Detrital Monazite Research Articles

Detrital monazite evidence for crustal evolution of the North and South American continents during the Boring Billion

Orogenic processes associated with the supercontinent cycle play crucial roles in the evolution of continental crust and surface environments. Detrital zircon records, useful archives of orogenic history, have recently suggested the possibility of orogenic quiescence during the Mesoproterozoic, the so-called Boring Billion. However, detrital zircon may not always provide a precise record of crustal evolution due to preservation bias. Detrital monazite, another beneficial accessory mineral, can provide key archives for a better understanding of the continental crust evolution over geological history. Here, we present the U–Pb ages, trace element abundances, and Nd isotope compositions of detrital monazites from four major rivers on the North and South American continents: the Mackenzie, Mississippi, Amazon, and Paraná rivers. The monazite U–Pb age data showed an uneven distribution, with peaks even during the Mesoproterozoic. The age distribution of the detrital monazites was broadly consistent with that of the detrital zircons in the same rivers. However, the two mineral's different occurrences and preservation potentials result in significant differences. The trace element and Nd isotope data of the detrital monazites indicate that the monazite U–Pb age peaks reflect the timing of the collision stage rather than the subduction stage. We further found cyclic secular variations in the detrital monazite Nd isotope compositions: their 143Nd/144Nd averages shifted from juvenile to reworked crustal signatures during the interval of supercontinent assembly, including the Proterozoic period. The Nd isotope shifts can be interpreted as crustal maturation through crustal re-melting and metamorphism driven by orogenic events. The monazite U–Pb age peaks and Nd isotope shift during the Mesoproterozoic suggest sustained crustal evolution rather than orogenic quiescence during the Boring Billion.

Paleozoic to Mesozoic paleotectonic reconstructions of Gondwana assembly: Insights from petrography, heavy mineral chemistry and detrital U–Th–total Pb monazite geochronology of sandstones in the Pranhita-Godavari Basin (SE India)

The provenance study of Paleo-Mesozoic sediments of the Pranhita-Godavari (P-G) Basin, located in the southeastern India is crucial for the reconstruction of the eastern Gondwanaland, including the India-Antarctica connection. This study examines petrography, heavy mineral chemistry and detrital monazite geochronology of the Permo-Carboniferous to Cretaceous, predominantly fluviatile sandstones in the P-G Basin to track the possible sediment sources in East Antarctica and Eastern India. The sandstones show a gradual shift in composition from feldspatho-quartzose to quartzose arenite from older to younger succession, accompanied by a change in source terranes in a changing setting from transitional continental to the cratonic interior. The heavy minerals of the sandstones are dominated by garnet, rutile, ilmenite, monazite and zircon in order of decreasing abundance. The mineral chemistry of garnet and rutile indicates the predominance of sources from amphibolite to granulite facies rocks with minor inputs from metapelitic sources. The increase in textural and mineralogical maturity of sandstones accompanied by a gradual increase in ilmenite alteration from the bottom to the top of the succession indicates the attainment of tectonic stability with time. U–Th–total Pb dating of detrital monazites yielded three distinct major clusters at (1) 2556–2125 Ma, (2) 969–715 Ma, and (3) 581–418 Ma. Based on the correlation of source composition and monazite geochronology and paleocurrent data, the source of sediments is traced to the orogens of the Eastern Ghats mobile belt, East Antarctica (including Rayner and Napier complex), Karimnagar granulite belt, Khammam schist belt, and Bhopalpatnam granulite belt, situated to the west, south, and southeast of the present outcrops of the P-G Gondwana succession. The younger age populations possibly represent the sediment input from Kuunga Orogen, which represents the youngest orogenic event (635–488 Ma) in the Gondwana assembly. The rocks of Kuunga orogeny, occurring to the south of the basin, was a minor contributor to the P-G Gondwana sediments of this basin. The new data supports that the Eastern Ghats Mobile Belt of India and East Antarctica were conjugate to each other till the Late Triassic Period, both of which contributed major sediments to the P-G Gondwana Basin.

