Amphibolite Facies Domain Research Articles

A holistic model for the origin of orogenic gold deposits and its implications for exploration

The term orogenic gold deposits has been widely accepted, but there has been continuing debate on their genesis. Early syn-sedimentary or syn-volcanic models and hydrothermal meteoric-fluid models are now invalid. Magmatic-hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships. The most plausible models involve metamorphic fluids, but the source of these fluids is equivocal. Intra-basin sources within deeper segments of the hosting supracrustal successions, the underlying continental crust, subducted oceanic lithosphere with its overlying sediment wedge, and metasomatized lithosphere are all potential sources. Several features of Precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic-fluid source. These include the presence of hypozonal deposits in amphibolite-facies domains, their anomalous multiple sulfur isotopic compositions, and problems of derivation of gold-related elements from devolatilization of dominant basalts in the sequences. The Phanerozoic deposits are largely described as hosted in greenschist-facies domains, consistent with supracrustal devolatilization models. A notable exception is the Jiaodong gold deposits of China, where ca. 120-Ma gold deposits are hosted in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization. Other deposits in China are comparable to those in the Massif Central and elsewhere in France, in that they are hosted in amphibolite-facies domains or clearly post-date regional metamorphic events imposed on hosting supracrustal sequences. If all orogenic gold deposits have a common genesis, the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package, or the associated metasomatized mantle wedge, with CO2 released during decarbonation and S- and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 °C. Although this model satisfies all geological, geochronological, isotopic, and geochemical constraints, and is consistent with limited computer-based modeling of fluid release from subduction zones, the precise mechanisms of fluid flux are model-driven and remain uncertain. From an exploration viewpoint, the model re-emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction-related orogenic belts and importance of continental-scale lithosphere-tapping fault and shear zones to focus large volumes of auriferous fluid. It confirms the importance of the consistent spacing between world-class deposits, broadly equivalent to the depth of the Moho, as derived from empirical observations.

Transtensional origin of multi-order cross-folds in a high-grade gneiss complex, southwestern Grenville Province: formation during post-peak gravitational collapse

The well-mapped western part of the Ottawa River Gneiss Complex (ORGC; new name), a large metamorphic core complex, hosts a system of gently plunging cross-folds of outcrop to regional scale situated in the ductile detachment zone between the lower grade cover and high-grade core of the complex. The cross-folds are buckle structures that deform the attenuated gneissic layering, plunge parallel to the regional elongation lineation, range from upright to recumbent, and exhibit distinctive hinge-parallel elongation lineations, all features of extension-dominated ductile transtension. Our L–S fabric data are consistent both with kinematic modelling that predicts progressive constrictional strain in the hinge zones of transtensional folds, and with dynamic modelling that predicts rotation of flattened fold limbs into moderately dipping attitudes. On the basis of petrologic data, we show that cross-folding postdated the peak Ottawan metamorphism and took place during retrogression and exhumation of the thrust-sheet stack. The cross-folds form an inclined system that is principally developed in retrograde melt-weakened amphibolite-facies rocks, with the transtensional origin implying that exhumation and retrogression of the high-grade core of the complex took place in an oblique extensional setting. A transtensional origin for the cross-folds removes the need to appeal to orogen-parallel regional shortening, an implausible requirement of previous interpretations, and is compatible with data indicating that much of the visible fabric and structure of amphibolite-facies domains of the ORGC developed during post-peak exhumation, retrogression, and gravitational collapse of the thrust-sheet stack.

Metamorphism and diachronous cooling in a contractional orogen: the Strandja Massif, NW Turkey

