Fluid Activity and Tectonic Evolution in the Northern Qilian High-pressure Metamorphic Belt

The Northern Qilian high-pressure metamorphic belt has experienced multipledeformation-metamorphism, which consists of at least four stages. In 550.8-526 Ma, eclogites wereformed. High temperature and pressure caused the escape of a large quantity of gas-liquid fluidsfrom rocks while silicate melt was generated. In the late stage, small amounts of CO_2 and H_2Oinfiltrating along fractures were introduced. In the formation of glaucophane schist (447-362 Ma),devolatilization reactions were dominated during the subduction-uplift stage of the paleoplate. Inthe uplift-exhumation stage (400-380 Ma) the increase of internal space of fractures in the rocksfavoured fluid infiltration and concentration. These fluids participated in hydration reactions inthe retro-metamorphism. The fluids participating in the mineral reactions have the compositions ofCaCl_2-NaCl-H_2O. In subsequent thrusting (<380 Ma), the metamorphic terrain was uplifted to theshallower crust and ductile-shearing deformation took place, which caused mainly dehydrationreactions of minerals. In a near-surface environment the metamorphic terrain experienced brittledeformation, forming many accompanying fractures. Immiscible CO_2 and low-salinity aqueous fluidsoccurred in these secondary microfractures and were trapped and sealed. The thermodynamic conditionsof different deformation-metamorphic stages of the metamorphic terrain were calculated and thecorresponding P-T-t path was deduced, showing that the metamorphic terrain has experienced aclockwise path indicated by T- and P-rising, and T- and P-falling processes. This reveals that thesubduction zone has undergone multiple tectono-dynamic processes, i.e. initial deep burial,subsequent quick uplift and near-surface tectonism.

The Lanshantou Kyanite-bearing Eclogite with Coesite Inclusions in the Sulu Ultrahigh-Pressure Metamorphic Belt and Its PTt Path

Coesite inclusions are found in kyanite from the Lanshantou eclogite in the Sulu ultrahigh-pressure (UHP) metamorphic belt. This discovery extends the stable region of kyanite to over 2.4 GPa. As an important UHP metamorphic belt in China, the Sulu eclogite belt is the product of A-subduction induced by strong compression of the Yellow Sea terrane to the Jiaodong-northereastern Jiangsu terrane during the interaction of the Eurasian plate and Palaeo-Pacific plate in the Indosinian. It stretches about 350 km and contains over 1000 eclogite bodies. Most eclogites in this belt belong to Groups B and C in the classification of Coleman et al., and commonly contain kyanite, while the Lanshantou eclogite belongs to Group A and contains coesite. The MgO, CaO and FeO contents in garnet and pyroxene show regular variation from the core to the rim, which reveals the PTt paths of progressive metamorphism during the Early Mesozoic (240-200 Ma) and retrogressive metamorphism during the Late Mesozoic and Cenozoic exhumation.

Investigation of Curie Point Depth in Sulu Ultrahigh-Pressure Metamorphic Belt,Eastern China

The Curie point depth of continental crust can reflect the regional tectonic pattern and geothermal structures. Analysis of magnetism is an efficient way to obtain the Curie point depth on a regional scale. This study systematically investigated the Curie point depth of Sulu （苏鲁） ultrahigh pressure （UHP） metamorphic belt （33°40＇N to 36°20＇N and 118°E to 120°E, ca. 60 000 km^2）, eastern China using aeromagnetic data. The results show that the Curie point depth of the Sulu region varies from 18.5 to 27 km. The shallowest Curie point depth （ca. 18.5 km） is located in Subei （苏北） subsidence, where the estimated temperature gradient value is about 31.35℃/km, which is comparable with the measured value of 30 ℃/km. In addition, a two-dimensional numerical solution of the heat conduction was used to calculate the temperature field to a depth of 30 km along the profile from Tancheng （郯城） to Lianshui （涟水） with a length of 139 km. The steady state model solved using the finite element method shows that the temperature around the Curie point depth is about 585.36 ℃, which is close to the Curie temperature （580℃） of magnetite at atmospheric pressure. These results provide new insights into the tectonic and continuous thermal structures of the Sulu UHP metamorphic belt.

