Archean Granite-greenstone Terrains Research Articles

Archean diapirism recorded by vertical sheath folds in the core of the Yalgoo Dome, Yilgarn Craton

In Archean granite-greenstone terrains, both vertical and horizontal tectonic processes can generate the typical dome-and-keel structural geometries. One of the classic Archean domes interpreted to result from a horizontal tectonic regime is the Yalgoo Dome in the Yilgarn Craton of Western Australia. In this contribution, we reassess the structural evolution of the Yalgoo Dome by detailing the structures exposed in the migmatitic core. The core contains multi-scale domes-and-basins. These structures were previously interpreted as the result of superposed folding. Our structural mapping shows that the dome-and-basin patterns result from vertical sheath folds developed in a single, progressive deformation event (D1). This first event most likely resulted from diapiric ascent of a buoyant partially molten tonalitic crust and was overprinted by two contractional episodes (D2–D3) both reflecting bulk EW shortening. The structural evolution proposed here points towards a shift from an early history of vertical tectonics dominated by diapirism to a regional regime dominated by horizontal tectonics.

Neoarchean ductile deformation of the Northeastern North China Craton: The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei, North China

Archean granitic gneiss domes and greenstone belts are well-preserved in eastern North China Craton (NCC), one of the oldest Archean terrains in the world. The Shuangshanzi ductile shear zone in Qinglong, eastern Hebei Province is located between an Archean granitic gneiss dome and a greenstone belt within an uplift in eastern NCC. Supracrustal rocks from the Neoarchean Shuangshanzi and Zhuzhangzi Groups, and some Archean granitic gneisses were involved in the shearing along the eastern margin. In the southern part, the narrow NE-trending shear zone dips NW with dip angles of 40–60° and, in the northern part, the shear zone dips NWN with dip angles of 70–85°. Microstructural and EBSD fabric analyses suggest that the shear zone was developed at upper greenschist facies to lower amphibolite facies conditions with deformation temperatures of 400–550°C. LA-ICP-MS zircon U-Pb dating of mylonitized granitic rocks and undeformed quartz diorite cutting the shear zone suggest that the Shuangshanzi ductile shear zone was formed between 2550Ma and 2452Ma. Detailed kinematic studies of the shear zone show a clear sinistral shear sense with a slightly oblique-slip component in the northern part and a sinistral transtensional slip component in the southern part. It is therefore suggested that the shear zone was formed during the Anziling doming with respect to the down-slipping Neoarchean Shuangshanzi and Zhuzhangzi Groups. The difference in kinematics along the southern and the northern sections is interpreted to be caused by the doming with an uneven clockwise spiral rotation.The BIF-rich supracrustal rocks have higher density than their neighboring granitic gneisses, and therefore can easily sink to form synclines by sagduction processes. The sagduction is mainly triggered by gravitational inversion of high density supracrustal rocks with respect to relatively light granitic gneisses within the dome. As a result, the gneisses synchronously moved upward. A shear zone was thus developed in accommodation of the upward and downward movements. It is possible that such a tectonic model also applies to many Archean granite-greenstone terrains.

Seismic signatures of complex geological structures in the Cue-Weld Range area, Murchison domain, Yilgarn Craton, Western Australia

The Murchison domain forms the northwest part of the Youanmi Terrane, a tectonic unit within the Neoarchean Yilgarn Craton in Western Australia. In the Cue-Weld Range area the Murchison domain has experienced a complex magmatic and deformation history that resulted in a transposed array of greenstone belts that host significant iron, gold, and base metal deposits. In this study, we interpret the upper 2s (about 6km) of a deep crustal seismic profile 10GA–YU1, near the town of Cue, and correlate rock units and structures in outcrop with corresponding reflections. We performed 3D constant velocity ray-tracing and calculate the corresponding travel times for the reflections for time domain pre-stack and post-stack seismic data. This allows us to link shallow reflections with mafic volcanic rocks of the Glen Group and basaltic rocks of the Polelle Group in outcrop. Based on our interpretation and published geological maps and data, we propose a model in which the local stratigraphy represents a refolded thrust system. To test our hypothesis, we applied 2D acoustic finite difference forward modeling. The corresponding synthetic data were processed in the same way as the acquired data. Comparisons between the acquired and the synthetic data show that the model is consistent with observations. We propose a new model for the subsurface of the Cue-Weld Range area and argue that some of the lithologies in the area are repeated structurally at different levels. Our approach highlights the benefit of imaging and modeling of deep seismic transects to resolve local structural complexity in Archean granite-greenstone terrains.

