凌瀟瀟 李秋立, 2** 劉宇, 2 唐國強(qiáng), 2 李嬌

1. 中國科學(xué)院地質(zhì)與地球物理研究所，巖石圈演化國家重點(diǎn)實驗室，北京 1000292. 中國科學(xué)院大學(xué)地球與行星科學(xué)學(xué)院，北京 100049

在地質(zhì)年代學(xué)的研究對象中，鋯石(ZrSiO4)以其富U貧Pb、分布廣泛、物理化學(xué)性質(zhì)穩(wěn)定、能記錄多種元素和同位素信息等特點(diǎn)而占有非常重要的地位。一些經(jīng)歷了復(fù)雜地質(zhì)事件的鋯石往往具有多期生長的內(nèi)部結(jié)構(gòu)，記錄了相應(yīng)巖石的多期演化歷史(陳道公等, 2001; 吳元保和鄭永飛, 2004)。具有高空間分辨率的離子探針(Secondary Ion Mass Spectrometry，SIMS)一般被認(rèn)作對復(fù)雜變質(zhì)鋯石進(jìn)行微區(qū)原位的微量元素、U-Pb年齡、氧同位素、鋰同位素和硅同位素等分析的首選工具，被廣泛應(yīng)用在各種地質(zhì)過程的研究中(吳福元等, 2007; Lietal., 2010b; 李秋立等, 2013; 楊亞楠等, 2014; Gaoetal., 2015; Liuetal., 2018)。

為利用多種元素和同位素體系聯(lián)合表征地質(zhì)現(xiàn)象，研究者希望能對同一鋯石顆粒，甚至在同一微區(qū)內(nèi)用最簡化的樣品前處理方法、在盡可能小的分析區(qū)域內(nèi)得到多種同位素的高精度數(shù)據(jù)(李獻(xiàn)華等, 2013; Schmitt and Vazquez, 2017)。例如，為獲得鋯石同一微區(qū)U-Pb年齡和氧同位素信息，選擇在一個分析點(diǎn)上測試氧同位素分析，不進(jìn)行樣品處理而繼續(xù)進(jìn)行U-Pb年齡測試；再比如在一顆變質(zhì)鋯石上，既測試樣品的核部，又測試樣品的邊部(Compstonetal., 1984)；更有個別樣品，適宜鋯石顆粒非常少，為了檢驗測試結(jié)果的可重復(fù)性，在一個顆粒的同一測點(diǎn)附近反復(fù)多次測試。以上所描述的這些測試情形均是常見現(xiàn)象，但是否存在干擾或存在多大程度的干擾目前尚沒有定量化論證。

由于二次離子復(fù)雜且不明確的發(fā)射機(jī)理，在使用離子探針分析測試的過程中，不同的測試條件都可能帶來測量的系統(tǒng)偏差。為了檢驗上述測試情況下分析結(jié)果的準(zhǔn)確性，本文采用目前最為均一的鋯石標(biāo)樣M257作為測試對象，通過模擬不同測試條件，來檢驗測量結(jié)果是否與標(biāo)準(zhǔn)值之間存在變化，以期能為研究者采用離子探針技術(shù)進(jìn)行鋯石分析時，在測點(diǎn)選擇和后期結(jié)果評價中起到參考作用。

1 鋯石樣品特征

鋯石標(biāo)準(zhǔn)物質(zhì)M257取自一顆已經(jīng)切割拋磨，重約5g左右的寶石級鋯石顆粒，破碎消耗了約1.5g進(jìn)行了大量元素含量、多種方法定年及多種同位素組成的均一性檢驗，目前已經(jīng)成為廣泛使用的鋯石U-Th-Pb元素含量、U-Pb年齡、氧同位素和鋰同位素標(biāo)準(zhǔn)物質(zhì)(Nasdalaetal., 2008; Lietal., 2011b)。鋯石M257的206Pb/238U比值推薦值為0.09100±0.00003(2σ)，207Pb/235U比值推薦值為0.7392±0.0003(2σ)，對應(yīng)206Pb/238U年齡的推薦值是561.3±0.3Ma(95%置信概率)，U含量推薦值為840×10-6，Th/U比值為0.27(Nasdalaetal., 2008; Lietal., 2011b)。

2 分析方法

將20個約300μm的M257鋯石顆粒按照傳統(tǒng)的雙面膠粘貼制靶方式制備成環(huán)氧樹脂靶，拋光至平整后清洗烘干，鍍約20nm厚純金，達(dá)到表面電阻<20歐姆水平(Lietal., 2009, 2010a)。

圖1 鋯石M257上用離子探針U-Pb年齡測試后的預(yù)剝蝕區(qū)域與測點(diǎn)的反射光圖其中虛線長方形標(biāo)示預(yù)剝蝕區(qū)域，實線橢圓標(biāo)示測點(diǎn)位置，朝向鋯石表面的箭頭方向指示一次離子束入射方向，離開鋯石表面的箭頭方向指示二次離子濺出方向. (a) M257@n指示第n次測試的測點(diǎn)位置，M257@nP是在M257@n位置上的重復(fù)測試；(b) M257@n指示第n次測試的測點(diǎn)位置，M257-afterO@n指示之前測試過氧同位素的測點(diǎn)位置上再測試年齡的位置；(c) M257@n指示第n次測試的測點(diǎn)位置，D、UP、L、R分別代表在第n個測點(diǎn)的下、上、左、右，M257@n(D, UP, L, R)預(yù)剝蝕區(qū)域與M257@n有重合的地方，如虛線長方形所示，測點(diǎn)不重合，如橢圓形所示；(d) M257@n指示第n次測點(diǎn)位置，n60L是在第n個測點(diǎn)左側(cè)60μm，兩個相鄰的預(yù)剝蝕區(qū)域間距15μmFig.1 The optical images of the M257 Zircon with the analysis craters in the center of the pre-sputter areas (polished epoxy mount, reflected light)

本研究共設(shè)計了四組實驗，第一組和第二組實驗均為測點(diǎn)的位置(X,Y)坐標(biāo)不發(fā)生改變，而剝蝕深度發(fā)生變化，即在同一個測點(diǎn)位置分析兩次。第三組和第四組實驗測點(diǎn)的(X, Y)坐標(biāo)發(fā)生改變，即在臨近的區(qū)域內(nèi)進(jìn)行多次分析。為了檢驗測試結(jié)果的重復(fù)性，參考國家計量技術(shù)規(guī)范要求，本實驗在相同儀器，相同測試條件下，短時間內(nèi)，重復(fù)測量次數(shù)都選為10次。