Geochemical Characteristics of Pb Isotope of High-Pressure Metamorphic Rocks and Foliated Granites from HP Unit of Tongbai-Dabie Orogenic Belt

Whole-rock Pb isotopic compositions of the high-pressure (HP) metamorphic rocks, consisting of two-mica albite gneisses and eclogites, and foliated granites from the HP metamorphic unit of the Tongbai-Dabie orogenic belt are firstly reported in this paper. The results show that the HP metamorphic rocks in different parts of this orogenic belt have similar Pb isotopic compositions. The two- mica albite gneisses have 206 Pb/ 204 Pb=17.657-18.168, 207 Pb/ 204 Pb=15.318-15.573, 208 Pb/ 204 Pb=38.315-38.990, and the eclogites have 206 Pb/ 204 Pb=17.599-18.310, 207 Pb/ 204 Pb=15.465- 15.615 , 208 Pb/ 204 Pb=37.968-39.143. The HP metamorphic rocks are characterized by upper crustal Pb isotopic composition. Although the Pb isotopic composition of the HP metamorphic rocks partly overlaps that of the ultrahigh-pressure (UHP) metamorphic rocks, as a whole, the former is higher than the latter. The high radiogenic Pb isotopic composition for the HP metamorphic rocks confirms that the subducted Yangtze continental crust in the Tongbai-Dabie orogenic belt has the chemical structure of increasing radiogenic Pb isotopic composition from lower crust to upper crust. The foliated granites, intruded in the HP metamorphic rocks post the HP/UHP metamorphism, have 206 Pb/ 204 Pb=17.128-17.434, 207 Pb/ 204 Pb=15.313-15.422 and 208 Pb/ 204 Pb=37.631-38.122, which are obviously different from the Pb isotopic compositions of the HP metamorphic rocks but similar to those of the UHP metamorphic rocks and the foliated garnet-bearing granites in the UHP unit. This shows that the foliated granites from the HP and UHP units have common magma source. Combined with the foliated granites having the geochemical characteristics of A-type granites, it is suggested that the magma for the foliated granites in the UHP and HP unit would be derived from the partial melting of the retrometamorphosed UHP metamorphic rocks exhumed into middle to lower crust, and partial magmas were intruded into the HP unit.

Interpretation of Aeromagnetic Anomalies of the Sulu Ultrahigh-Pressure(UHP) Metamorphic Belt,Eastern China

The Sulu ultra-high pressure(UHP)metamorphic belt in Eastern China is well known as the eastern extension of the Qingling-Dabie orogenic belt formed by subduction and collision between the Sino-Korean and Yangtze cratons.The main hole of the Chinese Continental Scientific Drilling(CCSD)project is located at the southern segment of the Sulu UHP metamorphic belt(34°25′N/118°40′E),about 17 km southwest of Donghai County.Integrated geophysical investigations using gravity,magnetic,deep

Retrogressive Microstructures: A Key to Post-Collisional Uplift and Extension Tectonics of Ultrahigh-Pressure Metamorphic Rocks from Dabie Orogenic Belt, China

A wealth of retrogressive microstructures have been discovered from the UHP metamorphic rocks in Dabie orogenic belt, namely, the ultrahigh-pressure (URP) eclogites, jadeite quartzites and kyanite-zoisite-quartz vein. The most important are pseudomorphic replacements of UHP minerals like coesite, the corona reaction textures iuduced by solid-solid reactions as well as the corona and symplectites induced by reactions involving fluid. According to the textural relationships the sequence of mineral Paragenesis and the metamorphic stages in the UHP eclogites can be delineated; the mineral geobarothermometry of the various stages of retrograde metamorphism is studied and a clockwise, nearly isothermal decompressive metamorphic PT-trajectory for the UHP eclogites can be reconstructed. In terms of the PT-trajectory the two stage post collision uplirt and exhumation processes are reflected. When the UHP metumorphic rocks extruded to the lower-middle crust partial melting happened which bad in turn caused tke crustal extension and the further exhumation or the UHP metomorphic rocks. Based on the field strain analysis combined with geochronological data a scenario or post collision uplift aud exhumation model is presented.

