Geochronology and petrogenesis of Cretaceous A-type granites from the NE Jiangnan Orogen,SE China

The Jiangnan Orogen is located at a key tectonic position along the junction between the Yangtze and Cathaysia blocks. We obtained detailed major and trace elements, whole-rock Nd + zircon Hf isotope data, and U–Pb age data from several Mesozoic granites, including the Fuling (FL), Taiping–Huangshan (TH), Lingshan (LS), Sanqingshan (SQS), and Baijuhuajian intrusions in order to investigate their sources and petrogeneses related to extension in South China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon from the FL, TH, SQS, and LS bodies yield Early Cretaceous ages of 124–135 Ma. These plutons are alkali-feldspar granites to syenogranites–monzogranites, and show A-type affinities. They have high K₂O and total alkali contents, and are enriched in rare earth elements (except for Eu), Zr, and other high-field-strength elements as well as high Ga/Al ratios, and are depleted in Ba and Sr. These granites are metaluminous to weakly peraluminous (ACNK from 0.81 to 1.27). The whole-rock ?Nd(T) values of??5.34 to??0.96 are coupled with zircon ?Hf(T) values (from??5.3 to +4.24), and all samples plot along the mantle array. Field observations, geochronology, geochemistry, Nd isotopic, and zircon Hf isotopic compositions suggest that they formed by the partial melting of Mesoproterozoic metamorphic basement, with input from juvenile, mantle-derived materials in the shallow (<30 km) crust at high temperatures (756–965°C). These melts underwent crystal fractionation of biotite, plagioclase, and K-feldspar. The upwelling of asthenosphere triggered partial melting of the metamorphic protolith in a back-arc or intra-arc rift setting, reflecting rollback of the Pacific plate. Our research adds new geochronologic constraints on Cretaceous (135–120 Ma) A-type granites from the NE sector of the Jiangnan Orogen. Combined with previous research, we suggest that three main episodes of late Mesozoic extensional tectonism took place in South China: (1) 190–170 Ma (mainly inland), (2) 165–120 Ma (including 165–150 Ma in SE Shi-Hang, 135–120 Ma in NE Shi-Hang, and ～125 Ma in the Lower Yangtze River Belt), and (3) 100–90 Ma (coastal area), showing an oceanwards younging trend due to the subduction of the Palaeo-Pacific plate.     

Early Cretaceous A-type Granites in the Dandong Area,NE China and its Geodynamical Implications

A-type granites, as an important petrologic sign to build up environmental recognition, were mainly formed in extensional tectonic settings. A biotite syenogranite from the Fenghuangshan pluton in Dandong, Liaoning Province gave SHRIMP zircon U-Pb ages of 122.5 ± 1.6 Ma, 124.9 ± 1.7 Ma and 126.9 ± 1.1 Ma. The monzogranites have SHRIMP zircon U-Pb ages of 118.2 ± 1.6 Ma, 128.1 ± 1.7 Ma and 131.6 ± 1.9 Ma, giving an emplacement age for the pluton in the Early Cretaceous. SiO2 is 65.48–74.49 wt%, whereas that of K2O is 4.16–6.44 wt%, and that of Na2O is 2.99–4.70 wt%. They also contain 13.24–15.76 wt% of Al2O3, with an A/CNK ratio of 0.92–1.10, averaging 1.02. The alkalinity rate (AR) ranges from 2.68 to 5.12, and this range is within the AR of peraluminous type rocks. The granites of Fenghuangshan pluton are characterized by high contents of Na and K and low contents of Ca (thermophile element) and Mg, which are features of A-type granites. The (Na2O + K2O) ? Fe2O3* × 5 ? (CaO + MgO) × 5 discrimination diagram also shows that Fenghuangshan pluton is an A2-type granite. The above granite has zircon εHf(t) values ranging from ?17.06 to ?9.09, with single-stage Hf model ages (TDM) of 1141 Ma to 1498 Ma and two-stage Hf crustal model ages (TDMC) of 1762 Ma to 2263 Ma. A comprehensive analysis suggests that the Fenghuangshan pluton might have been formed from the lithospheric-plate sliding during the late stages of evolution of hot rift structures and might have been closely associated with the tectonic settings of Mesozoic Eurasia and the ancient Pacific Plate.     

