鄂爾多斯盆地東部紫金山巖體特征與形成的動(dòng)力學(xué)環(huán)境
——盆地?zé)崃?巖漿活動(dòng)的深部作用典型實(shí)例剖析

楊興科,晁會(huì)霞,張哲峰,姚衛(wèi)華,董敏

(1.長(zhǎng)安大學(xué)西部礦產(chǎn)資源與地質(zhì)工程教育部重點(diǎn)實(shí)驗(yàn)室,陜西西安710054;2.中國(guó)石油長(zhǎng)慶油田分公司勘探開發(fā)研究院,陜西西安710021)

鄂爾多斯盆地東部紫金山巖體特征與形成的動(dòng)力學(xué)環(huán)境
——盆地?zé)崃?巖漿活動(dòng)的深部作用典型實(shí)例剖析

楊興科1,晁會(huì)霞1,張哲峰1,姚衛(wèi)華2,董敏1

(1.長(zhǎng)安大學(xué)西部礦產(chǎn)資源與地質(zhì)工程教育部重點(diǎn)實(shí)驗(yàn)室,陜西西安710054;2.中國(guó)石油長(zhǎng)慶油田分公司勘探開發(fā)研究院,陜西西安710021)

在鄂爾多斯盆地動(dòng)力學(xué)和熱力作用討論基礎(chǔ)上,以紫金山巖體為代表,進(jìn)行了鄂爾多斯盆地東部巖漿活動(dòng)的深部地質(zhì)背景、巖石學(xué)、地球化學(xué)、同位素年代學(xué)和構(gòu)造演化等研究。認(rèn)為盆地?zé)崃ψ饔檬桥璧貏?dòng)力學(xué)研究的弱點(diǎn)和難點(diǎn),盆地?zé)崃ψ饔镁呙黠@非均一性,熱力盆地特征復(fù)雜、類型多樣,盆地?zé)崃?gòu)造可分為五類。針對(duì)盆地?zé)崃ψ饔醚芯康谋∪跣院推渑c深部圈層活動(dòng)的復(fù)雜性及特殊性,提出了未來研究應(yīng)注意的要點(diǎn)。中生代鄂爾多斯盆地為克拉通內(nèi)改造疊合型盆地,盆地的形成演化和區(qū)域巖石圈深部具有明顯多階段或多世代沉降更替、演變遷移特點(diǎn)。紫金山巖體具有富堿、較富鐵、貧鎂、鈣,SiO2不飽和,屬堿性-過堿性系列;稀土元素含量高,無負(fù)銪異常;堿性巖微量元素構(gòu)造環(huán)境判別屬于大陸板內(nèi)拉張區(qū);巖漿活動(dòng)有多期性;鍶(87Sr/86Sr)、釹(143Nd/144Nd)同位素比值落入EMⅠ型地幔,巖漿物質(zhì)來源較深;單顆粒鋯石SHR IM P測(cè)年數(shù)據(jù)表明巖漿活動(dòng)主期在125～132M a間,為早白堊世。侏羅紀(jì)-白堊紀(jì)盆地東部及周緣存在著豐富的深部巖漿活動(dòng)-熱力作用,并發(fā)生了巖漿侵入或噴發(fā)活動(dòng)。中生代深部背景是處于呂梁軟流圈上涌區(qū),在呂梁軟流圈上涌柱軟塊區(qū)與西側(cè)厚硬塊區(qū)相間的上涌熱浮物質(zhì)聚集處,巖石圈破裂,造成盆地東部出現(xiàn)軟流圈熱浮物質(zhì)底侵和巖石圈局部減薄,底侵物質(zhì)再熔融上侵,形成了紫金山幔源巖漿侵入和火山噴發(fā)構(gòu)成的堿性復(fù)式巖體,代表鄂爾多斯盆地與華北陸塊在早白堊世經(jīng)受過一期重要的熱力構(gòu)造事件,它是該盆地東部呂梁軟流圈上涌、盆地東翼大面積抬升隆起、斷隆帶翹傾的表現(xiàn),此與盆地構(gòu)造動(dòng)力體制轉(zhuǎn)換期及巖漿活動(dòng)-熱事件對(duì)應(yīng)。中生代是該盆地油氣煤鈾等多種能源礦產(chǎn)形成的重要時(shí)期。構(gòu)造過程是:古生代屬于大鄂爾多斯盆地,與華北地區(qū)一同升降;中生代早期(T-J)為連續(xù)沉積區(qū),晚期(J3-K1)發(fā)生較強(qiáng)烈的構(gòu)造轉(zhuǎn)換,巖石圈減薄,地殼拉張伸展變形,伴隨巖漿侵入和火山噴發(fā),形成紫金山復(fù)式巖體;新生代為整體抬升剝蝕期。

盆地動(dòng)力學(xué);熱力作用;巖漿活動(dòng);構(gòu)造熱事件;深部作用;鄂爾多斯盆地;紫金山巖體

1 熱力構(gòu)造的研究現(xiàn)狀和構(gòu)造熱事件特點(diǎn)

1.1 盆地?zé)崃ψ饔檬桥璧貏?dòng)力學(xué)研究的難點(diǎn)

當(dāng)代大陸動(dòng)力學(xué)研究已經(jīng)進(jìn)入到建立東亞大陸中新生代演化的動(dòng)力學(xué)模型及其深部過程階段(鄧晉福等,2003)。大陸沉積盆地因盆地所蘊(yùn)藏豐富的多種礦產(chǎn)資源,在大陸動(dòng)力學(xué)研究中地位重要(劉池洋,2005,2008)。

盆地?zé)崃ψ饔煤蜔崃?gòu)造是盆地動(dòng)力學(xué)研究中的弱點(diǎn)和難點(diǎn)(鄧晉福等,2003;劉池洋,2005,2008;何登發(fā)和李德生,1995;馬宗晉等,2003;楊興科等,2005)。盆地?zé)崃Τ两党梢虻膭?dòng)力來源為中下地殼-地幔或其下,熱力作用為明顯非均一性,熱力盆地特征復(fù)雜、類型多樣(劉池洋,2008)。按巖漿-熱力作用影響深度分為五類(楊興科等,2005):(古)地?zé)岙惓Ｈ杭瘮嗔褞А⒒鹕綗嵋夯顒?dòng)帶(表淺層火山噴發(fā)-熱液活動(dòng)-淺成斑巖侵入型)、熱力背斜(熱穹隆)型、中深層侵入型(含殼內(nèi)熱異常柱型)、地幔熱柱型。

