LA-ICP-MS U-Pb dating and Hf isotopes of detrital zircon grains from siltstone of Danzhou Group in northern Guangxi and their geological significance
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摘要:
桂北丹洲群顶部拱洞组粉砂岩的碎屑锆石的阴极发光图像和Th/U(0.2~2.4)值显示,它们均为岩浆成因的锆石。锆石206Pb/238Pb年龄分布在730~769Ma和771~850Ma之间,这些锆石的Hf同位素成分范围较大,εHf(t)值和二阶段Hf模式年龄(TDM2)分别为-18.4~11.4和1020~2812Ma。此外,样品中还有一些年龄较老的锆石颗粒,207Pb/206Pb年龄为1910~3140Ma,εHf(t)值和二阶段Hf模式年龄(TDM2)分别为-13.6~3.4和2740~3635Ma。结合前人的研究推测,桂北丹洲群拱洞组沉积年龄小于等于706±10Ma,物源主要由扬子板块新元古代岩浆岩组成,也有少量太古宙岩浆岩的加入。推测中国华南地区存在对应于Rodinia超大陆聚合相关的格林威尔运动的响应。根据已测锆石的εHf(t)值和Hf二阶段模式年龄推断,研究区地壳生长主要经历3个阶段:① 3.64~3.25Ga,初生地壳出现在3.64Ga;② 2.98~2.37Ga;③ 2.19~1.28Ga,地壳生长的主要时期。
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关键词:
- 桂北丹洲群 /
- 碎屑锆石LA-ICP-MS U-Pb定年 /
- Hf同位素 /
- Rodinia超大陆 /
- 地壳生长
Abstract:This paper reports LA-ICP-MS U-Pb dating and Hf isotopes for detrital zircon grains of siltstone from Gongdong For-mation at the top of the Danzhou Group. The majority of zircon grains are transparent, euhedral and prismatic crystals with oscillato-ry zoning in CL images and have high Th/U ratios of 0.2~2.4, indicating an igneous origin for the zircon. The 206Pb/238Pb age distri-butions for the detrital zircon grains mainly range from 730Ma to 769Ma and 771Ma to 850Ma, and εHf(t)and two-stage Hf model ages (TDM2) range from -18.4 to 11.4 and from 1020Ma to 2812Ma, respectively. Moreover, there are some detrital zircon grains with relatively older ages with 206Pb/238Pb ages from 1910Ma to 3140Ma, and εHf(t)and TDM2 from -13.6~3.4 and 2740~3635Ma, respec-tively. Combined with previous researches, the authors infer that the maximum depositional age of the Gongdong Formation from Danzhou Group is 706±10Ma. The source region was predominated by Neoproterozoic magmatic rocks from Yangtze Block (ca. 750~830Ma) with the mixture of minor Archean magmatic rocks. There was developed the Greenville movement in South China re-sulting from the assembly of Rodinia supercontinent. In addition, on the basis of the εHf(t)and TDM2 data of the detrital zircon grains, the authors hold the existence of three stages for the crust growth in the study area:① 3.64Ga to 3.25Ga, with the juvenile crust at 3.64Ga; ② 2.98Ga to 2.37Ga; ③ 2.19Ga to 1.28Ga.
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坡北基性-超基性岩体位于塔里木板块东北部,区域上出露的地层主要为古元古界北山群、中元古界古硐井群、下古生界寒武系双鹰山组等,岩体形态主要受白地洼-淤泥河断裂控制,岩体长轴与该断裂平行,平面上呈相互联通的岩盆状,出露面积约180km2。前人对坡北岩体进行了专题地质填图[1],岩体的主要岩性为橄榄岩、橄榄辉长岩、辉长苏长岩、辉长岩等。辉长岩构成整个岩体的主体,其中有20多个超基性小侵入体。岩体内部赋存大型铜镍矿床,其中主要的含矿岩体为坡一、坡十超基性岩体,赋矿岩性主要为辉橄岩和纯橄岩,矿石以稀疏浸染状矿为主,品位较低,目前还没有进入开发利用阶段。
很多学者对坡北岩体的地球化学特征、岩浆演化等进行了大量的研究[2-8],获得主体辉长岩锆石U-Pb年龄为278±2 Ma和274±4 Ma[2, 4],对岩体内不同类岩石的岩浆演化关系研究较少。本文在系统收集和总结前人研究成果的基础上,对岩体中不同类型岩石的同位素年代学、岩石地球化学、矿物地球化学、同位素地球化学进行了研究,探讨岩体的形成时代与岩浆演化过程。
1. 地质背景
坡北岩体的填图单元主要可划分为辉长岩、辉长苏长岩、橄榄辉长岩、橄榄岩类(图 1),基性岩类与超基性岩类之间为侵入接触关系(图版Ⅰ)。
图 1 坡北基性-超基性岩体地质图[1]1—第四系;2—黑云母片岩夹黑云母斜长变粒岩及大理岩;3—绿帘阳起片岩、黑云石英片岩夹似层状、透镜状白云石英片岩;4—矽卡岩、大理岩;5—钾长花岗岩;6—黑云母花岗岩;7—闪长岩;8—辉长岩;9—辉长苏长岩;10—橄榄辉长苏长岩;11—橄榄辉长岩;12—橄榄岩类(包括二辉橄榄岩、含长二辉橄榄岩、纯橄岩);13—辉绿岩;14—花岗岩脉;15—石英脉;16—断层;17—面理构造;18—测年样品点位Figure 1. Geological map of Pobei basic-ultrabasic intrusion1.1 岩相学特征
橄榄岩类包括岩石类型有橄榄二辉岩、含长二辉橄榄岩、二辉橄榄岩、单斜辉石岩等,主要出露于坡北岩体的西南岩盆内。超基性岩体数量众多,形态各异,面积不等,主要沿北东东向不连续分布。其中坡一为最大的超基性岩体,形态为椭圆形,面积约1.8 km2。橄榄岩类在基性-超基性岩体中属于较晚侵位,岩石整体颜色较深,发育较强的蛇纹石化与伊丁石化,呈现为棕红色的伊丁石斑点。橄榄岩中含有稀疏浸染状的硫化物,是坡一、坡十小侵入体中的主要含矿岩石。
橄榄辉长岩在坡北岩体中广泛分布,侵入于辉长岩与辉长苏长岩中,地貌上表现为正地形。在西南岩盆中,橄榄辉长岩呈不规则的长条状,其长轴与区域断裂近于平行,在东北岩盆中,橄榄辉长岩呈环形脉状产出,发育矿物定向构造。岩石为灰黑色,具块状构造,表现出球状风化特点,岩石内部含有少量硫化物,呈星点状分布。由于橄榄石发生蛇纹石化与伊丁石化,局部可见红棕色的伊丁石斑点。
辉长苏长岩呈不规则形态侵入于辉长岩中,出露范围被辉长岩限定,主要出露于2个岩盆的中部。野外表现为风化后形成的碎块,岩石颜色为深绿色-黄褐色,大部分为纹层状构造。斜方辉石蚀变为绢石,呈褐黄色斑点,部分岩石中可见浸染状钛铁矿。
辉长岩可划分为2类,第一类为早期侵入的辉长岩,构成坡北岩体的主体,岩石颜色为青灰色,蚀变较其他岩性弱;另一类呈岩枝状侵入超基性岩内部,为细粒辉长岩,出露较少。
1.2 岩石学特征
纯橄岩(图版Ⅰ-a、b):岩石为深绿色,中细粒状镶嵌结构,块状构造。橄榄石含量可达95%以上,粒径为0.5~2.1 mm,呈不规则颗粒状紧密镶嵌生长,裂隙十分发育,蛇纹石化强烈,伴随着析出磁铁矿,磁性增强;辉石含量一般小于5%,呈不规则粒状分布于橄榄石晶粒之间,粒径小于0.2 mm。
橄榄辉长岩(图版Ⅰ-a、d):岩石为灰黑色,中细粒辉长结构,块状构造。斜长石含量约为60%,呈长条状或板状,半自形,粒径为0.5~3 mm;单斜辉石含量为30%,为不规则粒状到半自形短柱状,粒径为0.5~2 mm,可见辉石包裹斜长石颗粒;橄榄石含量为5%~7%,颗粒较大,粒径为0.5~2.5 mm,发育网状裂理,蚀变较轻。
橄榄辉长苏长岩(图版Ⅰ-e):岩石为灰褐色,中细-中粒辉长结构、包含结构,块状构造。斜长石含量约为50%,颗粒直径0.3~4 mm,自形-半自形,多为板状或长条状。可见斜长石与辉石互相包裹关系。其中斜方辉石含量为20%~25%,颗粒直径为0.2~2 mm; 单斜辉石含量为15%~20%,颗粒直径为0.3~2.5 mm; 橄榄石含量为5%~10%,颗粒直径为0.5~2 mm,内部裂理发育,周围可见斜方辉石反应边。
辉长岩(图版Ⅰ-c、f):岩石呈灰黑色,细粒辉长结构,块状构造。主要造岩矿物为斜长石和单斜辉石。斜长石含量为65%,半自形板状,粒径为0.2~1.5 mm;单斜辉石含量为35%,不规则粒状到半自形柱状,粒径为0.2~1.3 mm。部分辉石发生角闪石化,颗粒内部包裹斜长石颗粒。
2. 矿物地球化学特征
纯橄榄岩中橄榄石的MgO含量为47.6%~49.6%,FeO含量为8.7%~11.7%,Fo(镁铁比值)值为88.0%~90.9%;橄榄辉长岩中橄榄石的MgO含量为39.82%~41.30%,FeO含量为9.52%~15.81%,Fo值为82.7%~90.1%;橄榄辉长苏长岩中橄榄石的MgO含量为29.30%~42.80%,FeO含量为10.93%~18.58%,Fo值为80.5%~82.8%;辉长岩中橄榄石的MgO含量为30.98%~32.93%,FeO含量为30.35%~32.77%,Fo值为63.0%~66.1%。由此可见,坡北岩体纯橄榄岩中橄榄石Fo值最高,达到90.9%;辉长岩中橄榄石Fo值最低,为63.0%。
