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.

P-T path of metamorphism and U-Pb monazite and zircon age of the Kitoy terrane: Implication for Neoarchean collision in SW Siberian Craton

The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane(SW Siberian Craton).Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution.The first stage of regional metamorphism(M1)occurred at high-amphibolite facies conditions at T=780-800℃ and P=8-9 kbar.The second stage(M2)belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600-750℃ and pressure 2-4 kbar.Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses.Both of them correspond to the Neoarchean age:the age of M1 falls into the interval of ca.2489-2496 Ma,the age of M2-ca.2446-2456 Ma.The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton.

Metamorphism of the East Sector of the Southern Qinling Orogenic Belt and Its Geological Significance

The east sector of the southern Qinling belt is, lithologically, composed mainly of metapelites, ***qüartzites, marbles and small amount of metabasites and gneisses, whose protoliths are the Silurian, Devonian and less commonly the Sinian and Upper Palaeozoic. They have been subjected at least to two epochs of metamorphism. The early epoch belongs to progressive metamorphism which is centered on high amphibolite-granulite fades in the Fuping area and changed outwards into low amphibolite facies (staurolite-kyanite zone), epidote amphibolite facies (garnet zone) and greenschist facies (chlorite and biotite zones), the metamorphic age of which is about 220–260 Ma. This early-epoch metamorphism belongs to different pressure types: the rocks from greenschist to low amphibolite facies belong to the typical medium-pressure type which shows geothermal gradients of about 17–20 ***C/km and was probably produced by a crustal thickening process related to continental collision, and the high amphibolite-granulite facies belongs to the low-pressure type which shows geothermal gradients of about 25–38 ***C/km and was probably affected by some magmatic heats. Based on the basic characteristics of the P-T paths of the different facies calculated from the garnet zonations, it can be deduced that the metamorphism of medium-pressure facies series took place during an imbricated thickening process, rather than during the uplifting process after thickening. The late-epoch metamorphism belongs to dynamic metamorphism of greenschist facies which is overprinted on the early-epoch metamorphic rocks and is Yanshanian or Himalayan in age, probably related to intracontinental orogeny.

黑龙江依兰地区黑硬绿泥石片岩岩石学与P-T条件研究

依兰地区黑龙江杂岩中黑硬绿泥石片岩矿物组合为黑硬绿泥+绿泥石+多硅白云母+钠长石+透闪石+钾长石±黑云母。岩石矿物学研究表明黑硬绿泥石片岩形成于250～400℃,6～9kbar的变质条件下。黄褐色黑硬绿泥石呈束状、放射状集合体。黑硬绿泥石片岩形成于佳木斯地块向西与松嫩地块俯冲拼贴过程中蓝片岩变质作用的后期,压力稍有降低而温度略有升高的变质变形环境,是蓝片岩向绿片岩转变的蓝闪绿片岩相变质条件下的产物。

内蒙古大青山兴和岩群变质阶段划分与P-T-t轨迹分析

通过研究和总结内蒙古大青山兴和岩群变质岩石类型、矿物共生组合及特征矿物等方面的特点及规律,对兴和岩群变质作用期次进行划分,分为四个阶段:1、峰期前变质阶段,2、峰期变质阶段,3、近等压冷却阶段,4、峰期后降温降压阶段。同时对兴和岩群麻粒岩变质P-T-t轨迹的进行研究,结果表明中太古麻粒岩相变质过程为从基性-中性-酸性的变化特征。

