Eastern Domain Research Articles

Block Rotations in NW Iran in Response to the Arabia‐Eurasia Collision Constrained by Paleomagnetism

AbstractNorthwest Iran is a seismically active region dominated by NW‐SE trending strike‐slip faults, such as the North Tabriz and Qosha Dagh faults, and smaller NNE‐SSW striking faults. The Bozgush Mountains are shaped by these faults and divided into two domains that show a difference in strike. To quantify rotational tectonic deformation in NW Iran, we performed a paleomagnetic study along three transects of the Bozgush and Qosha Dagh Mountains with 127 sites. Our large new paleomagnetic data set shows that the Bozgush Mountains did not rotate as a single rigid block. In the western domain of the Bozgush Mountains, we find evidence for clockwise vertical axis rotations of ∼40°, while the eastern domain has rotated up to ∼80° clockwise. Declinations of the western Bozgush domain fit well with observed declinations in the Qosha Dagh Mountains. Fault patterns show that the eastern domain of the Bozgush Mountains is divided by a set of NNE‐SSW striking sinistral strike‐slip faults, which created domino‐style blocks that accommodated the additional 40° of rotation. We estimate that these extra rotations have resulted in around 4 km of N‐S shortening and more than 1.5 km of differential uplift.

Influence of spatial and seasonal asymmetries on long-range tropical cyclone prediction in the western North Pacific

The seasonal predictability of tropical cyclones (TC) in the western North Pacific (WNP) reported in previous studies are mainly based under the general consideration that the WNP is homogeneous in terms of its spatial and temporal characteristics. Here we present evidence that the western (Domain 1) and eastern (Domain 2) parts of the WNP exhibit spatial and seasonal asymmetric response to large-scale environments (e.g., asymmetrical sea surface temperature anomalies distribution) leading to distinct spatial and seasonal TC variability in the said domains. Exploring such asymmetries, we propose an alternative approach on the long-range predictability of TC genesis frequency in the WNP during its active TC season (i.e., June-November, JJASON) by separately predicting the TC genesis frequency in two domains (i.e., Domains 1 and 2) in two distinct seasons (i.e., June-August and September-October), respectively. Using a number of climate indices as predictors in different lead times, our regression-based models present its best significant seasonal predictability of TC genesis frequency during JJASON (i.e., r = 0.80, p < 0.01) that essentially captures the spatial and seasonal asymmetry in the WNP. It is expected that this study provides valuable insights on the long-range and more localized TC prediction in support of disaster risk reduction in the WNP region.

3D Crustal Architecture and Along‐Strike Variation in the Mid‐Northern South China Sea Rifted Margin

AbstractRifted margins often show apparent along‐strike variations at the continent‐ocean transition (COT) region, typically occurring gradually over hundreds‐to‐thousands of km between the “magma‐rich” and “magma‐poor” endmembers. In contrast, comparatively smaller‐scale lateral variabilities of rifting structure and faulting style in hyper‐thinned continental crust are not yet well described. The South China Sea (SCS) was recently defined as the archetype of a new “intermediate‐type” margin with neither excess magmatism nor mantle exhumation. However, along‐strike crustal variations along this new type of margin are still little explored. Based on previously unpublished 2D grid of seismic reflection lines and overlapping 3D seismic volumes, we have investigated the crustal structure, faulting style, and the lower crustal reflectivity along ∼400 km of the mid‐northern SCS margin. Our new maps of crystalline‐crust thickness and top basement show that the SCS extension developed in two segments with contrasting tectonic styles separated by a narrow boundary. The eastern domain, resembling a wide‐rift model, displays low‐angle detachment faults and high‐velocity lower crust mainly associated with syn‐rift magmatism indicating weak crustal rheology. The neighboring western domain, resembling a narrow rift model, displays steep crustal‐scale faults indicating comparatively strong rheology. The change from wide to narrow rift—or weak to strong rheology—occurs abruptly, which appears at odds with the current conventional wisdom of mostly gradual transitions over a long distance between rift models. We speculate that the inherited heterogeneity in mantle composition and 3D melt focusing effect may drive this abrupt along‐strike variability in the mid‐northern SCS.