Structure and timing of Neoarchean gold mineralization in the Southern Cross district (Yilgarn Craton, Western Australia) suggest leading role of late Low-Ca I-type granite intrusions

The formation of structurally controlled lode-gold deposits is a controversial subject with both magmatic and metamorphic fluids considered a feasible source for gold. Here we present a study from the Southern Cross district (Yilgarn Craton, Western Australia), where structurally controlled Neoarchean gold deposits are hosted in amphibolite facies greenstones. We combine geochronological data with structural analysis to constrain the timing and structural control of ore deposition. We show that gold mineralization took place between c. 2638 and 2630 Ma, contemporaneous with the onset of voluminous intrusions of Low-Ca, I-type granites, which are ubiquitous in Southern Cross and elsewhere in the Yilgarn Craton. We argue that the timing of the intrusions, their spatial association with gold deposits, their chemical composition, and isotopic signature are consistent with Low-Ca granites being a major fluid source for mineralization. We propose that the fluid release by cooling plutons was facilitated by transport along active amphibolite facies shear zones. As gold mineralization was synchronous with Low-Ca magmatism across large areas of the Yilgarn Craton, our model may be applicable to orogenic gold deposits in other parts of the Yilgarn Craton as well as other Archean granite-greenstone terrains with a ‘late granite bloom’.

Metamorphic rocks of the Murmansk domain (Kola Peninsula) as compared with the oldest rock associations of the northeastern Baltic shield, Canada, and Greenland

Rock associations characterized by heterogeneous sets of petrogeochemical parameters were compared by quantifying the degree of their similarity-dissimilarity and searching for discrimination trends between them. Using procedures specially developed for this purpose, it was demonstrated for the first time that the lithotectonic complexes of the Murmansk domain are fundamentally different from those of typical granulite-gneiss terrains and resemble the granite-greenstone terrains of the Baltic shield, Greenland, and Canada. Based on the whole data set, the Murmansk domain can be considered as a deeply eroded Archean granite-greenstone terrain retaining only the tonalite-trondhjemite-gneiss basement with abundant supracrustal enclaves. A trend of the compositional difference between the older and younger rock associations is similar to that between the tholeiitic and boninitic volcanic series. It was suggested that the petrogeochemical “age” trend reflects the initial stage of the compositional evolution of the metamagmatic rocks of the region from metamorphic rocks similar to tholeiites at the early stages to the Paleoproterozoic boninite-like rocks, which are believed to be linked to the unique PGE-bearing province of the northeastern Baltic shield. This implies that the specific metallogenic features of the region emerged already in the Archean, which supported the suggestion on the long duration of geological processes in the Early Precambrian.