滇西六合地区新生代正长斑岩中深源包体的矿物学特征与成因意义

在云南省鹤庆县六合乡河东村的正长斑岩中产出多种含石榴石的深源包体。文中详细介绍了这些包体的岩相学特征和退变质特征 ,提供了包体中主要造岩矿物的化学成分分析结果。根据包体中的矿物组合及主要造岩矿物的化学成分特征划分出了 5种包体类型 ,并运用单斜辉石地质温压计、角闪石地质压力计和石榴石单斜辉石Fe Mg交换地质温度计计算了包体形成和退变质的温压条件 ,初步确定石榴石透辉岩及石榴辉石岩来源于上地幔 (87～ 95km) ,在快速上升到下地壳时被正长斑岩岩浆捕获 ;石榴石透辉角闪岩、麻粒岩形成于下地壳 (45～ 5 5km ) ,石榴石斜长角闪岩形成于中下地壳 (约 30km) ,为壳源岩石包体。除石榴辉石岩外 ,其余 4种包体均经历了退变质作用。根据它们的显微结构特征、矿物化学特征及温压计算结果 ,划分了两个变质期次 ,构筑了包体形成及退变质作用的 p T轨迹 ,讨论了退变质过程中压力 深度的变化及意义 ,并推断在退变质过程中包体经历了富Na流体的交代作用。

太行山太古宙变质杂岩中富铝片麻岩的变质作用

太行山太古宙变质杂岩中富铝片麻岩主要分布在湾子岩系的底部，常常与大理岩密切伴生或者以似层状体产于花岗质片麻岩中。依据岩石结构和反应关系将变质作用分为早期、中期和晚期三个阶段。早期矿物组合为Ｇｔ（石榴石）＋Ｓｔ（十字石）＋Ｐｌ（斜长石）＋Ｍｓ（白云母）＋Ｂｉ（黑云母）＋Ｒｕ（金红石）＋Ｑｚ（石英）±Ｋ－ｆｓ（钾长石）；中期矿物组合为Ｇｔ＋Ｇｅｄ（铝直闪石）＋Ｂｉ＋Ｐｌ＋Ｉｌｍ（钛铁矿）＋Ｃｏ（刚玉）＋Ｓｉｌ１（毛发状夕线石）＋Ｑｚ＋Ｋ－ｆｓ±Ｍｓ；晚期矿物组合为Ｈｃ＋Ｋ－ｆｓ＋Ｓｉｌ２（针柱状夕线石）。矿物温度压力计和内部一致性热力学计算结果表明早期矿物组合形成于６８０℃和０．８ＧＰａ左右，刚玉、铝直闪石和毛发状夕线石组合形成于７３０℃～７５０℃和０．７ＧＰａ左右的很窄的Ｐ－Ｔ范围内，夕线石和尖晶石矿物组合的形成温度与前一组合相似或略高，压力偏低。在Ｐ－Ｔ空间上上述矿物组合的演化构成了一条近等温减压（ＩＴＤ型）的ＰＴｔ轨迹。

豫西东秦岭造山带低压变质带的变质变形和变质反应

豫西西峡北部低压变质带受到4次变形改造。低压变质作用主要发生在D_1和D_2变形间期,形成黑云母—红柱石、石榴石—红柱石、十字石—红柱石和堇青石—红柱石4个递增变质带。由矿物变质反应识别出堇青石—红柱石带的p-T趋势具有减压增温特点,这一演化特征可能反映变质作用具有地壳拉张的地球动力学特点。

豫西东秦岭造山带核部杂岩中钙质变质岩的变质作用演化

秦岭杂岩中的钙质变质岩经历了晋宁和加里东-海西两个巨构造-热旋回的强烈影响和改造。在加里东的深位(≥15km)接触热变晕的钙质变质岩中,保存了若干精美的非平衡结构。凭借非平衡结构的研究分析,重塑了接触热变质的递进变质和退变质阶段的反应形式以及冷却过程的P-T-X_(co_2)路径。

