Cordierite-bearing granulites from Ihosy,southern Madagascar:Petrology,geochronology and regional correlation of suture zones in Madagascar and India

Madagascar,a major fragment of Gondwana,is mainly composed of Precambrian basenent rocks formed by Mesoarchean to Neoproterozoic tectono-thernial events and recording a Pan-African metamorphic overprint.The Ranotsara Shear Zone in southern Madagascar has been correlated with shear zones in southern India and eastern Africa in the reconstruction of the Gondwana supercontinent.Here we present detailed petrology,mineral chemistry,metamorphic P-T constraints using phase equilibrium modelling and zircon U-Pb geochronological data on high-grade metamorphic rocks from Ihosy within the Ranotsara Shear Zone.Garnet-cordierite gneiss from Ihosy experienced two stages of metamorphism.The peak mineral assemblage is interpreted as garnet+sillimanite+cordierite+quartz+plagioclase+Kfeldspar+magnetite+spinel+ilmenite,which is overprinted by a retrograde mineral assemblage of biotite+garnet+cordierite+quartz+plagioclase+K-feldspar+magnetite+spinel+ilmenite.Phase equilibria nodelling in the system Na2 O-CaO-K2 O-FeO-MgO-Al2 O3-SiO2-H2 O-TiO2-Fe2 O3(NCKFMASHTO)indicates peak metamorphic conditions of 850-960℃ and 6.9-77 kbar,and retrograde P-Tconditions of<740℃ and<4.8 kbar,that define a clockwise P-T path.Near-concordant ages of detrital zircon grains in the garnet-cordierite gneiss dominantly exhibit ages between 2030 Ma and 1784 Ma,indicating dominantly Paleoproterozoic sources.The lower intercept age of 514±33 Ma probably indicates the timing of high-grade metamorphism,which coincides with the assembly of the Gondwana supercontinent.The comparable rock types,zircon ages and metamorphic P-T paths between the Ranotsara Shear Zone and the Achankovil Suture Zone in southern India support an interpretation that the Ranotsara Shear Zone is a continuation of the Achankovil Suture Zone.

Recognition of Ophiolite Belt and Granulite in Northern Area of Mian－Lue， Southern Qinling， China and Their Implication

A ophiolite belt associated with the tectonic melange is recoghzed in northern area of Mian-Lue, southern Qinling. The ophiolite is considered to originate in a island arc. The occurrence of the ophiolite indicates that a paleo-ocean or finite oceanic basin existed POSt-Prot6rozoic in southern Qiuling, implying the difference of the continental basement of Southern Qinling from the Yangtze craton. The ophiolitc and themelange may mark the paleo-suture zoic between the two plates. The basic granulite is found in eastern area (Anzishan) of the ophiolite belt. The p-T path for metamorphism of the granulite demonstrates a process of continental collision.

Garnet-bearing Granulite Facies Rock Xenoliths from Late Mesozoic Volcaniclastic Breccia, Xinyang, Henan Province

This paper presents the primary results of petrologic, mineralogical and petrochemical studies of garnet-bearing granulite facies rock xenoliths from Xinyang, Henan Province. These xenoliths, which are found in a pipe of late Mesozoic volcaniclastic breccia, are of high density (3.13–3.30 g/cm3) and high seismic velocity (Vp = 7.04–7.31 km/s), being products of underplating of basaltic magmas and had experienced granulite facies metamorphism. The underplating and metamorphism took place before the eruption of the host rock. Petrographical studies and equilibrium T-P calculations show that these xenoliths were captured at a 49 km depth and experienced at least a 16 km uplift before they were captured. The dynamics of the uplift could be related to the continent-continent collision between the North China plate and the Yangtze plate during the Triassic.

P-T-t Path of Mafic Granulite Metamorphism in Northern Tibet and Its Geodynamical Implications

