Late Paleoproterozoic Age Research Articles

Geochemistry and U–Pb zircon geochronology of S-type granites in the Karagwe Ankolean Belt, northwestern Tanzania: Implications for rare-metals mineralization

The Mesoproterozoic Karagwe Ankolean Belt in the Central Eastern Africa region hosts suites of granites that intruded supracrustal rocks and are associated with Sn–W mineralization. In northwestern Tanzania, the granites are S-type, peraluminous and calc-alkalic to alkalic-calcic in composition. Geochemical analyses of the granites reveal the following concentrations: SiO2 (71–77 wt%), Al2O3 (11–15 wt%), K2O (3–7 wt%), MgO (0.06–0.86 wt%), TiO2 (0.07–0.36 wt%) and Fe2O3T (0.71–2.40 wt%). The SiO2 contents correlate negatively with MgO, CaO and K2O and positively correlate with Nb, Ta, Zr, Sr, Ba, Hf, Th and the REE (Eu, Ce and Sm). Primitive mantle normalized spider plots show elevated LILE against depletions in Ba, Nb, Ti and La, suggesting inherited arc-magmatic signatures from the protolith. Chondrite-normalized REE spider plots show elevated LREE and relatively flat MREE and HREE as indicated by (La/Yb)cn = 2–9 and negative Eu* anomalies (0.05–0.24). Modelling of nearby Uha group sedimentary rocks partial melts, supports fractional crystallization and upper crustal contamination for generation of the KAB granites. Trace elemental ratios of Y/Nb, Nb/Ta, Zr/Hf and P205 suggest the granites are weakly mineralized to barren in Sn–W.The U–Pb zircon ages point to two successive and overlapping periods: from 1418 ± 15 Ma to 1395 ± 6 Ma (mean = 1406 Ma) and from 1385 ± 8 Ma to 1376 ± 11 Ma (mean = 1381 Ma). Inheritance U–Pb dates of xenocryst zircons, comprise early to late Paleoproterozoic ages ranging from 2376 ± 30 Ma, 2000 ± 27 Ma to 1901 ± 39 Ma, and from 1795 ± 7 Ma to 1738 ± 7 Ma, implying the participation of the Paleoproterozoic sedimentary rocks in the petrogenesis of the granites. A zircon rim overgrowth age of 1015 ± 26 Ma is interpreted to date a metamorphic/anatexis event that coincided with the c.1000 Ma amalgamation of the supercontinent Rodinia and the emplacement of Sn–W enriched granites. The ages of S-type granite magmatism (1418–1376 Ma) obtained from this study are restricted to the Mesoproterozoic within the widespread bimodal magmatism event c.1375 Ma.

U–Pb SHRIMP zircon dating and geochemistry of metapelites from the Shillong Meghalaya Gneissic Complex, NE India: Implications for nature of protolith and tectonic setting

The Sonapahar area of Shillong Meghalaya Gneissic Complex (SMGC) is an extension of the Central India Tectonic Zone within the Precambrian Indian shield. The study area mainly consists of metapelites, basic granulites, granitic gneisses and high-grade gneisses as metamorphic imprints. U–Pb SHRIMP zircon dating yields a late Paleoproterozoic age of 1672 ± 6 Ma, which is age of the metapelites protolith. The petrochronology and geochemistry of metapelites and granitic gneiss basement rocks have been studied to learn more about the SMGC's tectonic environment, involvement in the supercontinent cycle, crustal development and geodynamic context. In the NCKFMASHTO system, phase equilibria modelling of metapelites shows peak metamorphic stage at P-T conditions of 8.25 kbar/ 820°C. Cordierite is formed during retrograde metamorphism during the decompression phases. The negative anomalies in Nb, Sr and Ti indicate that crustal sources played a significant role in magmatic emplacement. Geochemical data from metapelites indicate that protoliths were trachy-andesitic in nature, generated during the syn-orogenic environment by subduction tectonism. The SMGC experienced significant tectonic activity throughout the Paleoproterozoic age when the subduction tectonic setting coincided with orogenic activity. The presence of Paleoproterozoic age in the study area, as well as Southwestern Australia and East Antarctica correlates the Sonapahar granulite with the Columbia supercontinent history.