Climate bottlenecks off Newfoundland and Labrador for Atlantic cod in relation to eastern Canadian marine protected areas

Climate change presents challenges for marine area-based conservation measures through altered habitat and associated species range shifts. We conducted statistical downscaling for the eastern Canadian coastal domain over a range of global climate models, focusing on habitat suitability for Atlantic cod ( Gadus morhua), a numerically depressed, but ecologically, economically, and culturally important species in this region. We examined cod egg survival, juvenile growth, and spawning habitat suitability, combining these into one habitat index to compare within-closure habitat suitability for multiple life stages through time. Areas of high cod egg habitat suitability are projected to shift northward and increase across all area closures studied, while optimum juvenile habitat shifts north and eastward, increasing in almost all closures except the south. Spawning habitat as a function of temperature and oxygen will likely decrease through time across the entire region, but less in northern locations. Overall cod habitat is forecasted to decline in the south of the region while increasing at central and northern latitudes, highlighting the importance of existing and developing northern shelf area closures. While warming will bring temperatures closer to optimum levels for cod in this cold-water system, oxygen limitation will become more prevalent in the south of the region and should be monitored as an important ocean health indicator.

Assessing the control factors upon glacial valley development in southernmost Patagonia (Fuegian Andes of Argentina)

Research on landscape glacial modelling provides particularly relevant information about the complex connection between climate change and relief evolution. Glacial valleys – the most distinctive landforms in alpine-type settings – were systematically mapped across the Fuegian Andes of Argentina, southernmost Patagonia, and quantitatively investigated in terms of the geoenvironmental agents that controlled their formation. A total of 646 troughs were identified and studied in four sub-areas with contrasting past glacial cover. Our observations demonstrate that longer valleys are also the deeper, less steep (in long profile), more sinuous and lower, and that maximum elevation was the main control of altitudinal range, mean and maximum slope, and minimum depth. Overall, it is considered that valley development was subject to conditioning by pre-glacial topography, geological structure and climatic forcings. Specifically, valley's spatial arrangement indicates that glaciers responsible for their erosion (possibly during the early Pleistocene) adjusted to a fluvial drainage network organized according to a marked structural control, mainly associated with Magallanes-Fagnano and Canal Beagle regional strike-slip systems. The predominance and higher degree of development of southern slope valleys reveal that north-south differential insolation effect was determinant in the Fuegian glaciers' balance during extensive time-lapses in glacial cycles, likely reflecting a scenario of relative aridity and comparatively clear skies. Morning-afternoon contrasts in solar radiation receipt and, specially, humid winds from the west (regional westerlies) would have also produced a moderate eastward bias in valley direction. In the western and central sectors, formerly covered by the Cordillera Darwin Icefield, the surface of Fagnano and Beagle outlet palaeolobes and other major collectors constituted a comparatively high base level for mountain glaciers' incision during full glacial conditions, leading to the creation of profuse, short hanging valleys. In the eastern domain, on the contrary, glaciers appear to have been essentially regulated by the topoclimatic factors, attaining greater dimensions and flowing down to lower altitudes in south- and southeast-facing slopes. Finally, in marginal, lower mountains (away from the main chain axis) ice is thought to have formed only under the most severe glacial episodes in the zone.

Geochemical characteristics and ore-forming mechanism of Luodian nephrite deposit, Southwest China and comparison with other nephrite deposits in Asia

