Ancient structural inheritance explains gold deposit clustering in northern Perú (original) (raw)
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Economic Geology, 2004
Introduction OROGENIC gold deposits, also referred to as mesothermal deposits (Groves et al., 1998), are widely distributed in accreted terranes that were deformed along the circum-Pacific margin (Goldfarb et al., 1998, 2001; Bierlein and Crowe, 2000) but remain relatively unrecognized on the western margin of South America. The reevaluation of several historical Peruvian, Bolivian, and Argentinean gold deposits (Zappettini and
Earth and Planetary Science Letters, 2006
Major and trace element concentrations and Nd isotope compositions of Ordovician volcano-intrusive rocks in the Puna region of northwestern Argentina suggest formation in a pericratonic setting above thickened and evolved continental crust. Input from juvenile sources was limited and there is no evidence for oceanic crust or the presence of a terrane-bounding suture in the study region. Geochronological constraints from 40 Ar/ 39 Ar (sericite-rich whole-rock) and Re-Os (arsenopyrite-pyrite) dating indicate initial deposition of gold in the turbidite-dominated Sierra de Rinconada during orogenic events in the Late Ordovician. This period corresponds to an epoch of major continental growth that includes development of abundant gold deposits along the long-lived and extensive accretionary margins of Gondwana. The ca. 440 Ma mineralisation ages represent the oldest recorded timing of gold emplacement in the central Andes. These ages also coincide with ca. 440 Ma ages obtained for the timing of mineralisation in each of the four largest orogenic gold deposits in the western Lachlan Orogen of eastern Australia. In contrast to analogous terranes elsewhere in the Central Andes (e.g., Peru and Bolivia), however, the Palaeozoic succession in northwest Argentina hosts relatively minor gold mineralisation. Possible explanations for the lack of a more substantial gold endowment include the (i) specific tectonic evolution of this region, (ii) absence of hydrated oceanic substrate in the northern Puna, (iii) lack of first-order, trans-crustal conduits, (iv) restriction of possible asthenospheric upwelling to a short period in the Early Ordovician, and (v) relatively limited extent of crustal shortening and thickening during Ordovician and subsequent orogenic events, when compared to analogous Palaeozoic metamorphic terrains elsewhere that are characterised by substantial orogenic gold endowment.
Detrital zircon fingerprint of the Proto-Andes: evidence for a Neoproterozoic active margin?
Neoproterozoic Palaeogeographic reconstructions of Rodinia conventionally place the western (Proto-Andean) margin of Amazonia against the eastern (Appalachian) margin of Laurentia. Separation and formation of the Iapetus Ocean is generally considered to have occurred later at ∼550 Ma. We examine the U–Pb detrital zircon “fingerprint” of autochthonous rocks from the northern and central segments of the Proto-Andean margin, which formed part of the western margin of Amazonia during the Late Neoproterozoic–Phanerozoic. The Proto-Andean margin is clearly the most feasible source region for most of the zircon grains, except for a 550–650 Ma sub-population, broadly age-equivalent to the Brasiliano/Pan-African Orogeny in eastern Amazonia. No obvious source for this detritus is known in the northern and central Andes. Derivation from eastern Amazonia is considered unlikely due to the stark paucity of detritus derived from the core of the Amazonian craton. Instead, we propose that a Late Neoproterozoic magmatic belt is buried beneath the present-day Andean belt or Amazon Basin, and was probably covered during the Eocene–Oligocene. If this inferred Neoproterozoic belt was an active margin, it would record the initiation of Proto-Andean subduction and imply at least partial separation of West Gondwana from its conjugate rift margin of eastern Laurentia prior to ca. 650 Ma. This separation may be linked to the ca. 770–680 Ma A-type magmatism found on eastern Laurentia in the southern Appalachians, and on the Proto-Andean margin in the Sierra Pampeanas and the Eastern Cordillera of Peru.
