Research On Geological Characteristics And Fe-Ti Mineralization Mechanism Of The Early Paleozoic Mafic-ultramafic Complex Belt On Both Sides Of The Ankang Fault, Southern Shaanxi

The study area is located in the south of ShaanXi province, an vital part of the south Qinling orogenic belt. Recent years, two mafic-ultramafic complex have been discovered on the northern and southern sides of AnKang fault, and the internal of mafic-ultramafic complex has a noticeable feature of Fe-Ti mineralization which contains a large amount of Ti-Fe mineral. Based on the field geologic inwestigation, petrographic examination, electron microprobe analysis, ziron U-Pb chronology, geochemical analysis for these mafic-ultramafic rocks were studied in this paper, and discussed the Fe-Ti mineralization mechanism related to mafic-ultramafic rocks.1、The main rock association of mafic-ultramafic rock in study area is multiple that have developed both intrusive rocks and extrusive rocks. The lithological association of extrusive rocks on two sides have significant differences that, the extrusive rocks on the northern side, transformed by strong deformation and metamorphism, mainly are amphibolite, garnet-amphibolite and tuff, which without deformation and metamorphism, the extrusive rocks on the southern side mainly are basalt and pyroclastic rocks. The lithological association of intrusive rocks is basically the same, mainly including gabbro and amphibolite pyroxene, gabbro and pyroxene amphibolite, gabbro-diabase, diabase-porphyrite, diabase.2、The metamafic-ultramafic rock, whose TiO2 content is rather changeable, can be divided into ore mafic-ultramafic rocks and non-ore mafic-ultramafic rocks. The geochemistry of mafic-ultramafic rock shows ore mafic-ultramafic rock is quite different from non-ore mafic-ultramafic rock. Ore mafic-ultramafic rock has characteristics of high alkaline and Ti, whose primitive mantle-normalized multi-element and Chondrite-normalized REE patterns are similar to that of OIB, and have obvious Eu abnormality. But the primitive mantle-normalized multi-element and Chondrite-normalized REE patterns of non-ore mafic-ultramafic rock is between that of E-MORB and OIB and has no obvious Eu abnormality.3、The minerals of mafic-ultramafic rock are mostly hornblende, plagioclase, garnet, pyroxene and accessory minerals like ilmenite, sphene. Mineral geochemistry characteristics show that the inter-growth association and structural characteristics between Ti-bearing mineral and main rock forming minerals are quite different: the Ti-Fe oxide on northern side is caused by metamorphism, which the Ti-Fe oxide on southern side mainly is the product of late magmatic differentiation. The feature, rich manganese and poor magnesium, of the titanium ore in Ankang fault is exactly the opposite of the magma type titanium iron ore found in PanZhiHua region of Panxi, HongGe and MianLue tectonic belt which is rich in magnesium and poor in manganese. Different from our predecessor’s knowledge of its formation.4、LA-ICP-MS zircon U-Pb harmonic age of mafic-ultramafic rock on northern side is between 429.5±9.9 Ma and 447.0±2.5Ma. It indicates that the mafic-ultramafic rock is formed in the early Paleozoic, formed during Ordovician and Sillurian. The mafic-ultramafic complex on southern side were formed in early Paleozoic, too(421.9±2.0Ma~436.0±4.5Ma). The mafic-ultramafic complex has basically the same age with found titanium magnetite rock mass in the studied area as well as the north of DaBaShan mafic rocks, so they are likely to be the magmatism products of the same source and period.