A nephrite deposit was recently discovered in Luodian, Guizhou Province, which belongs to the South China Plate and is located in the eastern Tethys tectonic domain. This study examines systematically the geochemical characteristics and mineralization mechanism of Luodian nephrite using various analytical techniques including polarized light microscopy, scanning electron microscopy, electron probe microanalysis, and laser ablation-inductively coupled plasma-mass spectrometry. The results show that the main mineral of Luodian nephrite is tremolite, and the secondary minerals include diopside, calcite, quartz, albite, talc, and iron and manganese oxides. The tremolite was present in three morphological forms which have the characteristics of multi-period mineralization. The Mg2+/(Mg2++Fe2+) ratio indicates that the Luodian nephrite deposit is a dolomite-related type deposit. The trace elements of Cr, Ni, and Co, and the ratios of Rb/Sr and Rb/Ba are much lower than those serpentinite-related type nephrite, and are within the range of those for basic magma contact metasomatic nephrite. The rare earth elements (REEs) show that the formation of Luodian nephrite originates from metasomatism of sedimentary rocks. Curves for the distribution of the chondrite-normalized REE pattern and the characteristics of the REEs in nephrite are identical to those for marble or limestone, and are clearly different from those for diabase, indicating that the formation of nephrite occurrs closer to the surrounding rock. Combined with chemical analyses and a geological survey, the results show that Luodian nephrite was formed by the contact metasomatism of basic diabase and carbonate rock during the Indosinian-Yanshannian (Late Triassic to Cretaceous) period. The diabase magma provided a high-temperature environment and the Si hydrothermal environment; the presence of the carbonate rock facilitated Ca and Mg to form nephrite under specific physical and chemical conditions. The comparison of geochemical compositions can help to distinguish the genetic type, reaction mechanism and origin characteristics of nephrite deposits. These results provide theoretical guidance for the search for nephrite deposits of dolomite-related type origin.

Республика Бурятия в панораме 100-летия: исторические вехи и достижения

Goals. The article aims to consider some key historical milestones and achievements in Buryatia’s nation-state building for over 100 years. The paper analyzes the conditions for the emergence of Buryat-Mongolian autonomy, and the factors that prompted reorganizations of the Republic’s political structure in the context of changes witnessed in the nationwide political agenda. Special attention is paid to the contribution of the Republic to the Great Victory, certain analytical emphases be laid on present-day challenges, achievements and development prospects. Materials and methods. The work examines unpublished documents stored at the State Archive of the Russian Federation, Russian State Archive of Sociopolitical History, and State Archive of Buryatia. The principles of historicism and consistency prove instrumental enough in reconstructing the process of nation-state building in Buryatia, identifying specific features, and tracing general trends of state development in the Republic’s political life. Results. On 30 May 1923, the Presidium of the All-Russia Central Executive Committee decided to unite Siberian and Far Eastern autonomous domains (oblasts) of Buryat-Mongols into one autonomous socialist Soviet republic centered around the city of Verkhneudinsk. It is then and there that the statehood of Buryat-Mongols — consolidated by a single territory, economic integrity, and historical ties of all resident peoples — was proclaimed. The shaping and rapid development of industries in the Republic, transformations in agriculture, education and health care converted the territory of Buryatia into a strong supporting point that would render every possible assistance to the nation during the Great Patriotic War. The post-war years up to the 1960s and early 1970s became a period of progressive development in all spheres of life. At the all-Union level, merits of the Republic were distinguished with the Order of Lenin (1958), Order of Friendship of Peoples (1972), and Order of the October Revolution (1973). Events of the late 1980s and the subsequent collapse of the USSR served as a test of state viability to the Republic. The economic depression led to an unprecedented deterioration of the social situation which could actually result in a severest interethnic conflict. However, the accumulated experiences of cross-cultural interaction, flexible administrative and managerial systems, high educational and scientific levels of the population, and a unified language environment proved instrumental in neutralizing negative trends and strengthening constructive ones — as part of interethnic dialogue within the new statehood of Russia. Despite the complicated processes of the 1980s–1990s, Buryatia confirmed its loyalty to the principles of federalism and integrity of Russia. Another important milestone was the 1994 adoption of the Constitution of the Republic of Buryatia. Over the past hundred years, the Republic has developed as a major political/legal entity of the Russian Federation — in cultural, economic, and other aspects. Nowadays, the peoples of Buryatia — regardless of faith and ethnic identity — join efforts to develop public economy and culture, shape a common destiny of the Republic and the country on the basis of friendship, harmony, and mutual understanding.

