Central Arc Research Articles

Subduction-related magmatism (SRM) and its effect on magma fertility; Oligocene-Miocene plutonism evolution in the center of Urumieh-Dokhtar magmatic arc, Iran

This study explores the Oligocene-Miocene subduction-related plutonic rocks (OMP) from central Urumieh-Dokhtar Magmatic Arc (UDMA) in the center of Alpine-Himalayan Orogenic Belt (AHOB). OMP range in composition from gabbro/diorite (∼34-32Ma) to tonalite (∼20Ma) with geochemical signatures of metaluminous calc-alkaline I-type granitoids. Geochemical analyses reveal enrichment in large ion lithophile elements and light rare earth elements relative to high field strength elements and heavy rare earth elements (La N /Yb N =3.05-4.45). Mineral and whole rock chemical variations reflect lower crust melting to crustal contamination over time, and magmatic chamber evolution. OMP chemical evolution can be attributed to two key factors: (1) incorporation of Th-rich sediment/crustal components from progressive lower crustal melting, and (2) injection of fertile mantle melts altering magma chamber composition. These factors rendered the OMP barren in Cu-mineralization, however, suggests a possible potential Cu-mineralization in Miocene intrusive rocks, where the enriched mantle fluids, derived from the subducted slab were more pronounced. This study proposed a geodynamic model to improve understanding of the UDMA magmatic evolution. Comparison of SRM plutonic rocks from the central UDMA, Southern Tibet, and Western Anatolia highlights the evolution of slab dynamics, crustal thickening, and extensional processes in “Oligocene-Miocene” magmatism during the eastward closure of Neotethys along the AHOB.

Tracking Magmatism and Metasomatism in Continental Arc Crust Root: Significance from Western Central Qilian Belt in NE Tibet, China

Abstract Mantle peridotites and pyroxenites from arc crust root record vital information about petrogenetic processes in supra–subduction environments, which are commonly obscured by subsequent metamorphic and/or metasomatic overprints. The Heigou Complex from the western Central Qilian arc root (NE Tibet, China) includes peridotites and pyroxenites. Petrography, bulk–rock and mineral geochemistry, zircon and titanite U–Pb ages, and bulk–rock Sr–Nd–Hf isotopes are presented to decipher its petrogenetic and metasomatic history. The peridotites display highly refractory compositions of low SiO2, Al2O3, CaO, but high MgO contents. Geochemical modeling indicates that these are the residues after up to ~22% melt extraction. The geochemical and isotopic data (87Sr/86Sr i = 0.7116–0.7179, εNd(t) = −4.2 to −7.1 and εHf(t) = −5.3 to −5.4) suggest the pyroxenitic protoliths were derived from a subduction-metasomatized mantle source. Combining petrographic and fractional crystallization simulation, the pyroxenites formed as cumulates through 50% to 80% differentiation of primitive basaltic magma in the arc root at ca. 523 Ma. Elevated LILEs (Rb, Sr, Pb, etc.) and LREE in bulk-rock and mineral compositions, together with microstructure evidence, suggest that mantle peridotite experienced mantle metasomatism. Subsequent hydrous melt (fluid) metasomatism during exhumation then reacted with the preexisting clinopyroxenite, leading to local Mg-hornblende, titanite and epidote formation. The timing of retrograde melt infiltration is constrained by a titanite U–Pb crystallization age of ca. 485 Ma. The combined evidence reveals a picture of continental arc magmatism and metasomatism at arc crust roots. Dehydration of the Proto-Tethys oceanic slab could induce flux melting in the mantle wedge that had undergone metasomatism, resulting in the generation of hydrous arc magmas. These arc magmas intruded the overlying lithospheric mantle, segregating pyroxenite cumulates. The ultramafic rocks at the arc crust root were subsequently modified by hydrous melt (fluid).

