Paleozoic Sedimentary Rocks Research Articles

First record of Halysites catenularius (Cnidaria-Tabulata) from the Silurian of Rancho Placeritos, Central Sonora, Mexico: Paleoecological and paleogeographical considerations

Halysites catenularius Linnaeus is reported from the Silurian strata that form outcrop in the Rancho Placeritos (San Antonio dolostone) located west of Hermosillo, capital of Sonora, Mexico. In this region, a sequence of Paleozoic sedimentary rocks of ages ranging from the Upper Ordovician to the Lower Mississippian is exposed. Halysites catenularius is identified as a reef buildings tabulate coral associated with calcareous algae, sponges, rugose corals, other tabulate corals, bryozoans, brachiopods and, pelmatozoans. The biota developed in shallow tropical seas from southwest of the North American craton, which was located near the paleoecuatorial line. The Silurian platform deposits of Sonora correlate with localities in the southern United States of America and northern Mexico (Sonora and Chihuahua) that were part of the margin of the North American craton. The description of Halysites catenularius contributes to the knowledge of the biota of the lower Paleozoic of Mexico, particularly the Silurian.

Kola-Kanin Monocline Composite Tectono-Sedimentary Element, Barents Sea

Abstract Kola-Kanin Monocline Composite Tectono-Sedimentary Element (KKM CTSE) is located in the Eastern Barents Sea offshore the Kola Peninsula. Tectonically it represents a SW rim of the East Barents Basin, one of the largest sedimentary depocentres in the Arctic. It is also an apparent SE continuation of the Finnmark Platform in the Norwegian Barents Sea; however, there are some differences between them in tectonic history and stratigraphy. The KKM is inferred to include Lower Paleozoic sedimentary rocks. These are not present in the Finnmark Platform due to the Caledonian orogeny. The younger section includes Devonian to Lower Permian siliciclastic and carbonate rocks, Permian-Triassic, Jurassic, and Lower Cretaceous siliciclastic strata. The entire sedimentary section is up to 10 km thick and is divided into three main successions, or tectono-sedimentary elements (TSE): (i) Syn-rift upper Cambrian to lower Ordovician, (ii) Middle Ordovician to Lower Triassic passive margin, and (iii) Middle Triassic to Lower Cretaceous (Albian) intracontinental basin. The KKM represents a potential region for the hydrocarbon exploration, but numerous prospects identified there have not been drilled due to significant exploration risks caused by the monoclinal dip and erosional truncation of the most of the KKM's section.

Условия образования рудовмещающих нижнесреднепалеозойских осадочных формаций Чаткало-Кураминских гор Узбекистана

The article describes stratiform lead-zinc and polymetallic deposits in Paleozoic sedimentary rocks of the southwestern Tien Shan of the Chatkal-Qurama Mountains using rhythmostratigraphic analysis developed by professor at Tashkent State University V. I. Popov (Popov et al., 1963; Popov, 1980). Tectonic movements play a major role in the formation of new structural elements of the lithosphere and the earth's surface. Large tectonic movements spread over large areas and become regional tectonic rhythms. Considerable phases of tectonic movements were divided into smaller phases. We observed the change in formational composition: the boundary and beginning of the rhythm series were dominated by clastic facies of mobile shallow water (surf-clastic), closer to the beltv — quiet-water or stagnant (Popov et al., 1963; Popov, 1980). We stadied the northwestern slopes of the Qurama ridge in the upper reaches of the Karakiya River. Lithological-facies sections and maps of actual materials were made in the study areas. Early Silurian sediments of the were formed in the conditions of a quiet-water (central-sedimentary) shallow-water basin, zones under the influence of bottom currents (bottom current) and deltaic (underwater deltaic) facies belt; Devonian-Lower Carboniferous sediments were accumulated in wave surf zone, bay (shallow-flood belt) and underwater delta (underwater delta belt). Three ore-bearing units with high contents of gold, copper, lead, zinc and a number of other metals were identified in the Lower Silurian terrigenous formations. Black dolomites of the stagnant zone of a shallow-water bay (shallow-bay facies) with high contents of lead were identified in the Devonian sedimentary formations. The confinement of increased concentrations of polymetals to certain layers and units of sedimentary dolomite rocks enriched in organic matter indicates that the accumulation of dispersed ore matter is syngenetic to the sedimentation process.

