Mesoproterozoic Age Research Articles

New U-Pb zircon ages from Cadomian basement of the Balkan fold-and-thrust belt of northern Bulgaria

New U-Pb zircon ages are preliminarily reported here from various high-grade units within the overall low-grade Balkan fold-and-thrust belt of northern Bulgaria. The Stakevtsi gneisses yielded Cadomian ages interpreted as magma crystallization ages ranging from 651±8 Ma to 601±3 Ma, some of the samples exhibited a significant proportion of Mesoproterozoic ages with peaks at 1.6 and 1.5 Ga. Paragneisses in the Barzyia Massif exhibit complex U-Pb zircon age patterns, with age peaks typically at 580 Ma and 540 Ma, but also Paleo- and Mesoproterozoic and younger at 430 Ma to 310 Ma. The Divchovoto gneisses yielded age spectra with a minor contribution of Archean, Paleo- and Mesoproterozoic grains and a dominant population of Cadomian ages at 610 Ma. In summary, most of the samples point to the north African provenance, however, some of the Stakevtsi gneisses indicate rather a Baltican provenance. This suggests that the pre-Variscan tectonics and juxtaposition of different terranes was complex in this segment the former Cadomian orogenic belt, but also the possible proximity of Baltica to Gondwana at the end of Neoproterozoic.

Petrogenesis and tectonic setting of mafic magmatism within the Laguna Amarga Metamorphic Complex, Andes of Catamarca, Argentina: Insights into the opening of the Cuyania/Precordillera terrane from the Ouachita rift

Neoproterozoic crystalline basement rocks are exposed as fault-bounded blocks over the high Andes of Catamarca. The crystalline basement is stratigraphically grouped into the unique Laguna Amarga Metamorphic Complex and represents the northern extension of the Cuyania/Precordillera terrane. Tabular bodies of meta-mafic rocks are widespread in the basement interspersed within a thick sequence of meta-sedimentary rocks derived from siliciclastic, calc-silicate, and limestone protoliths. Overall, the geochemical characteristics of meta-mafic rocks are in the compositional range of Normal-Mid Ocean Ridge Basalt (Normal-MORB), reflecting a common depleted-mantle source with varying degrees of partial melting. While preserving the typical bulk chemistry of MORB magmatism, some mafic magma underwent differentiation at emplacement, leading to the development of high-Ti mafic rocks. New U-Pb zircon geochronology reveals three distinct age peaks, with two coinciding with ages identified in the metasedimentary host rocks. The dominant Mesoproterozoic age cluster is linked to inherited zircon crystals assimilated within a single meta-mafic rock. In contrast, zircon ages from the late Ordovician to early Devonian are attributed to metamorphic overgrowths. Notably, the third age cluster, delineates a Late Neoproterozoic magmatic event, indicating the temporal span of mafic magmatism. The finding agrees with the best available age (576 ± 17 Ma) for mafic magmatism on the Precordillera Mafic-Ultramafic Belt. Stratigraphic relationships and geochemical fingerprints enable correlation among the meta-mafic rocks from Laguna Amarga, tracing a belt of mafic magmatism with an oceanic affinity that extends southward. Building upon previous works, this study reaffirms that the rift-drift transition of the Cuyania/Precordillera terrane, linked to the Ouachita rift opening from southeastern Grenville, evolved during the latest Neoproterozoic.

Decoding regressive depositional history from the Neoproterozoic Panium Sandstone Formation, Kurnool Group, India using ‘sequence stratigraphy’ analysis and detrital zircon geochronology

The Neoproterozoic Panium Sandstone Formation of the Kurnool Group (India) offers a unique scope for understanding regressive depositional history in a Neoproterozoic clastic shoreline. It is divided into two ‘Systems Tracts’ namely forced regression and lowstand. Process-based facies and paleo-environmental analysis identified twelve different facies types; grouped under four facies associations (FA I–IV) belonging to both continental and shallow-marine domains viz. distal braided fluvial, swash bar-foreshore runnel, upper shoreface bar-trough, and lower shoreface bar-interbar. Whereas the fluvial deposit (FA I), sharply and erosionally overlying the argillaceous shelf succession of the Owk shelf shale, represents the product of forced regression, the wave-dominated shallow marine deposits (FA II, III and IV) record the depositional history of lowstand in the coastline. A basin ward transition from unconformity (base of FA I) to correlative conformity (base of shallow marine deposits FA II, III, and IV) is documented. The shoreline had a north-northwest to south-southeast alignment and the north-eastward flowing fluvial system met the shoreline at a high angle. Detrital zircon geochronology from the Panium fluvial sandstone allowed documentation of Paleoproterozoic (~2050 Ma–1800 Ma) and Mesoproterozoic (~1500 Ma to ~1200 Ma) age clusters, in addition to earlier documented age clusters from the Banganapalle alluvial sandstone present at the basal part of Kurnool succession. The new age data suggest an addition of new provenances and in turn, tectonic intervention behind the regression in the Kurnool coastline that triggered Panium deposition. Further, the Paleoproterozoic age cluster, obtained from the Panium fluvial deposit, helped in the justification of solitary zircon grain occurrences within the Owk Shale, as described in earlier studies.

