东昆仑大格勒稀有金属矿化碳酸岩和橄榄岩斜锆石U-Pb年代学研究和找矿意义

Baddeleyite U-Pb Geochronology of Rare Metal Mineralized Carbonatite and Peridotite in Dagele Area of East Kunlun Orogen and Its Prospecting Significance

东昆仑大格勒地区发现稀有和稀土矿化碱性岩-碳酸岩杂岩体,表明东昆仑稀有和稀土金属成矿也具有较大的前景,在东昆仑地质过程研究和稀有金属找矿方面具有重要的意义.以大格勒杂岩体中碳酸岩和橄榄岩为目标,针对斜锆石开展地球化学和同位素年代学研究工作,橄榄岩中斜锆石化学成分主要为ZrO_(2)(96.48%~97.21%),其次为HfO_(2)(0.83%~1.17%)和Nb_(2)O_(5)(0.61%~0.93%),LA-ICP-MS U-Pb测年结果表明,^(207)Pb校正年龄加权平均值为381.0±2.3 Ma和417.5±3.4 Ma,T-W图的下交点年龄为381.1±2.3 Ma和417.7±3.4 Ma;碳酸岩中斜锆石化学成分主要为ZrO_(2)(91.1%),其次为HfO_(2)(4.3%)、Nb_(2)O_(5)(1.22%)和FeO(2.31%),^(207)Pb校正年龄加权平均值为381.5±2.5 Ma和416.5±4.5 Ma,T-W图的下交点年龄为381.8±1.8 Ma和416.7±4.5 Ma.推断碳酸岩的形成时代为381.8 Ma,橄榄岩的形成时代为417.7 Ma,暗示富集Nb元素的硅不饱和岩浆活动至少存在两期,东昆仑加里东碰撞造山带碰撞后-造山后岩石圈伸展、地幔部分熔融是其形成的最主要的地球动力学机制.推断晚志留世-泥盆纪是东昆仑十分重要的一个稀有金属成矿期,大格勒-诺木洪河地区是东昆仑稀有金属成矿的重要远景区之一.

The rare-metal and rare-earth mineralized alkaline-carbonatite complex was first discovered in the Dagele area of East Kunlun orogen.This discovery indicates that the East Kunlun orogen has great prospects for rare-metal mineralization.Related studies are vital for understanding the geological processes and searching for rare-metal deposits in East Kunlun orogen.This study reports the geochemistry and geochronology of baddeleyites from peridotite and carbonatite within the Dagele alkaline complex.Baddeleyites from peridotite mainly contain ZrO_(2)(96.48%-97.21%)with minor HfO_(2)(0.83%-1.17%)and Nb_(2)O_(5)(0.61%-0.93%).After common Pb correction using measured ^(207)Pb,they yield weighted average ages of 381.0±2.3 Ma and 417.5±3.4 Ma with low intercept ages of 381.1±2.3 Ma and 417.7±3.4 Ma,respectively.Baddeleyites from carbonatite are mainly composed of ZrO_(2)(91.1%),followed by HfO_(2)(4.3%),Nb_(2)O_(5)(1.22%),and FeO(2.31%).They yield weighted average ages of 381.5±2.5 Ma and 416.5±4.5 Ma with low intercept ages of 381.8±1.8 Ma and 416.7±4.5 Ma,respectively.It is inferred that the carbonatite and peridotite are formed at 381.8 Ma and 417.7 Ma,respectively.There are at least two stages of enrichment of Nb in the silica-unsaturated magma.Post-collisional and post-orogenic lithosphere extension and partial melting of mantle beneath the East Kunlun collisional orogen were considered as the geodynamic mechanism for its formation.Therefore,it is suggested that the Late Silurian-Devonian is an important period of rare-metal mineralization.The area between Dagela and Nuomuhong River is one of the important regions for prospecting of rare-metal mineralization.