From early Paleozoic subduction to end-Carboniferous post-orogenic collapse: New constraints on the tectonic evolution of the Central and South Tianshan (NW China)

Recognition of extensional events during orogenesis is critical for the reconstruction of geodynamic evolution of orogens, but is also a challenge due to multi-stage tectonic superimpositions. The South Tianshan is the southern margin of the Paleozoic Central Asian Orogenic Belt (CAOB) and a key for understanding the geodynamic evolution of the CAOB. Here we present new structural, geochronological and geochemical data for the Paleozoic sedimentary, igneous and metamorphic rocks in the Central and South Tianshan (NW China). Based on our new results and published data, we suggest that a neritic to terrestrial back-arc basin existed to the south of the Central Tianshan magmatic arc during the Early-Middle Devonian. We document a crustal anatectic event (∼304 Ma) associated with peraluminous granitic magmatism (∼305–295 Ma) in the South Tianshan. Multi-stage ductile deformation events witnessed the Paleozoic evolution from subduction-accretion to post-orogenic collapse of the Tianshan Orogen: (1) Late Devonian-Carboniferous regional top-to-the-north ductile shearing is related to the southward subduction of the South Tianshan back-arc basins; (2) late Carboniferous south-verging folds and brittle-ductile axial-plane cleavages correspond to back-thrusting resulted from the collision between Central Tianshan and Tarim; (3) latest Carboniferous ductile normal faults developed in migmatites define a dome-like structure linked with syn-anatectic exhumation of the middle crust during the post-collisional extension; and (4) regional dextral strike-slip faulting attributed to Permian lateral extrusion. Therein, two stages of crustal extension are key puzzle pieces to reconstruct the accretionary orogenic processes of the Paleozoic Tianshan.

SOURCES OF THE PALEOZOIC SEDIMENTARY ROCKS IN THE NORA-SUKHOTINO TERRANE: RESULTS OF Sm-Nd ISOTOPIC-GEOCHEMICAL STUDIES

The paper presents the first results on Sm-Nd isotopic-geochemical studies of the Paleozoic sedimentary rocks in the Nora-Sukhotino terrane at the northeastern flank of the South Mongolia-Khingan orogenic belt.According to the studies, the sedimentary rocks of the Zeya-Selemdzha and Amur fragments of the Nora-Sukhotino terrane are characterized by the two-stage Mesoproterozoic Nd-model age (TNd(DM2)=1.62–1.08 Ga) at negative εNd(0)=–9.5…–3.0 and εNd(T)=–5.8...–0.2. Based on previous geochemical and isotopic (U-Pb, Lu-Hf) studies of sedimentary rocks of the Nora-Sukhotino terrane, as well as on the available models for the formation of the South Mongolia-Khingan orogenic belt, it can be assumed that most of the Paleozoic sediments of the Nora-Sukhotino terrane were carried from the Mamyn terrane of the Argun superterrane with the participation of the island arc formations.

Contrasting rare earth element concentrations and mixing behaviors in the St. Lawrence Estuary and Saguenay Fjord

Rare earth elements (REEs) including Yttrium (Y) are commonly used as tracers of estuarine and oceanic mixing. The lanthanide series and yttrium are usually referred to as REYs. The geochemical behavior of REYs in estuarine environments is generally described as being non-conservative, with large-scale removal by particle scavenging. During mixing, partitioning of these elements occurs according to their source function and the stability of natural complexes, with heavy REEs typically forming more stable complexes than light REEs in solution. In this study, we compare the concentrations and partitioning of the 0.7 μm-filtered and 0.05 μm-filtered fractions of the dissolved REYs collected during the summers of 2017 and 2021 in the surface waters (< 3 m) of the St. Lawrence estuarine system (river, estuary and gulf) with those of the Saguenay Fjord, a tributary of the latter that drains the Mesoproterozoic rocks of the Canadian Shield. Whereas REYs do not mix conservatively in the St. Lawrence Estuary (SLE) in the summer, they nearly do so in the Saguenay Fjord (SF). REY concentrations are 2.5 to 6 times greater in the surface waters of the SF than those of the SLE at the same salinity and, in contrast to most estuaries including the SLE, the fjord waters are enriched in LREEs. The 0.05 μm-filtered REY concentrations are positively correlated with dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) concentrations in the SF but independent of both DOC and CDOM concentrations in the SLE. The CDOM in the fjord differs from that of the estuary as it is more aromatic and has a higher molecular weight. The formation of strong REE-humate complexes stabilizes REY ions in the SF surface waters and impedes their adsorption to and scavenging by solid surfaces during estuarine mixing. The LREE enrichment in the SF surface waters most likely reflects the geology of the fjord's drainage basin, more specifically the exposed Mesoproterozoic granites and gneisses of the Canadian Shield that are enriched in LREE relative to the younger Paleozoic sedimentary rocks exposed along the St. Lawrence Lowlands.