斜长石在各类岩石中多为填隙相,半自形-他形短柱状、板状。橄榄岩中斜长石牌号在68.1~87.2之间;橄榄辉长岩中斜长石牌号在73.8~85.4之间,为培长石,含长结构中被包裹的斜长石牌号较高,最高可达97,为钙长石;辉长苏长岩中斜长石牌号在49.4~68.4之间,为拉长石;辉长岩中斜长石牌号在68.3~70.7之间;坡北岩体中各类岩性中斜长石SiO2与An的相关性较好,呈负相关,辉长苏长岩中斜长石的牌号最低,仅49.4。
坡北岩体不同岩性中单斜辉石主要为透辉石,斜方辉石主要为古铜辉石与紫苏辉石。各岩性中单斜辉石成分相似,MgO和CaO含量连续变化,而且呈负相关关系,说明不同岩相具有相似的原始岩浆成分;TiO2含量和Alz(单斜辉石中Al在四面体配位位置所占比例)的百分比值具有裂谷环境堆晶岩中单斜辉石特征[9]。
3. 同位素测年
基性-超基性岩体中锆石一般较少,当岩浆结晶出斜长石时,指示岩浆达到硅饱和,具备形成锆石的条件,因此,基性-超基性岩定年一般挑选富含斜长石的岩石;当岩浆没有结晶出斜长石时,指示岩浆没有达到硅饱和,只能形成斜锆石,因此,对于不含斜长石的超基性岩定年,一般挑选斜锆石。总之,基性-超基性岩进行锆石定年,需要采集样品的量足够大,一般在20 kg以上。
对坡北基性-超基性岩体中各类岩石进行锆石年代学的研究,采用SHRIMP和LA-ICP-MS方法测试各类样品。由廊坊物化探队完成各类岩性样品的单颗粒锆石挑选,制靶、阴极发光照相,SHRIMP测试在北京离子探针中心,LA-ICP-MS测试在中国地质科学院地质研究所完成。锆石样品的挑选、制备和测试方法见参考文献[10-11]。本次选取坡北岩体内各岩相代表性岩石样品进行锆石U-Pb年代学研究。所选样品的岩性包括含长橄榄岩(PB-2)、橄榄辉长岩(PB23-21)、辉长苏长岩(Pd27-2)、辉长岩(P23-22)。
3.1 含长橄榄岩形成时代
橄榄岩样品PB-2为含长橄榄岩,测试方法为锆石SHRIMP U-Pb测年。阴极发光图像(图 2-a)显示锆石颗粒呈自形到半自形,粒径在50~200 μm之间,大多数锆石长宽比为1:1~2:1,少量大于4:1,大部分锆石发育明显的岩浆振荡环带,部分锆石晶体形态较好,晶棱清晰,表现出典型的岩浆锆石特征。
在U-Pb年龄谐和图中(图 2-a),测试结果可以划分为2期。测试结果年龄较大的一期,年龄范围为273.1±3.6~287.4±4.1 Ma,年龄加权平均值为280±2 Ma。而年龄较小的一期,点号为12、14、17、18、19、20,其年龄范围则集中在239.8±3.6~260.2±6.9 Ma之间。年龄较大一期锆石的Th/U值为0.15~0.36,年龄较小的一期锆石Th/U值为0.65~0.84,二者区别明显。
前人研究获得的坡北岩体各类岩性的形成年龄为270~280 Ma,可知样品橄榄岩的形成时代为较大一期的锆石年龄,即280±2 Ma。而年龄较小的这期锆石,可能是岩浆期后热液作用的结果。
3.2 辉长苏长岩形成时代
辉长苏长岩样品PD27-2测试方法为SHRIMP锆石U-Pb测年。阴极发光图像(图 2-b)显示锆石颗粒呈半自形,长轴长度为50~150 μm,大部分长宽比为2:1。部分锆石岩浆振荡环带清晰,且环带较宽,为典型的岩浆锆石特征。锆石Th/U值变化较大,在0.23~0.99之间。
在U-Pb年龄谐和图中(图 2-b),有7个数据点成群分布,2、5、7、8、11、12号点则在谐和线上零散分布。其中2、5、12号点的锆石可见不规则的继承内核,其年龄数据偏大,7、8、11号点锆石具有次生边,导致年龄偏小。其他7个点的年龄值相近,年龄区间为266.0±3.9~284.0±5.8 Ma,年龄加权平均值为273.5±2.9 Ma,为辉长苏长岩的岩浆结晶年龄。
3.3 辉长岩形成时代
辉长岩样品P23-22测试方法为锆石SHRIMP U-Pb测年。阴极发光图像(图 2-c)显示锆石颗粒呈自形-半自形,长轴长度为90~160 μm,大部分锆石的长宽比为2:1~3:1,少数为长柱状,其长宽比为4:1。大部分锆石晶体形态较好,具有明显的岩浆振荡环带。锆石Th/U值除7号点为0.22外,其余各点比值相近,为0.62~0.74,具有典型岩浆锆石的特征(Th/U>0.4)。
在U-Pb年龄谐和图中,测点数据几乎都落在谐和线上,获得的年龄区间为271.7±3.7~282.1±4.0 Ma,年龄加权平均值为277.1±2.2 Ma,代表了辉长岩样品P23-22的岩浆结晶年龄。
3.4 橄榄辉长岩形成时代
橄榄辉长岩样品PB23-21,用锆石LA-ICP-MS U-Pb方法测试年龄。阴极发光图像(图 2-d)显示锆石颗粒呈半自形-他形,长轴长度在60~180 μm之间,长宽比大部分为2:1~3:1。部分锆石发育较宽的岩浆振荡环带,锆石Th/U值在0.68~1.37之间,表现出典型的岩浆锆石特征。
在U-Pb年龄谐和图中,测点均落在谐和线上,所有分析点的206Pb/238U年龄值较一致,年龄区间为269.0±5.6~281.4±5.7 Ma,加权平均年龄为275.5±1.5 Ma,代表了橄榄辉长岩样品的形成年龄。
4. 岩石地球化学特征
4.1 主量元素
基性岩类的MgO含量相对于超基性岩类较低,Al2O3、CaO和Na2O的含量较高,且变化明显,可能与岩石中的斜长石含量有关。高的MgO含量和低的SiO2含量表明橄榄岩内部发生了橄榄石的堆晶作用。在SiO2-(Na2O+K2O)图解(图 3-a)中坡北所有样品点都落在亚碱性范围,在SiO2-(FeO/MgO)图解(图 3-b)中橄榄岩样品点落在拉斑系列,而基性岩的样品点落在钙碱性系列,即坡北岩体母岩浆为拉斑玄武系列,具有向钙碱性演化的趋势。
4.2 微量元素
从稀土元素配分图(图 4)可以看出,各岩类的稀土元素总量相差不大,分配模式一致,都为平坦型,都具有正Eu异常,但橄榄岩中的Eu异常相比其他岩类弱,可能是由于基性岩中存在斜长石的堆晶。微量元素原始地幔标准化蛛网图显示,各岩性都亏损高场强元素(如Nb、Ta、Zr、Hf),其中橄榄岩为弱的Nb、Ta负异常,不显示Zr、Hf负异常,橄榄岩的Sr含量也低于其他岩类,这与基性岩中长石含量较高相符。一般情况下,地幔各单元岩石样品微量元素经过原始地幔标准化后,蛛网图中没有明显的Nb、Ta负异常,地壳混染或地幔俯冲交代作用是Nb、Ta负异常的主要原因[16]。各类岩石总体显示较一致的分布模式,表明其虽然分不同阶段侵入就位,但应该为同源岩浆的产物。
5. 讨论
坡北岩体中不同类型岩石的稀土元素球粒陨石标准化图为平坦型,但橄榄岩中Eu异常不明显,基性岩中正Eu异常较橄榄岩明显。微量元素地幔标准化图中存在明显的Nb、Ta负异常与Zr、Hf负异常,而橄榄岩中的Nb、Ta、Zr、Hf负异常较其他岩性不明显。岩石地球化学数据总体显示出较一致的分布模式,表明不同类型岩石应该为同源岩浆的产物。坡北岩体不同岩性中单斜辉石的MgO和CaO含量、斜长石的SiO2含量和An值表现为连续变化,且呈负相关关系,进一步说明坡北岩体中不同类型岩石是同一母岩浆分离结晶的产物[17]。
坡北岩体西南段可见大量长城系古硐井群片岩与少数的下石炭统红柳园组大理岩等地层的残留顶盖或顶垂体,可作为坡北岩体发生同化混染的野外证据。当混染作用较强时则会出现拉斑玄武岩系列的镁铁质岩浆转化为钙碱性系列[18]。坡北岩体主量元素从橄榄岩的拉斑玄武岩系列转化为基性岩的钙碱性系列,应是地壳混染所致。在La/Nb-m/f图解(图 5-a)中,各岩性m/f值几乎连续变化,表明各岩性可能为同源岩浆演化的产物,且橄榄岩受地壳混染程度明显低于其他岩性。而同化混染作用会对岩浆Sr、Nd同位素组成产生影响,其中对于Sr同位素的影响大于Nd同位素。前人的Sr-Nd同位素研究成果表明[3, 15, 20-21],混染程度最小的橄榄岩起源于亏损地幔,总体具有向EMⅡ富集地幔端元演化的趋势,εNd(t)变化不大(6.63~-1.79),(87Sr/86Sr)i值变化较大(0.7009~0.7079),指示坡北岩体起源于亏损地幔,经历明显的地壳混染作用。
图 5 坡北岩体La/Nb-m/f图解(a)与(87Sr/86Sr)i-εNd(t)地壳混染模拟图(b)[19]Figure 5. Diagrams of m/f vs. La/Nb(a) and εNd(t)vs.(87Sr/86Sr)i (b) for crust mixing simulation in the Pobei intrusion结晶分异作用会导致岩浆成分连续性的变化,而地壳混染与之不同,更可能为突变性的影响岩浆成分。坡北基性-超基性岩的主量元素MgO、SiO2含量出现间断,本文采用地幔端元(DM),上地壳(UC)值((143Nd/144Nd)i=0.5115,(87Sr/86Sr)i=0.71)[22]和下地壳(LC)值((143Nd/144Nd)i=0.511,(87Sr/86Sr)i=0.72)[19]为端元进行粗略模拟,基性岩受到4%~15%下地壳物质的混染(图 5-b)。因此,超基性岩与基性岩的岩石地球化学特征差异应是地壳混染程度不同导致的,橄榄岩经历地壳混染程度明显低于其他岩类,导致其Sr的含量低于基性岩,Nb、Ta负异常较弱。