Tracing source and palaeo‐weathering conditions of quartzose sandstone in the Cretaceous Cambay Basin: A combined petrographical, geochemical and geochronological approach

Based on detrital monazite dating, mineral chemistry of tourmaline and rutile, bulk rock geochemistry, modal analysis of petrographic and palaeocurrent data, this study tracks the source of quartzose sandstone within the Cretaceous succession of the Cambay Basin primarily to rocks within the Aravalli‐Delhi Fold Belt. Monazite geochronology shows predominant peaks around 506 ± 11 Ma, 905 ± 12 Ma and a minor peak at 750 ± 20 Ma, 1485 ± 30 Ma relating sediment sources to the Aravalli‐Delhi orogeny and Pan‐African orogeny. The petrographic modal analysis of the moderate‐to‐well‐sorted Himmatnagar Sandstone indicates at least 91% quartz, with minor feldspar and rock fragments. The mineral chemistry of tourmalines in Himmatnagar Sandstone matches with Li‐ and Ca‐poor granitoid, pegmatites, metapelites and quartz tourmaline rocks. The trace element content of rutiles in sandstones corresponds to metapelitic sources. Detrital monazite dates and mineral chemistry of tourmalines and rutiles pinpoint the sediment source to the South Delhi Supergroup of rocks. The dominance of rounded zircons and tourmalines and abraded quartz overgrowth in the Himmatnagar Sandstone indicate the recycling of sediments, possibly from the Marwar Supergroup. Palaeoclimatic proxies based on mineralogy and geochemistry, particularly, the high value (93–97) of mineralogical index alteration, indicate intense chemical weathering of the source rocks under humid climatic conditions. Therefore, the combination of factors, including the quartzo‐feldspathic source rocks, intense chemical weathering under humid climatic conditions and the recycling of sediments facilitated the formation of quartzose sandstone within the Himmatngar Sandstone in the Cambay Basin.

Monazite and xenotime petrochronologic constraints on four Proterozoic tectonic episodes and ca. 1705 Ma age of the Uncompahgre Formation, southwestern Colorado, USA

Abstract The Proterozoic tectonic evolution of the southwestern USA remains incompletely understood due to limited constraints on the timing and conditions of the tectono-metamorphic phases and depositional age of metasedimentary successions. We integrated multi-scale compositional mapping, petrologic modeling, and in situ geochronology to constrain pressure-temperature-time paths from samples of Paleoproterozoic basement gneisses and overlying quartzites in southwestern Colorado, USA. Basement gneiss from the western Needle Mountains records metamorphic conditions of 600 °C at 0.75 GPa at 1764 ± 9 Ma and ~575 °C at 1741 ± 10 Ma. Gneiss sampled from drill core near Pagosa Springs, Colorado, records conditions of 700 °C at 1748 ± 9 Ma, 800 °C at 1.1 GPa at 1650 ± 40 Ma, 540 °C at 1570 ± 36 Ma, and 440 °C at 1424 ± 12 Ma. The Uncompahgre Formation was deposited at ca. 1705 Ma, as constrained by detrital monazite (1707 ± 8 Ma) and xenotime (1692 ± 40, 1725 ± 50 Ma), metamorphic xenotime (1650 ± 10 Ma), and published 40Ar/39Ar and detrital zircon data. Compositions of ca. 1705 Ma detrital monazite and xenotime are consistent with derivation from a garnet-bearing source in the Yavapai orogenic hinterland. The Vallecito Conglomerate and Uncompahgre Formation record macroscopic folding and greenschist-facies metamorphism at 1650 ± 10 Ma and temperatures of 270 °C to >570 °C at 1470–1400 Ma. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon geochronology yielded dates of 1775 ± 18 Ma from the Twilight Gneiss and 1696 ± 7 Ma from the Bakers Bridge Granite, supporting previous isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates. The Eolus Granite yielded a date of 1463 ± 6 Ma, which is older than previous 1.44–1.43 Ga ID-TIMS dates. The newly dated granite of Cataract Gulch is 1421 ± 12 Ma. In situ analysis of detrital and meta-morphic monazite and xenotime, igneous zircon, and quantitative thermobarometry, integrated with previously published constraints, indicate multiple tectonic episodes after the emplacement of 1800–1760 Ma arc-related rocks. The region experienced greenschist- to amphibolite-facies metamorphism (M1) from 1760 Ma to 1740 Ma, which was followed by the intrusion of granites at 1730–1695 Ma and deposition of the Uncompahgre Formation at ca. 1705 Ma, contemporaneous with the Yavapai orogeny. Metamorphism at 1680–1600 Ma was characterized by greenschist-facies conditions near Ouray, Colorado, and granulite-facies conditions near Pagosa Springs (M2) during the Mazatzal orogeny. From 1470 Ma to 1400 Ma, greenschist- to amphibolite-facies metamorphism (M3) and largely granitic plutonism occurred during the protracted Picuris orogeny. These results demonstrate the power of monazite and xenotime analyses to constrain depositional ages, provenance, and pressure-temperature-time (P-T-t) paths to resolve the compound orogenic history that is characteristic of most mountain belts.

