Continuous cratonic crust between the Congo and Tanzania blocks in western Uganda

Western Uganda is a key region for understanding the development of the western branch of the East African rift system and its interaction with pre-existing cratonic lithosphere. It is also the site of the topographically anomalous Rwenzori Mountains, which attain altitudes of >5000 m within the rift. New structural and geochronological data indicate that western Uganda south and east of the Rwenzori Mountains consists of a WSW to ENE trending fold and thrust belt emplaced by thick-skinned tectonics that thrust several slices of Proterozoic and Archaean units onto the craton from the south. The presence of Archaean units within the thrust stack is supported by new Laser-ICP-MS U–Pb age determinations (2637–2584 Ma) on zircons from the Rwenzori foothills. Repetition of the Paleoproterozoic units is confirmed by mapping the internal stratigraphy where a basal quartzite can be used as marker layer, and discrete thrust units show distinct metamorphic grades. The thrust belt is partially unconformably covered by a Neoproterozoic nappe correlated with the Kibaran orogenic belt. Even though conglomerates mark the bottom of the Kibaran unit, intensive brittle fault zones and pseudotachylites disprove an autochthonous position. The composition of volcanics in the Toro-Ankole field of western Uganda can be explained by the persistence of a cratonic lithosphere root beneath the northwardly thrusted Archaean and Palaeoproterozoic rocks of westernmost Uganda. Volcanic geochemistry indicates thinning of the lithosphere from >140 km beneath Toro-Ankole to ca. 80 km beneath the Virunga volcanic field about 150 km to the south. We conclude that the western branch of the East African rift system was initiated in an area of thinner lithosphere with Palaeoproterozoic cover in the Virunga area and has propagated northwards where it now abuts against thick cratonic lithosphere covered by a thrust belt consisting of gneisses, metasediments and metavolcanics of Neoarchaean to Proterozoic age.     

大别地区的变质作用及与碰撞造山过程的关系

大别造山带从南到北可分为５个变质构造单元：扬子北缘蓝片岩带、突松变质杂岩带、南大虽碰撞杂岩带、北大别变质杂岩带和北淮阳变质带。各个变质构造单元中不同岩石的变质作用可划分为３种类型：（１）超高压型。以含柯石英（及金刚石）的榴辉岩为代表,仅见于南大别碰撞杂岩带中,这类岩石的ＰＴ轨迹反映洋壳Ｂ型俯冲的特点。（２）高压型。见于大别山南部的蓝片岩带、宿松变质杂岩带和南大别杂岩中的变质沉积岩及部分片麻岩中,与     

豫南熊店高压变质岩的pttD轨迹

豫南熊店高压变质岩块体经历了６期变形和变质作用,即从深地壳层次挤压缩短体制下的不均匀韧性剪切、榴辉岩进变质作用,到中地壳层次挤压体制下的逆冲推覆、钠长绿帘角闪岩相退变质作用,到地壳浅层伸展体制下的脆性—韧性滑脱、绿片岩相变质作用,以及更浅层次的脆性变形,动力变质作用。高压变质岩的形成与向地壳中、浅层次的大幅度抬升均是在挤压机制下韧性变形作用的结果,而高压变质岩暴露到地表是伸展滑脱、断块升降和差异抬升所致。     

Deformation and Metamorphism of the Marble Mountain and Pony Camp Areas,Western Triassic and Paleozoic Belt,Central Klamath Mountains,Northwestern California

The Western Triassic and Paleozoic belt (WTrPz) is a regionally extensive, composite terrane correlative with Cache Creek-affinity rocks, a major crust-forming lithotectonic entity of the North American Cordillera. New structural, stratigraphic, and petrologic data suggest that a large tract of greenschist to amphibolite-grade metavolcanic and metasedimentary rock, previously considered to consist of several separate oceanic terranes, is, instead, a single fault-bounded, volcanic island arc, the Sawyers Bar terrane. It represents a mid-Jurassic, relatively intact, recrystallized nappe complex 5 to 10 km thick, extending over 100 km along strike in the central Klamaths. Protoliths of the complex are interpreted to be Lower Triassic (?) to mid-Jurassic supracrustal, volcanic arc-related units deposited, deformed, and metamorphosed within a suprasubduction zone adjacent to the continental margin. Metamorphism increases monotonically with depth in the nappe, ranging from prehnite-pumpellyite to lower greenschist-grade in the Pony Camp area on the south, through greenschist-grade in the medial Sawyers Bar area, to low-pressure amphibolite-grade metamorphism in the Marble Mountains on the north. The Pony Camp area generally lacks penetrative deformation. In the Marble Mountains, peak metamorphism largely postdates intense deformation; nevertheless, folding of fabrics and brittle deformation are common.

