Tectonic Significance Research Articles

A late Paleogene erosion event in the Sanshui Basin, southern margin of the South China Block and its tectonic significance

A late Paleogene erosion event in the Sanshui Basin, southern margin of the South China Block and its tectonic significance

Lithospheric Evolution and Uplift of the Tibetan Plateau During Continental Convergence: Evidence From Early Oligocene Pseudo leucite Phonolites from Southern Qian tang, Central Tibet

Abstract The Cenozoic collision of India and Eurasia clearly built the high-elevation Tibetan Plateau, but how this collision was accommodated, and the Tibetan Plateau uplifted, remains an area of study. The widespread occurrence of Cenozoic potassic–ultrapotassic lavas provides a valuable opportunity to constrain the relationship between surface deformation and underlying geodynamic processes. In this study, we report sanidine Ar–Ar dating, whole-rock geochemical and clinopyroxene Sr–Nd isotope analyses on pseudoleucite phonolites from the Yulinshan area of south Qiangtang (central Tibet) to determine their petrogenesis and regional tectonic significance. Sanidine Ar–Ar dating yields an Early Oligocene age of ca. 30 Ma, in agreement with previous studies. A high modal abundance of pseudoleucite in the samples indicates their ultrapotassic and silica-undersaturated composition. All of the rocks have typical arc-like geochemical signatures and enriched whole rock and clinopyroxene Sr–Nd isotope signatures. Based on thermodynamic phase equilibria modeling and our detailed study of the textural and in-situ compositional information of clinopyroxene, the intermediate to felsic potassic magmas are interpreted to have been formed through differentiation of primitive, mantle-derived, potassic magmas at shallow crustal levels. The inferred enrichment of the lithospheric mantle is probably related to subduction of the Songpan–Ganze continental lithosphere beneath Qiangtang after India-Asia collision. Voluminous Late Eocene–Early Oligocene magmatism in central Tibet may reflect partial removal of the mantle lithosphere, perhaps triggered by instabilities associated with previous lithospheric thickening. Our work provides additional constraints on the timing of mantle root loss that likely contributed to the surface uplift of central Tibet, which post-dated the cessation of upper crustal shortening and deformation.

Soft-sedimentary deformation structures and its tectonic significances in carbonate rocks of Mesoproterozoic Guandaokou Group, the North China Craton

Soft-sedimentary deformation structures and its tectonic significances in carbonate rocks of Mesoproterozoic Guandaokou Group, the North China Craton

Chronology, geochemistry and tectonic significance of the Taotugaenwusu diabase porphyrite in the northern margin of the Qaidam Basin

Chronology, geochemistry and tectonic significance of the Taotugaenwusu diabase porphyrite in the northern margin of the Qaidam Basin

Coupled role of climate and tectonics in the deposition of the late Quaternary sedimentary sequence in the southern margin of the central Ganga Plain, India

ABSTRACT The Ganga Plain’s sedimentation is primarily controlled by Himalayan tectonics, variations in monsoon intensity, and glacier size. However, the significance of intrabasinal tectonics, which is an interplay of the Himalaya tectonics and basement tectonic configuration of the Ganga Plain, in comprehending the late Quaternary Ganga Plain sedimentation remains unclear. In this study, the sediment provenance and extent of weathering experienced by the sediments are studied using the mineralogical and geochemical (major, trace, and rare earth elements) composition of a sedimentary cliff sequence exposed at the Ramnagar locality near the cratonic peripheral bulge in the southern Ganga Plain. In the Ramnagar cliff sediment section, two sediment packages, designated SP-A and SP-B, are identified based on mineralogy, texture, and geochemistry. These packages of sediments show mild chemical weathering and distinct geochemical compositions. The lower part (SP-A) of the Ramnagar cliff section is characterized by higher contributions from mafic sources (pyroxene, feldspar, and mica as dominant minerals), while the upper part (SP-B) is predominately derived from felsic sources (mica and feldspar as dominant minerals), which are supplied via the peninsular and the Himalayan rivers, respectively. The southern part of the central Ganga Plain shows evidence of a shift in the sediment provenance from mafic to felsic source rock at 40 ka. This study demonstrates how weathering and sedimentation are controlled by both regional tectonics and climate in the southern margin of the central Ganga Plain.