AbstractThe southern part of the Strandja Massif, northern Thrace, Turkey, comprises a basement of various gneisses, micaschists and rare amphibolite, and a cover of metaconglomerate and metasandstone, separated from each other by a pre-metamorphic unconformity. Metamorphic grade decreases from the epidote–amphibolite facies in the south to the albite–epidote–amphibolite/greenschist-facies transition in the north. Estimated P–T conditions are 485–530°C and 0.60–0.80 GPa in the epidote–amphibolite facies domain, and decrease towards the transitional domain between greenschist- and epidote–amphibolite facies. Rb–Sr muscovite ages range from 162.9 ± 1.6 Ma to 149.1 ± 2.1 Ma, and are significantly older (279–296 Ma) in the northernmost part of the study area. The Rb–Sr biotite ages decrease from 153.9 ± 1.5 Ma in the south to 134.4 ± 1.3 Ma in the north. These age values in conjunction with the attained temperatures suggest that the peak metamorphism occurred at around 160 Ma and cooling happened diachronously, and Rb–Sr muscovite ages were not reset during the metamorphism in the northernmost part. Structural features such as (i) consistent S-dipping foliation and SW to SE-plunging stretching lineation, (ii) top-to-the-N shear sense, and (iii) N-vergent ductile shear zones and brittle thrusts suggest a N-vergent compressional deformation coupled with exhumation. We tentatively ascribe this metamorphism and subsequent diachronous cooling to the northward propagation of a thrust slice. The compressional events in the Strandja Massif were most probably related to the coeval N-vergent subduction/collision system in the southerly lying Rhodope Massif.

Structural analysis of the northern Nagssugtoqidian orogen, West Greenland: an example of complex tectonic patterns in reworked high-grade metamorphic terrains

Structural analysis of the deeply eroded northern flank of the Palaeoproterozoic Nagssugtoqidian orogen shows marked regional variations in both the orientation and type of fabrics, as is characteristic of Precambrian high-grade terrains subjected to polyphase deformation. Here we investigate the relationship between strain, metamorphic grade, and the resulting structural patterns. The study area south of Aasiaat in West Greenland consists of amphibolite- to granulite-grade Archaean orthogneisses and relatively thin supracrustal units. The regional foliation displays a WSW–ENE to SW–NE strike associated with steep to moderate dips towards the WNW or SSE. Lineation trends are WSW–ENE and generally plunge gently towards the WSW. Mesoscopic fold hinges are usually colinear with the regional lineation. A systematic change in the plunge of lineations occurs across the south-western part of the study area. Towards the south, the lineation plunge progressively increases, despite the generally uniform strike of foliation. This southward increase of lineation pitch is typically associated with the transition from L > S or L = S shape fabrics in rocks characterised by a low pitch, to S > L or S fabrics in the zone of moderate to high pitch. The structural patterns point to subdivision of the study area into a southern domain mostly characterised by S or S > L shape fabrics and a moderate to high angle of lineation pitch, and a northern domain showing L > S or L = S fabrics and low angles of lineation pitch. This subdivision corresponds well with the map scale boundary between granulite facies rocks in the south and amphibolite facies rocks farther north. The observed structural pattern may be explained by two alternative tectonic models: (1) northward indentation of the previously cooled granulite block into the rheologically weaker amphibolite domain, and (2) strain partitioning within a mid-crustal transpression zone. In model 2 the northern domain represents a localised zone dominated by strike-slip kinematics, whereas the southern domain shows evidence of mostly coaxial shortening. Recent geochronology supports the indentator model in spite of limited available data. Despite the details and structural complexities of the two tectonic models, the granulite and amphibolite facies domains seem to form autochthonous segments of a crustal section linked by a transitional zone that was only reactivated and reworked during indentation or transpression. The Nagssugtoqidian compression was effectively transferred across this zone towards the northern amphibolite domain that suffered penetrative deformation during the Palaeoproterozoic event. The N–S shortening was accommodated through folding, indentation and/or strike-slip displacements, rather than by thrusting and folding as seen south of the study area.

Molybdenite Re–Os dating constrains gravitational collapse of the Sveconorwegian orogen, SW Scandinavia

Re–Os dating of molybdenite from small deposits is used to define crustal domains exhibiting ductile versus brittle behaviour during gravitational collapse of the Sveconorwegian orogen in SW Scandinavia. A 1019 ± 3 Ma planar quartz vein defines a minimum age for brittle behaviour in central Telemark. In Rogaland–Vest Agder, molybdenite associated with deformed quartz and pegmatite veins formed between 982 ± 3 and 947 ± 3 Ma in the amphibolite-facies domain (three deposits) and between 953 ± 3 and 931 ± 3 Ma west of the clinopyroxene-in isograd (two deposits) in the vicinity of the 0.93–0.92 Ga Rogaland anorthosite complex. The data constrain the last increment of ductile deformation to be younger than 0.95 and 0.93 Ga in these two metamorphic zones, respectively. Molybdenite is the product of an equilibrium between biotite, oxide and sulfide minerals and a fluid or hydrated melt phase, after the peak of 1.03–0.97 Ga regional metamorphism. Molybdenite precipitation is locally episodic. A model for gravitational collapse of the Sveconorwegian orogen controlled by lithospheric extension after 0.97 Ga is proposed. In the west of the orogen, the Rogaland–Vest Agder sector is interpreted as a large shallow gneiss dome, formed slowly in two stages in a warm and structurally weak crust. The first stage at 0.96–0.93 Ga was associated with intrusion of the post-collisional hornblende–biotite granite suite. The second stage at 0.93–0.92 Ga, restricted to the southwesternmost area, was associated with intrusion of the anorthosite–mangerite–charnockite suite. Most of the central part of the orogen was already situated in the brittle upper crust well before 0.97 Ga, and did not undergo significant exhumation during collapse. In the east of the orogen, situated against the colder cratonic foreland, exhumation of high-grade rocks of the Eastern Segment occurred between 0.97 and 0.95 Ga, and included preservation of high-pressure rocks but no plutonism.