Tectonic inversion of the Abanico basin eastern border and the structuring of the Aconcagua thrust-fold belt, southern Central Andes at 32°-33°S

Previous geologic studies and structural interpretations of the Meso-Cenozoic units in the Andean Principal Cordillera, between 32°- 33°S, have faced many difficulties due to the strong variability in volcanic deposits' thickness, the structural complexity that affects the involved units, and the scarcity of geochronological data that prevents defining a clear boundary between them. Structural-lithologic work carried out between 32°45′-33°S allowed us to recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys: one marine sedimentary unit assigned to the Cretaceous Mendoza Group and Late Jurassic exposures from the Río Damas/Tordillo Formation, and 3 volcano-sedimentary units mainly associated with Cenozoic volcanism represented by the Farellones, Abanico, and Cristo Redentor formations. The stratigraphic-structural model proposed in this work also allows for defining 3 structural domains throughout the study area: a western domain close to the Pocuro Fault Zone, a central domain, and an eastern domain close to the Alto del Juncal Fault Zone, next to the Chile-Argentina international border. The western and central domains show folds with larger wavelengths than the eastern domain, while the eastern domain shows intense deformation related to the emplacement and evolution of the Aconcagua fold and thrust belt. This deformation results from tectonic events which mainly occurred between the Upper Oligocene and Miocene. In the study region, these events caused a minimum shortening of ∼30 km in the Principal Cordillera. Based on the collected information, the Alto del Juncal Fault is also interpreted as the eastern Abanico basin bounding fault in which the Aconcagua fold-thrust belt is rooted.

Pre-Andean deformation and its influence on the shortening of the Southern Precordillera, Mendoza, Argentina

Andean structures preserve evidence of previous periods of deformation along the proto-Pacific margin of Gondwana. Particularly, the Southern Precordillera, in the southern Central Andes, presents a combination of different structural domains and a double vergence related to the reactivation of pre-Andean structures. This combination and the superposition of deformational events make it difficult to understand the stratigraphic systems and the evolution of the region. This contribution presents detailed information about the structures and evolution of the Southern sector of the Precordillera, focusing on the control exerted by Paleozoic structures over the recent Andean deformation, and the deformational styles of this fold-and-thrust belt. Three main structural domains are recognized. The western domain is characterized by high-angle back-thrusts that concentrate the highest amount of uplift. The central domain is composed of reverse double-vergence faults, and high-angle strike-slip faults. The eastern domain is characterized by pure contractional deformation and only east-verging structures. Four deformational events are recorded and analyzed along the Southern Precordillera at 32°30′S: (1) an Early Paleozoic compressional event, (2) a Late Paleozoic compressional event, (3) a Triassic extensional event, and (4) the Cenozoic Andean compressional event. Our model for the Cenozoic deformation of the Southern Precordillera is restricted to three stages of deformation. During the first stage, Paleozoic west-verging faults are reactivated. The second stage implies reactivation of Paleozoic and Permian-Triassic structures and the generation of reverse Andean faults. The final stage consists of the generation of NE-SW Andean thrusts.

Caribbean–South America interactions since the Late Cretaceous: Insights from zircon U–Pb and Lu–Hf isotopic data in sedimentary sequences of the northwestern Andes

The Northern Andes in Colombia developed along an active, convergent margin with a complex subduction-accretion/collision history since Triassic times. Sedimentary basins that developed within, or close to, the evolving margin provide an important record for the tectonic history. Here we present U–Pb and Hf isotopic data of detrital zircons from Late Cretaceous and Miocene sedimentary strata. Two sedimentary sequences deposited in an active margin setting are analyzed in this study along two roughly E–W trending transects. Targeted sedimentary sequences are the Late Cretaceous-Paleocene siliciclastic member of the Penderisco Formation outcropping in the Western Cordillera and the hemipelagic Miocene Beibaviejo Formation overlying the suture zone between the Western Cordillera and the Panama-Chocó Block (PCB). Provenance and Hf isotopic signatures for sediments and volcaniclastic sandstones associated with the Penderisco Formation indicate a maximum depositional age of ca. 57 Ma with input of detrital material from mixed sources from two major domains: an eastern ancient continental domain, and a western Cretaceous oceanic domain that defines the present Western Cordillera. The record from continental sources suggests a para-autochthonous to autochthonous syn-tectonic history. For the Beibaviejo Formation provenance and Hf isotopic data suggest the Penderisco Formation and Eocene rocks with oceanic affinity within the PCB as the main sources and define a middle Miocene maximum depositional age (∼16 Ma). Our results provide a new insight into the evolution of volcaniclastic sequences at the northwestern margin of South America and provide a new constraint on the timing of collision between the PCB and the Andean margin during the middle Miocene.

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.