内蒙古中部锡林浩特-西乌旗早三叠世A型酸性火山岩的地球化学特征及其地质意义

通过K—Ar年代学、元素、同位素地球化学研究,可以厘定内蒙古锡林浩特-西乌旗英安岩-流纹岩形成于早三叠世（K—Ar：245Ma）;其具有富硅碱,贫钙镁,显著的负Eu异常,低Ba、Sr丰度和高Rb／Sr比值,以及高Ga、Zr、Nb、Ce、Y等元素地球化学特征;并呈现相对富集的（^87Sr／^86Sr）i（0．7068～0．7099）和中等亏损的Nd（εNd（t）=＋1．66-＋3．34）的同位素特征。这些类似于A型花岗岩的地球化学特征。它们可能是内蒙中部近于同期发育的铝质A型花岗岩浆的喷出相,形成于慢源岩浆底侵新增生中下地壳的直接部分熔融,并伴随其后的分异作用。这些具有A2型花岗岩地球化学特征的酸性火山岩与同期拉斑玄武岩构成了造山后拉张环境下发育的特征性双峰式火山岩组合,这不仅为内蒙中部在早中生代已经结束块体拼合而进入造山后阶段提供了进一步的岩石学证据,而且暗示了地幔物质的加入在中亚造山带后造山时期陆壳的垂向生长过程中起最主要的作用。     

A study on A-type granites in Suzhou,China

The Suzhou granite suite is the anorogenic product, which is located on the inactive continental margin of east China. It was emplaced about 141 Ma ago, occurring as a stock with a polygonal outline on the surface, belonging to alkali potash-feldspar granites with K₂O > Na₂O, Reit’s alkali coefficient = 0.694, SiO₂ = 74.95, and Al₂O₃/(K₂O + Na₂O)mol= 1. Besides K and Na, Li and Rb are also rather high. Highlycharged metals such as Zr, Nb, REE, Y, Sn, Th, Ga and Zn are 10, or even 50 times higher than those in the ordinary granites. Halogen elements such as F and Cl are high in abundance with F = 2700 ppm and Cl = 170 ppm on average. The abundances of deep-source elements such as Ti, Al, Ca, Mg and P are relatively low, with A1₂O₃ = 12.65% and Ca + Mg < 1%. High Ga and low Al contents are typomorphically characteristic of A type granites. Biotite in the rocks is, for the most part, annite, usually filling in quartz and feldspar crystals, indicating that the crystallization of magma proceeded under relatively anhydrous condition. More than 40 kinds of accessory minerals have been identified, of which the mantle-derived mineral chrompicotite and moissanite is of great interest. Two different intrusions, the major and supplementary intrusions, can be distinguished in the granite suite. The rock-forming temperature is estimated to be 810°C, pressure 2.5 kbars, pH 8.1,¹⁸O/¹⁶O low(δ¹⁸O_WR = 6.19‰), and_fo₂= 10⁻¹⁶. The abundances of REE are high and Eu depletion is remarkable (δEu = 0.24). A variety of mineral deposits related to the Suzhou granite suite have been recognized.     

北秦岭西段早侏罗世A型花岗岩及其地质意义

本文通过岩相学、岩石地球化学、锆石U?Pb定年和Lu?Hf同位素组成分析等方法,对出露于北秦岭西段宝鸡岩体王家山一带的黑云母花岗岩和其中的包体进行了研究。结果表明,该花岗岩形成时代为187±2 Ma,属于高钾钙碱性—钾玄岩系列岩石,富集Rb、Th、U等大离子亲石元素以及Nb、Zr和Hf等高场强元素,亏损Ba、Sr和Eu,具有高的全岩锆石饱和温度(825℃~838℃),显示A型花岗岩特征,形成于造山后的板内环境,可能为秦岭岩群副变质岩与安山质岩石部分熔融的产物。暗色包体显示塑性流变特征,具有岩浆结构,发育针状磷灰石和具有复杂成分环带的更长环斑结构长石,是幔源岩浆注入酸性岩浆发生混合作用的产物,形成时代为191±2 Ma,其锆石Hf同位素组成变化范围较大,εHf(t)值介于-11.26~-2.51,主要为富集地幔部分熔融产物。综合本文及前人已有研究结果,认为~190 Ma的早侏罗世早期秦岭地区早中生代碰撞造山过程已经结束,区域开始逐渐进入板内伸展构造演化阶段。     

