發(fā)布時(shí)間：2018-02-07 14:29

  本文關(guān)鍵詞： 遼陽(yáng) 遼河群 酸性火山巖 鋯石U-Pb年代學(xué) 構(gòu)造背景　出處：《巖石學(xué)報(bào)》2017年09期 　論文類型：期刊論文

【摘要】：遼寧省遼陽(yáng)地區(qū)出露有大面積的古元古代遼河群地層,在遼河群里爾峪組及高家峪組中識(shí)別出一套酸性火山巖。本文通過對(duì)酸性火山巖同位素年代學(xué)及地球化學(xué)研究,用以限定遼河群形成時(shí)代,并進(jìn)一步探討其形成的動(dòng)力學(xué)背景。這套酸性火山巖巖性包括流紋巖、變流紋質(zhì)含角礫凝灰?guī)r、角巖化流紋巖和弱硅化流紋巖,對(duì)其中6件樣品利用LA-ICP-MS鋯石U-Pb方法測(cè)年。CL圖像顯示遼河群酸性火山巖中的鋯石均具典型的巖漿振蕩環(huán)帶結(jié)構(gòu)和較高的Th/U比值,顯示為巖漿鋯石。鋯石U-Pb年齡可分為3期:2190~2180Ma、2110~2100Ma、1970~1960Ma,結(jié)合其中存在繼承鋯石的結(jié)果認(rèn)為遼河群至少存在3期巖漿活動(dòng),將遼河群形成時(shí)代限制于2.19~1.96Ga,其形成時(shí)代大約持續(xù)了230Myr左右。野外接觸關(guān)系的觀察及酸性火山巖的年代學(xué)特征從另一個(gè)方面揭露遼河群總體為一套無(wú)序、局部有序的構(gòu)造地層,各巖組間不存在上下關(guān)系。前人研究表明"遼吉花崗巖"形成年齡為2.16Ga,通過野外觀察其與遼河群之間均為構(gòu)造接觸。D1442-1和D1444-2兩個(gè)樣品鋯石U-Pb測(cè)年結(jié)果為2180±12Ma、2190±13Ma,均略早于"遼吉花崗巖",結(jié)合其與遼河群野外關(guān)系,認(rèn)為"遼吉花崗巖"應(yīng)該不是作為沉積基底,而是與遼河群為同一構(gòu)造運(yùn)動(dòng)的產(chǎn)物。遼河群流紋巖Al_2O_3含量16.33%~16.90%,K_2O含量4.62%~4.77%,K_2O+Na_2O含量5.97%~7.54%,含鋁指數(shù)(A/CNK)比較高為1.27~1.50,為過鋁質(zhì)巖石,顯示富鋁、高鉀特征。此外流紋巖輕稀土富集,重稀土虧損,輕重稀土分餾明顯,具有明顯的負(fù)銪異常,虧損Ba、Sr、Ti,較高的Zr及(Zr+Nb+Ce+Y)含量、10000Ga/Al比值等特點(diǎn)都顯示為A型花崗巖,說明其形成于地殼減薄環(huán)境。本文在遼河群中識(shí)別出一套酸性火山巖與前人在南遼河群識(shí)別出的變質(zhì)流紋巖組成了酸性端元(2201~1960Ma),同時(shí)期存在的基性火成巖(2198~1869Ma)為基性端元,證明了遼河群"雙峰式火山巖"的存在,暗示遼河群形成于伸展拉張環(huán)境。
[Abstract]:A large area of paleoproterozoic Liaohe Group strata were exposed in Liaoyang area, Liaoning Province, and a set of acidic volcanic rocks were identified in Lianyu formation and Gaojiayu formation of Liaohe Group. The isotopic chronology and geochemistry of acidic volcanic rocks are studied in this paper. It is used to define the formation age of the Liaohe Group and to further explore the dynamic background of its formation. This set of acid volcanic lithology includes rhyolite, metamorphic kernel-bearing tuff, keratinized rhyolite and weakly silicified rhyolite. For 6 samples, the LA-ICP-MS zircon U-Pb dating images show that the zircons in the acidic volcanic rocks of the Liaohe Group all have typical magmatic oscillatory zone structure and high Th/U ratio. The zircon U-Pb age can be divided into three phases: 21902 180 Ma-21010 Ma-2100 Ma-1970Ma-1960Ma. combined with the result of inherited zircon, it is concluded that there are at least three magmatic activities in the Liaohe Group, and the results show that there are three phases of magmatic activity in the Liaohe Group. The formation age of Liaohe Group was limited to 2.19 ~ 1.96Ga, which lasted about 230Myr. The observation of field contact relationship and the chronological characteristics of acid volcanic rocks reveal that the Liaohe Group is a set of disordered and locally orderly tectonic strata in another aspect. Previous studies show that the age of formation of Liaoji granites is 2.16Ga, and the zircon U-Pb dating between Liaohe Group and Liaohe Group is tectonic contact. D1442-1 and D1444-2 are 2180 鹵12Ma-2190 鹵13Ma-zircon U-Pb dating results, which is slightly earlier than that of Liaohe Group. "Liaoji Granite", combined with its field relationship with Liaohe Group, It is considered that "Liaoji granite" should be the product of the same tectonic movement as Liaohe Group, not as sedimentary basement. The Al_2O_3 content of rhyolite in Liaohe Group is 16.33 ~ 16.90 and the content of K _ 2O is 4.62 ~ 4.77 and K _ 2O Na_2O is 5.97 ~ 7.54. The Al content of Liaohe Group is higher than that of Liaohe Group, which is a peraluminous rock, indicating that it is aluminum-rich, and the content of K _ 2O is 5.97 ~ 7.54% higher than that of Liaohe Group. In addition, the rhyolite is characterized by enrichment of light rare earths, depletion of heavy rare earths, obvious fractionation of light and heavy rare earths, obvious negative europium anomaly, depletion of Bajiu SrTiand high Zr and zirconium NB ce Y contents of 10000Ga / Al ratio, all of which show A-type granites. In this paper, a set of acidic volcanic rocks and metamorphic rhyolite identified in the South Liaohe Group have been identified as the basic terminal elements. The acidic end element is composed of the acidic end element, the basic igneous rock, which existed in the same period, and the basic igneous rock, which existed at the same time, and the basic igneous rocks of the same period. In this paper, a set of acid volcanic rocks and metamorphic rhyolite identified in the South Liaohe Group are identified as basic terminal elements. The existence of bimodal volcanic rocks in Liaohe Group suggests that Liaohe Group was formed in extensional and extensional environment.
【作者單位】： 中國(guó)地質(zhì)調(diào)查局沈陽(yáng)地質(zhì)調(diào)查中心;吉林大學(xué)地球科學(xué)學(xué)院;遼寧省礦產(chǎn)勘查院;
【基金】：中國(guó)地質(zhì)調(diào)查局地質(zhì)調(diào)查工作項(xiàng)目(12120113058400、DD20160048-05、12120113053400)資助
【分類號(hào)】：P588.14;P597.3

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