Eastern Subprovince Research Articles

Crustal architecture and tectonic development of western Queensland, Australia, based on deep seismic reflection profiling: Implications for Proterozoic continental assembly and dispersal

Interpretation of 2014–2015 deep crustal seismic reflection and magnetotelluric data has revised the architecture and geodynamic framework of western Queensland, with implications for the assembly and dispersal of the supercontinents Nuna, Rodinia and Gondwana. In the Mount Isa Province, crustal-scale boundaries of the Leichhardt River Domain, Kalkadoon-Leichhardt Domain and Eastern Subprovince are mapped in the third dimension. The Leichhardt River and Kalkadoon-Leichhardt domains have similar Nd isotopic T2DM model ages to provinces to the west, indicating they were part of ancestral North Australian Craton (NAC); the Eastern Subprovince is a separate terrane, with the Pilgrim Fault a collisional suture. The Gidyea Suture Zone separates the Mount Isa Province from the subsurface Numil Seismic Province. To the east, the west-dipping Yappar Fault separates east-dipping structures in the west from west-dipping structures in the east, forming a classic doubly vergent orogen within the upper plate of a convergent margin. The northwestern boundary of the Bernfels Seismic Province, the Kynuna Fault, truncates the Gidyea Suture Zone, implying this seismic province was welded to the NAC prior to initial deposition of the Etheridge Province. The Cork Fault truncates the north-south grain of the Mount Isa Province; the easternmost part of the NAC has been excised, presumably during breakup of Nuna. The subsurface Brighton Downs Seismic Province, formerly part of the northern Thomson Orogen, is a discrete seismic province, located between the NAC and the Thomson Orogen, and welded to the NAC during the accretion of Rodinia. Basement to the Thomson Orogen is a collage of microplates, accreted to the Brighton Downs Seismic Province during the assembly of Gondwana. By 530 Ma, eastern Australia faced an open Pacific Ocean, with the Thomson Orogen in a backarc setting. Thus, northeastern Australia contains a record of repeated continental accretion and breakup over at least three supercontinent cycles.

New age constraints for the Tommy Creek Domain of the Mount Isa Inlier, Australia

The Tommy Creek Domain is a complex, yet little studied, terrane in the Eastern Subprovince of the Mount Isa Province, northwest Queensland Australia. In this study, we take advantage of modern low-cost and rapid geochronology techniques to undertake an iterative dating approach integrated with detailed fieldwork to define the ages and extents of numerous lithologies and units of the Tommy Creek Domain. This includes some units not previously identified, lithologies previously grouped together based on field observations but now shown to have multiple distinct ages and dates not commonly represented in Mount Isan time–space plots. We identify an episode of felsic magmatism at ca 1640 Ma, and multimodal intrusions (ca 1615 Ma) immediately preceding the onset of the Isan Orogeny. A major rock package of the Tommy Creek Domain, the Milo beds, are characterised here as the youngest pre-Isan Orogeny sedimentary unit in the Eastern Subprovince (1660–1620 Ma), confirming that sedimentation and possibly rifting continued after deposition of the Soldiers Cap, Mount Albert and Kuridala groups (ca 1690–1650 Ma) before the onset of the Isan Orogeny (ca 1600 Ma). The Milo beds are thus age equivalent to the Mount Isa and McNamara groups of the Western Succession. There is evidence of a compositional shift in sedimentation coincident with the ca 1640 Ma Riversleigh Inversion event, previously only observed in the Western Subprovince in the Lawn Hill Platform. The application of geochronology as part of the mapping workflow can assist with differentiating geological units in terranes where field evidence is ambiguous and can aid in the focusing of objectives for field campaigns to enable the best possible interpretations to be made. KEY POINTS New ages constrain the Milo beds in the Tommy Creek Domain as the youngest stratigraphy in the Eastern Subprovince of the Mount Isa Province. The Milo beds are age equivalents of the McNamara and Mount Isa groups of the Western Subprovince of the inlier. Recognition of felsic and mafic intrusions with ca 1640 Ma and ca 1615 Ma ages. Evidence for Riversleigh Inversion event ca 1640 in the Eastern Subprovince.

