(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: 賽什塘礦區(qū)地層為一套濱−淺海相碎屑巖、泥質(zhì)巖夾碳酸鹽巖，普遍遭受淺變質(zhì)作用，各類巖石稀土元素配分曲線相似，均為輕稀土富集型，具中等銪負(fù)異常，具有一致性。巖相學(xué)及La/Yb—∑REE圖解判別表明：礦區(qū)變質(zhì)巖原巖屬沉積巖類，以砂巖和雜砂巖為主，未顯示與火山成因有關(guān)；前人所述“硅質(zhì)巖”并不具備典型硅質(zhì)巖的特征，其原巖應(yīng)為石英砂巖類，礦區(qū)未見(jiàn)明顯的熱水沉積作用。應(yīng)用w(Th)—w(Co)—w(Zr)構(gòu)造背景判別圖解以及與雜砂巖稀土元素特征值和典型構(gòu)造背景砂巖配分模式對(duì)比等方法進(jìn)行礦區(qū)構(gòu)造環(huán)境分析，認(rèn)為礦區(qū)形成環(huán)境同時(shí)具有活動(dòng)大陸邊緣型和大陸島弧型的特點(diǎn)，推斷其形成于三疊紀(jì)古特提斯洋陸緣的島弧−弧后盆地環(huán)境。
關(guān)鍵字: 變質(zhì)巖；原巖恢復(fù)；稀土元素；構(gòu)造環(huán)境；賽什塘
Saishitang mining area, 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 sedimentary sequence of Saishitang district is composed of offshore-neritic clastic rocks and argillaceous rocks with carbonate streaks, which are commonly metamorphosed weakly, with similar REE patterns enriched in LREE and moderate Eu negative anomaly. The lithofacies features and La/Yb—∑REE diagram indicate that the protoliths of metamorphite are sedimentary rocks, with main types of sandstone and greywacke and unrelated with volcanic process; the ‘silicalite’ defined previously does not have the typical characteristics of silicalite, whereas the protolith of this ‘silicalite’ should be quartz sandstone, and no obvious evidence of hot water deposition was found in the district. According to the w(Th)—w(Co)—w(Zr) diagram and correlation between greywacke REE features and sandstone REE distribution patterns of typical tectonic settings, the tectonic environment of the district displays both active continental marginal and continental island arc characteristics, which indicates that the Saishitang district is developed in arc-back basin located in margin of the Triassic Paleotethys.
Key words: meta-sedimentary rock; protolith reconstruction; rare earth elements; tectonic setting; Saishitang