内蒙古阿尔山地区中生代A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

在岩石学研究的基础上,运用LA-ICP-MS锆石U-Pb定年和地球化学方法,研究了阿尔山地区不同时代花岗岩体的成因和构造意义。研究表明,三广山中粒碱长花岗岩形成于印支期（228.5±3.0Ma）;南兴安似斑状碱长花岗岩形成于燕山期（141.7±2.6Ma）,捕获锆石年龄为1847±21Ma,反映该区可能具有前寒武纪结晶基底。两岩体岩石化学以富Si、高K、低Mg、贫Ca为特点,A/CNK值为1.00～1.05;富集高场强元素和轻稀土元素,亏损重稀土元素和大离子亲石元素,稀土元素配分模式为典型的右倾海鸥型。岩相学和地球化学特征显示,三广山和南兴安花岗岩均为A型花岗岩。其中,三广山花岗岩为A2型花岗岩,南兴安花岗岩为A1型花岗岩。全岩Sr-Nd同位素组成（εNd（t）值为2.26～5.58）表明,阿尔山地区花岗岩的源区可能为显生宙-新元古代期间从亏损地幔中新增生的地壳物质,但南兴安和三广山2个岩体的形成机制不同。三广山A2型花岗岩可能是古亚洲洋在三叠纪闭合后进入造山后阶段岩石圈伸展体制下的产物,而南兴安A1型花岗岩可能形成于早白垩世大兴安岭地区板内伸展作用下的拉张减薄环境。     

内蒙古固阳地区白云常合山A型花岗岩:年代学、地球化学、Hf同位素研究及其对Columbia超大陆裂解的响应

在对固阳白云常合山花岗岩详细的野外地质调查基础上,对其岩相学、地球化学、锆石U-Pb年代学及Lu-Hf同位素特征进行了综合研究。白云常合山花岗岩的地球化学特征显示其具有高SiO2（70.68%~77.21%）、富碱（7.88%~9.21%）、高Fe2O3T/MgO（12.60~90.38）和10000×Ga/Al（3.63~6.17）值,低Al2O3（11.70%~13.23%）、MgO（0.06%~0.24%）、CaO（0.23%~1.20%）的特征;微量元素富集Rb、Th、K等,亏损Ba、Sr、Eu、Ti、P;稀土元素总量较高,轻稀土富集,重稀土亏损,呈现典型的右倾"海鸥型"分布模式,具有明显的Eu负异常。通过锆石饱和温度的计算,得到白云常合山花岗岩的结晶温度为824~957℃,平均值为903℃,表明其形成于高温环境。这些特征与A型花岗岩相一致。锆石LA-ICP-MS年龄测试结果显示,白云常合山花岗岩形成于~1720Ma;锆石εHf（t）=-1.84~+6.08,以正值为主,单阶段模式年龄和二阶段模式年龄分别为1.9~2.2Ga和2.5~3.2Ga,岩浆源区主要是新太古代新生地壳,在上升过程中可能受到古老地壳物质的混染。构造环境判别图解显示其为A1型花岗岩,且有板内岩浆的特点,因此白云常合山花岗岩应该是大陆裂谷岩浆活动的产物。结合区域上与裂解事件有关地质体的同位素年代学资料,认为白云常合山花岗岩应该是固阳地区年龄可靠的最早响应哥伦比亚超大陆裂解的岩体。     