TWO PULSES OF MAGMATIC ACTIVITY DURING THE EARLY RIPHEAN KUONAMKA IGNEOUS PROVINCE FORMATION: PALEOMAGNETIC SUBSTANTIATION OF THE HYPOTHESIS

By the beginning of the 20th century, at least ten different generations of intrusive mafic bodies 1800–900 Ma were distinguished on the territory of the Anabar massif. The first modern age estimates, however, indicate the formation of the bulk of these bodies in a relatively short period of time ~1480–1500 Ma. Based on geochronological and paleomagnetic data, intrusive bodies with this age were combined into the Kuonamka large igneous province (LIP). However, a complex of paleomagnetic studies indicated the probable existence of at least two pulses of magmatic activity during the formation of this province, differing in age, possibly by ~20 Ma. We performed a paleomagnetic study of subvolcanic bodies of the main composition of Permo-Triassic (dykes) and Mesoproterozoic (sills) age, emerging to the surface in the valley of the middle reaches of the Kotui River. As expected, the studied dikes contain an ancient magnetization, the direction of which is typical for Permo-Triassic magmatic bodies of the region and the Siberian platform as a whole, and the paleomagnetic directions of the sills are close to those previously determined in the age-related subvolcanic bodies of the Kuonamka igneous province (1501±3 Ma) of the Anabar massif. The data obtained allow us to test the previously proposed hypothesis about the existence of two magmatic pulses ~1480 and 1500 Ma ago during the formation of the Kuonamka igneous province. The results of the analysis of already known and new paleomagnetic data obtained by us do not support this hypothesis. A refined paleomagnetic pole was proposed for the Siberian platform ~1500 Ma ago with coordinates 22.6° S, 65.0° E and A95=4.3°.

Mesoproterozoic age for andalusite in the lower Rocky Cape Group, northwest Tasmania

New U–Th–Pb chemical data from both electron probe microanalysis and U–Pb laser ablation-inductively coupled plasma mass spectrometry on monazite inclusions in giant andalusite porphyroblasts indicate that the lowermost subdivision of the Rocky Cape Group in northwest Tasmania underwent metamorphism at ca 1100 Ma. The Proterozoic Rocky Cape Group is a ∼10 km-thick succession of quartz arenite, siltstone and pelite. These sediments were deposited between ca 1450 and ca 1010 Ma. Metamorphism within the Rocky Cape Group ranges from the prehnite–pumpellyite to upper greenschist facies, locally reaching garnet grade. In the lowermost formation of the Rocky Cape Group, andalusite-bearing mineral assemblages in the Pedder River Siltstone formed prior to or synchronously with monazite development. The andalusite-bearing mineral assemblage indicates relatively low-pressure conditions of <200 MPa, consistent with the stratigraphic thickness of the Rocky Cape Group (∼10 km). However, the presence of the intermediate-temperature biotite–andalusite mineral assemblages (500 °C) in the study area suggests the contribution of additional heat sources. Garnet porphyroblasts were observed ∼2 km away. Similar-age medium-grade metamorphism and magmatism at about 1100 Ma have been observed regionally in the South Tasman Rise and East Tasman Plateau, and in areas that are thought to have been contiguous with northwestern Tasmania such as Dronning Maud Land, central Arizona (Yavapai–Mazatzal) and Belt–Purcell Basin in the southwestern and northwestern Laurentian crustal sequences. The pressure and temperature relationships, mineral associations and regional data suggest additional heat flow was present through the lower part of the Rocky Cape Group. The higher geothermal gradient could be attributed to burial during basin development and deposition of the upper Rocky Cape Group or associated magmatism on the margin of Laurentia during assembly of Rodinia.