State shifts in the deep Critical Zone drive landscape evolution in volcanic terrains

Volcanic provinces are among the most active but least well understood landscapes on Earth. Here, we show that the central Cascade arc, USA, exhibits systematic spatial covariation of topography and hydrology that are linked to aging volcanic bedrock, suggesting systematic controls on landscape evolution. At the Cascade crest, a locus of Quaternary volcanism, water circulates deeply through the upper [Formula: see text]1 km of crust but transitions to shallow and dominantly horizontal flow as rocks age away from the arc front. We argue that this spatial pattern reflects a temporal state shift in the deep Critical Zone. Chemical weathering at depth, surface particulate deposition, and tectonic forcing drive landscapes away from an initial state with minimal topographic dissection, large vertical hydraulic conductivity, abundant lakes, and muted hydrographs toward a state of deep fluvial dissection, small vertical hydraulic conductivity, few lakes, and flashy hydrographs. This state shift has major implications for regional water resources. Drill hole temperature profiles imply at least [Formula: see text] km[Formula: see text] of active groundwater currently stored at the Cascade Range crest, with discharge variability a strong function of bedrock age. Deeply circulating groundwater also impacts volcanism, and Holocene High Cascades eruptions reflect explosive magma-water interactions that increase regional volcanic hazard potential. We propose that a Critical Zone state shift drives volcanic landscape evolution in wet climates and represents a framework for understanding interconnected solid earth dynamics and climate in these terrains.

Genesis of the Mamuniyeh copper deposit in the central Urumieh-Dokhtar Magmatic Arc, Iran: Constraints from geology, geochemistry, fluid inclusions, and H–O–S isotopes

The Mamuniyeh Cu deposit is located in the central part of the Urumieh-Dokhtar Magmatic Arc (UDMA), 10 km south of the city of Mamuniyeh, Iran. Mineralization is controlled by faults with a NW-SE trend and hosted within an Eocene volcanic sequence and Oligo-Miocene hypabyssal calc-alkaline monzonitic and gabbroic bodies. Quartz + chalcopyrite veins are most abundant and high-grade ore containing up to 5 wt% Cu, although quartz + pyrite veins have the most abundant sulphide content. In addition, quartz + chalcopyrite + specular hematite ± pyrite veins/veinlets are another common mineralized assemblage in the Mamuniyeh copper deposit, with pyrite, chalcopyrite, bornite, and oxide minerals (specular hematite, titanomagnetite, and magnetite) typical of the hypogene stage. Chalcocite, covellite, and dignite also formed at the margins of primary sulphides in the supergene (paleoweathering) stage. The mineralized veins exhibit colloform, crustiform, open space-fillings, replacements, and dissemination textural characteristics associated with mineralizing assemblages with silicification, argillization, chloritization, and sericitization assemblages. The salinity for L > V fluid inclusions is between 1.74 to 11.7 wt% NaCl and for (V > L) inclusions between 1.7 to 11.4 wt% NaCl. The average homogenization temperature and salinity for quartz + chalcopyrite + pyrite veins is 186 °C and 4.9 wt% NaCl. In the quartz + chalcopyrite assemblage an average of 185 °C and 4.5 wt% NaCl and for quartz + chalcopyrite + specularite ± pyrite (QCSP) an average of 195 °C and 5.59 wt% NaCl was determined. In these three vein types, the fluid density has almost identical values ranging from 0.8 to 1.0 g/cm3. The mineralizing system evolved in two-stages; the first metal precipitation occurred at less than 1 km of crustal depths and second metal deposition stage at shallower crustal levels (less than 500 m). Although it appears that the boiling process occurred within the fluids of the area, the primary factor contributing to Cu mineralization was influenced by fluidmixing processes. The δ18O and δD values of ore fluids computed vary from + 6.08 to −0.50 ‰ and −92 to −71 ‰, respectively, indicative of the blending of oxidizing and cooler meteoric waters with primary magmatic fluids. Calculated values of δ34S of H2S in equilibrium with chalcopyrite ranges from −7.6 to −1.9 ‰ and H2S in equilibrium with pyrite ranges from −7.1 to −3.8 ‰, respectively; this is consistent with monzodiorite to gabbro as the magmatic sulphur source for copper mineralizing fluids. Furthermore, the QCSP vein data align more closely with primary magmatic water compared to other veins, suggesting that precipitation occurred mainly from magmatic fluids, which experienced depletion in δ18O due to mixing with meteoric waters (shallow oxygenated ground waters), which caused sulphide deposition. The geochemical features for these magmas show that contamination with crustal materials occurred during the ascent of the parent magma, as well as the role of suprasubduction fluids released from the subducting plate in mantle metasomatism. Based on all evidence, Cu mineralization in the Mamuniyeh deposit has been categorized as a low-sulphidation epithermal-type system, which formed during active magmatism in the central part of UDMA.