第一組實驗是模擬實際測試中，在一個顆粒的同一測點(diǎn)上反復(fù)多次測試的情況。在這組實驗中采用的一次離子束束斑為15μm×10μm，因此所對應(yīng)的預(yù)剝蝕區(qū)域是一個45μm×40μm的矩形。對靶A643中坐標(biāo)為(X, Y)的M257鋯石顆粒分析一次，第n個測點(diǎn)標(biāo)記為M257@n。然后在同一(X, Y)坐標(biāo)再分析一次，第n個測點(diǎn)的第二次分析結(jié)果標(biāo)記為M257@nP。依此類推，在10個顆粒上做10次重復(fù)實驗，共計10個測點(diǎn)，20次年齡分析結(jié)果。與標(biāo)記為M257@n的測點(diǎn)相比較，標(biāo)記為M257@nP的測點(diǎn)的測試位置(X, Y)不變，但剝蝕深度更深，其反射光圖如圖1a所示。

第二組實驗是模擬實際測試中，在一個位置先測試氧同位素，不進(jìn)行樣品處理直接再測試U-Pb年齡的情況。在這組實驗中采用的一次離子束束斑為30μm×20μm，因此所對應(yīng)的預(yù)剝蝕區(qū)是一個60μm×50μm的矩形。本實驗先對靶A643中M257的不同顆粒進(jìn)行了10次氧同位素測試，然后在測試過氧同位素的位置再測試U-Pb年齡，第n個測點(diǎn)標(biāo)記為M257-afterO@n，并在測試過程中間隔著測試未經(jīng)過氧同位素分析的M257顆粒，標(biāo)記為M257@n。依此類推，做10次重復(fù)實驗，共計20個測點(diǎn)，20次年齡分析結(jié)果。與標(biāo)記為M257@n的測點(diǎn)相比較，標(biāo)記為M257-afterO@n的測點(diǎn)的剝蝕深度更深，其反射光圖如圖1b所示。為避免干擾，任何一個標(biāo)記為M257@n的測點(diǎn)或M257-afterO@n的測點(diǎn)之間的間距在100μm以上。

第三組實驗?zāi)M實際測試中對具有復(fù)雜結(jié)構(gòu)，比如有核(幔)邊的鋯石，依次在核(幔)邊區(qū)域進(jìn)行測試的情況。在這組實驗中采用的一次離子束束斑為30μm×20μm，因此所對應(yīng)的預(yù)剝蝕區(qū)是一個60μm×50μm的矩形。在10個M257顆粒上約120μm×100μm的區(qū)域內(nèi)分別共做了5次實驗分析。一個分析區(qū)域的第一次(首次)測點(diǎn)位置為(X, Y)，標(biāo)記為M257@n，第二次測點(diǎn)位置為(X, Y-20)，標(biāo)記為M257@nD，第三次測點(diǎn)為(X, Y+20)，標(biāo)記為M257@nUP，第四次測點(diǎn)位置為(X-30, Y)，標(biāo)記為M257@nL，第五次測點(diǎn)位置為(X+30, Y)，標(biāo)記為M257@nR。以上實驗是依次按照首個測點(diǎn)下、上、左、右的順序類推，在5個區(qū)域內(nèi)做重復(fù)實驗，共計25個測點(diǎn)，25次年齡分析結(jié)果。然后改變測點(diǎn)的選擇順序，按照首個測點(diǎn)左、右、下、上順序在另外5個區(qū)域內(nèi)做重復(fù)實驗，共計25個測點(diǎn)，25次年齡分析結(jié)果。與標(biāo)記為M257@n的測點(diǎn)相比較，標(biāo)記為M257@n(D, UP, L, R)測點(diǎn)的剝蝕深度相同，但預(yù)剝蝕區(qū)域有重合，其反射光圖如圖1c所示。

因已確認(rèn)預(yù)剝蝕區(qū)域發(fā)生重疊存在影響，第四組實驗是在第三組實驗的基礎(chǔ)上，為找到安全測試距離而設(shè)計。在這組實驗中采用的一次離子束束斑為15μm×10μm，因此所對應(yīng)的預(yù)剝蝕區(qū)是一個45μm×40μm的矩形。同理，首個測點(diǎn)標(biāo)記為M257@n，然后在位置為(X-60, Y)的區(qū)域測試，標(biāo)記為M257@n-60L。依此類推，做10次重復(fù)實驗，共計20個測點(diǎn)，20次年齡分析結(jié)果。與標(biāo)記為M257@n的測點(diǎn)相比較，標(biāo)記為M257@n-60L的測點(diǎn)相鄰預(yù)剝蝕區(qū)域間隔為15μm，剝蝕深度相同，但預(yù)剝蝕區(qū)域不重合。其反射光圖如圖1d所示。

圖2 同一測點(diǎn)多次離子探針U-Pb年齡分析的206Pb/238U和207Pb/206Pb年齡結(jié)果圖2中的紅色線表示M257@n(即在鋯石顆粒上首次分析)的結(jié)果，藍(lán)色線表示M257@nP(即在已完成U-Pb年齡分析的鋯石顆粒上再次分析)的結(jié)果. 其中圖2a和圖2b為206Pb/238U年齡結(jié)果，圖2c為207Pb/206Pb年齡平均值. 圖2d可見M257@n的諧和年齡為560±5Ma，M257@nP的所有分析點(diǎn)的206Pb/238U年齡和207Pb/206Pb年齡在誤差范圍內(nèi)不一致Fig.2 Comparison of the 206Pb/238U ages and 207Pb/206Pb ages of zircon determined by SIMS twice on the same spot

3 分析結(jié)果

3.1 同一區(qū)域多次分析

3.1.1 同一測點(diǎn)多次U-Pb年齡分析

圖3 同一測點(diǎn)先氧同位素再U-Pb年齡分析的206Pb/238U和207Pb/206Pb年齡結(jié)果圖3中的紅色線表示M257@n(即在鋯石顆粒上首次分析)的結(jié)果，藍(lán)色線表示M257-afterO@n(即在已完成O同位素分析的鋯石顆粒上再次分析)的結(jié)果. 其中圖3a和圖3b為206Pb/238U年齡結(jié)果，圖3c為207Pb/206Pb年齡平均值. 圖3d顯示M257@n和M257-afterO@n的諧和年齡圖Fig.3 The 206Pb/238U ages and 207Pb/206Pb ages of zircon determined by SIMS in the same pit with previous O isotopes measurement

3.1.2 同一測點(diǎn)先氧同位素再年齡分析

3.2 相鄰區(qū)域分析

3.2.1 相鄰有重疊分析

第三組模擬實驗的結(jié)果顯示，如果預(yù)剝蝕區(qū)域有部分重疊，其U-Pb年齡也發(fā)生變化。而且預(yù)剝蝕區(qū)域重疊的位置和范圍不同，即測點(diǎn)的位置和測試順序不同，對年齡的影響程度不一樣。