Large-scale Mesoproterozoic iron formations in northwestern China

Iron formations (IFs) represent an economically important iron-rich rock type in the Precambrian geologic record. It is generally assumed that after ca. 1.85 Ga, large-scale IFs were not deposited for approximately 1.1 Gy. However, substantial IFs, including over 15 large- to small-scale iron deposits, have been identified recently in Northwest China, and they would constitute the largest Mesoproterozoic IFs globally if their Mesoproterozoic ages can be confirmed. Field observations reveal that these iron deposits are dominantly stratiform and stratoid within the thick clastic-carbonate and volcanic-sedimentary succession. The ores mainly comprise Fe-rich (specularite, hematite, and siderite) and Si-rich (jasper and quartz) minerals with banded or massive structures. Geochemical investigations of typical iron ores show high SiO2 and TFe2O3 and relatively low Al2O3 and TiO2 contents, indicating that they are primary chemical sediments with high hydrothermal and low detrital contributions. These features suggest that these iron deposits in the NQOB are typical IFs, which resemble the Archean and Paleoproterozoic IFs worldwide. New zircon U-Pb dating and lithostratigraphic correlations indicate that these IFs were deposited at ca. 1.1 Ga. The sizable ore reserves and Mesoproterozoic ages confirm that these IFs are the largest reported IFs for the billion years between 1.8 and 0.8 Ga. The large-scale Mesoproterozoic-aged IFs help fill the longest gap in Earth history where the IFs were thought absent from the geologic record and provide an unusual perspective to understand the reappearance mechanism of Precambrian IFs.

U-Pb (LA-ICP-MS) age of detrital zircons from sandstones of the crater part of the V. Grib kimberlite pipe and KL-01 magmatic object, Arkhangelsk diamondiferous province (north of the East European Platform)

Research subject. Detrital zircons from sandstones that contain no admixtures of magmatic material, sampled from the crater parts of the highly diamondiferous V. Grib kimberlite pipe and KL-01 magmatic object. Both objects are located in the north of the East European Platform, within the Arkhangelsk diamondiferous province, at a distance of ≈100 km from each other. Aim. To obtain the first data on the composition of the U-Pb isotope system of detrital zircons from sandstones of magmatic objects of the Arkhangelsk diamondiferous province in order to evaluate the ages of their sources and reveal correlations with known tectono-thermal events in the continental crust of the region. Materials and methods. Using the LA-ICP-MS method, data were obtained on the composition of the U-Pb isotopic system of 52 zircon grains from the sandstones of the V. Grib pipe and 143 zircon grains from the KL-01 sandstones. Results. Sources of various ages from Archean to Neoproterozoic were established for the studied zircons. However, the majority zircons have Mesoproterozoic age, namely 63 and 65% of grains from the V. Grib pipe and KL-01 object, respectively. The sandstones of the V. Grib pipe contain a larger amount of Meso- and Neo-Archean zircons (≈15%) and a smaller amount of Paleoproterozoic grains (≈14%) compared to those from the KL-01 object ≈7 and 20%, respectively. The population of zircons with the U-Pb ages of 900-700 Ma is absent in the two objects. The minimum age of zircons from sandstones of the crater of the V. Grib pipe (557 ± ± 9 Ma) and KL-01 object (609 ± 9 Ma) is consistent with that of formation of the Vendian sandstones in the area of the pipes of the Arkhangelsk diamondiferous province. Conclusions. The obtained U-Pb age for the studied detrital zircons generally correlate with the previously identified stages of tectono-thermal events in the continental crust of the northern territories of the East European Platform, with the exception of the Mesoproterozoic period 1.7-1.4 and 1.3-1.0 Ga ago, which corresponds to the predominant part U-Pb age values of the studied zircons.

On Earth’s habitability over the Sun’s main-sequence history: joint influence of space weather and Earth’s magnetic field evolution

ABSTRACT The aim of this study is to analyse the Earth habitability with respect to the direct exposition of the Earth atmosphere to the solar wind (SW) along the Sun’s evolution on the main sequence including the realistic evolution of the space weather conditions and the Earth magnetic field. The MHD code PLUTO in spherical coordinates is applied to perform parametric studies with respect to the SW dynamic pressure and the interplanetary magnetic field intensity for different Earth magnetic field configurations. Quiet space weather conditions may not impact the Earth habitability. On the other hand, the impact of interplanetary coronal mass ejections (ICME) could lead to the erosion of the primary Earth atmosphere during the Hadean eon. A dipolar field of 30 μT is strong enough to shield the Earth from the Eo-Archean age as well as 15 and 5 μT dipolar fields from the Meso-Archean and Meso-Proterozoic, respectively. Multipolar weak field period during the Meso-Proterozoic age may not be a threat for ICME-like space weather conditions if the field intensity is at least 15 μT and the ratio between the quadrupolar (Q) and dipolar (D) coefficients is $\frac{Q}{D} \le 0.5$. By contrast, the Earth habitability in the Phanerozoic eon (including the present time) can be hampered during multipolar low field periods with a strength of 5 μT and $\frac{Q}{D} \ge 0.5$ associated with geomagnetic reversals. Consequently, the effect of the SW should be considered as a possible driver of Earth’s habitability.