Detrital Zircon Geochronology of Upper Cretaceous to Paleocene Sandstones From South‐Central Wyoming: Evidence for Middle Campanian Laramide Deformation

AbstractLaramide deformation during the Late Cretaceous through early Eocene interrupted the east‐flowing drainage systems from the Sevier hinterland and segmented the Western Interior Foreland Basin in much of western North America into a series of intermontane basins and Precambrian basement‐cored uplifts. In Wyoming, the timing of Laramide deformation and its impacts on drainage patterns during the overlap in the Sevier and Laramide orogenies remain under debate. New detrital zircon U‐Pb geochronologic data from 11 outcrop samples (n = 3,085) in south‐central Wyoming suggest at least two provenance‐distribution phases, distinguished by a substantial increase in zircons of late Paleoproterozoic age (1800–1600 Ma) recorded at approximately 79 Ma. The most likely source of late Paleoproterozoic age zircons is Precambrian basement‐cored uplifts, specifically the Sierra Madre Mountains, signaling the possible middle Campanian initiation of Laramide uplift, earlier than previously recorded. When combined with complementary data sets from surrounding basins, the first provenance‐distribution phase is age discordant, with the earliest evidence of 1800–1600 Ma zircons in the Piceance Basin of Colorado (late Santonian to early Campanian). The second provenance phase shows repeating age distribution patterns that begin with significant contributions from 1800 to 1600 Ma zircon grains and end with much broader and evenly distributed population signatures, confirming previous interpretations of significant Laramide deformation during the Maastrichtian (approximately 70 Ma) as well as uplift and recycling of Upper Cretaceous formations at about 67 Ma.

Lu–Hf Isotopic Systematics of Zircon From Lower Crustal Xenoliths in the Belomorian Mobile Belt

The structure, geochemistry, and U–Pb and Lu–Hf isotopic composition of zircon crystals from garnet granulite xenoliths of the lower crust in the Belomorian mobile belt have been studied. It has been established that Early Paleoproterozoic zircon, 2.47 Ga in age, is primary magmatic and formed during crystallization of mafic rocks in the lower crust. Meso- and Neoarchean zircons are xenogenic crystals trapped by mafic melt during its contamination with older crustal sialic rocks. Metamorphic zircon grains have yielded a Late Paleoproterozoic age (1.75 Ga). A Paleozoic age has been established for a magmatic crystal formed due to interaction of xenoliths with an alkaline ultramafic melt, which delivered xenoliths to surface. The U–Pb datings and Lu–Hf systematics of crystals have been used to delineate the stages of formation and transformation of the lower crust in this region.

Grenvillian-aged reworking of late Paleoproterozoic crust of the southern North Australian Craton, central Australia: Implications for the assembly of Mesoproterozoic Australia

LA–ICP–MS U–Pb monazite and zircon geochronology from metapelites and migmatitic orthogneiss along the central southern margin of the North Australia Craton (NAC), central Australia, reveal the presence of a regional-scale Grenvillian-aged (ca. 1130Ma) deformation system. Grenvillian-aged deformation extends over a strike length of over 110km from the southern Aileron Province in the vicinity of Alice Springs to the Teapot Granite Complex within the Warumpi Province. There is also evidence for Grenvillian-aged migmatisation and resetting of monazite further west in the Mount Liebig area, which may extend the Grenvillian-aged footprint to a strike-length of at least 250km. Deformation associated with Grenvillian-aged reworking produced map-scale east–west trending folds and strongly foliated, steeply dipping shear zones that define the structural architecture of the interface region between the Aileron and Warumpi Provinces. Shallow, westerly-plunging folds associated with partial melting have evolved into shear zones and mylonites that record south-side up movement. Phase equilibria modelling of age-constrained garnet–biotite±sillimanite±cordierite-bearing metapelites from the southern Aileron and Warumpi Provinces suggest Grenvillian-aged metamorphism reached temperatures in the range of 775–820°C and pressures of 5–5.5kbar, corresponding to thermal gradients of ∼130–165°Ckbar−1. The extensive Grenvillian-aged system reworks and overprints late Paleoproterozoic (ca. 1650–1630Ma) high-grade metamorphic rocks. The Grenvillian-aged system occurs above a south dipping lithospheric-scale interface that has been geophysically imaged to depths of at least 200km. This feature was interpreted to represent a fossil subduction zone of late Paleoproterozoic age. However, the presence of regional-scale Grenvillian-aged deformation in the crust above this feature suggests that it may instead be Grenvillian-aged. If that is the case, deformation along the southern margin of the NAC may record suturing of the NAC with the Grenvillian-aged Musgrave Province to the south. This would effectively place the long-lived, Late Mesoproterozoic ultrahot orogen that is the Musgrave Province in southern central Australia in an upper plate tectonic setting, linked to the convergence of the NAC with the South Australian Craton.