Newly Discovered NE-Striking Dextral Strike-Slip Holocene Active Caimashui Fault in the Central Part of the Sichuan-Yunnan Block and Its Tectonic Significance

The Sichuan-Yunnan block is a tectonically active region in China, with frequent large earthquakes occurring in and around it. Despite most earthquakes being concentrated along boundary faults, intraplate faults also have the potential to generate damaging earthquakes. Remote sensing makes it possible to identify these potential earthquake source faults. During an active fault investigation in the Liangshan area, a distinct lithological boundary named Caimashui fault was found. The geometric distribution and kinematic parameter of the fault is crucial for assessing seismic hazards and understanding the deformation pattern within the Sichuan-Yunnan block. The Caimashui fault is mapped with remote sensing interpretation, a field survey, and UAV measurement. Through trenching and Quaternary dating, the Late Quaternary active characteristics of the fault are studied. The fault is a Holocene active dextral strike-slip fault with a reverse component, exhibiting a dextral strike-slip rate of ~0.70 ± 0.11 mm/a. Paleoseismic investigation shows that the last surface rupture event of the Caimashui fault occurred later than 4150 ± 30a BP, with a magnitude of M ≥ 7.0. The fault may act as a secondary splitting fault, absorbing the deformation caused by various sinistral strike-slip rates of the boundary faults and the potential energy from the counterclockwise rotation of the Central Yunnan micro-block.

Sedimentary Geological Characteristics and Tectonic Environment of Luojiamen Formation in Northern Zhejiang, Eastern Section of Jiangnan Orogenic Belt

This study advances our understanding of the Jiangnan Orogenic Belt by integrating high-precision geochronological data with interpretations of sedimentary and tectonic environments. Specifically, it addresses the controversy over the geological significance, origins, and tectonic significance of the Shengong Unconfomity: at the base of the Luojiamen Formation. This paper shows that the formation developed over four stages with the primary source of detritus lying in a volcanic arc to the south. The study also reassesses the “unconformity” between the Luojiamen Formation of the Heshangzhen Group and the Zhangcun Formation of the Shuangxiwu Group, concluding that it does not demarcate the end of the orogenic collision between the Cathaysia and Yangtze blocks.

U-Pb zircon and Sm-Nd geochronology of the dom Silvério group, SE Brazil: Implications for the evolution of the superposed Araçuaí and Minas-Bahia orogens

The Araçuaí orogen, the South American portion of the Brasiliano/Pan-African Araçuaí-West Congo orogenic system (AWCO), formed during the Ediacaran-Cambrian assembly of West-Gondwana. The basement of a substantial portion of the Araçuaí orogen comprises Archean and Paleoproterozoic rocks involved in the 2.1–2.0 Ga Minas-Bahia orogen. The Dom Silvério Group, which consists of mica schists containing layers and lenses of mafic, ultramafic, and Mn-rich rocks, as well as quartzites, graphite schists, marbles, and banded iron formations, defines a ca. 10 km-wide and 150 km-long belt in the southwestern portion of the Araçuaí orogen. This succession, currently interpreted as deep marine deposits or an ocean-floor assemblage of uncertain age - Paleoproterozoic or Neoproterozoic-, potentially records processes involved in critical evolutionary stages of the superposed Minas-Bahia and Araçuaí orogens. Aiming to characterize the age and tectonic significance of the Dom Silvério Group, we performed a geochronological and geochemical investigation on samples collected from selected lithotypes. U-Pb (LA-ICP-MS) determinations on detrital zircons revealed two distinct age spectra. Zircons extracted from the lower Dom Silvério schists define a spectrum characterized predominantly by Neoproterozoic age clusters with a maximum depositional age of 601 ± 10 Ma. Quartzites from the lower and upper sections of the group do not contain zircons younger than 1.9 Ga and show unimodal age distributions around 2067 Ma. The maximum depositional age estimated for these rocks is 2020 ± 6 Ma. The spectrum of the lower section schist indicates the turbidites of the Ediacaran Salinas Formation as their most probable correlative. In contrast, the quartzites and schists of lower and upper sections correlate with the Orosirian Itacolomi Group, the post-collisional assembly of the Minas-Bahia orogen. Sm-Nd isotope analyses and whole-rock geochemistry allow the discrimination of two generations of mafic rocks. The older generation, showing TDM model ages = 1.92 to 3.6 Ga and ƐNd(t) = -12.93 to +4.63, represents components of the basement. The younger generation, with TDM model ages = 1.0 Ga to 1.25 Ga and ƐNd(t) = +0.05 to +2.29, is similar to the ophiolitic rocks that occur imbricated with Ediacaran metasedimentary successions in the central portion of the Araçuaí orogen defining the Ribeirão da Folha accretionary belt. They show Th/Yb and Nb/Yb ratios of the EMORB-OIB mantle array and Nb/Y and Zr/Y ratios compatible with OIB and oceanic plateau basalts. The Dom Silvério Group is thus a complex that involves members of the Araçuaí and Minas-Bahia orogens. Their Ediacaran components materialize the southern extension of the Ribeirão da Folha accretionary wedge and, as such, provide further evidence for oceanic consumption during the development of the southern Araçuaí orogen.

