Re-understanding of the geological and geochemical characteristics of the Mesozoic intrusive rocks from Tongling area of Anhui Province,and discussions on their genesis
2012; Science Press; Linguagem: Inglês
ISSN
2095-8927
Autores Tópico(s)Geological and Geochemical Analysis
ResumoTongling area in Anhui Province is one of the most famous copper polymetallic deposits producers where magmatic rocks developed widely and the magmatism had a close relationship with the mineralization.Based on widespred collection for the previous research data and deep comprehension on the predecessors' achievements,and careful observation of petrography and systematic investigation of petrology,petrochemistry,trace element as well as isotope geochemistry,the geological and geochemical characteristics of the Mesozoic magmatic rocks in the Tongling area have been summarized,and the petrogenesis discussed.The results are as follows:(1) The ore-related magmatic rocks in Tongling formed in the Late Jurassic to Early Cretaceous(135 ～147Ma),and the duration of magmatic activities was approximately 10 to 15Ma;The intrusive rocks show zonal distribution along with east-west deep faults and hypabyssal intrusive output,mainly controlled by multistage faults in different directions and properties.(2) According to Q-A-P diagram,the intrusive rocks can be divided into pyroxene diorite,quartz diorite and granodiorite,and all of the three kinds of intermediate-acid dioritic rocks are belong to high potassic calc-alkaline series.(3) The similar geochemical characteristics of trace elements,rare earth elements and Pb-Sr-Nd-O isotope for the three kinds of intrusive rocks indicate that the magma was originated from an enriched lithospheric mantle and assimilated by the crustal materials.(4) The magma was likely derived from different layers of the magma chamber which were zonally distributed in the lower crust and randomly ascended,intruded in pulse,connecting with deep faults induced by tectonic movements;The zonal magma layers in the deep magma chamber maybe caused by a certain degree of liquational differentiation due to the convection and diffusion which was caused by temperature gradient;Fractional crystallization of mafic minerals,zircon and apatite may exist in the process of the magmatic evolution.(5) The geotectonic background of the Mesozoic regional magmatic activities of Tongling area maybe inside of the continental plate.The magmatism was closely relevant to subduction of the Paleo-Pacific plate,also restricted by pre-Mesozoic basement.The primary magma of the intermediate-acid intrusive rocks in this area is inferred to be a mixing of mantle-derived basaltic magma and lower crust-derived adakite-like magma which formed by underplating of the mantle-derived magma.
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