| During the Mesozoic period, the North China Craton (NCC) occurred intense tectonic magmatic activity, accompanied by a large-scale mineralization and extensional basin formation. Handan-Xingtai area is located within the Trans-North China Orogen, a major Paleoproterozoic suture zone that welds the Western and Eastern Blocks of the NCC. Early Cretaceous magmatism in the region not only provide vital constraints on the thermal -chemical state of the subcontinental lithospheric mantle (SCLM), but also contribute to a better understanding on the spatial and temporal evolution of the NCC destruction as well as the associated deep-Earth geodynamics. On the other hand, "Han-Xing skarn iron deposit", one of the large skarn iron deposits, belongs to the Taihang polymetallic metallogenic belt. The Early Cretaceous diorite rocks in this area are genetically associated with skarn iron mineralization, while the Early Cretaceous syenite has not yet been found associated with mineralization. Thus, performing a comparative study on the ore-bearing and ore-barren intrusions in the Handan-Xingtai district contributes to the exploration and evaluation of iron deposits in the region which is of significant importance.This PhD thesis focus on the Early Cretaceous intrusive rocks from the Handan-Xingtai district which is located within the Trans-North China Orogen by means of a combined study of petrography, mineralogical, geochemical, geochronological, and whole-rock Sr-Nd and zircon Hf-O isotope data, to constrain their petrogeneses and to identify the tectonic regime under which they originated. Meanwhile, we compared the ore-bearing and ore-barren intrusions in the Handan-Xingtai district based on petrography, mineralogical, geochemical and isotope data to summary the discriminating flag.These intrusive rocks from the Handan-Xingtai district composed of three rock belts in space, a NNE beaded distribution. Among them, the western rock belt composed the Fushan intrusive complex as the main body, mainly composed of gabbro diorite, hornblend diorite, diorite and porphyritic diorite. The central rock belt also known as Wu’an intrusive complex, mainly includes Qicun, Xincheng, Kuangshancun, Wu’an and Guzhen complexes. Drilling work has proven they are intermittent connected. The Wu’an intrusive complex has kinds of lithologic units, ranging from diorite to monzonitic rocks, mainly composed of diorite, monzodiorite, quartz monzodiorite, biotite diorite rocks, porphyritic diorite. While the east rock belt composed of Hongshan intrusive complex, consisting mainly of coarse grained biotite pyroxene syenite and light color syenite.The LA-ICP-MS zircon U-Pb data obtained from the three rock belts yielded a precise age of 140-119Ma,143-120Ma,141-125Ma, respectively, indicating that the three rock belts were emplaced in the Early Cretaceous.The mineralogical study indicates that the three rock belts have different physical and chemical conditions, the Western rock belt with the calculated crystallization temperature is 715-743℃, an average is 721℃; the pressure at 6.6-5 kbar, roughly equivalent to the magma chamber depth of 22-16 km. The Central Wu’an intrusive complex with the calculated crystallization temperature is 718-814℃, an average is 768 ℃. The pressure is between 8.9-6.2 kbar, roughly equivalent to the magma chamber depth of 22- 16 km. The zoning amphibole from core to rim reveals that the increased of Mg# is paralleled to that of the temperature, may be associated with the injection of mafic mantle derived magma. The eastern Hongshan syenite with the calculated crystallization temperature is 832- 850℃, an average of 842 ℃. The pressure of the Hongshan syenite is between 8.5- 8.2 kbar showing that the magma chamber depth is 28km.Samples from Fushan intrusive complex have 53.32-62.60 wt.% SiO2. The Mg# values are [Mg#= 100* Mg/(Mg+Fetot)] between 44 to 63, indicating the high magnesium features. Samples from Fushan intrusive complex fall in the high K calc-alkaline region. The calculated d(t) values are between -16.96 to -8.30, zircon δ18O values ranges from 6.04 to 8.69%o. Samples from the central Wu’an intrusive complex have 50.29- 69.30 wt.% SiO2. The Mg# values are between 30- 72, and samples fall in the high K calc- alkaline region. The calculated εNd(t) values are between-18.21 to -13.78, zircon δHf(t) values ranges from -33.8 to -16.3, zircon δ18O values are between 6.31- 8.26%o. The Hongshan intrusive complex has 56.75-68.16 wt.% SiO2, but with higher K2O (4.99-7.10 wt.%). The calculated sNd(t) values are between-6.19 and -11.17, zircon εHf(t) values vary from-17.3 to-13, zircon δ18O values are between 6.31-7.14‰. Samples from the intrusive rocks from the Handan-Xingtai district show sub-parallel chondrite-normalized REE pattern, characterized by LREE enrichment and HREE depletion, with slightly positive or no Eu anomalies. In the primitive mantle (PM) normalized trace element spider diagram, the intrusive rocks show a marked depletion of high field strength element (HFSE; Nb, Ta) and enrichment in large ion lithophile elements (LILE; Rb, Sr).Therefore, the Han-xing intrusive complex may have formed by the solid-state reaction between recycled crustal materials and their surrounding peridotite during the Late Archean to Paleoproterozoic subduction events. The different layers of the continental crust recycled into the mantle, leading to the geochemical nature of the heterogeneity, and the process may be similar to SARSH model. Among them, the Fushan intrusive complex were originated from the hornblende pyroxenitic veined-plus-peridotite source. The Wu’an intrusive complex experienced fractional crystallization during the magma ascent and a number of extraction as well as the replenishment process in the magma chamber. While the Hongshan syenite might be derived from partial melting of phlogopitic peridotite source region. During the Early Cretaceous, the NCC destruction had not happened in the Trans-North China Orogen. The Han-xing intrusive complex were formed in a strong lithospheric extension and thinning tectonic environment. Heating from the upwelling asthenosphere and decompression in the extensional regime would further facilitate extensive partial melting of the enriched lithospheric mantle beneath the Han-Xing district.The iron skarn mineralization was genetically related to the coeval magmatism in the Han-xing district. The total Rare earth elements (REE) in the ores were lower than diorite, but had the same overall trend. In the primitive mantle normalized trace element spider diagram, the trend of ore and diorite were same, indicating that the iron ore and magmatic rocks exposed a close genetic relationship. Mineralization and magmatism in the Hanxing district had a close genetic relationship, sodic metasomatism was an important way to deposit iron extraction and precipitation.Comparative study on the ore-bearing and ore-barren intrusions showed that high oxygen fugacity, temperature, pressure are more conducive to the mineralization. The content of K2O, MF value of biotite, geochemical characteristics of zircon, oxygen fugacity can effectively distinguish the ore-bearing from ore-barren intrusions.In summary, the Han-xing intrusive complex may have been formed by the solid-state reaction between recycled crustal materials and their surrounding peridotite during the Paleoproterozoic subduction events. The different layers of the continental crust recycled into the mantle and source and magma mixing processes happend, thus leading to the geochemical nature of the heterogeneity. The high oxidation states, temperature and pressure conditions may be considered as key factors that led to the iron mineralization in the Handan-Xingtai district. |
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