Magnesium isotope constraints on the role of recycled carbonate-rich sediments in the formation of ultrapotassic magmatic rocks at a continental arc setting

Magnesium isotope constraints on the role of recycled carbonate-rich sediments in the formation of ultrapotassic magmatic rocks at a continental arc setting

Tectonostratigraphic evolution of a marginal basin during the transition from arc collision to subduction: The case of the northern Pacific forearc of Colombia

Abstract The forearc of the northern Pacific region of Colombia (Atrato basin) initially formed in an intra-oceanic setting related to the Central American arc, and its sedimentary record provides a unique opportunity to study the evolution of source-to-sink systems during the transition from arc collision to subduction. Intracrustal weaknesses, and the highly oblique approach to the continental South American paleomargin, favored an initial soft collision of the island arc and associated marginal basins during the Early Miocene. This is suggested by the lack of widespread deformation in the collisional front and the accumulation of hemipelagic rocks with little terrestrial input, sourced by the colliding arc and the continental paleomargin. A regional unconformity associated with a shift toward terrigenous deposition is attributed to a harder collision and subsequent buoyancy-driven uplift of the oceanic terrane ca. 15–13 Ma. The final docking of the oceanic arc and related basins to the continent and coeval surface uplift near the suture zone ca. 12–7 Ma marked the transition from collision to subduction and the establishment of the Atrato basin as a continental forearc. This was accompanied by postcollisional arc magmatism, shallowing of accumulation depths to nearshore conditions, and a dramatic decrease in the sediment contribution of the continental paleomargin. Subsequent shallow subduction of the Coiba microplate caused the Late Miocene uplift of the coastal Baudó Range and the fragmentation of the Atrato basin into inner and outer (coastal) segments. This episode drove a shift from predominantly transverse to longitudinal drainage systems and the final transition from marine to terrestrial settings in northwestern Colombia.

Sustained Co‐Eruptive Increase in Seismic Velocity Below Great Sitkin Volcano Due To Magma Extrusion

AbstractVolcanic eruptions carry essential information on the dynamics of volcanic systems. Studies have documented variable eruption styles and eruptive surface deformation. However, co‐eruptive subsurface structural changes remain poorly understood. Here we characterize the seismic velocity changes from July 2019 to July 2023 at Great Sitkin Volcano in the central Aleutian volcanic arc, using single‐station ambient noise interferometry at five three‐component seismic stations. Coincident with the lava effusion since late July 2021, about two months after the explosive eruption on 26 May 2021, we observe a sustained velocity increase, most prominently to the northwest of the caldera. We attribute this velocity increase to the structural changes with magma extrusion, with the spatial variation controlled by the geometry of the magma system or the property of shallow volcaniclastics. Our findings offer insights into understanding co‐eruptive structural modifications at active volcanoes.

HIV in pregnant woman and children: Mother-to-child transmission of HIV in the Brazilian land border from 2010 to 2021.

HIV in pregnant woman and children: Mother-to-child transmission of HIV in the Brazilian land border from 2010 to 2021.

Expert‐based range maps cannot be replicated using data‐driven methods but macroecological conclusions arising from them can