Fluid Flow, Alteration, and Timing of Cu-Ag Mineralization at the White Pine Sediment-Hosted Copper Deposit, Michigan, USA

Abstract White Pine, located in Michigan’s Upper Peninsula, is an archetypal sediment-hosted stratiform copper deposit. The Midcontinent rift system is one of only seven basins globally that host a giant sediment-hosted stratiform copper deposit. Despite many similarities with other deposits of this type, White Pine displays some important differences, including the late Mesoproterozoic age, a thick basalt sequence, an apparent lack of evaporites, and a lacustrine depositional setting. This study analyzes paleofluid flow related to the formation of White Pine and places a particular emphasis on structural and diagenetic fluid pathways. Most of the ore is located in a 30-m-wide zone spanning the Copper Harbor Formation red beds and the overlying Nonesuch Formation shales. Sedimentation of these units was accompanied by subtle synsedimentary faulting. Premineralization phases include calcite concretions and nodules, illite and hematite grain coatings, isopachous chlorite rims, emplacement of liquid petroleum (now pyrobitumen), and bleaching. Mineralization introduced native copper into the footwall sandstones and a zoned suite of native copper and sulfur-poor copper sulfide minerals across a migrating redox front in the overlying shales where copper minerals nucleated on authigenic and detrital chlorite grains. Postmineralization phases include quartz cement, calcite cement, and calcite veins that partially overlapped inversion of synsedimentary faults. Contrary to previous studies, we identified evidence for only one phase of mineralization. An Re-Os chalcocite age of 1067 ± 11 Ma places mineralization 11 to 17 m.y. after host-rock deposition. Sulfide δ34S values of –14.0 to 29.9‰ suggest an important contribution from sour gas and thermochemical sulfate reduction of seawater. Carbon (δ13C) and oxygen (δ18O) isotope compositions of five calcite generations range from –15.1 to –1.3‰ and 10.4 to 41.3‰, respectively, and record early meteoric pore water displaced by later seawater. White Pine is both a sediment-hosted stratiform copper deposit and a paleo-oil field. Synsedimentary faults controlled the sedimentological character of the upper Copper Harbor Formation, and together these imparted a strong control on fluid flow and later diagenetic processes. Early oxidized meteoric fluids were displaced by liquid petroleum and sour gas, which were in turn succeeded by metal-rich but sulfate-poor oxidized seawater. Burial compaction during deposition of the overlying Freda Formation drove fluids through White Pine due to its situation on a paleotopographic high near the basin margin. Mineralization occurred at ~125°C at depths of ~2.0 km and spanned incipient basin inversion related to the distal effects of Grenvillian orogenesis. The hightenor copper mineral assemblage is the product of an abundant supply of metal from basaltic volcanic detritus in the Copper Harbor Formation and low seawater sulfate concentrations in late Mesoproterozoic oceans. This demonstrates that viable sediment-hosted stratiform copper systems can form when a readily leachable metal source rock is present, even if hypersaline and sulfate-rich brines are not.

Mesoproterozoic–Neoproterozoic chronostratigraphic framework and provenance analysis in the southeastern North China Craton and its tectonic significance

The Sishilichangshan area of southwestern Xuhuai Basin, located in southeastern North China Craton (NCC) and to the north of the Qinling–Dabie Orogenic belts, is a key, optimal area to study the regional evolution of the NCC because of its stratigraphic differences within the NCC. An integrated approach of the field investigation, element geochemistry, and detrital zircon U–Pb–Hf isotope analysis reveals essential information on the Mesoproterozoic–Neoproterozoic tectonic‐sedimentary evolution of the Xuhuai Basin. The youngest graphical peak ages of detrital zircons from the Shouxian Formation at the top of the Bagongshan Group, the Jiuliqiao Formation at the bottom of the Huainan Group, and the Anyangshan Formation are 1003 ± 25 Ma, 991 ± 80 Ma, and 832 ± 23 Ma, respectively. New age constraints and stratigraphic correlations show that the traditional Neoproterozoic strata in the southern Xuhuai Basin consist of Late Stenian to Early Tonian Bagongshan and Huainan groups, and the Late Tonian Anyangshan Formation, which overlapped unconformably with mid‐late Ediacaran or Cambrian Series 2 strata. The Anyangshan Formation is first termed in this study, and its equivalent strata occur sporadically in the southeastern, southwestern and northwestern NCC. The Tonian Shouxian, Jiuliqiao, and Anyangshan formations are characterized by detrital zircons of multi‐stage Mesoproterozoic ages and predominantly positive εHf(t) values, with differences in mineral composition, whole‐rock geochemistry, and the Early Neoproterozoic detrital zircon age population. Their possible provenance was a Grenvillian orogen extending from the North Qinling Terrane (NQT) to the central Korean Peninsula, supporting Late Mesoproterozoic to Early Neoproterozoic initial accretion related to the continental arc between the NCC and NQT. Tectonic transition from Late Stenian to Early Tonian (~1.18–0.94 Ga) collisional basin to mid‐late Tonian (0.94–0.74 Ga) rift basin is interpreted as the response of the NCC to the assembly and extension of the Rodinia Supercontinent.