A negotiation of power during the age of reforms in the Ottoman Empire: notables, tribes and state in Muş (1820-1840)

This article analyzes how a local notable on the eastern frontiers of the Ottoman Empire struggled for local power within the context of the early nineteenth century. Focusing on an era on the eve of the Tanzimat, this article seeks to indicate how the local dynasty of Muş – Alaaddin Pashazades – sought not only to maintain but also to strengthen their power and influence by taking advantage of their imperial and trans-imperial networks. Based on a variety of primary sources from Ottoman and British archives, this article explicates how in an age of fiscal, military, and administrative transformation, Emin Pasha from the Alaaddin Pashazades consolidated his power by skilfully manipulating inter-imperial wars, regional revolts, borderland and tribal matters with Iran, and the military reforms of the era. Providing a snapshot from an eastern sub-province of the Ottoman Empire, this article hopes to contribute to studies which deal with the multi-dimensional relations between imperial powers and provincial notables.

Similarity analysis of Ostracoda faunas in the Western Tethys during the Late Pliensbachian-Early Toarcian (Early Jurassic)

The present study is focused on the biogeographic dynamic quantification tested on ostracods of Upper Pliensbachian-Lower Toarcian. The calculation of similarity and distance indices made it possible to compare the contents of nine regions belonging to the palaeobiogeographic province of Western Tethys. The generic comparison realized for each chronological interval (Emaciatum Zone of the Late Pliensbachian and Polymorphum and Levisoni zones of the Early Toarcian) shows the presence of two subprovinces of ostracods during this time interval, the most stable in the westernmost part of the Tethys composed by the Traras (Algeria) and Lusitanian (Portugal) basins. This was probably facilitated by the presence of communication seaways. The other subprovince for ostracod is located in the eastern regions mainly composed by the Aquitanian Basin (France) and southern Germany. In regions such as the Iberian Cordillera (eastern Spain), the composition of the ostracod assemblages changed with more affinity to the eastern subprovince during the Late Pliensbachian and to the western subprovince during the Early Toarcian. Other regions such as the Central High Atlas (Morocco) and Umbria Marche Basin (Italy) show a remoteness of the ostracod assemblages during the studied interval. Otherwise, the Pielou criterion calculation confirms the absence of a geographical or chronological gradient among the studied regions probably related to oceanographic changes (the sea-level rise, the global warming and the development of oxygen depleted conditions in north central Europe).

U–Pb and Hf isotope data from zircons in the Macquarie Arc, Lachlan Orogen: Implications for arc evolution and Ordovician palaeogeography along part of the east Gondwana margin

The Ordovician Macquarie Arc in the eastern subprovince of the Lachlan Orogen, southeastern Australia, is an unusual arc that evolved in four vertically stacked volcanic phases over ~ 37 million years, and which is flanked by coeval, craton-derived, passive margin sedimentary terranes dominated by detrital quartz grains. Although these two terranes are marked by a general absence of provenance mixing, LA-ICPMS analysis of U–Pb and Lu–Hf contents in zircon grains in volcaniclastic rocks from 3 phases of the arc demonstrates the same age populations of detrital grains inherited from the Gondwana margin as those that characterise the flanking quartz-rich Ordovician turbidites. Magmatic Phase 1 is older, ~ 480 Ma, and is characterised by detrital zircons grains with ages of ~ 490–540 with negative ε Hf from 0 to mainly –7.78, 550–625 Ma ages with negative ε Hf from 0 to −26.6 and 970–1250 Ma (Grenvillian) with ε Hf from + 6.47 to −6.44. We have not as yet identified any magmatic zircons related to Phase 1 volcanism. Small amounts of detrital zircons also occur in Phase 2 (~ 468–455 Ma), hiatus 1 and Phase 4 (~ 449–443 Ma), all of which are dominated by Ordovician magmatic zircons with positive ε Hf values, indicating derivation from unevolved mantle-derived magmas, consistent with formation in an intraoceanic island arc. Because of the previously obtained positive whole rock ε Nd values from Phase 1 lavas, we rule out contamination from substrate or subducted sediments. Instead, we suggest that during Phase 1, the Macquarie Arc lay close enough to the Gondwana margin so that volcaniclastic rocks were heavily contaminated by detrital zircon grains shed from granites and Grenvillian mafic rocks mainly from Antarctica (Ross Orogen and East Antarctica) and/or the Delamerian margin of Australia. The reduced nature of a Gondwana population in Phase 2, hiatus 1 and Phase 4 is attributed to opening of a marginal basin between the Gondwana margin and the Macquarie Arc that put it out of reach of all but rare turbiditic currents.