Geochemical evolution of magmatism in Archean granite-greenstone terrains

Evolution of Archean magmatism is one of the key problems concerning the early formation stages of the Earth crust and biosphere, because that evolution exactly controlled variable concentrations of chemical elements in the World Ocean, which are important for metabolism. Geochemical evolution of magmatism between 3.5 and 2.7 Ga is considered based on database characterizing volcanic and intrusive rock complexes of granite-greenstone terrains (GGT) studied most comprehensively in the Karelian (2.9–2.7 Ga) and Kaapvaal (3.5–2.9 Ga) cratons and in the Pilbara block (3.5–2.9 Ga). Trends of magmatic geochemical evolution in the mentioned GGTs were similar in general. At the early stage of their development, tholeiitic magmas were considerably enriched in chalcophile and siderophile elements Fe2O3, MgO, Cr, Ni, Co, V, Cu, and Zn. At the next stage, calc-alkaline volcanics of greenstone belts and syntectonic TTG granitoids were enriched in lithophile elements Rb, Cs, Ba, Th, U, Pb, Nb, La, Sr, Be and others. Elevated concentrations of both the “crustal” and “mantle-derived” elements represented a distinctive feature of predominantly intrusive rocks of granitoid composition, which were characteristic of the terminal stage of continental crust formation in the GGTs, because older silicic rocks and lithospheric mantle were jointly involved into processes of magma generation. On the other hand, the GGTs different in age reveal specific trends in geochemical evolution of rock associations close in composition and geological position. First, the geochemical cycle of GGT evolution was of a longer duration in the Paleoarchean than in the Meso-and Neoarchean. Second, the Paleoarche an tholeiitic associations had higher concentrations of LREE and HFSE (Zr, Ti, Th, Nb, Ta, Hf) than their Meso-and Neoarchean counterparts. Third, the Y and Yb concentrations in Paleoarchean calc-alkaline rock associations are systematically higher than in Neoarchean rocks of the same type, while their La/Yb ratios are in contrast lower than in the latter. These distinctions are likely caused by evolution of mantle magmatic reservoirs and by changes in formation mechanisms of silicic volcanics and TTG granitoids. The first of these factors was likely responsible for appearance of sanukitoid magmatic rocks in the Late Mesoarchean. Representative database considered in the work includes ca. 500 precision analyses of Archean magmatic rocks.

The Timing of Mineralization in the Archean North Pilbara Terrain, WesternAustralia

Mineralizing events in the North Pilbara terrain of Western Australia occurred between 3490 and 2700 Ma and include the oldest examples in the world of many ore deposit types. These events were pulsed and associated with major volcano-plutonic episodes (volcanic-hosted massive sulfide, porphyry Cu, Sn-Ta pegmatite, mafic-ultramafic-hosted Ni-Cu-PGE, and epithermal deposits) and deformation events (lode Au deposits). In many cases, the mineralizing events are associated with extension, either in rifts, pull-apart or back-arc basins, or as the consequence of doming associated with granitoid diapirism. Although mineralizing events occurred throughout the evolution of the North Pilbara terrain, the largest deposits are related to the development of the Mallina basin, which is located between the older East and West Pilbara granite-greenstone terranes. Four volcano-plutonic and three deformation events occurred in and around the Mallina basin between 2950 and 2840 Ma. Mineralization in the East and West Pilbara granite-greenstone terranes is less intense and occurred over a much longer period. Compared to other Archean granite-greenstone terrains, the North Pilbara terrain is poorly endowed; the only known world-class deposit in this region is the Wodgina Ta-Sn pegmatite deposit, but large iron ore deposits are being mined in the northeastern North Pilbara terrain. The long history of crustal development and slow rate of crustal growth may be responsible for the diversity of mineral deposits and could account for the apparent poor endowment of the North Pilbara terrain.

The Chinamora batholith, Zimbabwe: structure and emplacement-related magnetic rock fabric

