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  中国地质 2019, Vol. 46 Issue (6): 1356-1371  
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吴建亮, 尹显科, 王波, 刘文, 雷传扬, 李威, 张伟. 2019. 藏北阿翁错地区中基性脉岩年代学、地球化学特征及其板内伸展构造作用[J]. 中国地质, 46(6): 1356-1371.  
Wu Jianliang, Yin Xianke, Wang Bo, Liu Wen, Lei Chuanyang, Li Wei, Zhang Wei. 2019. Geochemistry and geochronotry of intermediate-basic dikes in Awengcuo area of north Tibet and intraplate extensional structures[J]. Geology in China, 46(6): 1356-1371. (in Chinese with English abstract).  

藏北阿翁错地区中基性脉岩年代学、地球化学特征及其板内伸展构造作用
吴建亮, 尹显科, 王波, 刘文, 雷传扬, 李威, 张伟    
四川省地质调查院 稀有稀土战略资源评价与利用四川省重点实验室, 四川 成都 610081
摘要:班公湖—怒江缝合带在中生代的构造岩浆演化是青藏高原基础地质研究的热点之一。在该缝合带南部的北冈底斯地区发育有大量的中生代火山岩及相关岩浆岩,其岩石成因与成岩地球动力学背景长期以来存在较大的争议。本文以班公湖—怒江缝合带西段阿翁错地区的中基性脉岩为研究对象,对该地区广泛发育的脉岩的形成时代、岩石成因、构造环境以及动力学背景进行了探讨。研究区辉绿岩脉以低硅(SiO2=50.03%~51.13%)、低铝(Al2O3=15.52%~16.03%、低钛(TiO2=1.22%~1.31%)、富镁(MgO=9.19%~10.37%)、富钠(Na2O=3.10%~3.58%,Na2O/K2O=1.73~1.87)为特征;闪长岩脉以相对高硅(SiO2=55.58%~56.22%)、低镁(MgO=4.69%~4.64%)、低钛(TiO2=1.01%~1.06%)、高铝(Al2O3=17.74%~18.72%)、富钠(Na2O=1.55%~5.03%,Na2O/K2O=1.81~3.61)为特征,属于钠质低钾钙碱性系列岩石。二者轻重稀土元素分馏明显,均表现为右倾型,具弱的Eu负异常,重稀土元素总体上变化不大。微量元素上均表现出以富集Rb、U等大离子亲石元素和轻稀土(LREE)元素,亏损Nb、Ta、Ti高场强元素(HFSE)为特征。年代学分析结果显示研究区闪长岩脉LA-ICP-MS锆石U-Pb年龄为(99.2±1.2)Ma,辉绿岩脉LA-ICP-MS锆石U-Pb年龄为(108.4±2.9)Ma,属于早白垩世晚期向晚白垩世过渡期间,其岩浆源区遭受了一定程度的地壳物质的混染,后经历了不同程度的铁镁矿物和斜长石的结晶分离作用。构造环境分析显示研究区中基性岩脉形成于伸展构造环境下,其产状受区域应力场控制,其动力学背景可能与班公湖—怒江特提斯洋南向俯冲消减过程中板片断离导致的软流圈上涌,诱发岛弧和岛弧后方的地幔岩浆发生补充性对流循环而形成的伸展构造背景有关。表明研究区至少在99.2 Ma时,班公湖—怒江特提斯洋俯冲消减已经完成,由早期构造挤压环境转向晚期构造伸展环境。
关键词中基性岩脉    伸展构造    班-怒缝合带    地质调查工程    阿翁错    西藏    
中图分类号:P597+.3            文献标志码:A             文章编号:1000-3657(2019)06-1356-16
Geochemistry and geochronotry of intermediate-basic dikes in Awengcuo area of north Tibet and intraplate extensional structures
WU Jianliang, YIN Xianke, WANG Bo, LIU Wen, LEI Chuanyang, LI Wei, ZHANG Wei    
Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province, Sichuan Geological Survey, Chengdu 610081 Sichuan, China
Abstract: The Bangong Co-Nujiang suture zone and its tectonic-magmatic evolution constitute one of the hottest scientific problems related to fundamental geology of the Tibetan Plateau. The Mesozoic volcanic-intrusive rocks are widely distributed in the north Gangdese belt,which is also located in southern Bangong Co-Nujiang suture zone. The petrogenesis and geodynamic setting of those rocks remain controversial. In this paper,the authors reported the newly found intermediate-basic dikes in Awengcuo area which is located at the west segment of Bangong Co-Nujiang suture zone so as to explore these problems,and detailed LA-ICP-MS zircon U-Pb dating geochronological and element geochemical studies were carried out for the intermediatebasic dikes. The basic dikes exhibit SiO2 content of 50.03%-51.13%,Al2O3 content of 15.52%-16.03% with TiO2 content of 1.22%-1.31%,MgO content of 6.12%-8.51%,Na2O content of 3.10%-3.58%,with Na2O/K2O ratio of 1.73-1.87. The diorite dikes have values of SiO2 (55.58%-56.22%),MgO (4.69%-4.64%),Al2O3 (1.01%-1.06%) with TiO2 (1.01%-1.06%),Na2O (1.55%-5.03%),and Na2O/K2O (1.81-3.61). The diabase veins belong to alkaline basalt series and the diorites are subalkaline-series rocks. All of their light rare elements are concentrated evidently and heavy rare elements are deficient with a right dip distribution mode of REE,slightly negative Eu anomalies and content of HREE. On primitive mantle-normalized trace element diagrams,the intermediate-basic dikes display different degrees of enrichment of LIFEs (e.g.,Rb,U),relative depletion of HFSE (Nb,Ta,Ti). The zircon U-Pb dating of diorite-dyke yielded a weighted average age of (99.2±1.2)Ma,and the basic-dyke U-Pb dating yielded an age of (108.4±2.9)Ma,indicating that the diorite-dykes in Awengcuo area were formed at the late stage of early Cretaceous. The magma source region was mainly influenced by the crustal material and underwent different degrees of fractionation crystallization of mafic minerals and plagioclases when uplifting from the high magmatic chamber. The intermediate-basic dikes were generated in a contineral intraplate setting,as shown by analyzing tectonic setting,and its attitudes were controlled by the regional tectonic stress field. The tectonic dynamics background of the dikes formed in slab break-off caused asthenosphere upwelling extension during the Bangong Co-Nujiang Tethyan Ocean's southward subduction at the late stage of early Cretaceous,indicating that the Bangong Co-Nujiang Tethyan Ocean finished the subduction at 99.2 Ma at least,and the regional stress state turned from collision to intraplate extension at the late stage.
Key words: Intermediate-basic dikes    intraplate extensional structures    Bangong Co-Nujiang suture zone    geological survey engineering    Awengcuo area    Tibet    

1 引言

近年来,对沿缝合带、造山带分布地层及大规模花岗岩体内部的岩脉(群)研究和认识逐渐加深(Halls,1982李献华等,1997Dini et al., 2002罗照华等, 2006, 2008Allen,2010;),尤其造山带中发育的(中)基性岩脉通常被认为是在伸展背景下由地幔玄武质岩浆和受后期分异作用或地壳混染作用影响的岩浆充填区域性张性裂隙空间侵位而成,包含了丰富的幔源信息,常被作为大陆和大洋伸展构造作用的代表(Hoek and Seitz, 1995;董传万等, 2006),是造山带区域挤压背景向伸展背景转换的构造岩浆标志和产物(Dini et al., 2002;罗照华等, 2006; Allen, 2010),也是重要构造转换时间衡量的标尺(Yang et al., 2004;罗照华等, 2008),称为造山后脉岩组合(罗照华等, 2006),其空间展布对恢复古构造应力场亦有重要指示意义(Ancochea et al., 2003; Poland et al., 2004;江军华等, 2011)。此外,脉岩也可以反映岩浆源区的物质组成和演化历史(Scarrow et al. 1998; Xu et al., 2007; Mayborn et al., 2008)。

