Magma Mixing and Mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt

The East Kunlun Orogenic Belt(EKOB)in northeast margin of the Qinghai-Tibetan Plateau is an important part of the Central Orogenic System(COS).During the long-time geological evolution,complicated tectono

Magma Mixing and Mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt

The Changning Menglian belt is an important area of research on the evolution of the Paleo Tethys ocean structure,the belt can be solved such as the Changning Menglianbeltposition;sequencestratigraphy;sedimentary environment;nature and its tectonic evolution history and tectonic domain and Gut Tis relationship;therefore,the research on Chang Ning Menglian zone have a great significance to solve many problems of the Sanjiang fold belt in Tethys and Himalaya tectonic area.'Hot spring'is located in the west margin of the southern Changning Menglian belt,studying Yunnan Fengqing hot spring group'geological and petrology characteristics roundly and in depth,concluding the metamorphism and deformation characteristics,clarifying the metamorphism effect and its stages,understanding the association its combination with the Changning Menglian belt between,therefore it has the great significance to solve the geological evolution history in the Sanjiang area,especially the paleo Tethyan tectonic belt,as well as Gondwana and Eurasia boundaries and other major problem.Through collect and read the literature data,measurement of field section,geological investigation,research and Study on rock sheet indoor,rock composition test,electron probe testing system,summarize the geological characteristics and petrological characteristics of'hot springs group',and through the discussion of the geochemical characteristics of rocks,explore its rock assemblages,characteristics of original rock and analysis of metamorphism and deformation stages,to provide basic data for regional geological evolution.The study shows that the main lithology is biotite quartz schist,mica schist and epimetamorphic sandstone interspersed with a small amount of phyllonite,granulite,silicalite,carbonaceous slate and phyllitic cataclasite that contains some pressure breccia.The metamorphic mineral paragenetic assemblage of the representative rock is:M1 biotite(Bi)+plagioclase(Pl)+quartz(Q),and M2 muscovite(Mus)+quartz(Q).The protolith is felsic rock and sedimentary rock that belongs to argiloid.On the basis of comparison,the stratigraphic sequence of the protolith is consistent with the type section of Wenquan formation.Along with the subduction(Hercynian)-subduction(Indosinian)-orogenic(Yanshan Himalayan period)process of Changning Menglian belt,hot springs group experienced two stages of metamorphism and three stages of deformation,metamorphic temperature at400-500℃,the pressure is foucs on 0.3-0.62Gpa,and shown the retrograde metamorphism of the low greenschist facies.Geological age of hot springs formation is early Devonian(survey team of Yunnan District three units,1980),sedimentary environment is mainly shallow and semi deep sea,observed Bouma sequence in rock slice,therefore,the depositional environment may be fan or basin of sea,the sedimentary formations are mainly clastic rocksiliceous rock formation,the upper coal—contained formation.With the Changning Meng Lian ocean expansion,ocean island begin to develop,material deposition continuing,appearing volcano material,the protolith may contain volcano matter through studying the thin section.To the Late Permian,Crust of Changning Menglian ocean begin to subduct to the east of the Yangtze block,ocean basin began to close,but it still has formation here at this time,mainly shallow carbonate formation,with proceeding of subduction,in the low temperature groove(7Km deep),due to changes in temperature and pressurer,appearing metamorphism(M1)and deformation(D1)for the first time,the shear effect produced by deformation lead to some cleavage,occurring regional foliation S1,major metamorphic minerals formed in metamorphism is long flake biotite.The main metamorphic mineral assemblages are biotite(Bi)+feldspar(Pl)+quartz(Q).Subsequently,crustal uplift,depositional break,because the Changning Meng Lianyang has closed during the Indosinian period,Baoshan-Zhenkang block in the west and the Yangtze block in the east knocked each other.In the Indosinian,under the action of faults,the hot spring formation clipping and retracing,back to a position about1-2Km depth,the position is still belongs to the low temperature groove,and occurring axial cleavage in the core of the fold,namely S2.That is,the emergence of the second metamorphism(M2)and deformation(D2).The deformation is affected by the strong pressure,so the rock have dewatered,so the second metamorphic deformation process is affected by temperature(T),pressure(Ps)and fluid(C).The main metamorphic minerals in the second generation of metamorphism is Muscovite,while there have some of biotite formed in same period,find that the first phase of biotite parallel growth of rock slice,namely S1 parallel S2,and we can see incomplete metamorphism biotite,so the the Muscovite is formed by the first stage of metamorphism and metamorphic biotite.The main mineral of the second stage metamorphism is Muscovite(Mus)+quartz(Q) Then,the crust continues to rise,the sedimentary break continues.In the Jurassic Cretaceous start orogeny,namely Yanshan period intracontinental orogeny,occurred third deformation(D3),under extrusion shearing,S3 emergencing,after Yanshan intracontinental orogenic period,in Himalayan period there have large-scale nappe structure and differential uplift and faulting.So the third deformation(D3)strengthened,with weak metamorphism,sericite emergencing.

