北大别饶拔寨石榴辉石岩P-T-t轨迹及其构造意义

P-T-t轨迹作为变质岩的重要研究方法之一，对揭示岩石的构造演化过程具有重要意义。北大别饶拔寨镁铁-超镁铁岩形成的构造环境和就位过程长期以来尚存争议。本文通过岩相学观察、矿物化学研究和温压计计算，揭示出饶拔寨石榴辉石岩经历了四个变质演化阶段：1）超高压变质阶段（M1）：主要根据石榴子石中金红石的出溶，单斜辉石中石英的出溶和磷灰石中不透明矿物的出溶，结合前人研究，认为饶拔寨石榴辉石岩经历过超高压变质阶段（≥2.5GPa）；2）高压麻粒岩相阶段（M2）：矿物组合为石榴子石（变斑晶）和单斜辉石（基质）+斜长石（基质），记录的温压条件为T=648~700℃，P=1.47~1.94GPa；3）中压麻粒岩相阶段（M3）：以石榴子石外围发育的主要由斜方辉石+斜长石组成的内圈"白眼圈"为特征，形成的温压条件为T=781~796℃，P=0.92~0.98GPa；4）角闪岩相阶段（M4）：以石榴子石变斑晶周围发育的外圈"白眼圈"为特征，其矿物组合为角闪石+斜长石的后成合晶，形成的温压条件为T=663~685℃，P=0.50~0.58GPa。石榴辉石岩的锆石SIMS U-Pb定年得到了3组不同的交点年龄，分别为208.1~202.1Ma、227.6Ma和817.7Ma。根据锆石包裹体中角闪石+斜长石的组合，推断208.1~202.1Ma代表了角闪岩相变质年龄的下限，227.6Ma则是高压麻粒岩相的下限年龄，而新元古代年龄（817.7Ma）与区域上的变质岩原岩年龄一致，可能代表了其原岩年龄。结合前人研究，饶拔寨石榴辉石岩记录了顺时针的P-T-t轨迹，揭示了板片俯冲（超高压变质）-碰撞-折返（降压升温过程，~227Ma）-抬升（降压降温过程，208~202Ma）的完整过程。     

大别山及苏鲁地区微粒金刚石分类及其大地构造意义

1992年发现大别山首例微粒金刚石之后，又于2003年和2004年在大别山和苏鲁地区的榴辉岩薄片中和榴辉岩的人工重砂中发现了微粒金刚石。本文报道其中尚未发表的7颗，并对2颗较大的薄片中的微粒金刚石和2颗自由晶体金刚石进行拉曼光谱和红外光谱测试。研究结果表明，本区所有微粒金刚石都为IaA和IaB型金刚石的混合体。缺少Ib型金刚石，表明没有人造金刚石的混入。薄片中的金刚石大部分为石榴子石的包裹体，少数产出于颗粒之间，直径为30-180μm。自由颗粒微粒金刚石直径为400-700μm。在大别山北部，不但又一次找到了微粒金刚石，还在石榴子石中发现有单斜辉石、磷灰石和金红石的出溶。这表明北大剐不但是超高压地质体，而且可能是本区俯冲最深的地质体。     

Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan,China

A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well‐preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P–T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N₂‐bearing NaCl‐rich solutions, whereas it changed into CO₂‐dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low‐salinity fluids were involved. In situ UV‐laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (δ¹⁸O_VSMOW = c. 6.7‰) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid–rock interactions. Unusual MORB‐like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra‐high‐pressure (UHP) eclogites in the Dabie‐Sulu area. However, the age‐corrected initial ε_Nd(t) is ? 2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N₂ content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism.     

Well-preserved garnet growth zoning in granulite from the Dabie Mountains, central China

