地球化學(xué)方法在硅質(zhì)巖成因與構(gòu)造背景研究中的進(jìn)展及問題

張 聰, 黃 虎, 侯明才

(1.中國地質(zhì)大學(xué) 地球科學(xué)與資源學(xué)院，北京 100083；2.中國地質(zhì)調(diào)查局 油氣資源調(diào)查中心，北京 100029；3.成都理工大學(xué) 沉積地質(zhì)研究院，成都 610059)

地球化學(xué)方法在硅質(zhì)巖成因與構(gòu)造背景研究中的進(jìn)展及問題

張 聰1,2, 黃 虎3, 侯明才3

(1.中國地質(zhì)大學(xué) 地球科學(xué)與資源學(xué)院，北京 100083；2.中國地質(zhì)調(diào)查局 油氣資源調(diào)查中心，北京 100029；3.成都理工大學(xué) 沉積地質(zhì)研究院，成都 610059)

硅質(zhì)巖由于受后期風(fēng)化作用及成巖作用影響較弱，其地球化學(xué)特征常被用來討論硅質(zhì)巖成因和形成構(gòu)造背景。本文分析了硅質(zhì)巖的成因以及形成于不同構(gòu)造背景下硅質(zhì)巖的主元素、痕量元素、稀土元素、Si同位素和Sr-Nd同位素組成特征。在總結(jié)硅質(zhì)巖成因與構(gòu)造背景研究方法和進(jìn)展的同時(shí)，指出元素地球化學(xué)行為的錯(cuò)誤理解和硅化作用過程中SiO2稀釋劑作用的影響是造成利用地球化學(xué)方法判別硅質(zhì)巖成因和構(gòu)造背景時(shí)產(chǎn)生多解性的主要原因。而對硅質(zhì)巖成巖機(jī)理的再認(rèn)識表明：硅質(zhì)巖成巖過程中，SiO2對主元素和稀土元素起稀釋劑的作用；TiO2、Al2O3、MgO、K2O作為陸源組分，受成巖作用的影響比Fe2O3、MnO、CaO、Na2O、P2O5弱；成巖作用對頁巖或泥巖主元素的影響強(qiáng)于硅質(zhì)巖；硅質(zhì)巖的稀土元素含量除受沉積環(huán)境的控制外，還受硅化程度的影響。

硅質(zhì)巖;地球化學(xué);成因;成巖作用;構(gòu)造背景

硅質(zhì)巖相對于其他沉積物(砂巖、碳酸鹽等)分布較少，但是從太古代到新生代均有其沉積記錄。由于硅質(zhì)巖很少受后期風(fēng)化作用及成巖作用的影響，其地球化學(xué)特征記錄了熱液沉積、火山及陸源碎屑等的含量變化，對恢復(fù)古環(huán)境具有重要的意義[1-4]。因此，硅質(zhì)巖的地球化學(xué)特征常用來討論其成因和形成構(gòu)造背景[5-10]。隨著越來越多有關(guān)硅質(zhì)巖地球化學(xué)數(shù)據(jù)的報(bào)告，目前在利用硅質(zhì)巖的地球化學(xué)數(shù)據(jù)討論其成因和構(gòu)造背景時(shí)，常會出現(xiàn)多解性和人為性[11]。本文在總結(jié)前人利用硅質(zhì)巖地球化學(xué)特征判斷成因和構(gòu)造背景進(jìn)展的同時(shí)，分析造成目前利用硅質(zhì)巖判別成因時(shí)多解性的部分原因，并討論硅質(zhì)巖成巖過程中部分元素的地球化學(xué)行為。