Quaternary Activity Characteristics and Regional Tectonic Significance of the Jiulong Fault in Jiujiang, Jiangxi Province, China

Quaternary Activity Characteristics and Regional Tectonic Significance of the Jiulong Fault in Jiujiang, Jiangxi Province, China

Migmatite-Gneiss-Granite Basement of Southwestern Nigeria: Mineralogical and Geochemical Evidence for a Possible Common Ancient Protolith

Nigeria occupies southern section of the Pan-African orogenic belt and migmatite-gneiss-granite terrain forms a major component of its basement complex. Field geology, optical mineralogy and geochemical study of this rock unit in Idanre area, SW Nigeria were undertaken with a view to characterize them, elucidate their tectonic significance, and determine their origin. Major, trace and Rare Earth Elements (REE) composition were determined by XRF and ICP-MS techniques respectively in Bureau Veritas, Vancouver, Canada.

Evidence for off-ridge thermal interaction along the Carlsberg and Central Indian ridges and its tectonic significance

Evidence for off-ridge thermal interaction along the Carlsberg and Central Indian ridges and its tectonic significance

Spatial distribution and regional tectonic significance of the newly discovered Kalawenguquan fault in the interior of the Tian Shan Mountain Range, Western China

Quantifying the geometrical and kinematic aspects of faults within the Tian Shan Mountain Range is crucial for investigating the tectonic deformation patterns in the region. Through remote sensing image analysis using GaoFen-7 (GF-7) data and field geological surveys, we determined the geometric distribution and fault properties of the Kalawenguquan fault. The newly discovered Kalawenguquan fault spans more than 400 km and mainly strikes in the NEE direction, with some localized segments in the NE direction. The fault plane dips southward at angles ranging from 55° to 85°. The Kalawenguquan fault is a recently discovered Holocene active fault in the Tian Shan and is a thrust and left-lateral strike-slip fault. Based on geological survey findings and sediment dating data from the late Quaternary, the Kalawenguquan fault has a vertical sliding rate of approximately 0.41 mm/a. The left-lateral strike-slip rate was calculated to be 0.6–1.4 mm/a. We detected that at least two paleoseismic events occurred on the fault since 5.4 ± 0.4 ka. In the range of 41°-45° latitude, 45 % of the crustal shortening in the Tian Shan is absorbed by the internal structure.

