【摘要】：西藏班公湖-怒江縫合帶是我國(guó)重要的斑巖銅金礦成礦帶,成礦地質(zhì)條件極為優(yōu)越。多龍礦集區(qū)是班公湖-怒江縫合帶西段典型斑巖-淺成低溫?zé)嵋盒豌~(金)超大型礦床,區(qū)內(nèi)廣泛分布著美日切錯(cuò)組噴溢相火山巖,但其巖石成因、源區(qū)屬性、形成年代及地球化學(xué)動(dòng)力學(xué)背景尚不明確。本文對(duì)美日切錯(cuò)組安山巖及流紋巖進(jìn)行鋯石U-Pb測(cè)年,獲得結(jié)晶年齡分別為108.2±2.6Ma(MSWD=0.39)和109.3±2.2Ma(MSWD=1.70)。礦區(qū)安山巖及流紋巖具高硅(SiO2=60.89%~72.00%)、富鉀(K2O=3.08%~5.53%)、富堿(K2O+Na2O=6.88%~8.96%)、準(zhǔn)鋁質(zhì)-過(guò)鋁質(zhì)(A/CNK=0.92~1.28)特征,屬于高鉀鈣堿性及鉀玄巖系列巖石。其明顯均富集輕稀土(LREE)及大離子親石元素(LILE:Th、U、K、Pb及Rb),虧損重稀土(HREE)及高場(chǎng)強(qiáng)元素(HFSE:Ta、Nb、Ti及Zr),稀土總量(ΣREE)為141.52×10-6~236.05×10-6之間,LaN/YbN為10.42~11.05,δEu為0.65~0.80,具有中等負(fù)銪異常,顯示出典型島弧巖漿巖的特征。(87 Sr/86 Sr)i值為0.7050~0.7053,(143 Nd/144 Nd)i為0.5124~0.5126,εNd(t)值為-1.51~1.29,具有高Sr低Nd的特征。鋯石Hf同位素分析結(jié)果表明,流紋巖εHf(t)為+11.6~+15.5,平均值為+13.8,兩階段模式年齡平均值為288.0Ma;安山巖εHf(t)為+3.4~+8.0,平均值為+4.8,兩階段模式年齡平均值為813.1Ma;表現(xiàn)出明顯的幔源特征。綜合研究表明,美日切錯(cuò)組火山巖為班公湖-怒江新特斯洋洋殼向北的俯沖背景下,由俯沖板片脫水產(chǎn)生流體交代地幔楔發(fā)生部分熔融形成原始玄武質(zhì)巖漿,并在上升后,滯留在殼幔邊界形成新生下地殼,新生下地殼與持續(xù)底侵幔源玄武質(zhì)巖漿混合而部分熔融形成。其形成于典型島弧的構(gòu)造背景下,暗示班公湖-怒江洋在早白堊世晚期(108~109Ma)仍正在向北俯沖于羌塘地塊之下,可能尚未關(guān)閉。
[Abstract]:The Bangong Lake-Nujiang suture belt in Tibet is an important porphyry copper-gold deposit belt in China, and the ore-forming geological conditions are extremely superior. The Duolong ore concentration area is a typical porphyry-shallow hydrothermal copper (gold) superlarge deposit in the western part of the Bangongghu-Nujiang suture belt. The volcanic rocks of the spilled facies of the United States-Japan cut-off formation are widely distributed in the area, but their petrogenesis and source area attribute. The age of formation and the background of geochemical dynamics are not clear. In this paper, zircon U-Pb dating of andesite and rhyolite of the American-Japanese shear fault group has been carried out. The crystallization ages are 108.2 鹵2.6Ma (MSWD=0.39) and 109.3 鹵2.2Ma (MSWD=1.70), respectively. The andesite and rhyolite in the ore area are characterized by high silicon (SiO2=60.89%~72.00%), rich potassium (K 2O + 3.08%), alkali rich (K 2O Na2O=6.88%~8.96%) and quasi aluminous peraluminite (A/CNK=0.92~1.28). It belongs to the rocks of high potassium calc-alkaline and potassium basaltic series. They are obviously enriched in light rare earth (LREE) and large ion lithophile elements (LILE:Th,U,K,Pb and Rb), heavy rare earth (HREE) and high field strength elements (HFSE:Ta,Nb,Ti and Zr),). The total amount of rare earths (危 REE) is between 141.52 脳 10 脳 10 ~ 6 and 236.05 脳 10 ~ (6), the LaN/YbN is 10.42 ~ 11.05, and the 未 Eu is 0.65 ~ 0.80, showing the characteristics of typical island arc magmatic rocks. (87 Sr/86 Sr) I = 0.7050 ~ 0.7053, (143 Nd/144 Nd) i is 0.5124 脳 0.5126, 蔚 Nd (t) is-1.51? 1.29), which has the characteristics of high Sr and low Nd. Zircon Hf isotopic analysis shows that the 蔚 HF (t) of rhyolite is 11.6 ~ 15.5, the average value is 13.8, and the average age of two-stage model is 288.0 Ma. The 蔚 Hf (t) of the andesite is 3.4 ~ 8.0, with an average value of 4.8, and the average age of the two-stage model is 813.1Ma, showing obvious mantle-derived characteristics. The comprehensive study shows that under the background of the northward subduction of the Bangong Lake-Nujiang Xintesian Ocean crust, the volcanic rocks of the United States-Japan shear fault formation are partially melted to form primitive basaltic magma by dewatering the subduction plate to produce the fluid metasomatism mantle wedge, and after rising, the volcanic rocks of the United States and Japan formed the primitive basaltic magma. The Neo-lower crust is formed at the boundary of crust-mantle, which is partly melted by mixing with the basaltic magma of continuous underplating mantle-derived basaltic magma. It was formed in the tectonic setting of the typical island arc suggesting that the Bangong Lake-Nujiang Ocean was still subducting northward under the Qiangtang block in the late early Cretaceous (108~109Ma) and may not have been closed.
【作者單位】： 中國(guó)地質(zhì)大學(xué)(北京)地球科學(xué)與資源學(xué)院;中國(guó)地質(zhì)科學(xué)院礦產(chǎn)資源研究所;成都理工大學(xué);中鋁西藏金龍礦業(yè)股份有限公司;
【基金】：國(guó)土資源部公益性行業(yè)專(zhuān)項(xiàng)“斑巖-淺成低溫?zé)嵋撼傻V系統(tǒng)研究及勘查評(píng)價(jià)示范-以西藏多龍整裝勘查區(qū)為例”(編號(hào):201511017) 國(guó)家自然科學(xué)青年基金“西藏羌塘地體南緣鐵格龍南超大型淺成低溫?zé)嵋盒豌~(金)礦床保存條件研究”(編號(hào):41402178) 科技基礎(chǔ)性工作專(zhuān)項(xiàng)(項(xiàng)目編號(hào):2014FY121000)共同資助
【分類(lèi)號(hào)】：P597.3;P588.14

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