1 SiO2的來源

由于缺少硅質(zhì)微生物，目前對前寒武紀(jì)硅質(zhì)巖中的SiO2的起源還有較大爭議，主要存在以下幾種假設(shè)：從海水中直接沉淀硅[12]，深海熱液硅[13-14]，陸源或混合陸源組分的蒸發(fā)巖經(jīng)硅化作用生成[15]等。一般認(rèn)為，顯生宙以來的硅質(zhì)巖中SiO2的起源主要與硅質(zhì)生物活動有關(guān)[16]。研究表明，現(xiàn)代海洋中的溶解態(tài)硅80%來自河流的輸入，剩余部分則主要來自大氣﹑海底玄武巖的低溫風(fēng)化和海底熱煙囪[17]，并由富硅生物吸收以及死亡分解后，約3%的生源硅沉降形成A型蛋白石，再經(jīng)過CT型蛋白石沉降與溶解過程，最后轉(zhuǎn)化為硅質(zhì)巖[17-18]。另外，熱液活動有關(guān)的硅化作用、碳酸鹽中硅的置換作用[19]以及強(qiáng)堿條件下從膠體中沉淀[20-21]等在特定的沉積環(huán)境中均可能成為硅質(zhì)巖成巖過程中SiO2的重要來源。

2 硅質(zhì)巖的成因

硅質(zhì)巖由于受后期成巖作用改造，其原始組構(gòu)可能發(fā)生改變，進(jìn)而造成直接的礦物學(xué)證據(jù)缺失。目前，對于硅質(zhì)巖成因類型的研究主要依靠地球化學(xué)手段[22]。硅質(zhì)巖中的Fe和Mn的富集被認(rèn)為主要與熱液的參與有關(guān)，而Al和Ti的富集則主要與陸源物質(zhì)的輸入有關(guān)。據(jù)此，有學(xué)者[23]認(rèn)為海相沉積物中的wAl/wAl+Fe+Mn值(w表示質(zhì)量分?jǐn)?shù))可以用來衡量沉積物中熱液組分含量，該比值越小，反映其受熱液作用影響越明顯。Adachi等[24]和Yamamoto[25]在系統(tǒng)研究了不同成因的硅質(zhì)巖后，擬定了判別熱液成因與非熱液成因硅質(zhì)巖的wAl-wFe-wMn三角判別圖解。在該判別圖解上，非熱液成因硅質(zhì)巖的投點(diǎn)均落入富Al端元，而熱液成因硅質(zhì)巖的投點(diǎn)均落入富Fe端元。對大西洋中脊和東太平洋海隆的熱液沉積物研究表明，熱液沉積物的稀土元素經(jīng)球粒隕石標(biāo)準(zhǔn)化后均表現(xiàn)為明顯的Eu正異常[26-29]。另外，熱液硅質(zhì)巖中除了含大量微晶質(zhì)石英及少量黏土礦物外，常含有呈分散狀的褐鐵礦、方沸石、蒸發(fā)巖、石膏、硬石膏、自生的重晶石及黃鐵礦等礦物或其假晶[13-14,30]。

目前有關(guān)硅質(zhì)巖成因的研究主要借助于wAl-wFe-wMn判別圖[24-25]以及(wAl/wAl+Fe+Mn)-(wFe/wTi)判別圖[31]。這些成因判別圖中均利用Mn元素作為熱液成因的指示元素，而Murray[32]指出Mn元素容易受成巖作用的影響，是一種相對易遷移的元素?？紤]到這種原因，本文將已發(fā)表的顯生宙不同成因的硅質(zhì)巖樣品[1,24-25,33-42]投在(wAl/wAl+Fe)- (wFe/wTi)圖解(圖1-A)上，并與wAl-wFe-wMn判別圖(圖1-B)對比，可以發(fā)現(xiàn)2個(gè)判別圖的結(jié)果基本一致。即當(dāng)wAl/wAl+Fe>0.5、wFe/wTi<30時(shí)，代表非熱液成因；而當(dāng)wAl/wAl+Fe<0.35、wFe/wTi>30時(shí)，代表熱液成因。

