鋯石LA-ICPMS U-Pb年代學(xué)
(1. 中南大學(xué) 有色金屬成礦預(yù)測(cè)教育部重點(diǎn)實(shí)驗(yàn)室，長(zhǎng)沙 410083；
2. 中南大學(xué) 地球科學(xué)與信息物理學(xué)院，長(zhǎng)沙 410083)
摘 要: 位于青海東部的鄂拉山地區(qū)是青藏高原北部重要的構(gòu)造−巖漿−成礦帶。為探討該區(qū)巖漿巖−成礦作用，選取賽什塘礦區(qū)石英閃長(zhǎng)玢巖和花崗斑巖開(kāi)展了巖石主量元素、微量元素和鋯石U-Pb LA-ICPMS測(cè)試。主量元素結(jié)果顯示：賽什塘銅礦區(qū)雜巖體的石英閃長(zhǎng)玢巖和花崗斑巖屬于偏鋁質(zhì)巖石，具Ⅰ型花崗巖的特征，巖石系列屬于高鉀鈣堿性系列。巖石具弱或無(wú)Eu異常，石英閃長(zhǎng)巖和花崗斑巖具相似的微量元素特征，稀土元素配分模式一致，具輕稀土富集、重稀土虧損、富集大離子親石元素和虧損高場(chǎng)強(qiáng)元素特點(diǎn)。礦區(qū)巖體鋯石陰極發(fā)光照相顯示：鋯石全部具環(huán)帶結(jié)構(gòu)，顯示巖漿鋯石特征。鋯石U-Pb年代學(xué)顯示石英閃長(zhǎng)玢巖具巖漿環(huán)帶鋯石的27個(gè)測(cè)試點(diǎn)206Pb/238U加權(quán)平均年齡為(223.2±2.2) Ma (MSWD=0.82)；花崗斑巖具巖漿環(huán)帶鋯石的21個(gè)測(cè)試點(diǎn)206Pb/238U加權(quán)平均年齡為(219.9±2.6) Ma (MSWD=0.89)。因此，巖體形成于220 Ma左右，為印支晚期巖石圈拆沉作用產(chǎn)生殼−幔混合巖漿的產(chǎn)物。
關(guān)鍵字: 地球化學(xué)；鋯石LA-ICPMS U-Pb年代學(xué)；侵入巖體；賽什塘銅礦區(qū)；青海省
intrusive body in Saishitang copper deposit, Qinghai Province, China
（1. Key Laboratory of Metallogenic Prediction of Nonferrous Metals, Ministry of Education,
Central South University, Changsha 410083, China;
2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China）
Abstract:The Ela Mountain in the east of Qinghai Province is one of the important structural-magmatic- metallogenetic belts of northern Tibet. In order to discuss the magmatic mineralization in the area, quartz diorite porphyrite and granite-porphyry in the Saishitang polymetallic deposit were selected; whole-rock major and trace elements and zircon U-Pb LA-ICPMS ages were analyzed. Geochemically, they both belong to high-potassium calc-alkalic rock series, with no or weak Eu anomaly, and enrichment of LREE, LILE and depletion of HREE, HFSE. The cathodoluminescence images of zircon of intrusive rocks show all that the zircons are magmatic zircons which have zonal structure. The dating of LA-ICP-MS zircon U-Pb of two samples shows that 27 points of oscillatory zoned domains of quartz diorite porphyrite sample yield a group of weighted mean 206Pb/238U ages at (223.2±2.2) Ma (MSWD=0.82) and 21 points of oscillatory zoned domains of granite-porphyry sample yield a group of weighted mean 206Pb/238U ages at (219.9±2.6) Ma (MSWD=0.89). The intrusive rocks were formed about 220 Ma, resulted from lithospheric delemination after crustal thickening due to collision between continental plates in late Indosinian.
Key words: geochemistry; zircon LA-ICPMS U-Pb geochronology; intrusive body; Saishitang copper deposit; Qinghai Province
