甘肃北山中泥盆世哈尔特尔德勒花岗岩体的地球化学特征及其构造意义

GEOCHEMISTRY CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF THE HAERTEERDELE GRANITE MASS IN MIDDLE DEVONIAN IN BEISHAN,GANSU

牛圈子哈尔特尔德勒岩体具有高硅(Si>72.2%)、高碱(AR=2.9~5.1,K2O=3.86%~5.49%,Na2O=3.04%~3.83%)和高FeOT/MgO值(3.29~13.47)、低Al_2O_3(11.48%~13.42%)、贫CaO(0.57%~2.27%)和MgO(0.14%~0.78%)、低FeO T(1.33%~2.34%)的特征,A/NK值为1.43~1.77,A/CNK值为1.35~1.4,为过铝质高钾钙碱性花岗岩。ΣREE较高,LREE略富集((La/Yb)N=4.9~16),轻重稀土元素分馏不明显,Eu负异常明显(δEu=0.12~0.21);相对富集Rb、K、Pb等大离子亲石元素,强烈亏损Ba、Sr、P、Ti,Eu,并弱亏损Ta、Nb等元素;同时具有与地壳更为接近的Nb/Ta与Nd/Th值,显示了A(A2)型花岗岩的特征。LA-ICP-MS锆石定年获得哈尔特尔德勒岩体的206Pb/238U年龄为371.7±2.9 Ma,代表该岩体的形成年龄,表明其为中泥盆世岩浆活动的产物。结合区域构造演化以及与区域同时代A型花岗岩的对比显示,该岩体形成于后碰撞伸展环境。

The Haerteerdele granite mass in Niuquanzi shows a high content of Si （ 〉72. 2% ） , alkaline （ AR = 2.9？5.1,K20=3.86%？5.49%,Na2 0 = 3 . 0 4 %？3 . 8 3 % ） andFe0 T/Mg （3.29？13.47）,andalow content of A1203 （ 11.48% -13.42%）, CaO （0.57% -2.27%）, MgO （0.14% -0.78%） and FeOT （1. 33% ±2. 34% ） ？ It is determined that the granites are peraluminous granitoids of the calc-alkaline suite （ A/ NK = 1. 43 ±1. 77,A/CNK = 1 . 35 ±1. 4 ）,with the characteristics that an enriched pattern with a high 2 REE content and a slight high LREE content （ （ La/Y b ） N =4. 9 ？16）,unapparent fractionation of heavy and rare earth elements, obvious Eu negative abnormality （ 8Eu = 0. 12 .0. 21 ）,relatively large concentration of large ion lithophile elements such as Rb,K,Pb,strong depletion of the elements of Ba、Sr、P、T i,Eu,and weak depletion of Ta, Nb and other elements. Also the granites have the similar value in Nb/Ta and Nd/Th with the earthcrust, showing the characteristic of typeA （ A2 ） granite. The chronology result of LA- ICP-MS zircon dating shows the age of 206 Pb/23SU of the Haerteerdele granite mass is 371. 7 ±2. 9Ma, which represents the formation age of the granite mass and the formation period is the middle Devonian. Taking into consideration the regional tectonic evolution and the comparison with the contemporary type A granite, it shows that the granite mass is the product of postcollision to extension.