1.2 盆地?zé)崃ψ饔醚芯康谋∪跣院蛷?fù)雜性

盆地巖漿活動(dòng)和熱力作用是近年來研究的熱點(diǎn)之一,經(jīng)資料查詢檢索,以往對(duì)陸內(nèi)構(gòu)造-巖漿活動(dòng)及盆地?zé)崃ψ饔醚芯恐匾暡粔?馬宗晉等,2003;楊興科等,2005;楊興科,2003;劉池洋和孫海山,1999)。對(duì)鄂爾多斯盆地巖漿活動(dòng)-熱力作用研究更是相對(duì)較弱(楊興科等,2005,2006)。

沉積盆地動(dòng)力學(xué)研究說明,大中型沉積盆地的形成、發(fā)展、演化和改造,總體受地球深部系統(tǒng)內(nèi)動(dòng)力地質(zhì)作用的控制(劉池洋,2008),即多種能源礦產(chǎn)盆地的形成發(fā)展、演化和改造的根本原因在于深部作用,尤其是熱力作用。近年來研究揭示許多盆地深部存在大量的熱力作用及相應(yīng)的熱力構(gòu)造(楊興科等,2005;楊興科,2003),使熱力作用研究取得了較大進(jìn)展。

現(xiàn)多認(rèn)為熱力作用是多種能源盆地發(fā)育、發(fā)展及動(dòng)力學(xué)演化的主要改造方式之一,其占有重要位置。全球各構(gòu)造活動(dòng)區(qū)或如大型盆地周緣斷陷區(qū)發(fā)現(xiàn)的低阻高導(dǎo)層,應(yīng)是地殼內(nèi)的構(gòu)造活動(dòng)軟弱帶。多與熱力作用和深部地幔熱流體上升有關(guān),是深部巖漿活動(dòng)、部分熔融水氣流體及高溫塑性物質(zhì)流動(dòng)的會(huì)聚點(diǎn),直接引發(fā)深部巖漿活動(dòng)和熱力作用,引發(fā)淺表層的盆地沉降沉積和熱力-構(gòu)造改造。

近年研究已認(rèn)識(shí)到部分盆地深部熱力作用的相對(duì)活動(dòng)性、強(qiáng)烈性和復(fù)雜性。熱力作用在盆地周緣地表已有眾多表現(xiàn),如盆地周緣地?zé)崽锖偷責(zé)釘嗔褞?、殼下部分熔融層或殼?nèi)熱流體層。加強(qiáng)盆地?zé)崃ψ饔?、熱力?gòu)造及其相關(guān)特征與盆地形成、周緣隆升剝蝕、盆地?zé)崃Ω脑斓妊芯?是大陸動(dòng)力學(xué)研究的一個(gè)重要方面。大陸地殼更為復(fù)雜的多層次變形和熱流體作用下的多方式陸殼結(jié)構(gòu)的循環(huán)轉(zhuǎn)化過程、大陸地殼特殊的熱力構(gòu)造及多旋回演化、殼內(nèi)低速層和地殼熱異常柱的普遍存在、與深部作用相關(guān)的火山-巖漿-熱力構(gòu)造的復(fù)合作用等問題都將迫使我們面對(duì)各區(qū)地質(zhì)構(gòu)造史,在盆地動(dòng)力學(xué)的深化研究中提出相應(yīng)的具體對(duì)策和新思路。

1.3 盆地屬性和構(gòu)造熱事件特點(diǎn)

鄂爾多斯盆地位于華北地塊中西部(圖1),是華北(中朝)地塊內(nèi)印支期和其后的沉積盆地,中生代處于東部伸展和西部擠壓構(gòu)造區(qū)的多期反復(fù)交替影響區(qū),為殘延克拉通內(nèi)盆地(趙重遠(yuǎn),1992)或板內(nèi)復(fù)合克拉通盆地(李思田,1997)或易延疊合型盆地或歸為改造疊合型盆地(劉池洋等,2006),由于中生代該盆地的多期演化和后期改造,造成古生界天然氣和中生界油氣煤鈾聚集成藏定位,構(gòu)成一個(gè)多種能源礦產(chǎn)同盆共存的重要盆地(劉池洋等,2006)。侏羅紀(jì)-白堊紀(jì)的多能源礦產(chǎn)盆地的形成演化過程中至少發(fā)生了4次明顯的構(gòu)造變動(dòng)或劃分為4個(gè)階段(劉池洋等,2006;張泓,2005),也可從盆地的沉降演替和發(fā)育規(guī)模、沉積古地理變更、沉積中心遷移、構(gòu)造熱事件或巖石圈減薄變化、局部點(diǎn)式巖漿活動(dòng)(楊興科等,2005)、周緣斷陷和地震、軟流圈上涌等重要地質(zhì)事件分析判斷其深部構(gòu)造-巖漿活動(dòng)特點(diǎn)或動(dòng)力學(xué)背景。

前人研究已發(fā)現(xiàn)在該盆地的西部、南西部、北部或東部、南東部不同構(gòu)造部位均發(fā)現(xiàn)有規(guī)模不大的燕山期侵入巖或火山巖(楊興科等,2006,2008;趙重遠(yuǎn),1992;劉池洋等,2006;張泓,2005;寧夏回族自治區(qū)地質(zhì)礦產(chǎn)局,1990;山西省地質(zhì)礦產(chǎn)局,1989;楊俊杰,2002;何自新,2003;白斌等,2008;鄒和平等,2008;國(guó)家地震局《鄂爾多斯活動(dòng)斷裂系》課題組,1988)。如該盆地東部晉西撓褶帶中段和南段均出露規(guī)模不大的燕山期侵入巖或火山巖,但卻蘊(yùn)涵著豐富的盆地深部巖漿活動(dòng)-熱力作用的重要信息,有其重要的特殊性,對(duì)其進(jìn)行研究將有助于深化了解該盆地演化和多種能源礦產(chǎn)形成的內(nèi)外動(dòng)力學(xué)聯(lián)系及其重要科學(xué)價(jià)值。隨著近年對(duì)該盆地東緣深部構(gòu)造背景和成礦成藏規(guī)律研究,已認(rèn)識(shí)到該盆地東部及周緣存在著深部巖漿活動(dòng)-熱力作用(楊興科等,2006,2008),因此該盆地部分地段后期改造過程中存在熱力改造,也可劃歸板內(nèi)克拉通盆地的熱力改造-疊合型盆地。

