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Geochronology and Geochemistry of Late Devonian I- and A-Type Granites from the Xing’an Block,NE China:Implications for slab break-off during Subduction of the Hegenshan-Heihe Ocean

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Journal of Earth Science 2022年第1期33卷 150-160页

作者： Zheng Ji Wenchun Ge Hao Yang Yanlong Zhang Yu Dong Junhui Bi Xiwen Liu College of Earth Sciences Jilin UniversityChangchun 130061China Tianjin Center China Geological SurveyTianjin 300170China Jilin Provincial Water Resources and Hydropower Consultative Company Changchun 130021China

We present detailed geochronological,geochemical,and zircon Hf isotopic data for Late Paleozoic granitic rocks from Handagai and Zhonghe plutons in the Xing’an Block,NE China,aiming to provide constraints on their origin and tectonic implications.New zircon U-Pb ages indicate they were formed in the Late Devonian(ca.379 Ma) immediately after a striking 50 Ma magmatic lull(ca.430-380 Ma) in the Xing ’ an Block.Petrological and geochemical features suggest that the Handagai monzogranites and Zhonghe alkali-feldspar granites are I- and A-type granites,respectively,although both of them have high-K calc-alkaline features and positive zircon ε_(Hf)(t) values(+3.47 to +10.77).We infer that the Handagai monzogranites were produced by partial melting of juvenile basaltic crustal materials under a pressure of slab break-off of the Hegenshan-Heihe oceanic plate may account for the subduction-related extensional setting,as well as the transformation of arc magmatism from the Early-Middle Devonian lull to the Late Devonian-Early Carboniferous flare-up in the Xing’an Block.

关键词： Late Devonian granitoids geochemistry slab break-off Hegenshan-Heihe Ocean Xing’an Block

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The Late Triassic I-Type Granites from the Longmu Co-Shuanghu Suture Zone in the interior of Tibetan Plateau, China： Petrogenesis and Implication for slab break-off

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Acta Geologica Sinica(English Edition) 2018年第3期92卷 935-951页

作者： ZHAO Zhen WU Zhenhan LU Lu YU Junqiu WU Yanjun Chinese Academy of Geological Sciences Beijing 10037 China College of Paleontology Shenyang Normal University Shenyang 110034 China

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between POand SiO, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO, MgO, FeOt, MnO, CaO) and SiO. Almost all ε(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low NaO/KO ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.

关键词： the Late Triassic I-type granite slab break-off Longmu Co-Shuanghu Suture Tibetan Plateau China

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Mantle Response to slab breakoff in the North Qaidam Tectonic Belt: Geochemical Constraints from Syn-subduction Mafic Igneous Rocks

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Acta Geologica Sinica(English Edition) 2020年第S1期94卷 26-27页

作者： LI Xiucai NIU Manlan CAI Qianru WU Qi SUN Yi YUAN Xiaoyu LI Chen Hefei University of Technology Hefei Anhui 230009

slab breakoff originally denotes the detachment of dense subducted oceanic slab from the light subducted continental slab, which is driven by opposing buoyancy forces during continental collision(Davies and von Blanckenburg, 1995;von Blanckenburg and Davies, 1995). The breakoff of subducted oceanic slab can induce the upwelling of sub-slab asthenosphere through the slab window, and then heat the overriding lithospheric mantle resulting in the melting of its fertile layer within the metasomatic mantle wedge. The decompression partial melting of uprising asthenospheric mantle commonly produce mafic magma with depleted MORB-like geochemical signatures(Davies and von Blanckenburg, 1995;Cole et al., 2006;Wang et al., 2018), whereas the partial melting of enriched lithospheric mantle will produce mafic magma with alkaline, calc-alkaline or ultrapotassic features(von Blanckenburg and Davies, 1995). These mafic magmas rise into overlying lower crust and trigger crustal melting to generate the granitic magma. The North Qaidam tectonic belt(NQTB) records the evolutionary process of the South Qilian Ocean from subduction to closure. The subduction of oceanic and continental lithosphere to mantle depths is proven by the identification of oceanic-type and continental-type eclogites enclosed in crustal metapelite and gneiss from the North Qaidam tectonic belt(Song et al., 2006;Zhang et al., 2008;Zhang et al., 2010;Zhang et al., 2017). However, details of this process are not exactly constrained, in particularly, the closure timing of South Qilian Ocean. The study of characteristic mafic magmatism, combined with the previous studies of ultra-high pressure metamorphism, give us an excellent opportunity to trace the detailed processes associated with the transition from oceanic subduction to continental subduction, and assess the feasibility of slab breakoff in the North Qaidam tectonic belt. In this contribution, an integrated study of petrology, geochemistry, geochronology and Sr-Nd-Hf isotopes is performed on the mafic igneous