AbstractAimAnswering many fundamental and applied scientific questions relies on accurate geographic range maps for species, such as those compiled by experts working with the International Union for Conservation of Nature (IUCN). However, these maps are resource demanding to produce and only available for a limited number of organisms. Here, we test to what extent standardized, data‐driven methods based on publicly available occurrences can reproduce expert‐based IUCN range maps and the macroecological conclusions drawn from them.LocationGlobal.Time PeriodPresent.TaxaBirds.Materials and MethodsWe estimated the geographic ranges for 7385 non‐marine bird species which either were non‐migratory or had spatially connected breeding and wintering ranges from publicly available, georeferenced point occurrences. We then quantified the spatial overlap between these range estimates and the IUCN expert‐derived range estimates. Finally, we compared global species richness patterns and the environmental correlates that emerge from both approaches.ResultsWe find that range estimates based on point occurrence records overlap on average 52% with expert range estimates for the same species. The global species richness patterns estimated under both approaches are overall similar but show local and regional differences, for example, in the tropical Andes of northern South America and the Central Arc region of Africa. The estimated global drivers of richness are similar.Main ConclusionsExpert‐derived estimates of species distributions are not reproducible by data‐driven approaches relying on currently available public records, even for well‐documented taxa such as birds. However, these discrepancies do not substantially change our macroecological understanding of global drivers of bird diversity.

Magmatic evolution of the Kolumbo submarine volcano and its implication to seafloor massive sulfide formation

Seafloor massive sulfides form in various marine hydrothermal settings, particularly within volcanic arcs, where magmatic fluids may contribute to the metal budget of the hydrothermal system. In this study, we focus on the Kolumbo volcano, a submarine volcanic edifice in the central Hellenic Volcanic Arc hosting an active hydrothermal system. Diffuse sulfate-sulfide chimneys form a Zn-Pb massive sulfide mineralization with elevated As, Ag, Au, Hg, Sb, and Tl contents. These elements have similar behavior during magmatic degassing and are common in arc-related hydrothermal systems. Trace-element data of igneous magnetite, combined with whole rock geochemistry and numerical modelling, highlights the behavior of chalcophile and siderophile elements during magmatic differentiation. We report that, despite early magmatic sulfide saturation, chalcophile element contents in the magma do not decrease until water saturation and degassing has occurred. The conservation of chalcophile elements in the magma during magmatic differentiation suggests that most of the magmatic sulfides do not fractionate. By contrast, upon degassing, As, Ag, Au, Cu, Hg, Sb, Sn, Pb, and Zn become depleted in the magma, likely partitioning into the volatile phase, either from the melt or during sulfide oxidation by volatiles. After degassing, the residual chalcophile elements in the melt are incorporated into magnetite. Trace-element data of magnetite enables identifying sulfide saturation during magmatic differentiation and discrimination between pre- and post-degassing magnetite. Our study highlights how magmatic degassing contributes to the metal budget in magmatic-hydrothermal systems that form seafloor massive sulfides and shows that igneous magnetite geochemistry is a powerful tool for tracking metal-mobilizing processes during magmatic differentiation.

Middle–Late Jurassic subduction erosion caused by intra-oceanic arc subduction in central Tibet

Abstract Subduction erosion is crucial in crustal material recycling. However, subduction erosion caused by intra-oceanic arc subduction has not been sufficiently investigated. In this study, we provide new geological, geochronological, geochemical, and isotopic data from Dongco granodiorites in the central Bangong–Nujiang suture zone of central Tibet to explore subduction erosion caused by intra-oceanic arc subduction. Analysis shows that the ca. 158–155 Ma Dongco granodiorites originated from the subducted oceanic plate, and they were contaminated with accretionary wedge when they intruded the Dongco ophiolite. This suggests that the Dongco ophiolite was emplaced in the subducted accretionary wedge before the Late Jurassic. Based on the intra-oceanic arc affinity and lack of volcanic rocks of Middle Jurassic Dongco ophiolite and other regional data, we believe that the main body of the central intra-oceanic arcs and a portion of the western intra-oceanic arcs in the Meso-Tethys Ocean subducted beneath the southern Qiangtang terrane during the Middle–Late Jurassic. In addition, the different degree absence of the Jurassic accretionary wedge, forearc region, and arc magmatic rocks in the southern Qiangtang terrane indicate that the central and western parts of the southern Qiangtang terrane experienced both vigorous and relatively weak subduction erosion during the Middle–Late Jurassic, respectively. Thus, there is a significant spatiotemporal coupling between subduction erosion of the southern Qiangtang terrane and intra-oceanic arc subduction. Based on these studies and the research on subduction erosion, we suggest that subduction of the main body of the central intra-oceanic arcs and partial subduction of the western intra-oceanic arcs in the Meso-Tethys Ocean caused both vigorous and relatively weak subduction erosion of the southern Qiangtang terrane during the Middle–Late Jurassic, respectively. In addition, the increase in subduction rate also promoted Middle–Late Jurassic subduction erosion of the southern Qiangtang terrane.