表 1 坡北岩体中不同岩相SHRIMP锆石U-Th-Pb定年结果Table 1. SHRIMP U-Th-Pb isotopic dating results for the zircon from different lithofacies of the Pobei intrusion测点编号 含量/10-6 Th/U 同位素比值 年龄/Ma 206Pb 232Th 238U 207Pb/206Pb 1σ/±% 207Pb/235U 1σ/±% 206Pb/238U 1σ/±% 206Pb/238U 1σ 含斜长石橄榄岩(PB2-1) PB2-1 17.1 77 438 0.18 0.0504 3.0 0.314 3.3 0.04526 1.3 285.4 3.7 PB2-2 8.67 38 222 0.18 0.0539 2.6 0.339 3.0 0.04560 1.4 287.4 4.1 PB2-3 10.4 46 271 0.17 0.0495 2.7 0.3052 3.0 0.04470 1.4 281.9 3.9 PB2-4 13.4 75 355 0.22 0.0484 4.1 0.291 4.3 0.04356 1.4 274.8 3.7 PB2-5 7.87 52 212 0.26 0.0577 5.5 0.346 5.7 0.04343 1.5 274.1 4.0 PB2-6 7.26 29 186 0.16 0.0497 3.4 0.310 3.7 0.04529 1.5 285.5 4.2 PB2-7 10.4 48 273 0.18 0.0494 4.8 0.302 5.0 0.04429 1.4 279.4 3.9 PB2-8 18.8 133 492 0.28 0.0489 2.3 0.3006 2.7 0.04454 1.3 280.9 3.7 PB2-9 14.9 63 389 0.17 0.0539 2.0 0.3314 2.5 0.04456 1.4 281.0 3.9 PB2-10 14.5 52 372 0.15 0.0489 2.7 0.3037 3.1 0.04505 1.4 284.1 3.8 PB2-11 9.62 43 250 0.18 0.0479 7.5 0.295 7.7 0.04460 1.8 281.3 4.9 PB2-12 6.57 150 196 0.79 0.0543 4.2 0.293 4.5 0.03917 1.7 247.7 4.0 PB2-13 12.1 91 321 0.29 0.0555 3.9 0.336 4.3 0.04390 1.8 277.0 4.8 PB2-14 5.15 110 154 0.74 0.0538 3.4 0.289 3.8 0.03900 1.5 246.6 3.7 PB2-15 18.9 177 508 0.36 0.0508 2.4 0.3031 2.7 0.04328 1.3 273.1 3.6 PB2-16 21.4 113 564 0.21 0.0524 2.3 0.3184 2.7 0.04407 1.4 278.0 3.8 PB2-17 4.61 96 128 0.77 0.0453 13 0.257 13 0.0412 2.7 260.2 6.9 PB2-18 6.57 155 192 0.84 0.0468 4.9 0.256 5.1 0.03961 1.5 250.4 3.7 PB2-19 6.95 132 211 0.65 0.0413 9.0 0.216 9.1 0.03790 1.5 239.8 3.6 PB2-20 7.99 188 241 0.81 0.0530 3.1 0.282 3.4 0.03852 1.5 243.7 3.5 PB2-21 6.17 27 165 0.17 0.0459 9.2 0.273 9.3 0.04312 1.6 272.2 4.2 辉长苏长岩(PD27-2) Pd27-2-1 29.9 186 826 0.23 0.05058 1.5 0.2938 2.1 0.04213 1.5 266.0 3.9 Pd27-2-2 14.0 305 332 0.95 0.0521 2.1 0.3523 2.5 0.04902 1.4 308.5 4.1 Pd27-2-3 13.7 117 362 0.33 0.0505 3.1 0.306 3.4 0.04388 1.4 276.8 3.8 Pd27-2-4 7.21 294 185 1.64 0.0489 8.2 0.303 8.5 0.04503 2.1 284.0 5.8 Pd-27-2-5 12.2 284 295 0.99 0.0502 3.7 0.331 3.9 0.04783 1.4 301.2 4.1 Pd-27-2-6 15.2 349 410 0.88 0.0502 3.0 0.2981 3.3 0.04306 1.4 271.8 3.8 Pd-27-2-7 10.00 71 288 0.25 0.0531 2.3 0.2967 2.7 0.04053 1.4 256.1 3.6 Pd27-2-8 6.05 51 176 0.30 0.0458 6.1 0.250 6.3 0.03949 1.7 249.7 4.1 Pd27-2-9 17.9 143 487 0.30 0.0508 2.0 0.2988 2.4 0.04269 1.3 269.5 3.5 Pd27-2-10 12.8 113 337 0.35 0.0508 2.5 0.3099 2.9 0.04425 1.4 279.1 3.8 Pd27-2-11 13.9 188 473 0.41 0.0495 2.5 0.2334 2.8 0.03417 1.3 216.6 2.9 Pd27-2-12 13.0 108 332 0.34 0.0526 3.5 0.330 3.8 0.04549 1.4 286.8 4.1 Pd27-2-13 16.6 158 444 0.37 0.0513 3.1 0.306 3.3 0.04331 1.4 273.3 3.7 辉长岩(P23-22) 1 5.60 100 146 0.71 0.0424 11 0.257 11 0.04397 1.6 277.4 4.4 2 9.78 154 258 0.62 0.0570 2.3 0.3483 2.8 0.04429 1.5 279.4 4.0 3 8.88 168 234 0.74 0.0512 4.6 0.311 4.8 0.04399 1.4 277.5 3.9 4 15.2 266 398 0.69 0.0512 3.6 0.315 3.9 0.04454 1.4 280.9 3.7 5 9.51 169 246 0.71 0.0487 6.6 0.300 6.7 0.04474 1.5 282.1 4.0 6 18.0 101 476 0.22 0.0516 2.3 0.3130 2.6 0.04401 1.3 277.7 3.6 7 8.20 117 213 0.56 0.0489 6.5 0.298 6.7 0.04427 1.5 279.2 4.1 8 13.0 236 344 0.71 0.0484 3.9 0.292 4.2 0.04382 1.4 276.4 3.7 9 7.94 150 210 0.74 0.0482 7.0 0.290 7.2 0.04365 1.5 275.4 4.1 10 11.4 219 303 0.75 0.0530 3.3 0.320 3.7 0.04377 1.7 276.2 4.6 11 9.86 174 262 0.68 0.0529 2.9 0.319 3.3 0.04376 1.5 276.1 4.0 12 8.67 158 233 0.70 0.0542 3.6 0.323 3.9 0.04325 1.5 273.0 3.9 13 10.2 164 274 0.62 0.0492 3.6 0.292 3.9 0.04305 1.4 271.7 3.7 表 2 坡北岩体橄榄辉长岩(PB23-21)LA-ICP-MS锆石U-Th-Pb定年结果Table 2. LA-ICP-MS U-Th-Pb isotopic dating results for the zircon from olivine gabbro (PB23-21) of the Pobei intrusion测点编号 含量/10-6 Th/U 同位素比值 年龄/Ma 206Pb 232Th 238U 207Pb/206Pb 1σ/±% 207Pb/235U 1σ/±% 206Pb/238U 1σ/±% 206Pb/238U 1σ 橄榄辉长岩(PB23-21) 01 97 341.2 375.1 0.91 0.0524 0.11 0.3129 0.70 0.0434 0.07 273.6 4.6 02 172 614.1 611.0 1.01 0.0525 0.09 0.3112 0.64 0.0430 0.09 271.3 5.3 03 122 418.6 526.9 0.79 0.0522 0.09 0.3174 0.78 0.0441 0.09 278.1 5.3 04 179 642.0 616.8 1.04 0.0527 0.08 0.3122 0.67 0.0430 0.08 271.1 4.9 05 180 657.0 649.4 1.01 0.0521 0.08 0.3060 0.72 0.0426 0.09 269.0 5.6 06 101 355.5 405.3 0.88 0.0522 0.09 0.3117 0.64 0.0433 0.07 273.0 4.5 07 374 1351.5 1459.1 0.93 0.0519 0.08 0.3116 0.82 0.0435 0.10 274.5 6.3 08 158 542.2 663.9 0.82 0.0518 0.09 0.3153 0.75 0.0441 0.09 278.5 5.3 09 95 327.4 361.9 0.90 0.0523 0.11 0.3171 0.79 0.0440 0.09 277.4 5.5 10 62 212.0 284.0 0.75 0.0536 0.11 0.3206 0.71 0.0433 0.07 273.5 4.3 11 120 417.8 436.0 0.96 0.0522 0.09 0.3150 0.78 0.0437 0.09 276.0 5.4 12 157 540.0 550.0 0.98 0.0530 0.10 0.3227 0.76 0.0441 0.08 278.3 5.1 13 462 1646.2 1480.3 1.11 0.0521 0.07 0.3155 0.65 0.0439 0.08 276.8 4.7 14 2859 10438.6 10248.7 1.02 0.0523 0.06 0.3173 0.70 0.0439 0.09 277.2 5.4 15 132 456.9 531.5 0.86 0.0525 0.09 0.3186 0.66 0.0440 0.08 277.8 4.9 16 190 665.3 736.2 0.90 0.0520 0.08 0.3142 0.66 0.0438 0.08 276.2 4.8 17 205 688.5 1012.3 0.68 0.0521 0.09 0.3132 0.68 0.0436 0.08 275.0 4.7 18 89 305.3 357.9 0.85 0.0524 0.12 0.3162 0.80 0.0437 0.08 275.9 5.2 19 257 885.9 815.6 1.09 0.0530 0.10 0.3253 0.88 0.0445 0.09 280.4 5.7 20 91 314.4 410.5 0.77 0.0525 0.10 0.3129 0.71 0.0433 0.07 273.0 4.3 21 92 304.9 392.7 0.78 0.0531 0.09 0.3241 0.67 0.0443 0.06 279.3 3.8 22 517 1904.7 1350.5 1.41 0.0525 0.07 0.3105 0.62 0.0429 0.07 270.8 4.3 23 268 934.8 788.0 1.19 0.0525 0.08 0.3186 0.77 0.0440 