圖4 有部分預(yù)剝蝕區(qū)域重疊的U-Pb年齡分析的206Pb/238U和207Pb/206Pb年齡結(jié)果圖中紅色線表示M257@n(即在鋯石顆粒上首次分析)的結(jié)果，綠色線表示M257@nD(即在已完成首次分析的鋯石顆粒下方再次分析)的結(jié)果，黑色線表示M257@nUP(即在已完成首次分析的鋯石顆粒上方再次分析)的結(jié)果，藍(lán)色線表示M257@nL(即在已完成首次分析的鋯石顆粒左方再次分析)的結(jié)果，紫色線表示M257@nR(即在已完成首次分析的鋯石顆粒右方再次分析)的結(jié)果. 其中圖4a-d中分別是依次按照首個測點(diǎn)、下、上、左、右的順序類推，在5個區(qū)域內(nèi)做重復(fù)實驗的年齡分析結(jié)果，圖4a和圖4b為上述五次實驗的206Pb/238U年齡結(jié)果，圖4c為上述五次實驗的207Pb/206Pb年齡平均值，圖4d中顯示為上述五次實驗的的諧和年齡圖. 其中圖4e-h中分別是按照首個測點(diǎn)、左、右、下、上順序在5個區(qū)域內(nèi)做重復(fù)實驗的年齡分析結(jié)果，圖4e和圖4f為上述五次實驗的的206Pb/238U年齡結(jié)果，圖4g為上述五次實驗的的207Pb/206Pb年齡平均值，圖5h中顯示為上述五次實驗的年齡諧和圖Fig.4 The 206Pb/238U ages and 207Pb/206Pb ages of zircon determined by SIMS on the up/down/left/right region relative to the first measured position with overlapped pre-sputter area successively

圖5 預(yù)剝蝕區(qū)域不重疊的U-Pb年齡分析的206Pb/238U和207Pb/206Pb年齡結(jié)果圖中紅色線表示M257@n(即在鋯石顆粒上首次分析)的結(jié)果，藍(lán)色線表示M257@n-60L(即在已完成首次分析的鋯石顆粒X坐標(biāo)減小60μm處再次分析)的結(jié)果. 其中圖5a和圖5b為206Pb/238U年齡結(jié)果，圖5c為207Pb/206Pb年齡平均值，圖5d中顯示標(biāo)記為M257@n和標(biāo)記為M257@n-60L的諧和年齡圖Fig.5 The 206Pb/238U ages and 207Pb/206Pb ages of zircon determined by SIMS on the same zircon grain with visible distance

表1 測點(diǎn)相對位置對鋯石M257的離子探針U-Pb定年結(jié)果的影響

Table 1 The effect of relative measured position on zircon M257 SIMS U-Pb dating

測點(diǎn)的相對位置和分析順序206Pb/238U年齡表觀值(Ma, 2SE)206Pb/238U年齡與推薦值之間的偏差比同一測點(diǎn)多次U-Pb定年535±5Ma(n=10, MSWD=0.3)-5%同一測點(diǎn)先氧同位素再U-Pb定年552±5Ma(n=10, MSWD=0.1)-1.6%有部分預(yù)剝蝕區(qū)域重疊U-Pb定年下555±7Ma(n=5, MSWD=0.1)-1.1%上567±6Ma(n=5, MSWD=0.1)1.1%左624±8Ma(n=5, MSWD=0.1)11%右549±6Ma(n=5, MSWD=0.2)-2.2%有部分預(yù)剝蝕區(qū)域重疊U-Pb定年左590±7Ma(n=5, MSWD=0.2)5.1%右550±7Ma(n=5, MSWD=0.1)-2%下573±7Ma(n=5, MSWD=0.1)2.1%上578±7Ma(n=5, MSWD=0.1)3%預(yù)剝蝕區(qū)域不重疊U-Pb定年561±5Ma(n=10, MSWD=0.3)

3.2.2 相鄰無重疊分析

4 討論

4.1 測點(diǎn)相互影響因素探討

離子探針通過聚焦的一次離子束轟擊樣品表面而產(chǎn)生樣品信息的二次離子，通過樣品表面加以高壓使得二次離子加速并提取到后面的質(zhì)譜部分，二次離子產(chǎn)生的過程被稱為離子濺射?？梢姡坞x子的產(chǎn)生涉及多種因素，包括樣品本身情況和樣品表面高壓分布情況。Andersen and Hinthorne (1973)基于一種通過局部熱平衡(Local thermal equilibrium)理論，認(rèn)為多種礦物乃至玻璃樣品在離子濺射過程中某種元素形成的離子、原子、電子、分子碎片存在某種平衡，其相對比例關(guān)系很大程度上決定于轟擊點(diǎn)的表面溫度和電子密度。Hinthorneetal. (1979)認(rèn)為樣品的UO+/U+一定程度上可以反映樣品表面溫度，從而提出Pb+/U+比值與UO+/U+存在相關(guān)性，且理論上推導(dǎo)出Pb+/U+較樣品實際Pb/U比值大約高2倍左右。從現(xiàn)有數(shù)據(jù)來看，對于離子探針鋯石U-Pb分析，這個理論和實際觀察都相對比較吻合，但對于其它礦物的情況則會出現(xiàn)非常大的出入(Lietal., 2010a, b, 2011a, 2012, 2013; Lingetal., 2015, 2016)。如在沒有樣品表面吹氧情況下，斜鋯石Pb+/U+較實際值要低，而在CAMECA IMS儀器樣品表面吹氧情況下，Pb+/U+會較實際比值高近7倍(Lietal., 2010a)。離子探針金紅石U-Pb分析中Pb+/U+比值變化范圍極大，可從7倍到200倍(Lietal., 2011a)?？梢娺@種局部熱平衡理論對離子濺射的解釋尚存在較大不確定性。另外一種理論提出一次離子對樣品中結(jié)合鍵的破壞(bond-breaking)導(dǎo)致二次離子的產(chǎn)出(Schroeeretal., 1973)，因此不同元素二次離子的產(chǎn)率與被轟擊區(qū)域內(nèi)該元素的結(jié)合鍵能相關(guān)。Chaussidonetal. (2017)展示了對玻璃和輝石混合區(qū)域經(jīng)過一次離子轟擊后的情形，可見一次離子對樣品的剝蝕具有一定的選擇性，結(jié)合能較弱的玻璃成分被剝蝕得較多，而結(jié)合能強(qiáng)的輝石則被剝蝕地相對少。