3 硅質(zhì)巖的構(gòu)造背景判別

3.1 主元素

Murray[32]在系統(tǒng)地總結(jié)了顯生宙形成于不同構(gòu)造背景的硅質(zhì)巖地球化學(xué)特征后，認(rèn)為Al和Ti元素可以作為陸源物質(zhì)注入的標(biāo)志，并根據(jù)Al2O3、TiO2、Fe2O3和SiO2的比值關(guān)系，提出了區(qū)分洋中脊、大洋盆地和大陸邊緣硅質(zhì)巖的判別圖。目前，wAl2O3/wAl2O3+Fe2O3值被認(rèn)為是判別硅質(zhì)巖形成構(gòu)造背景的一個(gè)較好的指標(biāo)[32,39,44-45]。其中，大陸邊緣硅質(zhì)巖的wAl2O3/wAl2O3+Fe2O3=0.5～0.9；遠(yuǎn)洋盆地硅質(zhì)巖的wAl2O3/wAl2O3+Fe2O3=0.4～0.7；而洋中脊硅質(zhì)巖的wAl2O3/wAl2O3+Fe2O3<0.4[32]。

圖2 硅質(zhì)巖構(gòu)造背景判別圖Fig.2 Discrimination diagram of tectonic setting for cherts(據(jù)文獻(xiàn)[32]修改, 圖例同圖1)

Murray等[32]系統(tǒng)總結(jié)了顯生宙不同環(huán)境硅質(zhì)巖的地球化學(xué)特征，提出用(wAl2O3/wAl2O3+Fe2O3)-(wFe2O3/wTiO2)(圖2)來判別硅質(zhì)巖的形成環(huán)境。比較圖1-A和圖2可以發(fā)現(xiàn)二者表現(xiàn)出很好的相似性。這種相似性主要?dú)w因于Fe元素的富集與熱液成因有關(guān)，而其富集勢必會造成Fe2O3的富集，進(jìn)而在構(gòu)造背景判別圖上指示遠(yuǎn)洋或洋脊環(huán)境；而Al和Ti元素主要與陸源組分有關(guān)，其富集指示陸源成因，而Al和Ti元素的富集必然會造成Al2O3和TiO2的富集，進(jìn)而在構(gòu)造背景判別圖上指示大陸邊緣環(huán)境。那么，是否意味著這2個(gè)判別圖都可以同時(shí)用來判別硅質(zhì)巖的成因以及構(gòu)造背景呢？實(shí)際上從圖1-A中可以看出，熱液成因的硅質(zhì)巖主要形成于半深海、洋脊以及開闊海盆相關(guān)的環(huán)境，而非熱液成因的硅質(zhì)巖主要形成于遠(yuǎn)洋、大陸邊緣以及大陸架相關(guān)的環(huán)境。從圖2中可以看出，由于受熱液作用的影響，部分形成于島弧環(huán)境的硅質(zhì)巖投點(diǎn)落在遠(yuǎn)洋區(qū)，而部分形成于半深海及開闊海盆環(huán)境的硅質(zhì)巖投點(diǎn)落在圖上的洋脊區(qū)。這種現(xiàn)象表明，(wAl/wAl+Fe)-(wFe/wTi)圖可以用來判別硅質(zhì)巖的成因，而不能用于判別其構(gòu)造背景；而(wAl2O3/wAl2O3+Fe2O3)-(wFe2O3/wTiO2)圖可以用于判別硅質(zhì)巖的成因，卻不能準(zhǔn)確地判別部分硅質(zhì)巖的形成環(huán)境。目前已有不少研究[46-47]開始利用(wAl2O3/wAl2O3+Fe2O3)-(wFe2O3/wTiO2)圖解來判斷硅質(zhì)巖的成因而不是其形成的構(gòu)造背景。上述現(xiàn)象出現(xiàn)的原因主要在于wAl/wAl+Fe值與(wAl2O3+wFe2O3)值以及wFe/wTi值與wFe2O3/wTiO2值本身就存在內(nèi)在的定量關(guān)系。此外，熱液流體可以產(chǎn)生于海底深大斷裂、弧后盆地、洋脊、裂谷、島弧、熱泉等多種環(huán)境，與基性火山巖的噴出有關(guān)[24-25,48]。因此，不能簡單地通過硅質(zhì)巖地球化學(xué)判別圖來分析其形成的構(gòu)造背景，還必須結(jié)合與硅質(zhì)巖伴生的巖石組合的特征綜合分析其形成環(huán)境。