0.09 277.5 5.5 24 117 400.3 553.0 0.72 0.0523 0.09 0.3114 0.70 0.0432 0.07 272.8 4.4 25 126 426.9 503.2 0.85 0.0523 0.11 0.3167 0.72 0.0439 0.08 277.1 4.9 26 82 283.5 296.3 0.96 0.0524 0.11 0.3120 0.80 0.0432 0.08 272.5 5.3 27 399 1408.5 1336.4 1.05 0.0519 0.08 0.3109 0.64 0.0435 0.07 274.3 4.3 28 91 312.0 354.2 0.88 0.0522 0.10 0.3143 0.65 0.0437 0.06 275.4 3.7 29 214 737.0 924.6 0.80 0.0518 0.07 0.3087 0.67 0.0432 0.08 272.6 5.1 30 252 905.6 736.2 1.23 0.0516 0.08 0.3111 0.56 0.0437 0.06 275.6 3.5 31 527 1889.3 1717.8 1.10 0.0518 0.07 0.3075 0.60 0.0431 0.07 271.8 4.6 32 91 320.9 368.7 0.87 0.0528 0.11 0.3149 0.74 0.0433 0.09 273.2 5.6 33 316 1126.2 1053.9 1.07 0.0514 0.08 0.3121 0.72 0.0441 0.09 277.9 5.3 34 121 428.1 407.1 1.05 0.0514 0.10 0.3120 0.76 0.0440 0.08 277.5 4.9 35 122 425.8 588.2 0.72 0.0518 0.09 0.3099 0.70 0.0434 0.09 273.7 5.6 36 282 965.3 755.0 1.28 0.0515 0.08 0.3142 0.76 0.0443 0.11 279.2 6.8 37 328 1202.9 985.7 1.22 0.0514 0.07 0.3073 0.67 0.0434 0.09 273.9 5.5 38 192 691.7 676.7 1.02 0.0515 0.07 0.3152 0.81 0.0444 0.10 280.2 6.3 39 633 2305.6 1676.2 1.36 0.0515 0.06 0.3140 0.73 0.0442 0.10 278.8 6.0 40 327 1163.0 1032.5 1.13 0.0521 0.08 0.3201 0.76 0.0446 0.10 281.2 6.0 41 196 720.6 550.8 1.31 0.0518 0.08 0.3140 0.76 0.0439 0.10 277.1 6.0 42 98 339.1 378.8 0.90 0.0524 0.09 0.3224 0.69 0.0446 0.09 281.4 5.7 表 3 坡北岩体各岩性岩石全岩主量、微量和稀土元素分析结果Table 3. Whole-rock major, trace elements and REE data of the Pobei intrusion元素 HPS-06 HPS-12 HPS-14 HPS-17 HPS-19 HPS-23 HPS-25 HPS-27 HPS-31 HPS-32 P23-21 P317-8 P317-17 IB-20 2016PB-6 A-21 A-28 A-13 A-29 A-43 A-45 A-65 M-76 M-95 A-56 A-74 A-75 A-80 A-17 A-23 A-30 A-63 单辉橄榄岩 橄榄辉长岩 橄榄辉长岩 橄榄辉长苏长岩 辉长苏长岩 辉长岩 SiO2 38.4 38.5 38.1 38 40.2 39.3 36.9 39.2 40.7 40.7 46.43 48.6 47.06 48.75 45.56 47.62 49.01 50.64 50.59 47.15 47.37 49.23 51.56 48.42 51.27 48.71 49.58 48.44 47.84 47.79 51.06 50.38 TiO2 0.15 0.17 0.1 0.15 0.19 0.25 0.13 0.27 0.26 0.45 0.16 0.27 0.4 0.25 0.36 0.16 0.2 0.28 0.38 0.13 0.13 0.28 0.37 0.23 0.22 0.26 0.27 0.25 0.16 0.19 0.31 0.27 Al2O3 5.47 5.06 4.33 4.94 5.5 6.34 2.19 5.26 7.14 6.66 19.13 21.78 17.12 17.87 16.45 20.61 20.82 17.48 15.43 22.9 22.26 19.62 20.15 18.01 20.94 17.92 18.46 19.18 20.83 19.08 19.84 20.76 Fe2O3 11.5 13 12.3 11.4 11.5 11.1 12.1 10.8 10.9 10.9 4.47 4.51 7.61 4.85 5.96 6.33 5.8 6.56 7.36 4.9 5.07 5.65 7.17 5.12 4.65 6.23 6.88 6.45 5.97 6.12 5.58 5.23 MnO 0.16 0.2 0.18 0.17 0.16 0.16 0.16 0.15 0.16 0.16 0.07 0.08 0.12 0.09 0.09 0.09 0.09 0.12 0.13 0.07 0.07 0.09 0.12 0.09 0.09 0.11 0.11 0.1 0.08 0.09 0.09 0.1 MgO 32.8 33.1 33.1 33.4 31.6 32.7 37 33.4 32.1 31.7 10.58 6.59 10.45 10.21 10.22 10.61 8.47 9.02 10.15 7.77 8.61 8.25 7.07 10.08 6.92 9.5 9.24 8.92 9.13 9.9 6.67 7.39 CaO 2.9 3.4 2.46 2.52 4.13 3.37 1.61 3.41 3.73 3.59 15.26 14.88 13.67 16.16 14.35 11.45 12.6 12.48 13.1 13 12.82 13.81 10.6 15.21 12.28 14.38 12.91 13.79 10.44 12.04 12.55 11.65 Na2O 0.36 0.39 0.27 0.43 0.57 0.69 0 0.55 0.81 0.84 1.19 1.88 1.54 1.69 4.72 2.17 2.11 2.34 2.19 1.93 1.95 2.13 2.92 1.72 2.5 1.68 2.11 1.83 2.61 1.94 2.75 2.33 K2O 0.14 0.06 0.17 0.24 0.15 0.14 0.08 0.1 0.18 0.22 0.05 0.08 0.1 0.05 0.15 0.07 0.1 0.12 0.1 0.08 0.07 0.11 0.14 0.06 0.12 0.05 0.09 0.08 0.18 0.18 0.15 0.2 P2O5 0.018 0.028 0.015 0.025 0.022 0.036 0.02 0.029 0.032 0.038 0.01 0.01 0.02 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.03 0.02 0.02 0.02 烧失量 6.83 5.02 7.83 7.55 5.18 5 8.6 5.35 2.97 4 2.03 0.41 0.64 0.63 0.46 0.79 0.72 0.92 0.27 1.61 1.27 0.74 0.57 1.75 1.09 0.68 0.37 0.92 2.69 2.57 1 1.61 总计 98.73 98.93 98.86 98.83 99.2 99.09 98.79 98.52 98.98 99.26 99.38 99.09 98.73 100.56 98.34 99.92 99.94 99.98 99.72 99.56 99.64 99.93 100.7 100.71 100.1 99.54 100.04 99.98 99.96 99.92 100.02 99.94 Sc 8 7.27 7.24 6.53 12.6 7.32 8.11 12 8.35 8.29 15.8 29.93 18.76 26.18 23.95 15.5 20.08 29.42 31.07 18.21 15.31 26.53 22.09 40.18 8 7.27 7.24 6.53 7.32 8.11 7.72 12 Cr 2.08 1.21 2.15 1.97 1.97 2 2.42 2.21 2.09 1.93 594.91 174.43 642.9 226.32 379.01 554.1 594.5 482.1 382.5 407.3 450.4 548.6 225.1 687.9 2.08 1.21 2.15 1.97 2 2.42 2.22 2.21 Co 115 125 127 109 116 111 130 116 111 109 45.63 28.31 41.3 45.82 50.51 52.58 38.33 36.58 43.05 34.82 38.54 36.91 58.38 65.58 115 125 127 109 111 130 117 116 Ni 788 684 1070 805 786 952 1000 1020 952 927 236.32 38.5 107.72 149.08 160.94 172.7 134.5 58.03 69.14 111.2 155.4 72.81 49.41 97.34 788 684 1070 805 952 1000 1060 1020 Cu 109 92 186 48 118 59 104 50 48 52 153.37 20.27 49.27 46.83 65.9 85.76 43.13 31.9 68.27 63.08 60.91 32.29 33.52 48.66 109 92 186 48 59 104 43 50 Rb 5.6 1.21 4.69 7.68 4.22 5.59 2.97 3.09 5.16 5.29 2.2 2.21 2.09 1.06 0.92 3.18 3.34 3.34 3.22 3.74 2.98 3.46 3.91 1.57 5.6 1.21 