Formation and evolution of a Proterozoic magmatic arc: geochemical and geochronological constraints from meta-igneous rocks of the Ongole domain, Eastern Ghats Belt, India

Geochemical data and U–Pb zircon results are presented for the intrusive meta-igneous rocks of the Ongole domain, a granulite-facies terrain of the Eastern Ghats Belt in India, with the aim of inferring the tectonic setting and the timing of their formation. Geochemical data suggest that the intrusive meta-igneous rocks (mafic granulites and charnoenderbites) possess trace and rare earth element composition that are typical of magmatic arcs. They are subalkaline, enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high field strength elements like Nb, Ta and Ti. These characteristics indicate that the primary magmas of these rocks were derived by partial melting of a depleted mantle wedge that had been metasomatized by a slab component. Zircon grains collected from five charnoenderbites are large and euhedral to subhedral and display fine-scale oscillatory growth zoning in CL images, implying a magmatic origin. The grains frequently show narrow-to-broad unzoned overgrowths, implying a metamorphic origin. The oscillatory-zoned cores yield Paleoproterozoic concordia ages of ca. 1,750–1,710 Ma, interpreted as the time of magma emplacement. The unzoned overgrowths yield very late Paleoproterozoic ages of ca. 1,630–1,600 Ma, interpreted as the timing of metamorphism. An enderbite showing both magmatic and metamorphic concordia ages of ca. 1,605 Ma points to the existence of syn-metamorphic intrusions. Together, the presented geochemical and geochronological evidence suggests that the Ongole domain was a magmatic arc near the Indian continent during the Paleoproterozoic. Subsequently, the rocks were metamorphosed during the late Paleoproterozoic, and the terrain was accreted to the Indian craton during the early Mesoproterozoic. The formation and growth of the Ongole domain magmatic arc through subduction-related accretion can be correlated with the growth of Columbia (1.8–1.2 Ga), but its accretion to the Indian craton is apparently unrelated to the formation of any supercontinent on a global scale.

New age constraints for the Proterozoic Aravalli–Delhi successions of India and their implications

Proterozoic sedimentary successions of India are important archives of both the tectonic history of the Indian subcontinent and the geochemical evolution of Earth surface processes. However, the lack of firm age constraints on many of these stratigraphic units limits their current utility. Here, we present new detrital zircon age data from strata of the southern Aravalli–Delhi Orogenic Belt (ADOB) and the Rajasthan Vindhyan successions. The Alwar Group of the southern Delhi Supergroup yielded a large population of ∼1.2Ga detrital zircon grains, which refutes the 1.9–1.7Ga age assertion for this unit. Detrital zircon age distributions from the southern Alwar Group differ strongly from the Alwar Group of the “North Delhi Belt”, demonstrating miscorrelation between these two regions. The Jhamarkotra Formation of the Lower Aravalli Group contains a large population of 1.9–1.7Ga detrital zircon grains. Therefore, the unit cannot be ∼2.1Ga as traditionally assumed. Age distributions of the Aravalli and Delhi supergroups are similar to those of the lower and upper Vindhyan successions, and we postulate contiguous sediment sources for both regions, with strata of the tectonically deformed ADOB representing the distal margin equivalents of the Vindhyan successions. Additionally, a late Paleoproterozoic age for the Jhamarkotra Formation nullifies the hypothesis that the markedly positive carbonate δ13C values in this unit are linked to the 2.3–2.0Ga Lomagundi–Jatuli positive isotope excursion. The potential of a large late Paleoproterozoic (ca. 1.7 Ga) positive δ13C excursion contrasts with the long-held view of a prolonged period of carbon isotope stasis during the so-called ‘boring billion’.

Earliest Paleoproterozoic supracrustal rocks in the North China Craton recognized from the Daqingshan area of the Khondalite Belt: Constraints on craton evolution