3.2 稀土元素

由于海水中Ce3+容易被氧化為溶度積相對較小的Ce4+，Ce4+被鐵錳氫氧化物、有機(jī)物微?；蚪Y(jié)核吸附，進(jìn)而造成海水中剩余的溶解態(tài)Ce相對的虧損[49-50]。Murray等[34,51]通過對美國弗朗西斯科雜巖中硅質(zhì)巖的研究分析，總結(jié)了形成于不同構(gòu)造環(huán)境硅質(zhì)巖的地球化學(xué)特征。其中，硅質(zhì)巖中的稀土元素質(zhì)量分?jǐn)?shù)(w∑REE)和鈰異常δ(Ce)主要由海水中陸源輸入量、金屬物質(zhì)及埋藏速率控制。在洋脊及附近環(huán)境中，高埋藏速率減少了沉積物在海水中的暴露時(shí)間，進(jìn)而限制了從海水中吸附稀土元素，造成硅質(zhì)巖具有較低的稀土元素含量。在開闊洋盆環(huán)境中，從海水中的吸附作用控制了硅質(zhì)巖的稀土元素特征。由于缺少金屬粒子及陸源物質(zhì)的輸入且具有較低的埋藏速率，形成于開闊洋盆的硅質(zhì)巖常可以從海水中吸附較多的稀土元素。在大陸邊緣環(huán)境中，從海水中吸附以及繼承陸源微粒中的稀土元素均控制了硅質(zhì)巖中的w∑REE，而大陸架附近的高埋藏速率則可能限制了吸附作用所扮演的角色。另外，重結(jié)晶作用也會使硅質(zhì)巖富集稀土元素，因此大陸邊緣硅質(zhì)巖中的w∑REE往往具有一定的不確定性[34, 51]。相對于w∑REE的指示意義，δ(Ce)和(wLa/wCe)N對環(huán)境的指示意義更明顯。其中： 大洋中脊附近的硅質(zhì)巖δ(Ce)值為0.30±0.13，(wLa/wCe)N≥3.5；開闊洋盆的硅質(zhì)巖δ(Ce) 值為0.60±0.11，(wLa/wCe)N=2.0～3.0；大陸邊緣的硅質(zhì)巖δ(Ce) 值為1.09±0.25，(wLa/wCe)N值接近1.0[32, 34, 51]。(wLa/wYb)N對區(qū)分不同構(gòu)造環(huán)境的硅質(zhì)巖也具有重要意義[52-54]。Murray等[52]在大洋鉆探計(jì)劃和深海鉆探計(jì)劃中總結(jié)了不同環(huán)境下硅質(zhì)巖的稀土元素特征(圖3)。其中：形成于開闊洋盆環(huán)境的硅質(zhì)巖，由于主要從海水中吸附REE，其稀土元素常表現(xiàn)為輕稀土虧損以及明顯的鈰負(fù)異常，(wLa/wYb)N為0.8～1，并有超過一半的硅質(zhì)巖樣品的w∑REE<50×10-6；形成于受南極大陸大量陸源物質(zhì)輸入影響的被動大陸邊緣環(huán)境(SHL型)的硅質(zhì)巖，其稀土元素常表現(xiàn)為輕稀土弱富集的特征，并繼承了陸源沉積物的無鈰異常的地球化學(xué)特征，其(wLa/wYb)N為1.2～1.4，w∑REE平均值為113.7×10-6；而形成于有限洋盆環(huán)境 (大西洋型) 的硅質(zhì)巖，其稀土元素特征則處于上述二者之間，表現(xiàn)為輕稀土略分餾以及中等的鈰負(fù)異常。