The origin of dome-and-keel structural geometries in Archean granite–greenstone terrains appears to lack any modern analogues and is still poorly understood. The formation of these geometries is investigated using structural and anisotropy of magnetic susceptibility (AMS) data for the Chinamora batholith in Zimbabwe. The roughly circular-shaped batholith is surrounded by ca. 2.72–2.64 Ga greenstones. The batholith granitoid suites have been divided on the basis of their ages and fabric relationships into four distinct units: (i) banded basement gneisses; (ii) granodioritic gneisses; (iii) equigranular granites; and (iv) central porphyritic granites. In the gneissic granites a partial girdle (N–S) of poles to the magnetic foliation is developed that has been folded around a consistent, flat lying magnetic lineation plunging at shallow angles to the E or W. In the equigranular granites, the magnetic lineation generally plunges to the NW. The magnetic foliation has a variable strike, no clear trends can be distinguished. The AMS measurements of the porphyritic granite revealed a NW–SE striking foliation and showed subhorizontal magnetic lineations. The magnetic foliation is subparallel to the macroscopic foliation. Wall rocks are moderately inclined and show radial or concentric lineations, triaxial strain ellipsoids and kinematics that demonstrate off-the-dome sliding and coeval pluton expansion. The results of the observations do not point to a single emplacement process. Neither the observed structural data nor the magnetic fabric support a model envisaging spherically ‘ballooning’. It is argued that pluton diapirism played a major part in the formation of the fabrics in the gneisses, whereas the fabrics in the porphyritic granites reflect emplacement as laccolith-like sheets.

Hydrothermalism and diapirism in the Archean: gravitational instability constraints

In Archean granite–greenstone terrains, greenstone belts are interspersed between granitic plutons to form dome-and-basin structures. Although the hypothesis is widely debated, gravitational instabilities have been invoked to explain such structures, which are typical of Archean cratons. We used a numerical approach based on a Rayleigh-Taylor model to examine the possibility that these structures result from gravitational processes, giving a special emphasis to the alteration of the mafic–ultramafic volcanic rocks. We investigated (a) the influence of contemporaneous hydrothermal activity upon density and viscosity of mafic–ultramafic volcanics and (b) the perturbation of thermal conditions in the granitoid basement on its rheology. Variables included: (1) varying proportions of mafic–ultramafic volcanics and their thickness relative to a granitoid basement; (2) density and viscosity differences between fresh and altered rocks; (3) kinetics of alteration; and (4) thermal regime and viscosity of the basement. We adopted a multi-layer model with variable viscosity in which the upper layers represent an ultramafic–mafic volcanic pile and the underlying layers a granitic basement. We show that the high viscosities of fresh volcanic rocks and underlying basement granitoids normally prevent the development of gravity-driven deformation. The conditions required to produce the observed structures are realized only when: (a) a high proportion of the volcanic rocks are altered to a low-viscosity assemblage; and (b) the underlying granitic basement is moderately heated or migmatized.

Roots of an Archean volcanic arc complex: the Lac des Iles area in Ontario, Canada

The Lac des Iles area is located in the Wabigoon Subprovince, an Archean granite-greenstone terrain in the Superior Province in Ontario, Canada. The area consists of several unmetamorphosed plutons of biotite- and hornblende-tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss. The mafic/ultramafic bodies are concentric in shape and consist of periodotite, pyroxenite, gabbro and hornblende gabbro cumulates and diorite. The largest intrusion, the Lac des Iles complex, consists of several mafic and ultramafic centers. An internal SmNd isochron from the southern ultramafic complex gives an intrusion age of 2736 ± 28 Ma (MSWD = 1.5; ϵ Nd(t) = 1.2). This age is also assumed to be representative of the time of emplacement of the other mafic and ultramafic bodies as well as the unmetamorphosed tonalite plutons. The tonalitic gneiss represents older continental crust and had an ϵ Nd value of −1 at this time. The ϵ Nd(t) values of the felsic and mafic/ultramafic suites are positive, ranging from 0 to +2. This range can be explained if primary magmas derived from a depleted mantle reservoir assimilated continental crust, such as the tonalite gneiss, during their ascent. This implies that the tonalite magmas in the Lac des Iles area represent mixtures of the tonalite country rock and mantle magmas which formed by partial melting of depleted mantle or of mafic rocks underplated beneath the continental lithosphere. The morphology and the rock assemblages of the mafic and ultramafic intrusions in the Lac des Iles area resemble Alaskan-type intrusions which are common components of Phanerozoic magmatic arcs associated with subduction zones. In addition, the crystallization sequence in the mafic/ultramafic intrusions suggests that they are derived from a parental magma with high-Al basalt affinities. The mafic/ultramafic rocks are depleted in high field strength elements but enriched in large ion lithophile elements, and the tonalites belong to calc-alkaline rock series displaying fractionation trends towards trondhjemitic compositions. Thus, the Archean Lac des Iles area and the root zones of Phanerozoic active continental margins share many geological, geochemical and petrological features which would suggest that the Lac des Iles area formed in an Andean-type continental margin.

