內(nèi)蒙古烏拉山-大青山地區(qū)變泥質(zhì)巖的地球化學(xué)特征及構(gòu)造意義
發(fā)布時間：2018-09-04 07:41
【摘要】：烏拉山-大青山地區(qū)位于華北克拉通西北緣孔茲巖帶的中段,該地區(qū)出露大面積的古元古代高級變質(zhì)表殼巖系巖石,例如夕線(堇青)石榴二長片麻巖、石榴黑云二長片麻巖、黑云長英質(zhì)片麻巖、石榴石英巖、大理巖、磁鐵石英巖和鈣硅酸鹽巖等。其中該地區(qū)典型的變泥質(zhì)巖石(夕線(堇青)石榴二長片麻巖和石榴黑云二長片麻巖)多以似層狀產(chǎn)出,夕線(堇青)石榴二長片麻巖含有大量的石榴石、夕線石和/或堇青石,并保留典型的堇青石反應(yīng)邊結(jié)構(gòu)。巖石地球化學(xué)研究結(jié)果表明上述變泥質(zhì)巖石樣品明顯富Al2O_3,屬于過鋁質(zhì)巖石,其平均化學(xué)成分與上地殼平均值較為接近。樣品的稀土配分型式具有中等程度的輕重稀土元素分異,輕稀土明顯富集和弱銪負(fù)異常的特征。微量元素蛛網(wǎng)圖顯示變泥質(zhì)巖石樣品富集大離子親石元素如Rb和Ba,而高場強(qiáng)元素如Zr、Hf含量相對較低,且Nb、Ta、P和Ti呈明顯虧損的特征。多種原巖判別圖解顯示其原巖為一套富鋁粘土巖及雜砂巖,且成熟度較低,為近源沉積。多數(shù)樣品的CIA值低于太古宙后澳大利亞平均頁巖和北美頁巖的CIA值,反映其源巖經(jīng)歷了中等程度的風(fēng)化作用。物源以上地殼的長英質(zhì)成分為主,可能有古老沉積物的加入。多種構(gòu)造判別圖解表明研究區(qū)樣品形成于有演化島弧發(fā)育的活動大陸邊緣環(huán)境。結(jié)合前人對孔茲巖帶出露的變泥質(zhì)巖石的變質(zhì)作用研究普遍得到近等溫減壓型順時針P-T演化軌跡以及鋯石同位素年代學(xué)研究結(jié)果,綜合表明烏拉山-大青山變泥質(zhì)巖石形成于有演化島弧發(fā)育的活動大陸邊緣環(huán)境,中元古代物質(zhì)(2.1~2.0Ga)為其提供主要的沉積物源,隨后卷入~1950Ma華北克拉通西部古老陸塊之間的碰撞造山作用,經(jīng)歷了大規(guī)模麻粒巖相變質(zhì)作用,并于1920~1850Ma碰撞后折返至近地表。
[Abstract]:The Wula-Daqingshan area is located in the middle of the Kongzite belt on the northwest margin of the North China Craton. A large area of paleoproterozoic metamorphic crust rocks, such as the pomegranate gneiss, the pomegranate black cloud gneiss, are exposed in this area. Feldspar gneiss, pomegranate, marble, magnetite quartzite and calcium silicate, etc. The typical argillaceous rocks (pomegranate gneiss, pomegranate gneiss and pomegranate black cloud gneiss) in this area are mostly stratiform, and the pomegranate gneiss contains a great deal of garnet. Sillimanite and / or cordierite, and retaining the typical cordierite reaction edge structure. The results of petrogeochemical study show that the samples of argillaceous rocks mentioned above are obviously rich in Al2O_3, and belong to peraluminous rocks, and their average chemical composition is close to the average value of the upper crust. The rare earth distribution patterns of the samples have the characteristics of moderate light rare earth element differentiation, obvious enrichment of light rare earth elements and negative anomalies of weak europium. The trace element cobwebs show that the samples of argillaceous rocks are rich in large ion lithophile elements such as Rb and Ba, but the contents of high field strength elements such as Zr,Hf are relatively low, and Nb,Ta,P and Ti are obviously depleted. The original rock is a set of aluminum-rich clay rock and complex sandstone, and its maturity is relatively low, so it is a near-source deposit. The CIA values of most samples are lower than the CIA values of the average Australian shale and North American shale after Archean, indicating that the source rocks experienced moderate weathering. The feldspathic composition of the crust above the provenance is mainly composed of ancient sediments. Various tectonic discriminant diagrams show that the samples in the study area were formed in the active continental margin environment with the evolution of island arc. Combined with previous studies on metamorphism of altered shaly rocks from the Kongzi belt, the results of near isothermal decompression clockwise P-T evolution and zircon isotopic chronology are generally obtained. The results show that the argillaceous rocks of the Wula-Daqingshan Mountains were formed in the active continental margin environment where the island arcs developed, and the Mesoproterozoic material (2.1~2.0Ga) provided the main sediment source for them. The collision orogeny between the ancient continental blocks in the west of North China Craton at 1950 Ma underwent a large-scale granulite facies metamorphism and returned to the near surface after the 1920~1850Ma collision.