Metamorphic gradient modification in the Early Cretaceous Northern Andes subduction zone:A record from thermally overprinted high-pressure rocks

New field observations and petrological data from Early Cretaceous metamorphic rocks in the Central Cordillera of the Colombian Andes allowed the recognition of thermally overprinted high-pressure rocks derived from oceanic crust protoliths.The obtained metamorphic path suggests that the rocks evolved from blueschist to eclogite facies towards upper amphibolite to high-pressure granulite facies transitional conditions.Eclogite facies conditions,better recorded in mafic protoliths,are revealed by relic lawsonite and phengite,bleb-to worm-like diopside-albite symplectites,as well as garnet core composition.Upper amphibolite to high pressure granulite facies overprinting is supported by coarse-grained brown-colored Ti-rich amphibole,augite,and oligoclase recrystallization,as well as the record of partial melting leucosomes.Phase equilibria and pressure-temperature(P-T)path modeling suggest initial high-pressure metamorphic conditions M1 yielding 18.2-24.5 kbar and 465-580℃,followed by upper amphibolite to high pressure granulite facies overprinting stage M2 yielding 6.5-14.2 kbar and 580-720℃.Retrograde conditions M3 obtained through chlorite thermometry yield temperatures ranging around 286-400℃at pressures below 6.5-11 kbar.The obtained clockwise P-T path,the garnet zonation pattern revealing a decrease in X_(grs)/X_(prp)related to Mg#increment from core to rim,the presence of partial melting veins,as well as regional constraints,document the modification of the thermal structure of the active subduction zone in Northern Andes during the Early Cretaceous.Such increment of the metamorphic gradient within the subduction interface is associated with slab roll-back geodynamics where hot mantle inflow was triggered.This scenario is also argued by the reported trench-ward magmatic arc migration and multiple extensional basin formation during this period.The presented example constitutes the first report of Cretaceous roll-back-related metamorphism in the Caribbean and Andean realms,representing an additional piece of evidence for a margin-scale extensional event that modified the northwestern border of South America during the Early Cretaceous.

The Key Influence of Fluid in Metamorphic Rock Preserves, Mineral Assemblages, Compositions and Structures: Study from High-Pressure Eclogite and Its Amphibolization in the Western Dabie Mountains,Central China

The most of high/ultrahigh-pressure(HP/UHP)terranes of the world are characterized by the occurrence of numerous pods,lenses or layered blocks of eclogite and amphibolites(e.g.O’Brien,1997;Elvevold and Gilotti,2000;Zhang et al.,2003;and references there in).Field and petrological features suggest that amphibolites should

The Dabieshan Coesite-bearing Eclogite Terrain-A Late Archaean Ultra - high- Pressure Metamorphic Belt

A U -Pb zircon age of 2774±24 Ma for eclogite from the Bixiling rock body of Anhui Province, central China, indicates that the Dabieshan coesite-bearing eclogite was probably formed in the Late Archaean. A phengite Ar-Ar isochron age of 662±13 Ma for the eclogite confines also an upper limit age of its subsequent retrograde metamorphism in the Precambrian. The results of isotopic dating for such type of eclogite coincide with the geological features of its restricted occurrence within the Archaean metamaorphic terrain composed of the Dabie Group. It is believed that the Dabieshan coesite-bearing eclogite terrain might be a Late Archaean ultra-high-pressure metamorphic belt. The Dabie Mountains area was the eastward extension of the southern Qinling structural belt during the Triassic. Both the Dabie Group and the coesite-bearing eclogite hosted therein underwent a late-stage dynamic metamorphic event. The present authors have obtained a muscovite Ar-Ar isochron age of 192.6±2.8 Ma from plagioclase gneiss and a hornblende Ar-Ar plateau age of 230.7±4.6 Ma for the low amphibolite in eclogite respectively, which represent the Indosinian reworking ages of the original metamorphic rocks of the Dabie Group gneiss and coesite-bearing eclogite.