鄂爾多斯盆地中生代尤其是三疊紀(jì)-侏羅紀(jì),盆地分布范圍較廣,許多研究結(jié)論趨向認(rèn)為鄂爾多斯盆地可越過呂梁山、晉中-臨汾斷陷到太行山一帶(趙重遠(yuǎn),1992;李思田,1997;劉池洋等,2006;張泓,2005),且多稱為廣義的大鄂爾多斯盆地(李思田,1997;劉池洋等,2006)。在中生代該盆地東部到太行山一帶淺表部處于總體伸展應(yīng)力場(chǎng)、深部處于總體擠壓應(yīng)力場(chǎng)的構(gòu)造背景區(qū)。這類背景區(qū)容易造成巖石圈局部減薄(羅照華等,2006)和巖漿活動(dòng)-熱力作用。因此,與華北地區(qū)一樣,容易發(fā)生燕山期巖石圈減薄(楊起等,1988;孫少華和李小明,1997;鄭建平,1999;林舸等,2008)或中生代華北克拉通破壞(翟明國(guó),2008)及深部作用相關(guān)的構(gòu)造熱事件(楊興科等,2006,2008)。

圖1 鄂爾多斯盆地和紫金山巖體構(gòu)造位置及相帶劃分圖(據(jù)吳利仁,1966和相關(guān)圖件綜合修編)Fig.1 Tectonic loca tion of the Ordos basin and Zijishan com plex and rock phase subd iv iding of Zijin shan complex(comp rehensively amended byW u,1966 and correlativemaps)

2 盆地東部熱力作用——巖漿活動(dòng)的特征

2.1 盆地東部巖漿活動(dòng)的廣泛性

華北大陸內(nèi)部古生代和三疊紀(jì)相對(duì)比較穩(wěn)定,這種相對(duì)穩(wěn)定的狀態(tài)直到中生代中晚期燕山運(yùn)動(dòng)發(fā)生了顯著的改變,侏羅紀(jì)-白堊紀(jì)期間盆地東部的巖漿活動(dòng)相對(duì)廣泛而強(qiáng)烈,在盆地內(nèi)部和東緣沿?cái)嗔寻l(fā)生多種類型的巖漿侵入(楊起等,1988)。如太原西山煤田西部狐偃山堿性二長(zhǎng)巖體侵入年齡139～125M a,南部清交區(qū)鉆探揭示隱伏花崗閃長(zhǎng)斑巖巖株侵入年齡為105M a(楊起等,1988)。晚侏羅世-早白堊世這期巖漿活動(dòng)代表了鄂爾多斯盆地與華北陸塊在中生代中晚期統(tǒng)一經(jīng)受了一期重要而廣泛的熱力構(gòu)造事件。前人對(duì)呂梁山北側(cè)的鋯石裂變徑跡測(cè)年數(shù)據(jù)所反映的地層抬升冷卻年齡與華北陸塊構(gòu)造熱事件之后的降溫期略晚。采用裂變徑跡結(jié)合熱釋光研究表明鄂爾多斯盆地自晚古生代以來,至少發(fā)生過三次構(gòu)造熱事件或其后的抬升降溫過程,年齡大致為215M a、135M a和72M a(孫少華和李小明,1997)。對(duì)該盆地巖漿-熱力作用的區(qū)域動(dòng)力學(xué)背景,李思田(1997)認(rèn)為可能與中朝地塊側(cè)向擠出構(gòu)造有關(guān),劉池洋等(2006)認(rèn)為與周緣相鄰造山帶(中東亞興蒙構(gòu)造帶、秦嶺-大別構(gòu)造帶、特提斯-青藏構(gòu)造帶等)之間的相互作用,或與古太平洋向今太平洋構(gòu)造動(dòng)力學(xué)體制轉(zhuǎn)換及特提斯構(gòu)造動(dòng)力體制的演變等密切相關(guān)。

2.2 紫金山巖體特征——盆地東部巖漿活動(dòng)的代表

在對(duì)鄂爾多斯盆地東部巖漿巖體進(jìn)行相應(yīng)研究基礎(chǔ)上,依據(jù)主要巖體地質(zhì)地球化學(xué)特征、活動(dòng)期次等,發(fā)現(xiàn)該盆地東部存在一類中深成巖漿侵入及相應(yīng)的熱力構(gòu)造類型。同位素測(cè)年證明主期巖漿活動(dòng)時(shí)代為早白堊世。前人對(duì)該盆地東部巖漿巖已進(jìn)行過部分研究(山西省地質(zhì)礦產(chǎn)局,1989;黃錦江,1991;湯達(dá)禎等,1992;羅照華等,1999;周玲棣等,1996;Y ing etal.,2007;牟保磊等,2001)。早期測(cè)年法精度不高,數(shù)據(jù)較分散,近年來新的測(cè)試方法不斷發(fā)現(xiàn)一些新現(xiàn)象,如近年來相繼進(jìn)行的巖漿巖體鋯石U-Pb SHR IM P和LA-ICPM S及A r-A r測(cè)年,取得了一批同位素測(cè)年數(shù)據(jù)(楊興科等,2006,2008;劉池洋等,2006;肖媛媛等,2007;鄒和平等,2008)和構(gòu)造背景研究的新認(rèn)識(shí)。

紫金山巖體作為該盆地東部巖漿巖體的代表,位于晉西撓褶帶內(nèi)中部,出露在山西省臨縣北西部的紫金山一帶,呈巖筒、巖床狀侵入于中三疊世二馬營(yíng)組(T2er)灰綠色長(zhǎng)石砂巖夾紅色泥巖,多被第四系覆蓋(圖1)。以紫金山北部山神廟梁1767m高程點(diǎn)為中心,呈放射狀、半環(huán)帶狀分布。復(fù)式堿性巖體由外向內(nèi)大致分五個(gè)環(huán)帶(山西省地質(zhì)礦產(chǎn)局,1989)(圖1),可侵入到奧陶系-三疊系(山西省地質(zhì)礦產(chǎn)局,1989;黃錦江,1991),區(qū)域上處于近東西向吳堡隱伏斷裂(F1)和近南北向離石斷裂(F2)交會(huì)處。

2.3 紫金山巖體的巖石學(xué)及巖石化學(xué)特征

對(duì)紫金山巖體挑選3件樣品進(jìn)行多項(xiàng)測(cè)試(楊興科等,2006,2008),采樣位置見圖1,Z1坐標(biāo):東經(jīng)110°52′,北緯38°07′。樣品的化學(xué)成分測(cè)試在中國(guó)科學(xué)院地質(zhì)與地球物理研究所實(shí)驗(yàn)室完成,由XRF1500 X光熒光光譜儀、OES、AAS;微量元素和稀土元素用ICP-MS,經(jīng)國(guó)標(biāo)(GSR-1、2、3)監(jiān)控,誤差小于5%。Sm、Nd、Rb、Sr同位素測(cè)試在該所固體同位素實(shí)驗(yàn)室完成。樣品用HF+HC lO4在Teflon密閉容器中低溫溶解一星期,采用AG50W×8(H+)陽(yáng)離子交換柱和P507萃淋樹脂分離出純凈的Sm和Nd,在VG354質(zhì)譜計(jì)測(cè)量。年齡用Isop lot法計(jì)算,衰變常數(shù)λ147Sm=6.54×10-12a-1(牟保磊等,2001)。