Subsurface anatomy of the Irazú–Turrialba volcanic complex, inferred from the integration of local and ambient seismic tomographic methods

SUMMARY Irazú and Turrialba are a twin volcanic complex that marks a distinct stop in volcanism along the Central America volcanic arc. We present a new traveltime velocity model of the crust beneath Irazú and Turrialba volcanoes, Costa Rica, and interpret it considering the results of previous ambient noise tomographic inversions. Data were acquired by a temporary seismic network during a period of low activity of the Irazú–Turrialba volcanic complex in 2018–2019. Beneath the Irazú volcano, we observe low P-wave velocities (VP = 5 km s−1) and low velocity ratios (VP/VS = 1.6). In contrast, below the Turrialba volcano, we observe low S-wave velocities (VS = 3 km s−1) and a high VP/VS (= 1.85) anomaly. We found that locations of low VP and VS anomalies (−15 %) correspond well with shear wave velocity anomalies retrieved from ambient noise tomography. At shallower depths, we observe high VP and VS anomalies (+15 %) located between the summits of the volcanoes. Subvertical velocity anomalies are also observed at greater depths, with high VP and VS anomalies appearing at the lower limits of our models. We propose a complex structure of an intermediate magmatic reservoir, presenting multiphase fluid states of a liquid-to-gas transition beneath Irazú and a juvenile store of magmatic fluid beneath Turrialba, while shallow fluid transport provides evidence of magmatic–hydrothermal interactions.

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

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

Analysis of heat and mass transfer characteristics of supercritical CO2 in vertical U-tube

The heat and mass exchange of CO2 in a vertical U-tube under supercritical pressure was simulated. The effects of the geometry of the bend area, The center arc radius of the bend area and the different bend orientations on the flow heat transfer of supercritical CO2 in the U-tube were analyzed. The results show that in the bend area, the flow is affected by the combined action of centrifugal force and gravity, as well as the pipe structure, so the flow mixing is intense, and the heat transfer capacity is significantly enhanced. When the direction of the bend changes, the interaction between centrifugal force and gravity will affect the heat transfer at pipe bending. When the central arc radius r of the bend area increases from 0.5D to 3D, the heat transfer at the bend can be strengthened, but will weaken the heat transfer at the bend outlet area.

Hypothetical Learning Trajectory of Sector Area and Arc Length Using the Clockwork Context

Students' understanding on the concept of a circle especially the relationship between central angle, arc length, and sector area of the circle based on learning obstacle and learning trajectory need to be developed well by creating a good didactic design. Therefore, it is necessary to design hypothetical learning trajectories (HLT) for students in learning sector area and arc length using the clockwork context. The didactical design was developed through three stages, namely: (1) the preliminary design; (2) teaching experiment; and (3) retrospective analysis. This study focused on the first stage, since the main purpose of this research was to develop a series of learning activities to delve into the concept of sector area and arc length as proportional problem in the form of HLT. The HLT was designed using a realistic mathematics education (RME) approach. There are three anticipated learning obstacles in the design of the activities, including errors related to the concept of the relationship between arc length, circle circumference, sector area, and circle area; errors related to the concept of the relationship between the central angle, arc length, and sector area of a circle; as well as errors related to the connection of concepts in circle material with other mathematical material; and students' difficulties in problem solving questions.