The complex is bounded by low-angle, W-vergent, crustal-scale, mid-Jurassic thrusts. The Soap Creek Ridge fault juxtaposes Stuart Fork blueschists over the Sawyers Bar complex. The lower thrust is not definitely established, but must be situated beneath tectonic levels postulated by earlier workers. It may coincide with the previously unrecognized brittle-plastic Isinglass shear zone in the Marble Mountains, and a poorly exposed, unnamed low-angle fault in the Virgin Buttes region west of Pony Camp. In this area, mapping indicates that the Twin Sisters fault is a relatively minor high-angle break within the WTrPz, rather than being a crustal-scale terrane suture. Synmagmatic, brittle extensional faults are common, as are syn and postmetamorphic, regionally extensive, high-angle faults that internally imbricate the WTrPz; the latter are marked by sheared serpentinite. Folds within the Sawyers Bar nappe complex are NE to NW-trending and W-vergent. Structural evidence suggests that W-vergent thrusting, E-W contraction, regional Siskiyou metamorphism, penetrative deformation, and crustal thickening occurred at ～170 to 165 Ma, and preceded voluminous 167 to 162 Ma calc-alkaline plutonism. In the study areas, waning stages of Siskiyou deformation were characterized by thermal relaxation, uplift, extension, crustal thinning, and E-directed tectonic transport. Nevadan age contraction (155 to 150 Ma), prevalent to the west at lower structural levels of the WTrPz, is not recognized in the Sawyers Bar nappe; however, regionally developed open folding of Siskiyou metamorphic fabrics and rare superposed folding and axial-plane cleavage development in the Marble Mountains may reflect a Nevadan event. Brittle deformation that clearly post-dates Siskiyou folding is younger than 150 Ma, but is older than ～130 Ma, the age of the oldest marine strata that overlie the Klamath province regionally. Kinematic evidence from the eastern Marble Mountains suggests sinistral transtension of possibly latest Jurassic-Early Cretaceous age. Late-stage brittle deformation is permissibly Cenozoic; the Sawyers Bar thrust sheet was tilted a maximum of 30° to the south along the flanks of the Condrey Mountain dome during Cenozoic uplift.

The Sawyers Bar nappe complex is similar to other composite terranes in Phanerozoic convergent suture zones throughout the world. Like the Klamath Mountains, these areas also may represent different exposure levels within a single fault-bounded entity rather than an amalgam of disparate terranes.     

High pressure-low temperature metamorphism in the Gran Paradiso basement, Western Alps

The Gran Paradiso basement complex of the French and Italian Alps is composed of metasediments, termed the gneiss minuti, and metabasic rocks, both of which are intruded by a late Hercynian granite. The Bonneval gneiss, which crops out at the western edge of the complex, is composed of highly deformed metasediments, volcanics and volcaniclastic rocks. Eclogites, now highly altered, occur in the metabasic rocks. Kyanite and blue-green amphibole are locally present in the gneiss minuti and aegirine plus riebeckite occur in the Bonneval gneiss. A moderately high pressure - low temperature metamorphic event of probable Alpine age occurred in the basement complex. This metamorphic event differs from that in the overlying Sesia unit and ophiolites of the Schistes lustrés nappe in being at lower pressures (below the ab = jd₁₀₀+ qz transition) and post-dating the major (D2_A) deformation. The origin of the metamorphism is discussed and interpreted as a probable consequence of the overlying nappe pile which was emplaced during the D2_A event. Subsequent greenschist facies metamorphism in the basement complex is a consequence of thermal relaxation during uplift.     