Tectonic Evolution of an Early Precambrian High-Pressure Granulite Belt in the North China Craton

A large-scale high-pressure granulite belt (HPGB), more than 700 km long, is recognized within the metamorphic basement of the North China craton. In the regional tectonic framework, the Hengshan-Chengde HPGB is located in the central collision belt between the western block and eastern block, and represents the deep crustal structural level. The typical high-pressure granulite (HPG) outcrops are distributed in the Hengshan and Chengde areas. HPGs commonly occur as mafic xenoliths within ductile shear zones, and underwent multipile deformations. To the south, the Hengshan-Chengde HPGB is juxtaposed with the Wutai greenstone belt by several strike-slip shear zones. Preliminary isotopic age dating indicates that HPGs from North China were mainly generated at the end of the Neoarchaean, assocaited with tectonic assembly of the western and eastern blocks.

Post-Collisional Ductile Extensional Tectonic Framework in the UHP and HP Metamorphic Belts in the Dabie-Sulu Region, China

The present-day observable tectonic framework of the ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic belts in the Dabie-Sulu region was dominantly formed by an extensional process, mostly between 200 and 170 Ma, following the Triassic collision between the Sino-Korean and Yangtze cratons. The framework that controls the present spatial distribution of UHP and HP metamorphic rocks in particular displays the typical features of a Cordilleran-type metamorphic core complex, in which at least four regional-scale, shallow-dipping detachment zones are recognized. Each of these detachment zones corresponds to a pressure gap of 0.5 to 2.0 GPa. The detachment zones separate the rocks exposed in the region into several petrotectonic units with different P-T conditions. The geometry and kinematics of both the detachment zones and the petrotectonic units show that the exhumation of UHP and HP metamorphic rocks in the Dabie-Sulu region was achieved, at least in part, by non-coaxial ductile flow in the multi-layered detachment zones, and by coaxial vertical shortening and horizontal stretching in the metamorphic units, under amphibolite- to greenschist-facies conditions, and in an extensional regime. All ductile extensional deformations occurred at depths below 10 to 15 km, i.e. below the brittle/ductile deformation transition.

Petrology of the Non-mafic UHP Metamorphic Rocks from a Drillhole in the Southern Sulu Orogenic Belt,Eastern-Central China

The Drillhole ZK703 with a depth of 558 m is located in the Donghai area of the southern Sulu ultrahigh-pressure (UHP) metamorphic belt, eastern China, and penetrates typical UHP eclogites and various non-mafic rocks, including peridotite, gneiss, schist and quartzite. Their protoliths include ultramafic, mafic, intermediate, intermediate-acidic, acidic igneous rocks and sediments. These rocks are intimately interlayered, which are meters to millimeters thick with sharp and nontectonic contacts, suggesting in-situ metamorphism under UHP eclogite facies conditions. The following petrologic features indicate that the non-mafic rocks have experienced early-stage UHP metamorphism together with the eclogites: (1) phengite relics in gneisses and schists contain a high content of Si, up to 3.52 p.f.u. (per formula unit), while amphibolite-facies phengites have considerably low Si content (<3.26 p.f.u.); (2) jadeite relics are found in quartzite and jadeitite; (3) various types of symplectitic coronas and pseud

Precambrian Metamorphism of Tiya－Olokit Metamorphic Belt in Northern Balkal Region and its Metallogeny

The paper deals with results of petrological observations of the Precambrian rocks in the Tiya-Olokit metamorphic belt of the Northern Balkal region. Evoluhon of mstamorphic processes from Archean through to Paleozoic is characterized. Interrelations of metamorphic and ore formation processes are shown .Various genetic types of metamorphism and their metallogeulc speianzation (pyrihc-polylnetallic, gold-sulphide and others) are established.A great number of previously published analyses of garnets, biohtes, amphiholes, pyroxenes and muscovitde from metamorphic rocks have been made use of. The evoluhon of their compositions under progressive zoned metamorphism and diaphthoresis is revealed.

