Early Paleozoic subduction fingerprints of the Paleo-Asian ocean in easternmost Central Asian Orogenic Belt (CAOB): Identification of the oldest Alaskan-type complex in the CAOB
1
Citation
52
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract The early-stage subduction records of the Paleo-Asian ocean are poorly preserved in the eastern segment of the Central Asian Orogenic Belt (CAOB), which hinders constraints on the evolution of the whole CAOB. This study presents new age data and zircon Hf-O isotopes as well as bulk-rock geochemistry of the Wuxing mafic-ultramafic complex in the Xingkai massif in northeastern China, which has been identified as Alaskan-type complex with aspects of field occurrence, petrological and mineral assemblages, and mineral chemistry in our recently published work. The results indicate that the complex formed mainly between 517 Ma and 510 Ma with a lithological sequence of Sanying clinopyroxenite (517 Ma), then Sanying gabbro (514 Ma), and Erying hornblendite (513 Ma), and finally Erying hornblende clinopyroxenite (510 Ma). The lithological formation sequence is consistent with the intrusive relations between lithological phases and their irrelevant major element compositions and variable trace element patterns of the bulk rocks. The εHf(t) values of zircon in two samples in this study vary from from +4.45 to +7.61 and from −11.8 to +4.42, respectively and tend to be more depleted with age. These features suggest that the Wuxing complex was a product of long-term arc magmatism and experienced significant ancient crustal assimilation in early-stage magmas and negligible contamination in later ones. The presence of 1222 Ma and 706 Ma inherited zircon grains implies existence of Proterozoic basement in the Xingkai massif and its continental arc setting in Cambrian. The Wuxing complex is the oldest Alaskan-type complex found so far in the entire CAOB and is a good witness of the Paleo-Asian oceanic subduction in the easternmost CAOB. The older age of the Wuxing complex compared to the regional Hongqiling intrusion is also compatible with its Alaskan-type nature and platinum-group element mineralization, which are distinct to the Permian-Triassic Ni-Cu sulfide deposit-hosting maficultramafic intrusions in the southern CAOB.Keywords:
Massif
Basement
Ultramafic rock
Continental arc
Cite
Abstract The early-stage subduction records of the Paleo-Asian ocean are poorly preserved in the eastern segment of the Central Asian Orogenic Belt (CAOB), which hinders constraints on the evolution of the whole CAOB. This study presents new age data and zircon Hf-O isotopes as well as bulk-rock geochemistry of the Wuxing mafic-ultramafic complex in the Xingkai massif in northeastern China, which has been identified as Alaskan-type complex with aspects of field occurrence, petrological and mineral assemblages, and mineral chemistry in our recently published work. The results indicate that the complex formed mainly between 517 Ma and 510 Ma with a lithological sequence of Sanying clinopyroxenite (517 Ma), then Sanying gabbro (514 Ma), and Erying hornblendite (513 Ma), and finally Erying hornblende clinopyroxenite (510 Ma). The lithological formation sequence is consistent with the intrusive relations between lithological phases and their irrelevant major element compositions and variable trace element patterns of the bulk rocks. The εHf(t) values of zircon in two samples in this study vary from from +4.45 to +7.61 and from −11.8 to +4.42, respectively and tend to be more depleted with age. These features suggest that the Wuxing complex was a product of long-term arc magmatism and experienced significant ancient crustal assimilation in early-stage magmas and negligible contamination in later ones. The presence of 1222 Ma and 706 Ma inherited zircon grains implies existence of Proterozoic basement in the Xingkai massif and its continental arc setting in Cambrian. The Wuxing complex is the oldest Alaskan-type complex found so far in the entire CAOB and is a good witness of the Paleo-Asian oceanic subduction in the easternmost CAOB. The older age of the Wuxing complex compared to the regional Hongqiling intrusion is also compatible with its Alaskan-type nature and platinum-group element mineralization, which are distinct to the Permian-Triassic Ni-Cu sulfide deposit-hosting maficultramafic intrusions in the southern CAOB.