Magnetic fabrics of Paleozoic rocks across the Lachlan Transverse Zone from eastern New South Wales*

The anisotropy of magnetic susceptibility (AMS) was systematically measured for samples collected across the Lachlan Transverse Zone in the Eastern Subprovince of the Lachlan Orogen, New South Wales. Although the degree of anisotropy is usually moderate to low, it can be shown that the origin of the magnetic fabric is generally composite. Many localities are witness to a tectonic influence in addition to a magnetic foliation preserved from the time of rock formation (compaction). Furthermore, some localities indicate the presence of superimposed magnetic fabrics, potentially associated with a Silurian east–west direction of shortening, and a younger north–south (?) direction of shortening. Finally, the progressive southwards change in orientation of the magnetic lineation in the Molong area from north–south to east–west and then back to north–south again south of the Lyndhurst–Neville Fault suggests that the Lachlan Transverse Zone coincides with, and reflects, a major cross-structure in the Eastern Subprovince. AMS is thus a powerful tool to help map the fabric of Paleozoic rocks in the Tasmanides. Additional data will be required to help obtain a comprehensive picture of the tectonic history of the region.

Benambran Orogeny in the Eastern Lachlan Orogen, Australia

The Benambran Orogeny reflects the accretion of the intra-oceanic Macquarie Arc to the Gondwana Plate. The ultimate cause was the northwards strike-slip transport of the allochthonous Bega Terrane along the eastern margin of Gondwana, into a forearc position outboard of the Macquarie Arc. Ensuing oblique compression in the outboard part of the Gondwana Plate drove the Macquarie Arc into and under its backarc Wagga Basin, represented by the Girilambone – Wagga Terrane, and led to a combination of thrusting and major strike-slip faulting within, inboard and outboard of the arc over 10 million years. In this time frame, the Benambran Orogeny in the Eastern Subprovince of the Lachlan Orogen in New South Wales consists of two phases of exhumation – deformation, at ca 443 Ma (late Bolindian to early Llandovery) and ca 430 Ma (late Llandovery), separated by a relaxation/extensional event. Both phases involved deformation and exhumation of the Macquarie Arc and coeval quartz-rich turbidites and black shales of the Adaminaby Superterrane. Closure of the former backarc basin was facilitated by limited east-dipping subduction that generated the short-lived Fifield arc. The second phase of the Benambran Orogeny also involved deformation and exhumation of overlying Llandovery strata (e.g. the Yalmy Group) and syn- to post-tectonic emplacement of granitoids. In both phases, deformation of Adaminaby Superterrane rocks was more intense than deformation of arc rocks.

Tectonic setting of porphyry Cu – Au mineralisation in the Ordovician – Early Silurian Macquarie Arc, Eastern Lachlan Orogen, New South Wales

Available age data enable the recognition of four groups of porphyries that were emplaced during the ∼50 million year punctuated history of the earliest Ordovician to earliest Silurian intra-oceanic Macquarie Arc in the Eastern subprovince of the Lachlan Orogen. These porphyries were not emplaced during steady-state subduction. Porphyry groups 1 – 3 formed during critical events in the evolution of the arc related to interruptions and resumptions of arc activity. They are pre-accretionary in character, in that they formed in the arc that for most of the Ordovician lay on the Gondwana Plate, above a west-dipping subduction zone, and separated from the Gondwana margin by the Wagga Basin. In contrast, Group 4 porphyries are syn-accretionary and were emplaced into tilted and deformed volcanic and volcaniclastic packages during an extension or relaxation event in the multiphase Early Silurian Benambran Orogeny, attributed to the accretion of the arc and collapse of the former backarc basin. The Lachlan Transverse Zone is a major arc-normal corridor that favoured emplacement of many porphyries commonly, but not exclusively, shoshonitic in chemistry. All porphyry groups are potentially mineralised, with Groups 3 and 4 known to contain world-class Cu – Au deposits.