Petrology and Ni-Cu-Cr-PGE Mineralization of the Largest Mafic Pluton in Europe: The Early Proterozoic Burakovsky Layered Intrusion, Karelia, Russia

The largest mafic pluton in Europe (area = 630 km2, thickness = 5 to 7 km) is the early Proterozoic (2445 ± 4 Ma; Pb-Pb) Burakovsky Layered Intrusion (BLI). It is located in the southern part of Russian Karelia, in the SE part of the Baltic Shield, within an Archean granite-greenstone terrain. The BLI is overlain by Quaternary deposits, and our present understanding of its character, composition, and internal structure is based on geophysical surveys and the nature of the rocks at depth, as sampled by diamond drill core. In order to better understand the petrogenesis of the BLI, we present geologic, petrographic, mineral-chemical, and whole-rock chemical analyses from throughout the stratigraphic sequence. The BLI is a lopolith-like body and is divided into two major units: the Layered Series (LS), which exhibits layering that is discordant to the contact, and the Border Group (BG), with layering that conforms to the contact surface. The LS constitutes most of the BLI and consists of, from bottom to top: ...

IDADE U-Pb DO DIORITO POSSELÂNDIA, HIDROLINA, GOIÁS

The Posselândia Diorite intrudes Archean granite-greenstone terrains of the region of Hidrolina, Central Goias, Brazil. U-Pb radiometric determinations in two fractions of zircon crystals from the diorite yield an age of 2,146 ±1.6 Ma, interpreted as the cristallization age of the intrusion. The lack of deformation in the intrusion demonstrates that condolidation of the granite-greenstone terrains in the Hidrolina-Pilar de Goias-Crixas area took place before 2,146 Ma.

Structural deformation and mineralization in the early Proterozoic Liaojitite suite, Eastern Liaoning Province, China

The Liaojitite Suite, located in eastern Liaoning Province, China, formed in the eugeosyncline of an Early Proterozoic mobile zone. Structural deformation occurred during several orogenic episodes, especially during the second deformation of the third episode, the Luliang Orogeny, 1900–2000 Ma ago. Superposed dome-shaped structures and their unevenly distributed groups formed during the Luliang Orogeny constitute the principal tectonic style in the mobile zone. The tectonic style may be considered transitional in the evolution from an oval style in Archean granite-greenstone terrains to a linear style in Phanerozoic terrains. The superposed dome-shaped structures contain the Liaoji Granite in the cores, ringed successively by the Boron-bearing Series and the outer Turbidite Series. The simple appearances of the dome-shaped structures mask their complicated, multiply deformed nature, which is revealed by tracing their formation and evolution from primary volcanic domes to granitic diapirs and finally to superposed dome-shaped structures. The evolution of the superposed dome-shaped structures represents a change in crustal activity from simple shear to horizontal compression. Mineralization in the Liaojitite Suite was closely related to the three deformations of the Luliang Orogeny. Metallogenic elements were concentrated during the first deformation; physical re-emplacement of orebodies occurred during the second and third deformations.