The Upper Wulashan “Subgroup” at Daqingshan in the Khondalite Belt of the Western Block of the North China Craton contains an Early Paleoproterozoic (2.5–2.45Ga) supracrustal sequence, incorporating banded iron formations, which we refer to as the Daqingshan Supracrustal Rocks. They contain rounded to elliptical zircon grains that commonly show core–rim or core–mantle–rim structures and precise SHRIMP U–Pb dating of these domains allows the discrimination of a series of tectono-thermal events that straddle the Archean/Proterozoic boundary. Detrital zircon cores with oscillatory zoning have formation ages ranging from 2.55 to 2.50Ga, indicating derivation from Late Neoarchean magmatic rocks. As a result of exhumation and erosion, these became incorporated in earliest Paleoproterozoic sediments that were deposited between 2.50 and 2.45Ga and then underwent high-grade metamorphism at 2.45–2.40Ga. This event variously recrystallized the cores into two main domains: a dark inner domain and a gray outer domain, as imaged in cathodoluminescence. The gray domains commonly show sector zoning and have Th/U ratios of 0.1–0.5, a feature commonly noted in zircons recrystallized under high-grade metamorphic conditions. Metamorphic mantles are generally more homogeneous in structure and have lower Th/U ratios (commonly <0.1) than the recrystallized domains, although they show similar age distributions. However, they are difficult to distinguish when only two domains are present in the zircon and they represent a continuum of recrystallization. The rocks then underwent a second episode of high-grade metamorphism in the Late Paleoproterozoic, as revealed by thin overgrowth rims that are homogeneous or show only weak zoning, have low Th/U ratios (commonly <0.1), and record ages of 1.95–1.90Ga. This is the first time that two tectono-thermal events of Early and Late Paleoproterozoic age have been identified in single rock samples from the Western Block of the North China Craton. The conclusion that unequivocal earliest Paleoproterozoic sediments are present in the North China Craton is also supported by evidence that the Daqingshan Supracrustal Rocks are cut by anatectic garnet granite, previously dated at 2.39Ga. Combined with evidence obtained here and elsewhere in the North China Craton, we conclude that the 2.45–2.40Ga metamorphism was not an extension of the well-established, craton-wide Late Neoarchean tectono-thermal event, but a previously unrecognized episode that followed a short quiescent period that allowed sedimentation of the Daqingshan Supracrustal Rocks.

U–Pb ages and Hf isotope data from detrital zircons in the Neoproterozoic sandstones of northern Jiangsu and southern Liaoning Provinces, China: Implications for the Late Precambrian evolution of the southeastern North China Craton

The tectonic evolution of the North China Craton (NCC) from the Late Mesoproterozoic to the Neoproterozoic has been unclear. This paper reports the results of LA–ICP–MS U–Pb dating and in situ Hf isotope analysis of detrital zircons from Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces of southeastern NCC, and we go onto discuss how these results help constrain the Late Precambrian evolution of the NCC. Most analyzed zircon grains exhibit oscillatory growth zoning, and they have relatively high Th/U ratios (>0.4) and positive Ce anomalies as well as negative Eu anomalies, all of which suggests a magmatic origin. The detrital zircons from the Xinxing and Jinshanzhai formations in northern Jiangsu Province give weighted mean ages of 1753, 1635, 1486, and 1121Ma, and 2515, 2305, 1856, 925, and 825Ma, respectively, and the detrital zircons from the Diaoyutai and Xingmincun formations in southern Liaoning Province give ages of 1745, 1619, 1484, 1175, and 1077Ma, and 1798, 1623, 1150, 1020, and 934Ma, respectively. These results, together with previously published ages, indicate that (1) the Neoproterozoic strata in the northern Jiangsu and southern Liaoning provinces were deposited during a period from the Late Mesoproterozoic to Neoproterozoic, and (2) the sediments in the Neoproterozoic strata were sourced mainly from igneous rocks of Late Paleoproterozoic, Mesoproterozoic, and Early Neoproterozoic age, as well as from the ancient Precambrian basement of the NCC. The concordia plots for 291 detrital zircon grains give three prominent age groups of 1.86–2.5, 1.5–1.8, and 0.9–1.2Ga. The detrital zircon ages of 1.86–2.5Ga in the Neoproterozoic strata tie in with most of the Precambrian tectonic–magmatic–thermal events that occurred in the NCC. Zircon ages of 1.6–1.8Ga can be linked to rift magmatism of Late Paleoproterozoic age in the NCC. The detrital zircon ages of 0.9–1.2Ga can be related to Grenville-aged magmatism in the southeastern NCC. The zircons show negative ɛHf (t) values (−8.8 to −0.1), suggesting that the source rocks were dominated by reworked ancient Precambrian crust. The positive ɛHf (t) values (+0.3 to +10.8) and Hf model ages indicate that growth of continental crustal occurred at ∼2.7Ga, ∼1.9Ga, and ∼1.5Ga in the southeastern NCC.