The Arcuate Nappe Structure on the Northern Margin of the Wuliang Moutnains in Western Yunnan

The arcuate nappe structure on the north edge of the Wuliang Mountains in westernYunnan Province is a complex nappe structural system with multiple superimposed structures.The autochthonous system is a WNW-trending arcuate fold belt consisting of the Jurassic andCretaceous and the allochthonous system is mainly composed of Upper Triassic rocks. Generally,the nappe structure moved from south to north, with the hanging wall thrusting in a WNW direc-tion for a distance of over 10km. The deep nappe structural system was formed at depths ofabout 5-10km in an environment not exceeding the greenschist facies. It occurred in theOligocene (about 40-20 Ma).     

GEOLOGY OF THE NORTHERN ARUN TECTONIC WINDOW

GEOLOGY OF THE NORTHERN ARUN TECTONIC WINDOW1　BordetP .Recherchesg啨ｏｌｏｇｉｑｕｅｓｄａｎｓｌ’ＨｉｍａｌａｙａｄｕＮ啨ｐａｌ,r啨ｇｉｏｎｄｕＭａｋａｌｕ[R].EditionsduCNRS ,Paris ,196 12 75 . 2　BordetP .G啨ｏｌｏｇｉｅｄｅｌａｄａｌｌｅｄｕＴｉｂｅｔ (Himalayacentral) [J].M啨ｍｏｉｒｅｓｈｏｒｓｓ啨ｒｉｅｄｅｌａＳｏｃｉｅｔ啨ｇ啨ｏｌｏｇｉｑｕｅｄｅＦｒａｎｃｅ,1977,8:2 35～ 2 5 0 . 3　BurcfielBC ,ChenZ ,HodgesKV ,etal.TheSouthTibetanDetachmentSystem ,Hima…     

Raman spectrum of carbonaceous material: a possible metamorphic grade indicator for low-grade metamorphic rocks

Raman spectral analyses of carbonaceous material (CM) extracted from pelitic samples along two sections traversing the metamorphic belt of Taiwan were carried out in the present study. The results show similar spectral variations of CM with metamorphic grade as those documented in the literature. However, continuous sampling from zeolite facies through prehnite–pumpellyite facies to greenschist facies metamorphic rocks in the present study does reveal some interesting features on the Raman spectra of CM that were not noted before. Both the Raman D (disordered-)/O (ordered-) peak area (i.e. integrated intensity) ratio and the D/O peak width (i.e. full width at half maximum, FWHM) ratio of the CM decrease with progressive metamorphism, but the most prominent change in the D/O peak area ratio occurs in samples of lower greenschist facies metamorphic grade, while the most significant decrease in the D/O peak width ratio occurs in samples near the boundary of prehnite–pumpellyite facies and greenschist facies. This phenomenon is interpreted as a result of the decoupling of the changing rates of in-plane crystallite size and degree of defects of CM with progressive metamorphism. It is postulated that the Raman spectrum of CM can serve as a metamorphic grade indicator to distinguish samples of prehnite–pumpellyite facies metamorphic grade from those of greenschist facies metamorphic grade.     

A review of the stratigraphy and geological setting of the Palaeoproterozoic Magondi Supergroup,Zimbabwe – Type locality for the Lomagundi carbon isotope excursion

The Palaeoproterozoic Magondi Supergroup lies unconformably on the Archaean granitoid-greenstone terrain of the Zimbabwe Craton and experienced deformation and metamorphism at 2.06–1.96 Ga to form the Magondi Mobile Belt. The Magondi Supergroup comprises three lithostratigraphic units. Volcano-sedimentary rift deposits (Deweras Group) are unconformably overlain by passive margin, back-arc, and foreland basin sedimentary successions, including shallow-marine sedimentary rocks (Lomagundi Group) in the east, and deeper-water shelf to continental slope deposits in the west (Piriwiri Group). Based on the upward-coarsening trend and presence of volcanic rocks at the top of the Piriwiri and Lomagundi groups, the Piriwiri Group is considered to be a distal, deeper-water time-equivalent of the Lomagundi Group. The Magondi Supergroup experienced low-grade metamorphism in the southeastern zone, but the grade increases to upper greenschist and amphibolite facies grade to the north along strike and, more dramatically, across strike to the west, reaching upper amphibolite to granulite facies in the Piriwiri Group.     