班公湖—怒江缝合带西起班公湖,向东经改则、尼玛、丁青等地,后沿怒江进入滇西,在西藏境内长达2800 km;北接羌南—保山地块,南与冈底斯造山带相邻,是青藏高原众多缝合带中的重要组成部分(潘桂堂等, 2006;耿全如等,2011)。在班—怒缝合带南侧,发育面积广阔的冈底斯复合造山带,也是一条巨型的构造-岩浆岩带(潘桂堂等, 2006)。研究区内中基性脉岩就位于北冈底斯复合造山带西部,昂龙岗日—盐湖—班戈火山岩浆弧内,向北与班公湖—怒江缝合带相接,其中生代构造演化与北部班公湖-怒江特提斯洋的南向俯冲具有密切的成因联系(朱弟成, 2006; Zhu et al., 2009, 2010;康志强, 2010; Sui et al., 2013)。限于班公湖—怒江缝合带西段自身复杂的构造演化历史和藏北地区恶劣的自然环境以及极其艰苦的野外工作条件,使得有关缝合带及其周缘地区有许多关键基础地质问题存在诸多争议,而班公湖—怒江特提斯洋在中生代的汇聚消减及时空过程则更是其中争论的焦点之一。研究区中基性造山后脉岩群为研究班—怒特提斯洋中生代南向俯冲造山过程后伸展过程的研究和时代限定提供了较好的素材,同时该地区的中基性岩脉的研究工作还十分薄弱。故本次工作拟通过对班—怒缝合带以南的阿翁错地区发育的北西向基性辉绿岩脉和中性闪长岩脉的年代学和岩石地球化学的研究,分析其岩石成因和构造环境,为缝合带西段班—怒特提斯洋在中生代的构造演化研究提供了新的依据和研究资料。

2 地质背景及岩石学特征

研究区位于班公湖—怒江缝合带西段(图 1a)南侧昂龙岗日—盐湖—班戈火山岩浆弧内部。区域内地层主要出露侏罗系、白垩系、古近系以及第四系沉积物,其中以侏罗—白垩系沙木罗组(J3- K1s)、去申拉组(K1q)以及古近系牛堡组(E1-2n)等地层分布面积最广(图 1b)。区内断裂构造发育,主要为北西向和东西向,次为北东向构造,构成了区内的基本构造格架。区内大规模岩浆活动以白垩纪去申拉组中基性火山岩和酸性花岗岩为主,如北西向展布的阿翁错复式花岗岩体。

图 1 研究区大地构造位置(a,据Zhang et al., 2004)和区域地质简图(b) Fig. 1 Sketch map showing tectonic setting (a, after Zhang et al., 2004) and regional simplified geological map (b) of the study area

研究区内辉绿岩脉(图 2 a)和闪长岩脉(图 2 b)主要发育于阿翁错复式花岗岩体((109.1±1.0) Ma;雷传扬等,2019)和沙木罗组内部,与围岩呈侵入接触关系。围岩蚀变基本不发育或发育程度很弱。单条岩脉地表出露宽度大多在0.5~2 m,走向上延伸从十几米到数百米(图 1b)。脉岩间的距离各不相同,从数十至数千米之间不等。其中发育规模最大,数量最多的脉岩类型为闪长岩脉,次为辉绿岩脉。区内闪长岩脉和辉绿岩脉主体走向北西-南东向,次为北西西向,倾向上北东和南西者均有可见,倾角陡立。空间上二者均呈近于平行状,未见两者有穿插交切产出(图 1b),其走向与研究区及邻近区域主体构造线方位相近,其规模性产出与区域性张性断裂裂隙有关。

图 2 辉绿岩脉和闪长岩脉野外产状 a—辉绿岩脉侵入到沙木罗组板岩;b—闪长岩脉侵入到早白垩世花岗岩 Fig. 2 Representative photographs of diabase and diorite dikes from Awengcuo area, north Tibet a−Diabase dike intruded into slate of Shamuluo Formation; b−Diorite dike intruded into early Cretaceous granite

研究区中基性岩脉岩性为辉绿岩和闪长岩,镜下观察辉绿岩主要由由基性斜长石、单斜辉石、角闪石、绿帘石及副矿物磁铁矿等组成。基性斜长石含量约55%,单斜辉石含量为30%,角闪石为10%,绿帘石约4%,磁铁矿为1%。基性斜长石呈板条状,自形程度较好,粒径1~1.5 mm。单斜辉石呈他形粒状,充填在自形较好斜长石形成的空隙中,具辉石式解理,粒径达2~4 mm。角闪石呈柱状,粒径0.5~ 1 mm。闪长岩主要由角闪石和斜长石组成,另见少量的黑云母、石英及不透明矿物。岩石粒度较细,粒径多在0.5~1 mm。副矿物见磷灰石。地表脉岩已经发生不同程度的次生蚀变,如斜长石晶体蚀变为绿帘石和绿泥石等。

3 样品制备及分析方法

本次研究用于锆石U−Pb测年、主量、微量和稀土元素分析的样品主要采于西藏阿里地区日土县热帮乡阿翁错地区地表辉绿岩和闪长岩脉露头。样品破碎及锆石分选在河北省区域地质矿产调查研究所实验室完成。锆石阴极发光照相和LA−ICP −MS分析在武汉上谱科技有限公司测试完成。CL照相在JEOL−JXA−8100电子探针仪器上拍摄,锆石U−Pb同位素和微量元素含量分析采用Micro Las公司的GeoLas2005准分子激光剥蚀系统在美国Agilent公司的Agilent7500a型ICP-MS仪器上进行。锆石年龄以国际标准锆石91500作为外标,以GJ−1作为内标样品。激光束斑直径32 μm,分析方法见文献(Liu et al., 2008, 2010)。单个数据点误差为1σ,样品年龄加权平均值置信度为2 σ,置信水平为95%。

主量和微量元素分析在澳实分析检测集团-广州澳实矿物实验室进行。主量元素由荷兰生产的Axios仪器利用荧光光谱分析仪(XRF)测试分析,FeO含量由滴定法测试获得;微量和稀土元素分析采用电感耦合等离子体质谱仪(ICP−MS)分析。主量元素分析偏差优于5%,微量元素分析偏差优于10%。

4 年代学特征

本次工作对阿翁错地区辉绿岩脉和闪长岩脉分别采集了1件样品进行锆石U−Pb年代学分析。分析结果见表 1表 2。分选出来的锆石晶体形态及大小较为一致,多呈柱状自形晶,环带结构发育(图 3),属于岩浆成因锆石。各锆石具有较高的Th/ U比值(多在0.4以上),也显示出岩浆锆石的特征(Hoskin and Blcak, 2000)。对样品的锆石进行分析并经过数据处理。剔除不谐和年龄点外,辉绿岩脉有16个测点均分布于U−Pb谐和线上或其附近,具有较好的群落性,其206Pb/238U年龄加权平均值分别为(108.4±2.9) Ma;闪长岩脉有18个测点均分布于U−Pb谐和线上或其附近,群落性较好,其206Pb/238U年龄加权平均值分别为(99.2±1.2) Ma(图 3),该年龄代表了脉岩的侵位年龄,为早白垩世晚期及向晚白垩世过渡期间。

表 1 阿翁错地区闪长岩脉样品锆石LA-ICP-MS U-Pb分析结果 Table 1 LA-ICP-MS zircon U-Th-Pb analyses of of diorite dike, Awengcuo area, north Tibet
表 2 阿翁错地区辉绿岩脉样品锆石LA-ICP-MS U-Pb分析结果 Table 2 LA-ICP-MS zircon U-Th-Pb analyses of diabase dike, Awengcuo area, north Tibet
图 3 辉绿岩脉和闪长岩脉锆石阴极发光图像和U−Pb谐和图解 Fig. 3 CL images and U−Pb concordia diagrams of zircons of diabase and diorite dikes in Awengcuo aera
5 地球化学特征 5.1 主量元素特征

本文野外地质调查工作的基础上,对区内北西向辉绿岩脉和闪长岩脉系统采集了地球化学样品,分析结果见表 3。研究区辉绿岩脉样品SiO2含量变化在50.03%~51.13%,均值50.60%, 属基性岩。其(Na2O+K2O)含量在4.76%~5.50%,所有样品Na2O> K2O,Na2O/K2O比值为1.73~1.87;Al2O3含量为15.52%~16.03%,均值15.80%;Fe2O3含量变化范围2.45% ~2.93%,FeO含量变化范围5.79% ~6.19%;MgO含量较高,变化在9.19% ~10.37%,平均为9.54%;P2O5含量较低(0.41%~0.45%);TiO2含量变化在1.22%~1.31%,平均为1.28%,远低于洋岛拉斑玄武岩(2.63%)(Wilson, 1989),亦低于典型板内拉斑玄武岩(2.23%)和板内碱性玄武岩(2.9%) (Wilson, 1989),这可能是由于地壳岩石和地壳岩石的部分熔融体通常具有很低的TiO2含量(Wilson, 1989),而后的地壳混染作用也可能进一步使得基性岩浆的Ti含量下降(夏林圻等, 2007)。