Middle Ordovician trilobites from the Castillejo Formation, Eastern Iberian Range (NE Spain): taxonomic reappraisal, biostratigraphy, and correlation

Middle Ordovician trilobites found in 11 fossil localities from the areas of Alpartir, Aladrén, Luesma and Fombuena (Zaragoza province), and south of Calamocha (Teruel province) are studied. Most records come from the Alpartir Member of the Castillejo Formation, which is dated as Dobrotivian in age (late Darriwilian according to the global scale), with the only exception of two localities that are slightly older, from late Oretanian age (mid−late Darriwilian). In the overlying Sierra Member, three additional localities are recorded, which have estimated age ranges from late early to late Dobrotivian (latest Darriwilian, possibly reaching the Sandbian). A total of 21 different trilobite species were identified including Uralichas hispanicus, Parabarrandia crassa and “Panderia” beaumonti that are recorded for the first time in the Eastern Iberian Range. The main trilobite assemblage from the Alpartir Member belongs to the Placoparia tournemini Biozone, which correlates with numerous areas of southwestern Europe, and here occurs in a biofacies dominated by asaphids. The scarce data derived from the Sierra Member do not allow to distinguish biozones, although the incipient development of a trilobite biofacies adapted to sandy bottoms is recognized, which ends at the top of the Placoparia borni Biozone in the whole of southwestern Europe. The correlation of the trilobite assemblages with those of other formations represented in the Cantabrian, West Asturian-leonese and Central Iberian zones is also discussed, the latter probably related through the enigmatic Central Iberian Arc, a debated orocline of the Iberian Massif.

Magnetic Fabric and Paleomagnetic Analyses of the Zaghar and Tafresh Areas, Central Urumieh-Dokhtar Magmatic Arc, Iran

Magnetic fabric, paleomagnetic, and petrophysical studies were conducted on rocks in the Tafresh area of the central Urumieh-Dokhtar magmatic arc in Iran. The samples included Late Triassic dark gray sandstone, a mafic dyke, diorites, and a felsic dyke in the Zaghar region. Hydrothermal alteration in the Spid intrusion was investigated to understand the effects of alteration on magnetic fabric patterns. The AMS measurements support the theory that the Nayband Formation was constructed under a crustal extension regime. Magnetic susceptibility anisotropy in a microdioritic dyke indicates compression from the NNE-SSW, likely due to tectonic activity. AMS results from diorites in Zaghar suggest intrusions were emplaced in extensional spaces between the Tafresh and Chaghar thrust faults. The Spid intrusion’s magnetite is the primary carrier of magnetic susceptibility, but hydrothermal alteration has partly converted it into hematite, resulting in lower susceptibility and higher porosity in altered diorites. This process leads to a bimodal distribution of magnetic lineation trends. The Spid and Zaghar massifs underwent a northward tilt of about 30 degrees around an east-west axis following the Early Miocene. Post-Eocene rotations in the area are typically within ±20 degrees. This study demonstrates how magnetic properties can provide new insights into the evolution of tectono-magmatic processes and structural controls within a magmatic arc.

Fe–Mg Isotopes Trace the Mechanism of Crustal Recycling and Arc Magmatic Processes in the Neo‐Tethys Subduction Zone

AbstractThere has been intense debate on the mechanism of crustal recycling in subduction zones, and Fe–Mg isotopes may provide new constraints on this issue. This study reports Fe–Mg isotope data for mafic plutonic rocks from the eastern and central Gangdese arc, along with their associated trench sediments in southern Tibet. The δ26Mg values of the eastern Gangdese arc rocks show negative correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but positive correlations with εNd(t) and εHf(t) values. Conversely, the δ56Fe values of the eastern Gangdese arc rocks show positive correlations with (87Sr/86Sr)i and (206Pb/204Pb)i values, but negative correlations with εNd(t) and εHf(t) values. The Mg and Fe isotopic compositions of the central Gangdese arc rocks are comparable with those of the eastern ones, but they do not correlate with Sr–Pb–Nd–Hf isotopic compositions. Notably, the Fe–Mg isotopic compositions of most arc rocks fall between those of local trench sediments and the mantle wedge. Combined qualitative analyses and quantitative simulations suggest that: (a) the Fe–Mg isotope variations observed in the eastern Gangdese arc rocks highlight the important role of source mixing between sediment‐derived melts and peridotite, whereas (b) the Fe–Mg isotope variations observed in the central Gangdese arc rocks reflect the superposition of carbonated serpentinite‐derived Mg‐rich fluids‐peridotite source mixing and source melting. The strong correlations between Fe–Mg isotope ratios and traditional geochemical tracers provide further evidence for the recycling of crustal materials in subduction zones via various types of slab‐derived fluids and melts.

