本文關(guān)鍵詞： 粗面巖 鋯石U-Pb年齡 早白堊世晚期 年輕下地殼 會(huì)昌盆地　出處：《東華理工大學(xué)》2015年碩士論文　論文類(lèi)型：學(xué)位論文

【摘要】：江西會(huì)昌盆地位于武夷山中段,屬中國(guó)東南大陸晚中生代火山-侵入巖帶的一部分。本文系統(tǒng)研究了該盆地粗面巖產(chǎn)出的地質(zhì)背景、空間展布、地質(zhì)時(shí)代、巖石學(xué)以及巖石地球化學(xué)特征和Sr、Nd、Pb、O同位素地球化學(xué)特征,并據(jù)此探討了粗面巖的成因與構(gòu)造環(huán)境。會(huì)昌盆地以紅色碎屑沉積巖為主并夾有少量火山巖,粗面巖主要分布于盆地內(nèi)崠背村一帶紅色沉積巖系中,而在盆地內(nèi)站塘鄉(xiāng)一帶紅色沉積巖系中則發(fā)育有玄武巖。粗面巖的SHRIMP鋯石U-Pb測(cè)年結(jié)果顯示,14個(gè)分析點(diǎn)的206Pb/238U年齡變化范圍為114~108 Ma,加權(quán)平均年齡值為110.7Ma±1.0Ma,MSWD=0.47;玄武巖的SHRIMP鋯石U-Pb測(cè)年結(jié)果顯示,12個(gè)分析點(diǎn)的206Pb/238U年齡變化范圍為94.2~101.6Ma,加權(quán)平均年齡值為99.0Ma±1.0Ma,MSWD=1.14。這不僅指示粗面巖和玄武巖的形成地質(zhì)時(shí)代屬早白堊世晚期,而且說(shuō)明粗面巖形成的地質(zhì)時(shí)代早于玄武巖形成的地質(zhì)時(shí)代。會(huì)昌盆地粗面巖呈灰-灰綠色,斷面粗糙,致密塊狀構(gòu)造,斑狀結(jié)構(gòu),斑晶以堿性長(zhǎng)石為主,其次為角閃石、暗色礦物等。SiO2含量為59.0%~64.6%(平均為61.9%),富堿和鈉,Na2O含量為6.50%~7.70%(平均為7.03%),K2O含量為0.69%~3.23%(平均為1.84%),(Na2O+K2O)含量為7.19%~10.1%(平均為9.70%),K2O/Na2O比值為0.11~0.47(平均為0.26);在SiO2-(K2O+Na2O)圖上,除一個(gè)樣品外都落入堿性系列粗面巖或粗面英安巖范圍Qg;CIPW計(jì)算結(jié)果顯示,標(biāo)準(zhǔn)礦物Q含量為6.07%~14.7%(平均為9.95%),小于20%,屬粗面巖。MgO含量為0.28%~0.92%(平均為0.55%),TiO2含量為0.84%~0.94%(平均為0.90%),FeOt含量為4.17%~5.04%(平均為4.51%),CaO含量為0.87%~4.38%(平均為2.25),Al2O3含量為15.5%~18.9(平均為17.7%),A/CNK值為0.73~1.24,(平均為1.02),屬弱鋁質(zhì)-過(guò)鋁質(zhì)巖石。稀土總量較低,輕稀土明顯富集,重稀土強(qiáng)烈虧損,Eu負(fù)異常不明顯,∑REE含量為114×10-6~168×10-6,∑LREE含量為101×10-6~148×10-6,∑HREE含量為14.9×10-6~19.6×10-6,∑LREE/∑HREE比值為6.54~7.52,(La/Yb)N比值為24.9~34.2(平均為27.4),δEu的值為0.81~1.10(平均為0.98),在稀土曲線(xiàn)圖上呈明顯的右傾,具高壓型粗面巖的稀土特征。較低的Y和Yb含量,較高的Sr含量和Sr/Y比值,Y含量為8.99×10-6~11.7×10-6(平均為10.8×10-6),Yb含量為0.55×10-6~0.82×10-6(平均為0.7×10-6),Sr含量為329×10-6~836×10-6(平均為498×10-6),Sr/Y比值為36.5~71.8(平均為48.2),具有埃達(dá)克質(zhì)巖石的特征;Zr含量為203×10-6~219×10-6(平均為209×10-6),Ba含量為477×10-6~1123×10-6(平均為699×10-6),在Zr-Sr-Ba圖解上落入高Sr-Ba英安巖-流紋巖區(qū),顯示出深部地殼來(lái)源的特征;在不相容元素蛛網(wǎng)圖上顯示富集大離子親石元素(Cs、Rb、Ba、K等元素),強(qiáng)烈虧損高場(chǎng)強(qiáng)元素(Ta、Nd)。粗面巖(87Sr/86Sr)i值為0.7074~0.7082(平均為0.7077),(143Nd/144Nd)i值為0.512491~0.512497(平均為0.512494),(206Pb/204Pb)i值為18.10~18.19(平均為18.14),(207Pb/204Pb)i值為15.76~15.77(平均為15.77),(208Pb/204Pb)i值為38.52~38.53(平均為38.54),εNd(t)值為-1.99~-2.60(平均為-2.29),TDM2=1071 Ma~1120Ma(平均為1094 Ma),表明粗面巖具有年輕下地殼部分熔融產(chǎn)物的特征;在(87Sr/86Sr)i-(206Pb/204Pb)i、(143Nd/144Nd)i-(206Pb/204Pb)i和εNd(t)-(87Sr/86Sr)i圖解上,投影點(diǎn)皆位于DMM、EMⅡ端員之間,表明年輕下地殼源巖是由DMM和EMⅡ型地幔物質(zhì)混合型成的;綜合以上地球化學(xué)特征,會(huì)昌盆地粗面巖是由虧損地幔(DM)和Ⅱ型富集地幔部分熔融的產(chǎn)物混合形成的年輕下地殼再經(jīng)部分熔融形成的巖漿噴發(fā)地表而形成。