New insights on the interpretation of the provenance and evolution of the Silurian units in the central Precordillera, Argentina

In the central region of the Precordillera, San Juan Province, Silurian silicoclastic sedimentites of the Los Espejos Formation crop out in the Jáchal River area. To the south of this region, an equivalent unit is recognized in the San Juan River area (Tambolar Formation). Both units present similar lithological characteristics, however, it has not yet been defined if they share source areas of detrital contributions. On the other hand, for the Jáchal River sector, it is proposed to establish if there were changes in the regions from where the sub-basin received sediment contributions during the Devonian, which can be seen reflected in the detrital zircon contribution patterns of the overlying unit (Talacasto Formation). The present work is part of a series of studies tending to determine the nature and provenance of the Silurian-Devonian sequences of the Central Precordillera. On this occasion, detrital zircon patterns of the detrital sources of the Los Espejos Formation are analyzed and compared with the information obtained for the Silurian Tambolar Formation (San Juan River area) and the overlying Devonian Talacasto and Punta Negra formations (Jáchal and San Juan rivers areas). To characterize and compare the studied units, different methodologies were applied, namely sedimentary petrography, heavy minerals studies, and morphological and isotopic analyses of detrital zircons. The analysis of thin sections allowed determining textural and compositional parameters. Through the predominance of detrital minerals, it was possible to establish that the studied units are composed of quartzite-type rocks coming from mature areas, with low percentages of lithic components and abundant opaque heavy minerals of the hematite group. The study of heavy minerals, especially morphological and typological parameters of detrital zircons, allowed to establish recycled and plutonic sources as main modes, as well as the changes that occurred during the basin filling dynamics for Silurian and Devonian times. On the other hand, U–Pb isotopic analysis in detrital zircons indicate that the Pampean-Brasiliano orogenic cycle composes the main source of detritus with ages between 511 and 816 Ma. In second place are the Mesoproterozoic ages, represented by the interval from 1000 to 1350 Ma. The youngest detrital ages show a maximum sedimentation age of 478.5 ± 4.4 Ma (Tremadocian), indicating that younger sources of contribution correspond to the Famatinian Orogen. The Kolmogorov-Smirnoff test revealed that the studied Silurian-Devonian units studied have similar patterns of sedimentary contributions, which suggests that the sources of provenance were common in both regions and remained active throughout the entire time interval, without significant changes.

Age and origin of the Cortlandt intrusive complex, New York State: A detailed look at the Stony Point and Rosetown plutons

The Cortlandt Complex is a classic alkaline intrusive complex exposed along the Hudson River in southeastern New York. Early work by James Dana in the 1880s set the stage for over 100 additional studies over the next century. Studies in the past few decades have focused on constraining the genetic relationships between phases of the intrusive complex and the timing of emplacement relative to peak metamorphism and deformation during the Taconic orogeny.LA-MC-ICP-MS U/Pb zircon emplacement ages were obtained on five samples from the Cortlandt Complex. The five samples yielded dates ranging from 443 to 454 Ma, with an overall weighted mean emplacement age of 447.1 +/- 4.5 Ma. Three of the five samples contained inherited zircons, nearly all of Mesoproterozoic age. A sample of the adjacent Annsville Phyllite contained a diverse population of detrital zircons. The most common ages are between 1.25 and 1.85 Ga, although zircons of Neoarchean age are also present.The westernmost and relatively small Rosetown and Stony Point plutons are lithologically and compositionally diverse. Major and trace element trends indicate a complex petrogenesis, which is supported by variable initial isotope ratios. The geochemical data indicate that the mafic magmas were derived primarily from an asthenospheric mantle source, while the inherited zircons and more radiogenic isotope ratios of the silicic units imply a significant crustal component was involved in their formation.The timing and composition of intrusions in the Cortlandt Complex indicate that they are not the result of subduction related to the Taconic Orogeny. We suggest that the mafic units are the result of post-collisional, slab-failure induced asthenospheric upwelling, while the silicic units are primarily partial melts of Grenville-age, garnet amphibolites in the lower crust.