對比本實驗中觀察到的現(xiàn)象，無論是在經(jīng)過銫源轟擊的氧同位素分析點(diǎn)還是氧源轟擊的U-Pb分析后的點(diǎn)上的再次測試，都呈現(xiàn)出二次離子的產(chǎn)率增加的現(xiàn)象，而氧源轟擊后的再次轟擊所呈現(xiàn)出的二次離子產(chǎn)率增加現(xiàn)象更為顯著。從樣品形態(tài)上講，第二次原位的轟擊會加大測點(diǎn)的深度，而從銫源轟擊和氧源轟擊后所呈現(xiàn)的二次離子產(chǎn)率增加率的顯著不同暗示深度的增加不是增加二次離子產(chǎn)率的主要因素。以往研究發(fā)現(xiàn)，在離子探針中，被高能一次離子束轟擊的樣品表面會產(chǎn)生有5～10nm的一次離子的注入(Schmitt and Vazquez, 2017)。正是這種高能一次離子的注入，類似于衰變過程中高能粒子的造成的轟擊使得樣品的晶格發(fā)生一定程度的損傷，元素的結(jié)合能減弱，從而導(dǎo)致在同一測點(diǎn)上進(jìn)行第二次分析時，二次離子更容易被激發(fā)。氧源之所以在眾多氣體源嘗試后被選為適宜的一次離子源，與其造成金屬離子的產(chǎn)率的增加有直接的關(guān)系。

4.2 對SIMS U-Pb定年測試的選點(diǎn)建議

鋯石U-Pb體系定年是發(fā)展歷史最早、應(yīng)用最廣的定年方法之一。從U-Pb體系理論出發(fā)，所謂諧和的U-Pb年齡意味著207Pb/206Pb年齡與206Pb/238U年齡具有一致性。207Pb/206Pb年齡的計算僅涉及Pb同位素比值的測試，在離子探針質(zhì)譜分析中由于原子量較大，涉及的質(zhì)量分餾一般小于0.3%(Sternetal., 2009; Lietal., 2009, 2010a)。從本研究中不同情況下離子探針測試鋯石M257的207Pb/206Pb年齡的結(jié)果可以看出，不同選點(diǎn)情況下的207Pb/206Pb年齡變化范圍很小(557～565Ma)，在誤差范圍內(nèi)一致，具有很好的重現(xiàn)性。這表明不同選點(diǎn)情況下并不會造成Pb同位素的顯著分餾，其變化在離子探針分析中基本可以忽略。因此可以認(rèn)為選點(diǎn)位置的變化對207Pb/206Pb年齡結(jié)果沒有明顯影響。測點(diǎn)的位置和測試順序不同，會造成206Pb/238U結(jié)果發(fā)生-5% 到 11%的偏差，導(dǎo)致本是諧和的U-Pb體系表現(xiàn)為不同程度的不諧和，其結(jié)果可能會帶來錯誤的解釋。比如在本研究的第一組和第二組實驗中，對原測點(diǎn)的再次分析，校正后的樣品年齡在諧和圖上會表現(xiàn)為207Pb/206Pb年齡大于206Pb/238U年齡，可能會被解釋為Pb丟失。而在本研究的第三組實驗中，在原測點(diǎn)左側(cè)(一次離子入射方向的后方)的分析出現(xiàn)Pb/U表觀年齡較大幅度增加現(xiàn)象，對于本是諧和的樣品會表現(xiàn)為207Pb/206Pb年齡小于206Pb/238U年齡的反諧和現(xiàn)象，而對于本已發(fā)生少量Pb丟失的樣品則可能出現(xiàn)諧和的假象。

實際研究中會出現(xiàn)在一個顆粒上設(shè)置多個測點(diǎn)的需求，如變質(zhì)鋯石上對核部和邊部的分析、對樣品量少而珍貴的天體樣品中可定年礦物的重復(fù)分析等。已有天體樣品鋯石U-Pb數(shù)據(jù)報道中，經(jīng)常出現(xiàn)Pb-Pb年齡較為一致，而U-Pb年齡變化范圍較大的現(xiàn)象(Misawaetal., 2005; Zhouetal., 2013)，這與在一個顆粒上反復(fù)多次測試不無關(guān)系。雖然對于這種年齡古老的天體樣品多采用Pb-Pb年齡，多次測試的結(jié)果對其認(rèn)識并不造成大的影響，但對于年輕變質(zhì)巖的分析會有較大不同。年輕樣品Pb-Pb年齡的精度較差，因此多采用U-Pb年齡，測點(diǎn)選擇的影響人為地造成增大變質(zhì)階段年齡范圍的認(rèn)識。在變質(zhì)鋯石上依次測試樣品的核部和邊部，需要仔細(xì)檢查樣品的顆粒，需要兩個測點(diǎn)的預(yù)剝蝕區(qū)域之間有15μm以上的間隔，結(jié)果才會沒有影響。在不得已需要在預(yù)剝蝕區(qū)域有重合的同一顆粒多次分析的情況下，需注意將重要信息的位置設(shè)置為首個測點(diǎn)，同時必須避免第二個測點(diǎn)選擇位于前一個測點(diǎn)一次離子入射方向后側(cè)的情形。

為了同時獲得一個鋯石樣品的U-Pb同位素和氧同位素信息，選擇在一個分析點(diǎn)上做完氧同位素分析，不進(jìn)行樣品處理接著做U-Pb年齡分析，得到的U-Pb年齡可能偏小1.6%左右。對于粒度較大(比如大于100μm的顆粒)，建議重新拋光后鍍金再進(jìn)行年齡測試。對于小顆粒樣品，由于擔(dān)心多次打磨拋光可能造成樣品顆粒的丟失，因此做完氧同位素測試后直接做U-Pb年齡測試的顆粒，需要在結(jié)果的不確定度評定中增加系統(tǒng)誤差的比例。選擇進(jìn)行過氧同位素分析的標(biāo)樣進(jìn)行U-Pb分餾的校正，一定程度上可以抵消該誤差，這需要研究者在測試中注意標(biāo)樣測點(diǎn)的選擇。

5 結(jié)論

離子探針鋯石U-Pb定年工作已經(jīng)有近40年歷史，涉及儀器和樣品等多方面的影響因素也進(jìn)行過許多探討，而大多數(shù)工作均采用互不影響的多點(diǎn)測試來總結(jié)規(guī)律，而實際工作中所遇到的情況則復(fù)雜得多。本工作模擬了多種實際工作中可能遇到的鋯石U-Pb定年中測點(diǎn)的選擇情況，結(jié)果顯示，測點(diǎn)重合乃至預(yù)剝蝕區(qū)域有少量重疊的兩個測點(diǎn)，其第二個測點(diǎn)的Pb和U離子產(chǎn)率和Pb/U分餾情況都會受到不同程度的影響。相對一個顆粒上的首個測點(diǎn)，第二個測點(diǎn)的測試深度和預(yù)剝蝕區(qū)域的變化會給測試結(jié)果帶來-5%到+11%的系統(tǒng)偏差，尤以與首個測點(diǎn)的預(yù)剝蝕區(qū)域有重疊且位于一次離子入射方向后側(cè)的分析點(diǎn)會產(chǎn)生最為顯著的系統(tǒng)偏差。因此，在采用離子探針進(jìn)行副礦物U-Pb測試的時候，當(dāng)需要原位重復(fù)分析或在臨近區(qū)域多點(diǎn)分析時，需要特別注意多個測點(diǎn)的相對位置和分析順序。

