Petrology, petrogenesis, and geochronology review of the Cenozoic adakitic rocks of northeast Iran: Implications for evolution of the northern branch of Neo-Tethys

Cenozoic adakitic rocks of the northern part of the Central Iran Structural Zone (CISZ) are among the notable geological features of the terrains in northeast Iran, so a comprehensive comparison of several of these adakitic sequences is presented. This lithogeochemical analysis is constrained to examining adakitic magmatism of the three magmatic belts within the CISZ, which from southeast to northeast and from oldest to youngest are as follows: (a) south of Shahrood-Damghan, (b) north-northwest of Sabzevar-Neyshabour, and (c) south of Qouchan and west of Esfarayen. Radiogenic isotope analysis using Rb–Sr and Sm–Nd methods show that the adakitic rocks associated with Qouchan-Esfarayen magmatism have 0.512581 to 0.51288 initial 143Nd/144Nd and 0.703903 to 0.705627 initial 87Sr/86Sr, with εNd −0.86 to 4.98. Adakitic rocks in south to southeast Shahrood have 0.512775 to 0.512893 initial 143Nd/144Nd and 0.703746 to 0.705314 initial 87Sr/88Sr, with εNd 3.69 to 6.0, and adakites emplaced into the Sabzevar ophiolite have 0.512846 to 0.512911 initial 143Nd/144Nd and 0.70379 to 0.705019 initial 87Sr/86Sr contents with εNd of 5.26 to 6.54. Isotopic initial ratios of Nd and Sr support an origin involving partial melting of the subducting oceanic lithosphere of the northern branch of Neo-Tethys and the associated suprasubduction mantle wedge in producing these adakitic rocks

Reconstructing South China in Phanerozoic and Precambrian supercontinents

This paper is financially supported by a NSFC Major Program (41190070) entitled “Reconstruction of East Asian Blocks in Pangea”. PAC acknowledges support from the Australian Research Council grant FL160100168 and WW thanks the support from “Thousand Youth Talents Plan”.The history of the South China Craton and the constituent Yangtze and Cathaysia blocks are directly linked to Earth's Phanerozoic and Precambrian record of supercontinent assembly and dispersal. Exposed Archean rocks are limited to isolated fragments in the Yangtze Block that preserve a record of Meso- to Neo-Archean magmatism, sedimentation and metamorphism associated with a period of global craton formation and stabilization that corresponds with the assembly of the Kenor supercontinent/supercraton. However, there are insufficient data to link its history with other similar aged cratons. The tectonostratigraphic record in South China in the Paleoproterozoic, corresponding with the assembly of Nuna, suggests that rock units in the Yangtze Block were spatially linked with northwestern Laurentia and possibly Siberia, whereas Cathaysia was joined to northern India. During the formation of Rodinia at the end of the Mesoproterozoic through to that of Pangea in the mid-Paleozoic, Cathaysia remained joined to northern India. Early Neoproterozoic supra-subduction zone magmatic arc-back arc assemblages ranging in age from ~ 1000 Ma to 810 Ma occur within Cathaysia, along its northwestern margin, and along the southeastern margin of the Yangtze Block. These rocks provide a record of convergent plate interaction, which continued along the western margin of the Yangtze Block until around 700 Ma and correlates with similar along strike subduction zone magmatism in northwest India, Seychelles and Madagascar. During the final assembly of Gondwana in the early Paleozoic suturing of India-South China with the Western Australia-Mawson blocks along the Kuunga Orogen resulted in the accretion of the Sanya Block of Hainan Island with the rest of Cathaysia. The accretion of Laurussia to Gondwana in the mid-Paleozoic to form Pangea corresponds with the initiation of lithospheric extension along the northern margin of Gondwana and the separation of a number of continental blocks, including South China, which then drifted northward across the Paleo-Tethys to collide with the Asian segment of Pangea in the Permo-Triassic.PostprintPeer reviewe

Early Paleozoic tectonic evolution of the Xing-Meng Orogenic Belt: constraints from detrital zircon geochronology of western Erguna-Xing'an Block, North China

International audienceTo better constrain the Early Paleozoic tectonic evolution of the western part of the Erguna-Xing'an Block, detrital zircon U-Pb dating was applied on the Ordovician to Devonian sedimentary strata along the southeast part of the China-Mongolia border. Most of the zircons from five sedimentary samples display fine-scale oscillatory growth zoning and Th/U ratios higher than 0.1, indicating a magmatic origin. All five Ordovician-Devonian samples display the similar age distribution patterns with age groups at ∼440 Ma, ∼510 Ma, ∼800 Ma, ∼950 Ma, and few Meso- to Paleo-Proterozoic and Neoarchean grains. This age distribution pattern is similar to those from adjacent blocks in the southeastern Central Asian Orogenic Belt. Considering previous tectonic studies, we propose bidirectional provenances from the Erguna-Xing'an Block and Baolidao Arc. Consequently, a new model was proposed to highlight the Early Paleozoic tectonic evolution of the western Erguna-Xing'an Block, which constrains two main Early Paleozoic tectonic events of the Xing-Meng Orogenic Belt: (a) pre-Late Cambrian collision between Erguna-Kerulen Block and Arigin Sum-Xilinhot-Xing'an Block; (b) the Early Paleozoic subduction of Paleo-Asian Ocean and pre-Late Devonian collision between Erguna-Xing'an Block and Songliao-Hunshandake Bloc

