Journal of Geodynamics最新文献

{"title":"Ca. 835–823 Ma doming extensional tectonics in the west Jiangnan accretionary orogenic belt, South China: Implication for a slab roll-back event","authors":"Jinlong Yao ,&nbsp;Liangshu Shu ,&nbsp;Guochun Zhao ,&nbsp;Yigui Han ,&nbsp;Qian Liu","doi":"10.1016/j.jog.2021.101879","DOIUrl":"10.1016/j.jog.2021.101879","url":null,"abstract":"<div><p><span>The Neoproterozoic Jiangnan accretionary orogenic belt recorded the accretion and collision of the Yangtze and Cathaysia blocks to form a stablized South China Block, but related geometry and kinematics is poorly constrained, leading to largely varied tectonic models. Here, we present detailed field investigation and kinematic analysis of the plutonic-metamorphic complexes in the Yuanbaoshan and Sanfang areas of the west Jiangnan orogenic belt, which enables identification of extensional granite-cored domes. In the dome margins, down-dipping </span>lineations<span><span> display a radial pattern and dome dominated foliations are extensively developed. The shearing structures within the plutonic-metamorphic complexes display extensional shearing surrounding the Yuanbaoshan and Sanfang granitic dome cores. Gneissic granites and massive ones from both the Yuanbaoshan and Sanfang plutons yield comparable crystallization ages of ca. 835–823 Ma that are within age errors of each other, as are the sheared recrystallized asymmetric quartz veins and mylonites dated at 831 Ma. Overall ages of the deformed Sibao Group and the undeformed overlying Danzhou Group, along with those of the granite plutons and mylonites, suggest formation of the granite-cored domes at ca. 835–823 Ma, coeval to the timing of emplacement of the granitic plutons. Locally, top-to-the-E thrusting structures are also observed in the west Yuanbaoshan and Sanfang areas and are inferred as at ca. 860–835 Ma, coinciding well with E- or SE- directed structures developed elsewhere in the Jiangnan orogenic belt, but in contrast with doming extensional shearing structures. Therefore, overall geometry and kinematics in the west Jiangnan belt indicate development of granitic dome related extensional ductile shearing deformation dated at ca. 835–823 Ma and a possible top-to-the-E compressional ductile thrusting deformation within 860–835 Ma. Given the previously inferred </span>regional geology<span><span> observations, along with age and chemical data across the Jiangnan orogenic belt, the dominant extensional shearing deformation in the region argue for a slab roll-back event within an accretionary belt, typical of domes-and-basins structures formed in accretionary convergent continental margin. The top-to-the-E thrusting is here interpreted as corresponding to compressional regime generated by the west directed subduction of </span>oceanic crust beneath the northern Guangxi continental margin arc in the west Jiangnan orogenic belt.</span></span></p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42341284","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lithosphere ionosphere coupling associated with three earthquakes in Pakistan from GPS and GIM TEC","authors":"M. Arslan Tariq ,&nbsp;Munawar Shah ,&nbsp;Zishen Li ,&nbsp;Ningbo Wang ,&nbsp;M. Ali Shah ,&nbsp;Talat Iqbal ,&nbsp;Libo Liu","doi":"10.1016/j.jog.2021.101860","DOIUrl":"10.1016/j.jog.2021.101860","url":null,"abstract":"<div><p><span><span>Total Electron Content (TEC) derived from satellite-based measurements has been widely used for the detection of </span>ionospheric<span><span> perturbations associated with earthquakes. In this paper, we analyze Pre-Earthquake Ionospheric Anomalies (PEIAs) with TEC data from Global Positioning System (GPS) stations in two Pakistani regions, Islamabad (33.74°N, 73.16°E) and Multan (30.26°N, 71.50°E). These stations operate within seismogenic zones of three earthquakes in Pakistan and Tajikistan. We implement a statistical technique on daily TEC for the detection of PEIA. The results show that PEIAs appear in the form of enhancement during 08:00–12:00 UT (LT = UT+5 h) within 5–10 days before the mainshock. Global Ionospheric Maps (GIMs) over the </span>epicentre are examined on abnormal TEC days. Dense electron enhancements occur during 08:00−12:00 UT, i.e. before three M</span></span><em>_w</em>&gt; 5.0 earthquakes. Diurnal mean TEC deviates on the suspected days. It supports the anomalous signatures observed in the temporal and spatial distributions during the particular days. The geomagnetic and solar indices show no activity. These results endorse the existence of Lithosphere Atmosphere Ionospheric Coupling (LAIC) mechanism within the earthquake preparation period associated with the Pakistan and Tajikistan earthquakes.