The Ore-forming Mechanism of the Jiajika Pegmatite-Type Rare Metal Deposit in Western Sichuan Province:Evidence from Isotope Dating

Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma; however, these proposals are based mainly on analyses of fluid and melt inclusions. Here, we use the Jiajika pegmatite deposit, the largest spodumene deposit in Asia, as a case study to investigate ore forming processes using isotope dating. Dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4 ~ 3.9 Ma, an 4~Ar/39Ar age for muscovite of 182.9 ~ 1.7 Ma, and an 4~Ar/39Ar age for biotite of 169.9 ＋ 1.6 Ma. Based on these dating results and the 4~Ar/39Ar age of muscovite from the Jiajika pegmatite, a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems. This track indicates that the granite cooled over ^-40 m. y., with segregation of the pegmatite fluid from the granitic magma at a temperature of ~700~C. This result suggests that the Jiajika pegmatite formed not by fractional crystallization, but by segregation of an immiscible liquid from the granitic magma. When compared with fractional crystallization, the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization, and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities. We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits, and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.

Textures and melt-crystal-gas interactions in granites

Felsic intrusions present ubiquitous structures.They result from the differential interactions between the magma components(crystal,melt,gas phase) while it flows or when the flow is perturbed by a new magma injection.The most obvious structure consists in fabrics caused by the interactions of rotating grains in a flowing viscous melt.New magma inputs through dikes affect the buk massif flow,considered as global within each mineral facies.A review of the deformation and flow types developing in a magma chamber identifis the patterns that could be expected.It determines their controlling parameters and summarizes the tools for their quantification.Similarly,a brief review of the theology of a complex multiphase magma identifies and suggests interactions between the different components.The specific responses each component presents lead to instability development.In particular,the change in vorticity orientation,associated with the switch between monoclinic to triclinic flow is a cause of many instabilities.Those are preferentially local.Illustrations include fabric development,shear zones and flow banding.They depend of the underlying rheology of interacting magmas.Dikes,enclaves,schlieren and ladder dikes result from the interactions between the magma components and changing boundary conditions.Orbicules,pegmatites,unidirectional solidification textures and miarolitic cavities result from the interaction of the melt with a gaseous phase.The illustrations examine what is relevant to the bulk flow,local structures or boundary conditions.In each case a field observation illustrates the instability.The discussion reformulates instability observations,suggesting new trails for ther description and interpretation in terms of local departure to a bulk flow.A brief look at larger structures and at their evolution tries to relate these instabilities on a broader scale.The helical structures of the Ricany pluton,Czech Republic and by the multiple granitic intrusions of Dolbel,Niger illustrate such events.

Petrogenetic Peculiarities of Rare-Metal Granite of Limu,Guangxi

Limu granite massif is a rather typical Mesozoic rare-metal granite in South China . Studying Limu granite massif has important petrological significance for understanding the genesis of rare-metal granites .This paper deals with the typical petrographic characteristics and peculiarity of REE in massif , and discusses the genesis of Limu granite massif in terms of analysis of these characteristics . It is suggested that Limu granite massif is derivative product of a high ordered superimposed -remelting granitic magma .

Songjianghe biotite monzonitic granite zircon U-Pb geochronology and geochemical significance

The authors studied geochronology and geochemical data of the Songjianghe biotite monzogranite in the southern Zhangguangcai Range in order to determine its formation age,magma source,and tectonic environment. The results indicate that the Songjianghe biotite monzogranite was formed in the Middle Jurassic with an age of 168. 2 ± 2. 0 Ma( MSWD = 0. 93). The monzogranite was characterized by high alkali and low Ca O and Mg O,belonging to high-potassium calc-alkaline,metaluminous I-type granite. The rock is enriched in large ion lithophile elements such as Rb,Ba,and K and strongly depleted high field strength elements such as P,Ti,Nb,and Ta. It is concluded that the Songjianghe biotite monzogranite was derived from partial melting of amphibolite facies metamorphism mafic lower-crust and its formation was controlled by the Pacific Plate subduction.

Highly fractionated granites:Recognition and research

Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture,structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation,mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated(including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sign indicating compositional maturity of the continental crust, and they are also closely related to the rare-elemental(metal) mineralization of W,Sn, Nb, Ta, Li, Be, Rb, Cs, REEs, etc.