Lithological Features of Precambrian Gold-Bearing Rocks: Evidence from the Ukrainian Shield

Based on traditional petrochemical and nontraditional mineralogical methods (accessory zircon generation analysis), specific features of the primary composition of strongly metamorphosed rocks from some Early Precambrian Au-bearing rocks of the Ukrainian Shield (US) were studied. The confinement of several gold ore occurrences to primarily sedimentary Late Archean rocks of the Ukrainian Shield has been established and the possibility of their chemogenic origin is considered. The joint analysis of plicative tectonics and metamorphism facies in the study area demonstrated that Au-bearing primarily sedimentary (chemogenic) rocks of the Khashchevatoe–Zaval'ev Formation of the Bug Group (AR2) are confined to amphibolite-facies domains within tectonic (high-order synform) structures with a significant gold potential.

The application of GIS to unravel patterns of deformation in high grade terrains: a case study of indentor tectonics from west Greenland

Abstract The ability to compare, integrate and knit together multidisciplinary datasets in terms of subject, space and scale is critical to the recognition of geological patterns. In this contribution, we show that the use of Geographic Information Systems (GIS) is extremely valuable in detecting patterns associated with broad zones of deformation in high grade terrains. The GIS methodology facilitates the geological interpretation and development of models as it permits an easy and quick investigation of several geoscientific datasets by subject, space and scale. The GIS-based integration of structural, metamorphic, fabric type and aeromagnetic datasets collected in west Greenland shows that patterns seen within one dataset coincide with patterns observed in other datasets. Consequently, two major domains are recognized that are separated by a broad boundary zone. The southern block is characterized by a distinct, irregular magnetic signal coupled with granulite facies metamorphism and dominant S-type fabrics. The map scale geometry of this block controls the patterns observed within the amphibolite facies domain further north. Foliation and lineation patterns form an arcuate swing in strike about the southern block. Fabric types vary both around the strike swing and across strike. An indentor model that incorporates a rigid, cooled granulite block in the south bounded to the north by a rheologically weaker amphibolite facies domain can explain these patterns. The preserved metamorphic grade governs the rheology of the different, but essentially authochthonous blocks with the amphibolite facies domain being plastered and ‘moulded around’ the rigid granulite indentor. As patterns of remote geophysical and geological data closely correspond with one another, greater confidence may be placed in the application of remote geophysics in areas which lack abundant ground-based data.

A first find of retrogressed eclogites in the Odenwald Crystalline Complex, Mid-German Crystalline Rise, Germany: evidence for a so far unrecognised high-pressure metamorphism in the Central Variscides

Metabasic rocks were recently found in the Böllsteiner Odenwald, being part of the Variscan Mid-German Crystalline Rise (MGCR), that give evidence of a so far unrecognised eclogite-facies metamorphic event and testify, for the first time, to high-pressure metamorphism in the MGCR, the assumed suture zone of the European Variscides. Eclogite-facies metamorphism is indicated by both widespread clinopyroxene–plagioclase symplectites—interpreted as breakdown products of omphacite—and the composition of symplectitic clinopyroxene with measured jadeite contents of up to 27 mol%, extending into the omphacite field. Reintegration of numerous clinopyroxene–plagioclase symplectites implies minimum jadeite contents of the former omphacite of at least 38 mol%. For the eclogite stage, the four-phase assemblage omphacite-garnet-quartz-rutile can be reconstructed. A post-eclogitic overprint led to the formation of symplectitic intergrowths of clinopyroxene and plagioclase, amphibole–plagioclase coronas around garnet and domains with recrystallised amphibole and plagioclase. Preliminary P– T estimates for the eclogite-facies metamorphism indicate minimum pressures of some 16–17 kbar and temperatures of approximately 700±50 °C. Geothermobarometry for the subsequent symplectitic breakdown of omphacite yields some 14 kbar and 700 °C. P– T estimates on retrograde amphibolite-facies domains and on prograde mineral assemblages preserved in garnet cores point to a clockwise P– T path experienced by these rocks. The eclogites formed from a tholeiitic protolith, that may have been genetically linked to a continental extension zone or a young oceanic ridge or back-arc environment.