表 3 阿翁错地区中基性脉岩主量元素(%)和微量元素(10-6)组成 Table 3 Major elements (%), trace elements and REE composition (10-6) of the intermediate-basic dikes, Awengcuo area, north Tibet

研究区闪长岩脉样品SiO2含量变化在55.53%~ 56.22%,平均为55.95%,属中性岩,(Na2O+K2O)含量在5.46%~5.77%,所有样品Na2O>K2O,Na2O/K2O比值为2.14~2.45;Al2O3含量较高,变化在17.74%~ 18.01%范围内,平均为17.88%;TFe2O3含量变化范围为7.72%~8.01%,Fe2O3含量变化范围为1.65%~ 3.09%,FeO含量变化范围为4.14%~5.17%;MgO含量较高,变化在4.09%~4.64%,平均为4.37%;P2O5含量较低(0.46%~0.48%);TiO2含量变化在1.00%~1.06%,平均为1.04%。

在Zr/TiO2−Nb/Y图解(图 4a)上,辉绿岩脉样品投影全部落入碱性玄武岩区域内,闪长岩脉位于安山岩区域边缘,在SiO2 −全碱图解(图 4b)上辉绿岩脉样品均在Irvine分界线上方,而闪长岩脉位于曲线下方,故前者属于碱性火成岩系列,后者属于亚碱性火成岩系列。

图 4 藏北阿翁错地区Nb/Y − Zr/TiO2图解(a, 据Winchester and Floyd, 1977)和SiO2−Na2O+K2O岩石系列划分图解(b, 据Irvine and Baragar, 1971) Fig. 4 Zr/TiO2−Nb/Y diagram (a, after Winchester and Floyd, 1977) and SiO2−Na2O+K2O diagram (b, after Irvine and Barager, 1971) of intermediate-basic dikes from Awengcuo area, north Tibet
5.2 微量元素特征

研究区辉绿岩脉样品的稀土总量(∑REE)总体变化于142.4×10-6~174.8×10-6,∑REE较高,轻稀土元素总量(∑LREE)在130.4×10-6~160.5×10-6,远高于重稀土元素总量(∑HREE)11.95×10-6~14.44× 10-6。LREE/HREE=10.7~11.5,LREE明显相对富集。(La/Yb)N=12.7~13.9,(Gd/Yb)N=2.01~2.13,(La/ Sm)N=3.99~4.27,轻重稀土元素分异明显,反映其源区可能有石榴子石的残留(Wilson, 1993)。闪长岩脉样品的∑REE变化于152.8×10-6~164.4×10-6,总量较高,∑LREE为138.6×10-6~149.2×10-6,亦远高于∑HREE 14.20×10-6~15.17×10-6。LREE/HREE= 9.62~9.84,LREE亦相对富集。(La/Yb)N=10.8~11.6,(Gd/Yb)N=1.74~1.93,(La/Sm)N=4.07~4.27,轻重稀土元素分异明显。

在球粒陨石标准化稀土元素配分图解(图 5a)上,辉绿岩脉和闪长岩脉均表现为右倾型,反映其源区岩浆形成过程中部分熔融程度较低或具有较高的分离结晶程度;辉绿岩脉δEu=0.87~0.93,闪长岩脉δEu=0.87~0.92,均显示出弱的Eu负异常。由于岩浆作用中斜长石中Ca2+离子半径与Eu2+,Eu3+相近且电价相同,表现出相似的晶体化学性质(赖绍聪等, 2003),故Eu2+容易替代斜长石中Ca的位置,因此基性岩浆中Eu负异常可能与斜长石的分离结晶作用有关。

图 5 研究区中基性脉岩稀土元素球粒陨石标准化配分图(a)和微量元素原始地幔标准化蛛网图(b) (球粒陨石、原始地幔、N-MORB、E-MORB以及OIB数据均引自Sun and McDonough, 1989) Fig. 5 Chondrite-normalized REE patterns and primitive mantle-normalized trace element patterns of intermediate-basic dikes (after Sum and McDonough, 1989)

从微量元素原始地幔标准化图(图 5b)上来看,区内辉绿岩脉和闪长岩脉的分布模式相似,均表现出富集Rb、U等大离子亲石元素和亲稀土LREE元素,亏损Nb、Ta、Ti高场强元素,分异明显的特征,这可能是亏损地幔岩浆源区受到了一定程度的壳源物质混染(秦社彩,2010),显示出类似于受地壳混染的板内玄武岩和岛弧火山岩的地球化学特征。总体而言,研究区中-基性脉岩的稀土和微量元素分布曲线非常相似,轻重稀土元素分馏程度明显,整体表现为右倾模式,重稀土元素总体上变化不大,二者具有相似的地球化学特征。其明显富集轻稀土元素和Rb、U等大离子亲石元素,相对亏损Nb、Ta、Ti高场强元素,指示其可能与地壳物质的加入有关。各样品发育微弱的Eu负异常,暗示其可能经历了轻微程度的斜长石分离结晶作用。

6 讨论 6.1 地壳混染作用

在原始地幔标准化蛛网图上,研究区中基性岩脉Nb、Ta均表现出不同程度的相对亏损(图 5),主量元素TiO2含量较低(平均为1.27%),表明其岩石成因可能与地壳物质的混合有关(Wilson, 1993;夏林圻等, 2007)。研究区辉绿岩和闪长岩脉的La/Nb (辉绿岩脉La/Nb=2.20~2.36,均值2.28;闪长岩脉La/Nb=2.60~2.66,均值2.62)、Th/Nb(辉绿岩脉Th/ Nb =0.33~0.38,均值0.35;闪长岩脉Th/Nb=0.28~ 0.30,均值0.29)、以及Ba/Nb(辉绿岩脉Ba/Nb= 21.05~25.84,均值24.17;闪长岩脉Ba/Nb=30.94~ 34.96,均值32.51)都比较高,远高于原始地幔(La/ Nb=0.94;Th/Nb =0.117;Ba/Nb =9.0) (Weaver, 1991; Hart and Hauri, 1992),而与大陆地壳(La/Nb=25.0;Th/Nb =0.44;Ba/Nb =54.0)(Weaver, 1991; Hart and Hauri, 1992)较为接近,在Th/Ta-La/Yb图解上(图 6)位于富集Ⅰ型地幔和上地壳中间位置,也表明辉绿岩和闪长岩脉受到了一定程度的地壳混染。一般而言,原始OIB岩浆的Zr/Nb值较低,通常在2~4 (Weaver, 1991),远低于大陆地壳(Rudnick and Fountain, 1995; Jung and Jung, 2006)。研究区辉绿岩脉和闪长岩脉具有较大的Zr/Nb比值(辉绿岩脉Zr/Nb =8.76~9.40;闪长岩脉Zr/Nb =13.08~13.33)。此外,研究区中基性岩脉Nb/U平均值分别为10.86× 10-6 (9.94×10-6~12.20×10-6)和7.36×10-6 (3.74×10-6~ 9.93×10-6),亦低于MORB和OIB(37±10)×10-6(郑永飞, 1999),再加上两者La/Nb值较高和明显富集大离子亲石元素的特征,进一步证明了研究区辉绿岩脉和闪长岩脉均遭受了不同程度的大陆地壳混染。

图 6 研究区脉岩La/Yb-Th/Ta图解(底图据Condie, 1997) Fig. 6 La/Yb-Th/Ta diagram of dikes from Awengcuo area (base map after Condie, 1997)