桐柏-大别山区高压变质相的构造配置

作为华北和扬子陆块间的碰撞造山带桐柏大别山区以发育高压、超高压变质带为特征,从南到北变质相从低级到高级,代表俯冲带深度不同的变质产物,整体形成高压变质相系列。不过现今各变质相岩石的分布极受后期地壳规模的伸展构造控制,大别杂岩的穹隆作用更使高压变质相带的空间分布复杂化。超高压变质岩今日多呈大小不等的块体嵌布于相对低压的大别杂岩之内,造山带根部物质的热软化,使许多深层地幔物质得以像挤牙膏一样挤出于大别杂岩内。它们之中广泛发育着减压退变质的显微结构,与大别杂岩内一些麻粒岩相表壳岩所保存的减压退变质证迹一样,同是挤出作用和碰撞后隆升的构造证迹。高压相系的发育使南桐柏山和大别山迥然不同于桐商（ 商丹） 断裂以北的北秦岭北淮阳变质带。新近发表的同位素年代学（４０Ａｒ ３９ Ａｒ） 资料：３１６ ～４３４ Ｍａ ,已证明北秦岭是古生代变质带,它与桐柏－ 大别印支期碰撞造山带差异甚大。这两个变质地温梯度差异甚大的变质地体的拼合,说明华北和扬子陆块碰撞的主缝合带是商丹－ 桐商断裂带     

Metamorphic Rock-hosted Disseminated Gold Deposits—A Case Study of the Xiaotongjiapuzi Gold Deposit of Eastern Liaoning

The Xiaotongjiapuzi gold deposit occurs in a Palaeoproterozoic rift accretionary terrane in eastern Liaoning and is hosted by a carbonate formation of the Dashiqiao Formation, Liaohe Group. The metamorphic grade of the host rock is low amphibolite-high greenschist facies. Gold, which is mainly invisible, is distributed in pyrite and arsenopyrite. The grains of Au-bearing sulphide minerals are fine, ranging from 0.0 n to 1 mm. The wall-rock alterations are characterized by low-temperature silification, hydro-sericitization, sericitization and carbonatization. The homogenization temperatures of the fluid inclusions in quartz closely associated with gold mineralization range from 140 to 240° C. The metallogenic age represented by the Ar-Ar isotopic age of sericite is 167 Ma. Comparisons and studies show that the Xiaotongjiapuzi gold deposit can be classified as the submicron-sized disseminated deposit (analogous to the Carlin-type) hosted in metamorphic rocks.     

Horizontal contraction or horizontal extension? Heterogeneous Late Eocene and early Oligocene general shearing during blueschist and greenschist facies metamorphism at the Pennine-Austroalpine boundary zone in the Western Alps

Mylonitic structures related to two orogenic events are described from the upper and lower contacts of the Combin zone and the immediately overlying upper Austroalpine Dent Blanche nappe/Mont Mary klippe and the directly underlying lower Austroalpine Etirol-Levaz slice. The first event, Late Eocene in age, commenced during blueschist facies P-T conditions, but pre-dated the peak of subsequent greenschist facies overprint. The second event, Early Oligocene in age, took place during retrograde greenschist facies conditions. Most sense of shear indicators associated with the retrograde mylonites indicate top SE shearing, but subordinate top NW displacing shear sense indicators have also been mapped. Mylonitic top SE shearing appears to be restricted to the Combin zone and its upper and lower contacts. Within the Dent Blanche nappe and Mont Mary klippe and at the base of the Etirol-Levaz slice, structures were observed which developed during blueschist/greenschist facies conditions and are, in conjunction with the P-T-t history of these rocks, inferred to be older. Associated kinematic data indicate a top NW shear sense. Comparable blueschist/greenschist facies shear sense indicators have not been observed in the Combin zone. Nonetheless, the foliation in the Combin zone shows a progressive evolution from blueschist facies to greenschist facies to retrograde greenschist facies conditions. This indicates that the Combin zone and the immediately over- and underlying Austroalpine units shared a common tectono-metamorphic evolution since the Late Eocene. Finite strain data reveal oblate strain fabrics, which are thought to result from a true flattening strain geometry. Flow path modelling reveals a general non-coaxial deformation régime and corroborates significant departures from a simple shear deformation. In the study area, mylonitic top SE shearing in the Combin zone is attributed to Early Oligocene backfolding and backthrusting of the Mischabel phase. Temperature-time curves suggest slight reheating in the Monte Rosa nappe underneath and cooling in the Dent Blanche nappe above the Combin zone, hence confirming a thrust interpretation for this event. The top NW displacing structures are thought to result from Late Eocene emplacement of the Dent Blanche nappe and the Combin zone onto the Middle Pennine Barrhorn series along the Combin fault. As related structures initiated during mildly blueschist facies conditions in the Dent Blanche nappe and the underlying Combin zone and both were emplaced together onto the greenschist facial Barrhorn series, it is concluded that the structures developed as the nappes moved upward relative to the earth's surface. Thus the Combin fault is regarded as a thrust. The geometry of this structure indicates that the Combin fault is an out of sequence thrust that locally cut down section. Hence, top NW out of sequence thrusting caused local thinning of the metamorphic/structural section in association with horizontal shortening. Out of sequence thrusts cutting down section, and back-thrusts, offer the possibility of explaining the pronounced break in the grade of metamorphism across the Combin fault, i.e. the contact between the eclogite facial Zermatt-Saas zone and the overlying lower grade Combin zone, by contractional deformation.     