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101860","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41293327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An integrated critical approach to off-fault strike-slip motion triggered by the 2011 Van mainshock (Mw 7.1), Eastern Anatolia (Turkey): New stress field constraints on subcrustal deformation","authors":"Mustafa Toker ,&nbsp;Ali Pınar ,&nbsp;Nihan Hoşkan","doi":"10.1016/j.jog.2021.101861","DOIUrl":"10.1016/j.jog.2021.101861","url":null,"abstract":"<div><p>In this study, we retrieved the finite source characteristics of the October 23, 2011 Van earthquake (<em>Mw 7.1</em>) using the teleseismic waveforms to focus on the source location. The outstanding off-fault aftershock sequence of the Van mainshock was readily explained by calculating the Coulomb stress changes imparted to the surrounding crust. This may be accomplished through finite source modelling to examine the stress interaction between the fault, ruptured by the Van mainshock, and the surrounding fault(s) triggered by the same mainshock. In addition, to provide further support for the Coulomb failure stress changes in the off-fault area, centroid moment tensor (CMT) inversion of the off-fault aftershocks was performed and stress tensors were derived from their focal solutions. This identified the dominant fault slip, the constraints of the crustal stress fields and illuminated the crustal nature of the stress interaction. The off-fault aftershocks showed a strike-slip stress regime in rotational (to NW) and non-rotational (to N) stress fields of the upper and lower crusts, respectively. However, this was inconsistent with a horizontal compressional stress direction striking to the north. This suggests that a local source and/or rotation of lateral variation in stress magnitudes in crustal and sub-crustal structures strongly perturbed the regional stress field. It was also evident that these strike-slip aftershocks increased the intensity of stress in an off-fault area, NE of the source rupture. This revealed a uniquely triggered strike-slip motion, activated and rooted in the weak lower crust. We conclude that the Van mainshock rupture source area, associated with the stress changes imparted to the surrounding crust, had undergone anomalous modifications to generate distinctive off-fault aftershock responses in the entire crust, and also triggered and loaded the weak lower crust. We hypothesize that the strike-slip motion, the so called “transfer fault”, as a distinctly triggered slip event, was generated or selectively activated by subcrustal ductile processes in the absence of mantle lid beneath the study area. However, local slab fragmentation, tearing and cold mantle beneath the study area lead to paradigm changes in interpreting the strike-slip motion and subcrustal deformation. The presence of a small piece of oceanic lithosphere, consistent with fragmented, torn slab and cold mantle, may be an alternative hypothesis that remains to be tested. The Van earthquake, combined with careful examination of associated off-fault aftershocks, revealed new information about stress field constraints on subcrustal deformation. This investigation also provided insights into an important role of stress interaction, with a newly discovered transfer fault within the off-fault area, which extends through the entire crust beneath Lakes Van and Erçek areas.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101861","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42272581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The slab gap-related Late Cretaceous-Paleocene magmatism of southern Patagonia","authors":"César R. Navarrete ,&nbsp;Gabriela I. Massaferro ,&nbsp;Guido A. Gianni ,&nbsp;María Belén Lastra","doi":"10.1016/j.jog.2021.101869","DOIUrl":"10.1016/j.jog.2021.101869","url":null,"abstract":"<div><p>The only Late Cretaceous-Paleocene intraplate magmatic unit of southern Patagonia, known as the Las Mercedes basalt, is petrogenetically studied in its geodynamic context. The outcrops of this unit are thin ridges located in a narrow 50 km wide latitudinal strip (∼48 °S) of the central region of the Deseado Massif, generated by pahoeoe-type lava flows that probably covered large ancient streams and rivers. Compositionally the rocks are metaluminous basanites and alkaline and subalkaline basalts uninfluenced by slab-derived components with Mg# ranging from 53.9–65. The origin of this intraplate igneous manifestation would have been related to the opening of a Late Cretaceous-Paleocene trench-perpendicular slab tear of the Aluk subducting plate. This event induced the decompression melting of the sub-slab silica-deficient garnet pyroxenite asthenosphere causing the extrusion of a discrete volume of basalts. The slab anisotropy was generated by the slab-dip change in a transition region from a flattened sector (north of ∼48 °S) related to a large flat-slab (<em>Nalé flat-slab</em>) to one with steeper subduction angle (south of ∼48 °S). Also, this slab tearing would be responsible for the anomalous occurrence of intraplate magmatism located in the same latitudinal strip of the Las Mercedes basalt but in the Andean magmatic arc region, which together represent the only Late Cretaceous igneous activity unrelated to the magmatic arc in central-southern Patagonia and southern Andean region.