Low-Temperature Fluorocarbonate Mineralization in Lower Devonian Rhynie Chert, UK

Rare earth element (REE) fluorocarbonate mineralization occurs in lacustrine shales in the Lower Devonian Rhynie chert, Aberdeenshire, UK, preserved by hot spring silicification. Mineralization follows a combination of first-cycle erosion of granite to yield detrital monazite grains, bioweathering of the monazite to liberate REEs, and interaction with fluorine-rich hot spring fluids in an alkaline sedimentary environment. The mineral composition of most of the fluorocarbonates is referable to synchysite. Mineralization occurs at the surface, and the host shales subsequently experience maximum temperatures of about 110 ℃. Most fluorocarbonate mineralization originates at much higher temperatures, but the Rhynie occurrence emphasizes that low-temperature deposits are possible when both fluorine and REEs are available from granite into the sedimentary environment.

SHRIMP U–Pb geochronology of Mesoproterozoic basement and overlying Ocoee Supergroup, NC–TN: dating diagenetic xenotime and monazite overgrowths on detrital minerals to determine the age of sedimentary deposition

Sedimentary rocks of the Ocoee Supergroup crop out in the Appalachian Blue Ridge of western North Carolina and eastern Tennessee. This ∼12 km thick sequence of strata was mapped as nonconformably overlying Mesoproterozoic crystalline basement (about 1.20–1.02 Ga) and beneath the lower Cambrian Chilhowee Group, leading to the traditional interpretation that the Ocoee Supergroup was deposited between about 1.02 and 0.54 Ga. This interpretation was challenged by Unrug and Unrug (1990, Geology, 18: 1041–1045) and Unrug et al. (2000, Geological Society of America Bulletin. Vol. 112, pp. 982–996), who claimed that Paleozoic fossils were recovered from rocks of the Walden Creek Group (upper Ocoee), and thereby created a new tectonic model for the origin of Laurentia. To resolve the age controversy concerning the time of deposition of the Ocoee Supergroup, diagenetic xenotime overgrowths on detrital zircon and diagenetic monazite on detrital monazite were dated by the U–Pb method. Sensitive High Resolution Ion Microprobe ages of diagenetic xenotime from three samples of sandstone (Thunderhead Sandstone, Cades Sandstone, and Shields Formation) indicate that the Ocoee Supergroup was deposited in the interval of about 580–550 Ma. A sample of Sandsuck Formation (uppermost Ocoee) yielded xenotime overgrowths of about 410 Ma, probably related to post-depositional low-grade metamorphism. Various origins of xenotime overgrowths may be distinguished by trace element distributions. Ages and trace element concentrations of monazite overgrowths support the xenotime age results, although concordia systematics are complicated by high concentrations of common Pb and inheritance of ages (∼1.2 and 0.6 Ga). These age data support the observed field relations for a late Neoproterozoic depositional age of the Ocoee Supergroup.

Long-distance transport of clastic material revealed by monazite and muscovite dating: Albian arenites, extra-Carpathian Poland

The absolute ages based on chemical UPb dating of monazite (CHIME) and 40Ar/39Ar muscovite were used for provenance determination of the Albian arenites of the southern part of the extra-Carpathian Poland. The ages of detrital monazites allowed a division of the study area into two domains: western and eastern, related to the Miechów and Lublin areas respectively. The western domain is characterized by a unimodal distribution of monazite ages – 330–380 Ma that unequivocally indicates a Variscan provenance of the detrital monazite. The muscovite 40Ar/39Ar method applied to a western domain sample yielded a primary 360.0 ± 1.21 Ma age, confirming a Variscan source of the detrital material. The eastern domain is characterized by a polymodal distribution of monazite ages and is further divided into two subdomains: northeastern and southeastern. Both subdomains are characterized by a polymodal distribution of monazite ages peaking at 390–490 Ma; 0.8–1.1 Ga; ca. 1.5 Ga and ca. 1.8 Ga, indicating the Caledonian, Sveconorwegian, Hallandian-Danopolonian plus Gothian and Svecofennian origins of the detrital monazite. The southeastern subdomain additionally has a significant amount of detrital monazite with 330–380 Ma ages, suggesting a notable influence of a Variscan source. The 40Ar/39Ar muscovite data from the northeastern subdomain sample, ca. 476.4 ± 1.27 and subordinate 496.4 ± 2.83 Ma, confirms that a Caledonian source area was active during sedimentation of the Albian deposits. Detrital muscovite from southeastern subdomain sample yielded two ages: 478.1 ± 3.71 Ma and 502.1 ± 0.65 Ma also indicating a Caledonian age of the detrital muscovite. The monazite and muscovite data indicate at least two independent main ultimate source areas: the Bohemian Massif for the Miechów area (western domain) and the Baltic Shield for the Lublin area (eastern domain). The results document an over 1200 km long transport of clastic material in the Central European Sedimentary Basin during the Albian.

