本文關(guān)鍵詞： 粗面巖 SHRIMP鋯石U-Pb年齡 Sr-Nd-Pb-O同位素 年輕下地殼 早白堊世早期 沽源鈾礦田　出處：《地球化學(xué)》2017年02期 　論文類型：期刊論文

【摘要】：沽源鈾礦田位于開源-赤峰斷裂帶以南的華北古板塊北緣,燕遼Mo-U-Ag-Pb-Zn多金屬成礦帶西段和沽源-紅山子鈾成礦帶西南段,鈾礦賦存在粗面巖-流紋巖組合中。2個(gè)粗面巖樣品(樣號(hào)分別為GY101和GY108)的鋯石均具有明顯的環(huán)帶結(jié)構(gòu),Th/U比值高,屬典型的巖漿成因鋯石。SHRIMP鋯石U-Pb測(cè)年結(jié)果表明:GY101粗面巖13個(gè)分析點(diǎn)的206Pb/238U年齡范圍為142~136 Ma,加權(quán)平均值為(138.4±1.3)Ma,MSWD=0.47;GY108粗面巖12個(gè)分析點(diǎn)的~(206)Pb/~(238)U年齡范圍為143~137 Ma,加權(quán)平均值為(139.5±1.3)Ma,MSWD=0.49,指示地質(zhì)時(shí)代屬早白堊世早期。粗面巖具有較高的SiO_2、K_2O+Na_2O含量和K_2O/Na_2O、Fe_2O_3/FeO比值,在SiO_2-(K_2O+Na_2O)圖解中落在堿性系列粗面巖或粗面英安巖范圍,在SiO_2-K_2O圖解中落在橄欖玄粗巖系列范圍,結(jié)合標(biāo)準(zhǔn)礦物Q含量小于20%,屬典型的高鉀堿性粗面巖。稀土元素含量高,富集輕稀土,Eu負(fù)異常不明顯,稀土分布模式為右傾輕稀土富集型,具高壓型粗面巖的稀土元素特征;富集大離子親石元素K、Rb、Ba、Pb和高場(chǎng)強(qiáng)元素Zr、Y,虧損Nb、Ta、Sr、Ti元素,具高Sr-Ba英安巖-流紋巖的微量元素特征。較低的Ti/Zr、Nb/Ta比值和較高的Rb/Sr比值,具有殼源火山巖的特征;具有較高的(~(87)Sr/~(86)Sr)_i(0.707781~0.708156)、εNd(t)( 5.31~ 5.83)和δ~(18)OVSMOW(7.08‰~8.05‰),較小的tDM2(1361~1376 Ma),較低的(~(206)Pb/~(204)Pb)_i(16.97~17.00)、(~(207)Pb/~(204)Pb)_i(15.06~15.62)和(~(208)Pb/~(204)Pb)_i(36.73~36.80),在ε_(tái)(Nd)(t)-(~(87)Sr/~(86)Sr)_i圖解中落在EMⅠ富集地幔與虧損地幔的聯(lián)線附近,在(~(208)Pb/~(204)Pb)t-(~(206)Pb/~(204)Pb)_t圖解中落在靠近EMⅠ富集地幔的下地殼和地幔之間,在(~(87)Sr/~(86)Sr)_i-(~(206)Pb/~(204)Pb)_t和(~(143)Nd/~(144)Nd)_i-(~(206)Pb/~(204)Pb)_t圖解中均落在EMⅠ富集地幔端元附近,在Zr/Al_2O_3-TiO_2/Al_2O_3和Y-Zr判別圖解中都落在板內(nèi)構(gòu)造環(huán)境內(nèi)。可見,沽源鈾礦田粗面巖的成因可用兩階段模式進(jìn)行解釋:中元古代源于EMⅠ富集地幔和虧損地幔的巖漿混合并在底侵于下地殼的過程中受到少量古老下地殼物質(zhì)混染后形成年輕下地殼;中侏羅世晚期-晚侏羅世發(fā)生的擠壓構(gòu)造事件導(dǎo)致地殼加厚,早白堊世早期在拉張構(gòu)造環(huán)境下加厚地殼的年輕下地殼發(fā)生部分熔融形成的粗面質(zhì)巖漿噴出地表形成粗面巖。
[Abstract]:The Guyuan uranium ore field is located in the northern margin of the North China paleo-plate south of the open-source Chifeng fault zone, the western section of the Yanliao Mo-U-Ag-Pb-Zn polymetallic metallogenic belt and the southwestern section of the Guyuan-Hongshanzi uranium metallogenic belt. The uranium deposits occur in the trachyte-rhyolite assemblage. The zircon samples of two trachyte samples (GY101 and GY108, respectively) have obvious zonal structure and high Th / U ratio. Typical magmatic zircon SHRIMP zircon U-Pb dating results show that the 206Pb / 238U age range of 13 analysis points of the: GY101 trachyte is 142136Ma. the weighted average is 138.4 鹵1.3MMSWDU 0.47GY108 trachyte with a 206PbP / 238U age range of 143137Ma.The weighted mean value is 139.5 鹵1.3MMSWDU 0.49. It is shown that the geological age belongs to the early Cretaceous. The coarse rock has a high SiO2S / K _ 2O Na_2O content and a K _ 2O / Na _ 2O / Na _ 2O / T _ 2O _ 3 / Feo ratio. It falls in the range of alkaline series trachyte or trachyte, in SiO_2-K_2O diagram, in the range of olivine trachyte series, and in combination with the standard mineral Q content less than 20%, it is a typical high potassium alkaline coarse rock with high REE content. The negative anomalies of EU enriched with LREE are not obvious, and the REE distribution pattern is right LREE enrichment type, which is characterized by REE of high pressure coarse-faced rocks, and is rich in large ion lipophilic elements K ~ (+) Rb ~ (+) Ba ~ (+) Pb and high field strength elements Zr ~ (2 +) Y, and is depleted of NB ~ (2 +) Taer Sr ~ (2 +) Ti. It has the characteristics of trace elements of high Sr-Ba dolomite and rhyolite. The lower Ti / ZrN NB / Ta ratio and the higher Rb/Sr ratio have the characteristics of crust-source volcanic rocks. The smaller tDM2(1361~1376 Mai, the smaller tDM2(1361~1376, the lower 20204Pbt rbt rsrrrsrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrnnbrnrrrrrrnnbrrrnrr.204pbr-nbrnbr-nbrrrrrr-204pbr-nbr-nbrr-nbrr-nbr-nbrrr-208pbnr-208Pbnr-208Pb / m is close to 6.736.80, and is close to the upper mantle at the bottom of the map of the earth's crust, near the bottom of the map of the earth's crust, near the bottom of the earth's crust, and near the bottom of the Pb6EM map, where the upper mantle is located near the bottom of the earth's crust, and in the lower part of the earth's crust, there is a loss in the mantle, and in the lower part of the earth's crust, there is a loss in the mantle, and in the upper mantle, there is a loss in the earth's crust, and in the upper mantle, there is no difference between the two groups. The smaller tDM2(1361~1376 is 8.05 鈥，

本文編號(hào)：1507050