Growing the Paleo- to Mesoproterozoic margin of the SW Amazonia and the transition from an accretionary to a collisional system

Despite a general consensus of a petrogenetic link in Paleo- to Mesoproterozoic times between the Rio Apa Terrane (RAT) and the Ventuari-Tapajós and Rio Negro-Juruena provinces of the SW Amazonian Craton, their connection with the adjoining Paraguá Terrane is still tentative. Here, we test the connection between SW Amazonia, Rio Apa and Paraguá terranes by comparing an extensive dataset of new and published zircon U–Pb–Hf isotopic data. A locally weighted scatterplot smoothing (LOWESS) curve based on a near continuous zircon εHfT time series (∼1400 data) indicates that the Western domain of the RAT, the San Diablo domain (southern Paraguá Terrane), and the Ventuari-Tapajós Province are characterized by a crustal reworking array associated with the recycling of the Amazonian Archean crust. Change-point statistical analysis indicates the time of a switch from this reworking array to an episode of juvenile input into the magmatic sources at 1809–1805 Ma (95 % confidence), giving rise to the juvenile Eastern domain of the RAT, the Paraguá Terrane and the Rio Negro-Juruena Province. This secular zircon εHfT evolution is interpreted to represent a switch from advancing (crustal reworking) to retreating (juvenile input and crustal growth) episodes in the Paleo- to Mesoproterozoic accretionary orogen of SW Amazonia. Similar temporal isotopic patterns are recorded in modern accretionary orogens such as the Andes. This data supports a petrogenetic link between the RAT, the Paraguá Terrane, and the SW Amazonian Craton. We postulate that the Mesoproterozoic Alto Guaporé orogeny (ca. 1470–1430 Ma, accretionary phase) eventually juxtaposed the high-pressure/medium-temperature (amphibolite facies) RAT and the high-temperature (granulite facies) Paraguá Terrane along the SW margin of Amazonia, establishing a paired metamorphic belt during Rodinia assembly. The newly formed RAT-Paraguá-Amazonia connection lasted until at least ca. 1110 Ma based on the expression of the Rincon del Tigre-Huanchaca large igneous province that crosscut the Amazonia-Paraguá and RAT. The timing of fragmentation and drift of the RAT and the Paraguá Terrane from the SW Amazonia is still unknown.

Atmospheric Blocking Trends and Seasonality around the Antarctic Peninsula

Abstract We analyze the seasonal evolution and trends of atmospheric blocking from 1979 to 2018 using a geopotential-height-based method over two domains, one located to the west (150°–90°W, 50°–70°S) and the other over and to the east (90°–30°W, 50°–70°S) of the Antarctic Peninsula. Spatial patterns of geopotential heights on days with blocking feature well-defined ridge axes over and west of much of South America, and days with the most extreme blocking (above the 99th percentile) showed upper-tropospheric ridge and cutoff low features that have been associated with extreme weather patterns. Blocking days were found to be more frequent in the first half of the period (1979–98) than the second (1999–2018) in all seasons in the west domain, whereas they seem to be more common over the eastern (peninsula) domain in 1999–2018 for austral winter, spring, and autumn, although these differences were not statistically significant. West of the Antarctic Peninsula, blocking days occur most frequently when the Antarctic Oscillation (AAO) is negative, whereas they are more frequent over the peninsula when the AAO is positive. We propose that our blocking index can be used to indicate atmospheric blocking affecting the Antarctic Peninsula, similar to how the Greenland blocking index has been used to diagnose blocking, its trends, and impacts over the Arctic.

A continental back-arc setting for the Namaqua belt: Evidence from the Kakamas Domain