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101869","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47894421","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A GNSS velocity field for geophysical applications in Fennoscandia","authors":"Halfdan Pascal Kierulf ,&nbsp;Holger Steffen ,&nbsp;Valentina R. Barletta ,&nbsp;Martin Lidberg ,&nbsp;Jan Johansson ,&nbsp;Oddgeir Kristiansen ,&nbsp;Lev Tarasov","doi":"10.1016/j.jog.2021.101845","DOIUrl":"10.1016/j.jog.2021.101845","url":null,"abstract":"<div><p>In Fennoscandia, tectonics, Glacial Isostatic Adjustment (GIA), and climatic changes cause ongoing crustal deformation of some millimetres per year, both vertically and horizontally. These displacements of the Earth can be measured to a high degree of precision using a Global Navigation Satellite System (GNSS). Since about three decades, this is the major goal of the Baseline Inferences for Fennoscandian Rebound, Sea-level, and Tectonics (BIFROST) project.</p><p>We present a new velocity field for an extended BIFROST GNSS network in the ITRF2008 reference frame making use of the GNSS processing package GPS Analysis Software of MIT (GAMIT). Compared to earlier publications, we have almost doubled the number of stations in our analysis and increased the observation time span, thereby avoiding the early years of the network with many instrument changes. We also provide modelled vertical deformation rates from contributing processes, i.e. elastic deformation due to global atmospheric and non-tidal ocean loading, ice mass and hydrological changes as well as GIA. These values for the vertical component can be used for removal of these contributions so that the residual uplift signal can be further analysed, e.g., in the context of local or regional deformation processes or large-scale but low-magnitude geodynamics.</p><p>The velocity field has an uplift maximum of 10.3 mm/yr in northern Sweden west of the Gulf of Bothnia and subsidence exceeding 1 mm/yr in northern Central Europe. The horizontal velocity field is dominated by plate motion of more than 20.0 mm/yr from south-west to north-east. The elastic uplift signal sums up to 0.7–0.8 mm/yr for most stations in Northern Europe. Hence, the maximum uplift related to the past glaciation is ca. 9.6 mm/yr. The residual uplift signal after removal of the elastic and GIA contribution may point to possible improvements of the GIA model, but may also indicate regional tectonic and erosional processes as well as local deformation effects. We show an example of such residual signal discussing potential areas of interest for further studies.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101845","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43249568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A black hole particle swarm optimization method for the source parameters inversion: application to the 2015 Calbuco eruption, Chile","authors":"Leyang Wang ,&nbsp;Xibo Jin ,&nbsp;Wenbin Xu ,&nbsp;Guangyu Xu","doi":"10.1016/j.jog.2021.101849","DOIUrl":"10.1016/j.jog.2021.101849","url":null,"abstract":"<div><p><span>The traditional genetic algorithm and simulated annealing methods have been widely used in geophysical modeling. However, these nonlinear inversion methods require a lot of calculations, many control parameters and are unstable. In this paper, a particle swarm optimization algorithm combined with black hole strategy (BH-PSO) is proposed to solve these problems. The comprehensive experiments show that the BH-PSO method consumes less time than the simulated annealing (SA) method and has a higher accuracy than the genetic algorithm (GA). It is more applicable to the inversion of parameters of volcanic magma chamber, and easier to be generalized to other kinematic source parameters inversion. Based on BH-PSO method, Sentinel-1 data, composite dislocation model (CDM), Yang model and Mogi model, the magma chamber parameters of Calbuco eruption in 2015 were retrieved. The results show that the RMSE of CDM model is 1.1 cm, which can better fit the surface deformation than the Mogi model and Yang model. The final results show that the magma chamber is located about 0.8 km northeast of the crater, about 9 km below the surface, and the total volume of the erupted volcanic material obtained with the CDM Model is of 0.209 km</span>³, without considering dense rock equivalent.