新疆西准噶尔接特布调A型花岗岩年代学、地球化学及岩石成因

西准噶尔乃至整个北疆地区广泛发育晚古生代后碰撞花岗岩类。接特布调岩体作为一个典型的代表, 岩石类型主要有中粗粒二长花岗岩和正长花岗岩, 是认识西准噶尔花岗岩岩石成因及构造-岩浆演化的关键。本文对接特布调岩体进行高精度锆石LA-ICP-MS U-Pb测年, 获得二长花岗岩和正长花岗岩的加权平均206Pb/238U年龄分别为(287±9) Ma(n=10, MSWD=0.92)和(278±3) Ma(n=14, MSWD=0.43), 确定其形成于早二叠世, 属于300 Ma前后准噶尔周边地区后碰撞岩浆活动的产物。岩石地球化学研究表明, 前人认为的接特布调I型花岗岩应归属于A型花岗岩。正长花岗岩具有高硅(SiO2: 76.11%~76.82%), 富碱(Na2O+K2O: 8.47%~8.49%), 低钛(TiO2: 0.04%~0.05%), 贫钙(CaO: 0.36%~0.42%)的特征。二长花岗岩与其类似, 高硅(SiO2: 68.35%~71.80%), 富碱(Na2O+K2O: 6.80%~7.86%), 低钛和钙(TiO2: 0.29%~0.82%, CaO: 1.76%~2.87%), 均属于准铝质或弱过铝质(ACNK: 0.98~1.09)高钾钙碱性系列。正长花岗岩相对于二长花岗岩具有相对较低的稀土元素总量(ΣREE)(分别为23.8×10-6~49.3×10-6, 95.23×10-6~222.2×10-6), 并具有明显的负Eu异常(Eu/Eu*分别为0.01~0.02, 0.57~0.72), 另外, 正长花岗岩相对二长花岗岩明显地富集大离子亲石元素(Rb、Th、K)及高场强元素(Zr、Hf、Nb), 而强烈亏损Ba、Sr、Eu、Ti等, 具有较高的10000Ga/Al比值(>2.44)。依据微量元素比值及相关判别图, 可将接特布调花岗岩体进一步细分为A1型和A2型。接特布调岩体就位于后碰撞环境, 来源于由年轻的地幔来源物质组成的下地壳。在后碰撞岩浆活动的初期, 年轻的下地壳部分熔融形成具有岛弧印迹的A2型二长花岗岩岩浆, 随着岩石圈进一步伸展, 可能在局部出现类似裂谷的环境, 即形成显示裂谷特征的A1型正长花岗岩岩浆。     

Petrogenesis of ca 1.50 Ga granitic gneiss of the Coompana Block: filling the ‘magmatic gap’ of Mesoproterozoic Australia

The Coompana Block is an essentially unknown basement province that separates the Gawler Craton of South Australia from the Yilgarn Craton of Western Australia. Previously unstudied granitic gneiss intersected by deep drilling in the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. Granitic gneiss intersected at ～1500 m depth in Mallabie 1 diamond drillhole is metaluminous and dominantly granodioritic in composition. The granodiorites have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. U – Pb LA-ICPMS dating of magmatic zircons provides an age of 1505 ± 7 Ma, interpreted as the crystallisation age of the granite protolith. ? _Nd values are high with respect to exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The granitic gneiss is interpreted to be a fractionated melt of a mantle-derived parental melt. The tectonic environment into which the precursor granite was emplaced is not clear. One possibility is emplacement within an extensional environment. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the ‘Australian Mesoproterozoic magmatic gap’ of ca 1.50 – 1.35 Ga, and is a possible source for ca 1.50 detrital zircons found in sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province.     