Recent Holocene activity and regional tectonic significance of the northern segment of the red river fault zone

The Red River Fault Zone is a large-scale right-lateral strike-slip fault zone with relatively strong activity during the Quaternary Period. This fault, located on the southeastern margin of the Qinghai‒Tibetan Plateau, plays a key role in the extrusion, rotation and escape of the continental blocks constituting the Qinghai‒Tibetan Plateau. Furthermore, this fault represents the southwestern boundary of the Sichuan–Yunnan Block, which has experienced strong deformation and frequent seismic activity. The northern segment of the Red River Fault Zone is the most active part of the whole fault. However, surface erosion and vegetation coverage have obscured the activity of the northern segment; therefore, the study of its activity has obviously been insufficient. There is still controversy over whether all the secondary faults on the northern segment are active Holocene faults. Studying the activity characteristics of the northern segment, which is densely populated, is particularly important for seismic risk prevention in this area. Based on remote sensing interpretations and field geological surveys, this paper describes the latest activity characteristics of the Cangshan Piedmont Fault, Fengyi–Dingxiling Fault and Midu Basin Margin Fault, including their spatial distributions and kinematic characteristics. According to the ages of the offset strata in profiles, the above three secondary faults were all active in the late Holocene. The latest active age of the Cangshan Piedmont Fault was later than 543-494 cal BP, and two palaeoseismic events that occurred in this section during the Holocene occurred at 2700 and 473 cal BP. The latest active age of the Fengyi–Dingxiling Fault was later than 2760–2700 cal BP; in this section, one Holocene palaeoseismic event occurred between 1777 cal BP and 2730 cal BP, another occurred between 2730 cal BP and 5664 cal BP, and the third occurred between 6449 cal BP and 8360 cal BP. The latest active age of the Midu Basin Margin Fault was later than 558-510 cal BP, and two Holocene palaeoseismic events occurred later than 2318-2114 cal BP and 558-510 cal BP. Based on the results of this paper and previous studies, we believe that the Fengyi–Dingxiling Fault on the northern segment of the Red River Fault Zone is at risk for future strong earthquakes. Additionally, abundant geological and geomorphologic evidence suggests that the northern segment is dominated by normal faults, reflecting the local strain response to secondary clockwise rotation of the Sichuan–Yunnan Block along the boundary fault. This finding is in line with the eastwards extrusion and escape of materials on the Qinghai‒Tibetan Plateau caused by the northwards and northeastwards pushing of the Indian Plate. To a certain extent, these observations reflect the tectonic deformation coordination between block rotation and boundary fault slip in the Sichuan–Yunnan Block in the context of continental block extrusion on the Qinghai–Tibetan Plateau.

The Discovery of the New UHP Eclogite from the East Kunlun, Northwestern China, and Its Tectonic Significance

The Discovery of the New UHP Eclogite from the East Kunlun, Northwestern China, and Its Tectonic Significance

Initial sedimentation after the closure of the Sumdo Paleo-Tethys Ocean: Implications for early Mesozoic tectonics in the East Tethys domain

The closure of the Paleo-Tethys Ocean and subsequent collisional orogenesis in the early Mesozoic played an important role in the formation of the Qinghai–Tibetan Plateau. However, the final closure of the southernmost Paleo-Tethys branching ocean basin in the Qinghai–Tibetan Plateau—known as Sumdo Paleo-Tethys Ocean—and collision between Central and Southern Lhasa terranes remain controversial. In particular, the tectonic significance of early Mesozoic volcanism and sedimentation in the Lhasa terrane is unknown, but crucial for understanding the final stages of ocean closure. Here, we investigate the depositional ages and provenance of detrital zircon in clastic sedimentary rocks, as well as the petrogenesis of the interbedded andesite from the volcano-sedimentary sequence of the Late Triassic to Early Jurassic Xionglai Formation in the Tangjia-Sumdo area. Detrital zircon dates from the Xionglai Formation define five age peaks at 180–200 Ma, 230–340 Ma, 500–620 Ma, 1000–1240 Ma, and 1600–1800 Ma. Detrital zircon trace elements and Hf isotopic characteristics are interpreted to represent derivation from an accretionary wedge and later magmatism related to oceanic slab break-off as well as a minor component from coeval magmatic rocks in the Nyainrong-Nang area in northern Lhasa terrane. Interbedded andesite has a magnesian andesite signature and yields ages of 192–184 Ma with zircon εHf(t) values that range from −3 to +1. We interpret these data as the andesite being sourced from sediment-derived melts that interacted with the overlying mantle wedge in a post-collision extensional setting. Our study suggests that the closure of the Sumdo Paleo-Tethys Ocean and subsequent collision between Central Lhasa and Southern Lhasa terrane may have happened in Late Triassic-Early Jurassic. The final closure of the multi-Paleo-Tethys Ocean and subsequent collision in the Qinghai–Tibetan Plateau may have induced initial subduction of the Meso-/Neo-Tethys Ocean, representing the tectonic transition from collision/post-collision to subduction/accretion in the Qinghai–Tibetan Plateau during the Late Triassic to Early Jurassic.