中基性岩浆发生地壳物质的混染一般为两种形式:即岩浆在上升侵位过程中与地壳物质发生混染和侵位之前岩浆源区发生的地壳物质或流体交代混染(谢桂青等, 2002)。考虑到区内近平行排列且宽度不大的中基性脉岩是在伸展构造环境下形成的,岩浆上升速率很快,在地壳中滞留时间短,上升过程中与地壳发生显著程度混染的可能性不大(罗照华等, 2006);而且笔者在野外观察到的岩脉发育明显的冷凝边和烘烤边,与围岩接触界线截然,说明岩浆在侵位后经历的是快速冷却和固化的过程,其在上升过程中与地壳物质发生混染的可能性较小,说明基性岩浆在上升侵位过程中没有显著的地壳物质混染,其地壳混染作用可能主要发生在岩浆源区,代表了研究区在洋陆转换过程中发生过壳幔相互作用。

6.2 结晶分离作用

岩浆岩形成过程中发生的结晶分离作用是岩浆演化过程中极为重要的过程之一。对于中基性岩浆来讲,富铁富镁矿物的结晶分离作用十分常见,常用岩石的Mg、Cr、Ni等元素的含量加以判别。已有研究显示,直接来源于原始地幔的岩浆岩具有很高的MgO、Cr、Ni的含量(Cr=300×10-6~500× 10-6,Ni>300 × 10-6,Mg# =68~76)(Frey et al., 1978; Hart and Davis, 1978)。在经历了不同程度的橄榄石、辉石等铁镁矿物的结晶分离作用后,其MgO、Cr、Ni含量则明显降低(Jung and Masberg, 1998; Jung and Jung, 2006; Wilson, 1989)。研究区辉绿岩脉的Cr= 540×10-6~560×10-6,Mg#=66.0~68.7,表明其未经历明显的镁铁矿物的结晶分离作用;而研究区内闪长岩脉Cr=45×10-6~65×10-6,Ni=32×10-6~47× 10-6,Mg#=51.1~53.4,表明其经历了橄榄石、辉石等矿物的结晶分离(Righter, 2000),属于原始岩浆演化的产物。研究区两类岩脉均据弱的Eu负异常,则暗示了岩浆演化过程中经历了有限的斜长石结晶分异作用。对于基性脉岩来讲,由于其岩浆上升速率较快,在地壳中滞留的时间很短,其矿物的结晶分离作用普遍发生在岩浆源区部分熔融以后上升至岩浆房或在岩浆房中停留的过程。

6.3 构造环境分析

目前对于中基性岩石的构造环境的判别多利用不活动元素的协变关系,因为高场强元素如Nb、Ta、Zr、Hf等在蚀变和变质作用过程中具有良好的稳定性,是研究岩石成因和岩浆源区属性的良好示踪剂(任军虎等, 2010;张昕等, 2018)。已有研究表明,一般板内玄武岩Zr、Hf元素含量分别在149× 10-6~213×10-6和3.44×10-6~6.36×10-6;火山弧玄武岩的Zr、Hf元素平均含量分别为40×10-6、1.17×10-6,而MORB型玄武岩Zr、Hf平均含量分别为90×10-6~ 96×10-6、2.4×10-6~2.6×10-6(Pearce, 1982)。夏林圻等(2007)指出,大陆玄武岩和岛弧玄武岩除发育明显Nb-Ta负异常和弱Ti负异常的特征外,岛弧玄武岩总体上以低的Zr含量(小于130×10-6)和Zr/Y比值(小于4)而与大陆玄武岩,无论是否遭受地壳和岩石圈混染,都具有较高的Zr含量(大于70×10-6)和Zr/Y比值(大于3)相区别。研究区辉绿岩脉样品的Zr、Hf元素含量分别为125 × 10-6~144 × 10-6(均值138.5×10-6)、3.0×10-6~3.5×10-6(均值3.3×10-6),Zr/Y比值为7.2~7.6;闪长岩脉样品的Zr、Hf元素含量分别为168×10-6~178×10-6(均值173.2×10-6)、3.6×10-6~3.9×10-6(均值3.3×10-6),Zr/Y比值为8.1~8.4,可见二者与板内玄武岩地球化学特征相近。样品中辉绿岩脉Nb、Ta元素含量为13.3×10-6~16.1×10-6(均值15.2×10-6)、0.70×10-6~0.90×10-6(均值0.82×10-6),闪长岩脉Nb、Ta元素含量为12.7×10-6~13.6×10-6(平均13.1×10-6)、0.80×10-6,也与板内玄武岩和碱性玄武岩的Nb、Ta含量(分别为13×10-6~84×10-6、0.73× 10-6~5.9×10-6)相近,远高于岛弧拉斑玄武岩和钙碱性玄武岩的Nb、Ta含量(分别为1.7×10-6~2.7×10-6、0.1×10-6~0.18×10-6),以及洋中脊玄武岩MORB的Nb、Ta含量(w(Nb) =4.6 × 10-6w(Ta) =0.29 × 10-6) (Pearce, 1982)。整体上来看,区内辉绿岩脉和闪长岩脉的特征元素含量更接近于板内玄武岩。此外,区内辉绿岩脉的Hf/Th比值(0.59~0.67),闪长岩脉的Hf/Th比值(0.97~1.03),也位于板内玄武岩(小于8) (Condie, 1989)的变化范围之内。

在2Nb-Zr/4-Y(图 7a)中,6件辉绿岩脉和5件闪长岩样品均位于板内碱性玄武岩和板内拉斑玄武岩区;利用浓度不受地壳混染影响的Zr、Y作为判别因子(夏林圻等, 2007)的Zr-Zr/Y图解(图 7b)判别,各样品也全部落入板内玄武岩区域内及附近;在Ta/Hf-Th/Hf图解(图 7c)中,样品点全部落入大陆拉张带或初始裂谷玄武岩范围,进一步表明工作区北西向发育的中基性岩脉(群)形成于伸展构造环境。

图 7 藏北阿翁错地区中基性岩脉Nb-Zr-Y(a)、Zr-Zr/Y(b)、Ta/Hf-Th/Hf(c)构造判别图解 a—Nb-Zr-Y图解(据Meschede, 1986);b—Zr-Zr/Y图解(据Pearce, 1982);c—Th/Hf-Ta/Hf图解(据汪云亮等, 2001) Fig. 7 Tectonic discrimination diagrams for intermediate-basic dikes from Awengcuo area, north Tibet a-Nb-Zr-Y diagram (after Meschede, 1986); b-Zr/Y-Zr diagram (after Pearce, 1982); c-Ta/Hf-Th/Hf diagram (after Wang et al., 2001)

基性脉岩及岩墙群在区域应力场中是区域构造节理系统的代表,也是侵位前古应力场的脆性破裂的综合反映(Walker and Eyre, 1995),属于地壳伸展体制下深源岩浆浅部就位的产物,其形成时代可以代表裂解的初始标志,也为造山过程的动力学研究提供了初始约束(Walker and Eyre, 1995;侯贵廷等, 2003)。在研究区西部班公湖地区,康磊等(2012)获得早白垩世晚期红其拉普岩体((107.2± 0.9)Ma)是班怒缝合带后碰撞阶段地壳加厚的产物。李华亮等(2014)报道的甲维花岗闪长岩脉((90.7±1.2)Ma)形成于幔源玄武质岩浆底侵加厚下地壳部分熔融形成,代表了班怒缝合带晚白垩早期的热隆伸展事件。江军华等(2011)也将研究区西部的班公湖地区晚白垩世南北向分布的花岗岩脉和闪长岩脉作为碰撞后伸展作用的开始阶段标志。本文报道的早白垩世—晚白垩世过渡阶段的中基性脉岩时代也是该时代班—怒洋俯冲汇聚过程中由挤压背景转向伸展体制后的深源岩浆浅部就位的产物,这与图 7中所反映的伸展构造环境较为一致,而在研究区周缘的晚白垩世地层(如上白垩统竟柱山组磨拉石建造)也基本未见到挤压变形,其主要构造形迹以正断层和拆离断层为主,这也反映了班怒洋与北冈底斯地块由早白垩世俯冲碰撞向晚白垩世板内构造体制的转换。类似的地质作用和过程也常见于藏南雅江缝合带闭合后拉张条件下形成的中基性脉岩,如藏南江孜—哲古一带基性-中基性岩墙群(江思宏等, 2007)、林周盆地古—始新世闪长玢岩和花岗斑岩(董铭淳等, 2015;岳雅慧等, 2015)以及南木林地区晚白垩世辉绿岩与花岗质脉岩(叶丽娟等, 2015)等。