Peru reveal 1.15 Ga of intermittent magmatism along central Western Amazonia, the Earth's oldest active open continental margin. The eastern Peruvian batholiths are volumetrically dominated by plutonism related to the assembly and breakup of Pangea during the Paleozoic-Mesozoic transition. A Carboniferous-Permian (340-285 Ma) continental arc is identifi ed along the regional orogenic strike from the Ecuadorian border (6°S) to the inferred inboard extension of the Arequipa-Antofalla terrane in southern Peru (14°S). Widespread crustal extension and thinning, which affected western Gondwana throughout the Permian and Triassic resulted in the intrusion of the late-to posttectonic La Merced-San Ramón-type anatectites dated between 275 and 220 Ma, while the emplacement of the southern Cordillera de Carabaya peraluminous granitoids in the Late Triassic to Early Jurassic (220-190 Ma) represents, temporally and regionally, a separate tectonomagmatic event likely related to resuturing of the Arequipa-Antofalla block. Volcano-plutonic complexes and stocks associated with the onset of the present Andean cycle defi ne a compositionally bimodal alkaline suite and cluster between 180 and 170 Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma) is detected near the southwestern Cordilleran border with the Altiplano. Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123 Ma) are restricted to isolated occurrences spatially comprising less than 15% of the Eastern Cordillera intrusives. Only one remnant of a Late Ordovician intrusive belt is recognized in the Cuzco batholith (446.5 ± 9.7 Ma) indicating that the Famatinian arc system previously identifi ed in Peru along the north-central Eastern Cor di llera and the coastal Arequipa-Antofalla terrane also existed inboard of this parautochthonous crustal fragment. Hitherto unknown occurrences of late Mesoproterozoic and middle Neoproterozoic granitoids from the south-central cordilleran segment defi ne magmatic events at 691 ± 13 Ma, 751 ± 8 Ma, 985 ± 14 Ma, and 1071-1123 ± 23 Ma that are broadly coeval with the Braziliano and Grenville-Sunsás orogenies, respectively. Our data suggest the existence of a continuous orogenic belt in excess of 3500 km along Western Amazonia during the formation of Rodinia, its "early" fragmentation prior to 690 Ma, and support a model of reaccretion of the Paracas-Arequipa-Antofalla terrane to western Gondwana in the Early Ordovician with subsequent detachment of the Paracas segment in form of the Mexican Oaxaquia microcontinent in Middle Ordovician. A tectonomagmatic model involving slab detachment, followed by underplating of cratonic margin by asthenospheric mantle is proposed for the genesis of the volumetrically dominant Late Paleozoic to early Mesozoic Peruvian Cordilleran batholiths.
Journal of the Geological Survey of Brazil , 2018
*Corresponding author Evandro Klein The Novo Progresso Formation, located in southeastern Tapajós Gold Province, at its boundary with the Iriri-Xingu Domain, south of the Amazonian Craton, is composed of quartz-and lithic-arenites and siltstones with volcanic/volcanoclastic contributions, and was deposited in fluvial and lake systems. Reconnaissance detrital zircon U-Pb LA-ICP-MS data on a lithic arenite indicate maximum depositional age around 1840 Ma, whereas structural relationships suggest a minimum age of 1780 Ma. The zircon age spectrum shows two well-defined peaks at 1846 and 1968 Ma, and statistically secondary peaks ranging from 2185 Ma to 2973 Ma. εHf values vary from +8.1 to-14.5 (T DM = 2.13 to 3.95 Ga), whereas the εNd values range from-2.5 to-3.3 (T DM = 2.31 to 3.21 Ga), with one positive value of +4.5 (T DM = 1.81 Ga). These data and the lithological composition indicate that surrounding Orosirian rocks from Tapajós and Iriri-Xingu were the main sources for the sediments, with subordinate contributions from older and more distant domains of the Amazonian Craton. In addition, the Hf systematics suggest a ~2.50 Ga-old crustal growth event and a ~3.95 Ga-old hidden component in the eastern portion of the Amazonian Craton. The deposition of the Novo Progresso Formation is related to the development of the large Orosirian intracra-tonic rift system known as Uatumã Silicic Large Igneous Province (1.89-1.80 Ga), which cut across the Amazonian Craton, following the final stages of magmatism in the Tapajós Gold Province.
Peru reveal 1.15 Ga of intermittent magmatism along central Western Amazonia, the Earth's oldest active open continental margin. The eastern Peruvian batholiths are volumetrically dominated by plutonism related to the assembly and breakup of Pangea during the Paleozoic-Mesozoic transition. A Carboniferous-Permian (340-285 Ma) continental arc is identifi ed along the regional orogenic strike from the Ecuadorian border (6°S) to the inferred inboard extension of the Arequipa-Antofalla terrane in southern Peru (14°S). Widespread crustal extension and thinning, which affected western Gondwana throughout the Permian and Triassic resulted in the intrusion of the late-to posttectonic La Merced-San Ramón-type anatectites dated between 275 and 220 Ma, while the emplacement of the southern Cordillera de Carabaya peraluminous granitoids in the Late Triassic to Early Jurassic (220-190 Ma) represents, temporally and regionally, a separate tectonomagmatic event likely related to resuturing of the Arequipa-Antofalla block. Volcano-plutonic complexes and stocks associated with the onset of the present Andean cycle defi ne a compositionally bimodal alkaline suite and cluster between 180 and 170 Ma. A volumetrically minor intrusive pulse of Oligocene age (ca. 30 Ma) is detected near the southwestern Cordilleran border with the Altiplano. Both post-Gondwanide (30-170 Ma), and Precambrian plutonism (691-1123 Ma) are restricted to isolated occurrences spatially comprising less than 15% of the Eastern Cordillera intrusives. Only one remnant of a Late Ordovician intrusive belt is recognized in the Cuzco batholith (446.5 ± 9.7 Ma) indicating that the Famatinian arc system previously identifi ed in Peru along the north-central Eastern Cor di llera and the coastal Arequipa-Antofalla terrane also existed inboard of this parautochthonous crustal fragment. Hitherto unknown occurrences of late Mesoproterozoic and middle Neoproterozoic granitoids from the south-central cordilleran segment defi ne magmatic events at 691 ± 13 Ma, 751 ± 8 Ma, 985 ± 14 Ma, and 1071-1123 ± 23 Ma that are broadly coeval with the Braziliano and Grenville-Sunsás orogenies, respectively. Our data suggest the existence of a continuous orogenic belt in excess of 3500 km along Western Amazonia during the formation of Rodinia, its "early" fragmentation prior to 690 Ma, and support a model of reaccretion of the Paracas-Arequipa-Antofalla terrane to western Gondwana in the Early Ordovician with subsequent detachment of the Paracas segment in form of the Mexican Oaxaquia microcontinent in Middle Ordovician. A tectonomagmatic model involving slab detachment, followed by underplating of cratonic margin by asthenospheric mantle is proposed for the genesis of the volumetrically dominant Late Paleozoic to early Mesozoic Peruvian Cordilleran batholiths.