Mafic granulites have been found as structural lenses within the huge thrust system outcropping about 10 km west of Nam Co of the northern Lhasa Terrane, Tibetan Plateau. Petrological evidence from these rocks indicates four distinct metamorphic assemblages. The early metamorphic assemblage (M1) is preserved only in the granulites and represented by plagioclase+hornblende inclusions within the cores of garnet porphyroblasts. The peak assemblage (M2) consists of garnet+clinopyroxene+hornblende+plagioclase in the mafic granulites. The peak metamorphism was followed by near-isothermal decompression (M3), which resulted in the development of hornblende+plagioclase symplectites surrounding embayed garnet porphyroblasts, and decompression-cooling (M4) is represented by minerals of hornblende+plagioclase recrystallized during mylonization. The peak (M2) P-T conditions of garnet+ clinopyroxene+plagioclase+hornblende were estimated at 769-905℃ and 0.86-1.02 GPa based on the geothermometers and geobarometers. The P-T conditions of plagioclase+hornblende symplectites (M3) were estimated at 720-800℃ and 0.55-0.68 GPa, and recrystallized hornblende+plagioclase (M4) at 594-708℃ and 0.26-0.47 GPa. It is impossible to estimate the P-T conditions of the early metamorphic assemblage (M1) because of the absence of modal minerals. The combination of petrographic textures, metamorphic reaction history, thermobarometric data and corresponding isotopic ages defines a clockwise near-isothermal decompression metamorphic path, suggesting that the mafic granulites had undergone initial crustal thickening, subsequent exhumation, and cooling and retrogression. This tectonothermal path is considered to record two major phases of collision which resulted in both the assemblage of Gondwanaland during the Pan-African orogeny at 531 Ma and the collision of the Qiangtang and Lhasa Terranes at 174 Ma, respectively.

Granulite Genesis and Tectonic Evolution in Tongbai Area:Single Zircon Evaporation Ages and Nd Isotopic Geochemistry

According to the age measurements of single zircon evaporation method, combined with the study of Nd isotopic geochemistry in Tongbai area, the protolith age of basic granulites is about 1 010 Ma; the protolith age of intermediate acid granulites is probably more than 904 Ma, which is close to the age of the basic granulites. The basic granulites would be the nature occurrence of basic magma underplating beneath the base of lower crust in the North Qinling crustal vertical growth event at about 1 000 Ma. However, the intermediate acid granulites were the result of the mixing fusion between the lower crust material and the underplating basic magma, which shows a strong crust mantle interaction. The 470-480 Ma are the peak metamorphic ages of the basic and intermediate acid granulites, which related to the crust bi direction shortening and crust thickening due to the Erlangping back arc basin southward subduction and the paleo Qinling oceanic plate northward subduction.

Important Events and Chronological Framework of the Early Precambrian Granulite Terrain,Northwestern Hebei Province

Based on the chronological data and relevant geological evidence, the chronological framework of the major geological events of the granulite terrain in northwestern Hebei Province and its adjacent areas has been established. Basic lava eruption occurred in the span of 2868-2932 Ma, resulting in the formation of the early crust. The TTG magma emplacement took place c.2761 Ma ago. Subsequently basic magma intruded into the supracrustal rocks at 2650 Ma, resulting in crustal thickening. The thickening was enhanced at 2561-2503 Ma by the widespread intrusions of granodioritic magma. In the period of 2477-2461 Ma charnockite intruded, accompanied by regional granulite facies metamorphism. The second stage of granulite facies metamorphism occurred c. 2300 Ma ago, and finally pink granite intrusions at 2144-2087 Ma resulted in the formation of a granite zone.

LA-ICP-MS U-Pb Zircon Dating for Felsic Granulite, Huangtuling Area, North Dabieshan: Constraints on Timing of Its Protolith and Granulite-Facies Metamorphism, and Thermal Events in Its Provenance

Information about the protolith of the Huangtuling granulite in North Dabieshan has been unavailable. The complex evolution history of the rock and its host basement must be further discussed. LA-ICP-MS U-Pb dating was conducted on three textural domains in zircon from a high-temperature, high-pressure felsic granulite in the Huangtuling area, North Dabieshan, Central China. The metamorphic growth-derived detrital zircon domain yields a 207^ pb/206^Pb age in the range of （2 49±54 ） -- （2 500±180） Ma. The magmatic genesis-derived detrltal zircon domain gives a 207^pb/ 206^Pb age ranging from 2 628 Ma to 2 690 Ma, with an oldest 206^ pb/ 238^U age of （2 790 ± 150） Ma. The metamorphic overgrowth or metamorphic recrystallization zircon domain yields a diesordia with an upper intercept age of （2 044. 7 ± 29.3 ） Ma. Compositions of the mineral assemblage, major element geochemistry, and especially the complex interior texture of the zircon suggest that the prololith of the felsic granulite is of sedimentary origin. Results show that the protolith material of the granulite came from a provenance with a complex thermal history, i.e. -2.8 Ga magmatlsm and -2.5 Ga metamorphism, and was deposited in a basin not earlier than 2.5 Ga. The high-temperature and high-pressure granulite-facies metamorphic age was precisely constrained at （2.04±0.03） Ga, which indicates the granulite in Huangtuling area should be a relict of a Paleoproterozoic UHT （ultrahigh temperature） metamorphosed slab.

