Abstract
There are series of Cu-Ni sulfide-bearing mafic-ultramafic intrusions widespread in north JilinProvince,Northeastern China. The intrusions formed in Xing’an-Mongolian Orogenic Belt near to the northeastern margin of North China Craton. The complexes were formed in almost same period according to the zircon U-Pb dating reported recently, which means that the complexes were formed in same tectonic period and belong to one tectonic magmatic event. The rock assemblages are different from the ophiolite type and Yidun type in orogenic belt. The mafic-ultramafic complexes formed in the range from 217 Ma to 232 Ma coeval with A-type granites in the area, which formed bimodal igneous rock assemblage. According to the regional angular unconformities, there were existed the orogenies of Caledonian, Hercynian, Early Indosinian, Late Indosinian and Yanshanian. The Early Indosinian coeval with orogenic I-type granites and sanukitie that suggesting the lithosphere thickening in the extrusion tectonic setting of orogenic processes, however the Late Indosinian coeval with bimodal igneous rock assemblage that suggesting the lithosphere thinning in the extension tectonic setting of post-orogenic processes in the Xing’an-Mongolian Orogenic Belt. Chemical composition of the mafic-ultramafic rocks has the characteristics of high-Mg and low-K tholeiites related with inter-continental post-orogenic tectonic setting. The trace elements indicate their formed in conditions of continental extension belt or initial rift and has the characteristics of revolution from oceanic island arc, volcanic arc of continental margin to continental extended belt. The low initial Sr isotopic ratios and positive εNd(t) values suggest that the initial magma of the complexes come from the parting melting of depleted lithospheric mantle. The depleted ithospheric mantle was new formed supported by zircon Hf isotope in Hongqiling complex. The depleted lithospheric mantle may be caused by the asthenosheric mantle upwelling and underplating in the tectonic setting of extension during the Late Indosinian post-orogenic processes.
Highlights
The mafic-ultramafic magmatism is the major geological procession in mantle and was controlled by various factors, but tectonic setting is more important factor for restricting the activity and the nature of the magma
As the zircon U-Pb dating method for mafic-ultramafic intrusion was used frequently and the advance on research of Xing’an-Mongolian Orogenic Belt, the intrusions were regarded as Early Triassic period from extrusion to extension system related to the colliding orogeny between the North China Plate and Siberia Plate [13], and regarded as Late Triassic period from extension system related to the post-orogeny [12,14]
1) There are similar zircon U-Pb age of the maficultramafic complexes in north Jilin Province, range formed 217 Ma to 232 Ma, which means that the complexes were formed in Late Indosinian period and belong to one tectonic magmatic event
Summary
The mafic-ultramafic magmatism is the major geological procession in mantle and was controlled by various factors, but tectonic setting is more important factor for restricting the activity and the nature of the magma. There are tow major different tectonic settings in Jilin Province divided by Huifahe-Gudonghe deep fault, the southern part is be long to North China Craton and the northern part is be long to Xing’an-Mongolian Orogenic Belt [7]. As the zircon U-Pb dating method for mafic-ultramafic intrusion was used frequently and the advance on research of Xing’an-Mongolian Orogenic Belt, the intrusions were regarded as Early Triassic period from extrusion to extension system related to the colliding orogeny between the North China Plate and Siberia Plate [13], and regarded as Late Triassic period from extension system related to the post-orogeny [12,14]. We summarized the rock assemblages of mafic-ultramafic intrusions in Northern Jilin Province, discussed the ages of the complexes and mag- matic events. The tectonic setting of the complexes is discussed in terms of extension in post-orogenic processes and magmatic sources of the complexes are discussed associated with the lithochemistry
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