南极大陆超高温变质作用及其大地构造背景

超高温变质作用对认识大地构造-热演化以及地壳成分分异等具有重要意义。南极大陆发育典型的超高温变质作用,分布于不同的构造域。主要的超高温地质单元包括内皮尔杂岩、茹尔(赖于尔)群岛、拉斯曼丘陵、吕措-霍尔姆杂岩以及席尔马赫丘陵等。不同地质单元的超高温变质作用分布规模不同,恩德比地内皮尔杂岩的超高温变质作用分布广泛(~15000 km^(2)),而席尔马赫丘陵等地的超高温变质作用分布有限,超高温变质作用规模与出露特征的不同可能暗示了不同的成因机制与热源。各超高温地质单元中发育丰富多样的超高温矿物组合,如假蓝宝石+石英组合、斜方辉石+矽线石组合、尖晶石+石英组合以及含大隅石、刚玉、三元长石或富Al斜方辉石的矿物组合,在变质基性岩中还发育石榴子石+单斜辉石+斜长石±高钛角闪石等矿物组合。丰富多样的矿物组合为研究超高温变质作用矿物反应机制提供了重要基础。不同超高温地质单元,乃至同一超高温地质单元内不同区域的P-T-t轨迹类型不同,如有些超高温变质作用具有显著的近等温减压轨迹,而有些超高温变质作用主要记录近等压降温轨迹,反映了不同的演化历史或构造背景。南极大陆超高温变质作用可分5个期次,包括中太古代晚期(2850 Ma),新太古代末期—古元古代早期(2585~2450 Ma),新元古代早期(格林维尔期,约1000~900 Ma),新元古代晚期(泛非期早期,650~605 Ma)和新元古代末期—早古生代(泛非期晚期,570~500 Ma),与超大陆(或超级克拉通)演化存在密切联系。不同的超高温变质作用可能与板块构造演化的不同阶段有关,如弧后盆地或造山带垮塌阶段等;但超高温变质作用并不局限于现今板块构造体制。南极大陆多数超高温地质单元的研究程度还相对较低,对其矿物反应机制、变质演化轨迹、形成时代及持续时间、熔融反应及熔体成分演化等还缺乏深入认识,制约了对这些超高温变质作用的热源、动力学机制和构造背景等的准确解释,将来需要加强研究。

阿尔泰晚古生代超高温麻粒岩流体特征及其意义

北疆阿尔泰造山带南缘晚古生代超高温麻粒岩存在高铝斜方辉石＋夕线石＋石英和尖晶石＋石英等超高温特征矿物组合，其退变质作用主要以典型的降压反应矿物堇青石的形成为标志。对其中新发现的石榴子石及石英流体包裹体开展显微测温和激光拉曼探针分析，结果表明：基质中的石英以及被石榴子石包裹的石英中孤立分布的原生流体包裹体成分为近纯CO2（部分含少量的N2），均一温度在10．1～29℃之间，其对应的密度在0．631～0．861g／cm^3。石榴子石中的原生和假次生CO2包裹体费米峰差在104．1cm^-1左右，低于石英中CO2包裹体的费米峰差（～104．7cm^-1），暗示其密度低于石英中的CO2包裹体。由CO2流体包裹体密度所得到的等容线从P—T轨迹退变质阶段的下方穿过结合区域地质背景，我们初步认为阿尔泰超高温麻粒岩的形成与幔源岩浆底侵有关。基性岩浆的底侵不但提供了异常高的地温梯度，同时其所释放的大量CO2降低了水活度，使得变质作用峰期的特征矿物得以保存。低密度的CO2流体指示了阿尔泰超高温麻粒岩沿顺时针P—T轨迹紧随超高温峰期变质之后快速抬升降压，捕获的同变质流体包裹体因腔体体积增大而密度降低的一种退变质过程。

Metamorphic Characteristics and Tectonic Implications of the Kadui Blueschist in the Central Yarlung Zangbo Suture Zone,Southern Tibet