樣品巖石化學(xué)分析結(jié)果投點(diǎn)于TAS圖解定為粗面安山巖、響巖質(zhì)堿玄巖及響巖;火山巖投點(diǎn)定為粗面巖、安粗巖、響巖及似長(zhǎng)巖(楊興科等,2008)。巖石化學(xué)特征是:SiO2不飽和或極不飽和,含量在48.44%～61.81%。根據(jù)堿度率圖解,判別該巖體屬堿性-過堿性系列。具有富堿、較富鐵、貧鎂、鈣等。從A l2O3-SiO2變異圖顯示,為低鋁質(zhì)區(qū),鋁含量稍低。主要巖石類型是:Z1-霓輝正長(zhǎng)巖、Z4-粗面斑巖、Z5-粗面安山巖。

2.4 紫金山巖體地球化學(xué)和巖漿源區(qū)信息特征

本次稀土元素測(cè)試結(jié)果另見文獻(xiàn)(楊興科等,2008)細(xì)述。綜合前人和本次測(cè)試結(jié)果共13件樣品,經(jīng)重新計(jì)算后的REE各參數(shù)特征是:(1)稀土元素總量高,達(dá)45.50～270.20μg/g,是球粒隕石13.70～81.39倍;(2)輕稀土富集,達(dá)41.94～249.92μg/g,是球粒隕石19.75～117.66倍;(3)ΣLREE>ΣHREE,輕重稀土元素比值范圍在3.94～19.69,表明輕重稀土元素發(fā)生了較強(qiáng)烈的分餾,具富集型稀土配分模式;(4)(La/Yb)N達(dá)3.25～55.04,說明曲線具負(fù)斜率,具有略向右傾的分布型式;(5)(La/Sm)N,(Gd/Yb)N值變化大,分別為1.49～12.06和0.42～0.80,表明輕稀土分餾程度和重稀土分餾程度有較大的差別;(6)δEu=0.94～1.27,無明顯負(fù)Eu異常。

堿性巖微量元素測(cè)試結(jié)果見表1。其構(gòu)造環(huán)境判別如Th/Zr-Nb/Zr圖(圖2)表明,該巖體為大陸板內(nèi)拉張環(huán)境,與大陸板內(nèi)地幔巖石圈源區(qū)信息相近。

表1 紫金山堿性巖微量元素測(cè)試結(jié)果及相關(guān)參數(shù)Tab let 1 Trace element results and related parameters of the Zijin shan alka line rock

圖2 紫金山巖體大地構(gòu)造環(huán)境的Th/Zr-Nb/Zr雙對(duì)數(shù)判別圖(底圖據(jù)孫書勤等,2007)Fig.2 Th/Zr and Nb/Zr double logarithmic plot for identification of tectonic settings for the Zijin shan complex

根據(jù)對(duì)該巖體全巖氧同位素分析(閻國(guó)翰等,1988),各期巖石δ18O變化范圍較窄,為7.9‰～9.2‰,平均8.4‰。一般認(rèn)為源于地幔的超鎂鐵質(zhì)巖及基性巖,其氧同位素變化在5.5‰～9.0‰,堿性巖略高(李兆鼐,2003)。即氧同位素δ18O數(shù)據(jù)說明其與地幔巖漿來源的巖石氧同位素?cái)?shù)據(jù)一致。

堿性巖同位素Rb、Sr、Sm、Nd分析結(jié)果見表2。依據(jù)公式:(87Sr/86Sr)0=87Sr/86Sr-87Rb/86Sr(eλt-1),計(jì)算得各樣的鍶同位素初始值(87Sr/86Sr)0為0.70422～0.70512,進(jìn)而計(jì)算得ISr值為0.704528～0.706399。而幔源巖石Sr同位素初始比值范圍為0.702～0.706,可見其落入了幔源范圍;EMⅠ型地幔87Sr/86Sr現(xiàn)代值為0.7050～0.7055(任康緒等,2004),根據(jù)87Sr/86Sr現(xiàn)代值看,多數(shù)落入了EMⅠ型地幔范圍內(nèi)(圖3a)。說明盆地東部紫金山堿性巖體的巖漿源區(qū)為下地殼或具有富集地幔的特點(diǎn)。此與近年來的最新研究認(rèn)識(shí)基本一致(馬宗晉等,2003;楊興科等,2008;楊永恒,2006;胡建勇,2007)。

根據(jù)釤、釹同位素?cái)?shù)據(jù),143Nd/144Nd初始值為0.512457～0.512516,εNd(t)為-5.93～-10.90,顯示富集地幔特點(diǎn)(143Nd/144Nd的現(xiàn)今值為0.512638),接近I型巖漿巖,向EMⅠ型區(qū)靠近(圖3b)。故該巖體物質(zhì)來源較深,源于下地殼或上地幔。

羅照華(1988)研究認(rèn)為中國(guó)東部地幔中占主導(dǎo)的巖石是尖晶石二輝橄欖巖,胡建勇(2007)認(rèn)為紫金山堿性巖體的重稀土元素間分餾不顯著,揭示其源區(qū)可能不存在石榴石而是來自尖晶石地幔,且在二長(zhǎng)巖中發(fā)現(xiàn)尖晶石橄欖巖包體。

表2 紫金山巖體Sm、Nd、Rb、Sr同位素分析結(jié)果Table 2 Com position of Sm,Nd,Rb and Sr isotopes of the Zijin shan complex

圖3 紫金山巖體Sr-Nd同位素和巖漿源區(qū)判別圖Fig.3 Sr-Nd isotope of the Zijinshan complex and discrimination of magma source