Paleomagnetic study of Siluro‐Devonian volcanic rocks from the central Lachlan Orogen: Implications for the apparent pole wander path of Gondwana

The apparent pole wander (APW) path for Gondwana is still not clearly established, in particular, for Silurian‐Devonian times. A controversial debate places authors who argue for an “X path,” running directly through Africa on a reconstruction of Gondwana against those who advocate a large loop passing by southern South America, the “Y path.” Most of the paleomagnetic data used to draw this loop come from the Lachlan Orogen (Australia). A paleomagnetic study was carried out in the well‐dated Ambone and Ural volcanics in the central subprovince of Lachlan Orogen, New South Wales. Anisotropy of magnetic susceptibility measurements confirms detailed mapping of the region and shows that these massive dacitic sills and/or lava flows are flat lying. Among the different localities studied, only one yields interpretable paleomagnetic results. Two components of magnetization can be identified: a midtemperature direction yielding a corresponding pole in Australian coordinates λ = 67.9°S/ϕ = 084.4°E (B = 5; n = 21; dp = 17.5°/dm = 23.1°) and a high‐temperature direction with a corresponding VGP λ = 24.4°S/ϕ = 060.6°E (B = 5; n = 25; dp = 1.4°/dm = 2.5°). The first is interpreted as corresponding to an Early Carboniferous pole position and can be regarded as an overprint probably related to the Early Carboniferous Kanimblan orogenic event. The second does not correspond to any expected Silurian‐Devonian or younger pole position. This magnetization is thought to be primary in origin; however, secular variation has apparently not been averaged out in the single lava flow sampled. Therefore the earliest Devonian paleopole position probably lies in a 30° cone around the obtained VGP, and this position can only match the X‐type APW path for Gondwana. It is in particular very different from coeval poles obtained in the eastern subprovince of the Lachlan Orogen, and it is mostly used as key poles supporting the Silurian‐Devonian loop for the APW path of Gondwana. Therefore some poles from the Lachlan Orogen must be affected by rotation to explain these results. The Lachlan Orogen was hence not stable up to the mid‐Paleozoic, and data from this region should not be used as representative for Gondwana.

Geochemical provinciality in the Cretaceous basaltic magmatism of Northern Madagascar: mantle source implications

The northern part of the Late Cretaceous flood-basalt province of Madagascar is formed by lava flows, dykes and intrusive complexes. These range from tholeiitic to weakly alkaline and have composition from basalts to basaltic andesites (with rare, more evolved, rocks). The magmatic evolution is dominated by low-pressure crystal fractionation of olivine, Cr-spinel, plagioclase and clinopyroxene. The erupted rocks form two subprovinces, in terms of incompatible element concentrations or ratios and geographical position. The mafic and intermediate samples from the western subprovince have low abundances of high field strength elements (e.g. Nb 2–9 ppm; Zr 50–230 ppm), negative Nb anomalies on mantle-normalized diagrams, and a wide range of initial (88 Ma) 143 Nd/ 144 Nd (0.51293–0.51197; ε Nd +7.9 to −10.9). These elemental and isotopic variations are compatible with melting of predominantly N-MORB-like mantle and variable low-pressure crustal contamination. The mafic samples of the eastern subprovince are mildly enriched in incompatible elements (e.g. Nb 6–25 ppm; Zr 109–330 ppm), with the highest values found in tholeiites from the east Mahajanga basin, Tampoketsa Kamoreen and Tamatave. They also have a comparatively narrow range of initial 143 Nd/ 144 Nd (0.51276–0.51258; ε Nd +5.1 to +1.0), consistent with derivation from incompatible element enriched mantle sources and minor subsequent crustal contamination. The marked differences in the chemical and isotopic characteristics of the samples imply variable degrees of partial melting of hotter than normal, chemically heterogeneous, mantle sources at pressures where spinel to garnet are residual phases. No clear evidence is seen for a chemical component similar to that represented at present by the Marion hotspot lavas.