内蒙古莫尔道嘎地区晚三叠世-早侏罗世花岗岩的年代学、地球化学及其地质意义

本文对内蒙古莫尔道嘎地区(额尔古纳地块)花岗质岩石行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学研究, 确定其形成时代、岩石成因, 从而揭示区域构造背景。莫尔道嘎地区花岗岩中的锆石均呈半自形-自形, 震荡生长环带明显, 暗示其岩浆成因。测年结果显示, 研究区花岗岩可划分为两个期次: 晚三叠世(~216Ma)和早侏罗世(201~195Ma)。莫尔道嘎地区晚三叠世-早侏罗世花岗岩的地球化学属性相似, 它们具有高硅(SiO₂=67.09%~77.05%)、富铝(Al₂O₃=12.18%~16.83%)、贫铁(Fe₂O₃^T=1.30%~3.48%)等特征, 属于准铝质-过铝质(A/CNK=0.97~1.13)、高钾钙碱性系列, 具有I型花岗岩的地球化学属性。此外, 晚三叠世-早侏罗世花岗岩相对富集大离子亲石元素(LILEs)和轻稀土元素(LREEs), 亏损重稀土元素(HREEs)和高场强元素(HFSEs, Nb、Ta、P、Ti等), 具有与俯冲带环境下形成的火成岩类似的特征。额尔古纳地块上同时期的钙碱性系列岩石组合的发现, 进一步表明莫尔道嘎地区晚三叠世-早侏罗世花岗岩形成于活动大陆边缘环境。结合前人对东北地区中生代火成岩时空变异分布特征的研究, 本文莫尔道嘎地区晚三叠世-早侏罗世花岗质岩体形成与蒙古-鄂霍茨克大洋板片南向俯冲作用密切相关。

     

黑龙江省漠河县富源沟林场含电气石花岗岩的形成时代及地质意义

本文对额尔古纳地块北段的富源沟林场含电气石花岗岩体进行了LA-ICP-MS锆石U-Pb同位素定年和岩石地球化学研究。含电气石花岗岩的锆石206Pb/238U年龄加权平均值为458±4 Ma（MSWD = 1.8）,表明含电气石花岗岩形成于晚奥陶世初期。岩石地球化学特征表明该花岗岩应为高钾钙碱性系列（K2O = 3.45%～4.83%）,铝饱和指数A/CNK＞1.1（1.11～1.28）,属强过铝质的S型花岗岩,富集Th、U、Rb、K等元素,相对亏损Sr、Ba、 Nb、Ti、 P、Eu等元素,是同碰撞构造背景下地壳部分熔融的产物。结合前人研究资料和本文数据提出,富源沟林场含电气石花岗岩的形成与额尔古纳地块和兴安地块的碰撞拼贴有关,形成于额尔古纳地块与兴安地块碰撞拼贴作用所引发的碰撞构造背景,由于地缘因素,构造岩浆作用滞后于额尔古纳地块东缘的碰撞拼贴时限,是额尔古纳地块和兴安地块碰撞拼贴的远程效应。     

西藏北冈底斯扎独顶A型花岗岩锆石U-Pb年代学、地球化学及其地质意义

西藏北冈底斯早白垩世花岗岩分布广泛;扎独顶岩体作为其中的一个典型代表,其分布广泛,呈岩基型式产出,在岩性上属二长花岗岩。在岩石化学上扎独顶岩体具有富Si O2(70.05%~74.97%)和K2O(4.09%~5.35%),贫Ca O(0.93%~2.19%)、Ti O2(0.22%~0.52%)和Al2O3(12.81%~14.24%)的特征;属于准铝质-弱过铝质(A/CNK=0.99~1.0)高钾钙碱性系列。岩体稀土元素总量偏高(∑REE=199.36×10-6~247.91×10-6),相对富集轻稀土元素(LREE/HREE=5.82~6.88),Eu负异常明显(δEu=0.30~0.45),球粒陨石标准化分布模式呈向右缓倾的V型。微量元素显示其富集Rb、Th、K、Zr和Hf,亏损Nb、Ta、Sr、Ba、P和Ti,(Zr+Nb+Ce+Y)平均值为427.63。全岩锆石饱和温度(828~838°C)表明岩浆形成温度高。上述岩石地球化学特征表明扎独顶岩体为A型花岗岩。扎独顶岩体LA-ICP-MS锆石U-Pb年龄为(103.8±1.0)Ma,表明其形成于早白垩世晚期;在构造判别图解上位于碰撞后的A2型花岗岩区,是在碰撞后岩石圈伸展背景下,由于软流圈物质上涌导致岩石圈地幔与壳源熔体部分熔融并经历过一定程度的混合作用而形成的。     