From granulite fluids to quartz-carbonate megashear zones:The gold rush

At peak granulite-facies metamorphic conditions, lower continental crust is arguably fluxed by large amounts of two key low water activity fluids： （i） high-density CO2 and/or （ii） concentrated saline so- lutions. These fluids are either internally-derived, generated by mineral reactions or dehydration melting or, notably for CO2, externally-derived, issued from the underlying mantle. Postmetamorphic evolution results in complete disappearance of these fluids, except for minute remnants preserved in minerals as fluid inclusions. Two major processes are involved： （i） at peak conditions, granitoid magmas form, migrate upward, and crystallize as shallow intrusions in the upper crust （mineralized porphyry types or reduced intrusions）; （ii） during the rapid decompression which almost systematically follows a period of post-peak isobaric cooling, especially for ultrahigh-temperature granulites （anticlockwise P-T paths）, quartz-carbonate megashear zones are formed by repeated periods of seismic activity. Seismic activity may continue until all free fluids have disappeared, resulting in the ultramylonites and pseudotachylites that are found in many granulite domes. A great majority of vein-type Au deposits worldwide occur in the above-mentioned settings or nearby. We suggest that the Au has been scavenged by the granulite fluids, then redistributed and concentrated during the formation of veins and related phenomena.

Preliminary Statistics of Temperatures and Pressures for Formation of Eclogites,Granulites and Peridotites in China

The rock forming temperatures and pressures represent the p T points of the local regions in the lithosphere at a certain age, providing some important information on rock formation. Based on the preliminary statistics on the temperatures and pressures for the formation of eclogites, granulites and peridotites in China, the variant ranges are given, in this paper, of temperatures, pressures and linear geothermal gradients of eclogites, granulites and peridotites. In addition, since the eclogite is different from granulite and peridotite in the p T diagram, these three rocks can be classified into two groups: the first group includes eclogites and the second group granulites and peridotites. Then, the p T correlation functions of these two groups of rocks are provided. Finally, the two groups of rocks have different geothermal gradients at the same pressure gradient or have different pressure gradients at the same geothermal gradient. The temperatures and pressures for the formation of the rocks can be calculated from the mineral chemical compositions, but the depths ( H ) for the rock formation can be calculated only under the hypotheses of given p H (or T H ) correlation functions. The explanations for the ultrahigh pressure metamorphism vary obviously with different hypotheses.

Discovery and Genetic Mechanism of Basic Granulite in the Altay Orogenic Belt, Xinjiang, NW China

Altay granulite (AG), which represents the product of high-grade metamorphism in the lower crust, was newly found in the Wuqiagou area, Fuyun County in the Altay orogenic belt, Northwest China. It is composed mainly of hypersthene, augite, basic plagioclase, amphibole and brown biotite. Its mineral compositions of amphibole and biotite are rich in Mg/(Mg+Fe2+) and Ti. Geochemically, the AG is enriched in Mg/(Mg+Fe2+) and A12O3, and poor in CaO, with depletion of U, Th, K and Rb contents. Furthermore, geochemical data reflect that the protolith of the AG is igneous-genetic calc-alkaline basalt formed under an island arc environment. The AG has ZREE of 92.38-96.58 ppm and enriched LREE model with weak positive Eu anomaly of 1.09-1.15. In the MORB normalized spider diagram, the AG shows tri-doming pattern with a strong negative Nb anomaly and medium negative P and Ti anomalies, reflecting that the AG has tectonic relation with subduction or subduction-related materials. The P-T conditions of peak metamorphism of the AG are 750-780℃ and >0.6-0.7 GPa. Retrograde metamorphism implies that the protolith of the Altay granulite might undergo a metamorphic process along a clockwise P-T trajectory. Therefore, the formation and evolution of the AG may have a genetic association with continental collision/orogeny and the AG was taken into the Late Paleozoic meta-strata by way of tectonic emplacement.

Granulite-facies Middle-Lower Crustal Xenoliths from Nushan Alkali Basalt in Northeastern Anhui Province,China

Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely found.Basic two-pyroxene granulites(pyriclasites) were formed at 720-810℃ and 7-8kb.Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the pa-rental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma.The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China ,which implies the inhomogeneity regarding to the early evolution of the North China terranc.