4.69 7.68 5.59 2.97 2.35 3.09 Sr 20 46 12 16.9 121 83.1 11.8 88.2 116 84.8 329.7 403.77 248.74 347.17 342.92 227.5 261.2 238.5 208.9 338.7 295.9 265 497.9 406.4 317.7 268.4 305.1 326 337.5 218.9 316.6 306.9 Y 2.14 3.91 1.73 3.19 3.88 4.05 2.83 4.15 4.06 5.76 4.25 6.33 7.04 6.72 7.73 2.59 3.53 5.91 7.51 2.26 2.35 5.09 7.02 7.96 3.57 4.62 3.87 3.54 2.64 3.63 4.5 3.8 Zr 7.21 15.2 4.61 11.7 10.1 21.9 9.46 18.9 17.1 27.8 4.97 9.28 11.18 6.68 10.71 4.73 6.22 7.66 10.76 4.03 5.52 8.36 11.22 10.18 5.76 5.52 7.2 7.38 5.38 5.78 6.25 7.16 Nb 0.09 0.16 0.13 0.2 0.17 0.47 0.15 0.36 0.27 0.48 0.11 0.28 0.24 0.1 0.1 0.09 0.17 0.14 0.15 0.1 0.14 0.19 0.47 0.13 0.13 0.06 0.14 0.16 0.12 0.12 0.15 0.25 Ba 2.32 1.61 2.55 1.82 18 10.6 3.47 8.74 19 9.85 13.57 28.68 30.09 15.35 11.37 15.02 23.48 31.19 18.19 20.55 17.35 26.2 72.58 25.64 23.8 16.54 25.73 27.81 27.21 15.69 35.51 33.05 La 0.19 0.38 0.22 0.32 0.45 0.98 0.38 0.74 0.76 1.09 0.84 1.55 1.67 1.05 0.94 0.66 0.95 0.99 0.9 0.91 0.84 1.14 2.28 1.08 0.89 0.62 0.78 0.81 0.94 0.78 0.89 1.24 Ce 0.53 1.23 0.55 1.02 1.22 2.58 1.11 2.18 2.19 3.16 2.05 3.8 4.03 2.74 2.82 1.63 2.25 2.22 2.51 1.73 1.93 2.74 5.02 3.07 2.1 1.73 2.02 2.15 2.14 1.88 2.22 2.83 Pr 0.1 0.21 0.08 0.17 0.2 0.39 0.17 0.35 0.36 0.5 0.31 0.55 0.62 0.46 0.5 0.23 0.31 0.39 0.42 0.28 0.27 0.4 0.67 0.5 0.3 0.28 0.3 0.32 0.29 0.28 0.33 0.38 Nd 0.58 1.19 0.47 0.99 1.11 1.78 1.01 1.75 1.76 2.71 1.66 2.89 3.47 2.48 2.93 1.28 1.61 2.14 2.4 1.32 1.33 2.14 3.43 3.01 1.51 1.66 1.77 1.73 1.46 1.51 1.73 1.78 Sm 0.22 0.45 0.19 0.36 0.42 0.52 0.36 0.46 0.53 0.82 0.59 0.87 1.14 0.91 1.06 0.4 0.48 0.73 0.91 0.33 0.36 0.69 0.92 1.07 0.5 0.6 0.61 0.58 0.4 0.54 0.62 0.48 Eu 0.12 0.16 0.11 0.14 0.18 0.25 0.12 0.2 0.27 0.37 0.43 0.63 0.63 0.54 0.64 0.39 0.43 0.54 0.53 0.4 0.4 0.52 0.73 0.67 0.54 0.43 0.45 0.41 0.45 0.41 0.54 0.5 Gd 0.23 0.48 0.23 0.37 0.55 0.59 0.41 0.63 0.54 0.97 0.78 1.21 1.54 1.24 1.41 0.56 0.69 1.09 1.34 0.5 0.54 0.98 1.37 1.49 0.71 0.88 0.84 0.77 0.59 0.71 0.87 0.66 Tb 0.05 0.11 0.04 0.09 0.11 0.11 0.09 0.12 0.11 0.18 0.14 0.2 0.24 0.22 0.27 0.09 0.11 0.19 0.22 0.08 0.08 0.16 0.2 0.24 0.11 0.15 0.14 0.13 0.09 0.13 0.14 0.11 Dy 0.36 0.65 0.3 0.47 0.71 0.66 0.5 0.76 0.68 1.06 0.88 1.23 1.75 1.44 1.64 0.52 0.72 1.2 1.5 0.46 0.48 1 1.51 1.76 0.71 0.99 0.88 0.79 0.55 0.77 0.88 0.71 Ho 0.07 0.15 0.07 0.11 0.16 0.14 0.11 0.17 0.16 0.23 0.18 0.25 0.32 0.29 0.32 0.12 0.15 0.25 0.31 0.09 0.1 0.2 0.29 0.33 0.15 0.2 0.18 0.16 0.11 0.16 0.18 0.14 Er 0.22 0.37 0.17 0.35 0.4 0.4 0.34 0.44 0.44 0.65 0.47 0.72 0.88 0.78 0.92 0.33 0.38 0.72 0.87 0.27 0.28 0.58 0.92 0.93 0.39 0.52 0.47 0.44 0.32 0.43 0.5 0.44 Tm 0.03 0.05 0.03 0.04 0.07 0.06 0.05 0.06 0.06 0.09 0.06 0.09 0.14 0.1 0.12 0.05 0.06 0.09 0.13 0.03 0.04 0.08 0.13 0.13 0.06 0.07 0.07 0.06 0.05 0.06 0.07 0.06 Yb 0.22 0.4 0.18 0.3 0.41 0.39 0.28 0.41 0.41 0.58 0.41 0.67 0.71 0.68 0.74 0.28 0.36 0.6 0.71 0.18 0.23 0.45 0.8 0.73 0.38 0.47 0.4 0.33 0.29 0.37 0.4 0.44 Lu 0.04 0.06 0.02 0.04 0.06 0.07 0.05 0.07 0.06 0.1 0.06 0.09 0.11 0.09 0.1 0.04 0.06 0.09 0.12 0.03 0.04 0.07 0.12 0.11 0.06 0.07 0.06 0.06 0.05 0.06 0.06 0.06 Hf 0.2 0.37 0.13 0.28 0.3 0.5 0.27 0.45 0.45 0.71 0.2 0.3 0.42 0.29 0.45 0.15 0.22 0.26 0.4 0.12 0.16 0.29 0.34 0.41 0.19 0.22 0.24 0.26 0.18 0.22 0.23 0.22 Ta 0.01 0.02 0.01 0.03 0.02 0.04 0.02 0.03 0.01 0.04 0.03 0.04 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.02 0.02 0.03 0.02 0.02 0.02 Th 0.02 0.05 0.03 0.08 0.07 0.21 0.06 0.11 0.05 0.13 0.08 0.17 0.13 0.07 0.04 0.05 0.1 0.16 0.1 0.12 0.08 0.11 0.8 0.81 0.06 0.02 0.04 0.04 0.09 0.05 0.06 0.13 U 0.03 0.01 0.03 0.18 0.04 0.06 0.02 0.03 0.01 0.04 0.03 0.07 0.08 0.13 0.03 0.02 0.05 0.19 0.37 0.21 0.04 0.04 1.29 1.4 0.06 0.03 0.13 0.11 0.06 0.13 0.07 0.08 Pb 2 0.42 1.13 2.56 1.09 1.24 1.02 0.7 0.81 0.85 1.37 1.12 1.1 0.6 0.52 1 1.18 1.07 0.86 1.04 0.86 0.83 2.34 1.46 0.96 0.8 0.82 1.4 1.26 1.35 1.08 1.51 来源 [6] 本文 [14] [15] 注:主量元素含量单位为%,微量和稀土元素含量单位为10-6 6. 结论
综合上述研究,笔者发现坡北基性-超基性杂岩体中,不同岩相形成时代上相似,辉长岩相和橄榄辉长岩相出露面积大,锆石U-Pb年龄相对较集中,而橄榄岩相和辉长苏长岩相出露面积小,锆石U-Pb年龄受到一定的干扰。不同岩相的岩石地球化学及矿物地球化学相似,但是受岩浆结晶分异作用和地壳混染作用影响,不同岩相中橄榄石的Fo值、斜长石的牌号、单斜辉石的MgO和CaO含量存在差异;特别是橄榄岩相受堆晶作用影响,与其他岩相相比,岩石地球化学成分上存在一定的差异。本次取得的主要认识如下。
(1) 坡北岩体主要由橄榄岩、橄榄辉长岩、辉长苏长岩、辉长岩等组成;各岩类形成年龄集中在270~280 Ma之间,其中辉长岩年龄为277.1±2.2 Ma;辉长苏长岩年龄为273.5±2.9 Ma;橄榄辉长岩年龄为275.5±1.5 Ma;含斜长石橄榄岩年龄为280.0±2.0 Ma,超基性岩结晶时间最早。
(2) 坡北岩体中不同类型岩石的微量与稀土元素地球化学数据显示出较一致的分配模式,具有同源岩浆演化的特征;结合Sr-Nd同位素数据,坡北岩体起源于亏损地幔,受到4%~15%下地壳物质的混染。
(3) 坡北岩体中不同类型岩石的年代学、岩石地球化学、矿物晶体化学及同位素地球化学特征具有一定差异,主要与岩浆结晶分异及地壳混染程度有关。
致谢: 感谢武汉上谱科技有限责任公司相关老师在U-Pb测年过程中给予的悉心指导和帮助,感谢中国地质科学院地质研究所大陆构造与动力学实验室王铮助理工程师在Hf同位素测试过程中给予的帮助,感谢审稿专家对论文提出的宝贵修改意见。 -
表 1 丹洲群拱洞组碎屑锆石U-Th-Pb同位素数据(样品号:HK-19)