圖3 深海鉆探計(jì)劃(DSDP)和大洋鉆探計(jì)劃(ODP)硅質(zhì)巖的稀土元素行為控制因素綜合圖Fig.3 Schematic diagram summarizing processes controlling the REE composition of DSDP and ODP cherts(據(jù)文獻(xiàn)[52])

大陸邊緣沉積物如果混入了未分異的火山碎屑則不顯示銪負(fù)異常[39,55]。Taylor等[56]認(rèn)為在后太古代沉積物中負(fù)銪異常的缺失與火山巖序列第一次循環(huán)沉積有密切關(guān)系。值得注意的是，對Murray等[34]發(fā)表的弗朗西斯科雜巖中形成于不同環(huán)境硅質(zhì)巖的數(shù)據(jù)處理發(fā)現(xiàn)，洋脊及兩翼硅質(zhì)巖(wLa/wYb)N=0.74±0.14，開闊洋盆硅質(zhì)巖(wLa/wYb)N=1.30±0.84，而大陸邊緣硅質(zhì)巖(wLa/wYb)N=0.75±0.22。可以看出洋脊和大陸邊緣硅質(zhì)巖(wLa/wYb)值明顯低于SHL型硅質(zhì)巖，也明顯低于河流沉積物的1.85[57]和上地殼平均組成的1.17[56]；而形成于開闊洋盆硅質(zhì)巖的(wLa/wYb)N值變化較大，但明顯高于一般海水的0.5。造成這種結(jié)果的原因可能是由于形成于開闊洋盆的巖層被覆蓋得太多，所分析的數(shù)據(jù)較少(共4個(gè)硅質(zhì)巖樣品)[34]。但是，日本西南部晚二疊世早期-早三疊世早期遠(yuǎn)洋硅質(zhì)巖(n=17)的(wLa/wYb)N=1.00±0.34[1]，也反映了硅質(zhì)巖成巖過程中輕重稀土的分異受多方面因素控制(如硅質(zhì)巖沉積過程中是否選擇性從海水中吸附稀土元素，埋藏速率的快慢與繼承性吸附陸源微粒中稀土元素的主次關(guān)系，成巖后期改造作用的影響等)。

此外，Pirajno等[30]和Kerrich等[58]分別報(bào)告了澳大利亞古元古代裂谷和東非大陸裂谷環(huán)境硅質(zhì)巖的地球化學(xué)特征。其中，澳大利亞古元古代裂谷硅質(zhì)巖(n=10)：δ(Ce)=0.91±0.28，δ(Eu)=0.87～20.65，平均值為6.59，(wLa/wCe)N=1.16±0.36，(wLa/wYb)N=0.46±0.40，w∑REE=15.18×10-6±14.48×10-6；而東非大陸裂谷馬加迪堿性湖的硅質(zhì)巖(n=8)：δ(Ce)=5.23±4.27，δ(Eu)=0.43±0.05，(wLa/wCe)N=0.32±0.19，(wLa/wYb)N=0.55±0.43，w∑REE=(26.54±14.48)×10-6。2種硅質(zhì)巖均形成于伴生有熱泉的淺水堿性鹽湖環(huán)境，均表現(xiàn)為較低的(wLa/wCe)N、(wLa/wYb)N、w∑REE值以及相對開闊洋盆和洋脊環(huán)境硅質(zhì)巖較高的鈰異常值。但是，馬加迪堿性湖的硅質(zhì)巖卻表現(xiàn)出明顯的鈰正異常[δ(Ce)最大值為14.2]，明顯的銪負(fù)異常；而澳大利亞古元古代裂谷環(huán)境硅質(zhì)巖則具有較弱的鈰異常，明顯的銪正異常[僅1個(gè)樣品δ(Eu)=0.87，其他δ(Eu)均大于1.8]，并含重晶石。前者硅質(zhì)巖的形成主要與繼承高堿性流體(其高堿性水環(huán)境pH>10.5)化學(xué)組成有關(guān)[58]，后者則與熱液流體的參與有很大關(guān)系[30]。