A study of the NW Kakamas Domain in South Africa/Namibia provides a new, unified lithostratigraphy and evolutionary history applicable to the whole Namaqua Sector. The Mesoproterozoic history ranges from ∼1350 Ma to 960 Ma, but isotopic evidence suggests it was built upon pre-existing Paleoproterozoic continental crust that extended west from the Archaean Craton. In eastern Namaqualand, early rift-related magmatism and sedimentation at ∼1350 Ma occurred in a confined ocean basin. Subsequent tectonic reversal and subduction at ∼1290–1240 Ma led to establishment of the Areachap, Konkiep and Kaaien Domains. In the Kakamas Domain, widespread deposition of pelitic sediments occurred at ~1220 Ma (Narries Group). These contain detrital zircons derived from proximal crust with ages between ∼2020 Ma and 1800 Ma (western Palaeoproterozoic domains) and 1350–1240 Ma (eastern early Namaqua domains), suggesting pre-sedimentation juxtaposition. The pelites underwent granulite grade metamorphism at ∼1210 Ma (peak conditions: 4.5–6 kbar and 770–850 °C), associated with voluminous, predominantly S-type granitoid orthogneisses between ∼1210 Ma and 1190 Ma (Eendoorn and Ham River Suites) and low-angle ductile (D2) deformation which continued until ∼1110 Ma, interspersed with periods of sedimentation. This enduring P-T regime is inconsistent with the expected crustal over-thickening associated with the generally-accepted collision-accretion Namaqualand model. Rather, we propose the Namaqua Sector is a ‘hot orogen’ developed in a wide continental back-arc with subduction west of the present-day outcrop. The observed high geotherm resulted from thinned back-arc lithosphere accompanied by an influx of mantle-derived melts. Ductile D2 deformation resulted from “bottom-driven” tectonics and viscous drag within the crust by convective flow in the underlying asthenospheric mantle. This extended tectonothermal regime ceased at ∼1110 Ma when SW-directed thrusting stacked the Namaqua Domains into their current positions, constrained in the Kakamas Domain by late- to post-tectonic I-type granitoids intruded between ∼1125 Ma and 1100 Ma (Komsberg Suite). The thermal peak then shifted west to the Bushmanland and Aus Domains, where voluminous granites (1080–1025 Ma) were associated with high-T/low-P granulite facies thermal metamorphism and mega-scale open folding (D3). Unroofing of the Namaqua Sector is marked by large-scale, NW-trending, sub-vertical transcurrent dextral shear zones and associated pegmatites and leucogranites at ∼990 Ma.

Cenozoic deformation in the eastern domain of the North Qaidam thrust belt, northern Tibetan Plateau

Abstract The present topography of the northern Tibetan Plateau is characterized by the northwest-trending Eastern Kunlun Range, Qaidam Basin, and Qilian Shan, which figure importantly into the evolution and mechanism of Tibetan plateau development during Cenozoic Indo-Asian convergence. Understanding the Cenozoic deformation history and the source-to-sink relationship through time has significant implications for deciphering the growth history of the northern Tibetan Plateau. Despite decades of study, the timing, pattern, and mechanisms of deformation across the northern Tibetan Plateau are still vigorously debated. The North Qaidam thrust belt, located between the Qaidam Basin and Qilian Shan thrust belt, provides a valuable record of Cenozoic deformation in the northern Tibetan Plateau. Here, we present the results of new geologic mapping, structural and sedimentology analysis, and apatite fission track thermochronology to constrain the Cenozoic evolution history and reconstruct the paleogeomorphology of the eastern domain of the North Qaidam thrust belt and its foreland, the Wulan Basin. Our analyses reveal the North Qaidam thrust belt experienced multi-phase exhumation since the Cretaceous. A period of Eocene localized thrust-related uplift of the North Qaidam thrust belt initiated shortly after India-Asia collision, and lower erosion rates in the Oligocene allowed the thrust belt to expand along-strike eastward. Local uplift shed sediments to the southwest, directly into the Qaidam Basin. Reactivation of the proximal thrust faults and initiation of the northwest-striking right-slip Elashan fault at ca. 15–10 Ma drove the final accelerated mid-Miocene cooling and denudation to the surface. This phase of deformation established the overall framework morphology of the northeastern margin of the Tibetan Plateau, including the overall structure of the basins and ranges.

The Proto- and Palaeo-Tethys tectonic evolution in Southeastern Tibetan Plateau: Constraints from detrital zircon dating of metasedimentary rocks from the Diancang Shan complex

ABSTRACT Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete ‘Wilson Cycle’ from early Palaeozoic to the Late Triassic.

