江西会昌盆地粗面岩年代学与地球化学特征

发布时间：2018-02-16 11:57

  本文关键词： 粗面岩 锆石U-Pb年龄 早白垩世晚期 年轻下地壳 会昌盆地　出处：《东华理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：江西会昌盆地位于武夷山中段,属中国东南大陆晚中生代火山-侵入岩带的一部分。本文系统研究了该盆地粗面岩产出的地质背景、空间展布、地质时代、岩石学以及岩石地球化学特征和Sr、Nd、Pb、O同位素地球化学特征,并据此探讨了粗面岩的成因与构造环境。会昌盆地以红色碎屑沉积岩为主并夹有少量火山岩,粗面岩主要分布于盆地内岽背村一带红色沉积岩系中,而在盆地内站塘乡一带红色沉积岩系中则发育有玄武岩。粗面岩的SHRIMP锆石U-Pb测年结果显示,14个分析点的206Pb/238U年龄变化范围为114~108 Ma,加权平均年龄值为110.7Ma±1.0Ma,MSWD=0.47;玄武岩的SHRIMP锆石U-Pb测年结果显示,12个分析点的206Pb/238U年龄变化范围为94.2~101.6Ma,加权平均年龄值为99.0Ma±1.0Ma,MSWD=1.14。这不仅指示粗面岩和玄武岩的形成地质时代属早白垩世晚期,而且说明粗面岩形成的地质时代早于玄武岩形成的地质时代。会昌盆地粗面岩呈灰-灰绿色,断面粗糙,致密块状构造,斑状结构,斑晶以碱性长石为主,其次为角闪石、暗色矿物等。SiO2含量为59.0%~64.6%(平均为61.9%),富碱和钠,Na2O含量为6.50%~7.70%(平均为7.03%),K2O含量为0.69%~3.23%(平均为1.84%),(Na2O+K2O)含量为7.19%~10.1%(平均为9.70%),K2O/Na2O比值为0.11~0.47(平均为0.26);在SiO2-(K2O+Na2O)图上,除一个样品外都落入碱性系列粗面岩或粗面英安岩范围Qg;CIPW计算结果显示,标准矿物Q含量为6.07%~14.7%(平均为9.95%),小于20%,属粗面岩。MgO含量为0.28%~0.92%(平均为0.55%),TiO2含量为0.84%~0.94%(平均为0.90%),FeOt含量为4.17%~5.04%(平均为4.51%),CaO含量为0.87%~4.38%(平均为2.25),Al2O3含量为15.5%~18.9(平均为17.7%),A/CNK值为0.73~1.24,(平均为1.02),属弱铝质-过铝质岩石。稀土总量较低,轻稀土明显富集,重稀土强烈亏损,Eu负异常不明显,∑REE含量为114×10-6~168×10-6,∑LREE含量为101×10-6~148×10-6,∑HREE含量为14.9×10-6~19.6×10-6,∑LREE/∑HREE比值为6.54~7.52,(La/Yb)N比值为24.9~34.2(平均为27.4),δEu的值为0.81~1.10(平均为0.98),在稀土曲线图上呈明显的右倾,具高压型粗面岩的稀土特征。较低的Y和Yb含量,较高的Sr含量和Sr/Y比值,Y含量为8.99×10-6~11.7×10-6(平均为10.8×10-6),Yb含量为0.55×10-6~0.82×10-6(平均为0.7×10-6),Sr含量为329×10-6~836×10-6(平均为498×10-6),Sr/Y比值为36.5~71.8(平均为48.2),具有埃达克质岩石的特征;Zr含量为203×10-6~219×10-6(平均为209×10-6),Ba含量为477×10-6~1123×10-6(平均为699×10-6),在Zr-Sr-Ba图解上落入高Sr-Ba英安岩-流纹岩区,显示出深部地壳来源的特征;在不相容元素蛛网图上显示富集大离子亲石元素(Cs、Rb、Ba、K等元素),强烈亏损高场强元素(Ta、Nd)。粗面岩(87Sr/86Sr)i值为0.7074~0.7082(平均为0.7077),(143Nd/144Nd)i值为0.512491~0.512497(平均为0.512494),(206Pb/204Pb)i值为18.10~18.19(平均为18.14),(207Pb/204Pb)i值为15.76~15.77(平均为15.77),(208Pb/204Pb)i值为38.52~38.53(平均为38.54),εNd(t)值为-1.99~-2.60(平均为-2.29),TDM2=1071 Ma~1120Ma(平均为1094 Ma),表明粗面岩具有年轻下地壳部分熔融产物的特征;在(87Sr/86Sr)i-(206Pb/204Pb)i、(143Nd/144Nd)i-(206Pb/204Pb)i和εNd(t)-(87Sr/86Sr)i图解上,投影点皆位于DMM、EMⅡ端员之间,表明年轻下地壳源岩是由DMM和EMⅡ型地幔物质混合型成的;综合以上地球化学特征,会昌盆地粗面岩是由亏损地幔(DM)和Ⅱ型富集地幔部分熔融的产物混合形成的年轻下地壳再经部分熔融形成的岩浆喷发地表而形成。
[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�閲忓拰Sr/Y姣斿，

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