Ground magnetic survey and 3D geophysical model of ultrabasic rocks from the Martín García Complex (Buenos Aires, Argentina)

The Martín García Complex, which crops out at the homonymous island of the Río de la Plata Estuary, is composed of intermediate to silicic orthogneisses and granitoids, hornblende and olivine gabbros, and felsic dykes of Paleoproterozoic and Mesoproterozoic ages, as well as serpentinized ultrabasic rocks of unknown age. A major part of this igneous-metamorphic basement is covered by sediments and vegetation, hiding the relationships between the different rock units, and hindering their study. Therefore, a ground magnetic survey and the consequent 3D geophysical modeling were conducted to elucidate the geometry of the ultrabasic bodies in the subsurface. Normal and reverse dipolar sub-circular and elongated (∼ENE-WSW) magnetic anomalies were identified. It is proposed that Cr-rich spinels would be responsible for some of the detected magnetic anomalies. Our results suggest the existence of three magnetic units with a dyke-type geometry, all of them with ∼ENE-WSW trend and steep dip. The magnetic survey and 3D modeling allowed us to confirm the continuity and extension in the subsurface of the ultrabasic bodies cropping out discontinuously on the surface. According to their crosscutting relationships, a post-Stenian age is proposed for these rocks. Magnetic patterns identified in Martín García Island are similar to those observed in western Uruguay, suggesting that the Martín García Complex would be part of the Piedra Alta Terrane (Río de la Plata Craton).

Late Paleozoic cratonal sink: Distally sourced sediment filled the Anadarko Basin (USA) from multiple source regions

AbstractThe Anadarko Basin (south-central USA) is the deepest basin on the North American craton and occupies a region largely surrounded by major, late Paleo-zoic plate-margin (Marathon-Ouachita-Appalachian) and intraplate (Ancestral Rocky Mountains) orogenic systems, albeit a distal arm of the latter. The Anadarko Basin hosts an exceptionally voluminous record of Pennsylvanian strata, and much of this fill has been attributed to erosion of the adjacent Wichita uplift—composed of granitic and rhyolitic rocks of Cambrian age—separated from the basin by a fault zone exhibiting 12 km of vertical separation. This work incorporates thin-section petrography (102 samples) and U-Pb detrital zircon geochronology of sandstone samples (12 samples) from core and outcrop of the Middle Pennsylvanian Red Fork Sandstone (and equivalents) as well as slightly younger Upper Pennsylvanian units (Tonkawa, Chelsea, and Gypsy sandstones) in order to interpret drainage pathways and evolution of those pathways toward and into the Anadarko Basin (Oklahoma) and evaluate the relative importance of the major provenance regions.Our petrographic analysis indicates sandstones with arkosic compositions are limited to the region immediately adjacent to (north of) the Wichita uplift. All remaining samples, which reflect the vast bulk of sediment in the depocenter, including sediment on the northern and eastern Anadarko shelf, are litharenites. Analysis of kernel density plots of the U-Pb ages of detrital zircons together with multidimensional scaling analysis of the Middle Pennsylvanian samples indicate three groups of similar provenance: (1) samples dominated by Cambrian ages from locations directly adjacent to the Wichita uplift; (2) samples dominated by Neoproterozoic ages from locations along the northern shelf of the Anadarko Basin; and (3) samples dominated by Mesoproterozoic ages from locations along the eastern Anadarko shelf and the basin center. These samples are spatially discrete, indicating partitioning of drainage networks during the Middle Pennsylvanian, with two continental-scale fluvial systems entering the Anadarko Basin from the north (transversely) and east (axially). The lack of Cambrian ages in the depocenter and (northern) shelf samples indicate that the Wichita uplift supplied only limited sediment to the basin; sediment derived from the uplift was trapped in fringing fans directly adjacent to the uplift. In contrast to the patterns exhibited by the Middle Pennsylvanian samples, Upper Pennsylvanian samples exhibit more uniform U-Pb ages across the basin. This indicates the relatively rapid evolution of the Appalachian-derived northerly and easterly drainages into an integrated system that flowed axially across the (overfilled) mid-continent basins to the ultimate continental sink in the Anadarko Basin.

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.