High-pressure/low-temperature metamorphism in northern Hubei Province, central China

Abstract The Qinling–Dabie accretionary fold belt in east-central China represents the E–W trending suture zone between the Sino-Korean and Yangtze cratons. A portion of the accretionary complex exposed in northern Hubei Province contains a high-pressure/low-temperature metamorphic sequence progressively metamorphosed from the blueschist through greenschist to epidote–amphibolite/eclogite facies. The 'Hongan metamorphic belt'can be divided into three metamorphic zones, based on progressive changes in mineral assemblages: Zone I, in the south, is characterized by transitional blueschist–greenschist facies; Zone II is characterized by greenschist facies; Zone III, in the northernmost portion of the belt, is characterized by eclogite and epidote–amphibolite facies sequences. Changes in amphibole compositions from south to north as well as the appearance of increasingly higher pressure mineral assemblages toward the north document differences in metamorphic P–T conditions during formation of this belt. Preliminary P–T estimates for Zone I metamorphism are 5–7 kbar, 350–450°C; estimates for Zone III eclogites are 10–22 kbar, 500 ± 50°C.
The petrographic, chemical and structural characteristics of this metamorphic belt indicate its evolution in a northward-dipping subduction zone and subsequent uplift prior to and during the final collision between the Sino-Korean and Yangtze cratons.     

Metamorphic Rock-hosted Disseminated Gold Deposits--A Case Study of the Xiaotongjiapuzi Gold Deposit of Eastern Liaoning

The Xiaotongjiapuzi gold deposit occurs in a Palaeoproterozoic rift accretionary terrane in eastern Liaoning and is hosted by a carbonate formation of the Dashiqiao Formation, Liaohe Group. The metamorphic grade of the host rock is low amphibolite-high greenschist facies. Gold, which is mainly invisible, is distributed in pyrite and arsenopyrite. The grains of Au-bearing sulphide minerals are fine, ranging from 0.0 n to 1 mm. The wall-rock alterations are characterized by low-temperature silification, hydro-sericitization, sericitization and carbonatization. The homogenization temperatures of the fluid inclusions in quartz closely associated with gold mineralization range from 140 to 240° C. The metallogenic age represented by the Ar-Ar isotopic age of sericite is 167 Ma. Comparisons and studies show that the Xiaotongjiapuzi gold deposit can be classified as the submicron-sized disseminated deposit (analogous to the Carlin-type) hosted in metamorphic rocks.     

