International Geology Review

Li, Hao-Ran; Qiao, Jian-Feng; Sun, Feng-Yue; Qian, Ye; Wang, Yan-Zhang; Bakht, Shahzad; Liu, Hao-Tian; Gu, Yan

doi: 10.1080/00206814.2023.2251547pmid: N/A

The Eastern Kunlun Orogenic Belt (EKOB), located north of the Qinghai-Tibetan Plateau, recorded voluminous late Palaeozoic – early Mesozoic intermediate-acid volcanic rocks. The tectonic evolution of the Palaeo-Tethys Ocean from initial subduction and final closure and post-collision extension has been hotly debated. This study examines the petrogenesis of Palaeozoic to Early Mesozoic volcanic rocks at six locations: Xiahe, Elashankou, Jirimai, Harizha, Nagengkangqieer, and Yazigounan. The investigation involves detailed field observations, petrology, zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemical analysis. The rocks analysed represent three episodic volcanic events. The ca. 257–245 Ma volcanic rocks were derived from magma mixing response to the subduction. The ca. 227–220 Ma highly fractionated I-type volcanics were derived from partial melting of the ancient lower crust, with varying contribution proportions of mantle materials. The ca. 216 Ma A-type volcanic rocks derived from partial melting of the juvenile crust. In this study, using existing regional geological data and spatiotemporal distribution of the magmatic region, combined with our new data, we attempt to propose more rational models to reveal the tectonic evolution of the Palaeo-Tethys Ocean, and we recognize three significant time nodes: (1) Ca. 240 Ma marks the final closure time of the Palaeo-Tethys Ocean. (2) Ca. 230 Ma indicates the vital tectonic regime transition from compression to extension response to slab break-off and continued lithospheric delamination. (3) Ca. 216 Ma mark the beginning of the final stage of orogeny in the EKOB, and mild magmatism lasts to ca. 200 Ma in response to the mountain collapse.

Chen, Youliang; Zhan, Guoxin; Qu, Lipeng; Yin, Guiqin; Guo, Yanhong; Zheng, Yuwen; Guo, Rui; Yin, Guan; Zhang, Chengjiang

doi: 10.1080/00206814.2023.2255649pmid: N/A

Here new evidence of the isotope geochronology and the geochemistry from the Yuanmou-Miyi complexes reveal the Precambrian tectono-magmatism geodynamic process in the study area. The Yangtze Block basement with 1.81- ~1.77 Ga and negative ε Hf(t) values of −7.8 to −0.7 corresponded to the assembly of the Columbia-supercontinent. However, the rifting magmatic event of ~ 1.70 Ga, which caused the continental crust extension-thinning in the study area, may exert influence on the subduction-magmatism in the Grenvillian period. The Yuanmou-Miyi complexes of 1.19- ~1.00 Ga are characterized by (La/Sm)N＞1, depletion in HFSEs, negative anomalies of Nb-Ta, and enrichment of LILEs, which show a genetic link with the subduction-magmatism. The temporal tendency that the magmatism from Yuanmou to Miyi gradually became younger, may be responsible for the subducting direction. The subduction caused the reactivation of the Anninghe-Lvzhijiag fault zone, and created the rupture windows of the subduction slab, leading to upwelling of the deep magma. These granitoids were derived from the partial melting of the mantle wedge, while the small-scale gabbro dikes intruded into the granitoids were likely spillover products from the asthenosphere mantle melts through the rupture windows.

Ersoy, Yalçın E.; Candan, Osman; Sarı, Bilal; Uysal, İ̇brahim; Palmer, Martin R.