Late Miocene evolution of the eastern Deep Algarve basin: Interaction of bottom currents and gravitational processes in a foredeep setting

Foreland basins are normally dominated by turbidite deposits in the early stages of their evolution. In this work, we show evidences of bottom current influence in the Algarve basin, which evolved as a foredeep basin of the Betic-Rif orogeny, during which the paleo-Mediterranean Outflow Water (MOW) was active through the Betic and Rifian corridors. Seismic interpretation identified four stages of sedimentary evolution (Stages I-IV) in the eastern domain of the Deep Algarve basin. Stages I and II correspond to the Late Miocene contourite depositional system during the late Tortonian to early Messinian, interrupted by the emplacement of the allochthonous unit of the Gulf of Cádiz. Bottom currents reworked the initial turbiditic sediments in the eastern Deep Algarve basin, as the downstream continuation of the Guadalquivir sands turbidite system, forming contourite drifts prior to the severe weakening or cessation of the paleo-MOW around mid-Messinian. Stages III and IV represent the evolution of the turbidite system with a lack of bottom current influence, through the downstream translation and lateral migration of meandering submarine channels, and their subsequent abandonment, during the late Messinian. The Tortonian to Messinian evolution of bottom current is modulated by the water-mass exchange between the Mediterranean and the Atlantic due to the shallowing of gateway sills and subsequent restriction of the paleo-MOW through the Betic and Rifian gateways around ∼6.4 Ma. Tectonic and glacioeustatic changes related to the orbital forcing exerted control over both the turbidite and contourite depositional systems, where tectonic pulses of about 400-kyr dictated their large-scale morphosedimentary evolution and interactions.

From microanalysis to supercontinents: Insights from the Rio Apa Terrane into the Mesoproterozoic SW Amazonian Craton evolution during Rodinia assembly

AbstractDeciphering the tectono‐metamorphic evolution of Precambrian terranes can be difficult due to reworking by later superimposed events. Whole‐rock elemental and isotopic geochemistry and zircon U–Pb geochronology are often employed in those studies, but these approaches are often not sensitive to the presence of multiple events and medium‐grade metamorphic episodes. The Rio Apa Terrane (RAT), an allochthonous fragment of the Amazonian Craton, is a crustal block with a well‐characterized crustal evolution but with no detailed thermal constraints for its tectono‐metamorphic evolution. In contrast to previous studies, we show the existence of four tectono‐metamorphic events at c. 1,780, c. 1,625, c. 1,420–1,340, and c. 1,300–1,200 Ma on the basis of apatite, titanite, and rutile U–Pb, in situ white‐mica Rb–Sr, and in situ garnet Lu–Hf geochronology combined with mineral chemistry and phase‐equilibria modelling. The c. 1,780 Ma event is recorded in the basement of the Western domain, representing an extensional event coeval with the development of its Eastern domain in response to the retreat stage of the accretionary system. This is followed by juxtaposition of the Western and Eastern domains along a major crustal boundary at c. 1,625 Ma, which is defined by the magnetic profiles and zircon U–Pb–Hf data across the boundary. The third and fourth events correspond to progressive high‐pressure/medium‐temperature (HP/MT) metamorphism, characterized by an anticlockwise P–T path, suggesting a convergent‐to‐collisional tectonic setting. The RAT was accreted to the adjoining Paraguá Terrane at c. 1,420–1,340 Ma under an isobaric P–T evolution spanning ~530°C to 600°C and ~10.0 kbar. Subsequently, the combined Rio Apa and Paraguá terranes collided with the SW Amazonian Craton at c. 1,300–1,200 Ma, reaching P–T conditions of ~560–580°C and ~10.9–11.7 kbar during crustal thickening. This study reveals for the first time the existence of a HP/MT metamorphic evolution related to the growth of the SW Amazonian Craton as part of an accretionary orogenic system during Rodinia assembly in the Palaeoproterozoic to Mesoproterozoic.