Silurian‐Devonian Lithospheric Thinning and Thermally Softening Along the Northern Margin of the Tarim Craton: Geological Mapping, Petro‐Structural Analysis and Geochronological Constraints

AbstractWhile the western part of northern Tarim Craton has long been considered as a Paleozoic passive margin, a pronounced Silurian‐Devonian magmatism developed on eastern part of this margin may indicate different but active margin setting. In this contribution, detailed structural mapping, petro‐structural analysis, and geochronological investigations were conducted in the Korla area, eastern part of northern Tarim Craton. Three main generations of fabrics were recognized. The earliest pervasive fabric is an originally sub‐horizontal metamorphic S1 foliation that is in part associated with migmatization characterized by high temperature/low pressure metamorphic mineral assemblages, interpreted as reflecting crustal extension. S1 foliation was affected by D2 contraction forming regional‐scale F2 upright folds associated with sub‐vertical axial planar foliation S2. D3 is marked by development of NW‐SE oriented dextral fault, asymmetric mega‐folding of S2 and spaced NW‐SE‐striking S3 foliation, likely in response to dextral transpression. Geochronological data indicate that D1 extension occurred from ca. 420 to 410 Ma, D2 contraction started around 410 Ma and lasted till 400 Ma or later, and D3 transpression was ongoing around ∼370 Ma. Integrated with regional data, an updated geodynamic model is proposed by interpreting the Central Tianshan, South Tianshan and NE Tarim Craton as an early Paleozoic supra‐subduction system. We suggest that the Silurian‐Devonian event reflects thermal softening and horizontal stretching of the supra‐subduction crust, resulting in drifting of the Central Tianshan continental arc from the proto Tarim Craton in association with opening of the South Tianshan back‐arc basin in‐between.

Age- and sex-related differences in sympathetic vascular transduction and neurohemodynamic balance in humans.

Bursts of muscle sympathetic nerve activity (MSNA) and the ensuing vasoconstriction are pivotal determinants of beat-by-beat blood pressure regulation. Although age and sex impact blood pressure regulation, how these factors affect the central and peripheral arcs of the baroreflex remains unclear. In 27 young [25 (SD 3) yr] males (YM; n = 14) and females (YF; n = 13) and 23 older [71 (SD 5) yr] males (OM; n = 11) and females (OF; n = 12), femoral artery blood flow, blood pressure, and MSNA were recorded for 10 min of supine rest. Sympathetic baroreflex sensitivity (i.e., central arc) was quantified as the relationship between diastolic blood pressure and MSNA burst incidence. Signal averaging was used to determine sympathetic vascular transduction into leg vascular conductance (LVC) for 12 cardiac cycles following MSNA bursts (i.e., peripheral arc). Older adults demonstrated attenuated sympathetic transduction into LVC (both P < 0.001) following MSNA bursts, and smaller increases in sympathetic transduction as a function of MSNA burst size and firing pattern compared with young adults (range, P = 0.004-0.032). YM (r2 = 0.36; P = 0.032) and OM (r2 = 0.51; P = 0.014) exhibited an inverse relationship between the central and peripheral arcs of the baroreflex, whereas females did not (YF, r2 = 0.03, P = 0.621; OF, r2 = 0.06, P = 0.445). MSNA burst incidence was inversely related to sympathetic transduction in YM and OF (range, P = 0.03-0.046) but not in YF or OM (range, P = 0.360-0.603). These data indicate that age is associated with attenuated sympathetic vascular transduction, whereas age- and sex-specific changes are present in the relationship between the central and peripheral arcs of the baroreflex regulation of blood pressure.NEW & NOTEWORTHY Sympathetic vascular transduction is attenuated in older compared with young adults, regardless of biological sex. Males, but not females (regardless of age), demonstrate an inverse relationship between central (sympathetic baroreflex sensitivity) and peripheral (sympathetic vascular transduction) components of the baroreflex arc. Young males and older females exhibit an inverse relationship between resting sympathetic outflow and sympathetic vascular transduction. Our results indicate that age and sex exert independent and interactive effects on sympathetic vascular transduction and sympathetic neurohemodynamic balance in humans.