Ages, Magma Evolution And Sources Of The Mangling Ranitoid Pluton From The North Qinling

The Mangling granitoid pluton, located between the Heigou-Luanchuan Fault andQiaoduan-Waxuezi Deep Fault in the North Qinling belt, mainly intruded into theMiddle-Neoproterozoic Kuanping Group. This pluton consists of porphyritic biotitemonzogranites, mid-coarse-grained biotite monzogranites, mid-fine-grained monzogranites,pyroxene-bearing biotite-hornblende diorites and biotite K-feldspar granites.The LA-ICPMS zircon U-Pb dating, combined with previous age data, suggests that theMangling granitoid pluton can be divided into three stages: Early Jurassic, Late Jurassic-EarlyCretaceous and Middle Cretaceous. The first stage pyroxene-bearing biotite-hornblendediorites yielded a zircon U-Pb age of157±1Ma, and they are characterized by low silica andhigh alkali, suggesting metaluminous and shoshonitic to high K cal-alkaline series. Thesecond monzogranites with ages from148±1Ma to144±1Ma are rich in silica and alkali,being metaluminous to weak peraluminous and shoshonitic to high K cal-alkaline series withI-A type transitional features. The last stage biotite K-feldspar granites gave an age of124±2Ma, and are rich in silica, alkali but poor in magnesium with high aluminum saturationindex, indicating that they are peraluminous and high K cal-alkaline series and I-A transitionaltype granites.Mineralogical studies indicate that the minerals of Mangling granitoid pluton are mainlycomposed of feldspar, quartz and little dark mineral, the accessory minerals consist of titanite,apatite, zircon and magnetite. From the early to late stage, these minerals have a certainevolution. The first stage pyroxene-bearing biotite-hornblende diorites have more darkmineral content, they are mainly biotite, with a small number of amphibole and clinopyrixene.The content of dark mineral, mainly biotite, has decreased in the second and third stages. Onthe mineral component, the plagioclase compositions of rocks at different times have a slightchange, The end-member of the plagioclase (Ab) is increased from pyroxene-bearingbiotite-hornblende diorites to monzogranites, the plagioclase from earlier rocks are composedof andesine and labradorite, but the plagioclase from the second rocks are chiefly oligoclase;The biotite compositions of rocks at different times change little, they are characterized byrich in Ti, Al, Mg and K, and mianly magnesian biotite.From Late Jurassic to Early Cretaceous (pyroxene-bearing biotite-hornblendedioritesâ†'monzogranitesâ†'biotite K-feldspar granites), the SiO2content of these granitoidsincrease, but Al2O3, TiO2, MgO, CaO, P2O5and TFe2O3decreased. The REE contents of granitoids decrease from the early to late stage. The granites of the first two stages arecharacterized by enrichment of LREE, but the REE patterns of the third stage are anasymmetric arc. All the granitoids have slightly negative to positive Eu anomalies. TheMangling granites are enriched in large ion lithophile elements (K, Rb, Ba, Sr), and depletedin high-field strength elements (P, Nb, Ta, Ti). On the zircon Hf isotopic composition, the firststage pyroxene-bearing biotite-hornblende diorites are characterized by εHf(t) values of-10.37～-2.54, and the two-stage modle ages of1.37to1.87Ga; the second monzograniteshave a large variation in εHf(t) with manily changes in-15.46～-1.59, tDM2=1.30～2.18Ga,individual samples have a more negative εHf(t) values of-47.45～-33.2, tDM2=2.99～4.17Ga.Mineralogy, Geochemistry and zircon Hf isotopic compositions suggest complex sources forthe Mangling granitoids. The source of the pyroxene-bearing biotite-hornblende diorites ishomogeneous, but the monzogranites may have complex sources, old and juvenilecomponents. The old component is continental crust likely similar to Qinling Group and/orTaihua Group, and the juvenile one may be represented by the mafic magmatic enclaves in thepluton.The Mangling granitoid batholith is different from the ore-bearing granitoid batholith(such as Laojunshan pluton) in age, geochemistry and source material. While they are besimilar to the ore-bearing small porphyritic granite bodies (i.e., Naitai, Taoguanping, Xigoupluton) in temperature and source.