6.4 地球动力学意义

青藏高原大陆构造演化过程一般可划分为前板块基底形成阶段、板块体制洋陆转换阶段和板内造山成盆等3个阶段(李德威, 2008),而研究区所在区域属于班公湖—怒江蛇绿混杂岩带西段,经历了班公湖—怒江特提斯洋陆演化过程(潘桂棠, 2006;王剑和付修根, 2018)。目前对班公湖—怒江特提斯洋的中生代构造演化尚没有一个统一的认识。目前多数学者根据班—怒蛇绿混杂岩带及部分SSZ型蛇绿岩的研究成果,普遍认为班公湖—怒江特提斯洋盆在晚古生代—中生代即是连续存在的,在中侏罗世洋壳开始俯冲消减,于晚侏罗世—早白垩世闭合(邱瑞照, 2004;王忠恒等, 2005;陈玉禄等, 2006;潘桂棠, 2006;鲍佩生等, 2007;史仁灯, 2007; Fan et al., 2014;李华亮等, 2016)。但近年来研究表明班—怒洋盆可能到早白垩世中晚期才发生闭合(朱弟成, 2006;鲍佩生等, 2007; Zhu et al., 2009, 2010;康志强, 2010; Sui et al., 2013; Fan et al., 2014)。随着洋盆的萎缩和弧陆碰撞的发生,北冈底斯与南羌塘地块最终拼贴到一起,至晚白垩世早期进入到板内构造体制演化阶段(杨绍等, 2018),以沿班公湖—怒江缝合带及两侧近EW向线性分布的晚白垩世竟柱山组磨拉石(底砾岩石英ESR测年为(92.0±9.0) Ma, 古地磁底界年龄约为96 Ma)的出现为标志(李华亮等, 2016),其厚层红色山间磨拉石建造指示研究区发生洋陆转换后的快速隆升和快速剥蚀堆积,标志着班—怒特提斯的洋陆转换已经结束。

如前所述,阿翁错地区辉绿岩脉的形成时间为(108.4±2.9) Ma,闪长岩脉为(99.2±1.2) Ma,属早白垩世晚期向晚白垩世的过渡阶段,时间上略早于区域上竟柱山组底砾岩。它的出现指示班公湖地区由挤压动力转变为拉伸动力,标志着研究区班公湖—怒江特提斯洋已完成洋陆转换,由碰撞挤压进入伸展构造演化阶段,随后发生快速剥蚀形成牛堡组(E1-2n)巨厚层的红色磨拉石建造而进入陆内演化阶段历程。中基性岩脉可作为区域伸展作用的重要标志(Dini et al., 2002;罗照华等, 2006; Allen, 2010),研究区晚白垩世辉绿岩脉和闪长岩脉的发现表明此时该地区发生过一期重要的伸展事件。其形成的区域动力学背景可能与南羌塘地块和北冈底斯地块碰撞有关。在区内及整个缝合带南侧,越来越多的研究学者发现了规模较大的早白垩世火山岩浆活动,这可能与班—怒特提斯洋岩石圈的南向俯冲过程中发生的板片断离(Zhu et al., 2009, 2010, 2015; Sui et al., 2013)有关。Von Blanckenburg and Davis (1995)认为板片断离一般发生在洋盆消失、陆陆碰撞的初始阶段:当陆-陆碰撞作用发生时,高密度大洋岩石圈持续向下俯冲的过程中,低密度大陆岩石圈则受浮力影响不能发生向下的俯冲作用而与大洋岩石圈断离。大洋岩石圈板片断离作用则将导致软流圈上涌(Zhu et al., 2009, 2010, 2015;张亮亮等, 2011)。软流圈上涌过程将诱发岛弧和岛弧后方的地幔楔发生补充性对流循环,从而形成拉张作用力下的伸展构造背景(Taylor and Martinez, 2003),在该作用过程中,地幔部分熔融形成初始的玄武质岩浆上侵于区域性张裂隙中就位形成。这种缝合带地区碰撞后的伸展现象在整个青藏高原特提斯构造域中均有可见。本文的研究表明至少在99.2 Ma时,班公湖—怒江特提斯洋南向俯冲消减已经完成,由早期构造挤压环境转向晚期构造伸展环境,可作为班公湖—怒江特提斯洋中西段在早白垩世末期—晚白垩世早期最终消亡的标志之一。

7 结论

(1) 藏北阿翁错地区闪长岩脉LA-ICP-MS锆石U-Pb年龄为(99.2±1.2) Ma,辉绿岩脉LA-ICPMS锆石U-Pb年龄为(108.4±2.9) Ma。

(2) 阿翁错地区辉绿岩脉属于碱性玄武岩,闪长岩脉属于亚碱性系列岩石。二者轻重稀土元素分馏明显,均表现为右倾型,具弱的Eu负异常,重稀土元素总体上变化不大。微量元素上均表现出以富集Rb、U等大离子亲石元素和轻稀土LREE元素,相对亏损Nb、Ta、Ti高场强元素为特征。其岩浆源区遭受了一定程度的地壳物质的混染,后经历了不同程度的铁镁矿物和斜长石的结晶分离作用。

(3) 阿翁错地区中基性岩脉形成于伸展构造背境下,其动力学背景可能与班公湖—怒江特提斯洋南向俯冲消减有关。表明研究区至少在99.2 Ma时,班公湖—怒江特提斯洋俯冲消减已经完成,由早期构造挤压环境转向晚期构造伸展环境。

致谢: 匿名审稿人提出的宝贵修改意见和建议使得本文质量有了很大的提升,在此特别感谢!