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101849","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43522358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stress changes associated with the significant first subevent of the 2008 Wenchuan earthquake and implications for the rupture behavior transition","authors":"Yujiang Li ,&nbsp;Lianwang Chen ,&nbsp;Hong Li ,&nbsp;Yuanzhong Lu","doi":"10.1016/j.jog.2021.101859","DOIUrl":"10.1016/j.jog.2021.101859","url":null,"abstract":"<div><p>The rupture process of the Wenchuan earthquake demonstrated a transition from thrust-dominated slip to northeastward strike-slip motion along the Longmen Shan Fault Zone. The initial stress has been reported as playing a critical role in this process; however, the stress changes, especially those caused by the significant first subevent of the Wenchuan earthquake are not well understood. Here, we employ a three-dimensional finite element model of the Sichuan-Yunnan region to analyze the stress change caused by the significant first subevent and explore the possible influence on the following ruptures. The results indicate that the auxiliary maximum principal compressive stress (S_H) associated with the significant first subevent was horizontal and that the auxiliary stress regime was S_H&gt;S_h&gt;S_v, supporting the ongoing regional thrust motion near the southwestern segment of the rupture plane. However, in the northeastern segment, the auxiliary stress regime transitioned to S_H&gt;S_v&gt;S_h, demonstrating that the stress changes promoted the transition of the rupture behavior from predominantly thrust motion in the southwest to right-lateral strike-slip motion in the northeastern segment, which was also supported by the dominant shear stress change and the subtle normal stress change along the fault plane in the northeastern segment. In addition, our modeled results also indicate that the orientation of the maximum principal compressive stress changed from SEE to northeastward NEE along the strike of Longmen Shan Fault Zone. This anticlockwise rotation hastened the rupture behavior transition, suggesting that both the initial stress and the stress changes associated with the first subevent jointly controlled the following northeastward rupture of the Mw7.9 Wenchuan earthquake.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101859","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42232309","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A simple picture of mantle wedge flow patterns and temperature variation","authors":"Ikuko Wada","doi":"10.1016/j.jog.2021.101848","DOIUrl":"10.1016/j.jog.2021.101848","url":null,"abstract":"<div><p>The solid-state mantle flow is an important factor that controls the mass and heat transfer in the solid Earth. This study aims to provide a simple picture of three-dimensional (3-D) mantle flow patterns in the sub-arc region of subduction zones<span> based on the results of 3-D steady-state numerical models with varying subduction parameters. Here, the mantle wedge flow pattern is evaluated based on the azimuthal directions of the mantle inflow from the back-arc and the down-dip outflow. The outflow direction generally parallels the subduction direction, but the inflow direction relative to the outflow direction depends on the local subduction obliquity – the angle between the subduction direction and the strike-normal axis of the subducting slab. A change in the strike of the slab leads to a change in the obliquity and thus the inflow direction. Such change is common along curved margins as the strike of the slab tends to follow that of the margin, or vice versa. Along convex-arc-ward margins, the mantle inflow is deflected towards the region of lowest obliquity but with reduced vigor due to lower dynamic pressure gradients that partly drive the flow, resulting in a cooler mantle wedge. Along concave-arc-ward margins, the mantle inflow is deflected away from the region of lowest obliquity but with increased vigor, resulting in a hotter mantle wedge. These effects increase with decreasing radius of curvature. Along-margin change in the dip of the subducting slab also affects the inflow direction through its impact on the strike of the slab, but its effect is relatively small. We express the azimuthal inner angle between the inflow and outflow directions as a function of obliquity and apply the function to predict sub-arc mantle inflow directions in the circum-Pacific and neighboring regions. Within and among these margins, the inner angle varies over its full range of 0–180°. Most of the margins that are 1000s of kilometers in length are either straight or curved concave-arc-ward with large radii of curvature, for which small or gradual along-margin changes in the mantle inflow direction and the mantle wedge temperature are predicted. A large drop in the mantle wedge temperature by up to a couple of hundred degrees is predicted at short convex-arc-ward segments, such as at the Kuril-Japan and Bonin-Mariana junctions. The fringes of flat slab segments are curved with small radii of curvature, likely resulting in sharp lateral changes in the inflow direction and the mantle wedge temperature.