CAJ | 학술논문

洛古河地区含电气石花岗岩为二长花岗岩类,普遍碎裂或糜棱岩化,属高钾钙碱性岩系.SiO_2含量介于65.08%～73.18%之间,Na_2O+K_2O含量范围为5.49%～7.22%,K_2O＞Na_2O;Al_2O_3含量在14.42%～16.64%之间,铝饱和指数(A/CNK)为1.18～1.31,均大于1.1,CIPW标准矿物计算均出现刚玉分子,显示为强过铝质S型花岗岩的特点.稀土总量(∑REE)变化范围为97.4×10~(-6)～250.9×10~(-6),(La/Yb)N=5.85～21.95,平均12.2;δEu=0.37～0.59,平均为0.47,具有中等到强的负铕异常.微量元素反映其类似弧火山岩,但又有某些差别.地球化学特征反映其岩浆可能来源于盆地基底的砂质岩石部分熔融,形成于同碰撞构造环境,为同碰撞花岗岩.
락고하지구함전기석화강암위이장화강암류,보편쇄렬혹미릉암화,속고갑개감성암계.SiO_2함량개우65.08%～73.18%지간,Na_2O+K_2O함량범위위5.49%～7.22%,K_2O＞Na_2O;Al_2O_3함량재14.42%～16.64%지간,려포화지수(A/CNK)위1.18～1.31,균대우1.1,CIPW표준광물계산균출현강옥분자,현시위강과려질S형화강암적특점.희토총량(∑REE)변화범위위97.4×10~(-6)～250.9×10~(-6),(La/Yb)N=5.85～21.95,평균12.2;δEu=0.37～0.59,평균위0.47,구유중등도강적부유이상.미량원소반영기유사호화산암,단우유모사차별.지구화학특정반영기암장가능래원우분지기저적사질암석부분용융,형성우동팽당구조배경,위동팽당화강암.
The Luoguhe area along the southern part of the Heilong River is located in northwestern Mohe County, Heilongjiang Province. Many copper, lead, zinc, tungsten-molybdenum ore bodies and Early Paleozoic granites were found in recent years. Moreover, the Luoguhe tourmaline-bearing granites (TLTG) that had never been reported before were also discovered. On the basis of petrological and petrogeochemical characteristics of the Luoguhe tourmaline-bearing granites, this paper studied the probable provenance and tectonic setting of these rocks.The Luoguhe tourmaline-bearing granites are cropped out in the western part of the upper Heilongjiang basin within Ergun block. The basement rocks of this basin are composed mainly of Paleoproterozoic Xinghuadukou Rock Group,Early Cambrian Ergun Formation and Early Paleozoic granites, and the cap rocks consist of Early-Middle Jurassic sedimentary formation and Late Jurassic-Early Cretaceous volcanic rocks. Tectonically, the study area is predominated by faults, with well-developed thrust-nappes and ductile shear belts. The Luoguhe tourmaline-bearing granites should be assigned compositionally to monzonitic granite, which comprises perthite (30%～40%), plagioclase (20%～28%), quartz (30%～40%) and biotite (1%～3%) with minor accessory tourmaline (2%～5%), zircon and apatite. Due to fragmentation and mylonitization, most of the studied rocks display porphycroclastic texture. The accessory mineral tourmaline which occurs both in the porphycroclast and in the matrix displays bamboo joint texture in the former case and allotriomorphic granular texture in the latter case. The analyses of samples show that the studied rocks should be classified as adamellite in the Q-ANOR diagram, belonging to the high-K calc-alkaline series. The Luoguhe tourmaline-bearing granites have the following characteristics: SiO_2=65.08%～73.18%, K_2O+Na_2O=5.49%～7.22%, K_2O>Na_2O, Al_2O_3=14.42%～16.64%, and A/CNK=1.18～1.31 (>1.1). Moreover, corundum can be found in the CIPW norm minerals, possessing some features of strongly peraluminous granites. Chondrite-normalized REE patterns of the tourmaline-bearing granites are characterized by ∑REE 97.4×10~(-6)～250.9×10~(-6), (La/Yb)_N 5.85～21.95 (12.2 on average) and pronounced negative Eu anomalies (δEu=0.37～0.59), consistent well with REE patterns of basement metasandstone in the study area. Primitive mantle-normalized element concentration patterns show remarkable negative anomalies of Ba, Sr, Ta, Nb, Ti, P and positive anomalies of Rb,Th ,U, La, Ce, Nd, Zr, Hf, Sm. Likewise, the patterns with some characteristics of island arc volcanic rocks are very similar to the patterns of basement metasandstone in the study area.According to the experiment on the provenance of strong peraluminous granites, it is most probable that the studied rocks (5 samples) whose CaO/Na_2O ratios are equal to 0.41～4.68 (>0.3 on average) can be genetically attributed to partial melting of basement metasandstone in the upper Heilongjiang basin, because the two different kinds of rocks have similar normalized patterns.In the R1R2 and RbYb+Ta discrimination diagrams, most of the studied rocks fall in the syn-collisional field and can thus be regarded as syn-collisional granites.Combined with zircon U-Pb dating (485±6 Ma) of the Luoguhe tourmaline-bearing granites, zircon SHRIMP dating (504～517 Ma) of the Luoguhe pluton, zircon crystallization age (480～494 Ma) and corresponding xenolith zircon ages (517～531 Ma) of Tahe pluton, it is thought that there existed two stages of granitic magmatic events in the Ergun block in Early Paleozoic, being 504～531 Ma and 480～494 Ma in age respectively. Accordingly, the first magmatic event occurred in the late stage of collision between the Ergun block and the Siberia block, and the second magmatic event might have led to the formation of Luoguhe tourmaline-bearing granites in response to the southeastward movement of Xing'an block towards the Ergun block, which had been collaged with the Siberia block. Due to subsequent compression, the crust was thickened and resulted in the remelting of metasandstone and the formation of the Luoguhe tourmaline-bearing granites with some features of strongly peraluminous syn-collisional S type granite.