Ultra-high pressure eclogites and granulites both occur in the Dabie Mountains, central China. A garnet porphyroblast from felsic granulite in the Dabie Mountains has been analysed for compositional zoning by electron microprobe. Two segments of the porphyroblast have opposite compositional variations. Segment I (from centre outward 9  mm to analytical point 18) has decreasing X_Sps and increasing X_Pyr, while Segment II (from analytical point 18, 1  mm outward to the rim) has increasing X_Sps and X_Alm and decreasing X_Pyr and X_Grs. The compositional zoning in segment I is considered as growth zoning and that in Segment II as diffusive retrograde zoning. Garnet growth zoning records a P–T  path prior to the peak granulite metamorphism. The minimum P – T  conditions are estimated to be 1.35  GPa and 850  °C for peak metamorphism, based on the highest Mg/(Fe+Mg) composition in the garnet (analytical point 18) and matrix hypersthene, biotite and plagioclase. A symplectitic corona surrounds the porphyroblast and appears to have formed at 0.6  GPa and 700  °C. The well-preserved growth zoning in garnet suggests a short residence time for the granulite at peak metamorphism and thus rapid tectonic uplift history. The P–T  path is consistent with that of ultra-high-pressure eclogite in the area. Tectonic movements during a collisional event could have brought both the granulite and the eclogite to their present positions.     

Contrasting Peridotite Types in the Dabie UHP Belt, Eastern China: the Raobazhai and Bixiling Ultramafic-mafic Complex

The Dabie UHP metamorphic belt, central China,contains two contrasting types of mafic-ultramafic complex. The Bixiling peridotite in the southern Dabie terrane contains abundant garnet (21.1-32.2 vol% )and thus has high CaO + Al2O3 (9.81-15.9 wt% ).     

Formation Depth of Coesite-Bearing Eclogite, Dabie UHPM Zone, China

The plastic deformation of garnet in coesite-bearing eclogite,quartz eclogite and garnet amphibolite of the UHPM complex in Yingshan County in the Dabie Mountains has been studied. The stress generated by the strong tectonic movement was an important component of the total pressure that resulted in the formation of the eclogite in the Dabie UHPM zone. The three-dimensional tectonic principal stresses and additional tectonic stress-induced hydrostatic pressure ［ps=(σ1 σ2 σ3)/3］ are reconstructed according to the differential stress and the strain ratio(α) of the garnet in the minor coesite-bearing eclogite of the Yingshan County. Then the gravity-induced hydrostatic pressure(pg) is calculated following the equation p minus ps,where p is estimated to be 2.8 Gpa based on the quartz-coesite geobarmeter. Therefore,the thickness of the rock column overlying the coesite-bearing eclogite in the Ying-shan County is determined ≥32 km. This estimation,significantly different from ≥100 km,the previous one obtained solely based on the weight/specific weight ratio(W/SW),offers a proper explanation for the puzzle that no tracer of the addition of mantle-derived material has been found in the Dabie UHPM zone during the process of UHPM,although a number of researchers claim that this process took place at the depth of the mantle(≥100 km). It is concluded that attention should be paid to the additional tectonic stress-induced hydrostatic pressure in the study of UHPM zones.     

Constraints on the early cooling rates of Mt. Dabie from diffusion modeling of chemical zoning of garnet

Diffusion modeling of zoning profiles in eclogite garnets from three different tectonic units of Mt. Dabie, UHPM unit, HPM unit and northern Dabie, was used to estimate the relative time span and cooling rates of these rocks. Modeling result for the Huangzhen eclogite garnet shows that the maximal time span for the diffusion-adjustment process is about 22 Ma since the peak-temperature metamorphism, which is the maximum time span from amphibolite facies metamorphism to greenschist facies metamorphism. The Bixiling eclogites had subjected to a cooling process at a rate of - 10℃/Ma from 750℃ to 560℃ during 20 Ma. The second cooling stage of the Raobazhai eclogite following granulite-facies metamorphism is an initial fast cooling process at a rate of about 25℃/Ma and then slowed down gradually. All these belong to a coherent Dabie collision orogen with differences in subduction depth and exhumation/uplifting path.     

北大别山仙桥中生代酸性火山岩地球化学特征、锆石U-Pb年龄及其成矿构造背景

东秦岭-北大别山构造-岩浆演化是热点研究问题,关于该带火山岩喷发时限存在较大的争议,其岩石成因和成岩构造环境尚不清楚。对北大别山西段仙桥膨润土矿床英安岩进行锆石U-Pb同位素测年和岩石地球化学研究,结果表明,仙桥酸性火山岩具有高钾(3.96%~5.01%)、富碱(K2O+Na2O介于7.97%~8.96%之间)、弱过铝质(A/CNK为1.0~1.15)等特点,属高钾钙碱性-钾玄岩系列火山岩。岩石轻稀土元素富集,重稀土元素亏损明显,负Eu异常不明显,Nb、Ta亏损明显,且具有高Nb/Ta、(La/Yb)N、Sr/Y值,表现为典型的埃达克质岩石地球化学特征。LA-ICP-MS锆石U-Pb同位素定年测得,仙桥成矿岩石英安岩喷发年龄为133±1 Ma,与邻区双桥膨润土、皇城山银矿床陈棚组火山岩的年龄一致。研究认为,仙桥火山岩具有埃达克岩的特征,由增厚下地壳物质部分熔融形成,产生于中生代后碰撞构造环境,在133 Ma左右,北大别山仙桥地区还未发生大规模的拆沉减薄的岩浆活动。     

