CAJ | 학술논문

夏日哈木矿区的正长花岗岩体呈岩株状出露于矿区北部。年代学研究表明,正长花岗岩中岩浆锆石LA-MC-ICP-MS U-Pb加权平均年龄为391.1±1.4Ma, MSWD＝0.06,属早泥盆世。岩石学及化学成分显示其属于高钾钙碱性、弱过铝质系列花岗岩。岩体高硅(SiO2=75.55%~76.10%)、富碱(Na2O+K2O=8.23%~8.46%)、高铁镁比(FeOT/MgO=17.40~42.59)、贫钙(CaO=0.54%~0.69%)、贫镁(MgO=0.03%~0.09%)；稀土配分曲线呈现“海鸥式”分布特征,显示强烈的Eu 负异常(δEu=0.09~0.12)；微量元素特征显示具有较高的 Ga(24.3×10-6~26.9×10-6)、Zr(132×10-6~363×10-6)和 Y(86.1×10-6~97.0×10-6)含量,较低的Sr(8.6×10-6~19.5×10-6)、Ba(14.0×10-6~37.9×10-6)含量,在微量元素原始地幔标准化蛛网图上显示明显的 Sr、Ba、P、Eu和 Ti的负异常。以上特征表明夏日哈木矿区正长花岗岩为铝质 A型花岗岩。岩石具有高的Rb/Sr(介于14.97~38.26,平均值22.63)和 Rb/Nb(介于13.84~16.13,平均值14.54),显示出壳源岩浆的成分特征。综合分析表明本区正长花岗岩为低压下长英质地壳部分熔融的产物。结合区域构造演化及构造判别,本文认为该区正长花岗岩形成于造山后伸展的构造环境。在晚志留世-早泥盆世,东昆仑地区构造体制经历了重要的转变,由挤压体制转变为造山后软流圈上涌、岩石圈减薄及地壳伸展。在伸展体制下,软流圈地幔上涌导致上覆长英质地壳直接部分熔融,形成本区A型正长花岗岩。
하일합목광구적정장화강암체정암주상출로우광구북부。년대학연구표명,정장화강암중암장고석LA-MC-ICP-MS U-Pb가권평균년령위391.1±1.4Ma, MSWD＝0.06,속조니분세。암석학급화학성분현시기속우고갑개감성、약과려질계렬화강암。암체고규(SiO2=75.55%~76.10%)、부감(Na2O+K2O=8.23%~8.46%)、고철미비(FeOT/MgO=17.40~42.59)、빈개(CaO=0.54%~0.69%)、빈미(MgO=0.03%~0.09%)；희토배분곡선정현“해구식”분포특정,현시강렬적Eu 부이상(δEu=0.09~0.12)；미량원소특정현시구유교고적 Ga(24.3×10-6~26.9×10-6)、Zr(132×10-6~363×10-6)화 Y(86.1×10-6~97.0×10-6)함량,교저적Sr(8.6×10-6~19.5×10-6)、Ba(14.0×10-6~37.9×10-6)함량,재미량원소원시지만표준화주망도상현시명현적 Sr、Ba、P、Eu화 Ti적부이상。이상특정표명하일합목광구정장화강암위려질 A형화강암。암석구유고적Rb/Sr(개우14.97~38.26,평균치22.63)화 Rb/Nb(개우13.84~16.13,평균치14.54),현시출각원암장적성분특정。종합분석표명본구정장화강암위저압하장영질지각부분용융적산물。결합구역구조연화급구조판별,본문인위해구정장화강암형성우조산후신전적구조배경。재만지류세-조니분세,동곤륜지구구조체제경력료중요적전변,유제압체제전변위조산후연류권상용、암석권감박급지각신전。재신전체제하,연류권지만상용도치상복장영질지각직접부분용융,형성본구A형정장화강암。
In this paper, we discuss the zircon U-Pb age, major and trace element geochemistry of the syenogranite intrusion in the north of the Xiarihamu ore district. Zircon U-Pb dating demonstrates that the weighted mean 206Pb/238U age for the zircons from the syenogranite is 391.1±1.4 Ma (MSWD=0.06), i.e., the Early Devonian. The syenogranite is slightly peraluminous and belongs to the high-K calc-alkaline series. The syenogranite is characterized by high SiO2 (75.55%~76.10%), high alkali (Na2O+K2O=8.23%~8.46%), high FeOT/MgO (FeOT/MgO=17.40~42.59), low CaO (0.54%~0.69%) and MgO (0.03%~0.09%) contents. The syenogranite is characterized by a“sea-gull”REE pattern and significant negative Eu anomaly (δEu=0.09~0.12), as well as enrichment of Ga (24.3×10-6~26.9×10-6), Zr (132.0×10-6~363.0×10-6) and Y (86.1×10-6~97.0×10-6), and depletion of Sr (8.6×10-6~19.5×10-6) and Ba (14.0×10-6~37.9×10-6). And thus, the syenogranite belongs to aluminous A-type granite. The high Rb/Sr (ranging from 14.97 to 38.26, and the average value is 22.63) and Rb/Nb ratios (ranging from 13.84 to 16.13, and the average value is 14.54) of the rock indicate a crustal origin. Combined with the regional tectonic evolution and geochemical discrimination, we suggest that the syenogranite was formed in a post-orogenic setting. During the Late Silurian-Early Devonian, the tectonic regime in the East Kunlun area changed from compression to extension due to asthenosphere upwelling. Under the extensional setting, the upwelling asthenosphere provided enhanced heat and triggered the partial melting of the overlying felsic crust, and produced the A-type syenogranite.