Characterization of carbonate veins in graywacke layers from the Humber zone (Quebec, Canada) and implications for strength recovery of damaged rocks by mineral precipitation

The Humber zone's Paleozoic sedimentary rocks, located on the rocky beaches of the Saint-Lawrence River in Quebec, Canada, exhibit interlayered calcareous greywacke beds and ductile shale. Fractures within these layers are characterized by either carbonate veins or barren joints, which are parallel arrays of planar fractures aligned in similar orientations. Fracture initiation occurred at either lithological interfaces or within brittle layers. The thickness of carbonate veins increases linearly with either bed thickness or layer-parallel extension strain, and carbonate precipitation occurred either simultaneously or ephemerally after the fracture opened. For a given bed thickness, veins are more closely and regularly spaced than joints, a feature that was successfully modeled using 2D finite element modeling. Both veins and joints follow a power-law relation between fracture spacing (s) and bed thickness (t), yielding a Weibull modulus of ∼2.5, a tensile strength of ∼9 MPa for the greywacke, and a shear flow strength of ∼1 MPa for the shale at the time of fracture formation. The different s-t relationships observed between joints and veins indicate that carbonate cementation results in 60% strength recovery for greywacke layers in the study area. This approach provides a new constraint on the degree of rock strength recovery due to mineral precipitation into opening fractures under natural conditions. The cementation-induced strength recovery inhibits stress axis permutation, and consequently, suppresses the formation of orthogonal veins.

Ediacaran-Ordovician tectonic and geodynamic drivers of Great Unconformity exhumation on the southern Canadian Shield

The Great Unconformity erosion surface between Paleozoic sedimentary rocks and Archean-Proterozoic basement has been related to erosion occurring during Snowball Earth glaciations, eustatic sea level fluctuations, and a range of tectonic and/or geodynamic mechanisms. Each class of mechanism predicts distinct timing and spatial patterns of exhumation. Snowball Earth glacial erosion is limited to 717-635 Ma and concentrated in narrow ice streams on continental margins. Sea-level related erosion is unconstrained in time but also spatially limited to continental margins. Tectonic and geodynamic mechanisms, in contrast, can result in exhumation distributed more broadly in time and space. We combine new zircon and apatite (U-Th)/He thermochronology data (ZHe, AHe) with independent paleodepth information from a continental interior location in southeastern Ontario, Canada to constrain the timing, magnitude, and regional pattern of exhumation associated with the Great Unconformity along a ∼650 km-long transect across the southern Canadian Shield. Here, the unconformity is defined by Middle Ordovician carbonates atop Archean-Proterozoic basement. ZHe analyses for seven basement samples display a range of dates from 960 ± 20 Ma to 37.5 ± 0.9 Ma that correlate negatively with radiation damage. AHe dates are ∼300-200 Ma and generally consistent across samples regardless of radiation damage. Independent evidence supports emplacement of both the 590 +2/-1 Ma Grenville dikes and the 577 ± 1 Ma Callander Complex in the study region at depths ≥6 km. The combined data require ≥6 km of exhumation between ca. 590-577 Ma and 470 Ma in the middle of our transect, with multi-km erosion up to ≥5 km elsewhere in the study area, well after the ca. 717-635 Ma Snowball Earth glaciations. These outcomes expand the spatial extent of an Ediacaran to early-Paleozoic exhumation signal previously inferred elsewhere across the Shield to ∼1.1 million km2. Thick Ediacaran successions on the Laurentian margins are complementary depositional signals of this erosion. The enormous spatial extent of Great Unconformity exhumation across the continental interior of the Canadian Shield is incompatible with glacial erosion and eustatic sea-level change as the primary causes. Instead, we attribute exhumation to tectonic and geodynamic mechanisms, which may include isostatic rebound, dynamic topography, plume activity associated with the Central Iapetus Magmatic Province, rifting during opening of the Iapetus Ocean, and development of the Transcontinental Arch.

Early Mesozoic orogenic gold mineralization in the North Qinling Terrane: Insights from rutile U-Pb, mica and K-feldspar 40Ar/39Ar, and H-O-S-Pb isotopes of the Yangxie gold deposit