Sr, Nd isotopes and geochemistry of the Bayuda Desert high-grade metamorphic basement (Sudan): an early Pan-African oceanic convergent margin, not the edge of the East Saharan ghost craton?

The high-grade metamorphic basement of the Bayuda Desert is situated at the inferred transition between the juvenile Neoproterozoic mainly greenschist facies Arabian–Nubian Shield (ANS) and the pre-Neoproterozoic mainly amphibolite facies domain of the East Saharan Ghost Craton. New geochemical and Sr–Nd isotope data reveal that this basement in Bayuda constituted a Neoproterozoic oceanic convergent margin succession with limited and probably late input of old material. Within this series, garnet amphibolites and epidote–biotite gneisses have geochemical characteristics of HFSE-depleted tholeiitic basalts and low- to medium-K dacites and rhyodacites, indicating magmatism in an oceanic island arc or back-arc basin environment. This magmatism occurred at 806±19 Ma (Sm–Nd 11 WR isochron), similar in age to arc magmatism in the ANS. Leucocratic gneisses, muscovite schists and garnet–biotite schists form the dominant meta-sedimentary rocks of the study area. They were primarily derived from two different sources: volcanogenic sediments from a Neoproterozoic island arc (T DM Nd model ages between 790 and 900 Ma) and terrigeneous sediments from an older continental source (T DM Nd model ages up to 2100 Ma). The volcanosedimentary succession was metamorphosed under amphibolite facies conditions prior to 670 Ma, probably at approximately 700 Ma. The high-grade metamorphism is related to a frontal collisional event that also produced syn-collisional peraluminous granites preserved as muscovite–biotite gneisses. Meta-igneous rocks from eastern Bayuda have ε Nd values at 806 Ma of +5.2±0.4, indicating a less depleted mantle source (crustal contamination can be excluded) than the neighbouring Gabgaba–Gebeit terrane ( ε Nd, ca. +7) from the Arabian–Nubian shield. Less depleted mantle source is also known at Jebel Moya to the south, and inside the Arabian–Nubian Shield to the southeast of Bayuda. Lithological and structural similarities (dominantly northeast striking foliation) with the Bayuda Desert succession occur in many parts of central and western Sudan, suggesting a comparable geodynamic evolution. It is proposed that a Neoproterozoic oceanic convergent margin (Bayuda type succession) collided at approximately 700 Ma to the northwest with the East Saharan ghost craton, whose easternmost limit must lie below or more to the west than previously thought.

U-Pb monazite ages in amphibolite- to granulite-facies orthogneiss reflect hydrous mineral breakdown reactions: Sveconorwegian Province of SW Norway