参考文献
Allen C M. 2010. Evolution of a post-batholith dike swarm in central coastal Queensland, Australia:Arc-front to backarc?[J]. Lithos, 51(4): 331-349.
Ancochea E, Brändle J L, Huertas M J, Cubas C.R, Hernan F. 2003. The felsic dikes of La Gomera (Canary Islands):Identification of cone sheet and radial dike swarms[J]. Journal of Volcanology and Geothermal Research, 120(3): 197-206.
Bao Peisheng, Xiao Xuchang, Su Ni, Wang Jun. 2007. Geochemical characterristics and isotopic dating for the Dongcuo Ophiolite Tibet Plateau[J]. Science in China (ser. D), 37(3): 298-307 (in Chinese).
Chen Yulu, Zhang Kuanzhong, Yang Zhimin, Luo Tao. 2006. Discovery of a complete ophiolite section in the Jueweng area, Nagqu County, in the central segment of the Bangong Co-Nujiang junction zone, Qinghai-Tiebet Plateau[J]. Geological Bulletin of China, 25(6): 694-699 (in Chinese with English abstract).
Condie K C. 1997. Sources of Proterozoic mafic dyke swarms:Constraints from Th/Ta and La/Yb ratios[J]. Precambrian Reasearch, 81: 3-14. DOI:10.1016/S0301-9268(96)00020-4
Condie K C. 1989. Geochemical changes in baslts and andesites across theArchean-Proterozoicboundary:Identificationandsignificance[J]. Lithos, 23(1/2): 1-18.
Dini A, Innocenti F, Rocchi S, Tonarini S, Westerman D S. 2002. The magmatic evolution of the late Miocene laccolith-pluton-dyke granitic complex of Elba Island, Italy[J]. Geological Magazine, 139(3): 257-279. DOI:10.1017/S0016756802006556
Dong Chuanwang, Zhang Dengrong, Xu Xisheng. 2006. SHRIMP UPb Dating and Lithigeochemistry of basic-intermediate dike swarms fron Jinjiang, Fujian Province[J]. Acta Petrologica Sinica, 22(6): 1696-1702 (in Chinese with English abstract).
Dong MingChun, Zhao Zhidan, Zhu Dicheng, Liu Dong, Dong Guochen, Mo Xuanxue, Hu Zhaochu, Liu Yongsheng, Zou Zihao. 2015. Geochronology, geochemistry, and petrogenesis of the intermediate and dykes in Linzhou Basin, Southern Tibet[J]. Acta Petrologica Sinica, 31(5): 1268-1284 (in Chinese with English abstract).
Fan J J, Li C, Xue C M, Wang M. 2014. Petrology geochemistry and geochronology of the Zhonggang ocean island northern Tiber:Implications for the evolution of the Bangongco-Nujiang oceanic arm of Neo-tethys[J]. International Geology Review, 56(12): 1504-1520. DOI:10.1080/00206814.2014.947639
Frey F A, Green D H, Roy S D. 1978. Integrated models of basalt petrogenesis:A study of quartz tholeiites to olivine melilitites from South Eastern Australia utilizing geochemical and experimental petrological data[J]. Journal of Petrology, 19(3): 463-513. DOI:10.1093/petrology/19.3.463
Geng Quanru, Pan Guitang, Wang Liquan, Peng Zhiming, Zhang Zhang. 2011. Tethyan evolution and metallogenic geological background of the Bangong Co-Nujiang belt and the Qiangtang massif in Tibet[J]. Geological Bulletin of China, 30(8): 1261-1274 (in Chinese with English abstract).
Halls H C. 1982. The importance and potential of mafic dykes warms in studies of geodynamic processes[J]. Geoscience Canada, 9(3): 145-154.
Hart S R, Davis K E. 1978. Nickel Partitioning between olivine and silicate melt[J]. Earth amd Planetary Science Letters, 40: 203-219. DOI:10.1016/0012-821X(78)90091-2
Hart S R, Hauri E H. 1992. Mantle plumes and entrainment:Isotopic evidence[J]. Science, 256(5056): 517-520. DOI:10.1126/science.256.5056.517
Hoek J D, Seitz H M. 1995. Continental mafic dyke swarms as tectonic indicators:An example from the Vestfold Hills, East Antarctica[J]. Precambrian Research, 75(3/4): 121-139.
Hoskin P W, Black L P. 2000. Metamorphic zircon formation by solid, state recrystallization of protolith igneous zircon[J]. Journal of Metamorphic Geology, 18(4): 423-439.
Hou Guiting, Li Jianghai, Halls H C, Qian Xianglin. 2003. The flow structures and mechanics of Late Precambrian mafic dyke swarms in North China Craton[J]. Acta Geologica Sinica, 77(2): 210-215 (in Chinese with English abstract).
Irvine T N, Baragar W R A. 1971. A guide to the chemical classification of the common volcanic rocks[J]. Canadian Journal of Earth Sciences, 8(5): 523-548. DOI:10.1139/e71-055
Jiang Junhua, Wang Ruijiang, Qu Xiaoming. 2011. Crustal extension of the Bangong Lake Arc Zone, western Tibetan Plateau, after the closure of the Tethys Oceanic basin[J]. Earth Science-Journal of China University of Geoscience, 36(6): 1021-1032 (in Chinese with English abstract).
Jiang Sihong, Nie Fengjun, Hu Peng, Liu Yan, Lai Xinrong. 2007. Geochemical characteritics of the mafic dyke swarms in South Tibet[J]. Acta Geologica Sinica, 81(1): 60-70 (in Chinese).
Jiang Y H, Jiang S Y, Zhao K D, Ling Hongfei. 2006. Petrogenesis of Late Jurassic Qianlishan granites and mafic dykes, Southeast China:Implications for a back-arc extension setting[J]. Geological Magazine, 143(4): 457-474. DOI:10.1017/S0016756805001652
Jung C, Jung S, Hoffer E. 2006. Petrogenesis of Tertiary mafic alkaline magmas in the Hocheifel, Germany[J]. Journal of Petrology, 47(8): 1637-1671. DOI:10.1093/petrology/egl023
Jung S, Masberg P. 1998. Major- and trace-element systematics and isotope geochemistry of Cenozoic mafic volcanic rocks from the Vogelsberg (central Germany):Constraints on the origin of continental alkaline and tholeiitic basalts and their mantle sources[J]. Journal of Volcanology and Geothermal Research, 86(1): 151-177.
Kang Lei, Xiao Peixi, Gao Xiaofeng, Zhu Haiping, Xi Rengang, Guo Lei, Dong Zengchan. 2012. The age and origin of the Kongjirap Pluton in Northwestern Tibetan Plateau and its tectonic significance[J]. Acta Geologica Sinica, 86(7): 1063-1076 (in Chinese with English abstract).
Kang Zhiqiang, Xu Jifeng, Wang Baodi, Chen Jianlin. 2010. Qushenla Formation volcanic rocks in north Lhasa block:Products of Bangong Co-Nujiang Tethy's southward subduction[J]. Acta Petrologica Sinica, 26(10): 3106-3116 (in Chinese with English abstract).
Lai Shaocong, Liu Chiyang, Yi Haisheng, O'Reilly S Y, Zhang Ming. 2003. The In situ La-ICP-MS analysis and trace element features for the feldspars form Cenozoic trachyandesite in North Qiangtang, Tibetan Plateau[J]. Chinese Journal of Geology, 38(4): 539-545 (in Chinese with English abstract).
Lei Chuanyang, Wu Jianliang, Yin Xianke, Liu Wen, Wang Bo, Li Wei, Yuan Huayun, Zhang Wei, Yin Tao, Pei Yalun. 2019. Geochronology, geochemistry and geodynamic significance of Awengcuo composite pluton and its dark microgranular enclaves in the north of Tibet[J]. Geological Bulletin of China, 38(4): 494-508 (in Chinese with English abstract).