内蒙古苏尼特左旗东苏A型花岗岩的锆石U-Pb年龄、地球化学特征及地质意义

位于苏尼特左旗东部的东苏二长花岗岩是索伦缝合带重要组成部分,具有高硅(SiO_2=69.76%~75.58%)、高碱且相对富钾(K2O+Na2O=6.99%~9.16%,K2O/Na2O=0.70~1.69)、相对富铝(铝饱和指数A/CNK=1.04~1.13)、高TFeO/MgO值(3.43~11.26)、贫镁(MgO=0.08%~0.50%)的特征;微量元素地球化学性质表现出相对富集轻稀土,Ba、Sr、Nb、Eu强烈负异常,Rb、Th、Ta等不相容元素富集的特征。主量和微量元素均表现出铝质A型花岗岩的特征。采用锆石LA-ICP-MS U-Pb法获得206Pb/238U值的加权平均年龄为221.5±0.81 Ma(MSDN值为0.57),表明该岩体为晚三叠世岩浆活动的产物。结合区域地质资料及地球化学信息可以判断该东苏花岗岩为后造山伸展阶段长英质地壳物质(变杂砂岩)部分熔融的产物。它的出现,标志着古亚洲洋演化的结束,索伦缝合带在晚三叠世的碰撞已达末期。     

西藏那曲地区早白垩世A型花岗岩成因及其构造意义

班公湖-怒江缝合带及其两侧广泛分布早白垩世岩浆岩,它们是班公湖-怒江洋俯冲消减及拉萨地块与南羌塘地块碰撞过程的直接响应,为研究特提斯大洋演化、青藏高原早期陆块聚合提供了重要素材。本文报道了班公湖-怒江缝合带中段那曲地区黑云母二长花岗岩的锆石U-Pb定年、岩石地球化学和锆石Hf同位素分析结果。锆石LA-ICP-MS U-Pb定年结果表明,黑云母二长花岗岩形成于114～113 Ma(早白垩世晚期)。地球化学分析表明,岩石显示出高钾钙碱性—钾玄岩系列特征,同时具有高的Ga/Al×10000比值(介于2.02～3.15之间,平均为2.61)和Zr+Nb+Ce+Y含量(平均为524.87×10^-6)。此外,锆饱和温度和锆石Ti温度计共同指示岩浆形成于高温的环境(>800℃),这些特征与典型的A型花岗岩相一致。黑云母二长花岗岩中锆石具有低的ε_Hf(t)值(10.1～6.4),对应的Hf同位素二阶段模式年龄(t_DM2)为1852～1547 Ma,指示其岩浆可能源自安多微陆块中下地壳古老结晶基底的部分熔融。结合区域研究成果,认为那...     