In the Rogaland–Vest Agder terrain of the Sveconorwegian Province of SW Norway, two main Sveconorwegian metamorphic phases are reported: a phase of regional metamorphism linked to orogenic thickening (M1) and a phase of low-pressure thermal metamorphism associated with the intrusion of the 931 ± 2 Ma anorthosite-charnockite Rogaland igneous complex (M2). Phase M1 reached granulite facies to the west of the terrane and M2 culminated locally at 800–850 °C with the formation of dry osumilite-bearing mineral associations. Monazite and titanite U-Pb geochronology was conducted on 17 amphibolite- to granulite-facies orthogneiss samples, mainly from a suite of 1050 +2/−8 Ma calc-alkaline augen gneisses, the Feda suite. In these rocks, prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012–1006 Ma. In the Feda suite and other charnockitic gneisses, concordant to slightly discordant monazite at 1024–997 Ma probably reflects breakdown of biotite during granulite-facies M1 metamorphism. A spread of monazite ages down to 970 Ma in biotite ± hornblende samples possibly corresponds to the waning stage of this first event. In the Feda suite, a well defined monazite growth episode at 930–925 Ma in the amphibolite-facies domain corresponds to major clinopyroxene formation at the expense of hornblende during M2. Growth or resetting of monazite was extremely limited during this phase in the granulite-facies domain, up to the direct vicinity of the anorthosite complex. The M2 event was shortly followed by cooling through ca. 610 °C as indicated by tightly grouped U-Pb ages of accessory titanite and titanite relict inclusions at 918 ± 2 Ma over the entire region. A last generation of U-poor monazite formed during regional cooling below 610 °C, in hornblende-rich samples at 912–904 Ma. This study suggests: (1) that monazite formed during the prograde path of high-grade metamorphism may be preserved; (2) that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of REEs and Th, and/or fluid mobilisation; (3) that the U-Pb system in monazite is not affected by thermal events up to 800–850 °C, provided that conditions were dry during metamorphism.

Large‐scale fluid infiltration, metasomatism and re‐equilibration of Archaean basement granulites during Palaeoproterozoic thrust belt construction, Ungava Orogen, Canada

Abstract The metamorphic history of the Archaean Superior Province crystalline basement in the Palaeoproterozoic Ungava Orogen attests to the importance of structural and geohydrological controls on a retrograde amphibolite‐granulite transition. Two distinct metamorphic suites, separated in age by nearly one billion years, are recognized in extensively exposed tonalitic to dioritic metaplutonic gneisses. The older suite comprises c. 2.7‐Ga granulite facies assemblages (orthopyroxene‐clinopyroxene‐hornblende‐plagioclase‐ilmenite ± biotite ± quartz) that record moderate pressures (±5 kbar) and high temperatures (±800° C). A younger, c. 1.8‐Ga suite resulted from amphibolitization of the granulites and is characterized by regionally extensive amphibolite facies mineral zones that broadly parallel the basal décollement of the overlying Proterozoic Cape Smith Thrust Belt. Deformation/mineral growth relationships in the amphibolitized basement indicate that extensive hydration and re‐equilibration of the Archaean granulites occurred during thrust belt deformation. The transition from granulite facies to amphibolite facies assemblages is characterized by the growth of garnet‐hornblende‐quartz ° Cummingtonite coronas between plagioclase and orthopyroxene‐clinopyroxene, as well as titanite coronas on ilmenite. Multi‐equilibrium thermobarometry on the coronitic assemblages documents re‐equilibration of the granulitic gneiss to 7.7 kbar at 644° C in the south and 9.8 kbar at 700° C in the north. The variably deformed, amphibolite facies domain sandwiched between the coronitic garnet zone and the basal décollement is marked by significant metasomatic changes in major element concentrations within tonalite. These changes are compatible with equilibrium flow of an aqueous‐chloride fluid down a temperature gradient. The source of fluids for basement hydration/metasomatism is interpreted to be dehydrating clastic rocks in the overlying thrust belt, with fluid flow probably focused along the basal décollement.

Zircon and rutile U-Pb geochronology of the Niquelândia layered mafic and ultramafic intrusion, Brazil: constraints for the timing of magmatism and high grade metamorphism

Abstract The Niquelândia intrusion is among the largest layered intrusions in the world. It is part of a 350 km long belt of large mafic-ultramafic complexes in central Brazil. Both intrusion and country rocks were subjected to highgrade metamorphism ranging from amphibolite to granulite facies, and associated ductile deformation. The first U-Pb zircon and rutile ages for this region are presented. Zircon fractions from a meta-anorthosite from the upper gabbro-anorthositic unit are variably discordant (0–28% with regard to the lower intercept) along a mixing line from 777±10 Ma lower intercept and 1583±25 Ma upper intercept. Zircon fractions from a later quartz diorite within the Central Mafic Unit are variably discordant (0–14% with regard to the lower intercept) along a mixing line from 794−6+4 lower intercept and 1565±22 upper intercept. The upper intercepts for both rocks, interpreted to be the magmatic age, overlap and suggest a Mesoproterozoic age for the intrusion. The lower intercept is interpreted to be the high-grade metamorphic event. Zircons from two quartz-rich blastomylonites representing different metamorphic domains and cutting through the layered intrusions were analyzed. A single zircon from the amphibolite facies domain blastomylonite gives a concordant (−0.3%) 207 Pb 206 Pb age of 777±3 Ma, and a single zircon from the granulite facies blastomylonite gives a 207 Pb 206 Pb age of 786±5 Ma (−0.8% discordance). Both results are consistent with the lower intercept ages and set the 770–795 Ma interval for the high-grade metamorphic event. Rutile ages (∼650 Ma) are considerably younger than zircon metamorphic ages and suggest a milder regional tectonomagmatic episode or a complex and long-lasting cooling history for the region. The U-Pb data provide evidence for an important Mesoproterozoic extensional tectonic event in central Brazil. It also sets the 770–795 Ma interval for the high-grade amphibolite to granulite facies prograde metamorphism, interpreted to represent the timing of a continental collision event.