doi: 10.1080/00206814.2023.2258393pmid: N/A

The east-west trending Taurides form a curved area in central eastern Anatolia known as the Gürün Curl. In order to understand the origin of the Gürün Curl and Tauride evolution in general, the results of a new field study of this region have been synthesized together with previously published data. We suggest that the geodynamic evolution of the area began with the likely presence of a Tethys Ocean transform fault. This fault separated the Taurides into the Akdere Sector in the west and the Munzur Sector in the east in the Late Cretaceous. During the late Santonian–early Campanian, ophiolites obducted onto the Munzur Sector, while platform sediments continued to accumulate in the Akdere Sector. This was followed by the development of an Andean-type arc-type magmatism (the Baskil Arc) during the early–middle Campanian in the Munzur Sector. Continued closure of the Tethys led to the collision of the Bitlis Massif in the south of the Munzur Sector in the Campanian. This, in turn, resulted in continental subduction and slab roll-back that was controlled by a Subduction Transform Edge Propagator (STEP) Fault that lay on the original transform fault between the Akdere and Munzur sectors. Because the subducted slab was free at its western corner, the western edge rolled back faster than in the east, leading to an asymmetrical extensional regime on the upper plate that created the late Campanian Hekimhan Basin. While these geodynamic events were taking place in the Munzur Sector, the Akdere Sector was in a platform setting. During the Palaeocene, the Late Mesozoic units of the Akdere Sector began to overthrust on the Hekimhan Basin and the ophiolites. Following the Palaeocene, all these tectonostratigraphic units were covered by Eocene sediments around the Gürün Curl of which the modern appearance was completed by the Miocene to Recent movements along the strike-slip faults.

Rojo-Pérez, Esther; Fuenlabrada, José M; Díez Fernández, Rubén; Arenas, Ricardo

doi: 10.1080/00206814.2023.2258394pmid: N/A

The evolution of the Gondwana along the flank of the West African Craton was complex and is far from understood. Subduction-related activity along this margin spanned between c. 750 and 500 Ma. Sections close to African cratons record the earliest stages, while Autochthonous and Allochthonous domains of the Variscan Belt preserve the latest stages of the arc system, essentially between c. 540 and 500 Ma. The geochemistry of the Ediacaran-early Cambrian siliciclastic series deposited along this Cadomian active margin preserves the evolutionary history of their sources, which are related to activity in the arc and nearby continental areas. In this sense, the SW Iberian Massif (Ossa-Morena Complex) preserves a section of this Ediacaran-early Cambrian peri-Gondwanan arc. Its evolution can be tracked through the characterization of the subduction-related magmatism (including the Mérida Massif) and coeval metasedimentary record (Serie Negra Group and Malcocinado Formation) during a time interval spanning almost 100 m.y., from pre-602 Ma to at least c. 534 Ma. This study reveals that arc magmatism is closely linked with synorogenic deposition in a complex way so far unexplored. Arc recycling is revealed by the isotopic equivalence of synorogenic strata to the first magmatic event (pre-602 Ma), and by geochronological data of the arc-building pulses. The earliest magmatic pulses (c. 602–550 Ma) are characterized by significant crustal input, likely favoured by subduction erosion. Subsequently, magmatism evolved towards larger mantle involvement (c. 540–534 Ma), likely associated with progressive variation in the slab angle. These slab-mantle-upper plate interactions generated changes in the arc dynamics leading to an extensional setting with alkaline magmatism during the Cambrian. This review proposes a model of petrogenetic and geodynamic arc evolution between the Ediacaran and the Early Cambrian. The gathered data could improve the accuracy of future palaeogeographic reconstructions for the northern margin of Gondwana.

Wang, Lintao; Yu, Shengyao; Sun, Guozheng; Lv, Pei; Peng, Yinbiao; Jiang, Xingzhou; Dai, Liming; Liu, Yongjiang; Li, Sanzhong