Kanfenggou UHP Metamorphic Fragment in Eastern Qinling Orogen and Its Relationship to Dabie-Sulu UHP and HP Metamorphic Belts, Central China

In the Central Orogenic Belt, China, two UHP metamorphic belts are discriminated mainly based on a detailed structural analysis of the Kanfenggou UHP metamorphic fragment exposed in the eastern Qinling orogen, and together with previous regional structural, petrological and geochronological data at the scale of the orogenic domain. The first one corresponds to the South Altun North Qaidam North Qinling UHP metamorphic belt. The other is the Dabie Sulu UHP and HP metamorphic belts. The two UHP metamorphic belts are separated by a series of tectonic slices composed by the Qinling rock group, Danfeng rock group and Liuling or Foziling rock group etc. respectively, and are different in age of the peak UHP metamorphism and geodynamic implications for continental deep subduction and collision. Regional field and petrological relationships suggest that the Kanfenggou UHP metamorphic fragment that contains a large volume of the coesite and microdiamond bearing eclogite lenses is compatible with the structures recognized in the South Altun and North Qaidam UHP metamorphic fragments exposed in the western part of China, thereby forming a large UHP metamorphic belt up to 1 000 km long along the orogen strike. This UHP metamorphic belt represents an intercontinental deep subduction and collision belt between the Yangtze and Sino Korean cratons, occurred during the Paleozoic. On the other hand, the well constrained Dabie Sulu UHP and HP metamorphic belts occurred mainly during Triassic time (250-220 Ma), and were produced by the intracontinental deep subduction and collision within the Yangtze craton. The Kanfenggou UHP metamorphic fragment does not appear to link with the Dabie Sulu UHP and HP metamorphic belts along the orogen. There is no reason to assume the two UHP metamorphic belts as a single giant deep subduction and collision zone in the Central Orogenic Belt situated between the Yangtze and Sino Korean cratons. Therefore, any dynamic model for the orogen must account for the development of UHP metamorphic rocks belonging to the separate two tectonic belts of different age and tectono metamorphic history.

Crustal structure in Dabieshan UHP metamorphic belt and its tectonic implication

The model of Dabieshan crustal structure has been obtained on the basis of the deep seismic sounding data in thisarea. The 2-D crustal structure shows the feature of the collision orogens and provides some deep geophysicalevidences of the ultra-high pressure (UHP) metamorphic belt. The 3-D upper-crustal velocity struCture reveals thatthe velocity distribution at 2 km deep obviously relates to the surface geological setting and the UHP metarnorphicbelt has the higher velocity at 5~10 km deep. The observed data of Bouguer gravity anomalies reveal a largerrange of negative anomalies in Dabieshan area while the positive anomalies in the UHP metamorphic belt is calculated from the 3-D upper-crustal velocity structure. The 2-D crustal model along the seismic profile shows thatthe 'root' beneath the orogen is only 4-5 km thick and the velocity in the uppermost mantle changes a little in thelateral direction. The inconsistency between the observed and calculated Bouguer gravity anomalies mainly resultsfrom the crust, and at least the middle-upper crust should yield the negative anomalies. The material density of thecrust in the UHP metamorphic belt should be lower than that in the surrounding areas. This material with lowerdensity relates to the collision processes in which Yangtze crust subducted nor'thward to 100 km deep and thenreturned to the crust.

The discovery of TiO_(2)-Ⅱ,the α-PbO_(2)-structured high-pressure polymorph of rutile,in the Suizhou L6 chondrite

We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.

Elemental geochemistry and Nd isotopic characteristics of the metasedimentary rocks from the metamorphic belt in central Jiangxi: Provenance and tectonically environmental constraints

The metamorphic belt in central Jiangxi, located in the compound terrain within the Cathaysia, Yangtze Block and Caledonian fold zone of South China, is composed dominantly of meta-argillo-arenaceous rocks, with minor amphibolite. These rocks underwent amphibolite-facies metamorphism. The meta-argillo-arenaceous rocks show large variations in major element composition, but have similar REE patterns and trace element composition, incompatible element and LIE enrichments [high Th/Sc ({0.57}-{3.59}), La/Sc ({1.46}-{12.4}), La/Yb ({5.84}-{19.0})] and variable Th/U ratios, with ΣREE=129-296μg/g, δEu={0.51}-{0.86}, and (La/Yb)-N={3.95}-{12.9}. The Nd isotopic model ages t-{DM} of these rocks vary from 1597 to 2124 Ma. Their {}+{143}Nd/+{144}Nd values are low [ε-{Nd}(0)={-11.4} to {-15.8}]. Some conclusions have been drawn as follows: (1) The metamorphic rocks in central Jiangxi Province are likely formed in a tectonic environment at the passive continental margin of the Cathaysia massif. (2) The metamorphosed argillo-arenaceous rocks are composed dominantly of upper crustal-source rocks (Al- and K|rich granitic or/and sedimentary rocks of Early Proterozoic), which experienced good sorting, slow deposition and more intense chemical weathering. (3) According to the whole-rock Sm-Nd isochron ages (1113±49 to 1199±26 Ma) of plagioclase-amphibole (schist) and Nd isotopic model age t-{DM} (1597-2124 Ma) of meta-argillo-arenaceous rocks, the metamorphic belt in central Jiangxi Province was formed during the Middle Proterozoic (1100-1600 Ma).