Geodynamics and metallogeny of the Lachlan Orogen

The Palaeozoic Lachlan Orogen of eastern Australia is an accretionary orogen made up of structurally thickened oceanic successions, including turbidites from deep‐sea fans, andesitic volcanics from remnant island arcs, forearc sediments and slices of oceanic crust. Accretion of these units has been inferred to occur by collapse of a marginal basin during double divergent subduction within a complex southwest Pacific‐style oceanic setting. The small basin closed behind, and in the backarc position to, a major, long‐lived subduction system off Gondwanaland in the Palaeozoic. Stepwise deformation and metamorphism from Late Ordovician through Early Carboniferous times formed three distinct geological subprovinces that have interacted with each other through time and space. Metallogeny relates directly to these three provinces and their position within this tectonic framework. In the Western Subprovince, Ordovician turbidites host major lode Au deposits (e.g. Bendigo and Ballarat, central Victoria) because of structural thickening and metamorphism within a coupled thick turbidite wedge ‐ oceanic crustal layer above an inferred flat, west‐dipping subduction zone. In the Central Subprovince a Late Ordovician to Early Silurian high‐T metamorphic belt hosts Sn–W ± Mo skarn/greisen deposits as part of a more evolved, differentiated magmatic arc associated with northwest‐trending, east‐dipping subduction beneath the Tabberabbera Zone. In the Eastern Subprovince, porphyry Cu–Au deposits (e.g. Goonumbla and Lake Cowal, central‐northern New South Wales) formed within an Ordovician oceanic island arc, and volcanic‐hosted massive‐sulfide deposits (e.g. Captains Flat and Woodlawn, eastern New South Wales) formed in younger Silurian forearc sediments. Both deposit types are related to the outboard, long‐lived, west‐dipping subduction zone off Gondwanaland.

U–Pb Geochronology of Paleoproterozoic Rocks in the Southern Part of the Kedougou-Kéniéba Inlier, Senegal, West Africa: Evidence for Diachronous Accretionary Development of the Eburnean Province

The Kedougou-Kéniéba Inlier (KKI) in eastern Senegal is the westernmost exposed part of the Paleoproterozoic (Birimian/Eburnean) Baoulé-Mossi domain on the West African craton. Regional mapping indicates that the southern, relatively well preserved part of the KKI contains two northeast trending volcanic belts, the Mako and Falémé belts with associated Na-rich granitoid stocks. These belts are separated by the Diale-Dalema metasedimentary basin, containing the extensive syn- to late-kinematic K-rich Saraya batholith and other basin-type plutons. A similar pattern of northeast trending volcanic belts and sedimentary basins is also seen in Ghana and eastern Côte d'Ivoire, i.e. in the eastern part of the Baoulé-Mossi domain, as well as in central Côte d'Ivoire where, however, primary lithological relationships seem to be more obliterated by later tectono-thermal overprint. U–Pb ages were determined on single zircon and monazite from rocks in the KKI to investigate its relationship with the rest of the Baoulé-Mossi domain. A rhyolite from the Falémé belt gave a zircon age of 2099±4 Ma. Granitoid rocks from the Falémé (2) and Mako (1) volcanic belts possess zircon ages of 2082±1, 2080±1 and 2076±3 Ma, respectively. Reversely discordant monazites from a muscovite-bearing phase of the Saraya batholith in the Diale-Dalema basin yielded an interpreted igneous age of 2079±2 Ma and a metamorphic age of 2064±4 Ma. Detrital zircons from a quartz wacke in the Diale-Dalema basin all gave the same age within error, defining an average age of 2165±1 Ma for the source. Inherited zircon, 2155±34 Ma in age, was seen in the felsic flow from the Falémé belt while the Mako belt granitoid rock contains inheritance at least as old as 2122±5 Ma. These data indicate that volcanic belts in the KKI are substantially younger than the 2150–2190 Ma Birimian volcanic and associated plutonic rocks of the eastern Baoulé-Mossi domain, despite their geological similarities. Syn- to late-kinematic basin-type plutons in the KKI are also younger than lithologically similar 2090–2115 Ma old plutons in Ghana and eastern Côte d'Ivoire (eastern part of the Baoulé-Mossi domain). These relationships are consistent with previous suggestions that Paleoproterozoic rocks of the Baoulé-Mossi domain may be divided into an older eastern subprovince and an approximately 50–100 Ma younger western subprovince. They also show that supracrustal and intrusive Paleoproterozoic rocks in both subprovinces as well as over the entire domain developed diachronously from east to west. The data support an accretionary tectonic model for Paleoproterozoic growth of the West African craton.