Phytoplankton dynamics based on satellite inherent optical properties and oceanographic conditions in a patagonian gulf frontal system in relation to the adjacent continental shelf waters

The dynamics of phytoplankton across a seasonal frontal system formed in San José Gulf (SJG, Patagonia Argentina) and in neighbouring shelf waters was assessed based on bio-optical satellite data (2003–2018) and spring and summer in situ samplings. Bio-optical properties of the water masses on the eastern (ED) and western (WD) domains of the seasonal frontal system of SJG showed clear differences: the year-round-vertically-mixed waters from the WD, strongly connected with the adjacent shelf waters, evidenced a brief and strong single phytoplankton bloom, while those from the ED, showing lower exchange with shelf waters and a strong vertical stratification during the warm season, displayed an earlier and long-lasting spring phytoplankton bloom, followed by a late-summer and autumn bloom, both associated with the development and erosion of the seasonal thermocline. Waters from the entire system are optically influenced by the absorption of coloured dissolved organic matter and detritus (cdom + detritus), suggesting a strong sediment load contribution from the continent and the seabed. To remark, a strong correlation between satellite chlorophyll-a (Chla-sat) and absorption by phytoplankton (aphy443) in the outer shelf waters differs from the weak correlation of those variables in the gulf's water masses, whose optical parameters are more complex. In situ Chla records may indicate wind-driven upwelling and downwelling areas in the northern and southern coasts of the ED. Dissolved nitrogen was identified as the limiting macronutrient for phytoplankton growth in the ED during summer. This work contributes relevant ecological information that may support management actions on the SJG shellfish artisanal fishery.

Source diversity of Late Neoproterozoic granitoid magmatism across an orogen-scale lineament in southern Brazil and Uruguay: Whole-rock geochemistry, zircon geochronology and Sr-Nd-Hf isotope evidence

Granitoids of similar Brasiliano age (638–540 Ma) are widespread in southern Brazil and Uruguay on both sides of an orogen-parallel lineament comprising from south to north, the Sierra Ballena, Dorsal de Canguçu and Major Gercino shear zones. We reviewed mineralogy, geochemistry and geochronology of granitoids that occur in the two domains located east and west of the mentioned lineament. Most of the granitoid magmatism is calc-alkalic to alkali-calcic and magnesian to ferroan, but variations are observed (aluminosity increases in eastern relative to western domain granitoids, and alkaline intrusions are more frequent in the western domain). Considering mineralogy and geochemistry the K-rich calc-alkaline granitoids (KCG) type of Barbarin's predominate, but amphibole-rich calc-alkaline granitoids (ACG), muscovite-bearing peraluminous granitoids (MPG) and peralkaline and alkaline granitoids (PAG) type affinities (although subordinate) do also occur. High-barium-strontium (HiBaSr) granitoids (with and without shoshonitic affinity) are frequent in the western but sporadic in the eastern domain. Granitoids intruding in the western domains of Santa Catarina, Rio Grande do Sul and Uruguay generally display crystallization ages between 638 and 540 Ma, Archaean to Neoproterozoic inherited zircon ages (3365–640 Ma) and strongly evolved isotopic signatures and model ages (ϵNd600 of −8.5 to −32; Nd TDM2 ages of 1.9–3.7 Ga; ϵHf (t) of −0.46 to −35.7 and Hf TDMCrustal ages of 1.5–3.6 Ga). Granitoids from the eastern domain, while showing a similar range of crystallization ages (630–543 Ma), generally reveal contrastingly younger inherited zircon ages (774–642 Ma) and less evolved isotope characteristics and model ages (ϵNd600 of −2.3 to – 11.8, Nd TDM2 of 1.4–2.1 Ga; ϵHf(t) of −0.21 to −12.5 and Hf TDMCrustal ages of 1.5–2.4 Ga).The assessment of the data compiled for this contribution indicate that: a) in southern Brazil and Uruguay, the Sierra Ballena-Dorsal de Canguçu-Major Gercino Lineament, act as a remarkable tectonic regional boundary between domains whose granitoids generally (but not always) show a pattern of contrasting whole-rock key chemical indicators, zircon inheritance, isotope signatures and model ages reflecting different granitoid sources; b) granitic melt production took place from the interaction of sources of different age (e.g. old Archaean to Paleoproterozoic crust and/or of Tonian age arc-materials) and composition (e.g. crustal sources: metaigneous rocks, metasediments vs. mantle-derived sources: juvenile basaltic melts and/or metasomatized mantle); c) crustal components strongly outweigh mantle ones in the source of the granitoids, suggesting that recycling was the chief mechanism; d) however, the spatial association of plutonic intermediate to basic rocks and felsic granitoids is sometimes significant in some sectors of southern Brazil and may be indicative of the adding up of new material from the mantle (i.e “crustal growth” processes) to the crust within a post-collisional environment.