The North Qinling Terrane is located between China’s second largest, Early Cretaceous gold province (southern North China Craton) to the northeast and the third largest, Triassic gold province (western South Qinling Terrane) to the southwest. However, only several small- to medium-sized Au deposits and occurrences have been found so far in the North Qinling Terrane, and their genesis and possible links with the gold mineralization in the above two large gold provinces remain unclear. In this study, we present a comprehensive geochronology, stable and radiogenic isotope geochemistry study of the Yangxie gold deposit in the North Qinling Terrane to provide new insights into gold genesis in the North Qinling Terrane and its genetic relations to the neighboring gold provinces. The Yangxie gold deposit consists of quartz-sulfides veins that are hosted by NW- and NE-striking brittle faults cutting amphibolite- to granulite-facies metamorphic rocks of the Paleoproterozoic to Neoproterozoic Qinling Group. Gold mineralization is represented by four paragenetic stages consisting of milky quartz-K-feldspar (I), light grey quartz-pyrite (II), light grey quartz-polymetallic sulfides (III), and quartz-calcite (IV). Gold was deposited mainly in stages II and III, forming abundant native gold grains that occur as inclusions in pyrite, microfracture infillings in sulfide minerals, or interstitial growths to other ore and gangue minerals. Ore-related alteration assemblages comprise mainly quartz, sericite, muscovite, K-feldspar, and calcite. Hydrothermal rutile is widely recognized in gold ores and texturally intergrown with gold-bearing pyrite and other alteration minerals, indicating synchronous precipitation of rutile and gold. Laser ablation ICP-MS U-Pb dating on two rutile samples yield reproducible dates of 214.6 ± 5.5 Ma (MSWD = 0.82, 2σ) and 210.1 ± 6.9 Ma (MSWD = 1.3, 2σ), which are interpreted as the time of gold deposition. 40Ar/39Ar dating of sericite, muscovite, and K-feldspar from the alteration assemblages yield more scattered and younger dates ranging from 199.8 ± 1.1 to 119.3 ± 0.6 Ma, which are considered as the cooling ages of the deposit related to later tectonothermal events. Oxygen and hydrogen isotopes of ore-related quartz and extracted fluid inclusion waters are 10.4 ∼ 15.0 and −87.7 ∼ -67.2 per mil, respectively. Pyrite and galena have variable δ34S values ranging from −9.4 to 0.5 per mil. These sulfides have lead isotopic compositions of 17.956–18.067 for 206Pb/204Pb, 15.565–15.621 for 207Pb/204Pb, and 38.045–38.301 for 208Pb/204Pb. The isotope data collectively suggest that the ore-forming fluids and metals were derived from the devolatilization of the early Paleozoic sedimentary rocks distributed in the North Qinling Terrane. The results presented here, combined with independent studies, show that the Yangxie deposit was a product of the Late Triassic orogenic gold mineralization event that formed the western South Qinling gold province. Recognition of the Late Triassic Yangxie gold deposit suggests that faults within and around the metamorphosed Paleozoic sedimentary rocks and subsidiary faults affiliated to the Shangdan Suture in the North Qinling Terrane could be favorable targets for further Triassic orogenic gold exploration.

Paleogeographic Reconstruction of Precambrian Terranes Reworked by Phanerozoic Orogens: An Example Based on Detrital Zircon REE From Lhasa Terrane in Southern Tibet

AbstractPaleogeographic reconstruction of Precambrian terranes reworked by Phanerozoic orogens (e.g., the Tibetan Plateau) results in complex lithotectonic relations due to intracrustal reworking by tectonothermal events. Detrital zircon rare earth element (REE) databases at global (global major river sands) and regional (the Gangdese Mountains, southern Tibet) scales reveal trends in and Eu/Eu* that effectively record the crustal evolution of the source, including crustal thickness and redox state of the magma that generated the zircons. Regional comparisons of these chemical markers provide a new approach for paleogeographic reconstructions that we apply to study the origin of the Lhasa terrane, southern Tibet. Using Precambrian to early Paleozoic sedimentary and igneous rocks in the Lhasa terrane and compiling detrital zircon analyses from the northern margin of Gondwana, we show that the Lhasa terrane had an African affinity in the Rodinia–Gondwana supercontinent cycles (ca. 1.4–0.4 Ga).

The Hercynian tectonics in the Tassili-n-Ajjers area, Algeria: A possible continuous stress-strain regime?

This work shed some light on the multiple tectonic phases occurred during the late Hercynian Orogeny that is related to the global plate tectonic geodynamics and their effects in the Tassili-n-Ajjers plateau area, which is located in the south-eastern edge of Saharan platform in Algeria, and known to be the southern margin of the Paleozoic Illizi Basin, wherewell preserved Paleozoic sedimentary rocks outcrop. Three Hercynian tectonic phases have been evidenced in the area are: Early Carboniferous (E1), Late Carboniferous-Permian (E2), and a Late Permian-Early Triassic (E3). The Hercynian tectonic regime in the Tassili-n-Ajjers area that was dominated by strike-slip movements during E1 and E2 tectonic phases changed into an extensional regime during E3 tectonic phase. Paleo-strain determination, folds axis distribution and the kinematic analyses of the strain field of the Hercynian active tectonic show a continuous deformation regime rather than discrete tectonic phases. Moreover, the progressive deformation regime is strongly supported by the absence of tectonic unconformities between Late Devonian/Early Carboniferous - Early Permian. At a large-scale, this continuous deformation appears as a result of a progressive closure of Rheic and western Paleotethys Oceans, and the clockwise rotation of African plate which occurred during the Hercynian/Variscan orogeny. Therefore, we could consider that the most part of Algerian Saharan platform has registered the far-field effects of this orogeny and provides a suitable illustration of an intracontinental deformation.