柴北缘鱼卡地区达肯大坂岩群的地质特征与构造环境

柴达木北缘鱼卡河地区的达肯大坂岩群可划分为斜长角闪岩岩组和片岩岩组。斜长角闪岩岩组主要由变质基性火山岩和碎屑岩组成,火山岩的地球化学特征指示为岛弧环境构造;片岩岩组分布在柴达木山西南侧,为一套陆源碎屑岩建造。该岩群遭受了三幕构造变形,前两幕褶皱变形是造山作用的产物,具有近似的北西-南东向或北北西向的褶皱枢纽,近共轴褶皱叠加的构造样式指示了北东-南西向挤压收缩的动力学背景。达肯大坂岩群遭受中压高绿片岩相-角闪岩相的变质,变质程度往北东方向递减,可与其南柴达木盆地一侧的高压-超高压变质带构成双变质带。结合最近从达肯大坂岩群中获得的锆石年龄,推断该岩群形成于大陆边缘的弧后盆地,时代为新元古代晚期-早古生代,是柴北缘早古生代造山带的重要组成部分。     

Architecture and Kinematics of the Dabie Orogen,Central Eastern China

The geometry of the Dabie Mountains is manifested in terms of the distribution of petro-tectonic units in three dimensions. It is identified into three segments from east to west, four horizons in vertical profiles and eight petrotectonic units from north to south. Three segments are the east, middle and west segments. Four horizons, from top to bottom, are two different meta-tectonic melange in the uppermost part, underthrust basement and cover below them, and mantle at the bottom of the profiles. Eight petro-tectonic units from north to south are: (1) the hinterland basin, (2) the meta-flysch, (3) the ultramafic rock belt (UM) Sujiahe eclogite belt (SH), (4) eclogite belt 2 (Ec2) with most eclogites of continental affinity, (5) eclogite belt 1 (Ecl1) with some eclogite of oceanic affinity, (6) the Dabie complex or underthrust basement of the Yangtze continent, (7) the Susong and Zhangbaling Groups or underthrust cover of the Yangtze continent and (8) the foreland belt. The (3), (4) and (5) units belong to meta-tectonic melange. Some ultrahigh pressure metamorphic minerals such as coesite and micro-diamonds have been found in (3) and (4) units; a possible ultrahigh pressure mineral,clinozoisite aggregate pseudomorph after lawsonite, was found in unit (5). The three tectonic units are speculated to be coherent initially; the UM and SH units are suggested to be the root belt in the east, middle and west segments respectively.The kinematics of the Dabie orogen is divided into three stages: top-to-south thrusting during the eclogite-granulite facies metamorphism, top-to-north extension during the amphibolite metamorphic stage, and faults or shear bands of brittle deformation and greenschist facies metamorphism were formed in the post-orogenic stage since the Late Jurassic and the movement pictures of these faults is different from each other.     

U–Pb zircon study of tectonically bounded blocks of 2940–2840 Ma crust with different metamorphic histories,Paamiut region,South-West Greenland: implications for the tectonic assembly of the North Atlantic craton

New fieldwork, map interpretation, petrography and single zircon U–Pb geochronology has allowed the identification of different crustal blocks in the Paamiut region, in the southern portion of the West Greenland Archaean Craton. Changes of metamorphic grade from only amphibolite facies to granulite facies (some subsequently retrogressed) corresponds with zones of Archaean high strain ductile deformation ± mylonites. U–Pb zircon dates are presented for the TTG (tonalite, trondhjemite, granodiorite) protoliths from each block in the Paamiut region, and the southern portion of the previously identified Tasiusarsuaq terrane lying to the north. The southern part of the Tasiusarsuaq terrane contains 2880–2860 Ma TTG rocks and underwent amphibolite facies metamorphism. Structurally underneath the Tasiusarsuaq terrane to the south is the Sioraq block containing 2870–2830 Ma TTG rocks partly retrogressed from granulite facies. Structurally underneath and to the south is the Paamiut block, dominated by 2850–2770 Ma granodioritic rocks that have only undergone amphibolite facies metamorphism. Also structurally overlying the Paamiut block, but cropping out separately from the Sioraq block, is the Neria block. This appears to be dominated by 2940–2920 Ma gneisses that have been totally retrogressed from granulite facies and strongly deformed. In the southernmost part of the region the Neria block overlies the greenschist to lowermost amphibolite facies Sermiligaarsuk block that contains the ⩾2945 Ma Tartoq Group. Rocks from all the blocks record ancient loss of Pb from zircons and some new zircon growth at 2820 Ma, interpreted to indicate a high grade metamorphic event at that time, including granulite facies metamorphism in the Sioraq and Neria blocks. The blocks of different metamorphic grade are interpreted to have moved to their current positions after the 2820 Ma metamorphism, explaining the change in metamorphic history across some mylonites and ductile shear zones which deform and retrogress granulite facies textures. The juxtaposed blocks and their contacts were subsequently folded under amphibolite facies conditions. The contacts are cut by undeformed Palaeoproterozoic dolerite dykes which post-date amphibolite facies metamorphism. These results, together with previously published data from the Godthåbsfjord region (north of Paamiut) shows that the North Atlantic Craton in West Greenland from Ivittuut in the south to Maniitsoq in the north (∼550 km) consists of a mosaic of ductile fault-bounded packages that attained their present relative positions in the late Archaean.     