2.5 巖體鋯石SHRIMP測(cè)年和巖漿活動(dòng)時(shí)代

在野外調(diào)研、采樣分析基礎(chǔ)上,挑選3件鋯石樣按常規(guī)方法先分選約數(shù)百粒鋯石,在雙目鏡下挑選出晶型完好、具代表性的鋯石顆粒制成樣品靶并拋光,然后進(jìn)行可見光和陰極發(fā)光(CL)照相(楊興科等,2008),再選定待測(cè)年齡的鋯石點(diǎn)位,在北京離子探針中心SHRI MP-Ⅱ上進(jìn)行測(cè)試。在測(cè)定過程中,鋯石樣和與置于同一樣品靶上的澳大利亞地調(diào)局標(biāo)準(zhǔn)鋯石TEM的測(cè)定交替進(jìn)行,每測(cè)定4個(gè)樣品,測(cè)定一次標(biāo)準(zhǔn)鋯石。每次分析記錄7次掃描的平均值。用標(biāo)準(zhǔn)鋯石TEM(417M a)(B lack et al.,2003)進(jìn)行元素間的分餾校正。Pb/U校正公式用Pb/U=A(UO/U)2(C laoue-Long et al.,1995)。應(yīng)用置于調(diào)試靶上的另一標(biāo)準(zhǔn)鋯石SL13(年齡:572 M a;U含量:238μg/g)標(biāo)定鋯石的U,Th和Pb含量。用PRAWN程序(Wiliiams and Buick,1996)進(jìn)行數(shù)據(jù)處理。普通鉛根據(jù)實(shí)測(cè)204Pb校正。所測(cè)Z4和Z5鋯石年齡數(shù)據(jù)經(jīng)重新計(jì)算后列于表3和圖4。

Z4樣分析了10個(gè)點(diǎn),鋯石為長(zhǎng)條形和短柱狀,色深、棱角明顯、環(huán)帶清晰。年齡值在119～139M a間,平均(132.0±2.1)M a(圖4a)(楊興科等,2008),MSWD=1.6。Th/U值在1.297～2.346之間,平均為1.598,具有巖漿鋯石的特點(diǎn)。Z5樣分析了12個(gè)點(diǎn),鋯石為不規(guī)則短柱狀,晶形好,色深。年齡集中于兩個(gè)區(qū)段,有6個(gè)點(diǎn)平均為(125.0±6.7)M a(圖4b),M SWD=0.079;有5個(gè)點(diǎn)平均為(293±17)M a,M SWD=1.7,后者可能為捕獲的鋯石(楊興科等,2008)。Th/U值在0.691～1.738之間,平均為1.186。

統(tǒng)計(jì)表明,粗面斑巖(Z4)和粗面安山巖(Z5)鋯石SHR IM P測(cè)年在(132.0±2.1)M a～(125.0±6.7)M a,相當(dāng)于早白堊世,由淺成侵入或火山噴發(fā)作用形成,代表了呂梁山地區(qū)軟流圈上涌事件,是該盆地東部和呂梁地區(qū)盆山轉(zhuǎn)換的深部巖漿活動(dòng)的顯示,與華北陸塊早白堊世發(fā)生的較普遍的構(gòu)造轉(zhuǎn)換、巖石圈減薄和軟流圈上涌底侵及構(gòu)造熱事件有一致性。其中捕獲有早期293M a或更早的巖漿鋯石。

3 構(gòu)造背景和深部巖漿活動(dòng)——熱力作用過程

3.1 構(gòu)造背景

古生代鄂爾多斯盆地與華北地區(qū)一同整體抬升,前人所稱的大鄂爾多斯盆地(趙重遠(yuǎn),1992;李思田,1997;劉池洋等,2006;張泓,2005),均為巖石圈厚塊區(qū)。三疊紀(jì)-侏羅紀(jì),該盆地東部及呂梁山一帶為連續(xù)沉積區(qū),深部構(gòu)造環(huán)境一致。晚侏羅世-白堊紀(jì),盆地及周緣區(qū)發(fā)生強(qiáng)烈的構(gòu)造轉(zhuǎn)換,盆地周緣區(qū)地層變形較強(qiáng)烈。早白堊世,構(gòu)造應(yīng)力狀態(tài)和地殼變形樣式發(fā)生了重大變化、巖石圈引張伸展和減薄,導(dǎo)致裂陷盆地發(fā)育及巖漿侵入與火山噴發(fā),形成了紫金山巖體等,這是盆地內(nèi)油氣煤鈾等多種能源礦產(chǎn)形成的重要階段。喜馬拉雅期以來,本區(qū)

一直處于整體抬升、剝蝕狀態(tài)。

表3 紫金山巖體鋯石SHRIMPU-Pb年齡Table 3 SHRIMP zircon U-Pb age for the Zijinshan complex

圖4 紫金山巖體鋯石SHRIM PU-Pb年齡圖Fig.4 Concordia diagram of SHRIMP zircon U-Pb age of the Zijnshan complex

3.2 巖石圈減薄與深部作用過程

鄂爾多斯盆地作為一板內(nèi)復(fù)合克拉通盆地,位于華北陸塊中西部(圖1),中生代淺表部處于總體伸展應(yīng)力場(chǎng)、深部處于總體擠壓應(yīng)力場(chǎng)的構(gòu)造背景區(qū)。這類背景區(qū)容易造成巖石圈局部減薄(羅照華等,2006)。

巖石圈減薄的后果是:(1)熱軟流圈取代了被拆沉下去的巖石圈,使上伏地殼快速加熱,產(chǎn)生大范圍巖漿活動(dòng);(2)引起上伏地殼快速抬升;(3)下地殼被快速加熱流變,轉(zhuǎn)換為伸展體制。在盆地周緣斷陷區(qū)的地震層析成像揭示上地?；虻貧?nèi)有大量低速體,這是由于軟流圈上涌并取代巖石圈引起的。

邢集善等(2007)以地震層析分析數(shù)據(jù)為基礎(chǔ),結(jié)合大地電磁測(cè)深和熱流值,對(duì)中國(guó)東部上地幔巖石圈-軟流圈構(gòu)造及其變異進(jìn)行研究,認(rèn)為中生代較大型深部構(gòu)造(如軟流圈上涌體)的地震層析影象可存留至今,中生代軟流圈上涌是相應(yīng)淺表燕山期花崗質(zhì)巖形成的根源,與許多金屬礦集區(qū)密切相關(guān),而新生代軟流圈上涌是大陸裂谷(如汾渭裂谷)、玄武巖噴發(fā)和大型油氣田形成的基礎(chǔ)(邢作云等,2005)。中生代華北陸塊軟流圈柱狀上涌一般可至70km深,在鄂爾多斯盆地為相對(duì)巖石圈厚硬塊區(qū),在該盆地東部和呂梁山區(qū)存在深約75km的呂梁軟流圈上涌柱區(qū)(圖5),中生代其淺表部對(duì)應(yīng)晉中-臨汾斷陷和鄂爾多斯盆地東部先坳后隆的演化歷程。當(dāng)深部熱浮物質(zhì)上涌至巖石圈底界時(shí),遇阻而沿巖石圈之間的相對(duì)薄弱帶側(cè)涌,形成面積型柱頭,柱身則與西側(cè)的鄂爾多斯巖石圈厚區(qū)形成陡接觸帶,由于熱力集中,易使該處巖石圈破裂,熱浮物質(zhì)快速上涌至地殼底部(底侵),再注入淺表形成一套偏堿性侵入雜巖或出現(xiàn)鐵礦區(qū)(邢作云等,2006;鄭建平,1999)。有多種形式和不同程度的軟流圈上涌及巖石圈減薄。因此,在鄂爾多斯盆地東部和呂梁山地區(qū)及晉中-臨汾斷陷的下部發(fā)生了較顯著的巖石圈減薄及軟流圈上涌。以紫金山堿性巖體為代表的復(fù)式巖體應(yīng)是該期軟流圈上涌、熱浮物質(zhì)底侵和巖石圈減薄事件的產(chǎn)物。