The Kadui blueschist is located in the central section of Yarlung Zangbo suture zone （YZSZ）, southern Tibet, and has been subjected to the subduction of the Neo-Tethyan Ocean below the Asian Plate and provides important clues for better understanding the evolution of the India-Asia convergence zone. In this paper, the systematical petrographic and mineral chemical studies were carried out on the Kadui blueschist, which reveal a mineral assemblage of sodic amphibole, chlorite, epidote, albite and quartz with accessory minerals of titanite, calcite and zircon. Electron microprobe analyses demonstrate that amphibole shows zoned from actinolite core to ferrowinchite/riebeckite rim composition indicating that the sodic amphibole has formed during a prograde metamorphic event. The protolith of the blueschist is an intermediate-basic pyroclastic rock. The calculated pseudosection indicates a clockwise P-T path and constrains peak metamorphic conditions of about 5.9 kbar at 345 ℃. This condition is transitional between pumpellyite-actinolite, greenschist and blueschist facies with a burial depth of 20-22 km and a thermal gradient of 15-16 ℃/km. This thermal gradient belongs to high pressure intermediate P/T facies series and is possibly related to a warm subduction setting of young oceanic slabs. Our new findings indicate that the Kadui blueschist in the central part of YZSZ experienced a rapid subduction and exhumation process as a response to a northward subduction of the Neo-Tethyan oceanic lithosphere during the initial India-Asia collision stage.

周口店地区接触变质岩的演化:来自碳质拉曼光谱温度计的证据

燕山板内构造带是华北克拉通中部遭受长期造山演化作用的活动区,详细的岩浆活动和变质作用研究对于恢复其造山热演化过程具有重要意义。构造带内周口店地区的房山岩体是中生代燕山运动晚期的产物,但关于房山岩体周缘受到接触热变质作用的古老地体变质演化历史却缺乏详细的研究。本研究在房山岩体红柱石-黑云母接触变质带内采集了岩石样品,通过岩相学的详细观察和碳质物拉曼光谱温度计的计算,得到了以下认识:岩石中红柱石斑晶核部的碳质包体记录下了早期区域变质过程的变质温度(约550℃),红柱石斑晶及边部中的碳质包体共同记录了峰期变质温度条件(约598℃),岩石基质中碳质包体可能记录了岩石接触热变质的峰后期变质温度(598~574℃)。研究结果表明,接触热变质带的岩石受到房山侵入岩释放的热量而迅速加热,在达到峰期变质温度后又随岩体的冷却而降温,导致了近等压的p-T-t轨迹。

Petrology of Garnet Amphibolites from the Hualong Group: Implications for Metamorphic Evolution of the Qilian Orogen, NW China

The Qilian Orogen marks the junction of the North China, South China and Tarim cratons. The mechanism of continental growth during the formation of the orogen remains unclear. Based on detailed fieldwork, we present a systematic study of petrography, mineral chemistry and phase equilibria of garnet amphibolites from the Hualong Group, which represents the Precambrian basement in the southern accretionary belt of the Qilian Orogen. The garnet amphibolites mainly consist of amphibole, plagioclase, garnet and quartz, with minor pyroxene, biotite and ilmenite. A peak stage of upper amphibolite facies to low-temperature granulite facies metamorphism and retrograde metamorphism in the amphibolite facies affected the samples. Garnet has a homogeneous composition of Alm66-71Grs14-17Prp9_12Sps3-s, amphibole is ferro-hornblende, biotite belongs to the ferro-biotite species and pyroxene is dominated by orthopyroxene with few clinopyroxene. Pseudosection modeling of the garnet amphibolite samples indicates clockwise P-T paths. The samples witness peak metamorphism at conditions of -4.9-6.3 kbar and -755-820 ℃ in the upper amphibolite facies to low- temperature granulite facies, and retrograde cooling and decompression at conditions of-2.5-3.1 kbar and -325-545 ℃. It is inferred that peak metamorphism with high temperature and low pressure occurred at ca. 450 Ma during northward subduction of the South Qilian oceanic crust beneath the central Qilian Block. When continental collision occurred between the central Qilian and the Qaidam blocks, the Hualong Block was aecreted onto the South Qilian accretionary complex and experienced amphibolite facies retrograde metamorphism at ca. 440 Ma.