Table 1 U-Th-Pb isotope data for detrital zircon grains fromGongdong Formation in Danzhou Group (Sample: HK-19)
点号 Th/U 铅同位素比值及误差 年龄及误差/Ma 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ 207Pb/206Pb ±1σ 208Pb/232Th ±1σ 1 1.5 0.1279 0.0014 1.3656 0.0171 0.0805 0.0009 0.0447 0.0004 776 8 874 7 1208 21 885 7 2 1.4 0.1215 0.0019 1.0770 0.0597 0.0642 0.0026 0.0441 0.0008 739 11 742 29 749 82 872 15 3 1 0.1226 0.0019 1.2502 0.0600 0.0785 0.0023 0.0464 0.0009 745 11 824 27 1159 58 917 17 5 0.8 0.1160 0.0017 1.0137 0.0474 0.0688 0.0021 0.0458 0.0009 707 10 711 24 894 63 905 17 6 0.9 0.1214 0.0014 1.2101 0.0227 0.0757 0.0010 0.0486 0.0005 739 8 805 10 1086 27 959 9 7 1.1 0.1199 0.0016 1.0707 0.0369 0.0724 0.0017 0.0452 0.0006 730 9 739 18 996 46 893 12 8 0.8 0.3517 0.0042 5.7701 0.1901 0.1300 0.0019 0.1087 0.0014 1943 20 1942 29 2098 25 2085 26 10 0.3 0.1303 0.0015 1.3014 0.0227 0.0730 0.0009 0.0477 0.0006 790 8 846 10 1013 26 941 11 11 0.5 0.3653 0.0041 8.2370 0.1776 0.1622 0.0018 0.1070 0.0012 2007 19 2257 20 2478 19 2055 21 12 0.9 0.1286 0.0018 1.2802 0.0581 0.0721 0.0021 0.0420 0.0008 780 11 837 26 990 57 831 15 13 1.5 0.1284 0.0015 1.3790 0.0298 0.0804 0.0012 0.0425 0.0004 779 8 880 13 1207 29 841 8 14 1.2 0.1261 0.0014 1.5223 0.0273 0.0848 0.0011 0.0401 0.0004 765 8 939 11 1310 25 795 7 17 0.9 0.1314 0.0016 1.1880 0.0361 0.0671 0.0014 0.0421 0.0006 796 9 795 17 840 42 833 11 18 0.2 0.4065 0.0045 8.0073 0.1490 0.1416 0.0015 0.1349 0.0015 2199 21 2232 17 2247 19 2557 27 19 0.6 0.3909 0.0044 7.0752 0.1552 0.1320 0.0015 0.1055 0.0011 2127 20 2121 20 2125 20 2028 20 22 1.7 0.1248 0.0014 1.3757 0.0218 0.0808 0.0010 0.0374 0.0003 758 8 879 9 1217 23 743 6 24 0.9 0.4518 0.0053 10.3996 0.3385 0.1600 0.0020 0.1301 0.0015 2403 24 2471 30 2456 21 2472 27 25 0.9 0.1483 0.0019 1.4037 0.0532 0.0675 0.0015 0.0369 0.0006 892 11 891 22 854 46 732 12 27 1 0.1286 0.0016 1.3455 0.0452 0.0716 0.0015 0.0404 0.0006 780 9 866 20 974 42 800 11 28 1 0.1400 0.0016 1.4749 0.0230 0.0770 0.0009 0.0461 0.0004 845 9 920 9 1120 23 911 8 30 1 0.1294 0.0015 1.3466 0.0236 0.0763 0.0010 0.0416 0.0004 785 8 866 10 1104 25 825 8 31 0.5 0.2278 0.0026 3.8563 0.0745 0.1230 0.0014 0.0828 0.0009 1323 13 1605 16 2000 21 1609 16 34 1.6 0.1804 0.0030 1.9028 0.1375 0.0741 0.0025 0.0465 0.0010 1069 16 1082 48 1044 67 919 20 35 2.2 0.1327 0.0022 2.1332 0.1268 0.1069 0.0033 0.0427 0.0008 803 13 1160 41 1748 55 846 15 36 1.1 0.1375 0.0016 1.4122 0.0271 0.0755 0.0010 0.0402 0.0004 831 9 894 11 1082 27 798 8 37 1.5 0.1355 0.0015 1.4474 0.0257 0.0791 0.0010 0.0392 0.0004 819 9 909 11 1174 25 777 7 38 0.8 0.4790 0.0053 10.8197 0.1935 0.1657 0.0018 0.1191 0.0011 2523 23 2508 17 2515 18 2275 20 39 1.3 0.1339 0.0015 1.4799 0.0325 0.0773 0.0011 0.0414 0.0004 810 9 922 13 1128 29 819 8 40 1.9 0.1403 0.0016 1.5250 0.0283 0.0771 0.0010 0.0384 0.0004 846 9 941 11 1125 26 762 7 41 1.1 0.1242 0.0015 1.3032 0.0335 0.0761 0.0013 0.0381 0.0005 755 9 847 15 1097 33 755 9 42 2 0.1247 0.0017 1.4777 0.0609 0.0840 0.0021 0.0467 0.0006 757 10 921 25 1291 48 922 12 43 0.5 0.3277 0.0036 5.3420 0.0685 0.1236 0.0013 0.0841 0.0007 1827 17 1876 11 2008 18 1632 13 45 1.9 0.1278 0.0014 1.3844 0.0211 0.0807 0.0009 0.0402 0.0004 775 8 882 9 1214 23 797 7 46 1.7 0.1239 0.0014 1.4050 0.0228 0.0818 0.0010 0.0416 0.0004 753 8 891 10 1240 24 823 7 47 0.4 0.3664 0.0040 7.9664 0.1168 0.1566 0.0016 0.1193 0.0011 2012 19 2227 13 2419 17 2278 20 48 0.9 0.1278 0.0014 1.3298 0.0216 0.0736 0.0009 0.0441 0.0004 776 8 859 9 1031 24 873 8 50 1 0.1410 0.0026 1.5663 0.1190 0.0720 0.0031 0.0399 0.0012 850 15 957 47 986 86 791 22 52 0.8 0.1238 0.0024 1.0980 0.0891 0.0605 0.0032 0.0425 0.0013 753 14 752 43 621 32 842 26 53 0.6 0.5089 0.0057 12.6676 0.2778 0.1802 0.0020 0.1365 0.0014 2652 24 2655 21 2655 18 2587 24 55 0.2 0.1326 0.0015 1.2181 0.0234 0.0685 0.0009 0.0466 0.0007 803 9 809 11 884 28 920 13 56 0.6 0.3177 0.0035 6.6179 0.1242 0.1485 0.0016 0.0970 0.0009 1779 17 2062 17 2329 19 1871 17 57 0.8 0.1281 0.0014 1.2817 0.0236 0.0740 0.0010 0.0434 0.0004 777 8 838 10 1040 26 859 8 58 0.7 0.1290 0.0017 1.1541 0.0422 0.0669 0.0016 0.0426 0.0007 782 10 779 20 835 49 842 14 60 1.4 0.1278 0.0021 1.2811 0.0729 0.0737 0.0025 0.0484 0.0009 775 12 837 32 1034 68 955 16 61 1.2 0.1355 0.0020 1.2282 0.0567 0.0697 0.0020 0.0402 0.0007 819 11 814 26 918 59 797 14 62 1 0.1282 0.0015 1.2805 0.0254 0.0725 0.0010 0.0399 0.0004 778 8 837 11 1000 28 791 8 63 1.4 0.3886 0.0049 6.9856 0.3021 0.1323 0.0021 0.1000 0.0013 2117 23 2110 38 2129 28 1926 23 65 1.4 0.1278 0.0014 1.3714 0.0206 0.0797 0.0009 0.0423 0.0004 776 8 877 9 1191 23 837 7 66 0.9 0.1281 0.0015 1.3583 0.0273 0.0769 0.0011 0.0436 0.0004 