关键词： mafic igneous rocks mantle slab break-off North Qaidam early Paleozoic

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Zircon dating,Hf-Sr-Nd-Os isotopes and PGE geochemistry of the Tianyu sulfide-bearing mafic-ultramafic intrusion in the Central Asian Orogenic Belt,NW China

Zircon dating,Hf-Sr-Nd-Os isotopes and PGE geochemistry of t...

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中国科学院地质与地球物理研究所第11届（2011年度）...

作者： Dongmei Tang~(a,*),Kezhang Qin~a,Chusi Li~(b,*),Liang Qi~c,Benxun Su~a,Wenjun Qu~d ~aKey Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China ~bDepartment of Geological Sciences,Indiana University,Bloomington,IN 47405,USA ~cInstitute of Geochemistry of Chinese Academy of Sciences,Guiyang,550002,China ~dNational Research Center of Geoanalysis,Chinese Academy of Geological Sciences,Beijing,100037,China

The Tianyu mafic-ultramafic intrusion is one of many important sulfide-bearing mafic-ultramafic intrusions in the eastern Tianshan terrane located in the southern margin of the Central Asian Orogenic Belt in north Xinjiang, NW China.The origin of sulfide mineralization in these intrusions,their relationship with Permian basalts and Atype granites,and the geodynamic setting of the bimodal magmatism in the region are controversial.In this paper we use zircon U-Pb age,Hf-Sr-Nd-Os isotope and lithophile-chalcophile trace element constraints from the Tianyu mafic-ultramafic intrusion to address these important issues.The U-Pb age of zircon from the Tianyu intrusion determined by SIMS is 280±2 Ma.This confirms that the Tianyu intrusion is coeval with most sulfidebearing mafic-ultramafic intrusions and some basalts and A-type granites in the Tianshan region.Similar to coeval basalts in the nearby Tuha basin,the Tianyu intrusive rocks are characterized by negative Nb anomaly and elevatedε values varying between -1 and +4.6.The negative Nb anomaly in the Tianyu intrusion is not as pronounced as in the coeval A-type granites but theε values for these bimodal rocks are similar.Theε values of zircon from the Tianyu intrusion are positive,varying between 3 and 8.These values suggest that the parental magma of the Tianyu intrusion was dominated by melt derived from a depleted source mande.Theγ values of pyrrhotite from the Tianyu intrusion are high,ranging from 725 to 995,which can be modeled by selective assimilation of sulfide from the lower and upper crusts.Negative Pt anomaly is present in relatively sulfide-rich samples such as semi-massive and massive sulfide ores but not in sulfide-poor samples,which is more consistent with the effect of post-magmatic hydrothermal alteration than the original signature of the parental magma.The results of modeling using the compositions of selected disseminated sulfide samples suggest that the parental magma of the Tianyu intrusion was depleted in all PGE,which is consistent with previo

关键词： slab break-off Asthenosphere upwelling Mafic-ultramafic rocks Magmatic Ni-Cu deposit Tianyu intrusion Central Asian Orogenic Belt China

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