Subdued state of tectonism of the Great Basin interior relative to its eastern margin based on deep resistivity structure

Lower-crustal fluid content and physical state of the central and eastern subprovinces of the Great Basin are compared on the basis of their deep electrical resistivity structure as derived from two, detailed east-west profiles of magnetotelluric (MT) soundings. A simple, but powerful and effective transformation of each profile's data allows derivation of a single characteristic MT sounding for each subprovince which is essentially free of the effects of middle- to upper-crustal lateral heterogeneity. The characteristic soundings are amenable to layered Earth inversion, yielding broad-scale, model resistivity profiles into the uppermost mantle. A striking difference in lower-crustal electrical resistivity is apparent between the two subprovinces. The tectonically more active eastern domain has a lower-crustal conductance of ∼ 3000 siemens (S) at a model depth around 15 km, while that of the relatively subdued Great Basin interior is only ∼ 750 S with a depth around 22 km. Thicknesses of the two subprovince conductors are resolvable independent of their resistivity (∼ 20 km at 7 Ω-m in the east and ∼ 15 km at 20 Ω-m in the interior). This allows estimates of fluid-filled porosity in the deep crust assuming highly saline brines and predominantly grain-edge interconnection. Nominal values are 0.4 vol% for the eastern subprovince but only ∼ 0.15 vol% for the central region. These porosities are consistent with fluid percolation models for ductile crustal rocks, assuming on-going fluid replenishment by basaltic underplating in the eastern Great Basin and with little fluid input occurring in the central Great Basin in the last 5–10 Ma. Resistivity of the uppermost mantle in both regions is greater than that of the lower crust. This implies relatively lesser fluid/melt contents or poorer interconnection in the shallow mantle.

Two generations of Birimian (Paleoproterozoic) volcanic belts in northeastern Côte d'Ivoire (West Africa): consequences for the ‘Birimian controversy’