Petrography and geochemistry of successions from northwest Bolivia

A complete section of Paleozoic sedimentary rocks has been sampled in northwest Bolivia to investigate compositional changes based on petrographic but mainly geochemical data. Studies of Paleozoic succession in southern Peru, northern Chile and northwest Argentina allowed to decipher the paleotectonic history of the region for the Paleozoic (e.g. compilations in Bahlburg et al., 2009). However, a few is only known about the area geographically in between. We focus here on an area in the vicinity of the capital La Paz, where the Paleozoic belongs paleogeographically to the so-called ‘altiplano’ and the ‘Cordillera Oriental del Norte’ and tectonically to the ‘Faja de Huarina del Norte’. The objective of the study is, hence, to establish a first complete stratigraphic insight of the Paleozoic to enable further studies on key formations or horizons. While the abovementioned areas to the north and south do reflect in the sedimentary record the emergence of a continental arc during the Ordovician, followed by a significant tectonic quiescence during the late Silurian and Devonian and succeeded by the evolution of a second active margin with a continental arc during the late Paleozoic, these events are not visible in the Bolivian samples which is sandwiched between the westerly Arequipa Massif and the eastern Sunsas belt, both composed of mainly metamorphic rocks.The Paleozoic section in northwest Bolivia shows highly recycled quartz-arenites of Ordovician age followed by Silurian and Devonian successions mainly composed of subangular to surrounded detritus, moderately sorted, devoid of significant typical metamorphic detritus. During the late Paleozoic, the rocks tend to a larger variability, partly even poorly sorted, higher amount of angular grains and the occurrence of volcaniclastic debris. Geochemically the same trend can be observed, with strongly recycled successions during the Ordovician (Zr/Sc 20–200) followed by moderately recycled rocks (mainly Zr/Sc 10–20100) with typical trace element composition for unrecycled upper continental crust (UCC). During the Permian, sediments which are less weathered and slightly less fractionated in their overall geochemical composition, have been deposited. The geochemistry may point to the evolution of late Paleozoic volcanism, recorded in overlying, but however, Triassic rocks. Significant increase or even typical UCC values of compatible elements or ratios are absent besides Cr and Ni increase in Ordovician rocks. The absence of any significant input of arc related detritus can be explained by not effective sediment dispersal system to transport arc related detritus into the depositional area. The low compositional and low to moderate textural maturity throughout the entire post-Ordovician stratigraphy implies relatively proximal sources and insignificant intra-basinal recycling. This together with the absence of metamorphic detritus, allows in proposing thick homogeneous sedimentary successions with low or no metamorphic overprint as major sources. Those covered possibly the today exposed metamorphic successions of the aforementioned basin surroundings. Sedimentary or any other lithologies older than the Ordovician and younger than Mesoproterozoic are nearly unknown in the region, besides one exception (Chilla beds; Bahlburg et al., 2020). Those hypothetical deposits would be at this stage of knowledge the best explanation.

Alpha spectrometry isotopic ratios indications in the Paleozoic sedimentary rock of El Gor area, Southwestern Sinai, Egypt: insights on uranium mobility age

The study area is located between longitude 33° 18' 00" − 33° 21' 00" E and latitude 28° 59' − 29° 01' N and covers approximately 700 km2. Uranium and thorium isotopes were determined by alpha spectrometry. The activity concentrations of 238U, 234U and 235U were ranged between 245.5 ± 8.3–465.2 ± 15.2 Bq.kg−1 with an average 345.5 ± 10.4–452.5 ± 9.3 Bq.kg−1 and 890.5 ± 21.3 Bq.kg−1 with an average 632.3 ± 14.9–11.40 ± 0.5 Bq.kg−1 and 21.50 ± 1.4 Bq.kg−1, respectively. The activity concentration of 232Th, 230Th and 228Th were ranged between 153.1 ± 0.3–318.1 ± 2.9 Bq.kg−1, 149.5 ± 0.7–280.8 ± 2.2 Bq.kg−1 and 36.9 ± 0.1–60.5 ± 0.9 Bq.kg−1. The 230Th/232Th activity ratios in all samples were lower than 20, indicating that these samples have been contaminated by detrital 230Th. Th/U ratio varied between 1.3 and 2.1 with an average 1.8; all values were lower than 3.5, indicated enrichment of uranium. 234U/238U activity ratios that higher than unity indicates that an isotope of uranium has migrated within the rock. From the isotopes of uranium and thorium and their activity ratios, the isochron age for the collected samples was about 58.96 ka.