圖5 華北大陸地區(qū)中生代38.7°N東西向地震層析成像和深部構(gòu)造綜合研究剖面(據(jù)邢作云等,2006;鄭建平,1999綜合修編)Fig.5 EW trend ing 38.7°N seism ic tom ography and com prehen sive study profile of deep structures of the Nor th Ch ina con tinen t in M esozo ic era(comp rehensively am ended by X ing et al.,2006 and Zheng,1999)

由于巖石圈減薄后,深部巖漿因快速上侵而伴隨快速冷卻,呂梁構(gòu)造帶巖石圈下部物質(zhì)的密度變小使地殼產(chǎn)生均衡調(diào)整,從而出現(xiàn)地殼大面積快速抬升,使原有擠壓能量釋放完畢,此后呂梁構(gòu)造帶進(jìn)入伸展跨塌階段。由于高地勢(shì)的重力能,在地殼上部發(fā)生地殼應(yīng)力狀態(tài)總體由擠壓轉(zhuǎn)為伸展,這種巖石圈整體的伸展則主要與巖石圈減薄(鄭建平,1999)引起的熱地幔上涌導(dǎo)致上部巖石圈加熱相關(guān)(圖5)。

中國(guó)東部巖石圈減薄或華北地區(qū)巖石圈大規(guī)模減薄作用的時(shí)間可能主要在早白堊世(陳根文等,2008;吳福元等,2003),即130M a。這是減薄事件的主要峰期,代表了鄂爾多斯盆地東部與華北地區(qū)一同經(jīng)受了中生代大規(guī)模巖石圈減薄。

3.3 深部巖漿活動(dòng)——熱力作用的地質(zhì)意義

前人對(duì)該盆地東部及東鄰區(qū)沁水盆地晚侏羅世-早白堊世古地溫梯度和古大地?zé)崃髦颠M(jìn)行測(cè)定,確定在中生代晚期存在一期強(qiáng)烈的構(gòu)造熱事件。沁水盆地內(nèi)巖體同位素年齡和其周邊地區(qū)巖漿活動(dòng)年齡表明這次構(gòu)造熱事件發(fā)生在晚侏羅世至早白堊世(任戰(zhàn)利,1997;任戰(zhàn)利等,1999)。

紫金山位于鄂爾多斯硬塊東側(cè)與呂梁軟塊陡接觸帶,其深部構(gòu)造呈現(xiàn)軟流圈上涌柱(軟塊)與巖石圈厚區(qū)(硬塊)相間的格局。上涌之熱浮物質(zhì)聚集處,巖石圈破裂,熱浮物質(zhì)(熱流體)便沿此破裂處上涌并底侵下地殼,然后再熔融上侵,在淺部形成一套堿性巖體(邢作云等,2006),從而形成紫金山幔源型巖體(圖5)。表明鄂爾多斯盆地東部具有發(fā)生深部巖漿活動(dòng)和熱力作用的條件。

已有研究表明,在早白堊世發(fā)生過一次強(qiáng)烈的構(gòu)造熱事件,盆地東部出現(xiàn)了幔源巖漿侵入和火山噴發(fā),即形成紫金山巖體。在鄂爾多斯北部杭錦旗黑石頭溝下白堊統(tǒng)砂巖之上發(fā)現(xiàn)的玄武巖層,經(jīng)A r-A r測(cè)年為(126.2±0.4)M a(鄒和平等,2008);而東北部同期有張家口組流紋巖噴發(fā)(126±1M a)(楊進(jìn)輝等,2006),這些均是華北巖石圈強(qiáng)烈減薄和部分殼幔物質(zhì)混合的結(jié)果。早白堊世盆地東部出現(xiàn)的深源巖漿侵入這一構(gòu)造-熱事件應(yīng)是該盆地東部呂梁軟流圈上涌、盆地東翼大面積抬升隆起、斷隆帶翹傾的表現(xiàn)。說明當(dāng)時(shí)的盆地東部存在有特殊的區(qū)域深部熱力構(gòu)造事件發(fā)生的背景條件。

4 結(jié)論與討論

(1)盆地?zé)崃ψ饔檬桥璧貏?dòng)力學(xué)研究的弱點(diǎn)和難點(diǎn),有重要意義,熱力作用研究具有薄弱性、復(fù)雜性、特殊性,研究應(yīng)注重要點(diǎn)。

(2)鄂爾多斯盆地構(gòu)造位置特殊,中生代盆地東部巖漿活動(dòng)-熱力作用較特殊,為小規(guī)模的復(fù)式堿性巖體,深部活動(dòng)信息豐富。

(3)紫金山堿性巖體是鄂爾多斯盆地東部巖漿活動(dòng)的代表,富堿,低鋁,稀土元素總量較高,輕稀土富集,無明顯負(fù)銪異常。87Sr/86Sr、143Nd/144Nd比值落入EMⅠ型地幔,巖漿來源較深。堿性巖微量元素構(gòu)造環(huán)境判別屬于大陸板內(nèi)拉張區(qū)。

(4)單顆粒鋯石SHR IM P測(cè)年厘定紫金山巖體晚期巖漿活動(dòng)主要在125～132M a,屬早白堊世。

(5)盆地東部早白堊世中深成巖漿侵入型-噴出型熱事件,代表了呂梁山區(qū)軟流圈上涌事件,是盆地東部盆山轉(zhuǎn)換的深部顯示,與華北陸塊早白堊世巖石圈減薄熱事件具有一致性。