Detrital zircon, monazite and tourmaline reveal the magmatic and metamorphic history of the Himalayan orogen from Archean to present

The litho-tectonic structure of the Himalaya is the result of multiple orogenic cycles. However, its pre-Cenozoic history is not well understood, which limits our ability to constrain the stratigraphy, structure, and tectonism in the Himalayan orogen. This issue can be potentially addressed by detrital mineral geochronology and isotopic studies, which can be used to reconstruct the magmatic and metamorphic records from past to present. In this study, we collected three river sand samples from the central Himalaya, which originated from the interior of Ama Drime Massif (ADM), Greater Himalayan Sequence (GHS) outside of the ADM, and the boundary between the ADM and GHS, respectively, and then conducted a geochronological study of detrital zircon and monazite, and obtained detrital zircon Hf and tourmaline B isotope data. Detrital zircon of the river sand from the ADM only records the 1.9–1.7 Ga magmatic event, while age groups of 3.5–2.4, 1.1–0.7, and 0.6–0.4 Ga are observed in the GHS outside the ADM. Detrital tourmaline from the GHS has heavy B isotopic signatures with δ11B = −15‰ to −7‰, similar to the values for GHS leucogranites. Detrital tourmaline from the ADM has δ11B = −20‰ to −13‰, similar to the Lesser Himalayan Sequence (LHS). Integrating these results with previous metamorphic and thermochronological works, we interpret that the ADM represents deeply buried LHS rocks beneath the GHS, which underwent a significant uplift assisted by the detachments on its two sides during the Miocene. Furthermore, zircon Hf isotopic variations indicate that the north Indian margin was an active convergent boundary during the Paleoproterozoic, Neoproterozoic, and Paleozoic, in relation to supercontinent amalgamation. Detrital monazite records two major thermal events in the Cenozoic era. A large proportion of detrital monazite yield ages from 25 to 20 Ma, indicating that the collision entered a mature stage at this time, during which thickened Himalayan crust formed and widespread anatexis occurred. A tectonic style transition in the Himalayan hinterland from shortening that thickened the crust to extension that thinned it occurred during the middle to late Miocene (15–10 Ma) in the Himalaya.

Tracing high-pressure metamorphism in the eastern Himalayan syntaxis using detrital zircon and monazite from modern stream sediments

The timing of high-pressure (HP) metamorphism in the eastern Himalayan syntaxis is important for understanding the India-Asia collisional processes, but it remains elusive. To reveal the metamorphic history of the eastern Himalayan syntaxis, we performed a study of geochronology, trace elements, and mineral inclusions of detrital zircon and monazite from modern stream sediments in the eastern Himalayan syntaxis. Detrital zircon comprise magmatic and metamorphic domains with different zoning. Inherited magmatic zircon domains have high Th/U, low (Dy/Yb)N, and retain ages of 1798−360 Ma. Metamorphic zircon domains with low Th/U, high (Dy/Yb)N, and inclusions of garnet, kyanite, and/or clinopyroxene probably formed under HP conditions. They yield age groups of 49−35 Ma, 33−17 Ma, and 12−7 Ma. The low Th/U and low (Dy/Yb)N metamorphic zircon domains probably formed during retrogression and yield age groups of 27−16 Ma and 10−6 Ma. Detrital monazite yield age distributions similar to those of the low (Dy/Yb)N metamorphic zircon except for the 821−402 Ma inherited cores. The (Dy/Yb)N of 31.6−5.7 Ma monazite decreases with increasing Y content, which indicates that it likely formed under the retrograde stage during garnet breakdown. Based on the oldest metamorphic ages, the initial India-Asia collision occurred no later than 50−44 Ma in the eastern Himalayan syntaxis. The multimodal age patterns of the metamorphic zircon and monazite indicate that the Indian continent underwent multistage HP and retrograde metamorphism in the eastern Himalayan syntaxis. The nearly contemporaneous HP and retrograde metamorphism indicate that the Indian continent continued subducting while the earlier HP metamorphic slices detached and exhumed.