【作者單位】： 中國地質(zhì)科學(xué)院地質(zhì)研究所;
【基金】：國家自然科學(xué)基金項目(41430210、41502181、41302153) 中國地質(zhì)調(diào)查局地質(zhì)大調(diào)查項目(DD20160121、12120114061901) 科技部“973”項目(2012CB416603) 中國地質(zhì)科學(xué)院基本科研業(yè)務(wù)費(fèi)(J1512)聯(lián)合資助
【分類號】：P588.345
本文編號：2221432
[Abstract]:The Wula-Daqingshan area is located in the middle of the Kongzite belt on the northwest margin of the North China Craton. A large area of paleoproterozoic metamorphic crust rocks, such as the pomegranate gneiss, the pomegranate black cloud gneiss, are exposed in this area. Feldspar gneiss, pomegranate, marble, magnetite quartzite and calcium silicate, etc. The typical argillaceous rocks (pomegranate gneiss, pomegranate gneiss and pomegranate black cloud gneiss) in this area are mostly stratiform, and the pomegranate gneiss contains a great deal of garnet. Sillimanite and / or cordierite, and retaining the typical cordierite reaction edge structure. The results of petrogeochemical study show that the samples of argillaceous rocks mentioned above are obviously rich in Al2O_3, and belong to peraluminous rocks, and their average chemical composition is close to the average value of the upper crust. The rare earth distribution patterns of the samples have the characteristics of moderate light rare earth element differentiation, obvious enrichment of light rare earth elements and negative anomalies of weak europium. The trace element cobwebs show that the samples of argillaceous rocks are rich in large ion lithophile elements such as Rb and Ba, but the contents of high field strength elements such as Zr,Hf are relatively low, and Nb,Ta,P and Ti are obviously depleted. The original rock is a set of aluminum-rich clay rock and complex sandstone, and its maturity is relatively low, so it is a near-source deposit. The CIA values of most samples are lower than the CIA values of the average Australian shale and North American shale after Archean, indicating that the source rocks experienced moderate weathering. The feldspathic composition of the crust above the provenance is mainly composed of ancient sediments. Various tectonic discriminant diagrams show that the samples in the study area were formed in the active continental margin environment with the evolution of island arc. Combined with previous studies on metamorphism of altered shaly rocks from the Kongzi belt, the results of near isothermal decompression clockwise P-T evolution and zircon isotopic chronology are generally obtained. The results show that the argillaceous rocks of the Wula-Daqingshan Mountains were formed in the active continental margin environment where the island arcs developed, and the Mesoproterozoic material (2.1~2.0Ga) provided the main sediment source for them. The collision orogeny between the ancient continental blocks in the west of North China Craton at 1950 Ma underwent a large-scale granulite facies metamorphism and returned to the near surface after the 1920~1850Ma collision.
【作者單位】： 中國地質(zhì)科學(xué)院地質(zhì)研究所;
【基金】：國家自然科學(xué)基金項目(41430210、41502181、41302153) 中國地質(zhì)調(diào)查局地質(zhì)大調(diào)查項目(DD20160121、12120114061901) 科技部“973”項目(2012CB416603) 中國地質(zhì)科學(xué)院基本科研業(yè)務(wù)費(fèi)(J1512)聯(lián)合資助
【分類號】：P588.345
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