Pressure-temperature Evolution of the Metapelites in the Motuo Area, the Eastern Himalayan Syntaxis

The Motuo area is located in the east of the Eastern Himalayan Syntaxis.There outcrops a sequence of high-grade metamorphic rocks,such as metapelites.Petrology and mineralogy data suggest that these rocks have experienced three stages of metamorphism.The prograde metamorphic mineral assemblages （M1） are mineral inclusions （biotite ＋ plagioclase ＋ quartz ± sillimanite ± Fe-Ti oxides） preserved in garnet porphyroblasts,and the peak metamorphic assemblages （M2） are represented by garnet with the lowest Xsps values and the lowest XFe# ratios and the matrix minerals （plagioclase ＋ quartz ± K-feldspar ＋ biotite ＋ muscovite ＋ kyanite ± siilimanite）,whereas the retrograde assemblages （M3） are composed of biotite ＋ plagioclase ＋ quartz symplectites rimming the garnet porphyroblasts.Thermobarometric computation shows that the metamorphic conditions are 562-714℃ at 7.3-7.4 kbar for the M1 stage,661-800℃ at 9.4-11.6 kbar for the M2 stage,and 579-713℃ at 5.5-6.6 kbar for the M3 stage.These rocks are deciphered to have undergone metamorphism characterized by clockwise P-T paths involving nearly isothermal decompression （ITD） segments,which is inferred to be related to the collision of the India and Eurasia plates.

Mineral chemistry,P-T-t paths and exhumation processes of mafic granulites in Dinggye,Southern Tibet

The mafic granulites in Dinggye,as various scale lense-shaped enclaves within the high Himalayan crystalline rock series,occur along mylonitic foliations at the junction between the Southern Tibetan Detachment System(STDS)and the Xainza-Dinggye normal fault system.The main lithological assemblage comprises garnet plagioclase pyroxenite,garnet two-pyroxene granulite,pyroxene garnet amphibolite and so on.The detailed petrological analyses show that these mafic granulites underwent at least four-stage metamorphic evolution.The first metamor-phic stage,the garnet+clinopyroxene+quart mineral assemblage(M1)was probably formed un-der eclogite facies,the second stage,the plagioclase+clinopyroxene symplectite mineral as-semblage(M2)was produced under high-pressure granulite facies by the early decompressive breakdown of M1 mineral assemblage,the third stage,the plagioclase+clinopyroxene+hypersthene symplectite mineral assemblage(M3)was formed at granulite facies by the late period decompressive breakdown of M1 and M2 mineral assemblages and the final stage,pla-gioclase+hornblende mineral assemblage(M4)was formed by hydrolysis of earlier mineral as-semblages during late uplifting.The detailed mineral composition analyses suggest that garnets and clinopyroxenes within M1 and M2 mineral assemblages display similar compositions to the equivalents in the B and C types of eclogites,whereas the M3 clinopyroxenes are akin to these of the same kind of minerals in the granulite.These mineral chemistry features and P-T estimates calculated by mineral thermometers and barometers indicate that the early stage relic porphyro-blasts(M1)could be formed at the eclogite facies,the early decompressive breakdown(M2)occurred at the high-pressures granulite facies of 1.35―1.48 GPa and 625―675℃,the M3 mineral assemblage recorded the granulite facies of 0.7―0.95 GPa and 775―900℃and M4 plagioglase+hornblende retrograde mineral assemblage was produced under the amphibolite facies metamorphism with pressure of 0.4 to 0.75 GPa and temperature at between 660 and 700℃.These construct P-T paths from crustal subduction overthickening to tectonic uplift tectono-thermal evolution.The mineral chemical characteristics and P-T condition at every metamorphic stage of these granulites indicate that these rocks experienced the eclogite facies metamorphism during the early stage.Subsequently,these mafic granulites underwent the three-stage exhuma-tion of the eclogite facies tectonic uplift,isostatic uplift related to the transformation from ec-logite/high-pressure granulite to granulite facies and extensional uplift.