</span></p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101848","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44272939","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of multi-seamount subduction on accretionary wedge deformation: Insights from analogue modelling","authors":"Chunyang Wang ,&nbsp;Weiwei Ding ,&nbsp;Wouter P. Schellart ,&nbsp;Jiabiao Li ,&nbsp;Chongzhi Dong ,&nbsp;Yinxia Fang ,&nbsp;Tianyao Hao ,&nbsp;Zhengyi Tong","doi":"10.1016/j.jog.2021.101842","DOIUrl":"10.1016/j.jog.2021.101842","url":null,"abstract":"<div><p>Deformation patterns caused by the subduction of a single seamount or aseismic ridge have been well studied in analogue and numerical models. However, the effects of sequential multi-seamount subduction on accretionary wedge deformation have rarely been investigated in details. We performed a series of analogue modelling experiments of sequential subduction involving two seamounts of variable shape, spacing and rheological properties of strata to better understand the deformation mechanisms of an accretionary wedge with multi-seamount subduction. The results demonstrate that a seamount significantly hinders the seaward propagation of the accretionary wedge and facilitates lateral propagation. Two structural quiet zones form at the leading and trailing edges of the subducted seamount in the early stage of collision. As the seamount deeply penetrates into the wedge, the structural quiet zone in the leading edge is remoulded by a duplex structure, which may help the upward transport of deep subducted sediments back into the shallow area. Comparatively, the structural quiet zone in the trailing edge remains undeformed because it is situated in the stress shadow of the seamount. Deformation of the strata between two subducting seamounts may occur by thrusts laterally propagating into the seamount gap, which is facilitated by the décollement layer. The modelling results provide insights into the complex deformation mechanisms related to seamounts collision observed in the accretionary wedge offshore from the Costa Rica margin.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101842","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46097490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The magmatic evolution of the Neotethyan rift: Geochronologic, isotopic, and geochemical evidence from A-type felsic magmatism, NW Iran","authors":"Ghasem Nabatian ,&nbsp;Xian-Hua Li ,&nbsp;Maryam Honarmand ,&nbsp;Rasoul Esmaeili","doi":"10.1016/j.jog.2021.101829","DOIUrl":"10.1016/j.jog.2021.101829","url":null,"abstract":"<div><p>The Ajabshir rhyolitic magma in the northwest (NW) of Iran is an Early Carboniferous (332.5 ± 2.2 Ma), approximately 50m-thick succession, consisting of quartz, alkali feldspar, and biotite phenocryst with a porphyritic texture. This magmatic unit occurred as lava flows and sills intruded into the early Cambrian Lalun Formation. The Ajabshir magma has a calc-alkaline to high potassic calc-alkaline affinity and peraluminous character and displays many of the classic features of A-type magmas, enrichment in HFSEs (Zr + Nb + Ce + Y = 664–808 ppm), Nb (120−218 ppm), Zr (298−362 ppm), Ga (34−38 ppm), Ce (100−132 ppm), high Ga/Al and FeO*/(FeO*+MgO), zircon saturation temperature, and low contents of CaO, Sr, and Eu. The LREE enrichment, non-depletion in HREE, and negative Eu anomalies in the chondrite normalized diagrams exhibit similarities to the REE patterns of “hot-dry-reduced rhyolites”, further pointing to the evolution of Ajabshir rhyolitic magma from an OIB-type parental melt via a fractional crystallization process. The zircon yield εHf_(t) values of +1.4 to +5.5 correspond to two-stage zircon Hf model ages of 0.9–1.2 Ga. The δ¹⁸O values of the zircon range from +5.8‰ to +7.37‰. The zircon isotopic data together with whole-rock geochemical signatures suggest that the mantle-derived magma was modified by crustal components during its ascent to the surface. The Ajabshir A-type rhyolitic magma provides more evidence for an extensional tectonic setting during the Early Carboniferous in NW Iran, contemporaneous with the rifting of the Neotethyan Ocean at the northern margin of Gondwana.</p></div>","PeriodicalId":54823,"journal":{"name":"Journal of Geodynamics","volume":null,"pages":null},"PeriodicalIF":2.3,"publicationDate":"2021-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.jog.2021.101829","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48465356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}