UPb ages have been measured on zircon, monazite and titanite from gneiss, granitoids and rhyolite of the Paleoproterozoic Birimian/Eburnean province in the northern Haute Comoé area, northeastern Côte d'Ivoire, West Africa. Dating reveals that two distinct generations of Birimian volcanic belt terranes (Téhini belt in the east, Ouango Fitini belt in the west), separated in age by a 50 m.y. time span, occur proximal to each other in the Haute Comoé North area, at the Ouango Fitini shear zone. This sinistral NNE-trending high-strain zone seemingly represents a regionally important, several hundred kilometers long lineament on the Man shield dividing the Paleoproterozoic Birimian/Eburnean province, seen up to now as a single entity, into an eastern and a western subprovince. The eastern subprovince, which covers Ghana, eastern Côte d'Ivoire and probably many parts of Burkina Faso, typically displays ∼2185-2150 Ma belt volcanism and coeval belt plutonism. Evidence for 2100 Ma extrusive volcanism is absent. The western subprovince (e.g. central Côte d'Ivoire, western Mali, and probably Guinea) is characterized by younger, ∼2105 Ma old volcanic belts and coeval belt plutons. Supracrustal and intrusive rocks of the 2185-2150 Ma time span are at least locally present as various gneisses which previously had been termed ‘Dabakalian’. A granodioritic biotite gneiss in the western gneiss-granitoid terrane of the Haute Comoé area (=western subprovince), resembling ‘Dabakalian’ gneisses further south, gives a crystallization age of 2152 ± 2 Ma, identical to the age of a belt pluton in the Téhini volcanic belt (2152 ± 3 Ma). This suggests that those greenschist-facies supracrustal rocks originally termed ‘Birimian’ in Ghana by Kitson (1918) are coeval with gneisses in Côte d'Ivoire termed ‘Dabakalian’ by Lemoine (1988). Consequently, the invoked ‘Burkinian’ deformation event, which was assumed to separate Dabakalian basement and Birimian supracrustal rocks, cannot exist. Rather, Birimian rocks of the eastern subprovince may be correlative with protoliths of the higher-metamorphic Dabakalian rocks present in the western subprovince. The term ‘Bandamian’ is suggested to refer to the 2105 Ma old suite of supracrustal rocks of the western subprovince, the term ‘Birimian’ being restricted to the 2185-2150 Ma old volcanic/volcaniclastic rock suite of the eastern subprovince (Ghana). If the Birimian/Eburnean province on the Man shield consists of two different-aged subprovinces, the relative scarcity of economic gold deposits in central Côte d'Ivoire, as compared to Ghana, could not only be a function of underexploration of the area, but also of different geological processes having formed the terranes of the (older) eastern and the (younger) western subprovince.

A PROVÍNCIA DE GRANITOS ESTANÍFEROS DE GOIÁS

The granites of the Goias Tin Province (GTP) are distributed in four subprovinces in the south-central state of Goias: Rio Tocantins (RT), Rio Parana (RP), Pirenopolis-Goianesia (PG) and Ipameri (IP). The tin granites are intrusive in the Granite-gneiss Complex (Archaean?) and in the Tincunzal Formation (Early Proterozoic), and outcrop among Middle Proterozoic metasediments. Massifs of the western subprovinces (RT, PG, IP) are situated in the inner part of the Uruacu Fold Belt and are surrounded by strongly deformed sediments metamorphosed in amphibolite or upper greenschist facies. Eastern subprovince (RP) massifs occur in the outer part of this belt, domain of weakly metamorphosed and deformed Arai Middle Proterozoic sediments. Tin granites of the RT and RP subprovinces differ in structure, texture and metalogenesis. The former (Serra da Mesa Type) consist of strongly deformed ellipsoidal bodies of batholitic dimensions and display a conspicuous border foliation, similar to mantled domes. RP Subprovince by granites (pedra Branca Type) are weakly deformed by subvolcanic plutons. All granitic bodies are dominantly biotite granities, sometimes muscovitized, with a very restricted hornblende fades in the RT Subprovince. Post-magmatic changes like albitization and greisenization are very common and associated tin deposits occur in albitites, biotites, greisenized granites, exo and endogreisen, pegmatites, and quartz veins. Common associations are: 1) cassiterite-tantalite-columbite-wolframite in albitized granites and pegmatites in the west and 2) cassiterite-fluorite-sulphides in the east. Goias tin granites are predominantly peraluminous with an alkaline trend in the western types. Ali of them are correlate with A- or S-type granites and are similar to some tin granites of the Amazon Craton. Granites of the Ilmenite Series are represented by non-altered biotite granites whereas hydrothermally altered granites represent the Magnetite Series. Rare earth element (R.E.E.) signatures are characteristic of tin granites. Biotite granites, albitized granites, and greisen as well as rhyolites of the base of Middle Proterozoic metassediments have the same REE pattern, with strong negative Europium anomalies. Geochronological data indicate ages between 1,650-1,800 Ma in the western granites (Serra da Mesa Type) and 1,400 Ma in the eastern examples (Pedra Branca Type).