北祁连山俯冲杂岩带的构造演化

北祁连位位于华北克拉西部阿拉善地块与中祁连－柴达木泛地块之间是我国最具特色的大陆造山带之一。带内发育有震旦纪－中寒武世的裂谷火山岩，晚寒武世－奥陶纪蛇绿岩，中晚奥陶世岛弧火山岩，晚奥陶世弧后拉张盆地火山－沉积岩，志留纪残余海盆相复理石和泥盆纪山间磨粒石等，中间夹两条变质和变形特征不同的加里东期俯冲杂岩带；南带为深层俯冲，北带为浅层俯冲杂岩；这两条杂岩石可能形成于同一俯冲带的不同深度，俯冲杂岩带中岩     

The transition from brittle to ductile deformation in the Sambagawa metamorphic belt, Japan

The dominant deformation mechanism during the Sambagawa metamorphism changes from brittle to ductile with increasing metamorphic temperature. The magnitude of plastic strains inferred from the shapes of deformed radiolaria in metachert increases sharply across the boundary between the epidote-pumpellyite-actinolite zone and the epidote-actinolite zone. The synmetamorphic crack density of metachert is an indicator of the contemporaneous brittle strain of rocks, and it decreases sharply as the grade reaches the epidote-actinolite zone. Hence, the ratio of the ductile strain to the brittle strain of metachert decreases rapidly across the transition to the epidote-actinolite zone of the Sambagawa metamorphic belt.
The sharp change of the ductile strain magnitude also takes place at the epidote-actinolite grade in the Shimanto metamorphic belt of Japan, an example of the intermediate pressure facies series of metamorphism. It is concluded that the transition from brittle to ductile deformation takes place at about 300-400°C. and is independent of pressure of metamorphism.     

Metamorphic evolution of the central Southern Cross Province,Yilgarn Craton,Western Australia

Two contrasting styles of metamorphism are preserved in the central Southern Cross Province. An early, low‐grade and low‐strain event prevailed in the central parts of the Marda greenstone belt and was broadly synchronous with the first major folding event (D₁) in the region. Mineral assemblages similar to those encountered in sea‐floor alteration are indicative of mostly prehnite‐pumpellyite facies conditions, but locally actinolite‐bearing assemblages suggest conditions up to mid‐greenschist facies. Geothermobarometry indicates that peak metamorphic conditions were of the order of 250–300°C at pressures below 180 MPa in the prehnite‐pumpellyite facies, but may have been as high as 400°C at 220 MPa in the greenschist facies. A later, higher grade, high‐strain metamorphic event was largely confined to the margins of the greenstone belts. Mineral assemblages and geothermobarometry suggest conditions from upper greenschist facies at P–T conditions of about 500°C and 220 MPa to upper amphibolite facies at 670°C and 400 MPa. Critical mineral reactions in metapelitic rocks suggest clockwise P–T paths. Metamorphism was diachronous across the metamorphic domains. Peak metamorphic conditions were reached relatively early in the low‐grade terrains, but outlasted most of the deformation in the higher grade terrains. Early metamorphism is interpreted to be a low‐strain, ocean‐floor‐style alteration event in a basin with high heat flow. In contrast, differential uplift of the granitoids and greenstones, with conductive heat input from the granitoids into the greenstones, is the preferred explanation for the distribution and timing of the high‐strain metamorphism in this region.