Response of zircon U?Pb isotopes and whole-rock geochemistry to CO2 fluid-induced granulite-facies metamorphism, Kabbaldurga, Karnataka, South India

The arrested, prograde amphibolite- to granulite-facies transition at Kabbaldurga, south India, overprints Archacan amphibolite-facies nebulitic gneisses and the late Archaean Closepet granite. Previous studies have shown that this facies transition was controlled by a channelled influx of a dehydrating fluid, assumed to be CO2, at ∼750°C and 5.5 kbar confining pressure. The effect of this type of prograde transition on zircon U−Pb isotopic systematics and whole-rock geochemistry has been studied using ∼1 kg amphibolite-facies, transitional and granulite-facies domains from a single block of gneiss. The zircon populations from all three domains have essentially similar morphology and U−Pb systematics. This similarity shows that at the conditions under which the prograde granulite-facies transition took place via fluid influx, the zircon U−Pb systematics were not disturbed by the process. Using the pooled data from all three domains, it is concluded that the protolith of the gneiss formed at 2965±4 Ma (2σ), and that zircons also grew during an anatectic event common to all domains at 2528±5 Ma. The granulite-facies metamorphism has not been dated directly due to the lack of response to the zircon U−Pb isotopic systematies to it. However, field and petrographic criteria dictate that its maximum age is 2528±5 Ma, the age of the anatectic event common to each domain in the gneiss block, which was overprinted during the granulite-facies event. For most major and trace elements, consistent enrichment or depletion trends associated with the transition to granulite facies cannot be identified with confidence. However, the granulite-facies portion is LREE (light-rare-earth-element)-enriched and H (heavy) REE-depleted compared with the amphibolite-facies domain, and the transitional domain is at intermediate values. The isotopic and geochemical evidence presented supports the conclusion that the granulite-facies charnockitic rocks at Kabbaldurga were not formed by removal of an anatectic melt, but that they formed later by simple metamorphic overprint of amphibolite-facies rocks.

The photogeological recognition of ancient orogenic belts in Africa

Photogeological interpretation, assisted by some ground control, has been used to delineate areas of the crystalline basement in which structures formed during a particular tectonism are predominant. Such areas are referred to as 'tectonic domains'. They are recognized principally by distinctive tectonic style, by characteristic trend and axial direction, by metamorphic grade and by the sequence ot imposition of tectonisms. These criteria may be supported by geophysical data. It is unusual for all the criteria to be satisfied photogeologically, but with some ground information it is possible to draw maps which show the distribution of tectonic domains. The tectonic domain map of Karamoja, north-east Uganda, shows four domains: an early granulite facies (charnockitic) east-striking domain ( A ); a second, north-striking, more widely developed amphibolite facies domain ( B ) in which A structures are reworked and partly obliterated; a C domain which cuts across the A and B domains in a series of straight, penetrative and partially cataclastic, north-west-trending structural belts which are parallel to the Aswa Zone of central Uganda; and the Karasuk domain of recumbent flaggy folds named after the Karasuk Group. Each domain is laterally bounded, replaced or 'overprinted' by another. These relationships are illuminated by those established elsewhere in northern Uganda, and the tectonic domain map is thought to depict the interplay in north-east Uganda of the Watian, Aruan and Ghuan tectonisms which may be orogenies, and to include the Mozambiquian front impinging upon older structures. The value of the method of mapping tectonic domains lies in presenting, with a minimum of field-work, something approaching the normal tectonic map and so depicting the outlines of the ancient orogenic belts. Data such as age-determinations can be attached to the tectonic domain maps.