北大别的多阶段高温变质作用与部分熔融及其地球动力学过程和大地构造意义

北大别经历了三叠纪高温超高压变质作用和多阶段折返历史,因而榴辉岩中广泛发育多期减压结构,极少保留早期的超高压变质记录,这为它们不同变质阶段的温度条件估算带来了巨大困难。然而,目前流行的微量元素温度计为北大别榴辉岩的峰期及之后的退变质阶段温度的确定提供了可能性。根据锆石中Ti和金红石中Zr温度计,结合传统矿物对温度计的计算数据,获得了北大别榴辉岩中多阶段高温（>900 ℃）条件的数据,证明研究区经历了从超高压榴辉岩相→石英榴辉岩相→高压麻粒岩相阶段的高温变质过程。并且,北大别经历了折返初期（207±4 Ma）的减压熔融和碰撞后燕山期（约130 Ma）的加热熔融作用。长时间的高温变质作用与多期部分熔融也许正是北大别长期难以发现柯石英和有关超高压变质证据等的重要原因。因此,这些成果有助于甄别北大别的岩石成因和演化过程以及大别山多岩片差异折返模型的建立和完善。     

大别地块超高压变质省的构造变形研究

构造解析的基本目的是建立构造事件造成的地质体几何学、运动学、动力学和流变学。大陆碰撞造山带内含柯石英及微粒金刚石等矿物组合的超高压（ＵＨＰ） 变质岩的形成和折返,是极为复杂的地球动力学过程。与世界上已知大多数超高压变质带相似,中国大别地块内超高压变质省现今观察到的主体构造形式,主要是在碰撞或超高压变质峰期后伸展体制下形成的。通过对大别超高压变质省内伸展组构及挤压（ 碰撞） 组构的鉴别、分析,结合有关超高压变质带构造学研究领域的简略综述指出,在揭示超高压变质带的形成及折返动力学过程中,构造解析的思维和工作方法是行之有效的     

大别造山带东段扬子陆块和华北陆块间缝合带的位置

大别山为扬子陆块和华北陆块之间的碰撞造山带.构造-岩石单元的岩石组成、同位素年代学资料和构造关系表明, 大别山东段主要由扬子陆块北缘不同变质程度的变质基底和少量浅变质盖层组成, 没有代表蛇绿混杂岩和华北陆块南缘古生代活动大陆边缘的火山-侵入岩建造.各主要构造-岩石单元间的界线为超高压变质岩折返过程中形成的伸展型剪切带, 大别山北部的伸展-逆冲推覆构造也是超高压变质岩折返过程中伸展构造的一部分, 其中不存在具有缝合带意义的重要构造界线.因此, 在大别山东段, 华北陆块和扬子陆块间的缝合带既不是水吼-五河剪切带, 也不是磨子潭-晓天断裂.根据地球物理资料推测, 南北陆块间的缝合带应分布在信阳-舒城断裂的前缘, 但现在覆于合肥盆地中新生代沉积之下.      