Rare-Earth Element Geochemistry of Eclogites from the Ultra-High Pressure Metamorphic Belt in Central China

Based on their REE contents and REE patterns, eclogites from the ultra\|high pressure metamorphic belt in central China may be roughly divided into six types including LREE\|rich, LREE\|rich+positive Eu anomaly, LREE\|rich+negative Eu anomaly, REE pattern\|smooth, MREE\|rich and HREE\|rich. The LREE\|rich, LREE\|rich+positive Eu anomaly and LREE\|rich+negative Eu anomaly types of eclogites are dominant. REE types of eclogites in different areas can be compared and the REE features of the same REE type of eclogites in different areas are similar. The results of reconstruction of the primary rocks show that the primary rocks of eclogites possibly are dominated by continental tholeiites which are the product of partial melting of relatively fertile mantle and the rocks of tholeiite crystallization\|differentiation. There is perfect evolution relationship among the primary rocks of the LREE\|rich, LREE\|rich+positive Eu anomaly and LREE\|rich+negative Eu anomaly types of eclogites and among those of the REE pattern smooth and MREE\|rich types of eclogites, the former three types were derived from continental settings and the latter two from nearly oceanic settings. Meanwhile, it is concluded that the mantle sources of primary rocks of the eclogites are inhomogeneous and the primary rocks of eclogites in this area appear to have undergone varying degree of crustal contamination.

SHRIMP zircon U-Pb dating of a small tonalite intrusion in metamorphic belt of Chinese Altai orogen and its geological implication

Small granitic intrusions occur in the progressive metamorphic belts of the Chinese Ahai orogen. SHRIMP U-Pb analyses were performed on zircons separated from a tonalite intrusion and yielded a concordant age of 409.6±3.7 Ma （ MSWD = 0.93 ）, restricting the emplacement and crystallization of the tonalite intru- sion to the Early Devonian. Combined with the existing geological data of the contemporary large granitic plutons in the Chinese Altai orogen, the tonalite is considered to be formed together with other granitic rocks in a continental arc setting. The tonalite intrusion has consistent foliation with its country rocks, indicating the strain resuiting in the regional deformation should be very strong during or after the early Devonian.

Thermal history of a Late Mesoproterozoic paired metamorphic belt(?)during Rodinia assembly:New insight from medium-pressure granulites from the Aravalli-Delhi Mobile Belt, Northwestern India

In this study, we investigate the possible record of a Late Mesoproterozoic paired metamorphic belt in the Aravalli-Delhi Mobile Belt(ADMB), NW India using a suite of supracrustal and metaigneous granulites from the Pilwa-Chinwali granulite terrain at the north-western margin of the ADMB. Using metamorphic reaction textures, mineral chemistry, metamorphic reaction history, geothermobarometric computations and electron microprobe dating of monazite in 5 samples of pelitic granulite, leptynite gneiss, enderbite and charnockite, we have deduced a medium-pressure granulite facies metamorphism(P between 4.9 and 6.8 kbar, T> 760-815℃) along a heating-cooling, counterclockwise P-T path between 1.09 and 1.01 Ga. When collated with published metamorphic and chronological constraints and geological settings of the adjoining crustal domains of the ADMB, these findings provide new insights into the developments of two tectonic domains of contrasting thermal gradients at ca. 1.0 Ga, consistent with metamorphic transformations in tectonically thickened middle-lower crustal sections during continental collision to continental subduction and in the root zones of spatially adjacent island arc, as part of the Rodinia supercontinent assembly event.