doi: 10.1080/00206814.2023.2258534pmid: N/A

Earth’s first continental crust is formed by Archaean and mainly consisted of tonalite–trondhjemite–granodiorite with a small amount of diorites (DTTGs), which has an essential role in probing early crust–mantle dynamic regime and in understanding the formation mechanism of continental crust. Here, we present zircon U‒Pb dating and Lu‒Hf isotopes, whole-rock geochemistry, and petrography on DTTGs rocks in the Dunhuang Block. Three episodes of DTTGs were emplaced circa 2.67 Ga, 2.60 Ga, and 2.50 Ga. The circa 2.67 Ga TTGs exhibit high SiO2 contents (68.14–71.70 wt%), low MgO contents (0.65–1.31 wt%), and high ratios of (La/Yb)N (146 on average), with their enriched Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t) = -5.77–0.53], indicating origination from partial melting of amphibolites at thickened lower crust. In contrast, the circa 2.60 Ga transitional TTGs exhibit relatively high MgO contents (2.80–3.39 wt%), flat REE (Rare earth element) patterns with moderate ratios of (La/Yb)N (20.49 on average), and dispersed Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t)= −3.99–3.08]. Accordingly, circa 2.60 Ga transitional TTGs melts were produced by partial melting of the shallower crust induced by mantle-derived magma upwelling. The circa 2.50 Ga diorites exhibit low SiO2 (55.72–59.11 wt%) but high MgO (3.51–4.52 wt%) contents with positive Nd-Hf isotopes [ƐHf (t) = -0.16–4.17 and ƐNd (t) = 2.00–4.45], suggesting that they originated from partial melting of mantle wedges metasomatized by fluid from subduction slabs. Combined with the detailed petrogenetic studies and crustal thickness variation, we conclude that the complex crust–mantle interaction may be an essential reason for the Neoarchaean diversity of DTTGs from the Dunhuang Block, which experienced prolonged arc accretion before Neoarchaean, followed by delamination between 2.67 and 2.60 Ga and subsequently transitioned to subduction.

Ao, Aliba

doi: 10.1080/00206814.2023.2263769pmid: N/A

Tectonic slices of greenschist – epidote blueschist – epidote amphibole schist – garnet epidote amphibole schist are exposed in the northern part of the NOC. Metamorphic P-T conditions and P-T paths of the garnet epidote amphibole schist and epidote blueschist were determined with the help of pseudosection calculations in the MnNCKFMASHTO system using the software Perple_X. The garnet epidote amphibole schist records a pre-peak metamorphic stage at ~12 kbar and ~360°C in the lawsonite blueschist facies field. Lawsonite and glaucophane are not preserved in the rock and are attributed to progressive metamorphic reactions during prograde metamorphism. The peak metamorphic stage is constrained at ~14 kbar and ~570°C in the hornblende eclogite facies field. Post-peak metamorphism shows slight cooling and decompression from ~550°C and ~13 kbar, possibly down to ~350°C and ~7 kbar in the greenschist facies field. These three metamorphic stages reveal a clockwise metamorphic P-T path of evolution for the garnet epidote amphibole schist. The geotherm at metamorphic peak P-T condition is ~12.5°C/km, which is hotter by ~350°C compared to thermal models of mature subduction zones but shows good agreement with models of warm subduction zones. Therefore, the low geothermal gradient of ~8°C/km during the prograde metamorphism possibly reflects the subduction of cold Neo-Tethyan ocean crust when the temperature conditions of the subduction zone were still warm. The epidote blueschist shows peak metamorphism at ~10 kbar and 380°C with a clockwise P-T path. It indicates metamorphism at a more mature stage of subduction. Buoyancy-driven exhumation along the subduction channel due to the serpentinization of the upper mantle wedge played a vital role in the detachment and exhumation of the tectonic slivers of metamorphic rocks from different depth sections in the northern margin of the NOC.

Casas, Josep Maria; Murphy, J. Brendan; Díez Montes, Alejandro; Sánchez-García, Teresa; de Poulpiquet, Jacques; Álvaro, J. Javier; Guimerà, Joan

doi: 10.1080/00206814.2023.2263787pmid: N/A

We propose that the 495-470 Ma Ollo de Sapo magmatism in the Iberian Massif was the result of a mantle plume event in the Furongian-Early Ordovician. This plume was located beneath the northwestern margin of Gondwana and caused rapid and extensive melting of Ediacaran arc-related crustal rocks and their derived sediments. Mafic magmas due to plume partial melting underplated the crust and were emplaced at mid-lower crustal levels (~15km), and provided the heat for crustal melting. Manifestations of the plume include (i) pronounced magnetic anomalies in the region which match the distribution of Ollo de Sapo rocks, (ii) the Toledanian unconformity (and gap), which is attributed to thermal doming, and (iii) the significant thickness variations in Lower to Middle Ordovician sedimentary successions in adjacent areas. In a more regional context, we infer that the plume was one of a cluster of plumes impacting the Gondwana periphery and that it contributed to the birth and development of the Rheic Ocean throughout Gondwana margin breakup.