Revisiting the paleogeographic position of South China in Gondwana by geochemistry and U Pb ages of detrital monazite grains from Cambrian sedimentary rocks

South China is placed in a range of positions along the northern margin of East Gondwana in the early Paleozoic reflecting uncertainties in linking U Pb ages of detrital zircon to potential sources. Using detrital monazite U Pb ages from Cambrian sedimentary rocks, we argue for a position outboard of northeastern India. Detrital monazite yields predominantly earliest Neoproterozoic and earliest Cambrian age peaks at circa 945 Ma and 528 Ma, with minor end Mesoproterozoic and late Paleoproterozoic to early Mesoproterozoic ages. Compared with the U Pb age distribution pattern of detrital zircon from the same samples, the monazite data highlights input from earliest Cambrian metapelites. These earliest Neoproterozoic and earliest Cambrian detrital monazite grains match with ages and Th and U contents of monazite from northeastern India, but are different from those from northwestern India and northern Australia, and thus enable tighter constraints on the paleogeography of South China than detrital zircon data alone. • U Pb ages of detrital monazite from the Cambrian sandstones in the southern part of South China are analyzed. • Cambrian detrital monazite from the southern part of South China yields predominantly age peaks at circa 945 Ma and 530 Ma. • South China was linked to the northeastern India margin of East Gondwana in the Cambrian. • Detrital monazite can provide a more accurate record of provenance than detrital zircon.

Ree minerals in black shales of the paleoproterozoic Mikhailovka formation (Baikal-Patom Highland, Siberia)

he paper characterizes REE mineralization from carbonaceous metapelites of the Paleoproterozoic Mikhailovka Formation, which is the most ancient gold-bearing horizon of the Lena province (Bodaibo district, Irkutsk region). The conditions of metamorphism of the studied samples do not exceed those of chlorite-muscovite subfacies of greenschist facies (ilmenite-pyrrhotite isograde). The metamorphic allanite is a main REE host, which crystallized before the last stage of plastic deformation and folding. The matter source for its formation is related to REE and Th absorbed on organic matter and clay minerals, as well as the detrital monazite. Late hydrothermal-metasomatic processes resulted in its replacement by hydroxycarbonates (hydroxybastnaesite, ancylite) and hydrous phosphates of light REEs (rhabdophane?), while Th precipitated as a hydrous silicate. Findings of low-temperature metamorphic monazite and xenotime are also described.

Tracing remnants of Ediacaran S-type granitoids from beach placers in SE Madagascar

Southeast Madagascar hosts several major deposits of beach placers, the provenance of which is little understood. To redress this imbalance, we present new laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) U-Pb ages, and trace elements of zircons and monazites, as well as Hf isotopes of zircons from heavy mineral beach sands at Taolagnaro (Fort Dauphin) in SE Madagascar. The ages of detrital zircon grains range from 650 Ma to 450 Ma and from 1900 Ma to 1700 Ma (one grain has an age of 2633 Ma), and detrital monazite ages range from 574 Ma to 484 Ma. The Ediacaran−Cambrian zircons (650−450 Ma) and monazites (574−484 Ma) record a major Pan-African orogenic event in SE Madagascar. Geologically, the 650−450 Ma ages correlate well with coeval granitic gneisses in southern Madagascar, and a few 1900−1700 Ma ages can be linked to putative Paleoproterozoic protoliths of metasedimentary rocks from the Anosyen Domain and from the Itremo Group of central Madagascar. The zircon mineral chemistry indicates that some of the grains (P>25 μmol g−1) were sourced from S-type granitic rocks. The monazite chemistry points toward a metamorphic provenance from garnet-bearing amphibolite facies rocks, such as migmatitic gneisses in southern Madagascar. The Hf isotopic compositions of detrital zircons indicate reworking of their probable Paleoproterozoic−Archean source rocks. We conclude that the beach sand zircons and monazites were largely sourced from the uplifted and eroded Anosyen and Androyan Domains in SE Madagascar, and with minor contributions from central Madagascar, which were all transported by rivers to the ambient ocean to the southeast.