Hyperspectral cathodoluminescence, trace element, and U-Pb geochronological characterization of apatite from the Ernest Henry iron oxide copper-gold (IOCG) deposit, Cloncurry district, Queensland

Hyperspectral cathodoluminescence (CL), geochemical, and geochronological characterization of a series of apatite-bearing samples from within and around the Ernest Henry IOCG deposit, NW Queensland, Australia, have revealed complex mineral parageneses and a spectrum of U-Pb ages that point to the effects of multiple geological processes. No two samples are identical, either in geochemistry or texture, despite their relative proximity to one another (all samples within 5 km from Ernest Henry). Hyperspectral CL maps reveal diverse internal textures and emissions ranging from near infrared (NIR) to near ultraviolet (UV) with a complex series of spectra in all samples, requiring the fitting more than 40 individual peaks (both sharp and broad) to capture the observed variability. Imaging analyses via LA-ICPMS show that apatite from the Ernest Henry district is enriched above background in a variety of trace elements, including Na, Mg, Al, Si, V, Mn, As, Sr, Y, the rare Earth elements (REEs), Pb, Th, and U. Samples outside the ore zone display chondrite-normalized REE profiles that are consistent with either a magmatic or hydrothermal origin, whereas ore zone apatite exhibits profiles that are decidedly hydrothermal in nature. Moreover, specific zones within ore zone apatite grains are very As-rich (up to 7 wt% As2O5), and the effect of such high As on the hyperspectral CL signature of these zones is a pronounced dampening of CL emission, regardless of REE concentrations. Uranium-Pb dating of the same samples (via LA-ICPMS) has yielded a diverse array of overlapping Mesoproterozoic ages ranging from 1,580 ± 34 Ma to 1,533 ± 61 Ma. These results correlate to published ages that constrain hydrothermal alteration in the Ernest Henry area, both before and during Cu-Au mineralization. Collectively, these data highlight the complexity of apatite studies at Ernest Henry, the broader Cloncurry district, and probably analogous terranes elsewhere. A combination of micro-scale methods such as those used in this study are shown to be essential for accurately deciphering geological information contained within petrogenetic indicator minerals.

Qaidam block situated in the interior of Rodinia and Gondwana: New magmatic and metamorphic constraints

Some Precambrian microcontinental blocks, generally embedded in the Phanerozoic orogenic belts, are keys to constrain supercontinent assembly and dispersal as well as play an important role in the ocean-continent transition. The Qaidam block is considered as a Precambrian continental fragment surrounded by Paleozoic orogens. The previous reconstruction models commonly placed the Qaidam block in the peripheries rather than the interiors of the Rodinia and Gondwana supercontinents due to the lack of two global events at 1.2–1.0 Ga and 0.65–0.5 Ga. In this study, we present new zircon U–Pb–Hf isotope data and whole-rock geochemical data for the high-grade orthogneisses and low-grade metavolcanic rocks in the western Qaidam block. Zircon U–Pb dating displays three age groups at approximately 0.55 Ga, 0.75 Ga, and 1.1 Ga. The Ediacaran to early Cambrian age in zircon rims from orthogneisses is interpreted as a metamorphic origin, consistent with the timing of the latest Ediacaran–early Cambrian ultrahigh temperature metamorphism recorded in Mg-Al and mafic granulites. The late Mesoproterozoic age in magmatic zircons of orthogneisses and the middle Neoproterozoic age of metavolcanic rocks reflect two magmatic events. Combining with wide magmatic and metamorphic records of 1.0–0.9 Ga in the Qaidam block, we suggest that the Qaidam block experienced a prolonged subduction–collision process during the late Mesoproterozoic to early Neoproterozoic, followed by a 0.8–0.75 Ga anorogenic event related to the continental rifting environment within an already assembled Rodinia. These data show that the Qaidam block likely maintained a long-term connection with East Gondwana from the late Mesoproterozoic to the latest Cambrian and occupied interior positions in Rodinia and Gondwana rather than in their periphery. It probably did not separate from East Gondwana until the latest Ediacaran–early Cambrian.

Provenance of pre- and Carboniferous sequences of the Esquel-Arroyo Pescado-Tepuel regions (Argentine Patagonia): A combined U–Pb and Hf isotope study of detrital zircon and constraints on depositional setting