原特提斯洋在滇西南地区的俯冲记录：来自保山地块奥陶纪花岗岩的年代学、地球化学以及Hf-Nd同位素的支持

中国西南地区在早古生代期间位于冈瓦纳大陆北缘, 该地区保存有早古生代岩浆岩记录, 它们的形成与原特提斯洋的演化密切相关。本文报道了滇西南地区保山地块平达乡附近的早古生代花岗岩的岩石学、全岩主-微量地球化学、LA-ICP-MS锆石U-Pb年龄、锆石Hf同位素和磷灰石Nd同位素组成, 以探讨保山地块早古生代花岗岩的岩石成因、岩浆源区性质以及岩体形成的地球动力学机制。通过对保山地块平达花岗岩中岩浆锆石开展LA-ICP-MS U-Pb同位素测试, 结果显示花岗岩形成于465.9~454.9Ma, 是中-晚奥陶世岩浆作用的产物。平达岩体主体岩性为二长花岗岩, 主要矿物组成为斜长石、石英和碱性长石(条纹长石和正长石), 次要矿物为黑云母和白云母。本文报道的花岗岩样品显示出高的SiO₂(72.16%~76.87%)和Al₂O₃(12.50%~14.36%)含量, 低的MgO(0.12%~0.64%)、Mg^#(20.9~35.9)、Cr和Ni含量以及较高的Rb/Sr和Rb/Ba比值; 结合花岗岩较高的A/CNK值(1.06~1.45), 显示弱过铝质至强过铝质的特征, 表明其属于S型花岗岩。此外, 平达岩体二长花岗岩样品具有低的Al₂O₃/TiO₂比值和变化的CaO/Na₂O、Rb/Sr、Rb/Ba比值, 表明其岩浆源区包含泥质岩石和砂质岩石, 显示混合源区的特征。结合滇西南早古生代二长花岗岩变化较大的锆石ε_Hf(t)值(-11.10~-4.05)、磷灰石ε_Nd(t)值(-8.76~-6.96)和Hf同位素二阶段模式年龄(2140~1704Ma), 表明它们的岩浆源区为古元古代地壳中泥质岩石和砂质岩石混合源区。综合滇西南地区广泛发育的早古生代岩浆岩以及同时期的蛇绿混杂岩记录, 本文认为保山地块早古生代S型花岗岩是地壳沉积组分部分熔融的产物, 形成于原特提斯洋西向俯冲相关的活动大陆边缘背景。

     

Petrology and geochemistry of A-type granites from Khanak and Devsar areas of Bhiwani district,southwestern Haryana

Petrological and geochemical characteristics of the granites from the Khanak and Devsar areas have been discussed in this paper. Based on field, petrographical and geochemical observations, three types of granites (grey, green and pink granite) have been identified in these areas. Grey granites consist of quartz, plagioclase, biotite, hornblende as essential minerals and hematite, zircon, annite, monazite & rutile as accessory minerals. Petrographically, green granites are same as grey granites including perthite and zircon as accessory minerals. Pink granites consist of quartz, k-feldspar and biotite in Khanak whereas in Devsar granites alike as Khanak granites, but plagioclase is replaced by perthite and occurs as dominantly. Microscopically, granites of both areas show porphyritic, hypidiomorphic, granophyric, perthitic and micro granophyric textures. Geochemically, major oxide elements (except alkalies) and trace elements (Ba, Sr, Cr, Ni, V, Cu, Zn, Ga, Pb, Th and Zr) are more in green and grey granites of Khanak and Devsar areas than pink granites. Generally, they show enrichments in SiO₂, Na₂O+K₂O, Fe/Mg, Rb, Zr, Y and and AI (Agpaitic Index) (ranges from 0.10 to 1.18) and depletion in MgO, CaO, P, Ti, Ni, Cr and V indicate their A-type affinity which is very similar to the A-type granites of MIS (Malani igneous suite) in northwestern peninsular India. Green and grey granites of Devsar area show high concentrations of Heat production (HP) 9.68 & 11.70 μWm^-3 and total Heat Generation Unit (HGU) i.e 23.04 & 27.86 respectively. On the other hand, pink granites of Khanak area display a higher enrichment of HP (16.53 μWm^-3) and HGU (39.37) than those granites of Devsar area. Overall, they have much a higher values of HP and HGU than the average value of continental crust (3.8 HGU), which imply a possible linear relationship with the surface heat flow and crustal heat generation in the rocks of MIS. From the petrography as well as the chemistry of Khanak and Devsar granites, it is suggested that they might have derived from the different degree of partial melting from the similar source of magma.     