Metamorphism and zircon U-Pb dating of high-pressure pelitic granulites from glacial moraines in the Grove Mountains, East Antarctica

The Grove Mountains are an inland continuation of the Prydz Belt in East Antarctica. Detailed metamorphic petrological and zircon U-Pb geochronological studies are performed on the high-pressure （HP） pelitic granulites from glacial moraines in the Grove Mountains. The metamorphic peak mineral assemblage of the HP pelitic granulites is characterized by garnet ＋ kyanite ＋ K-feldspar ＋ biotite ＋ plagioclase ＋ quartz, and the subsequent medium-pressure （MP） granulite facies retrogression is characterized by sillimanite replacing kyanite, the formation of the biolite ＋ sillimanite symplectite in the matrix. These mineral assemblages and their P-T estimates based on the P-T pseudosection constructed in MnNCKFMASHT system define a clockwise P-T path involving metamorphic peak of 11.6–13.6 kbar at 817–834°C followed by a near-isothermal decompression of 6.7–7.5 kbar at 806–828°C, comparable with those of associated HP mafic granulites from glacial moraines in the Grove Mountains. Zircon U-Pb dating, coupled with available metamorphic age data obtained for HP mafic granulites, reveals HP metamorphism occurred at 540–545 Ma. Combining the previous research results, the HP pelitic granulites and contemporary HP mafic granulites were widely distributed in glacial moraines from the Grove Mountains, suggesting at least part of the Grove Subglacial Highlands underwent Pan-Afrian HP granulite facies metamorphism, which provides new evidence for a collisional tectonic setting of the Pan-Afrian Prydz Belt.

Geochronological Study of Caledonian Granulite and High-Pressure Gneiss in the Dabie Mountains

Using the single—zircon evaporation technique and U—Pb method, the authors have conducted an isotope geochonological study of the Huilanshan granulite and Shima garnet-bearing plagioclase gneiss (“country rocks” of the Shima eclogite) in the Dabie Mountains. The study shows that these rocks have peak metamorphic ages of 443–455 Ma, which are essentially consistent with that of the Caledonian high—ultrahigh pressure eclogites. This indicates the existence of the Caledonian collisional orogeny in the Dabie Mountains.

Petrology and SHRIMP zircon geochronology of granulites from Vesleknausen, Lützow-Holm Complex, East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism

We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the L＆#252;tzow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss （charnockite and minor biotite gneiss）, mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750e850 ？C, approximately 150 ？C lower than those estimated for met-asedimentary gneisses from Rundv？gshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss, yielded a Concordia upper intercept ages of 2507.9 ？ 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundv？gshetta-Vesleknausen-Strandnibba region in southwestern L＆#252;tzow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc mag-matism. The Neoarchean magmatic terrane was tectonically mingled with other fragments （such as metasedimentary units in northern L＆#252;tzow-Holm Bay） by subduction/collision events during the as-sembly of Gondwana supercontinent, and subsequently underwent w850 ？C granulite-facies meta-morphosed during Neoproterozoic to Cambrian final collisional event.

The Sm-Nd Geochronology of the High Pressure Basic Granulite in Laixi, Eastern Shandong

A high pressure basic granulite ultramafic rock belt, which is about 200km long and trends toward NE, occurs in the late Archaean orthogneiss in Laixi Laiyang Qixia area, eastern Shangdong. This belt is located east to the Su Lu UHPM terrane and west to the Archaean rocks of the North China craton, therefore, its geological situation and implication for collision between the North China plate and the Yangtze plate is very important. The analyzed sample of high pressure basic granulite has decreasing pressure metamorphic texture. The mineral assemblage of retrograde metamorphism is of granulite facies. The sample yields an internal mineral whole rock Sm Nd isochron age of 1725Ma. The T(DM) age of whole rock is 2788Ma. These data are very similar to those of high pressure basic granulites in Northern China craton. Considering the petrological and geochemical characteristics and isotopic ages, the high pressure granulite ultramafic rock belt in eastern Shandong is suggested to belong to the North China craton and to be of the early Precambrian lower crust. Their lifting from the lower crustal level is related to collision between the North China plate and the Yangtze plate.

Petrological Investigations and Zircon U-Pb Dating of High Pressure Felsic Granulites from the Yushugou Complex, South Tianshan, China