3.3 痕量元素

痕量元素中的某些元素含量也可能是判別硅質(zhì)巖成因及沉積-構(gòu)造環(huán)境的指標(biāo)。Girty等[39]、Kato等[13]先后對硅質(zhì)巖中的Th、U、Sc和Cr含量對物源及構(gòu)造環(huán)境的指示意義做了部分研究。其中，形成于大陸邊緣環(huán)境的硅質(zhì)巖具有較高的wTh/wSc值(1左右)以及wTh/wU值(一般大于3.8)；而形成于相對遠(yuǎn)離大陸邊緣環(huán)境的硅質(zhì)巖常具有較低的wTh/wSc值(0.01～0.3)和wTh/wU值(0.6～5.0)[39,59]。李獻(xiàn)華[45]總結(jié)Murray等[34]發(fā)表的形成于不同環(huán)境硅質(zhì)巖的痕量元素特征，發(fā)現(xiàn)洋中脊和大洋盆地硅質(zhì)巖的V含量明顯高于大陸邊緣硅質(zhì)巖，而Y含量則相反，洋中脊和大洋盆地硅質(zhì)巖的wV/wY明顯高于大陸邊緣硅質(zhì)巖。贛東北蛇綠混雜巖帶中硅質(zhì)巖wTi/wV=42～97，wV/wY<2.6，與大陸邊緣硅質(zhì)巖相當(dāng)(wTi/wV≈40，wV/wY≈2.0)，明顯不同于洋中脊硅質(zhì)巖 (wTi/wV≈7，wV/wY≈4.3)和大洋盆地硅質(zhì)巖 (wTi/wV≈25，wV/wY≈5.8)[45]。南天山庫米什銅花山地區(qū)蛇綠混雜巖帶中與泥巖互層產(chǎn)出的紅色硅質(zhì)巖的wTh/wSc=0.56～4.35，其源區(qū)物質(zhì)主要來自未分異巖漿??；而成夾層產(chǎn)于基性熔巖中的綠色硅質(zhì)巖的wTh/wSc=0.57～0.87，反映有洋內(nèi)弧物質(zhì)的加入[59]。目前，一般認(rèn)為V、Cr、Ni、As、Sr、Mo、Ag、Cd、Sb、Ba、U等元素的高富集可能與熱液活動有關(guān)，而Zr、Hf、Ta、Nb、Th等元素的高富集主要與陸源物質(zhì)的輸入有關(guān)[1,60]。但是，由于成巖過程中SiO2的稀釋劑作用，勢必會影響硅質(zhì)巖中部分痕量元素的地球化學(xué)行為，是否可以準(zhǔn)確地利用這些痕量元素含量來判斷硅質(zhì)巖的成因和形成構(gòu)造背景，還有待更多的研究檢驗(yàn)。

3.4 Si同位素

3.5 Sr-Nd同位素

Weis等研究認(rèn)為硅質(zhì)巖Sr、Nd同位素可以用來探討其形成年代[71]以及其同位素比值初始值可以很好地判別其形成的構(gòu)造環(huán)境[72]。Kunimaru等[35]和Shimizu等[44]通過對日本二疊系—三疊系大量硅質(zhì)巖的地球化學(xué)及Sr、Nd同位素的研究，探討了成巖過程中硅質(zhì)巖的均一化問題，進(jìn)一步表明硅質(zhì)巖的Sr、Nd同位素可以用來判別其形成時(shí)代和環(huán)境。其中，受陸源碎屑輸入影響明顯的硅質(zhì)巖有較高的87Sr/86Sr初始比值以及較低的εNd(t)值，而形成于遠(yuǎn)離大陸邊緣環(huán)境的硅質(zhì)巖具有與海水相似的Sr-Nd同位素組成[較低的87Sr/86Sr初始比值以及較高的εNd(t)值][44,72]，與形成于相關(guān)環(huán)境硅質(zhì)巖的主元素和稀土元素判別結(jié)果一致[35,44]。目前，中國有關(guān)硅質(zhì)巖的Sr、Nd同位素的研究應(yīng)用主要體現(xiàn)在同位素年代學(xué)方面[73-75]，僅有少量文獻(xiàn)涉及硅質(zhì)巖的形成環(huán)境[22,76]。