Implications of Magnetic Properties in the Concentration and Distribution of REEs in Beach Placer Monazites: A Case Study from Chhatrapur Coast, Odisha

Abstract The concentration of monazite, a rare earth and thorium phosphate, in the heavy mineral-bearing sands of Chhatrapur coast varies from 0.09 to 0.16%. Under the microscope, monazite displays color variation from colorless to various shades of yellow, green and brown. The color variation is further reflected in the chemistry of individual grains. Such monazites of distinct colors and different chemistry also show variation in their paramagnetic properties. Representative detrital monazites separated under varied magnetic field strength were analysed for their rare earth elements, Th and U content. The electron probe micro analysis (EPMA) data indicate that monazites separated under low magnetic field strength (separated at 0.80 amps) are characterized by their higher Nd, Sm, HREE, Y and U as well as low Th content, whereas those separated at 1.10 amps contain low Nd, Sm, HREE with negligible Y and U content as well as higher Th content. The wider variation in the concentration of different rare earths in varied magnetic field strength is a function of varied magnetic susceptibility of individual elements. Hence, the physical method for separation of monazite using magnetic properties may facilitate to segregate the monazites of a particular chemical composition with respect to their constituent elements like U, Th and rare earths based on their magnetic properties.

Evincing the presence of a trans‐Gondwanian mobile belt in the interior of the Princess Elizabeth Land, East Antarctica: insights from offshore detrital sediments, rock fragments, and monazite geochronology

East Gondwana was assembled through the stitching of the Indo‐Antarctica and Australo‐Antarctica domains which also represents the key Gondwana‐forming regions in present‐day East Antarctica. However, the Indo‐Antarctica and Australo‐Antarctica boundaries remain speculative and contentious, as the thick Antarctic Ice sheet precludes direct geological characterization of these terranes. In addition, the exact role of the Gamburtsev Subglacial Mountains, present in the interior of Princess Elizabeth Land (PEL), during the amalgamation of Gondwana, has not been well understood. We present new mineralogical data of offshore sediments from Prydz Bay to infer the geology of the interior of the PEL terrain, East Antarctica. Coast marginal outcrops dominantly expose igneous and granulite facies metamorphic rocks. Heavy minerals characterization of the rock fragments followed by consideration of the outcrop geology indicate a possible contribution of sediments from the far interior of PEL terrain. Total U–Pb chemical geochronology of detrital monazites dominantly shows a bimodal age distribution ascribable to Stenian to Tonian (~1,100 Ma, 900 Ma) event ages and a younger Pan‐African event (~500 Ma). Besides these, Tonian‐Cryogenian (~700 Ma) ages from texturally constrained monazites of a low‐grade schist rock fragment is reported for the first time from this sector. Consideration of glacial flow directions and the nature of rock fragments indicate their sourcing from the distal hinterland. The possible provenance is inferred to be from the Gamburtsev Subglacial Mountains.

Limited expression of the Paleoproterozoic Oklo natural nuclear reactor phenomenon in the aftermath of a widespread deoxygenation event ~2.11–2.06 billion years ago

The only known case of natural fission reactors is hosted by high-grade uranium (U) deposits at Oklo-Okelobondo and Bangombé in sandstones of the ~2.1 Ga Francevillian Group, Gabon. However, the geochemical influence of the depositional environment on this unique natural nuclear phenomenon has not been clearly established. Localized, unusually high vanadium (V) enrichments are thought to have prevented such natural nuclear fission reactors from occurring in other Francevillian U deposits (e.g., Mounana, Boyindzi, and Mikouloungou). However, while U-bearing detrital monazite derived from Archean rocks surrounding the Francevillian basin is viewed as the main source of U, the source of V remains poorly constrained. Here, we combine petrographic and whole-rock geochemical data for the Francevillian Group sedimentary rocks, coupled with previously documented geochemical data for the Archean basement. These data suggest that, although ultramafic to mafic igneous rocks of the Mesoarchean Bélinga Group, and to some extent Archean granitoids, were likely important sources of V to the Francevillian U deposits, they were not the only source of the abnormally high V concentrations in the U deposits that did not produce natural nuclear reactors. Instead, hydrocarbon migration from V-rich black shales of the Upper Francevillian Group, deposited during widespread and protracted deoxygenation of the Paleoproterozoic ocean at the end of the Lomagundi Carbon Isotope Excursion (LE) at ~2.11–2.06 Ga, resulted in a redox front that precipitated the U deposits. These migrated V-rich hydrocarbons likely account for the high V concentrations, which ultimately prevented natural fission reactions from occurring in these U deposits. Similarities with other pyrobitumen-bearing Paleoproterozoic U deposits worldwide suggest that organic-rich source rocks, which deposited in open-marine settings under widespread hyper-euxinic conditions in the aftermath of the LE, played a key role in preventing the Oklo natural nuclear reactor phenomenon from reaching a larger extent.