Massif
Basement
Ultramafic rock
Continental arc
Cite
Citations (1)
The rocks of the stratified mafic-ultramafic massifs of the Nizhziderbinskiy complex (NW of the Eastern Sayan Mountains) are divided in chemical composition into three groups: ultramafic (dunites, vehrlites), subultramafic (clinopyroxenites, websterites) and mafic (gabbronorites, gabbro). The binary cards have registered the primary trends of rocks evolution. Taking into consideration the data organized by the collection of the evolved groups of rocks, the massifs of the Nizhniderbinskiy complex are rating to peridotite-pyroxenite-gabbroid formation.
Ultramafic rock
Massif
Peridotite
Cite
Citations (0)
Permian mafic‐ultramafic intrusions have great significance for understanding the geodynamic evolution of the Late Palaeozoic eastern Tianshan Orogen due to containing important information on the nature of mantle sources, crust–mantle interaction, and magmatic differentiation. Increasingly, more Permian mafic‐ultramafic intrusions are discovered in the Jueluotage belt, especially in the Kangguer ductile shear zone, whereas the mafic‐ultramafic intrusions in the Aqishan–Yamansu belt are ill‐informed. In this study, we provide zircon U–Pb geochronological, geochemical, and Sr–Nd–Pb–Hf isotopic data of a newly identified hornblende gabbro suite at the Shaquanzi Fe–Cu deposit in the Aqishan–Yamansu Belt. Zircon U–Pb dating results indicate that the Shaquanzi hornblende gabbro was emplaced at Early Permian (ca. 274–265 Ma). The rocks are calc‐alkaline and have arc‐like geochemical features, including enrichments in large‐ion lithophile elements (LILEs: Rb, Ba, K, Pb and Sr) and light rare‐earth elements (LREEs: Nb, Ta, Zr, Hf, and Ti), and depletions in high‐field‐strength elements (HFSEs) with markedly negative Nb and Ta anomalies. The rocks also exhibit depleted‐mantle isotopic signatures, with positive bulk‐rock ε Nd (t) values of +3.34 to +4.44 and positive zircon ε Hf (t) values of +2.8 − +8.7, which are relatively more enriched than those of coeval mafic‐ultramafic intrusions from the Kangguer ductile shear zone, but similar to those in the Central Tianshan Massif. We suggest that the Shaquanzi mafic intrusion suite was generated by 10–30% partial melting of a depleted‐mantle source at over 85 km depth, corresponding to the garnet to garnet‐spinel stability field. And the mantle source had likely been metasomatized by slab‐derived fluids of previous subduction. Integrating with geochemical data of the coeval mafic‐ultramafic and felsic intrusive rocks in the adjacent tectonic belts of eastern Tianshan Orogen, we speculate that the Shaquanzi mafic intrusion was formed in a post‐collision extensional setting, probably triggered by slab breakoff. Metasomatism of the depleted lithospheric mantle had likely occurred during the pre‐Permian subduction of the Kangguer oceanic slab.
Hornblende
Ultramafic rock
Petrogenesis
Geochronology
Cite
Citations (3)
The Baishiquan Cu-Ni sulfide deposit is located in the northern part of the Center Tianshan Massif,south of the Aqikuduke-Shaquanzi fault of the Eastern Tianshan Mountains.Ore-body was formed by the magmas and lay within the mafic-ultramafic complex.Zircons from the mineralized gabbro of the orefield yield a crystallization age of 281.2±0.9Ma.These gabbro and peridotites of the Baishiquan mafic-ultramafic complex have high Mg content.With enriched LILE(Rb、Ba、K、Sr),LREE and HFSE (U、Pb),these rocks have negative Ce anomalies and depleted HIFE(Th、Nb、Ta、Ti).These data indicate that the Baishiquan complex has the characters of mantle-derived and arc island magmas.Combined with analyses of the geological and tectonic characters of the Baishiquan complex,we conclude that the Baishiquan complex was formed in an island setting or active margin.This indicates that a subduction event was reasonable in the Eastern Tianshan Mountains in the Early Permian,thus the Paleo-Asian Ocean did not close until the later Early Permian.
Ultramafic rock
Lile
Massif
Cite
Citations (40)
Ultramafic rock
Felsic
Cite
Citations (16)
Massif
Geochronology
Charnockite
Cite
Citations (73)
Massif
Ultramafic rock
Amphibole
Diorite
Devonian
Anorthosite
Cite
Citations (15)