北大别铙钹寨榴辉岩的多期变质与熔流体交代作用

铙钹寨镁铁-超镁铁质岩体被认为是北大别地体下方岩石圈地幔的碎块,并随着三叠纪的华北和华南的大陆碰撞而一同经历了深俯冲和折返过程,对其进行详细的研究可以为我们更好地理解陆-陆碰撞过程中的壳幔相互作用、物质迁移、多期变质和熔流体交代等地球动力学过程提供信息。本文应用电子探针和LA-ICP-MS对铙钹寨榴辉岩进行了系统的元素环带、出溶结构和熔体包裹体研究,揭示出该岩体至少经历了三期变质事件,两期矿物出溶和两期熔体交代过程。峰期变质矿物组合为含金红石出溶体的石榴石核部+其内包裹的绿辉石,石榴石中金红石±磷灰石矿物出溶体和绿辉石包裹体中的金红石±石英±磷灰石出溶片晶指示该岩体确定经历过超高压变质作用,流体活动以高盐度的卤水±氮气的流体为主,峰期变质作用过程中无熔体活动痕迹。高压麻粒岩相变质矿物组合为Ⅱ期石榴石+紫苏辉石+基质具有出溶石英片晶结构的富Na单斜辉石,流体活动以CO2流体为主,熔体包裹体记录了在折返初期,高压麻粒岩相变质之前存在一期小规模的硫化物熔体活动。晚期角闪岩相退变质矿物组合为透辉石+角闪石+长石,流体活动以低盐度水溶液为主,并伴随着一期壳源的硅酸盐熔体交代事件。根据矿物环带、出溶结构和熔体包裹体化学组合及分布特征,并结合前人的研究成果,我们得出了该岩体较为完整的变质演化和熔-流体交代的P-T-t-E/F/M轨迹。     

西藏日喀则地区白朗蛇绿岩中石榴辉石岩的岩石地球化学、年代学及其构造意义

白朗石榴辉石岩位于西藏南部雅鲁藏布江蛇绿岩带上,地处于日喀则地区白朗县境内,因其具有重要的大地构造位置和意义,得到了国内外诸多学者关注。国内外学者对该岩体的研究有助于深入剖析雅鲁藏布江蛇绿岩带的就位机制。本文以白朗石榴辉石岩为研究对象,其野外产出为构造岩块,围岩为没有变形特征的蛇纹石化地幔橄榄岩,早白垩世昂仁组和紫红色硅质岩也没有构造变质现象,且石榴辉石岩与蛇纹石化地幔橄榄岩间界限截然。通过对其进行岩石地球化学和年代学的研究,并结合大地构造动力学观点,认为西藏日喀则地区石榴辉石岩属钙碱性超基性岩,形成于无流体无水的稳定物理化学环境中,略亏损高场强元素Th、Ta、Nb等,锆石LA-ICP-MS U-Pb年龄为149.0±3.1Ma,且锆石εHf(t)平均值为+17.7,说明原始岩浆主要源于亏损地幔,且没有发生岩浆混染。总结:本文确定白朗石榴辉石岩原始岩浆来源于上地幔,并且该岩石的形成与印度板块和欧亚板块俯冲有关,但在该岩石形成过程中印度板块和欧亚板块没有发生陆陆碰撞。     

大别造山带中上地壳变形特征——皖中张八岭地区印支—燕山早期构造变形研究

张八岭构造带是大别造山带的一部分,是造山带中上地壳出露地区。通过运用构造-地层学的理论和方法,以及对张八岭地区1：5万地质填图资料的分析和典型地区的构造解剖,认为：区内张八岭(岩)群与南华系—震旦系及其以上地层之间不存在强烈的构造运动界面,其作为大别造山带的组成部分发生了强烈的变形作用;印支—燕山早期区内主要存在3期构造变形：早期为一系列呈NXVW、近EW向的紧闭同斜褶皱,中期以韧性剪切带发育为特征,晚期以NW向SE的逆冲推覆作用伴生NNE向为主的宽缓褶皱。三期变形相互叠加,形成区内基本构造格架。伴随着扬子地块向华北地块的俯冲与碰撞,中上部地壳发生褶皱、逆冲推覆(前缘滑覆)作用等,三期变形为一递进变形过程。     

Petrochemical constraints for dual origin of garnet peridotites from the Dabie-Sulu UHP terrane, eastern-central China