(6)構(gòu)造背景和演變過程是:古生代為大鄂爾多斯盆地與華北地區(qū)一同升降;中生代為連續(xù)沉積區(qū);中生代晚期(J3-K1)發(fā)生較強(qiáng)烈的構(gòu)造轉(zhuǎn)換,巖石圈減薄,地殼拉張伸展,隨巖漿侵入和火山噴發(fā),深部出現(xiàn)有呂梁軟流圈上涌柱,熱浮物質(zhì)上涌至鄂爾多斯巖石圈厚區(qū)的陡接觸帶,發(fā)生底侵和再熔融上侵,形成紫金山堿性復(fù)式巖體;其與深部軟流圈上涌、盆地東部先坳后隆、周鄰礦集區(qū)和油氣煤鈾多能源礦產(chǎn)的形成階段對(duì)應(yīng)。

中國(guó)沉積盆地因其區(qū)域構(gòu)造位置特殊,盆地?zé)崃ψ饔玫谋憩F(xiàn)方式極為復(fù)雜和特殊,常難以直接查明,故多有被忽略之勢(shì)。故對(duì)盆地?zé)崃ψ饔醚芯繎?yīng)注意要點(diǎn):(1)由于熱力作用的復(fù)雜性和特殊性,應(yīng)不斷完善盆地?zé)崃ψ饔醚芯績(jī)?nèi)容和體系;(2)需要結(jié)合當(dāng)代地球系統(tǒng)科學(xué)進(jìn)行盆地多種地質(zhì)-地球物理-地球化學(xué)等綜合研究,確認(rèn)盆地深部是否存在熱力作用;(3)盆地深部常出現(xiàn)地殼結(jié)構(gòu)的不均一,不但淺表部,而且深部均存在此類結(jié)構(gòu)不均一現(xiàn)象,即盆地深部結(jié)構(gòu)為各向異性。盆地各向異性,表現(xiàn)出相當(dāng)特殊的深部熱力作用。由于盆地經(jīng)歷過一定程度的構(gòu)造應(yīng)力和熱力改造作用,多造成盆地原貌與現(xiàn)今面貌差別較大,對(duì)其中油氣和多種能源礦產(chǎn)評(píng)價(jià)影響較大。經(jīng)常會(huì)增加油氣勘探的復(fù)雜性。應(yīng)注意地質(zhì)與地球物理和地球化學(xué)綜合研究,將地表、中淺層與深層構(gòu)造和熱力作用的各類跡象緊密結(jié)合。

致謝:感謝劉池陽(yáng)教授在盆地?zé)崃ψ饔梅治龊?73項(xiàng)目研究中的指導(dǎo)和幫助、以及對(duì)本文的詳細(xì)審閱并提出建議性修改意見,使本文的論證組織更加嚴(yán)密和邏輯化。同時(shí)感謝邢集善教授級(jí)高工在華北和山西深部構(gòu)造特征研究資料的提供和有益討論、李有柱教授在巖石學(xué)和地球化學(xué)方面的撰文修改幫助,鄭孟林博士、楊明慧副教授、楊永恒、陳虹碩士在野外采樣和室內(nèi)樣品加工測(cè)試中的幫助!

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Ying J F,Zhang H F,Sun M,Tang Y J,Zhou Xinhua and Liu X M.2007.Petrology and geochemistry of Zijinshan alkaline instrusive complex in Shanxi Province,western North China Craton:Implication for magmamixing of different sources in an extensional regime.Lithos,98(1-4):45-66.

Abstract:In the study of tectonic kinetics of basins,thermal process and thermal structure are the weakness and difficulty.In recent years,according to the influencing depth of magma-therm alaction,there are five types of thermal tectonic units:(ancient)geothermal anomaly gathered fault zone,volcanic hydrothermal active zone(volcanic eruption of shallow layer-hydrothermal action-hypabyssal porphyry intrusion),thermaldome,intermediate-deep intrusion(including intercrustal thermal anomaly plume)and mantle thermalplume.

The Ordos basin is not only one of the basin in which oil fields were found earliest,it is also the second biggest petrolifer ous basin.It is located in the middle-west of the north China b lock,which is in the binding dom =ain of east and west tectonic regions influenced by multistage repeated extension and compressions,and it is a composite craton basin form ed by over lapping of multi-stage andmulti-system structures on the basisof the originalO rdos basin,belongs to interior intracrat on basin.In the eastern Ordosbasin,more attention was paid in the past to study earth-quake and magma activity on the basin margin such as the Fen(river)-Wei(river)rift in the southeast margin part of the basin.In the eastern part of the basin,westpart of the Shanxi flexural fold belt is a large monoc line stratum,which is sloping from east to west.There are a series of open and flat meridional,latitudinal extending sub-folds and a nearly east-westward fracture named the Wubu Fracture(F1)which developed w ell.In the east of study area,there isa fracture named the Lishi Fracture(F2)in south and north direction.Most folds and fractures belong to semi concealed style.Along with the study of tectonic background,mineralization and petroleum accumulation in the basin,we have recognized that there exists point type of thermal process from deep sourced magma in the eastern basin and its periphery.

By field investigation,sample analysis,SHRIMP age determination and implication for magma source,and according to the characteristics of geology and geochemistry,the stage and sequence of magmatic activity and latest SHRIMP chronology were discussed,which led to a suggestion that there would have been a type of middle-deep sourced magma intruding in the eastern partof the basin,China.The main period of a magma thermal process by SHRIMP chronology is early Cretaceous,and then the magma activity sequence can be determined.The acquisition of geochemical and dating data has an important significance to analyze the tectonic evolution and its background of the study area.