致謝 許文良教授、吳春明教授、吳元保教授和胡兆初教授對本文提出了許多建設(shè)性意見和建議，在此一并致謝。

附表1a 同一測點(diǎn)多次離子探針U-Pb年齡分析的原始計數(shù)值

Appendix Table 1a The raw data of zircon determined by SIMS twice on the same spot

測點(diǎn)號測量相對順序PB(nA)90Zr216O+204Pb+206Pb+207Pb+208Pb+238U+232Th16O+2238U16O+2206Pb+238U+238U16O+2238U+PositionX(μm)Y(μm)M257@119423830.175304456343325211506944770.2262.8-54891666M257@239402580.272724306133339311270917790.2182.7-42531026M257@358.7407050.173074336073310511312930830.2212.8-26341608M257@478.7411100.273184316103225411073917420.2272.8-18101487M257@598.7415340.274064376193232611347925510.2292.9-11611575M257@6118.7402840.171974246183263211173910250.2212.8-52591355M257@7138.840983070994195973202311041901700.2222.84661263M257@8158.9435750.177624576573453911840976980.2252.814171555M257@9179.1431960.177094576453460111916974770.2232.819251436M257@10199427830.175604476443390311724958030.2232.824841394Average 8.9416810.174164386253320311420935800.2232.8M257@1P29528880.1976658082844653152901286980.2192.9-54891666M257@2P48.9509450.1956056278644672149381247650.2142.8-42531026M257@3P68.7518710.1984658184244512153871295300.2212.9-26341608M257@4P88.7517290.1957256378843347148281258380.2212.9-18101487M257@5P108.7518830964156881243283150681264750.2232.9-11611575M257@6P128.8518250.1965256381044103151191254820.2192.8-52591355M257@7P148.8512350.1933054778042781146671226590.2182.94661263M257@8P169.1561300.11041861485946839162341372460.2222.914171555M257@9P189.1542430.11011159186046337159501334920.2182.919251436M257@10P2095409001001959783945476158171320400.222.924841394Average 8.9526840.1979257782044600153301286220.222.9Deviation(%) 26.4 3231.631.334.334.237.4-1.72.3

附表1b 同一測點(diǎn)先氧同位素再U-Pb年齡分析的原始計數(shù)值

Appendix Table 1b The raw data of zircon determined by SIMS in the same pit with previous O isotopes measurement

測點(diǎn)號測量相對順序PB(nA)90Zr216O+204Pb+206Pb+207Pb+208Pb+238U+232Th16O+2238U16O+2206Pb+238U+238U16O+2238U+PositionX(μm)Y(μm)M257@1117.5425020.11073063989227606138301315420.3894.837881271M257@1237.54247601095563991127758140401316480.3954.739971163M257@1357.5427650.11080462990727813142421336330.3884.846181178M257@1477.5411910.21044661986627096137321284050.3864.7-54903069M257@1597.54130601064262687727215137601288930.3914.7-52472939M257@16117.54156901060362587927036137111292450.3924.8-41802924M257@17137.5411990.11031461486826840135211263040.3844.7-34252773M257@18157.5419800.11073563490327566141221313290.3894.8-33723119M257@19177.54098301040861587426976138511272790.3864.7-25922944M257@20197.5416530.11061463289627234140331301110.394.8-16042968Average 7.5417621062562788727314138841298390.3894.8M257-afterO@1127.5454190.11150668296330325156131425030.3794.722181211M257-afterO@1247.54584201170468997830414155691451920.3854.830741196M257-afterO@1367.54262701088264492828405144691356550.3834.836881271M257-afterO@1487.5433650.11095364891228398144721357480.3864.838801208M257-afterO@15107.54462901153267997029413152971431720.3924.945061234M257-afterO@16127.54533301152567396729572151531416740.394.846181078M257-afterO@17147.5426560.11093764190428307145191359640.3864.8-54902969M257-afterO@18167.5433200.11111666093528477148051376410.394.8-52473039M257-afterO@19187.54256701097465191927976143691353750.3924.8-45202942M257-afterO@20207.5443690.11159968298329427151811425040.3944.8-41803024Average 7.544013 1127366594629071149451395430.3884.8Deviation(%)5.4 6.166.66.47.67.5-0.31

附表1c 不同測點(diǎn)但有部分預(yù)剝蝕區(qū)域重疊的U-Pb年齡分析的原始計數(shù)值

Appendix Table 1c The raw data of zircon determined by SIMS on the up/down/left/right region relative to the first measured position with overlapped pre-sputter area successively