Li Dewei. 2008. Three-stage tectonic evolution and metallogenic evolution in the Qinghai-Tibet Plateau and its adjacent area[J]. Earth Science-Journal of China University of Geosciences, 33(6): 723-742 (in Chinese with English abstract). DOI:10.3799/dqkx.2008.089
Li Hualiang, Gao Cheng, Li Zhenghan, Zhang Zhang, Peng Zhimin, Guan Junlei. 2016. Age and tectonic significance of Jingzhushan Formation in Bangong Lake Area, Tibet[J]. Geotectonica et Metallogenia, 40(4): 663-673 (in Chinese with English abstract).
Li Xianhua, Hu Ruizhong, Rao Bing. 1997. Geochronology and geochemistry of Cretaceous mafic dikes from northern Guangdong, SE China[J]. Geochmica, 26(2): 14-31 (in Chinese with English abstract).
Liu Y S, Hu Z C, Cao S, Günther D, Xu J, Gao C G, Chen H H. 2008. In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[J]. Chemical Geology, 257(1/2): 34-43 (in Chinese with English abstract).
Liu Y S, Hu Z C, Zong K Q, Gao C G, Xu J, Chen H H. 2010. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS[J]. Chinese Science Bulletin, 55(15): 1535-1546. DOI:10.1007/s11434-010-3052-4
Luo Zhaohua, Lu Xinxiang, Wang Bingzhang. 2008. Post-orogenic dike complexes and implications for metallogenesis[J]. Earth Science Frontiers, 15(4): 1-12 (in Chinese with English abstract). DOI:10.1016/S1872-5791(08)60034-2
Luo Zhaohua, Wei Yang, Xin Houtian, Zhan Huaming, Ke Shan. 2006. Petrogenesis of the post-orgenic dike complex-Constraints to Lithosphere delamination[J]. Acta Petrologica Sinica, 22(6): 1672-1684 (in Chinese with English abstract).
Mayborn K R, Lesher C E, Connelly J N. 2008. Geochemical constraints on the late-stage evolution of basaltic magma as revealed by composite dikes within the Kangamiut dike swarm, West Greenland[J]. Lithos, 104(1/4): 428-438.
Meschede M. 1986. A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram[J]. Chemical Geology, 56(3): 207-218.
Pan Guitang, Mo Xuanxue, Hou Zengqian, Zhu Dicheng, Wang Liquan, Li Guangming, Zhao Zhidan, Geng Quanru, Liao Zhongli. 2006. Spatial-temporal framework of the Gangdese orogenic belt and its evolution[J]. Acta Petrologica Sinica, 22(03): 521-533 (in Chinese with English abstract).
Pearce J A. 1982. Trace element characteristics of lavas from destructive plate boundaries[J]. Andesites, 8: 525-548.
Poland M P, Fink J H, Tauxe L. 2004. Patterns of magma flow in segmented silicic dikes at Summer Coon volcano, Colorado:AMS and thin section analysis[J]. Earth and Planetary Science Letters, 219(1): 155-169.
Qiu Ruizhao, Zhou Su, Deng Jinfu, Li Jinfa, Xiao Qinghui, Cai Zhiying. 2004. Dating of grabbro in the Shemalagou ophiolite in the western segment of the bangong Co-Nujiang ophiolite belt, Tibet-with a discussion of the age of the banggong Co-Nujiang ophiolite belt[J]. Geology in China, 31(3): 262-268 (in Chinese with English abstract).
Ren Junhu, Liu Yiqun, Zhou Dingwu, Feng Qiao, Zhang Kun, Dong Zhongliang, Qin Pingli. 2010. Geochemical characteristics and LaICP-MS Zircon U-Pb dating of basic dykes in the Xiaomiao Area, Eastern Kunlun[J]. Journal of Jilin University (Earth Science Edition), 40(4): 859-868 (in Chinese with English abstract).
Righter K. 2000. A comparison of basaltic volcanism in the Cascades and western Mesico:Composition diversity in continental arcs[J]. Tectonophysics, 318: 99-117. DOI:10.1016/S0040-1951(99)00308-X
Rudnick R L, Fountain D M. 1995. Nature and composition of the continental crust:A lower crustal perspective[J]. Reviews of geophysics, 33(3): 267-309. DOI:10.1029/95RG01302
Scarrow J H, Leat P T, Wareham C D, Millar I L. 1998. Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith:A record of arc evolution[J]. Contribution to Mineralogy Petrology, 131(2/3): 289-305.
Shi Rengdeng. 2007. Restricting to age of the Bangong-Nujiang ocean from Banggong Lake SSZ ophiolite[J]. Chinese Sciencec Bulletin, 52(2): 223-227 (in Chinese with English abstract). DOI:10.1360/csb2007-52-2-223
Sui Qingling, Wang Qing, Zhu Dicheng, Zhao Zhidan, Chen Y, Santosh M, Hu Z C, Yuan H L, Mo X X. 2013. Compositional diversity of ca.110 Ma magmatism in the northern Lhasa Terrane, Tibet:Implications for the magmatic origin and crustal growth in a continent-continent collision zone[J]. Lithos, 168: 144-159.
Sun S S, McDonough W F. 1989. Implications for Mantle Composition and Processes Chemical and Isotopic Systematics of Oceanic Basalts: Implications for Mantle Composition and Processes[M]. Geological Society, London, Special Publications, 42(1): 313-345.
Taylor B, Martinez F. 2003. Back-arc basin basalt systematics[J]. Earth and Planetary Science Letters, 210(3): 481-497.
Von Blanckenburg F, Davis J H. 1995. Slab break off:A model for syncollisional magmatism and tectonics in the Alps[J]. Tectonics, 14: 120-131. DOI:10.1029/94TC02051
Walker G P L, Eyre P R. 1995. Dike complexes in America Samoa[J]. J. Volc. Geother. Res., 69: 241-245. DOI:10.1016/0377-0273(95)00041-0
Wang Yunliang, Zhang Chengjiang, Xiu Shuzhi. 2001. Th/Hf-Ta/Hf identification of tectonic-setting of basalts[J]. Acta Petrologiea Sinica, l7(3): 413-421 (in Chinese).
Wang Jian, Fu Xiugen. 2018. Sedimentary evolution of the Qiangtang Basin[J]. Geology in China, 45(2): 237-259 (in Chinese with English abstract).
Wang Zhongheng, Wang Yongsheng, Xie Yuanhe, Sun Zhonggang, Qu Yonggui, Li Cunzhi, Jiang Xuefei. 2005. The Tarenben oceanicisland basalts in the middle part of the Bangong-Nujiang suture zone, Xizang and their geological implations[J]. Sedimentary Geology and Tethyan Geology, 25(1/2): 153-162 (in Chinese with English abstract).
Weaver B L. 199l. The origin of ocean island basalt endmember composition:Trace element and isotopic constraints[J]. Earth Planet Sci. Lett., 104: 381-397. DOI:10.1016/0012-821X(91)90217-6
Wilson M. 1993. Magmatic differentiation[J]. Journal of the Geological Society, 150(4): 611-624. DOI:10.1144/gsjgs.150.4.0611
Wilson M. 1989. Igneous Petrogenesis[M]. London: Unwin Hyman.
Winchester J A, Floyd P A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements[J]. Chemical Geology, 20: 325-343. DOI:10.1016/0009-2541(77)90057-2
Xia Linqi, Xia Zuchuan, Xu Xueyi, Li Xiangmin, Ma Zhongping. 2007. The discrimination between continental basalt and island arc basalt based on geochemical method[J]. Acta Petrologica et Mineralogica, 26(1): 77-89 (in Chinese with English abstract).