New insights of the crustal structure across Estonia using satellite potential fields derived from WGM-2012 gravity data and EMAG2v3 magnetic data

Global WGM-12 gravity and EMAG2v3 magnetic models were used to present new information of the Estonian crust. The Estonian Precambrian crystalline basement, composed of Paleo-Meso Proterozoic metamorphic and igneous rocks, is covered by a Paleozoic sedimentary rock deposit 100–800 m thick. The present work aims to map structural patterns and recognise physical layers of the crust over Estonia using global potential models. The gravimetric data was used to identify the depth of the Moho and Conrad discontinuities. The magnetic data has been processed to calculate the Curie point depth (CPD), which was then used to estimate heat flow (HF) values in the study area. The depth of the Moho indicates an average value of 60 km, while the average depth of the Conrad discontinuity is around 18 Km. The depth of the CPD reveals an average value of 15 km. Different derivative techniques were applied over the residual part of both potential models, to delineate and map geophysical lineaments. The subsurface of Estonia has been divided into six petrological-structural zones: Tallinn, Alutaguse, Jõhvi, West-Estonian, Tapa and South-Estonian. Geophysical lineaments in each zone subsurface division delineates a NW-SE trend, perpendicular to the NE-SW oriented Fenno-Sarmatian collision. To visualise the anomalous crustal variations over Estonia, different profiles showing varying values of potential fields, CPD and heat flow are presented, especially around the Precambrian Rapakivi granitic plutons and in the Paldiski-Pskov deformation zone, due to the high contrast observed by mapping the different results over these areas.

Provenance of lower Paleozoic sedimentary rocks in Tasmania and Waratah Bay, southern Victoria: constraints from detrital zircon hafnium isotopes and trace-element geochemistry

Nine Paleozoic sedimentary formations from western Tasmania and two from the Lachlan Orogen—one in northeast Tasmania and one in Waratah Bay in Victoria—contain detrital zircons that fall into major U–Pb age clusters at 2.0–1.4, 1.25–0.95 and 0.62–0.49 Ga. The zircon Th/U ratios and rare earth element (REE) patterns suggest a magmatic origin for detrital zircons in all these rock sequences. The REE geochemical signatures on bivariate discrimination diagrams indicate that most of the zircons originated in continental orogenic settings. The oldest group of zircons have a southwest Laurentian signature previously recognised from Proterozoic metasedimentary rocks in Tasmania. The 1.25–0.5 Ga zircons from all the samples have very similar εHfi values. They are not statistically different from those of typical Lachlan Orogen sandstones and resemble those in Rodinia and early Gondwana orogenic belts. The εHfi values of the Cambrian zircons within the Pioneer Sandstone are similar to the Mount Read Volcanics but cannot be distinguished on εHfi values from other sources in East Gondwana. The detrital zircon provenance of the Bear Gully Chert Bed at the base of the Digger Island Marlstone at Waratah Bay includes the west Tasmanian Proterozoic, the East Gondwana margin and the Macquarie Arc. This mixed provenance provides evidence for the late Cambrian docking of VanDieland with East Gondwana. KEY POINTS New zircon Hf isotope data are reported for early Paleozoic sedimentary rocks in Tasmania and Waratah Bay, southern Victoria. The western Tasmania basement was the dominant source for Tasmanian sandstones and a minor source for the Lachlan Orogen sandstones on the northeast margin of VanDieland. The mixed provenance of the Bear Gully Chert supports a late Cambrian accretion of VanDieland to the East Gondwana margin. The youngest zircons in the Bear Gully Chert at Waratah Bay were potentially sourced from the Macquarie Arc.

Fault Orientation and Relocated Seismicity Associated with the 12 December 2018 Mw 4.4 Decatur, Tennessee, Earthquake Sequence

AbstractSmall-to-moderate size earthquakes have occurred along the Eastern Tennessee Seismic Zone (ETSZ) for decades, resulting in the second highest seismicity rate in Central and Eastern United States following the New Madrid Seismic Zone. However, the underlying tectonic setting of seismicity in the ETSZ remains unclear. The recent December 2018 Mw 4.4 earthquake near Decatur, Tennessee, provides an opportunity to study one of the largest recent events in this region, after the 2003 Mw 4.6 Fort Payne, Alabama, earthquake. Here, we use a matched filter technique to detect additional microearthquakes around the Mw 4.4 mainshock. We create templates from 967 cataloged earthquakes spanning over 15 yr (January 2005–July 2020) in the ETSZ. These templates are used to detect missing events four weeks before to four weeks after the mainshock. We calculate the magnitudes of new events using principle component fitting between templates and newly detected events. Two relocation algorithms, XCORLOC and hypoDD, are used comparatively to relocate detected events. We construct focal mechanism solutions for earthquakes around the mainshock using HASHpy, and refine the focal mechanism and depth solution of the mainshock using the cut-and-paste method. The mainshock appears to have occurred at a depth of approximately 5–6 km, which is deeper than the decollement (4–5 km) that separates the Grenville-age basement rock and the Paleozoic sedimentary rock. In addition, the mainshock appears to rupture bilaterally along an east–northeast-trending strike-slip fault, which is consistent with the relocated aftershock locations and one of the nodal planes of the mainshock. The occurrence of the 2018 Mw 4.4 mainshock at a relatively shallow depth and its close proximity to the Watts Bar Nuclear Power Plant highlight the need to reevaluate seismic hazard associated with moderate-size earthquakes along the ETSZ.

