper crust geochemical signatures,which may be originated from partial melting of the Meso-Proterozoic continental crust in the collision setting between the Tengchong Block and Baoshan Block.(c)The Early Eocene granitoids have metaluminous,calc-alkaline I-type and S-type granites dual affinity,with relatively high(^(87)Sr/^(86)Sr)iratios of 0.711-0.736,ε_(Nd)(t)values of-9.4 to-4.7,showing crust-mantle mixing geochemical signatures.They may have been originated from partial melting of the late Meso-Proterozoic upper crustal components mixed with some upper mantle material during the ascent process of mantle magma caused by the subduction of the Neo-Tethyan Putao-Myitkyian oceanic crust,and collision between the Western Burma Block and the Tengchong Block.It is these multi-stage subductions and collisions that caused the spatial and temporal distribution of the granitic rocks in the Tengchong Block.

PRELIMINARY STUDY ON GEOTECTONIC EVOLUTION AND METALLOGENIC CONDITIONS OF JIAODONG GOLD METALLOGENIC PROVINCE,SHANDONG, CHINA

The results have demonstrated that the studying area underwent four stages of geotectonie evolution,namely, pre-geosyneline, geosyneline, platform and diwa stages. The gold deposits were formed during diwa stage of the iste Yanshanian Age, undergoing multi-tectono-magmatic activities. Jiaodong Group of the Upper Archean Erathem was the source bed of gold deposits. Granitie msamatic aetivities dived the ore-forming elements transporting. Tectonic activities controlled the formation, the distribution of gold deposits and the scale and the shape of ore body, ete.. The gold deposits exhibit the eharacteristics multi-source of ore-forming elemcnts, multi-genesis, multi-ote-conttolling foctors, multi-genstical types and multi-stage mineralization. They belong to mantle-erust deposits.

History of tectono-magmatic evolution in the Western Kunlun Orogen

Based on the statistical and analytical data on more than 170 isotopic ages published since the 1980s of magmatic rocks, metamorphic rocks, tectonites and ores from the Western Kunlun Orogen, and the characteristics of sedimentation, magmatism, metamorphism and tectonic activities in the region studied in conjunction with geological field investigations and necessary supplementary isotope data, five stages of tectono-magmatic evolution, i.e. Ar3-Pt21 tectono-magmatic active stage (Ⅰ) , Pt22 stable stage (Ⅱ), Pt31-P2 active stage (Ⅲ), T1-T2 stable stage (Ⅳ) , and T3-Q active stage (Ⅴ) can be distinguished in the Western Kunlun Orogen. Moreover, the tectono-magmatic active style and general trend, the characteristics of tectonic settings, etc. of each stage and substage in the region studied are also discussed .

Permian-Triassic magmatic evolution of granitoids from the southeastern Central Asian Orogenic Belt:Implications for accretion leading to collision

Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents.How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB),the largest Phanerozoic accretionary orogenic belt,is an intriguing question.In this paper,we present new U-Pb age,geochemical and isotopic data for Permian-Triassic granitoids from middle Inner Mongolia,Northern China in the southeastern CAOB,and delineate the magmatic transition from subduction to(soft)collision.The magmatic record of soft collision is identified and characterized by thickened lower crust-derived high Sr/Y granitoids with a sub-linear distribution along the Solonker suture zone.Granitoids from Early Permian to Late Permian became more enriched in whole-rock Nd and zircon Hf isotopic compositions(εNd(t)values from 2.4 to-19.5,εHf(t)values from 11.6 to-33.7),indicating increasing incorporation of old crust.The change in peak timing of magmatism from west(ca.264 Ma)to east(ca.251 Ma)along the Solonker suture zone implies"scissor-like"closure of the Paleo-Asian Ocean.Integrated with previous studies,a three-stage tectonic model from the Permian to Triassic by accretion leading to collision on the south-eastern margin of CAOB is proposed.(1)Early Permian(>ca.285 Ma):Juvenile magmatism on an active continental margin with double-sided subduction of the Paleo-Asian Ocean;(2)Middle Permian to Middle Triassic(ca.285–235 Ma):Magma source transition from juvenile to old crust induced by a tectonic switch from arc to"scissor-like"closure and subsequent intracontinental orogenic contraction;(3)Late Triassic(<ca.235 Ma):A-type and alkaline magmatism in response to post-collisional extension.