Provenance and stratigraphic age of pre-Carboniferous or pre-glacial (Esquel and Arroyo Pescado formations) and Carboniferous glacial (Valle Chico Formation) metasedimentary units exposed in the southwestern sector of the North Patagonian Argentine region are analyzed by sedimentary petrology and combined U–Pb and Lu–Hf isotope on detrital zircons. Additionally, a sample of the Jaramillo Formation (Tepuel Group) allowed comparison and correlation to the Carboniferous deposits in the type area of the Tepuel-Genoa basin.Despite differences, samples of all units studied indicate deposition linked to an arc tectonic environment using ternary petrological diagrams. U–Pb detrital zircon age distribution of the Esquel Formation show a dominance of Famatinian, Pampean-Brazilian and Mesoproterozoic ages, whereas the Arroyo Pescado Formation displays a predominant Mesoproterozoic data cluster. On the other hand, the Valle Chico Formation records a main input of post-Famatinian or Chanic (Devonian) ages and minor Gondwanic (Carboniferous) ages. The Jaramillo Formation is unique due to the remarkable unimodal concentration of Gondwanic ages (Carboniferous) and the scarcity of older than Famatinian detrital zircon ages. The maximum sedimentation age is Lochkovian (Lower Devonian) for the Esquel Formation and, Tournaisian and Tournaisian-Visean (lower Carboniferous) for the Valle Chico and Jaramillo formations, respectively; the youngest records for the Arroyo Pescado Formation indicate a middle Cambrian to Middle Ordovician age. Most Mesoproterozoic zircon grains show a remarkable juvenile Hf isotopic character and a slight age difference between U–Pb and Hf TDM data. These records are equivalent to those identified in different units of the Paleozoic of the Patagonian region and the Malvinas/Falkland Islands, where the Mesoproterozoic detrital zircons with positive εHf (t) values indicative of a juvenile character are present. The conspicuous participation of Mesoproterozic zircons ages within the pre-Carboniferous units supports the probable existence of an unexposed Mesoproterozoic crust in the North Patagonian region, as mentioned by previous authors.The allochthonous or autochthonous character of South Patagonia is tested using combined U–Pb ages and initial Hf-isotope compositions of single zircons. The allochthonous alternative of South Patagonia in the pre-Carboniferous stage, favours contributions from eastern Antarctica, South Africa, Malvinas/Falkland Islands and local sources such as the Deseado Massif and the suspected Chaitenia terrane. An autochthonous scenario suggests that the North Patagonian, Deseado Massifs, Malvinas/Falkland Islands and local areas (Chaitenia terrane) were the main source for the pre-Glacial and Glacial studied units, with minor influence from distant regions of South America.

Sm–Nd isotope whole rock and garnet from the southwestern grenvillian Oaxacan Complex, Mexico: A review of garnet closure temperature and structural implications

The Oaxacan Complex represents the largest outcrop of late Mesoproterozoic age, granulite-facies metamorphic rocks in Mexico. The southwestern Oaxacan Complex was studied using the Sm–Nd isotopic system in whole-rocks and garnets. The use of garnet for dating granulites is a good approach because garnet is usually a rock-forming mineral in this facies, it strongly prefers heavy over light rare earth elements, and its closure temperature is close to the range of the granulite facies. Since the studied garnets display resorbed borders, they are interpreted as pre- or syn- Grenvillian-age granulitic peak. Their closure temperatures, calculated using the Dodson equation and the Nd diffusion coefficients, are 720–770 °C (5–30 °C/my). The whole-rock Sm–Nd evolution lines intersect the depleted mantle model at ca. 1.7–1.4 Ga, although two paraderivate samples intersect at 2.2–2.1 Ga, suggesting a protolith from an older continental crust. In nearby outcrops, Sm–Nd isochron garnet-whole rock ages follow a certain NW-SE trend, displaying two hypothetical age groups: old ages (976-954 Ma) and young ages (920-907 Ma). The younger age garnet's group display Ti and LREE-MREE rim enrichments with respect to their cores that imply diffusional resetting processes. Folding and faulting structures suggest that these two age groups correspond to different structural levels during the early cooling history of the Oaxacan Complex.

An Insight into the Indian Diamond Exploration and Mining: Past and Present

Abstract Indian diamond mining was known the world over for ages, for the production and trading of gem-quality diamonds till the beginning of the 18th century. The ancient Indian writings and the earlier reports of the Geological Survey of India (GSI) provide a wealth of information on the distribution of diamond host rocks, mining, quality, and trade of diamonds. Both primary (kimberlites &amp; lamproites) of Mesoproterozoic age and secondary Neoproterozoic diamondiferous (Neoproterozoic diamondiferous placer conglomerate &amp; gravel) type diamond are confined to the four cratons of Peninsular India, namely the Dharwar, Bastar, Bundelkhand, and Singhbhum Craton. Since 1950s GSI brought out significant results in terms of diamond resources and their grades. The National Mineral Policy paved the way for the entry of Indian and foreign companies into diamond exploration and exploring the known areas. However, diamond rich areas in Chhattisgarh and Madhya Pradesh are yet to be exploited, till such time India will continue to depend on import.