内蒙古阿尔山地区中生代A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

在岩石学研究的基础上,运用LA-ICP-MS锆石U-Pb定年和地球化学方法,研究了阿尔山地区不同时代花岗岩体的成因和构造意义。研究表明,三广山中粒碱长花岗岩形成于印支期(228.5±3.0Ma);南兴安似斑状碱长花岗岩形成于燕山期(141.7±2.6Ma),捕获锆石年龄为1847±21Ma,反映该区可能具有前寒武纪结晶基底。两岩体岩石化学以富Si、高K、低Mg、贫Ca为特点,A/CNK值为1.00~1.05;富集高场强元素和轻稀土元素,亏损重稀土元素和大离子亲石元素,稀土元素配分模式为典型的右倾海鸥型。岩相学和地球化学特征显示,三广山和南兴安花岗岩均为A型花岗岩。其中,三广山花岗岩为A2型花岗岩,南兴安花岗岩为A1型花岗岩。全岩Sr-Nd同位素组成(εNd(t)值为2.26~5.58)表明,阿尔山地区花岗岩的源区可能为显生宙—新元古代期间从亏损地幔中新增生的地壳物质,但南兴安和三广山2个岩体的形成机制不同。三广山A2型花岗岩可能是古亚洲洋在三叠纪闭合后进入造山后阶段岩石圈伸展体制下的产物,而南兴安A1型花岗岩可能形成于早白垩世大兴安岭地区板内伸展作用下的拉张减薄环境。     

Neoproterozoic A-type granites of the Garevka massif, Yenisey Ridge: Age, sources, and geodynamic setting

This paper presents the results of geochemical, isotopic (Sm-Nd), and geochronological (U-Pb and Ar-Ar) investigations of leucogranites from the Garevka massif in the Transangara segment of the Yenisey Ridge. The most distinctive geochemical characteristics of these A-type granitoids are the enrichment in silica, potassium, iron, and fluorine and a considerable depletion in europium. Using U-Pb zircon geochronology, the age of the Garevka leucogranites was estimated as 752 ± 3 Ma, which allowed us to attribute them to a previously established Neoproterozoic tectonic event related to the collision of the Central Angara terrane and the Siberian craton. The parental melts of the granitoids were probably derived by melting of a mixed source composed of continental crustal rocks of Paleoproterozoic and Mesoproterozoic and (or) Neoproterozoic ages. Based on the obtained petrological, geochemical, and geochronological data, the leucogranites of the Garevka massif were assigned to the Neoproterozoic postcollisional Glushikha complex.     

内蒙古阿尔山地区中生代A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

在岩石学研究的基础上,运用LA-ICP-MS锆石U-Pb定年和地球化学方法,研究了阿尔山地区不同时代花岗岩体的成因和构造意义。研究表明,三广山中粒碱长花岗岩形成于印支期（228.5±3.0Ma）;南兴安似斑状碱长花岗岩形成于燕山期（141.7±2.6Ma）,捕获锆石年龄为1847±21Ma,反映该区可能具有前寒武纪结晶基底。两岩体岩石化学以富Si、高K、低Mg、贫Ca为特点,A/CNK值为1.00~1.05;富集高场强元素和轻稀土元素,亏损重稀土元素和大离子亲石元素,稀土元素配分模式为典型的右倾海鸥型。岩相学和地球化学特征显示,三广山和南兴安花岗岩均为A型花岗岩。其中,三广山花岗岩为A2型花岗岩,南兴安花岗岩为A1型花岗岩。全岩Sr-Nd同位素组成（εNd(t)值为2.26~5.58）表明,阿尔山地区花岗岩的源区可能为显生宙—新元古代期间从亏损地幔中新增生的地壳物质,但南兴安和三广山2个岩体的形成机制不同。三广山A2型花岗岩可能是古亚洲洋在三叠纪闭合后进入造山后阶段岩石圈伸展体制下的产物,而南兴安A1型花岗岩可能形成于早白垩世大兴安岭地区板内伸展作用下的拉张减薄环境。     