Journal of South American Earth Sciences, 2015
In early Paleozoic time the PerueBolivia Trough at the South American Gondwana margin accommodated large volumes of siliciclastic detritus of hitherto largely unknown provenance. A multi-method provenance study of framework components, heavy minerals and whole rock geochemistry of Ordovician to Devonian formations of southern Peru and northern Bolivia reveals the predominant contribution from upper crustal sources. Main heavy minerals include zircon, tourmaline, rutile, apatite, garnet, epidote, monazite, and titanite and are strongly biased diagenetically towards the stable phases. Electron microprobe single grain analysis of tourmaline and rutile indicate that detrital tourmalines were derived mainly from metasedimentary, and subordinately, from granitic sources. Cr/Nb ratios in rutiles point to a metamafic derivation for 20e40% of grains, the remainder originating in felsic lithologies. Zr in rutile thermometry indicates a provenance from relatively high-grade metamorphic rocks transformed at temperatures between 500 C and 900 C, with clusters at c. 600 C, 700 C and 800 C. UePb geochronological analysis of rutiles was largely unsuccessful due to high concentrations of common Pb. Three ages could be obtained and fall between 525 and 545 Ma, probably linking this detritus to the hidden Neoproterozoic orogen in what are now Cordillera Oriental and Sierras Subandinas. The most notable feature of the whole rock geochemical data is a high Cr content in the majority of samples, which otherwise have a composition similar to weathered upper continental crust. The elevated Cr contents indicates that ophiolitic rocks were either exposed to erosion abundantly in the source areas or had previously supplied significant volumes of detritus to intermittent sediment storage systems now eroded into the studied sedimentary rocks. Potential source candidates include the Ordovician metamorphic Tapo Ultramafic Complex in the Cordillera Oriental of central Peru, and the island arcs and ophiolite complexes of the Rondonia-San Ignacio Orogen (1550e1200 Ma) on the SW Amazonia craton. Considering the available evidence we conclude that a provenance from the Rondonia-San Ignacio Orogen is more likely.
An extensive in situ Lu-Hf isotopic study of zircon from the Eastern Cordilleran batholiths of Peru using laser ablation multi-collector inductively coupled mass spectrometry (LA-MC-ICPMS) reveals a systematic covariance between granitoid magma sources and tectonic regimes which shaped the proto-Andean margin of central Western Amazonia since N 1.15 Ga. The Hf isotope systematics are characterised by a range in initial 176 Hf/ 177 Hf compositions for a given intrusive event suggesting mixing of material derived from the Paleoproterozoic crustal substrate and variable addition of juvenile sources from Neoproterozoic to Cenozoic time. Intrusives associated with phases of regional compressive tectonism correspond to mean initial εHf values of −6.73, −2.43, − 1.57 for the Ordovician (Famatinian), Carboniferous-Permian and Late Triassic respectively, suggesting a minimum crustal contribution between 40% and 74% by mass. The average initial Hf systematics from granitoids associated with periods of regional extension such as the middle Neoproterozoic, Permian-Triassic and Cenozoic Andean back arc plutonism are consistently shifted towards positive values (mean initial εHf = −0.7 to +8.0) indicating systematically larger inputs of juvenile magma (25% to 38% of ancient crust by mass). In the absence of evidence for significant lateral accretion of exotic crust, the time integrated Hf record from the central proto-Andean margin of western Amazonia suggests crustal reworking was the dominant process during episodes of arc magmatism, implying that most crustal growth took place vertically via crustal underplating of isotopically juvenile, mantle derived melts during intervals of crustal extension.