鄂东南—赣西北地区中生代中酸性侵入体岩浆起源、演化与成矿

作者以野外工作为基础,通过对本区侵入体侵入顺序的确定,结合岩浆起源和演化的研究,将鄂东南—赣西北地区中生代中酸性侵入体划分为9个单元、4个超单元。主要根据岩浆岩与成矿的时间关系,将本区内生成矿作用划分为8个成矿阶段并查明了其与岩浆岩单元的时间、空间关系。依据控制成矿作用的岩浆物质同源性,建立了与超单元相对应的5个成矿亚系列。通过区域构造演化的研究,提出了本区导岩构造的演化控制了不同构造阶段岩浆岩单元的空间分布,从而总结和阐明了受本区岩浆侵入所控制的铁、铜矿床的空间分布规律。

THE MAGMA GENESIS AND EVOLUTION, AND MINERALIZATION OF THE MESOZOIC GRANITOIDS IN THE SOUTHEAST HUBEI PROVINCE AND NORTHWEST JIANGXI PROVINCE

The Southeast Hubei Province and Northwest Jiangxi Province was geologically situ-ated in the west part of Low-Yangtze geological block, in which the important tectonicmovements which produced majority of magmatic rocks and ore deposits, happended inMesozoic. in Mesozoic, the direction of tectonic compressing stress was in the NNE-SSWduring the end of the Triassic Period and early Jurassic Period, then changed to NWW-SEE during the late Jurassic Period and finally changed back to NNE-SSW during the Cre-taceous Period. We can divide three tectonic compressing periods (I, ⅡandⅢ).Based on our field works, especially the large scale granitoids mapping, we determi-nated the boundary lines of intrusive bodies and their intrusion sequences. Then utilizedthe materials about petrology, mineralogy, rare element geochemistry .and isotopic age da-ta, we divided nine intrusive units, which made up four super-units and occupied twobatholith segments. The first super-unit included unit I; the second included units Ⅱ.ⅢⅣ and V; the third incIuded unit Ⅵ and the fourth included units Ⅶ,Ⅷand ⅨThe intrusive bodies of the first super-unit and the earliest unit in the second super-u-nit. the ones of the rest of the second super-unit and the third super-unit, and the ones ofthe fourth respectively formed in the Ⅰ,Ⅱ, and,Ⅲtectonic compressing period. So theywere respectively scattered along the direction of NNE--SSW, NWW--SEE, and NNE--SSWunder the controls of the direction changes of magma-led structures.The study results of stages of mineralization indicated that there were eight stages ofmineralization in five minerogenetic sub-series of ore deposits (MSOD), which were theMSOD of iron ore-deposit. iron-copper ore-deposit, copper ore-deposit, and iron ore-de-posit. lead-zinc ore-deposit as time went on. The first three MSODs followed magma in-frusion of the first three super unit. and the rest did the fourth. Because the ore deposit ac-companied magma in trusive bodies, the distributions of the intrusive bodies of different su-per-units controlled over the distributions of ore deposits of different MSODs. For thisreason, iron ore zones were scattered along the direction of NNE-SSW, and iron-copper.copper ore zones along the direction of NWW-SEE.In the above, we explained how the iron ore-deposits and iron-copper, copper ore-de-posits were distributed, and why. What are followed is what determinated the pattern ofthe MSOD evolution. To answer this question, we made a approach to magma genesis andevolution through the analysis of petrology and rare element geochemistry. The resultstold us that magmas of intrusive bodies in the same super-unit came from the same magmasource, and the magmas of different intrusive bodies in every super-unit evolved throughfractional crystallization. That is, the super-units from different magma source controlledover the different MSODs.The composition cbanges from the core to the rim of minerals showed that theamounts of iron in biotite and hornblende decreased obviously in these intrusive bodies ac-companied the MSOD of iron ore-deposit, which probably reflected the forming of oremagma. In combination witb the isotopic data, we found that the assimilation becamestronger and stronger from intrusive bodies of unit I to that of unit Ⅵ As the intrusivebodies of late unit assimilated more carbonate wallrock, the amounts of FeO in magma de-creased rapidly. On the other hand. the fractional crystallization also contributed to theFeO decrease. The rapid decreasing of FeO would induce the copper mineralization.