滇东北东川下田坝A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

通过对滇东北东川下田坝地区黑云母二长花岗岩和似斑状钾长花岗岩2种岩体的地球化学分析及对黑云母二长花岗岩的U-Pb同位素测试,得到如下认识：黑云母二长花岗岩和似斑状钾长花岗岩总体地球化学特征相似,主量元素表现出高SiO2（平均71.7%）、过铝质（A/CNK指数在1.03～1.52）的特征,过碱指数在0.95～1.37之间,总体属于钙碱系列;稀土元素总量较高（ΣREE平均313×10-6）,（Ce/Yb）N均值为8.85,（La/Yb）N均值为9.54,呈现轻稀土元素（LREE）富集,仅Eu亏损（δEu均值0.31）的海鸥型右倾模式;大离子亲石元素Rb、Th、U、K等相对富集,高场强元素Nb、Ta、Sr、Ti等呈明显负异常,说明岩浆源岩以陆壳成分为主;Ga/Al均值为2.69,(Zr+Nb+Ce+Y)均值为383;微量元素Sr、Eu低,富集Nb、Zr等元素,反映其源区存在斜长石的残留;锆石饱和温度为724～786℃,表明初始岩浆温度较高。上述特征说明,下田坝花岗岩为典型的A型花岗岩,形成于中上地壳的板内伸展背景。黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为801.1±6.6Ma,同时受到762.1±6.2Ma热事件的影响,与新元古代Rodinia超大陆裂解事件在时间上一致,亦与东川铜矿成矿时代相符,说明新元古代裂谷环境的岩浆事件范围可扩大至滇东北东川,并可能引发热液成矿作用。     

佳木斯地块构造演化

佳木斯地块位于中亚造山带东段,是我国东北地区一个重要的大地构造单元,古生代以来经历了复杂的多构造体系叠合的演化过程。本文在总结近二十年已报导的相关研究成果基础上,结合笔者近年工作,探讨了佳木斯地块的基底属性和来源,重塑了佳木斯地块西缘碰撞拼贴,以及东缘俯冲-增生的构造演化过程。研究表明,佳木斯地块具有亲冈瓦纳大陆的构造属性,裂离后经历了长距离的北漂。与松辽地块先后两次拼合,首次发生于中志留世(～425Ma),在晚二叠世前后(～250Ma)沿原缝合带位置发生裂解,拉张出新的有限洋盆(牡丹江洋),并于侏罗纪(185～145Ma)与松辽地块沿牡丹江-依兰构造带再次碰撞拼贴,形成了高压变质的黑龙江增生杂岩带。而佳木斯地块东缘受晚石炭世-晚三叠世(305～250Ma)泛大洋的俯冲-增生事件影响,形成了跃进山增生杂岩,随后于中侏罗世-早白垩世(165～128Ma)在古太平洋板块的西向俯冲作用下,形成了饶河增生杂岩。因此,佳木斯地块的构造演化既涉及了晚古生代古亚洲洋构造域的消亡,又经历了中生代古太平洋构造域的叠加与改造,而黑龙江杂岩的形成标志着古太平洋构造体制与古亚洲洋构造体制的转换始于晚三叠世(～210Ma)。     

滇东北东川下田坝A型花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其构造意义

通过对滇东北东川下田坝地区黑云母二长花岗岩和似斑状钾长花岗岩2种岩体的地球化学分析及对黑云母二长花岗岩的U-Pb同位素测试,得到如下认识:黑云母二长花岗岩和似斑状钾长花岗岩总体地球化学特征相似,主量元素表现出高SiO2(平均71.7%)、过铝质(A/CNK指数在1.03~1.52)的特征,过碱指数在0.95~1.37之间,总体属于钙碱系列;稀土元素总量较高(ΣREE平均313×10-6),(Ce/Yb)N均值为8.85,(La/Yb)N均值为9.54,呈现轻稀土元素(LREE)富集,仅Eu亏损(δEu均值0.31)的海鸥型右倾模式;大离子亲石元素Rb、Th、U、K等相对富集,高场强元素Nb、Ta、Sr、Ti等呈明显负异常,说明岩浆源岩以陆壳成分为主;Ga/Al均值为2.69,(Zr+Nb+Ce+Y)均值为383;微量元素Sr、Eu低,富集Nb、Zr等元素,反映其源区存在斜长石的残留;锆石饱和温度为724~786℃,表明初始岩浆温度较高。上述特征说明,下田坝花岗岩为典型的A型花岗岩,形成于中上地壳的板内伸展背景。黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为801.1±6.6Ma,同时受到762.1±6.2Ma热事件的影响,与新元古代Rodinia超大陆裂解事件在时间上一致,亦与东川铜矿成矿时代相符,说明新元古代裂谷环境的岩浆事件范围可扩大至滇东北东川,并可能引发热液成矿作用。