測點(diǎn)號測量相對順序PB(nA)90Zr216O+204Pb+206Pb+207Pb+208Pb+238U+232Th16O+2238U16O+2206Pb+238U+238U16O+2238U+PositionX(μm)Y(μm)M257@117570180.113650804111336101185541600390.3784.4-46921135M257@267564490.113549798112435345182941583420.3834.5-32021298M257@3117.157266013544800109735916181701574990.3774.4-19221395M257@4167.256233013042763107334959178751525930.3734.4-13391438M257@5217.358092014007821118937325192811638320.3754.4-4921464Average 57012 13558797111935929184351584610.3774.4M257@1-D27561430.113264777109135506182311563410.3744.4-46921115M257@2-D77567970.113432794111135656184661590050.3774.5-32021278M257@3-D127.1579290.113286786109935816182891574490.3714.4-19221375M257@4-D177.2584060.113392787110436359187721589990.3684.4-13391418M257@5-D227.359161013988827117338159197581660370.3674.4-4921444Average 57687 13472794111636299187031595660.3714.4 Deviation(%) 1.2 -0.6-0.4-0.311.50.7-1.6-0.3M257@1-UP37381590.1822048267128919127321023610.2843.5-46921155M257@2-UP87.1404430880152372229572134341084670.2983.7-32021318M257@3-UP137.2407730.1871451772829822132821077040.2923.6-19221415M257@4-UP187.2417700.1882951975030057136231091670.2943.6-13391458M257@5-UP237.3417860.1907353475631508141661125100.2883.6-4921484Average 40586 872751572629976134471080420.2913.6 Deviation(%) -28.8 -35.6-35.4-35.1-16.6-27.1-31.8-22.8-18.3 M257@1-L474597401137666794831927142471234510.3563.9-47221135M257@2-L97.14716601142667494632272143811251210.3543.9-32321298M257@3-L147.2474330.11112565992331987140101225120.3483.8-19521395M257@4-L197.34775401117165893732361143631229540.3453.8-13691438M257@5-L247.34820901154967996433842149471272520.3413.8-5221464Average 47307 1132966894432478143891242580.3493.8 Deviation(%) -17 -16.4-16.2-15.6-9.6-21.9-21.6-7.5-13.2 M257@1-R57456680.1874251173834407150851146030.2543.3-46621135M257@2-R107.1466270.1891752673932946151611162790.2713.5-31721298M257@3-R157.2480400912253575135419154551193670.2583.4-18921395M257@4-R207.3480880895952574635624155521178150.2513.3-13091438M257@5-R257.3484490917954277937140161901213540.2473.3-4621464Average 47374 898452875135107154881178840.2563.4 Deviation(%) -16.9 -33.7-33.8-32.9-2.3-16-25.6-32.1-23.8 M257@11266.9549920.113083771108334176174391520150.3834.437401874M257@12316.9540030.112852754109433049171591489700.3894.544991721M257@13366.853310012782751106533036170021484280.3874.5-56662570M257@14416.7530540.112985765108433184173341499630.3914.5-46082460M257@15466.752168012369725102431991166161440300.3874.5-35772457Average 53505 12814753107033087171101486810.3874.5 M257@11-L276.9534540.112936760107434047164221440490.384.237101874M257@12-L326.9542780.112921760106934564167951456960.3744.244691721M257@13-L376.8527670.112729747105733062161421429190.3854.3-56962570M257@14-L426.7524490.112898756105933180164521444260.3894.4-46382460M257@15-L476.751309012472732102332071158311395480.3894.4-36072457Average 52851 12791751105633385163281433280.3834.3 Deviation(%) -1.2 -0.2-0.3-1.30.9-4.6-3.6-1-4.4 M257@11-R286.9528760.11140267491534273168031398840.3334.137701874

續(xù)附表1c

Continued Appendix Table 1c

測點(diǎn)號測量相對順序PB(nA)90Zr216O+204Pb+206Pb+207Pb+208Pb+238U+232Th16O+2238U16O+2206Pb+238U+238U16O+2238U+PositionX(μm)Y(μm)M257@12-R336.8510560.11109865491532576162481349930.3414.145291721M257@13-R386.8510270.11097565190533072163101350350.3324.1-56362570M257@14-R436.75013901094364491633082163641344640.3314.1-45782460M257@15-R486.74989501074263089932170159241317030.3344.1-35472457Average 50999 1103265191033035163301352160.3344.1 Deviation(%) -4.7 -13.9-13.5-15-0.2-4.6-9.1-13.8-8.9 M257@11-D296.9548840.11184469496737030171691414930.323.837401854M257@12-D346.85494901173369097036552171471404120.3213.844991701M257@13-D396.8533090.11133566494435952166991368980.3153.8-56662550M257@14-D446.7530940.11143967594836392169731381170.3143.8-46082440M257@15-D496.75334801138667393835145165981367010.3243.9-35772437Average 53917 1154767995336214169171387240.3193.8Deviation(%) 0.8 -9.9-9.8-10.99.5-1.1-6.7-17.7-14.8M257@11-UP306.935830072084265962854611643908460.2533.237401894M257@12-UP356.834128066723945562750311025851670.2433.144991741M257@13-UP406.834198067773985642745211148863840.2473.1-56662590M257@14-UP456.733999068474005652756811163868430.2483.2-46082480M257@15-UP506.733423066083875382625210800841200.2523.2-35772477Average 34315 68234015642746411156866720.2483.2Deviation(%) -35.9 -46.8-46.7-47.3-17-34.8-41.7-35.9-29.8

附表1d 不同測點(diǎn)且預(yù)剝蝕區(qū)域不重疊的U-Pb年齡分析的原始計數(shù)值

Appendix Table 1d The raw data of zircon determined by SIMS on the same zircon grain with visible distance

測點(diǎn)號測量相對順序PB(nA)90Zr216O+204Pb+206Pb+207Pb+208Pb+238U+232Th16O+2238U16O+2206Pb+238U+238U16O+2238U+PositionX(μm)Y(μm)M257@1119430770.175684526393404811719963530.2222.831831410M257@1239436080.175204476103352911428950930.2242.839511432M257@1358.9418470.172984295963289411271924690.2222.849131285M257@1478.9412760.172654296153263611185918590.2232.8-50912997M257@1598.9415050.172564266033292211182918050.222.8-40962938M257@16118.7411140.172904306163250611290917680.2242.8-31963196M257@17138.7401480.170604175903197010896889850.2212.8-23482982M257@18158.9421370.275474466333382111742951050.2232.8-13902947M257@19179420130.175364416283375611548948390.2232.8-32871595M257@20198.9406370.172694326183297911246918620.222.8-40411355Average 8.941736 73614356153310611351930140.22.8 M257@11-60L29426240.175484456343398311780963040.2222.831231410M257@12-60L48.942946075394476273329511493953330.2262.938911432M257@13-60L68.9417760.173654336113254011325927690.2262.948531285M257@14-60L88.9406670.171934256083260311032904930.2212.8-51512997M257@15-60L108.8403300.171174215843206510901894460.2222.8-41562938M257@16-60L128.7408230.172524316163203611255913660.2262.9-32563196M257@17-60L148.7400470.170174176003177610956890220.2212.8-24082982M257@18-60L169.1417560.174584366273341811633934690.2232.8-14502947M257@19-60L188.9416050.274784436373314511367940160.2262.8-33471595M257@20-60L208.9407020.173364336233283711381925030.2232.8-41011355Average 8.941328 73304336173277011312924720.2242.8 Deviation(%) 1 0.40.4-0.310.30.60.60.4