As a window of insight into the lower crust, high pressure granulite has received much attention since last decade. Yushugou high pressure granulite-peridotite Complex was located in the northeast margin of Southern Tianshan, NW China. Previous ideas agreed that the peridotite unit in Yushugou, combined with the ultramafic rocks in Tonghuashan and Liuhuangshan, represent an ophiolite belt. However, the metamorphic evolution and tectonic mechanism of the Yushugou high pressure （HP） granulite remain controversial. Petrological investigations and phase equilibrium modelling for two representative fclsic granulitc samples suggest two stages metamorphism of the rocks in Yushugou Complex. Granulite facies metamorphism （Stage I） with P-T conditions of 9.8-10.4 kbar at 895-920℃ was recorded by the porphyroblastic garnet core; HP granulite facies metamorphism （Stage II） shows P-T conditions of 13.2-13.5 kbar at 845-860℃, based on the increasing grossular and decreasing pyrope contents of garnet rims. The Yushugou HP felsic granulites have recorded an anti- clockwise P-T path, characterized by the temperature decreasing and pressure increasing simultaneously. The LA-ICP-MS isotopic investigations on zircons from the felsic granulite show that the protolith ages of the granlulites are -430 Ma, with two age groups of-390 Ma and 340-350 Ma from the metamorphic rims of zircon, indicating the Stage I and II metamorphic events, respectively. A tectonic model was proposed to interpret the processes. The investigated felsic granulite was derived from deep rooted hanging wall, with Stage I granulite facies metamorphism of -390 Ma, which may he related to the Devonian arc magmatic intrusion; Stage II HP granulite facies metamorphism （340-350 Ma） may due to the involvement of being captured into the subducting slab and experienced the high pressure metamorphism.

A Sm－Nd mineral isochron of mafic granulite from the Sφstrene Island， East Antarctica

Redetedrination of the metamorphic age of the gsrnet-bearing mafic wholeulite from the Sstrene Island, Esat Antarctica has been made and an isochron of wholerock-garnet-pyroxene-plagioclase is obtained, giving an age of [604±28(2σ)] Ma. Itis pointed out that this age represents the time of peak granulite facies metamorphism ofthe area. As to the geological relation of the Sstrene Island with the Bolingen Islandsand the Larsemann Hills to the east, it is deduced from the rock assemblages, metamorphic superposition, spatial changes and metamorphic ages between the above regions that the degree of the superposition of the later low pressure metamorphism is becoming stronger from west to east. While the evolution of the earlier medium pressure to later low pressure implies probably the substages of the same metamorphic cycle.

The potential role of fluids during regional granulitefacies dehydration in the lower crust

High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting, fluid-aided solid-state dehydration, or varying degrees of both. On the localized meter scale, solid-state dehydration, due to CO：-rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock, normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur. Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which, along with accompanying amphibolite-facies rocks, form traverses of lower crust. This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale. The more prominent of these fluid-induced textures in the granulite- facies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite. The fluids believed responsible take the form of concentrated NaCl- and KCl- brines from a basement ultramafic magma heat source traveling upwards along grain boundaries. Additional experimental work involving CaSO4 dissolution in NaCl-brines, coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks, have demonstrated the possibility that NaCl-brines, with a CaSO4 component, could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths. These results, taken together, lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it.Their presence allows for rapid mass and heat transport and subsequent mineral genesis and mineral re- equilibration in the rocks through which they pass.

Characteristics of Lower Crustal Granulite Xenoliths from the East Qinling Orogenic Belt and Their Tectonic Significance

The Tongbai granulites are present mainly as xenoliths in granodioritic gneisses. The xenoliths with a zircon age of 470Ma are older than the host rocks of granodioritic gneisses which yield a zircon age of 435Ma. It is suggested that the granulites were transported from the lower crust to the upper level along with granodioritic magma. Geothermometrical and geobarometrical studies based on the coexisting minerals (Opx-Cpx and Opx-Gar) show that the granulites were crystallized at 818-840℃ and 9.5-9.8 ×108 Pa corresponding to the lower crust. Tectonically, the Shangdan suture zone conshtutes the boundary between the North China and Yangtze plates. The zone is characterized by the occurrence of ophiolites in the western part and by that of granulites in the eastern part. So the western part marks the upper crustal level of the Qinling belt, while the eastern part represents the exposure of a deeper level. The results of isotopic dating and the geochemical characteristics of the xenoliths are consistent with those of meta-tholeiltes of the ophiolites in the western part.Therefore, it is assumed that both ophiolites found in the west and granulites found in the east all represent the renmants of the ancient Qinling ocean plate. The difference is that the ophiolites are pieces of obductal fragments from the ocean floor during the subduction in the Early Palaeozoic.However, in the Tongbai area, when the ocean floor was subducting towards the lower crust, it underwent a granulite facies metamorphism. Subsequently, granodioritic magma formed by partial melting trapped some fragments of granulite upwards.

Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China

The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg+Fe^2+),and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg+Fe^2+), Al2O3 and depletion of U, Th and Rbcontents. The AG has moderate ∑REE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750℃-780℃ and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.