Xie Guiqing, Hu Ruizhong, Jia Dacheng. 2002. Geological and Geochemical characteristics and its significance of mafic dikes from Northwest Jiangxi Province[J]. Geochimica, 31(4): 329-338 (in Chinese with English abstract).
Xu X W, Zhang B L, Qin K Z, Mao Q, Cai X P. 2007. Origin of lamprophyres by the mixing of basic and alkaline melts in magma chamber in Beiya area, western Yunnan, China[J]. Lithos, 99(3/4): 339-362.
Yang J H, Chung S L, Zhai M G, Zhou Xinhua. 2004. Geochemical and Sr-Nd-Pb isotopic compositions of mafic dikes from the Jiaodong Peninsula, China:Evidence for vein-plus-peridotite melting in the lithospheric mantle[J]. Lithos, 73(3): 145-160.
Ye Lijuan, Zhao Zhidan, Liu Dong, Zhu Dicheng, Dong Guochen, Mo Xuanxue, Hu Zhaochu, Liu Yongsheng. 2015. Late Cretaceous diabase and granite dike in Namling, Tibet:Petrogenesis and implications for extension[J]. Acta Petrologica Sinica, 31(5): 1298-1312 (in Chinese with English abstract).
Yang Shao, Li Dewei, Chen Guifan, Li Hualiang, Zhang Shuo, Zhou Tao. 2018. The discovery of the Wuluqiong magnetite deposit in Tibet and its geological characteristics[J]. Geology in China, 45(6): 1214-1227 (in Chinese with English abstract).
Yue Yahui, Ding Lin. 2006. 40Ar/39Ar geochronology, geochemistry characteristics and genesis of the Linzhou basic dikes, Tibet[J]. Acta Petrologica Sinica, 22(4): 855-866 (in Chinese with English abstract).
Zhang K J, Xia B D, Wang G M, Li Y T, Ye H F. 2004. Early Cretaceous stratigraphy, depositional environments, sandstone provenance, and tectonic setting of central Tibet, western China[J]. Geological Society of America Bulletin, 116(9): 1202-1222. DOI:10.1130/B25388.1
Zhang Liangliang, Zhu Dicheng, Zhao Zhidan, Liao Zhongli, Wang Liquan, Mo Xuanxue. 2011. Early Cretaceous granitoids in Xainza, Tibet:Evidence of slab break-off[J]. Acta Petrologica Sinica, 27(7): 1938-1948.
Zhang Xin, Wu Cailai, Chen Hongjie. 2017. The U-Pb zircon dating of the granite dike in Nanzhao pluton and it's constraints on tectonic setting in Yanshanian[J]. Geology in China, 44(5): 938-958 (in Chinese with English abstract).
Zheng YongFei. 1999. Chemical Geodynamics[M]. Beijing: Science Press, 137-143 (in Chinese with English abstract).
Zhu D C, Li S M, Cawood P A, Wang Q, Zhao Z D, Liu S A, Wang L Q. 2015. Assembly of the Lhasa and Qiangtang terranes in central Tibet by divergent double subduction[J]. Lithos, 245: 7-17.
Zhu Dicheng, Mo Xuanxue, Zhao Zhidan. 2008. Zircon U-Pb geochronology of Zenong Group volcanic rocks in Coqen area of the Gangdese, Tibet and tectonic significance[J]. Acta Petrologica Sinica, 24(3): 401-412.
Zhu Dicheng, Pan Guitang, Mo Xuanxue, Wang Liquan, Liao Zhongli, Zhao Zhidan, Dong Guocheng, Zhou Changyong. 2006. Late Jurassic-Early Cretaceous geodynamic setting in middle-northern Gangdese:New insights from volcanic rocks[J]. Acta Petrotogica Sinica, 22(3): 534-546 (in Chinese with English abstract).
Zhu D C, Mo X X, Niu Y L, Zhao Z D, Wang L Q, Liu Y S, Wu F Y. 2009. Geochemical investigation of Early Cretaceous igneous rocks along an east-west traverse throughout the central Lhasa Terrane, Tibet[J]. Chemical Geology, 268: 298-312. DOI:10.1016/j.chemgeo.2009.09.008
鲍佩声, 肖序常, 苏犁, 王军. 2007. 西藏洞错蛇绿岩的构造环境:岩石学、地球化学和年代学制约[J]. 中国科学(D辑), 37(3): 298-307.
陈玉禄, 张宽忠, 杨志民, 罗涛. 2006. 青藏高原班公湖-怒江结合带中段那曲县觉翁地区发现完整的蛇绿岩剖面[J]. 地质通报, 25(6): 694-699. DOI:10.3969/j.issn.1671-2552.2006.06.007
董传万, 张登荣, 徐夕生. 2006. 福建晋江中-基性岩脉的锆石SHRIMP U-Pb定年和岩石地球化学[J]. 岩石学报, 22(6): 1696-1702.
董铭淳, 赵志丹, 朱弟成, 刘栋, 董国臣, 莫宣学, 胡兆初, 刘永胜, 邹子昊. 2015. 西藏林周盆地中酸性脉岩的年代学、地球化学和岩石成因[J]. 岩石学报, 31(5): 1268-1284.
耿全如, 潘桂堂, 王立全, 彭智敏, 张璋. 2011. 班公湖-怒江、羌塘地块特提斯演化与成矿地质背景[J]. 地质通报, 30(8): 1261-1274. DOI:10.3969/j.issn.1671-2552.2011.08.013
侯贵廷, 李江海, Halls HC, 钱祥麟. 2003. 华北前寒武纪镁铁质岩脉的流动构造及侵位基质[J]. 地质学报, 77(2): 210-215. DOI:10.3321/j.issn:0001-5717.2003.02.009
江军华, 王瑞江, 曲晓明. 2011. 青藏高原西部班公湖岛弧特提斯洋盆闭合后的地壳伸展作用[J]. 地球科学——中国地质大学学报, 36(6): 1021-1032.
江思宏, 聂凤军, 胡朋, 刘妍, 赖欣荣. 2007. 藏南基性岩墙群的地球化学特征[J]. 地质学报, 81(1): 60-70.
康磊, 校培喜, 高晓峰, 朱海平, 奚仁刚, 过磊, 董增产. 2012. 青藏高原西北缘红其拉普岩体的岩石成因、时代及其构造意义[J]. 地质学报, 86(7): 1063-1076. DOI:10.3969/j.issn.0001-5717.2012.07.003
康志强, 许继峰, 王保弟, 陈建林. 2010. 拉萨地块北部去申拉组火山岩:班公湖-怒江特提斯洋南向俯冲的产物?[J]. 岩石学报, 26(10): 3106-16.
雷传扬, 吴建亮, 尹显科, 刘文, 王波, 李威, 袁华云, 张伟, 尹滔, 裴亚伦. 2019. 藏北阿翁错复式岩体及其暗色微粒包体年龄、地球化学与地球动力学意义[J]. 地质通报, 38(4): 494-508.
赖绍聪, 刘池阳, 伊海生, O'Reilly S. Y, 张明. 2003. 北羌塘新生代火山岩长石矿物激光探针原位测试及其微量元素特征初探[J]. 地质科学, 38(4): 539-545. DOI:10.3321/j.issn:0563-5020.2003.04.015
李德威. 2008. 青藏高原及邻区三阶段构造演化与成矿演化[J]. 地球科学——中国地质大学学报, 33(6): 723-742.
李华亮, 高成, 李正汉, 张璋, 彭智敏, 关俊雷. 2016. 西藏班公湖地区竟柱山组时代及其构造意义[J]. 大地构造与成矿学, 40(4): 663-673.
李献华, 胡瑞忠, 饶冰. 1997. 粤北白垩纪基性岩脉的年代学和地球化学[J]. 地球化学, 26(2): 14-31. DOI:10.3321/j.issn:0379-1726.1997.02.004
罗照华, 卢新祥, 王秉璋. 2008. 造山后脉岩组合与内生成矿作用[J]. 地学前缘, 15(4): 1-12. DOI:10.3321/j.issn:1005-2321.2008.04.001
罗照华, 魏阳, 辛后田, 詹华明, 柯珊, 李文韬. 2006. 造山后脉岩组合的岩石成因——对岩石圈拆沉作用的约束[J]. 岩石学报, 22(6): 1672-1684.
潘桂棠, 莫宣学, 侯增谦, 朱弟成, 王立全, 李光明, 赵志丹, 耿全如, 廖忠礼. 2006. 冈底斯造山带的时空结构及演化[J]. 岩石学报, 22(3): 521-533.
邱瑞照, 周肃, 邓晋幅, 李金发, 肖庆辉, 蔡志勇. 2004. 西藏班公湖-怒江西段舍马拉沟蛇绿岩中辉长岩年龄测定——兼论班公湖-怒江蛇绿岩带形成时代[J]. 中国地质, 31(3): 262-268. DOI:10.3969/j.issn.1000-3657.2004.03.004
任军虎, 柳益群, 周鼎武, 冯乔, 张琨, 董忠良, 秦萍莉. 2010. 东昆仑小庙基性岩脉地球化学及LA-ICP-MS锆石U-Pb定年[J]. 吉林大学学报(地球科学版), 40(4): 859-868.
史仁灯. 2007. 班公湖SSZ型蛇绿岩年龄对班-怒洋时限的制约[J]. 科学通报, 52(2): 223-227. DOI:10.3321/j.issn:0023-074X.2007.02.016
汪云亮, 张成江, 修淑芝. 2001. 玄武岩类形成的大地构造环境的Th/Hf-Ta/Hf图解判别[J]. 岩石学报, 17(3): 413-421.
王剑, 付修根. 2018. 论羌塘盆地沉积演化[J]. 中国地质, 45(2): 237-259.
王忠恒, 王永胜, 谢元和, 孙忠刚, 鲁宗林, 曲永贵, 李存直, 姜雪飞. 2005. 西藏班公湖-怒江缝合带中段塔仁本洋岛型玄武岩的发现及地质意义[J]. 沉积与特提斯地质, 25(1/2): 153-162.
夏林圻, 夏祖春, 徐学义, 李向民, 马中平. 2007. 利用地球化学方法判别大陆玄武岩和岛弧玄武岩[J]. 岩石矿物学杂志, 26(1): 77-89. DOI:10.3969/j.issn.1000-6524.2007.01.011
谢桂青, 胡瑞忠, 贾大成. 2002. 赣西北基性岩脉的地质地球化学特征及其意义[J]. 地球化学, 31(4): 329-338. DOI:10.3321/j.issn:0379-1726.2002.04.004
杨绍, 李德威, 陈桂凡, 李华亮, 张硕, 周涛. 2018. 西藏乌鲁穷含铜磁铁矿床的发现及地质特征[J]. 中国地质, 45(6): 1214-1227.
叶丽娟, 赵志丹, 刘栋, 朱弟成, 董国臣, 莫宣学, 胡兆初, 刘永胜. 2015. 西藏南木林晚白垩世辉绿岩与花岗质脉岩成因及其揭示的伸展背景[J]. 岩石学报, 31(5): 1298-1312.
岳雅慧, 丁林. 2006. 西藏林周基性岩脉的40Ar/39Ar年代学、地球化学及其成因[J]. 岩石学报, 22(4): 855-866.
张亮亮, 朱弟成, 赵志丹, 廖忠礼, 王立全, 莫宣学. 2011. 西藏申扎早白垩世花岗岩类:板片断离的证据[J]. 岩石学报, 27(7): 1938-1948.
张昕, 吴才来, 陈红杰. 2017. 秦岭南召岩体中花岗岩脉的锆石UPb定年:对燕山期构造环境的约束[J]. 中国地质, 44(5): 938-958.
郑永飞. 1999. 化学地球动力学[M]. 北京: 科学出版社, 137-143.
朱弟成, 莫宣学, 赵志丹. 2008. 西藏冈底斯带措勤地区则弄群火山岩锆石U-Pb年代学格架及构造意义[J]. 岩石学报, 24(3): 401-12.
朱弟成, 潘桂堂, 莫宣学, 王立全, 廖忠礼, 赵志丹, 董国臣, 周长勇. 2006. 冈底斯中北部晚侏罗世-早白垩世地球动力学环境:火山岩约束[J]. 岩石学报, 2(3): 534-546.