Based on the discussion of the dynamic process and thermodynamic effect of the Ordos basin,as rep resented by the Zijinshan complex,the magma activity in the eastern part of the O rdosbasin with the respect of deep geological background,petrology,geochemistry,isotopic dating and tectonic evolution is studied.The research holds the view that the thermodynamic process is weakness and difficulty in the light of study on tectonic kinetics of basins.The thermodynamic process of the basin is evidently inhomogenous and the characteristics of the thermal basin are complicated and diverse.The basin thermal structure can be summarized into 5 categories.Aiming at weak researches of thermodynamic process and complication and specialty with deep lithosphere activity,them a in points needing attention for future research are put forward.In the Mesozoic,the Ordos basin belonged to intracratonic reform ed superposition basin.The development and evolution of the basin as well as the deep of regional lithosphere have the obvious characteristics of multi-stage or multi-generation settlement alteration,evolution and migration.The Zijinshan complex is rich in alkali,relatively rich in iron,poor in magnesium and calcium and unsaturated in SiO2,belonging to an alkaline-peralkaline series.The complex has high content of rare earth elem en ts,without negative Euabnormal.Tectonic setting discrimination of trace elements of the alkaline rock belongs to an extension area of the continental intraplate.The magmatic intrusion has many stages.The rate of87Sr/86Sr and143Nd/144Nd are fallen into the range of EMⅠ lithospheric mantle,which show s that the igneous material com es from a deeper source.The SHRIMP chronology of single-grain zircon show s that the main stage o fmagmatic activity is in 125～132Ma,is equal to early Cretaceous.In the Jurassic-Cretaceous,a large amount of deep magma activity and thermodynamic process took p lace in the eastern basin and its periphery,along with mag a intrusion and eruption.The deep background of the region in the Mesozoic was the upwelling area of Lüliang asthenosphere.The lithosphere broke in the spot where the interphase between the Lüliang asthenosphere soft block and western masshard block,in which the thermal up welling material aggregated.A s the result,there occurred intrusion of thermal material of asthenosphere and partly lithospheric thinning and then the underplating materials melted and intruded upward,form ed the alkali composite body,which is composed of the Zijinshanm antle-source magma intrusion and volcanoeruption.The complex rep resents that in early C retaceous Ordos basin and the No rth China p late experienced a stage of significant therm al structural events,w hich is the rep resentative of the Lüliang asthenosphere up welling in eastern basin,large-scale up liftelevation and tilting of a fault-up liftzone in the east limb of the basin.These features are consistent with the transition of tectonic and dynamic regime and magma activity-thermalevent.The Mesozoic is the significant period in which multi-energy resource mineral deposits(oil-gas-coal-uranium,etc)of the basin w ere form ed.

Itwas comparatively steady in the Paleozoic and Triassic inside the North China b lock and such state of steadychanged obviously at Yanshanian Movement in middle-late Mesozoic.Magmatic activity was relatively strong in the period of the Jurassic-Cretaceous,and accordingly many kinds of magmas intruded through faults inside the basin and in its east margin.

This stage of deep magmatic activity from late Jurassic to early Cretaceous rep resented that there experienced one significant and extensive tectonic thermal event in the Ordos basin associated with the North China b lock in middle-late Mesozoic.The tectonic thermal event experienced tectonic inversion in early Cretaceous(135～125M a),in them idd le-later stage of basin evolution,and the time of initial up welling of the basin is correspond to that of tectonic inversion and coincides with the tectonic thermal even t in North China.

The Zijinshan area is located in the steeply contact belt between the east of the Ordos lump and Lüliang soft b lock.In the deep,up welling plume of asthnosphere(softb lock)and thickening area of lithosphere(hard b lock)was in interval location.In the point of hot up welling materials assembled,the lithosphere broke,the hot liquid up welled and basal eroded the lower crustalong the fracture,then liquation,form ed a set of alkaline and alkali complex,so that form ed the Zijinshanm antle-derived comp lex.

The research show s that from late Jurassic to early Cretaceous,there happened a stage of strong tectonic events in the North China block in which the Ordosbasin was located.Therefore,magma intrusion orvolcaniceruption activity happened in the Mesozoic in the east part of the basin and the area of the Taihang Mountains,led to form the Zijinshan comp lex.Inside the basin,there existed point deep-sourced intrusive rocks in the range of cover.A ll these show that the setting of the regional thermal process was special at that time,and that there existed definite setting conditions of the regional thermal process in the depth of the basin.The thermal process of this stage gave rise to upwelling of the Lüliang b lock dome,tilting of fault-up lift zone and large-scale up lift elevation of the east limb of the basin.

The sequence of tectonic evolution of magmatic-thermalactivity in the study area is listed as follow s:Firstly,in the Early Paleozoic,the area along with the North China b lock was up lifted in mass which indicated by absence of late Ordovician-early Carboniferous sediment.Secondly,the deep magma intruded and monzonite and aegirine-augite syenite formed in the study area.In the further east of the basin around the Taihang Mountains,there existed amagmatic intrusion process in the dep th.According to SHRIMP chronology we find that the magmatic zircons were well developed in 343M a and 287～293M a,which imp lies that a series of magma thermal events happened at that time.Thirdly,from the Triassic to Jurassic,east part of the basin and around the Lüliang Mountains was in the section of continuously sedimentary sequence.Finally,the Yanshanian tectonic activity w as very intense in the basin and its neighborhood with violent deformation in the strata,and intense structuralactivity manly occurred in latter Jurassic.In Cretaceous period,tectonic stress and crust deformation pattern in North China had been greatly changed:the main structure activity is the tension of the lithosphere with weak comp ression,and the lithosphere became thinning and thinning violently,while the crust endured extensional deformation.Then the riftbasin and riftvalley developed well,along with widespread magmatism and volcanism:141～154M a,125～132M a.In the study area,there formed trachyte porphyry,trachyandesite,trachytic volcanic breccia and phonolitic volcanic breccia,partly malignite and nepheline syenite and so on.Them agmatic pluton formed in the period is the primary type in the surface and shallow well in the basin margin now a days and also is the concentrating section of numerous dating data.From Himalayan period late-recentperiod,this area was in the state of up lift in mass and denudation atall times.

The main tectonic processesare:In Paleozoic Era,the basin originated from the great O rdosbasin,ascending and descending along with the North China region accordingly.In early M esozoic(T-J),the basinwas in the section of continuously sedimentary sequence.Duringlate Mesozoic(J3-K1),drastic tectonic transformation occurred,lithosphere became thinner,mantle stretched and deform ed,accompanied by magma intrusion and volcano eruption,then Zijinshan complex was form ed.In Neozoic Era,the whole basin experienced up lift and erosion.

Keyword s:basin dynamics;thermodynamic process;magma activity;thermal structuralevent;deep process;Ordos basin;Zijinshan complex

Character is tics of the Zijinshan complex and Its Dynamic Environment in the East of theO rdos Basin—Analysis of a Classic Example on the Deep Processes of Thermal-Magma Activity in the Basin

YANG Xingke1,CHAO Hu ix ia1,ZHANG Zhefeng1,YAO Weihua2and DONGM in1
(1.MOE Key Laboratory of Western Mineralization Resources and Geologica l Engineering,Chang′an University,X i′an 710054,Shaanxi,China;2.Changqing Oilfield Company of PetroChina,X i′an 710021,Shaanxi,China)

P542;P313;P314;P 611.1

A

1001-1552(2010)02-0269-13

2009-07-26;改回日期:2009-12-01

國(guó)家973項(xiàng)目(編號(hào):2003CB214601)資助。

楊興科(1961-),男,教授,博士生導(dǎo)師,礦產(chǎn)普查與勘探專業(yè),研究方向:構(gòu)造地質(zhì)與礦產(chǎn)及盆地分析。