Metamorphism and Zircon Geochronological Studies of Metagabbro Vein in the Yushugou Granulite-Peridotite Complex from South Tianshan,China

Yushugou granulite-peridotite complex,located at the east part of the northern margin of South Tianshan,may represent an ophiolitic slice subducted to 40–50 km depth with high-pressure granulite facies metamorphism.Although a lot of studies have been conducted on rocks in this belt,the rock association and tectonic background of the ophiolitic slice are still in dispute.A detailed study on petrology,phase equilibrium modeling and U-Pb zircon ages have been performed on the metagabbro vein in peridotite unit to constrain the tectonic evolution of the Yushugou granulite-peridotite complex.Three stages of mineral assemblage in the metagabbro were defined as stage I:Cpx^A+Opx^A+Pl^A,which represents the original minerals of the metagabbro vein;stage II:Cpx^B+Opx^B+Pl^B+Spl,which represents the mineral assemblage of granulite facies metamorphism with peak P-T conditions of 4.2–6.9 kbar and 940–1070℃;stage III is characterized by the existence of prehnite,thomsonite and amphibole in the matrix,indicating that the metagabbro vein may be influenced by fluids during retrograde metamorphism.Combined with the crosscut relationship,it can be deduced that the metagabbro vein,together with the peridotite in Yushugou granulite-peridotite complex has experienced similar high-temperature granulite facies metamorphism.The zircon chronological data shows that the protolith age of the metagabbro vein is 400.5±6.2 Ma,reflecting Devonian magmatism event and the granulite facies metamorphism occurred at^270 Ma which may be related to the post-collisional magmatism.

一种变胞式工业机器人时间最优轨迹规划

根据变胞式工业机器人工作原理,建立了其工作轨迹模型,并基于该模型提出了一种变胞式工业机器人时间最优的轨迹规划方法。该方法着重考虑机器人构态变换过程,将轨迹规划问题转化为内外层嵌套的优化问题进行分析。分别给出该优化问题的设计变量、目标函数以及约束条件,得到了变胞式工业机器人时间最优轨迹规划问题的数学模型。运用所提出的方法对本课题组自研制的变胞式码垛机器人进行轨迹规划研究,根据其工作轨迹模型,建立了优化设计问题数学模型,在给出关节角度插值函数系数的确定方法后,采用嵌套粒子群算法对该优化问题进行求解,得到了优化后的关节角度函数以及理论工作轨迹,与实验所得的实际工作轨迹进行对比,验证了所提方法的可行性。该研究工作为变胞式机器人的运动规划研究提供了参考。

Study and implication of the high-pressure felsic granulite in the Qinling complex of East Qinling

There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃ and 1.3 -1.6GPa and has experienced two stages of retrograde metamorphism at 600- 650 ℃, 0.8-1.0GPa and 500-600℃, 0.3-0.6GPa, forming two retrograde metamorphic assemblages of margarite + plagiodase (PlI)+quartz and sillimanite + biotite + plagioclase(PlII) + microdine+quartz, respectively. They construct a two-stage clockwise P-T path which shows down-pressure cooling in both early and late stage.

Petrological evidence for isobaric cooling of ultrahightemperature pelitic granulites from the Khondalite Belt,North China Craton

The ultrahigh-temperature(UHT) pelitic granulites from the Khondalite Belt, North China Craton(NCC), contain ilmenite in the matrix, which has been partially replaced by rutile. Based on this observation and the growth of biotite by garnet-consuming reaction, the UHT rocks are inferred to have recorded three metamorphic stages: the peak metamorphic stage(M1) and two retrograde metamorphic stages(M2 and M3). The M1 stage is represented by the assemblage of perthite+sillimanite+ ilmenite in the matrix, and quartz inclusions bearing(in the cores) garnet porphyroblasts. The M2 stage is defined by rutile-replacing ilmenite and growth of garnet mantles and rims containing acicular sillimanite inclusions, with the garnet+ perthite+ sillimanite+rutile+ ilmenite+ quartz assemblage. The M3 stage is recorded by the growth of biotite in the matrix, with the garnet+ biotite+ perthite+ sillimanite+rutile+ilmenite+quartz assemblage. Based on phase equilibrium modeling, an isobaric cooling path is reconstructed, which is consistent with the idea that mantle-derived magma provided the heat for the UHT metamorphism in the Khondalite Belt, NCC.