A >1300 km late Pan-African metamorphic belt in NE China: New evidence from the Xing'an block and its tectonic implications

The Xing'an Block is one of several fault-bounded crustal units in northern China located along the southeastern margin of the Central Asian Orogenic Belt (CAOB) and includes the Great Xing'an Range. The basement rocks constitute a khondalitic sequence of sillimanite- and garnet-bearing gneisses, hornblende–plagioclase gneiss and felsic paragneiss named the Xinghuadukou Complex. LA-ICP-MS zircon U–Pb dating of a sillimanite gneiss from Hanjiayuan indicates high-grademetamorphismoccurred at 496±3 Ma,with several older detrital zircon grains with ages extending from678±8 to 1373±17Ma.Asample of hornblende–plagioclase gneiss fromthe northern part of the Xinghuadukou Complex yields a metamorphic age of 496±7 Ma, whereas igneous zircon core ages range from601±15 to 1637±23Ma.Another sample of hornblende–plagioclase gneiss fromfarther south in the Xinghuadukou Complex yields a metamorphic age of 495±5 Ma, and magmatic core ages of 546±4 Ma. These data indicate that high-grade metamorphism occurred at ~500 Ma and that several earlier magmatic events are recorded in the area, including some in the Neoproterozoic. These new age data, togetherwith other recent data obtained fromthe Erguna, Songliao, Jiamusi and Khanka blocks, establish a N1300 kmPan-African khondalite belt along the southern margin of the CAOB

Morphology, trace elements, and geochronology of zircons from monzogranite in the Northeast Xing'an Block, northeastern China: constraints on the genesis of the host magma

The morphology, trace-element composition and geochronology of 43 zircon grains from two monzogranite samples from the Northeast Xing'an Block, northeastern China, were determined using cathodoluminescence imaging and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Three morphological subtypes (S3, S8 and S9) are recognized in the zircon grain samples, and subtype S8 is dominant, reflecting a calc-alkaline, moderately aluminous, high-pressure crystallization medium and a crystallization temperature of 700 +/- 50 degrees C. The zircon grains are characterized by oscillatory zoning, relatively high Th/U ratios (0.3-1.0), steep chondrite-normalized rare-earth element patterns, high Hf contents (>9000 ppm), positive Ce (Ce/Ce* = 4.84 to 2914) and negative Eu (Eu/Eu* = 0.24 to 0.90) anomalies, indicating a magmatic source. The Pb-206/U-238 ages of the two monzogranite samples are 180 +/- 1 and 181 +/- 1 Ma, respectively, implying an Early Jurassic emplacement age for the intrusion. The disparate geochemical behaviors of Hf, Th, and Nb within the zircons, as well as the U/Yb, Nb/Yb, Th/U, Nb/Hf, Th/Nb, and Hf/Th ratios, suggest a continental-crust source in a compressional-magmatic-arc or orogenic-tectonic setting, and a calc-alkaline parent magma. All of the grains show relatively high Ce4+/Ce3+ ratios, suggesting that they were derived from an oxidized magma, which favors enrichment of Cu-Mo elements in the granite porphyry

A >1300km late Pan-African metamorphic belt in NE China: New evidence from the Xing'an block and its tectonic implications

The Xing'an Block is one of several fault-bounded crustal units in northern China located along the southeastern margin of the Central Asian Orogenic Belt (CAOB) and includes the Great Xing'an Range. The basement rocks constitute a khondalitic sequence of sillimanite- and garnet-bearing gneisses, hornblende-plagioclase gneiss and felsic paragneiss named the Xinghuadukou Complex. LA-ICP-MS zircon U-Pb dating of a sillimanite gneiss from Hanjiayuan indicates high-grade metamorphism occurred at 496 ± 3. Ma, with several older detrital zircon grains with ages extending from 678 ± 8 to 1373 ± 17. Ma. A sample of hornblende-plagioclase gneiss from the northern part of the Xinghuadukou Complex yields a metamorphic age of 496 ± 7. Ma, whereas igneous zircon core ages range from 601 ± 15 to 1637 ± 23. Ma. Another sample of hornblende-plagioclase gneiss from farther south in the Xinghuadukou Complex yields a metamorphic age of 495 ± 5. Ma, and magmatic core ages of 546 ± 4. Ma. These data indicate that high-grade metamorphism occurred at ~. 500. Ma and that several earlier magmatic events are recorded in the area, including some in the Neoproterozoic. These new age data, together with other recent data obtained from the Erguna, Songliao, Jiamusi and Khanka blocks, establish a > 1300. km Pan-African khondalite belt along the southern margin of the CAOB. © 2011 Elsevier B.V.link_to_subscribed_fulltex