Controls on Timing of Hydrothermal Fluid Flow in South-Central Kansas, North-Central Oklahoma, and the Tri-State Mineral District

Paleozoic sedimentary rocks in the southern midcontinent of the United States have been affected by multiple events of deformation and fluid flow, resulting in petroleum migration, thermal alteration, Mississippi Valley-type mineralization, and a complex diagenetic history. This record is a hidden history of how cratonal settings respond to tectonic and non-tectonic drivers. The aim of this contribution is to better understand the controls on fluid migration in Paleozoic strata to evaluate whether hydrothermal activity is forced by tectonic or non-tectonic processes. This paper summarizes and vets the distribution of published dates related to thermal events in the southern midcontinent. In addition, we present new U-Pb dates obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) on calcite cements that were formed from hydrothermal fluids. These are from three samples from the Berexco Wellington KGS 1-32 core in Sumner County, Kansas; an ore sample from the Tri-State Mineral District, Neck City, Missouri; and a core sample from the Blackbird 4-33 well in Osage County, Oklahoma. Previous studies of these calcite samples provided evidence for hydrothermal fluid flow, with one of the Wellington samples possibly recording vertical hydrothermal fluid flow out of the basement. The sample from the Tri-State Mineral District (Missouri) yields a mid-Cretaceous age of 115.6±3.1 Ma. This age falls into the timing of the Sevier Orogeny along the west coast and the development of its foreland basin in the midcontinent. Calcites from the Mississippian interval in the Wellington KGS 1-32 core yield dates of 305±10.5 Ma and 305.1±9.1 Ma. Calcite in Mississippian strata from the Blackbird 4-33 core yields a date of 308.6±2.5 Ma. These dates from Mississippian calcite cements indicate hydrothermal fluid flow in the Late Pennsylvanian that coincides with the timing of the Marathon-Ouachita Orogeny or the Ancestral Rocky Mountains Orogeny. A calcite sample from the Ordovician Arbuckle Group from the Berexco Wellington KGS 1-32 core yielded an age of 5.6±1.6 Ma, coinciding with a time after high elevation uplift of the Rocky Mountains was already far advanced. We propose that this hydrothermal fluid flow may have been associated with increased meteoric recharge and increased regional fluid pressure in a basement aquifer that activated local seismic events far into the continental interior. The distribution of ages of hydrothermal fluid flow confirms a syntectonic driver during the Ouachita Orogeny and Ancestral Rocky Mountains Orogeny deformation. Continuation of hydrothermal fluid flow well into the Permian and tailing off early in the Triassic indicates a post-tectonic driver, where uplifted areas continued to provide the recharge from gravity-driven fluid flow, until the mountains were mostly beveled by the early part of the Triassic. A dearth of Triassic and Jurassic hydrothermal events suggests Gulf of Mexico rifting and extension were less important. Rejuvenation of hydrothermal fluid flow in the Cretaceous and continuing into the Paleogene indicates that elevation and regional flexure from both the Sevier and Laramide events continued to drive hydrothermal fluid flow far from the main sites of mountainous uplift and deformation. Finally, hydrothermal fluid flow associated with more recent uplift of the Rocky Mountains may have been activated by recharge events that pressurized a regional basement aquifer and triggered seismic activity.

Cambrian–Silurian sediments in the southeastern Qilian Orogen, NE Tibetan Plateau: Constraints on crustal and tectonic evolution of microcontinents in the northern Proto-Tethys Ocean

The Qilian Orogen preserves abundant Early Paleozoic records, revealing the tectonic evolution of the northern Proto-Tethys Ocean on the periphery of the northern margin of eastern Gondwana. We present detrital zircon U–Pb and Hf isotopes, and whole-rock element and Nd isotopic geochemical data on the Early Paleozoic sedimentary rocks in the southeastern Qilian Orogen. Detrital zircon grains from these rocks are clustered into seven distinct age groups: 495–426 Ma, 710–501 Ma, 1043–726 Ma, 1347–1054 Ma, 2009–1609 Ma, 2874–2274 Ma, and >3100 Ma. Detrital zircon and geochemical results suggest that their provenances are Early Paleozoic subduction–accretion related rocks, Neoproterozoic basements of the Qilian Block, and recycled sediments from Precambrian units. The whole-rock εNd(t) values of the sedimentary samples range from –13.0 to 2.5, and the εHf(t) values of Neoproterozoic–Early Paleozoic detrital zircon grains range from –28.6 to 15. Hf and Nd isotopes indicate marked growth and reworking of the continental crust in the early Neoproterozoic and Ordovician–Early Silurian. As revealed by age spectra of detrital zircon, we infer that the Qilian Block was tectonically related to blocks on the northern margin of eastern Gondwana during the Early Paleozoic, such as the North Qinling, Indochina and South China blocks. We also suggested that the Qilian Block experienced double-sided subduction of the North and South Qilian oceans, and developed sedimentation in the inter-arc and back-arc basins during the Ordovician to earliest Silurian. Finally, sedimentation occurred in an Early Silurian retro-arc foreland basin and Middle Silurian foreland basin during the syn-collisional stage.