Garnet peridotites occur as lenses, blocks or layers within granulite–amphibolite facies gneiss in the Dabie-Sulu ultra-high-pressure (UHP) terrane and contain coesite-bearing eclogite. Two distinct types of garnet peridotite were identified based on mode of occurrence and petrochemical characteristics. Type A mantle-derived peridotites originated from either: (1) the mantle wedge above a subduction zone, (2) the footwall mantle of the subducted slab, or (3) were ancient mantle fragments emplaced at crustal depths prior to UHP metamorphism, whereas type B crustal peridotite and pyroxenite are a portion of mafic–ultramafic complexes that were intruded into the continental crust as magmas prior to subduction. Most type A peridotites were derived from a depleted mantle and exhibit petrochemical characteristics of mantle rocks; however, Sr and Nd isotope compositions of some peridotites have been modified by crustal contamination during subduction and/or exhumation. Type B peridotite and pyroxenite show cumulate structure, and some have experienced crustal metasomatism and contamination documented by high ⁸⁷Sr/⁸⁶Sr ratios (0.707–0.708), low ε_Nd( t ) values (−6 to −9) and low δ¹⁸O values of minerals (+2.92 to +4.52). Garnet peridotites of both types experienced multi-stage recrystallization; some of them record prograde histories. High- P–T  estimates (760–970 °C and 4.0–6.5±0.2 GPa) of peak metamorphism indicate that both mantle-derived and crustal ultramafic rocks were subducted to profound depths >100 km (the deepest may be ≥180–200 km) and experienced UHP metamorphism in a subduction zone with an extremely low geothermal gradient of <5 °C km⁻¹.     

大别山北麓与华北上古生界稀土元素特征的对比研究

采用等离子体光谱方法测试了大别山北麓和华北东南部晚古生代砂泥岩样品的稀土元素含量，结果表明，大别山北麓石炭系样品具微弱的Eu负异常，δEu为0．915，分布曲线基本上呈近似直线或呈左高右低的宽缓的弧型；华北石炭－二叠系样品具明显的Eu负异常，δEu为0．637，分布曲线基本上呈左高右低的宽缓的“V”型，两者的稀土元素地球化学特征存在明显差异，根据稀土元素特征和其他地质资料，认为两者沉积物质的来源具有差异，在晚古生代，两者的物源没有联系，大别山北石炭系沉积的物源主要来自不成熟的上地壳的岛弧体系，反映华北板块南缘的活动大陆边缘性质，淮南矿区晚古生代沉积的物源主要来自北部成熟的上地壳，反映华北板块板内稳定的地台沉积。δ     

Petrological significance of prograde homogenization of growth zoning in garnet: an example from the Llano Uplift'pa

In the Llano Uplift of central Texas (USA), prograde homogenization of garnet growth zoning took place during moderate- to high-pressure dynamothermal metamorphism over a narrow temperature range near the transition from the amphibolite to the granulite facies. This subtle record of early dynamothermal metamorphism survived subsequent static metamorphism at low pressures in the middle-amphibolite facies, despite the destruction of most high-pressure mineral assemblages that originated in the early metamorphic episode. Geographically systematic variations in the degree of homogenization indicate that the uplift as a whole underwent high-pressure metamorphism, in accord with emerging tectonic models for the mid-Proterozoic evolution of the southern margin of the North American continent.     

Multi-stage pseudomorphic replacement of garnet during polymetamorphism: 1. Microstructures and their interpretation

Metapelites from the southern aureole of the Vedrette di Ries tonalite (eastern Alps) were variably overprinted by contact and earlier regional metamorphic events during pre-Alpine and Alpine metamorphic cycles. In these rocks, starting from a primary garnet mica-schist (garnet stage), a complex sequence of transformations, affecting the site of the garnet, has been recognized. In the outermost part of the aureole, the primary garnet sites are occupied by nodules of kyanite (kyanite stage). Closer to the tonalite, kyanite is replaced by staurolite (staurolite stage), which in turn is pseudomorphed by muscovite (muscovite stage). The aggregates of kyanite do not overgrow garnet directly; they post-date a stage (fibrolite stage) represented by the pseudomorphic alteration of garnet into fibrolitic sillimanite plus biotite. A further sericite stage is likely to have occurred between the fibrolite and kyanite stages. Preservation of the sub-spherical garnet shape during all these transformations and persistence of mineralogical and textural relicts from earlier stages were favoured by the very low strain experienced by the rocks since the garnet stage. The textural sequence is in agreement with the metamorphic history of this part of the Austroalpine basement of the Eastern Alps: the garnet and fibrolite stages, and the coeval main foliation of the samples, are referred to the high-grade Hercynian metamorphism; the kyanite stage to the Eo-Alpine metamorphism; the staurolite and muscovite stages to the Oligocene contact metamorphism. It is suggested that kyanite growth as microgranular aggregates took place in polymetamorphic rocks where static, high- P /low- T  metamorphism overprinted high- T  assemblages that contained sillimanite or andalusite.     