Amphibolite of the Xinghuadukou group from the Xinlin-Xiguitu belt, NE China: new evidence for the NE branch of the Paleo-Asian Ocean

Poster Session TS9.3/EMRP4.2: Reconstruction of East Asian Blocks in Pangea - no. EGU2017-9428The tectonic evolution of the Paleo-Asian Ocean (PAO) witnessed the cycling of two supercontinents, Rodinia and Pangea, in Earth's geological history. This long-lasting paleo-ocean was initiated by the breakup of the supercontinent Rodinia during the Early Neoproterozoic (1,2) and terminated by the final collage of the supercontinent Pangea from Central to Eastern (current coordinates) Asia, likely lasting to the Late Permian or Early Triassic (3,4). Numerous continental and island arcs, seamounts, mid-ocean ridges and micro-blocks were amalgamated responding to the subduction and consumption of the oceanic crust of the PAO, to form the most complex and long-living Phanerozoic accretionary orogenic belt, the Central Asian Orogenic Belt (CAOB) (5,6). Trapped by the collision and amalgamation of the eastern segment of CAOB, several rock suites of oceanic affinity were reported along the Xinlin-Xiguitu belt that connects the Erguna block to the northwest and the Xing'an block to the southeast in NE China, including the Toudaoqiao blueschist (7), Jifeng ophiolite (although the forming environment remains debatable, see 8 and 9), and Xinlin ophiolite (10,11). All these suites have been proposed to be the relics of the NE branch of the PAO. However, along the northeastern extension of this belt, outcropped the Xinghuadukou group that was previously thought Paleoproterozoic in age yet has been reconsidered to be Cambrian (12), the relationship of which and this belt remains unclear. In this study, a suite of amphibolite was collected from the Xinghuadukou group outcropped in the easternmost Xinlin-Xiguitu belt in NE China and conducted geochemical analysis to discuss their forming environment and tectonic implications. Samples display low SiO2 (45%-49%wt), low K2O (0.55%-1.07%wt) compositions, low in A/CNK, but high in A/NK and FeOt/MgO ratios. REE compositions are relative low (SigmaREE=52-122ppm) showing a flat chondrite normative pattern with slight enrichment in LREE ((La/Ya)N=1.5-2.4) and no Eu anomaly (Eu/Eu*=0.9-1.0). The LILE fractionation is indistinctive ((Sr/Y)N=1.1-1.8). Samples show an evident E-MORB affinity. Along with the previous studies, it can be concluded: 1) the protolith of the amphibolite of the Xinghuadukou group is a suite of tholeiitic basalt that formed in the oceanic islands environment; 2) with all the oceanic suites reported in Xinlin-Xiguitu belt, a branch of the Eastern PAO can be well defined, which likely existed from the Late Neoproterozoic to Late Cambrian, so called the Xinlin-Xiguitu Ocean. Acknowledgements: This study was financially supported by the National Natural Science Foundation of China (Projects 41190075, 41190070, 41230207, 41390441), the Hong Kong Research Grants Council General Research Fund (HKU7063/13P and 17301915), and the HKU Seed Funding Programme for Basic Research (201311159126). References: 1. N. L. Dobretsov et al., Gondwana Res. 6(2), 143-159 (2003). 2. J. Tang et al., Precambrian Res. 224, 597-611 (2013). 3. J. Y. Li, J. Asian Earth Sci. 26(3), 207-224 (2006). 4. P. R. Eizenhöfer et al., Tectonics 33(4), 441-463 (2014). 5. B. F. Windley et al., J. Geol. Soc. 164(1), 31-47 (2007). 6. W. Xiao et al., Annu. Rev. Earth Planet. Sci. 43, 477-507 (2015). 7. J. B. Zhou et al., J. Asian Earth Sci. 97, 197-210 (2015). 8. Z. Feng et al., Int. J. Earth Sci. 105(2), 491-505 (2016). 9. D. H. Ni, Int. J. Earth Sci. (2016). doi:10.1007/s00531-016-1412-2 10. R. S. Li, Heilongjiang Geology, 2(1), 21-32 (1991). 11. W. Yan et al., Earth Sci. - J. Chin. Uni. Geo. 8 (2014). 12. L. Miao et al., Chin. Sci. Bull. 52(8), 1112-1124 (2007)