Carboniferous and Permian evolutionary records for the Paleo‐Tethys Ocean constrained by newly discovered Xiangtaohu ophiolites from central Qiangtang, central Tibet

Geophysical Research Letters

et al. 2019

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To better constrain the origin and drift history of the North Qiangtang terrane (NQT), we report a well‐dated paleomagnetic pole from the Late Permian volcanics of the NQT that appears to average out secular variation. Our new results yield a paleolatitude of −7.6 ± 5.6°N at ~259 Ma for our sampling area, which confirms the NQT drifted northward during the Permian and Triassic periods. The equatorial paleolatitude of the NQT is similar to that of the coeval South China block, demonstrating that they were in close proximity. Combined with palaeontological and magmatic evidence, paleomagnetic constraints on the drift of the NQT in the Permian indicate that the NQT moved northward together with the South China block at this time. The paleolatitude evolution of the NQT implies that the NQT rifted from the northern margin of the Gondwana in the Devonian, which is earlier than the departure time of the South Qiangtang terrane.

Section: Discussionmentioning

confidence: 84%

Paleomagnetic Constraints on the Origin and Drift History of the North Qiangtang Terrane in the Late Paleozoic

Geophysical Research Letters

et al. 2019

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“…Data sources: Paleo‐Tethyan ophiolites (Xu et al, ; Xu & Castillo, ); Permian ophiolites from Longmuco‐Shuanghu suture (LSS; Zhang et al, ); Emeishan plume‐related basalts (modified from Xu et al, ) and picrites (J. Li et al, ; Z. C. Zhang et al, ); global oceanic sediments with average ɛNd and ɛHf values (ɛNd = −8.9, ɛHf = +2 ± 3), island arc lavas, ocean island basalt (OIB), mid‐ocean ridge basalt (MORB), and mantle array (εHf s= 1.59 × εNd + 1.28; Chauvel et al, ; Plank & Langmuir, ); and Sunda arc lavas (Handley et al, ). The Nd isotopic compositions of the mantle wedge prior to slab addition are estimated from the Permian ophiolitic normal MORB (NMORB)‐type basalts from LSS (Zhang et al, ), which are also within the range of the Emeishan plume‐related picrites. Hf isotopic compositions are calculated by assuming that the ɛNd and ɛHf values follow the mantle array.…”

Section: Resultsmentioning

confidence: 99%

“…Considering the tectonic framework of the Late Permian northward subduction of the Paleo‐Tethys oceanic crust represented by the LSS beneath the NQT (Liu, Ma, Guo, Sun et al, ; Yang et al, , ; Zhang et al, ), we suggest that the mantle source was generated in the subarc mantle wedge modified by subducted sediment‐derived aqueous fluids, based on the following points. The normal mid‐ocean ridge basalt (NMORB)‐type basalts in the Permian ophiolite suites from the LSS (Zhang et al, ) represent the regional depleted mid‐ocean ridge basalt (MORB) mantle composition. They are characterized by high εNd (t) values (+4.7 to +8.2), consistent with previous conclusions that Late Paleozoic Paleo‐Tethyan oceanic crust and modern Indian MORB originated from a similar mantle reservoir with high εNd (t) values (+4.3 to +11.5; Figure a; Xu et al, ; Xu & Castillo, ).…”

Section: Discussionmentioning

confidence: 99%

Late Permian Bimodal Volcanic Rocks in the Northern Qiangtang Terrane, Central Tibet: Evidence for Interaction Between the Emeishan Plume and the Paleo‐Tethyan Subduction System