Petrology and P–T evolution of garnet peridotites from central Sulawesi, Indonesia

Alpine‐type orogenic garnet‐bearing peridotites, associated with quartzo‐feldspathic gneisses of a 140–115 Ma high‐pressure/ultra‐high‐pressure metamorphic (HP‐UHPM) terrane, occur in two regions of the Indonesian island of Sulawesi. Both exposures are located within NW–SE‐trending strike–slip fault zones. Garnet lherzolite occurs as <10 m wide fault slices juxtaposed against Miocene granite in the left‐lateral Palu‐Koro (P‐K) fault valley, and as 10–30 m wide, fault‐bounded outcrops juxtaposed against gabbros and peridotites of the East Sulawesi ophiolite within the right‐lateral Ampana fault in the Bongka river (BR) valley. Six evolutionary stages of recrystallization can be recognized in the peridotites from both localities. Stage I, the precursor spinel lherzolite assemblage, is characterized by Ol+Cpx+Opx±Prg‐Amp ± Spl±Rt±Phl, as inclusions within garnet cores. Stage II, the main garnet lherzolite assemblage, consists of coarse‐grained Ol+Opx+Cpx+Grt; whereas finer‐grained, neoblastic Ol+Opx+Grt+Cpx±Spl±Prg‐Amp±Phl constitutes stage III. Stages IV and V are manifest as kelyphites of fibrous Opx+Cpx+Spl in inner coronas, and Opx+Spl+Prg‐Amp±Ep in outer coronas around garnet, respectively. The final (greenschist facies) retrogressive stage VI is accompanied by recrystallization of Serp+Chl±Mag±Tr±Ni sulphides±Tlc±Cal. P–T conditions of the hydrated precursor spinel lherzolite stage I were probably about 750 °C at 15–20 kbar. P–T determinations of the peak stage IIc (from core compositions) display considerable variation for samples derived from different outcrops, with clustering at 26–38 kbar, 1025–1210 °C (P‐K & BR); 19–21 kbar, 1070–1090 °C (P‐K), and 40–48 kbar, 1205–1290 °C (BR). Stage IIr (derived from rim compositions) generally records decompression of around 4–12 kbar accompanied by cooling of 50–240 °C from the IIc peak stage. Stage III, which post‐dates a phase of ductile deformation, yielded 22±2 kbar at 750±25 °C (P‐K) and 16±2 kbar at 730±40 °C (BR). The granulite–amphibolite–greenschist decompression sequence reflects uplift to upper crustal levels from conditions of 647–862 °C at P=15 kbar (stage IV), through 580–635 °C at P=10–12 kbar (stage V) to 350–400 °C at P=4–7 kbar (stage VI), respectively, and is identical to the sequence recorded in associated granulite, gneiss and eclogite. Sulawesi garnet peridotites are interpreted to represent minor components of the extensive HP‐UHP (peak P >28 kbar, peak T of c. 760 °C) metamorphic basement terrane, which was recrystallized and uplifted in a N‐dipping continental collision zone at the southern Sundaland margin in the mid‐Cretaceous. The low‐T , low‐P and metasomatized spinel lherzolite precursor to the garnet lherzolite probably represents mantle wedge rocks that were dragged down parallel to the slab–wedge interface in a subduction/collision zone by induced corner flow. Ductile tectonic incorporation into the underthrust continental crust from various depths along the interface probably occurred during the exhumation stage, and the garnet peridotites were subsequently uplifted within the HP‐UHPM nappe, suffering a similar decompression history to that experienced by the regional schists and gneisses. Final exhumation from upper crustal levels was clearly facilitated by entrainment in Neogene granitic plutons, and/or Oligocene trans‐tension in deep‐seated strike–slip fault zones.     

Petrology and Petrogenesis of the Eclogite in Mt.Dabie Area,Central China

The occurrence,mineralogy and geochemistry of eclogites in the Mt.Dabie area show that they were subjected to a high-pressure metamorphism together with the country rocks,but their petrochemistry and REE geochemistry show some difference from those of the country rocks.The geochemical characteristics of the eclogites are similar to those of bot continental tholeiitic basalt and oceanic tholeiitic basalt.The rocks probably subducted to the upper mantle with the Dabie metamorphic complex.When elevated to the surface,they were subjected to different staes of retrogressive metamorphism.