4 成巖作用過程地球化學(xué)行為的討論

其中:各主元素質(zhì)量分?jǐn)?shù)經(jīng)換算后滿足wSiO2+wSiO2*=100%，進(jìn)而可以得到硅質(zhì)巖中各主元素質(zhì)量分?jǐn)?shù)之間的理論趨勢線(圖4)。圖中純硅質(zhì)巖的各主元素質(zhì)量分?jǐn)?shù)為假設(shè)其SiO2質(zhì)量分?jǐn)?shù)為99%后據(jù)前面的公式計(jì)算得到，例如

wAl2O3(純硅質(zhì)巖)=

圖4 加利福利亞弗朗西斯科雜巖中硅質(zhì)巖和頁巖主元素端元混合模型Fig.4 Mixing models of the major elements in chert and shale from the Franciscan Complex(硅質(zhì)巖和頁巖數(shù)據(jù)據(jù)文獻(xiàn)[34])

5 結(jié) 論

利用硅質(zhì)巖元素地球化學(xué)特征研究其成因和構(gòu)造背景時(shí)，需要建立在對硅質(zhì)巖地球化學(xué)行為準(zhǔn)確理解的同時(shí)，考慮硅化作用過程中SiO2稀釋作用的影響，并需要結(jié)合其他巖石成因環(huán)境及古地理環(huán)境綜合考慮，而不能單獨(dú)依靠硅質(zhì)巖的某一項(xiàng)地球化學(xué)指標(biāo)進(jìn)行判別。相對于硅質(zhì)巖的主元素、痕量元素以及稀土元素對其成因及其大地構(gòu)造背景的指示作用的廣泛應(yīng)用，有關(guān)硅質(zhì)巖同位素的研究與應(yīng)用相對較少，隨著研究方法和測試技術(shù)的提高，這些都有待進(jìn)一步的探索。

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Progress and problems in the geochemical study on chert genesis for interpretation of tectonic background

ZHANG Cong1,2, HUANG Hu3, HOU Mingcai3

1.SchoolofEarthScienceandMineralResources,ChinaUniversityofGeosciences,Beijing100083,China; 2.OilandGasSurveyCenterofChinaGeologicalSurvey,Beijing100029,China; 3.InstituteofSedimentaryGeology,ChengduUniversityofTechnology,Chengdu610059,China

Silicolite is often used to discuss its genesis and tectonic setting duo to its immobility during the diagenesis and resistant to erosion. In the paper, the origin and major, trace, rare earth elements, Si and Sr-Nd isotopic compositions of cherts from different depositional environments are summarized. The progress and problems in the research of the origin and tectonic setting of cherts and some factors which caused its original multiple solution interpretation are also discussed. Diagenetic process study indicates that the SiO2acts as a diluent of the major elements and REEs during the depositional processes. As terrigenous materials of TiO2, Al2O3, MgO and K2O, the influence from the diagenetic silicification is weaker than that of Fe2O3, MnO, CaO, Na2O and P2O5. It reveals that the influence from the diagenetic silicification for shale or mudstone is stronger than that for chert, and its REEs are controlled not only by the deposition environments but also by the degree of the diagenetic silicification.

cherts; geochemistry; origin; diagenesis; tectonic setting

10.3969/j.issn.1671-9727.2017.03.03

1671-9727(2017)03-0293-12

2017-02-17。

國家自然科學(xué)基金項(xiàng)目(41502109); 國家“973”計(jì)劃項(xiàng)目(2015CB453000); 中國地質(zhì)調(diào)查項(xiàng)目(DD20160178011)。

張聰(1986-)，女，博士生，研究方向：地球化學(xué), E-mail:zh_cong520@qq.com。

黃虎(1987-)，男，講師，研究方向：沉積地球化學(xué), E-mail:118huanghu@163.com。

P588.244; P595

A