777 8 871 12 1117 28 862 9 67 1.3 0.3407 0.0042 6.3821 0.2477 0.1361 0.0021 0.1135 0.0013 1890 20 2030 34 2179 27 2172 24 68 2 0.1265 0.0014 1.4306 0.0274 0.0814 0.0011 0.0399 0.0004 768 8 902 11 1231 26 791 7 69 1.6 0.1271 0.0015 1.4205 0.0366 0.0802 0.0013 0.0389 0.0004 771 9 898 15 1201 33 772 8 70 1.3 0.1277 0.0015 1.3916 0.0270 0.0788 0.0011 0.0443 0.0004 775 8 885 11 1168 27 877 8 72 1.5 0.1279 0.0020 1.3012 0.0687 0.0726 0.0024 0.0411 0.0008 776 11 846 30 1004 65 814 15 75 1.8 0.1247 0.0016 1.3630 0.0421 0.0809 0.0016 0.0423 0.0005 758 9 873 18 1218 38 838 9 76 0.6 0.5460 0.0060 18.7385 0.3436 0.2430 0.0025 0.1551 0.0014 2809 25 3029 18 3140 16 2914 25 77 1.1 0.1250 0.0015 1.3401 0.0323 0.0756 0.0012 0.0398 0.0004 759 8 863 14 1084 32 789 9 79 0.7 0.2967 0.0033 6.2970 0.1025 0.1512 0.0016 0.0851 0.0008 1675 16 2018 14 2359 18 1651 14 80 1 0.2948 0.0038 4.2902 0.1695 0.1207 0.0021 0.1044 0.0014 1666 19 1692 33 1966 31 2007 26 81 0.5 0.4567 0.0051 10.1246 0.2459 0.1589 0.0018 0.1121 0.0013 2425 23 2446 22 2444 19 2147 24 82 1.1 0.3620 0.0041 6.4596 0.1485 0.1343 0.0016 0.1019 0.0010 1992 19 2040 20 2155 20 1962 18 83 0.8 0.3374 0.0042 5.4538 0.1983 0.1255 0.0019 0.0854 0.0013 1874 20 1893 31 2036 27 1656 24 85 0.8 0.4594 0.0051 10.6858 0.2360 0.1717 0.0019 0.1289 0.0013 2437 23 2496 21 2574 18 2451 22 86 1.2 0.1323 0.0017 1.2307 0.0426 0.0713 0.0016 0.0422 0.0006 801 10 815 19 965 44 836 12 87 1.1 0.3678 0.0041 8.3767 0.1806 0.1640 0.0019 0.0807 0.0008 2019 19 2273 20 2498 19 1569 15 88 1.7 0.1341 0.0015 1.4328 0.0233 0.0778 0.0009 0.0411 0.0004 811 8 903 10 1141 24 814 7 89 0.2 0.4116 0.0045 7.9881 0.1218 0.1412 0.0015 0.1074 0.0011 2222 20 2230 14 2242 18 2061 20 90 1.4 0.1263 0.0015 1.2999 0.0297 0.0750 0.0012 0.0339 0.0004 767 8 846 13 1067 31 674 7 92 1 0.1235 0.0015 1.1300 0.0370 0.0665 0.0022 0.0351 0.0007 751 8 768 18 833 73 697 13 93 1.6 0.1173 0.0017 1.0583 0.0381 0.0652 0.0023 0.0330 0.0006 715 10 733 19 789 73 657 12 94 1.4 0.1210 0.0012 1.1084 0.0257 0.0663 0.0015 0.0295 0.0005 736 7 757 12 815 48 587 10 95 1.6 0.1354 0.0017 1.2053 0.0383 0.0648 0.0022 0.0373 0.0007 818 10 803 18 769 69 740 15 96 0.6 0.3508 0.0043 5.9422 0.1281 0.1225 0.0025 0.0942 0.0020 1938 20 1967 19 1992 37 1820 37 97 1.4 0.1316 0.0018 1.1608 0.0345 0.0639 0.0019 0.0372 0.0008 797 10 782 16 739 24 739 16 98 0.7 0.1392 0.0019 1.2991 0.0447 0.0677 0.0023 0.0398 0.0011 840 11 845 20 859 70 789 21 99 2.3 0.1276 0.0016 1.1130 0.0238 0.0632 0.0013 0.0339 0.0007 774 9 760 12 722 42 674 13 100 2 0.1290 0.0019 1.1084 0.0328 0.0630 0.0020 0.0312 0.0007 782 11 757 16 706 69 622 13 101 2.4 0.1294 0.0016 1.1673 0.0295 0.0657 0.0017 0.0328 0.0008 785 9 785 14 798 54 652 16 102 1.4 0.1391 0.0020 1.2490 0.0371 0.0659 0.0021 0.0341 0.0011 839 12 823 17 1200 67 678 21 104 1.4 0.1224 0.0019 1.0384 0.0436 0.0624 0.0028 0.0285 0.0011 744 11 723 22 700 99 568 21 105 1.6 0.1268 0.0018 1.0735 0.0356 0.0623 0.0021 0.0310 0.0010 769 11 740 17 683 73 618 19 106 0.3 0.5570 0.0065 16.1080 0.3605 0.2098 0.0041 0.1234 0.0034 2854 27 2883 22 2906 32 2353 62 107 1.5 0.1321 0.0022 1.1502 0.0506 0.0633 0.0027 0.0343 0.0009 800 13 777 24 717 86 681 17 108 1.3 0.1301 0.0015 1.0967 0.0300 0.0610 0.0015 0.0335 0.0007 788 8 752 15 639 58 665 15 109 1.2 0.1211 0.0015 1.0231 0.0287 0.0614 0.0017 0.0317 0.0007 737 9 715 14 654 64 632 14 110 1 0.1237 0.0021 1.0895 0.0394 0.0639 0.0022 0.0334 0.0008 752 12 748 19 739 73 663 15 111 1 0.3236 0.0048 5.2312 0.1328 0.1169 0.0027 0.0874 0.0020 1807 24 1858 22 1910 9 1694 38 112 0.7 0.1145 0.0014 0.9719 0.0193 0.0612 0.0010 0.0313 0.0006 699 8 689 10 656 37 622 11 113 1.2 0.3597 0.0057 6.0394 0.1412 0.1221 0.0029 0.0965 0.0022 1981 27 1982 20 1987 43 1863 40 114 1.1 0.3414 0.0036 5.6829 0.1087 0.1202 0.0024 0.1051 0.0021 1894 18 1929 17 1959 35 2019 39 115 2.2 0.1244 0.0013 1.1103 0.0220 0.0645 0.0012 0.0363 0.0006 756 8 758 11 767 41 720 12 116 1.7 0.1306 0.0013 1.1795 0.0234 0.0654 0.0013 0.0380 0.0007 791 7 791 11 789 43 753 14 117 2.2 0.1224 0.0012 1.0672 0.0214 0.0632 0.0012 0.0322 0.0006 744 7 737 11 722 41 641 11 118 1.3 0.1274 0.0016 1.1309 0.0269 0.0644 0.0014 0.0345 0.0007 773 9 768 13 754 46 686 15 注:锆石U-Pb年龄值使用说明(包括正文、图及锆石Hf同位素计算):小于12亿年的数据均用锆石的206Pb/238Pb年龄,大于12亿年的数据均用锆石的207Pb/206Pb年龄 表 2 丹洲群拱洞组碎屑锆石Hf同位素数据(样品号:HK-19)
Table 2 Hf isotope data for detrital zircon grains for from Gongdong Formation in Danzhou Group (Sample: HK-19)