Petrogenesis and tectonic setting of the Neoproterozoic Douling dioritic–granodioritic–granitic intrusion in the northern Yangtze Block, Central China

Voluminous Neoproterozoic intermediate to felsic rocks intruded the Neoarchean Douling Complex in the South Qinling Belt of Central China, which may provide new constraints on the controversial issue about the nature of the continental margin of the Yangtze Block during the Neoproterozoic. This study presents zircon U–Pb geochronology, whole‐rock geochemistry and Sr–Nd isotope of the Douling dioritic–granodioritic–granitic intrusion, aiming to clarify its petrogenesis and tectonic significance. The dioritic–granodioritic–granitic rocks yield similar zircon U–Pb ages ranging from 735 to 705 Ma. The enrichment of light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs), and depletion of high‐ field‐strength elements (HFSEs) (e.g., Nb, Ta) are typical features of arc magmatic rocks. The whole‐rock Sr–Nd isotopic compositions show initial 87Sr/86Sr ratios ranging from 0.7034 to 0.7059, and εNd(t) values from −7.3 to −1.4. Elemental and isotopic data suggest that the Neoproterozoic dioritic–granodioritic–granitic rocks were co‐genetic and were generated by partial melting of lower crust materials combined with mantle‐derived melts. The granites were the derivative product of dioritic rocks by fractional crystallization of amphibolite, plagioclase, mica and zircon. Combined with literature data, we infer a subduction‐related setting for the northern margin of the Yangtze Block during the Middle Neoproterozoic, and a tectonic model of accretion along an Andean‐type active continental margin after the collision of the Douling micro‐block with the northern Yangtze Block is further proposed.

Geochemistry and tectonic significance of high-Fe bearing tholeiitic dykes from the southern part of Bastar Craton, Central India: An evidence for continental arc magmatism

Geochemistry and tectonic significance of high-Fe bearing tholeiitic dykes from the southern part of Bastar Craton, Central India: An evidence for continental arc magmatism

Petrogenesis and Tectonic Significance of Shenxianshui Alkaline Granite in Gejiu, Yunnan Province, China

AbstractThe Shenxianshui granites in the western Gejiu area were formed in the Late Cretaceous. Laser ablation inductively coupled plasma mass spectrometry indicates zircon U‐Pb ages ranging from 90.67 ± 0.7 to 85.97 ± 0.6 Ma. The intrusive rocks are peraluminous (A/CNK = 1.03 to 1.33) and calc‐alkaline, showing an affinity towards I‐type granite. Large ion lithophilic elements are enriched in K and Rb, while high field strength elements are depleted. Moreover, light rare earth elements are significantly enriched, showing a slight negative Eu anomaly (Eu/Eu* = 0.39 to 0.58). Shenxianshui granite has a relatively high initial Sr isotope ratio (87Sr/86Sr)i (0.7098–0.7105), negative εNd(t) values (−7.99 to −7.44) and negative εHf(t) values (−8.37 to −2.58). Combined with previous studies, these characteristics suggest that the Shenxianshui alkaline granites were formed in a post‐collision extensional environment. The alkaline granitic magma possibly originated from the partial melting of the lower crust during the Mesoproterozoic era and may have contained mantle source materials. Shenxianshui alkaline granite was formed from mixed magma with a high degree of crystal differentiation. The abundance of ore‐forming elements indicates that Shenxianshui granite has the potential to mineralize key metals and rare earth elements.