Neoproterozoic stratigraphy of the Southwestern Basement Province, Svalbard (Norway): Constraints on the Proterozoic-Paleozoic evolution of the North Atlantic-Arctic Caledonides

The Arctic archipelago of Svalbard, Norway, plays an important role in tectonic reconstructions of the Cambrian–Devonian Caledonian orogen in the North Atlantic and circum-Arctic regions. To elucidate the Proterozoic geological history of the Southwestern Basement Province of Svalbard and place its origin and displacement history in the context of regional tectono-stratigraphic events, we present new geological mapping, stratigraphic assignments, carbonate carbon (δ13Ccarb) and strontium (87Sr/86Sr) isotope chemostratigraphy, and detrital/igneous zircon U-Pb geochronology coupled with Hf isotope geochemistry from Neoproterozoic rocks exposed in southwestern Spitsbergen. The examined metasedimentary successions include a Tonian mixed carbonate-siliciclastic succession (the Nordbukta/Deilegga groups) that is regionally truncated by a Cryogenian (<650 Ma) angular unconformity (the Torellian unconformity), the age of which is confirmed herein by field relationships and re-analysis of previously reported detrital monazite data. New detrital zircon U-Pb data from the Nordbukta Group yield ca. 1030–1170, 1280–1400, 1430–1510, and 1580–1680 Ma age populations that are typical of North Atlantic (e.g., North and East Greenland, Scotland, and the Scandinavian Caledonides) Mesoproterozoic-Neoproterozoic sedimentary successions. Overlying Cryogenian–Ediacaran strata of the Sofiebogen, Dunderbukta, and Kapp Lyell (Bellsund) groups record rift-related sedimentation and host chemostratigraphic data that provide ties to the ca. 640(?)–635 Ma Marinoan snowball Earth glaciation. Detrital zircon U-Pb data from the Cryogenian Slyngfjellet, Jens Erikfjellet, and Konglomeratfjellet formations yield similar age spectra to the underlying Nordbukta and Deilegga groups, while younger Ediacaran strata of the Höferpynten and Gåshamna formations record a prominent shift to bimodal ca. 1850 and 2850 Ma U-Pb age populations. Integrating these data with previously published geochemical and geochronological datasets from Svalbard and other circum-Arctic Mesoproterozoic–Neoproterozoic successions, we propose that the Southwestern Basement Province represents a composite terrane composed of multiple peri-Baltican (Wedel Jarlsberg-Oscar II, Berzeliuseggene-Eimfjellet, and Prins Karls Forland terranes) and peri-Laurentian (Hornsund terrane) crustal fragments that were likely initially juxtaposed and/or amalgamated during the Caledonian orogeny. These terranes were subsequently complexly deformed and modified during the younger Devonian-Carboniferous Ellesmerian and Paleogene-Eocene Eurekan orogenic events that affected western Svalbard.

Early Mesoproterozoic evolution of midcontinental Laurentia: Defining the geon 14 Baraboo orogeny

New geochronologic data from midcontinental Laurentia demonstrate that emplacement of the 1476–1470 Ma Wolf River granitic batholith was not an isolated igneous event, but was accompanied by regional metamorphism, deformation, and sedimentation. Evidence for such metamorphism and deformation is best seen in siliciclastic sedimentary rocks of the Baraboo Interval, which were deposited closely following the 1.65–1.63 Ga Mazatzal orogeny. In Baraboo Interval strata, muscovite parallel to slatey cleavage, in hydrothermal veins, in quartzite breccia, and in metamorphosed paleosol yielded 40Ar/39Ar plateau ages of 1493–1465 Ma. In addition, U–Th–total Pb dating of neoblastic overgrowths on detrital monazite gave an age of 1488 ± 20 Ma, and recrystallized hematite in folded metapelite gave a mean U/Th–He age of 1411 ± 39 Ma. Post-Baraboo, arkosic polymictic conglomerate, which contains detrital zircon with a minimum peak age of 1493 Ma, was intruded by a 1470 Ma granite porphyry at the northeastern margin of the Wolf River batholith. This episode of magmatism, regional deformation and metamorphism, and sedimentation, which is designated herein as the Baraboo orogeny, provides a midcontinental link between the Picuris orogeny to the southwest and the Pinware orogeny to the northeast, completing the extent of early Mesoproterozoic (Calymmian) orogenesis for 5000 km along the southern margin of Laurentia. This transcontinental orogen is unique among Precambrian orogenies for its great width (~1600 km), the predominance of ferroan granites derived from partial melting of lower continental crust, and the prevalence of regional high T-P metamorphism related to advective heating by granitic magmas emplaced in the middle to upper crust.