Origin of granite-greenstone patterns, Yilgarn Block, Western Australia

Research Article| November 01, 1985 Origin of granite-greenstone patterns, Yilgarn Block, Western Australia John S. Myers; John S. Myers 1Geological Survey of Western Australia, 66 Adelaide Terrace, Perth, Western Australia 6000, Australia Search for other works by this author on: GSW Google Scholar Keith P. Watkins Keith P. Watkins 1Geological Survey of Western Australia, 66 Adelaide Terrace, Perth, Western Australia 6000, Australia Search for other works by this author on: GSW Google Scholar Geology (1985) 13 (11): 778–780. https://doi.org/10.1130/0091-7613(1985)13<778:OOGPYB>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John S. Myers, Keith P. Watkins; Origin of granite-greenstone patterns, Yilgarn Block, Western Australia. Geology 1985;; 13 (11): 778–780. doi: https://doi.org/10.1130/0091-7613(1985)13<778:OOGPYB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Yilgarn Block of Western Australia consists mainly of Archean granite-greenstone terrain with oval areas of granitoid rocks fringed by arcuate greenstone belts. In a typical part of this terrain the outcrop pattern is shown to result from large-scale dome-and-basin fold interference structures rather than diapiric emplacement of steep-sided batholiths.The greenstones and underlying granitoid rocks were initially deformed together in a subhorizontal tectonic regime. As a result, the granitoid rocks recrystallized and a gneissosity developed subparallel to the stratigraphy of the greenstones. Thick subhorizontal monzogranite sheets were later emplaced into the lower part of the greenstone sequence. Subsequent deformation generated two successive sets of folds with vertical axial surfaces at a high angle to each other. These folds formed dome-and-basin interference structures ranging from a few centimetres to more than 50 km in diameter. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The structural relationship between Archean granite–greenstone terrains and late Archean mafic dikes

Examples of Archean shield areas from Canada and Australia are used to demonstrate a consistent orthogonality in trend between late Archean mafic dikes (~2.5 Ga old) and the structure of granite–greenstone terrains whose orogenic history terminated no more than about 0.2 Ga prior to dike injection. The simplest explanation of this relationship is that the regional structural grain of the granite–greenstone terrains was formed by horizontal crustal compression, and that the direction of maximum horizontal stress remained unchanged up to and including the time of dike emplacement.

Archean metallogeny in southern Africa

The Archean granite-greenstone terrain of southern Africa possesses a number of unique characteristics. Not only is the shield area one of the smallest in the world but it is also one of the oldest crustal fragments still preserved. Estimates of lithic proportions show that, in the southern African Archean, the granitic rocks outnumber those of the volcanic belts (greenstone belts) by approximately 6:1--in marked contrast to the situation on the Canadian Shield where granite: greenstone ratios have been estimated to be approximately 1:2.In order to establish further details of the lithological proportions, the southern African Archean greenstone belts are described in terms of a three-stage stratigraphic model involving a Lower Ultramafic Unit at the base, followed by a Mafic-to-Felsic Unit and a terminal Sedimentary Unit. Planimeter studies demonstrate that on average the southern African greenstone belts possess a relatively high proportion of ultramafic and mafic volcanic and plutonic rock types and a correspondingly lower proportion of rocks of intermediate to felsic composition. The relative abundances of the various volcanic components of the lower two stratigraphic units are tabulated, and the lithic proportions are compared with similar data available from greenstone belts of the Superior Province in Canada. Geochemical data illustrating the nature of Archean volcanism in southern Africa and elsewhere are made available for purposes of comparison.The distribution patterns of a wide variety of Archean mineralization types, including the deposits associated with the ancient granites and pegmatites, are illustrated by means of mineral distribution maps. A close genetic relationship exists between the various lithological subdivisions of the Archean greenstone belts and the mineralization. Important deposits of chrome, nickel-copper, gold, and chrysotile asbestos are associated with the ultramafic-mafic component of the volcanic pile, whereas antimony, gold, and lesser amounts of mercury, barite, corundum, copper-lead-zinc, and massive sulfide iron-formations occur throughout the greenstone piles and commonly occur as chemical sediments terminating cycles of volcanism. These well-banded rocks, which probably formed by fumarolic-exhalative processes, also contain significant stratiform gold mineralization.The Archean mineralization of southern Africa is briefly compared and contrasted with that of the Canadian Shield and elsewhere. It is concluded that the disparity of lithological types and proportions between the Canadian and southern African shields is, together with differences in age, the underlying cause of the variability in the mineralization thus far encountered in the two regions.