Provenance of Meso- to Neoproterozoic cover sediments at the Ming Tombs, Beijing, North China Craton: An integrated study of U–Pb dating and Hf isotopic measurement of detrital zircons and whole-rock geochemistry

The North China Craton (NCC) was subjected to an extensional regime after the Lüliang movement at ~ 1.8 Ga and then was covered by an extensive Meso- to Neoproterozoic sedimentary succession, namely the Changcheng, Jixian and Qingbaikou Groups in ascending order. We report age spectra for detrital zircons and monazites, Hf isotopic systematics of detrital zircons, and whole-rock chemical and Nd isotopic compositions for sediments from the succession in the Ming Tombs area, Beijing, one of the typical Meso- to Neoproterozoic areas in the NCC. Detrital zircons of six sedimentary samples have two distinct age peaks at ~ 2.52 Ga and ~ 1.85 Ga. There are some detrital zircons at 2.4–2.0 Ga but none at 2.3 Ga and only a few > 2.7 Ga. The detrital zircon age spectra change with time. Sediments in the lower succession (Changcheng Group) and in the upper successions (Jixian and Qinbaikou Groups) are dominated by significant detrital zircon populations of late Neoarchean and late Paleoproterozoic ages, respectively. The ~ 2.5 Ga detrital zircons of the Changcheng Group have ε Hf(2.5 Ga) values and t DM(Hf) model ages mainly ranging from − 2 to + 7 and 2.8 to 2.7 Ga, respectively. Detrital monazites of a sample from the Jixian Group exhibit a major age peak between 1.95 and 1.80 Ga with some data between 2.0 and 1.95 Ga. The sedimentary rocks of the Changcheng Group are characterized by high K 2O contents (mostly 7.09–15.20%) and insignificant Eu anomalies (Eu/Eu* = 0.71–1.16). They have t DM(Nd) model ages ranging from 2.70 to 2.43 Ga, being older than the t DM(Nd) ages (2.11 and 1.99 Ga) of sedimentary samples from the Qingbaikou Group. Based on a comparison with ages for the early Precambrian (> 1.8 Ga) basement of the NCC, it can be concluded that (1) the sediments of the Meso- to Neoproterozoic cover were undoubtedly derived from the NCC itself or once neighboring terranes; (2) variations in the detrital zircon age spectra from the lower to the upper successions reflect provenance evolution in that the lower crustal late Paleoproterozoic rocks were exposed at the surface after the upper crustal late Neoarchean rocks had already been eroded.

Implications of lunar orbital periodicity from the Chaibasa tidal rhythmite (India) of late Paleoproterozoic age

Harmonic analysis of the sandstone foreset-laminae thickness series from the Chaibasa tidal rhythmite, India, clearly shows that a normal semidiurnal tidal system with synodic month of ;32 lunar days was in effect during the late Paleoproterozoic (2100‐1600 Ma). The minimum number of solar days in a lunar sidereal month was ;31. Published quantitative tidal-rhythmite data of others in combination with data derived from the Chaibasa tidal rhythmite indicate long-term stability of the lunar orbit and progressive increase in the Earth-Moon distance during the Proterozoic.

Red Bed-Hosted Oncolitic Manganese Ore of the Paleoproterozoic Soutpansberg Group, Bronkhorstfontein, South Africa

The Bronkhorstfontein manganese deposit near Tolwe, Limpopo province, South Africa, constitutes an exceptionally well preserved and unmetamorphosed shallow-marine manganese deposit of Late Paleoproterozoic age. It is the oldest known deposit that displays characteristics of economically important shallow-marine pisolitic manganese deposits of Mesozoic and Cenozoic age. Manganese mineralization at Bronkhorstfontein occurs as five laterally continuous, up to 2-m-thick, beds that are hosted by an alluvial red bed succession, preserved as part of an erosional outlier of the Wyllies Poort Formation, Soutpansberg Group. Manganiferous beds mark transgressive surfaces and formed in a storm-dominated, shallow-water environment of a deltaic to litoral setting. The massively bedded siliceous ore contains up to 41 wt percent Mn, at Mn/Fe ratios between 6 and 10. The mineralogy of the ore is simple; braunite, hematite, and quartz are the dominant constituents, with minor pyrolusite, cryptomelane, and chalcedony as products of supergene alteration. Rare earth element and trace element geochemical indicators suggest that the manganese mineralization originated as hydrogenetic Mn4+ oxyhydroxide precipitates, which were diagenetically transformed into braunite. The most striking feature of the manganese ores of the Bronkhorstfontein deposit is the beautiful preservation of various types of sedimentary particles, including well-rounded detrital quartz grains and hematite-chert pellets, as well as oncoids. The oncoids, in particular, are remarkable, because they are very similar in size, shape, and internal texture to modern biogenic analogues. Their abundance throughout the ore-bearing strata and their absence from the intercalated sediments strongly suggests that oncoid-building micro-organisms mediated manganese precipitation. This observation is used to suggest that microbial mediation may be of greater importance for the origin of shallow-marine manganese deposition than is indicated by currently accepted metallogenetic models for shallow-marine pisolitic manganese deposits.