U−Pb geochronology and microstructural analysis of apatite within a Proterozoic crustal-scale shear zone, Outer Hebrides, NW Scotland

U–Pb apatite geochronology is increasingly recognized as a valuable tool for constraining the age of mid-crustal ductile shear zones. The crustal-scale Outer Hebrides Fault Zone (OHFZ) within the Laurentian foreland of the Scottish Caledonides has long been of uncertain age and tectonic significance. Earliest deformation within the OHFZ was associated with top-to-the-NW ductile thrusting that formed a belt of greenschist facies mylonites within host Archean−Paleoproterozoic basement gneisses. Previous estimates for the timing of thrusting vary between c . 1600 Ma and c . 430 Ma. The mylonitic fabrics are defined by a recrystallized assemblage of quartz + albite/oligoclase + sericite + actinolite + epidote + apatite ± calcite, consistent with deformation temperatures of 400–500°C and within the range of reported closure temperatures for Pb diffusion in apatite. U–Pb (LA−ICP−MS) dating of two texturally distinct apatite grain types within the mylonites has yielded ages mostly in the range c . 1100–900 Ma. The OHFZ is therefore interpreted as a Grenville–Sveconorwegian structure that formed during the tripartite collision of Laurentia, Baltica, and Amazonia and the assembly of Rodinia. Supplementary material : U–Pb isotopic data (Table S1), trace element data (Table S2) and laser ablation spot images are available at https://doi.org/10.6084/m9.figshare.c.7084925

Chronological, Petrogenetic, and Tectonic Significance of Paleoproterozoic Continental Crust within the North China Craton during the Global Tectono-Magmatic Lull

Abstract The 2.45–2.20 Ga period during the early Paleoproterozoic era is considered to have witnessed a global “Tectono-Magmatic Lull (TML)” and thus marks a relatively quiescent period. Our study unveils a 2.45–2.20 Ga magmatic suite from the Xiong’ershan area in the southern North China Craton, offering some key constraints on localized active tectonics during the TML. Zircon U-Pb dating shows Paleoproterozoic ages for the meta-basalt (2.31, 2.28 Ga), Na-rich meta-andesite (~2.33 Ga), tonalite-trondhjemite-granodiorite (TTG) gneisses (2.36, 2.30 Ga), K-rich granodiorite (~2.29 Ga), and monzogranite (2.33, 2.27 Ga). The meta-basalts geochemically and petrographically belong to calc-alkaline basalts and show distinctive Nb, Ta, and Ti contents and primitive mantle normalized patterns from different places in the Xiong’ershan area. Combined with their enriched εHf(t) values, the magmas were derived from subduction-related enriched mantle sources within a convergent plate boundary. The meta-andesites display high MgO content (average 4.5 wt%) and Mg# (44–57), strongly fractionated rare-earth pattern, calc-alkaline affinity, and negative Nb, Ta, and Ti anomalies. The TTG gneisses are of high SiO2 type (>62 wt%), high (La/Yb)N (17.5, 39.2), and Sr/Y (50.2, 104.3) and mostly display positive Eu anomalies and high-pressure type. Zircons from these rocks show a relatively narrow range of δ18O isotope values (5.35‰, 6.79‰) with εHf(t) isotope characteristics (−9.3, −3.3), suggesting derivation from partial melting of a thickened mafic lower crust. The youngest K-rich granodiorite and monzogranite show high K2O/Na2O ratios (0.65, 2.45). Variable molar ratio Al2O3/(CaO+Na2O+K2O) (A/CNK) and low zircon εHf(t) values suggest that the K-rich granitoids formed from the partial melting of different levels of crust. The presence of meta-basalt to andesite assemblages and diverse intermediate to felsic magmatic rocks implies magmatic activity within a convergent plate boundary tectonic environment with potential influence from plume-triggered extensional processes, supported by evidence of slab rollback and upwelling of mantle material.