Provenance of late Paleozoic sedimentary rocks in eastern Kazakhstan: Implications for the collision of the Siberian margin with the Kazakhstan collage

• The sedimentary provenance is different across the Char Shear Zone in eastern Kazakhstan. • The Char Shear Zone represents the suture between the Siberian margin and the Kazakhstan collage in eastern Kazakhstan. • The oceanic basin between the Siberian margin and the Kazakhstan collage was closed after 321 Ma. To unravel when, where, and how multiple arc systems were amalgamated is crucial for understanding the accretion processes of the Central Asian Orogenic Belt. Here we focus on the collision of the Siberian margin and the Kazakhstan collage along the Char Shear/Suture Zone in eastern Kazakhstan. We conducted U–Pb dating and Hf isotope analysis for detrital zircons of clastic rocks across the collisional zone of the Siberian margin (the Irtysh-Zaisan Complex) and the Kazakhstan collage (the Zharma-Saur Arc and the Char Zone). Our results show that the Irtysh-Zaisan Complex carries abundant early Paleozoic detrital zircons and minor Precambrian zircons, but there is a lack of such zircon populations in the Zharma-Saur Arc and the Char Zone. Devonian to Carboniferous detrital zircons appear in all sampling tectonic units, in which ε Hf (t) values of Carboniferous zircons from the Zharma-Saur Arc and the Char Zone are characterized by a narrow range (∼10–17) that is different from a relatively wider range of ε Hf (t) values of ∼5–18 for the Carboniferous zircons in the Irtysh-Zaisan Complex. The distinct sedimentary provenances of the Irtysh-Zaisan Complex and the Zharma-Saur Arc/Char Zone confirm that their tectonic boundary lies along the Char Shear Zone in eastern Kazakhstan. As the Late Carboniferous sedimentary rocks from the Zharma-Saur Arc and the Char Zone do not receive detritus from the Siberian margin, we consider that the Ob-Zaisan Ocean between the Siberian margin and the Kazakhstan collage was closed later than the deposition of these sedimentary rocks (<321 Ma).

Patterns of distribution and peculiarities of formation of gold ore mineralization in metamorphic and black shale strata of Azerbaijan

&#x0D; &#x0D; &#x0D; &#x0D; The article discusses the patterns of distribution and the peculiarities of the formation of gold mineralization in the metamorphic and black shale strata of Azerbaijan in order to determine metallogenic specialization. Mineragenic analysis of gold-bearing territories was carried out using numerous data of quantitative studies of the substance of the studied objects: ore-bearing sedimentary and metamorphic strata, ore bodies and processes ore genesis. The spatio-temporal relationships of gold-bearing mineralization of various material-morphological types, conditioned by lithological-geochemical conditions and time of manifestation of lithogenetic processes and metamorphism, have been determined. In the petrographic description of the studied rocks, two groups were distinguished: Early Paleozoic crystalline shales and Upper Paleozoic sedimentary rocks. It has been determined that the shales were initially enriched with gold during sedimentogenesis. In subsequent processes of metamorphism, part of the gold was removed from the shale and redeposited, and thus spread unevenly. Favourable zones of ore deposition could lead to the concentration of gold in shales in industrial conditions. In the studied crystalline shales, attention is drawn to the contents of Pt and Pd, the commonest elements of the platinum group. The Pt content in shales is 0.08 g / T on average, while the clarke for clayey shales is 0.03 g / t, i. e. almost three times higher than the clarke. Even more contrasting is the content of the platinum group element, palladium. In shales, the Pd content is 0.046 g / t. These data, together with the high gold content in the shales, can be considered as a typomorphic geochemical feature of the crystalline shales of the Asrikçay massif of the pre-Jurassic basement of the Lesser Caucasus. The studies have shown that during the formation of gold mineralization in metamorphic and black shale strata, an important role was played by the features of the host carbonaceous sedimentary complexes, which served as additional sources of noble and associated metals. Some of the ore elements in unaltered sediments have their own mineral forms.&#x0D; &#x0D; &#x0D; &#x0D;