附表2a 同一測點(diǎn)多次離子探針U-Pb年齡分析的定年結(jié)果

Appendix Table 2a The result of zircon determined by SIMS twice on the same spot

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sM257@118342260.270.030.741.70.0911.50.0590.6562.613.7562.27.2562.18.2M257@238532340.270.040.7421.70.0921.50.0590.7558.414.4563.77.35658.3M257@358562320.270.010.7461.70.0911.50.0590.857217.9565.87.5564.38.2M257@478352250.270.050.7351.70.0911.50.0590.7550.115.1559.67.1561.98.1M257@598342280.270.040.7391.80.0911.50.0591556.721561.67.8562.88.1M257@6118452310.270.020.7361.60.0911.50.0590.555511.65607561.28.2M257@7138232250.2700.7341.70.091.50.0590.8566.218.35597.5557.38.2M257@8158392270.270.020.7361.60.0911.50.0590.6556.413560.175618.1M257@9178442300.270.030.7381.80.0911.50.0590.9569.420561.27.6559.28.1M257@10198382290.270.040.7331.60.091.50.0590.5561.111.4558.36.9557.78Average 560.8 561.2 561.2 RSD (%) 1.2 0.4 0.5M257@1P29122420.260.010.7051.60.0861.50.0590.4578.39.7542.16.6533.57.7M257@2P49182450.270.010.7121.60.0881.50.0590.5554.911.7546.16.85447.9M257@3P69362480.260.020.6991.60.0861.50.0590.5562.710.7538.46.6532.67.7M257@4P89122390.260.010.6981.60.0861.50.0590.5556.89.9537.86.6533.47.7M257@5P109132430.270.010.71.60.0861.50.0590.5560.411.8538.66.7533.47.7M257@6P129072440.270.010.7051.70.0881.50.0580.8538.716.7541.97.1542.67.9M257@7P148972390.270.010.6991.60.0871.50.0590.554910.2538.26.7535.77.8M257@8P169162420.260.020.6991.70.0861.60.0590.655812.5538.47.1533.88.2M257@9P189222460.270.020.6931.60.0861.50.0580.5542.19.8534.36.6532.57.7M257@10P209152440.2700.7071.60.0861.50.060.4587.29.4542.76.6532.27.7Average 558.8 539.8 535.4 RSD (%)2.7 0.6 0.8Deviation(%)-0.5 -4 -5

附表2b 同一測點(diǎn)先氧同位素再U-Pb年齡分析的定年結(jié)果

Appendix Table 2b The result of zircon determined by SIMS in the same pit with previous O isotopes measurement

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sM257@1118352210.270.020.7411.60.091.50.0590.6582.213.3563.17.1558.48.1M257@1238362250.2700.7431.70.0921.70.0580.5540.711.8564.27.5570.19M257@1358372250.270.020.7281.60.0911.50.0580.4534.29.5555.56.9560.78.3M257@1478472290.270.030.7351.70.091.60.0590.556611.2559.47.2557.78.5M257@1598422270.270.010.741.90.0911.80.0590.6559.913.4562.48.3563.19.7M257@16118462260.2700.7391.70.0911.50.0590.7565.415561.97.35618.2M257@17138322250.270.010.7461.70.0911.70.0590.5584.410.8565.97.5561.38.9M257@18158442290.270.020.7361.70.0911.60.0590.6563.212.3560.27.1559.58.3M257@19178382300.270.010.7411.60.0911.60.0590.4567.79.4562.77.1561.58.5M257@20198432290.270.010.7421.70.091.60.0590.4584.19.3563.37.2558.28.5Average 564.8 561.9 561.1RSD (%) 3 0.5 0.6 M257-afterO@1128472340.280.010.7341.70.091.50.0590.7573.515.4558.97.3555.48.2M257-afterO@1248552310.2700.7251.70.0891.50.0590.656113553.87.15528.1

續(xù)附表2b

Continued Appendix Table 2b

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sM257-afterO@1368582310.270.010.7251.70.0891.60.0590.4572.99.1553.77.1549.18.5M257-afterO@1488512290.270.020.7271.70.0891.60.0590.5566.9105557.3552.18.7M257-afterO@15108662330.2700.7191.60.0891.50.0590.4560.48.9550.36.8547.88.1M257-afterO@16128432280.2700.7251.70.091.60.0580.5543.810.7553.67.35568.6M257-afterO@17148602320.270.020.7181.60.0891.50.0590.45499.3549.56.7549.67.9M257-afterO@18168582330.270.010.7291.70.0891.60.0590.6577.312.9555.77.5550.58.6M257-afterO@19188582300.2700.7311.60.0891.50.0590.6578.312.4557.46.9552.38M257-afterO@20208622320.270.010.7261.80.091.60.0590.855716.4554.17.6553.48.5Average 564 554.2 551.8RSD (%) 2.1 0.5 0.5Deviation(%) 0.5 -1.2 -1.6

附表2c 不同測點(diǎn)但有部分預(yù)剝蝕區(qū)域重疊的U-Pb年齡分析的定年結(jié)果

Appendix Table 2c The result of zircon determined by SIMS on the up/down/left/right region relative to the first measured position with overlapped pre-sputter area successively

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sM257@118482280.270.010.7371.50.0911.50.0590.4560.78.3560.46.7560.38.1M257@268472270.270.020.7341.60.091.50.0590.4559.39.6558.66.7558.58M257@3118312220.2700.7461.50.0921.50.0590.4569.28.2565.96.7565.18.1M257@4168202230.2700.7351.60.0911.50.0580.4547.68.5559.76.7562.78.1M257@5218502320.2700.7351.60.0911.50.0590.5550.811.9559.76.9561.88.1Average 557.5 560.9 561.7 RSD (%) 1.5 0.5 0.4 M257@1-D28412280.270.020.7271.60.091.50.0580.5545.210.1554.76.75578M257@2-D78462280.270.020.7281.50.0891.50.0590.4566.68.3555.26.6552.47.9M257@3-D128212210.270.010.7321.60.091.50.0590.5571.511.9557.86.9554.58M257@4-D178232260.270.010.7271.60.091.50.0590.5556.111.4554.86.8554.48M257@5-D228462340.2800.7341.60.091.50.0590.4572.18558.86.7555.58Average 562.3 556.3 554.8 RSD (%) 2.1 0.3 0.3Deviation(%) 0.2 -0.8 -1.1M257@1-UP38102340.290.010.7431.60.0921.50.0590.5550.810.7564.16.9567.48.2M257@2-UP88102330.290.010.7521.60.0921.50.0590.6580.113.7569.27.2566.58.2M257@3-UP137982280.290.010.7521.60.0921.50.0590.5576.810.3569.66.9567.88.2M257@4-UP187892290.290.010.7441.60.0921.50.0590.7555.914.1564.57.1566.68.2M257@5-UP238132380.290.020.7451.60.0921.50.0590.6554.712.3565.47568.18.2Average 563.7 566.6 567.3 RSD (%) 2.4 0.5 0.1 Deviation(%) 0.5 1 1.1 M257@1-L48112170.2700.8261.60.1021.50.0590.4553.49611.67.2627.49M257@2-L98012140.2700.8251.60.1011.50.0590.5566.811.7610.97.3622.98.9M257@3-L147802070.270.010.8261.60.1011.50.0590.4572.59.1611.57.26228.9M257@4-L197792110.2700.8261.60.1021.50.0590.4564.69611.67.2624.38.9M257@5-L247972170.2700.8261.60.1021.50.0590.4559.28.9611.37.2625.58.9Average 563.3 611.4 624.4