Zhang

et al. 2018

JGR Solid Earth

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Many studies provide compelling evidence for a fossil mantle plume beneath the Late Permian Emeishan large igneous province located near the southeastern margin of the central Tibetan Plateau, a region associated with the Paleo‐Tethyan subduction system. However, little is known about whether direct plume‐subduction interaction occurred during the Late Permian. Here we report geochronological, mineralogical, geochemical, and Sr‐Nd‐Hf‐O isotopic data for the Late Permian (~259–256 Ma) bimodal volcanic rocks (BVRs) in the northern Qiangtang Terrane (NQT), central Tibet. These BVRs consist mainly of basalts, rhyolites, and rhyolitic tuffs. The rhyolites with A‐type affinity were generated by partial melting of newly underplated basalts. Geochemical and isotopic data suggest that two components (ocean island basalt‐type mantle and subducted sediment‐derived fluid) were involved in the generation of the basalts in an extensional back‐arc region. Considering the Permian tectonic evolution of the NQT, we propose that this enriched ocean island basalt‐type mantle was distinct from the Paleo‐Tethyan depleted upper mantle. It most likely originated from Emeishan‐plume material that flowed westward from the South China Block to the nearby NQT, driven by slab rollback‐induced counterflow. The presence of high‐temperature A‐type rhyolites in bimodal back‐arc magmatism also indicates a special subduction setting influenced by a nearby plume. Thus, we propose that the Late Permian BVRs were the result of interaction between the Emeishan plume and the Paleo‐Tethyan subduction system.

“…Recent studies subdivided the Qiangtang Block into the northern and southern Qiangtang Blocks (NQB and SQB) relative to the intervening Longmu Co-Shuanghu Suture Zone [Li, 1987;Li and Zheng, 1993;Metcalfe, 2013;Zhang et al, 2006;Zhai et al, 2011aZhai et al, , 2011bZhai et al, , 2013, which was regarded as the relic of the main Paleo-Tethys Ocean [Metcalfe, 2013;Zhai et al, 2011aZhai et al, , 2011bZhai et al, , 2013Zhu et al, 2013]. Since the amalgamation of NQB and SQB, accompanying the Paleo-Tethys Ocean closure in Early Permian [Zhang et al, 2016], the Qiangtang Block underwent a series of collisional events [Girardeau et al, 1984;Pan et al, 1998;Pan et al, 2012;Pearce and Deng, 1988;Tang and Wang, 1984;Wang et al, 2000;Zhu et al, 2013]. Collision with the Songpan-Ganzi Block to the north in the Late Triassic formed the Jinsha Suture (JS) [Pan et al, 1998;Wang et al, 2000] and collision with the Lhasa Block to the south in the Early Cretaceous formed the Banggong-Nujiang Suture (Figure 1b) [Girardeau et al, 1984;Hao et al, 2016aHao et al, , 2016bPan et al, 2012;Pearce and Deng, 1988;Tang and Wang, 1984;B.-D. Wang et al, 2016;Zhu et al, 2013], respectively.…”

Section: Introductionmentioning

confidence: 99%

Eocene adakitic porphyries in the central‐northern Qiangtang Block, central Tibet: Partial melting of thickened lower crust and implications for initial surface uplifting of the plateau

Wyman

et al. 2017

JGR Solid Earth

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The time and mechanism of crustal thickening and initial surface uplift of the Tibetan Plateau remain highly controversial. Here we report on zircon U‐Pb age, and mineral, element, and Sr‐Nd isotope composition data for Eocene adakitic porphyries in the Laorite Co area of central‐northern Qiangtang Block, central Tibet. Laser ablation‐inductively coupled plasma‐mass spectrometry zircon U‐Pb age dating shows that the porphyries were generated at 42–41 Ma. All samples display adakitic geochemical characteristics, such as high SiO2 and Al2O3, and low Y and Yb contents, and high Sr/Y and La/Yb ratios with positive Sr and negligible Eu anomalies and Nb‐Ta depletion. They also have low magnesium number (Mg #) (16–45) and high K2O (4.0–4.6 wt %) values, as well as high (87Sr/86Sr)i (0.7076–0.7080) and low εNd(t) (−5.9 to −4.4) values. These adakitic rocks were most probably generated by partial melting of thickened lower crust in the stability field of garnet, amphibole, and rutile but with relatively minor plagioclase. Moreover, such a crustal thickening process beneath this block likely occurred no later than the middle Eocene and was most probably caused by the southward subduction of the Songpan‐Ganzi Block in the early Cenozoic. In addition, the occurrences of exposed adakitic porphyries unambiguously indicate that exhumation process occurred after their formation. Thus, these ~42 Ma adakitic porphyries indicate the occurrence of significant exhumation since 42 Ma. Integrated with the thermochronological and paleoelevation data, we suggest that the initial surface uplift of the Qiangtang Block, triggered by crustal thickening, was underway by the middle Eocene (~42 Ma).