点号 年龄/Ma 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf 2σ εHf(0) εHf(t) 2σ TDM TDM2 fLu/Hf 1 776 0.219353 0.006281 0.282138 0.000030 -22.4 -8.6 1.1 1825 1020 -0.81 5 707 0.072002 0.001906 0.281938 0.000022 -29.5 -14.8 0.8 1894 1276 -0.94 6 739 0.058196 0.002005 0.282453 0.000029 -11.3 4.0 1.0 1162 1284 -0.94 7 730 0.114721 0.002999 0.282442 0.000023 -11.7 3.0 0.8 1210 1318 -0.91 9 737 0.052978 0.001515 0.282479 0.000022 -10.4 5.2 0.8 1109 1331 -0.95 11 2478 0.026945 0.000711 0.281292 0.000020 -52.3 2.0 0.7 2716 2878 -0.98 12 780 0.084112 0.002497 0.282416 0.000026 -12.6 3.3 0.9 1231 1357 -0.92 14 765 0.071027 0.002187 0.282358 0.000028 -14.6 1.1 1.0 1305 1376 -0.93 18 2247 0.010113 0.000281 0.281005 0.000021 -62.5 -12.7 0.8 3068 3635 -0.99 24 2456 0.012930 0.000350 0.280947 0.000027 -64.5 -10.1 1.0 3150 3633 -0.99 25 892 0.059806 0.001608 0.282423 0.000020 -12.4 6.4 0.7 1192 1404 -0.95 27 780 0.066628 0.002078 0.282221 0.000029 -19.5 -3.3 1.0 1497 1419 -0.94 28 845 0.111336 0.003463 0.282502 0.000029 -9.5 7.2 1.0 1135 1455 -0.90 31 2000 0.095880 0.002104 0.281371 0.000029 -49.6 -7.8 1.0 2707 3133 -0.94 36 831 0.070647 0.001974 0.282486 0.000029 -10.1 7.1 1.0 1113 1464 -0.94 37 819 0.079851 0.002488 0.282402 0.000030 -13.1 3.6 1.1 1251 1480 -0.93 38 2515 0.024262 0.000678 0.281306 0.000027 -51.8 3.4 0.9 2694 2818 -0.98 39 810 0.054110 0.001748 0.281968 0.000030 -28.4 -11.5 1.1 1844 1485 -0.95 41 755 0.047925 0.001671 0.282422 0.000029 -12.4 3.4 1.0 1196 1491 -0.95 43 2008 0.034244 0.000899 0.281269 0.000022 -53.2 -9.6 0.8 2760 3254 -0.97 45 775 0.087182 0.002445 0.282459 0.000027 -11.1 4.8 1.0 1166 1496 -0.93 48 776 0.060838 0.001670 0.282451 0.000024 -11.3 4.9 0.8 1154 1505 -0.95 50 850 0.055959 0.001554 0.282587 0.000027 -6.6 11.4 0.9 957 1542 -0.95 52 753 0.044033 0.001189 0.282224 0.000025 -19.4 -3.4 0.9 1458 1556 -0.96 53 2655 0.032016 0.000840 0.281053 0.000027 -60.8 -2.7 0.9 3048 3316 -0.97 55 803 0.096307 0.002506 0.282404 0.000029 -13.0 3.4 1.0 1249 1621 -0.92 56 2329 0.060331 0.001826 0.281380 0.000029 -49.2 0.0 1.0 2674 2892 -0.95 57 777 0.052260 0.001568 0.282393 0.000028 -13.4 2.9 1.0 1234 1643 -0.95 60 775 0.082866 0.002401 0.282354 0.000025 -14.8 1.1 0.9 1319 1674 -0.93 61 819 0.065627 0.001713 0.281999 0.000024 -27.4 -10.2 0.8 1798 1678 -0.95 62 778 0.060447 0.001703 0.282432 0.000025 -12.0 4.3 0.9 1181 1745 -0.95 63 2129 0.019084 0.000527 0.281344 0.000028 -50.5 -3.7 1.0 2633 2975 -0.98 65 776 0.181892 0.005012 0.282140 0.000030 -22.4 -7.8 1.1 1754 1800 -0.85 66 777 0.055295 0.001738 0.282379 0.000027 -13.9 2.3 1.0 1260 1800 -0.95 67 2179 0.026747 0.000692 0.281207 0.000030 -55.3 -7.7 1.1 2829 3265 -0.98 68 768 0.193127 0.004771 0.282366 0.000027 -14.4 0.1 0.9 1391 1808 -0.86 70 775 0.055633 0.001524 0.281995 0.000023 -27.5 -11.2 0.8 1794 1809 -0.95 79 2359 0.095668 0.002043 0.281448 0.000030 -46.8 2.7 1.0 2594 2740 -0.94 80 1966 0.018405 0.000473 0.281409 0.000022 -48.2 -5.0 0.8 2541 2929 -0.99 81 2444 0.027353 0.000719 0.281183 0.000023 -56.2 -2.6 0.8 2863 3148 -0.98 82 2155 0.014151 0.000423 0.281287 0.000024 -52.5 -5.0 0.8 2702 3076 -0.99 83 2036 0.038675 0.000924 0.281141 0.000022 -57.7 -13.6 0.8 2936 3525 -0.97 85 2574 0.051989 0.001255 0.281031 0.000030 -61.6 -6.1 1.1 3111 3466 -0.96 87 2498 0.026692 0.000816 0.281296 0.000022 -52.2 2.4 0.8 2718 2867 -0.98 88 811 0.161497 0.004032 0.281970 0.000030 -28.4 -12.7 1.1 1961 1886 -0.88 89 2242 0.015048 0.000415 0.281320 0.000022 -51.4 -1.9 0.8 2658 2944 -0.99 93 715 0.067517 0.001980 0.282279 0.000024 -17.4 -2.6 0.8 1410 1905 -0.94 94 736 0.057541 0.001597 0.282381 0.000025 -13.8 1.6 0.9 1252 2021 -0.95 95 818 0.030886 0.001072 0.282313 0.000029 -16.2 1.2 1.0 1329 2107 -0.97 96 1992 0.018463 0.000468 0.281237 0.000021 -54.3 -10.5 0.7 2773 3300 -0.99 97 779 0.081626 0.002245 0.282296 0.000029 -16.8 -0.8 1.0 1397 1371 -0.93 97 797 0.081366 0.002633 0.282469 0.000029 -10.7 5.5 1.0 1158 2186 -0.92 98 840 0.052788 0.001501 0.281752 0.000027 -36.1 -18.4 1.0 2134 2232 -0.95 99 774 0.218394 0.005379 0.281978 0.000029 -28.1 -13.8 1.0 2027 2306 -0.84 100 782 0.100439 0.002769 0.282180 0.000029 -21.0 -5.2 1.0 1587 2370 -0.92 104 744 0.055933 0.001592 0.282270 0.000030 -17.7 -2.1 1.1 1409 2395 -0.95 108 788 0.064820 0.001832 0.282317 0.000026 -16.1 0.3 0.9 1351 2404 -0.94 109 737 0.038962 0.001193 0.282480 0.000024 -10.3 5.3 0.9 1098 2444 -0.96 110 752 0.086209 0.002935 0.282427 0.000029 -12.2 2.9 1.1 1230 2517 -0.91 111 1910 0.060079 0.001492 0.281307 0.000030 -51.8 -11.2 1.0 2750 3277 -0.96 116 791 0.208042 0.006198 0.282101 0.000023 -23.7 -9.6 1.1 1880 2559 -0.81 117 744 0.161311 0.004125 0.282035 0.000029 -26.1 -11.7 1.0 1868 2572 -0.88 118 773 0.106784 0.002604 0.282274 0.000027 -17.6 -1.9 1.1 1443 2812 -0.92 注:锆石的εHf(t)值用各自的206Pb/238Pb(介于707~892Ma之间的锆石)或207Pb/206Pb(介于1910~2655Ma之间的锆石)年龄计算 -
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