續(xù)表2c

Appendix Continued Table 2c

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sRSD (%) 1.3 0 0.4 Deviation(%) 0.4 9 11.3 M257@1-R57582320.310.010.7151.60.0891.50.0580.5545.710.2547.86.7549.37.9M257@2-R107532280.30.020.7141.60.0881.50.0590.5567.810546.86.7543.47.8M257@3-R157502260.30.010.721.70.0891.50.0590.7555.915.6550.77.1549.97.9M257@4-R207402270.310.010.721.60.0891.50.0590.5554.210.1550.96.7550.67.9M257@5-R257562340.3100.7251.70.0891.50.0590.8568.716.7553.77.25507.9Average 558.4 550 548.6RSD (%) 1.7 0.5 0.5Deviation(%) -0.5 -2 -2.2M257@11268352220.270.010.741.50.0911.50.0590.4561.28.4562.66.7562.98.1M257@12318332230.270.010.7431.70.0921.60.0590.6553.313.2564.17.5566.88.7M257@13368392230.270.010.7371.60.0911.50.0590.5557.610.1560.76.8561.48.1M257@14418542290.270.010.7411.60.0911.50.0590.5560.69.8562.86.8563.38.1M257@15468332230.2700.7341.60.0911.50.0590.5551.610.6558.76.8560.48.1Average 556.9 561.8 563 RSD (%) 0.8 0.4 0.4 M257@11-L278142150.260.010.7831.60.0971.50.0590.4557.98.4587.36.9595.98.5M257@12-L328112170.270.010.7761.50.0961.50.0590.4561.38.4583.26.9589.58.5M257@13-L378182140.260.010.7711.60.0951.50.0590.7556.214.5580.47.3587.18.4M257@14-L428322200.260.010.7721.60.0961.50.0590.5553.710.4580.77588.38.4M257@15-L478212160.260.010.7721.60.0951.50.0590.6554.814580.87.3587.88.5Average 556.8 582.5 589.7RSD (%) 0.5 0.5 0.6Deviation(%) -0.7 3.8 5.1M257@11-R287992230.280.020.7231.60.0891.50.0590.4564.79.1552.46.7549.47.9M257@12-R337992230.280.010.7241.60.0891.50.0590.5560.710.6553.16.8551.38M257@13-R387992240.280.010.7241.60.0891.50.0590.4574.39.2553.16.7547.97.9M257@14-R438092290.2800.7221.60.0891.50.0590.4561.29.1551.76.7549.47.9M257@15-R487972240.2800.7211.60.0891.50.0590.5553.810.2551.16.7550.57.9Average 562.9 552.3 549.7 RSD (%) 1.3 0.2 0.2Deviation(%) 0.3 -1.6 -2M257@11-D297802200.280.020.7531.60.0931.50.0580.4546.69.15706.8575.98.3M257@12-D347722190.2800.7551.60.0931.50.0590.4559.39571.16.95748.3M257@13-D397762200.280.010.7471.60.0931.50.0590.5548.711.2566.26.9570.68.2M257@14-D447862240.290.010.7551.60.0931.50.0590.4564.495716.8572.78.2M257@15-D497742180.280.010.7521.60.0921.50.0590.6568.113.2569.57.1569.98.2Average 557.4 569.6 572.6RSD (%) 1.7 0.4 0.4Deviation(%) -0.6 1.5 2.1M257@11-UP307662280.300.7681.60.0941.50.0590.6569.213.8578.47.2580.88.3M257@12-UP357542260.300.7641.60.0941.50.0590.6567.612.9576.67.1578.98.3M257@13-UP407632290.30.010.7571.60.0941.50.0590.6556.613.2572.27.1576.68.3M257@14-UP457712300.30.010.7561.60.0941.50.0580.5546.511.55727579.18.3M257@15-UP507602270.30.010.7521.60.0931.50.0590.5553.211.7569.27.15748.4Average 558.6 573.7 577.9 RSD (%) 1.7 0.7 0.5 Deviation(%) -0.4 2.3 3

附表2d 不同測點(diǎn)且預(yù)剝蝕區(qū)域不重疊的U-Pb年齡分析的定年結(jié)果

Appendix Table 2d The result of zircon determined by SIMS on the same zircon grain with visible distance

測點(diǎn)號測量順序UThTh/Uf206放射成因同位素比值同位素年齡(Ma)(×10-6)meas(%)207Pb235U±s(%)206Pb238U±s(%)207Pb206Pb±s(%)207Pb206Pb±s207Pb235U±s206Pb238U±sM257@1118432270.270.020.7391.60.091.50.060.6587.413.5561.77.1555.48.1M257@1238222180.270.030.7421.70.0911.50.0590.757715.5563.77.2560.58.1M257@1358332240.270.030.7321.60.0911.50.0590.5551.511.8557.76.9559.28M257@1478392260.270.030.7371.70.0911.50.0590.7561.214.2560.57.3560.38.3M257@1598332240.270.020.7351.60.0911.50.0590.5548.611.5559.27561.88.3M257@16118412290.270.040.7361.60.0911.50.0590.7553.914.4560.37.1561.88.1M257@17138362260.270.030.7421.70.0911.50.0590.8562.618563.67.6563.88.3M257@18158512320.270.040.7371.60.0911.50.0590.5556.511.6560.96.95628.1M257@19178512290.270.020.7351.60.0911.50.0580.5541.511.3559.56.95648.1M257@20198522310.270.030.7441.60.0911.50.0590.6575.813.35657.1562.38.2Average 561.6 561.2 561.1 RSD (%) 2.6 0.4 0.4 M257@11-60L28522300.270.010.7291.60.091.50.0590.5562.711.1555.96.9554.28.1M257@12-60L48372230.270.010.7361.60.091.50.0590.5572.811.15606.9556.88.1M257@13-60L68372260.270.030.7331.60.0911.50.0590.5552.111.4558.46.95608.1M257@14-60L88392260.270.030.7451.60.0921.50.0590.6564.813565.27565.38.2M257@15-60L108362250.270.020.7461.60.0921.50.0590.6570.212566.17565.18.2M257@16-60L128442300.270.030.7411.60.0911.50.0590.6575.413.4562.87.1559.78.1M257@17-60L148382280.270.030.7391.70.0911.50.0590.7571.915.9561.77.3559.28.1M257@18-60L168442320.280.020.7391.70.0921.50.0580.8543.317561.57.3566.18.2M257@19-60L188522280.270.040.7411.60.0911.50.0590.5566.311.6562.77561.88.2M257@20-60L208572330.270.040.7361.60.0911.50.0590.655512.7560.17.1561.38.2Average 563.4 561.4 561 RSD (%) 1.8 0.5 0.7 Deviation(%) 0.4 0.1 0