Source to sink systems of the upper permian longtan formation in the lower yangtze region, China: New insights from detrital monazite U–Pb ages and heavy mineral chemistry

The marine-continental transitional facies of the Upper Permian Longtan Formation in the Lower Yangtze region is a favorable prospect for shale gas exploration. The proposed various palaeogeographic maps are insufficiently detailed to effectively seek organic-rich shales. This study presents new observations of sedimentary sections and attempts to use heavy mineral (tourmaline and garnet) chemistry and monazite U–Pb ages to unravel the parent rock types and source-to-sink systems. The chemical compositions of heavy minerals indicate that the parent rocks are dominated by granitoids and associated pegmatites and aplites (intermediate to felsic igneous rocks), Fe-rich and Al-poor calc-silicate rocks and metasedimentary rocks. The parent rocks underwent amphibolite to granulite facies metamorphism at ca. 1.84 Ga. The comparisons of regional lithologies and geochronology suggest that the Paleoproterozoic Badu complexes mainly feed the deltaic deposits of the Longtan Formation, and the Middle Permian volcanics are the lesser donor. The source-to-sink systems are generally NW-directed from the continental erosional zone to prodelta environment, and the source-to-sink system of the Ningguo-Chaohu area is different from that of the Nanjing area. The combination of heavy mineral chemistry and geochronology are proved to be an effective tool in tracing parent rocks in the Lower Yangtze region.

Insights into Polyphase Phanerozoic Tectonic Events in SE China: Integrated Isotopic Microanalysis of Detrital Zircon and Monazite

Abstract Widespread Paleozoic and Mesozoic granites are characteristics of SE China, but the geodynamic mechanisms responsible for their emplacement are an issue of ongoing debate. To shed new light on this issue, we present an integrated geochronological and isotopic study of detrital zircon and monazite from Cambrian metasandstones and modern beach sands in the Yangjiang region, SE China. For the Cambrian metasandstone sample, detrital zircon displays a wide age range between 490 and 3000 Ma, while monazite grains record a single age peak of 235 Ma. The results suggest that a significant Triassic (235 Ma) metamorphic event is recorded by monazite but not zircon. For the beach sand sample, detrital zircon ages show six peaks at ca. 440, 240, 155, 135, 115, and 100 Ma, whereas detrital monazite yields a dominant age peak at 237 Ma and a very minor age peak at 435 Ma. Beach sand zircon displays features that are typical of a magmatic origin. Their Hf–O isotopes reveal two crustal reworking events during the early Paleozoic and Triassic, in addition to one juvenile crustal growth event during the Jurassic–Cretaceous. The beach sand monazite records intense Triassic igneous and metamorphic events with significant crustal reworking. Such early Paleozoic and Triassic geochemical signatures of detrital zircon and monazite suggest they were derived from granitoids and metamorphic rocks which formed in intraplate orogenies, i.e., the early Paleozoic Wuyi–Yunkai Orogeny and Triassic Indosinian Orogeny. The Jurassic–Cretaceous signature of detrital zircon may reflect multistage magmatism that was related to subduction of the Paleo-Pacific Plate beneath SE China.

Composition and age of monacite fragments from superior jurassic terrigenous sediments of bazhenov formation foundation (multan area in west siberia)

Bazhenov Formation is regarded as the main oil-bearing stratum mothering nearly all the fields of the Western Siberia Oil-Gas-bearing Megabasin. Presently, it is one of the most studied formations of Siberia and, probably, Eurasia as a whole. While there is an enormous amount of studies devoted to the Bazhenov Formation, there are no detailed mineralogical studies at the modern hardware level. The age and sources of the terrigenous materials of the formation have not been studied as well. We have explored the detrital monazite from the upper-Jurassic terrigenous sediments of the Multan Area at the foundation of the Bazhenov Formation in the central part of Western Siberia, Surgut District. All the detrital rare earth phosphate is of the cerium kind being a monazite-(Се). The mineral is rather dissimilar in respect of its chemical properties, especially, the content of thorium. Some fragments have been subjected to superposed secondary changes. The detrital monazite is rounded to various degrees which is indicative of the various distances from the rare earth phosphate orebody washout. As per the chemical data, most of the monazite has been washed out from the medium and basic rocks (probably subalkaline or alkaline) as well as the sialic rocks (granitoids and associated veins). According to the chemical dating, most of the monazite fragments have been washed out of the very ancient Proterozoic formations and lower-Proterozoic rocks. Terrigenous materials derives probably from the rock assemblages of the eastern and south-eastern fringes of the Western Siberian megabasin such as the Proterozoic Yenisei Ridge or Lower-Proterozoic blocks of the Altay and Sayan Faulting.