CAJ | 학술논문

本文对冈底斯岩浆带中段谢通门塔玛地区碱长花岗岩进行了原位LA-ICP-MS锆石U-Pb定年和LA-MC-ICP-MS锆石Lu-Hf同位素分析。研究结果表明，采自该岩体不同部位的两件锆石U-Pb同位素加权平均年龄分别为（40.02±0.39）Ma和（40.65±0.32）Ma，具有几乎一致的地质年龄，即碱长花岗岩侵位结晶年龄为40 Ma左右。LA-MC-ICP-MS锆石Lu-Hf同位素研究显示，176Hf/177Hf比值在0.282633~0.282878，平均值为0.282765，计算所得的εHf（t）值介于-4.08~4.15，平均值为0.28，峰值在-1~+1之间；TDMC模式年龄在822~1373 Ma，平均值为1075 Ma，峰值年龄为1000~1200 Ma。其次，样品的εHf（t）值具有正负相间的特点，εHf（t）也相对较小，为典型的壳幔混染型，岩浆源区主要以古老地壳的熔融为主。综合研究表明，谢通门塔玛地区碱长花岗岩主要是由新特斯洋板片的断离，致使软流圈地幔上涌，引起拉萨地体地壳物质的熔融、再循环而形成的，在这个过程中有部分幔源物质的加入。
본문대강저사암장대중단사통문탑마지구감장화강암진행료원위LA-ICP-MS고석U-Pb정년화LA-MC-ICP-MS고석Lu-Hf동위소분석。연구결과표명，채자해암체불동부위적량건고석U-Pb동위소가권평균년령분별위（40.02±0.39）Ma화（40.65±0.32）Ma，구유궤호일치적지질년령，즉감장화강암침위결정년령위40 Ma좌우。LA-MC-ICP-MS고석Lu-Hf동위소연구현시，176Hf/177Hf비치재0.282633~0.282878，평균치위0.282765，계산소득적εHf（t）치개우-4.08~4.15，평균치위0.28，봉치재-1~+1지간；TDMC모식년령재822~1373 Ma，평균치위1075 Ma，봉치년령위1000~1200 Ma。기차，양품적εHf（t）치구유정부상간적특점，εHf（t）야상대교소，위전형적각만혼염형，암장원구주요이고로지각적용융위주。종합연구표명，사통문탑마지구감장화강암주요시유신특사양판편적단리，치사연류권지만상용，인기랍살지체지각물질적용융、재순배이형성적，재저개과정중유부분만원물질적가입。
In this paper, the authors conducted zircon LA-ICP-MS U-Pb dating and Lu-Hf analysis of the alkali-feldspar granite in Tama of Xietongmen region along the middle Gangdise magmatic belt. The results suggest that the weighted mean ages of two samples are (40.02 ± 0.39)Ma and (40.65 ± 0.32)Ma for the pluton, respectively. In essence, the two ages are of the same geological significance in that they both represent the crystallization age or emplacement age of the alkali-feldspar granite. Zircon Lu-Hf analytical data reveal that values of 176Hf/177Hf vary from 0.282633 to 0.282878 (averaging 0.282765), and the values ofεHf(t)range from-4.08 to 4.15 (0.28 on average) , with the peak values ofεHf(t)varying from-1 to 1. TDMC model ages are from 822 Ma to 1373 Ma (averaging 1075 Ma) with peak model ages being ca.1000-1200 Ma. The obvious feature is that the values of theεHf(t)show alternating positive and negative values, corresponding to a small value and indicating the crustal-mantle contamination process, which resulted from partial melting of the ancient crust. Combined with geological setting and study results, the authors consider that the alkali-feldspar granite might have generated from the slab break off of the Neo-Tethys oceanic crust, which led to upwelling of the asthenosphere and further induced the partial melting and recycling of the ancient crust. During the process, the mantle materials played a vital role in forming the alkali-feldspar granite in the study area.