[Abstract]:Jiangxi Huichang basin is located in the middle part of Wuyishan, the continental Southeast Chinese late Mesozoic volcano intrusive rock belt part. This paper systematically studies the geological background of the basin trachyte output spatial distribution, geological age, petrological and geochemical characteristics of rocks and Sr, Nd, Pb, O isotope geochemistry, and discusses the genesis and tectonic environment of trachyte. Huichang basin in red clastic sedimentary rocks with small volcano rocks, trachyte mainly distributed in Dongbei village in the basin area of red sedimentary rocks in the basin, and a station Tangxiang with red sedimentary rocks in developed basalt trachyte U-Pb SHRIMP zircon. The dating results show that, the 206Pb/238U age range 14 points for 114~108 Ma analysis, weighted average age = 110.7Ma + 1.0Ma, MSWD=0.47; SHRIMP zircon U-Pb dating results show that basalt, 12 analysis The 206Pb/238U age range point 94.2~101.6Ma, weighted average age = 99.0Ma + 1.0Ma, MSWD=1.14. not only indicates the formation geological age is early Cretaceous basalt and trachyte, and illustrate the geological age of geological age of trachyte formation in the Huichang basin. Early basalt trachyte is gray green, coarse. Dense massive structure, porphyritic structure, phenocrysts in alkaline feldspar, followed by hornblende, dark mineral content of.SiO2 was 59.0%~64.6% (average 61.9%), alkali and sodium content of Na2O was 6.50%~7.70% (average 7.03%), the content of K2O was 0.69%~3.23% (average 1.84%), 7.19%~10.1% ((Na2O+K2O) content an average of 9.70%), the ratio of K2O/Na2O to 0.11~0.47 (average 0.26); in SiO2- (K2O+Na2O) on the map, except in one sample into alkaline trachyte or trachydacite range Qg; CIPW results show, Standard mineral content of Q was 6.07%~14.7% (average 9.95%), less than 20%, belongs to trachyte.MgO content is 0.28%~0.92% (average 0.55%), the content of TiO2 was 0.84%~0.94% (average 0.90%), the content of FeOt was 4.17%~5.04% (average 4.51%), the content of CaO was 0.87%~4.38% (average 2.25), Al2O3 (the average content is 15.5%~18.9 17.7%), the A/CNK value is 0.73~1.24 (average 1.02), is weakly aluminous to peraluminous rocks. Lower total REE, significant enrichment of light rare earth and heavy rare earth strong losses and negative Eu anomaly is not obvious, the total REE content is 114 * 10-6~168 * 10-6 sigma, the content of LREE is 101 * 10-6~148 * 10-6. The total HREE content of 14.9 x 10-6~19.6 x 10-6, sigma Sigma LREE/ HREE = 6.54~7.52 (La/Yb) N ratio was 24.9~34.2 (average 27.4), including the Eu value of 0.81~1.10 (average 0.98), in the rare earth curve showed a right tilt, with characteristics of rare earth pressure type trachyte Y. And the low level of Yb, 杈冮珮鐨凷r鍚噺鍜孲r/Y姣斿，

本文編號(hào)：1515461