兴蒙造山带东段大陆弧后A型花岗岩特征与成因

提要：兴蒙造山带贺根山－黑河一线产出有大量晚古生代Ａ型花岗岩,其成因及形成环境一直存在争议。贺根山-黑河A型花岗岩带形成于晚石炭世-二叠纪（325～260Ma）,二叠纪进入岩浆作用高峰期。该花岗岩带主要表现为准铝质-弱过铝质（A/CNK=0.89～1.13）高钾钙碱性系列;高度富集LREE,Eu负异常明显;微量元素表现为富集Th、Pb和La元素,亏损Ba、Sr、Ce、P和Ti元素。研究表明晚石炭世—二叠纪古亚洲洋正处于向西伯利亚板块俯冲阶段,贺根山-黑河Ａ型花岗岩带应该形成于该俯冲带的弧后伸展环境。俯冲导致的软流圈上涌形成弧后的伸展环境,同时为大规模高温岩浆形成提供了热源,以及部分物源,这种壳－幔混合岩浆在深部结晶分异后沿弧后伸展断裂体系快速侵位是该花岗岩带形成的原因。     

秦岭东江口和柞水花岗岩的矿物成分特征及其形成的温压条件

对南秦岭东江口和柞水岩体的似斑状花岗岩类进行了偏光显微镜观察和电子探针(EPMA)、扫描电镜(SEM)矿物分析,在此基础上对岩体形成的温压条件进行了讨论.结果表明,这两种岩石的主要造岩矿物为石英、斜长石(更-奥长石)、钾长石、镁角闪石和镁质黑云母,副矿物为锆石、榍石、磁铁矿和磷灰石等.岩浆成分的变化可能是矿物环带结构和环斑结构形成的原因之一.东江口和柞水花岗岩类锆石结晶时岩浆温度为759～784℃,平均771℃;稀土元素在岩浆中饱和时岩浆的温度为741～800℃,平均773℃;斜长石结晶时岩浆温度624～641℃,平均632℃;角闪石结晶时岩浆温度610～668℃,平均632℃.岩体侵位深度约5.8km,压力约1.77×108 Pa,具有壳幔混源的特点.     

Geochronological and Geochemical Constrains on Petrogenesis of the Jietebutiao A-type Granite in West Junggar,Xinjiang

Late Paleozoic post-collisional granitoids are widespread in West Junggar,as well as northern Xinjiang.As a representative of those intrusions,the Jietebutiao granite occurs in the southwestern margin of the West Junggar（northwest China）,and is mainly composed of mid-coarsegrained monzogranite and syenogranite.In the present study,we report the results of high-precision zircon laser-ablation-inductively-coupled plasma mass-spectrometry U-Pb dating on the Jietebutiao granite for the first time,and yield weighted mean ²⁰⁶Pb/²³⁸U ages of 287±9 Ma and 278±3 Ma for monzogranite and syenogranite,respectively.The Jietebutiao granite has a pronounced A-type affinity;it is metaluminous to slightly peraluminous;has a high-K calc-alkaline composition;high concentrations of Na₂O + K₂O,varying from 6.8 to 8.5 wt%;high FeOt/MgO;10 000a/Al ratios,a low CaO,MgO,and TiO₂ content;enriched in some large ion lithophile elements（LILE,such as Rb and Th） and high field strength elements（HFSE,such as Zr,Hf,and Y）;and depleted in Sr,Ba,and Ti.In addition,the granite has a relatively high rare earth element（REE） content（except for Eu）, with significant negative Eu anomalies（Eu/Eu^* = 0.01-0.72）,and showing slight tetrad REE patterns and non-charge and radius controlled（CHARAC） trace element behavior.Petrographic,geochemical, and geochronological data suggest that the parental magma of Jietebutiao intrusions are of mixed origin,and are most probably formed by the interaction between the lower crust- and mantle-derived magmas in the Early Permian post-collisional tectonic setting.The basaltic magmas underplated and interacted with the lower crust that was dominated by deeply buried arc（and back-arc basin） series and the oceanic crust formed in the Paleozoic,and then triggered the partial melting of the juvenile lower crust,producing voluminous granitic melts and forming the Jietebutiao A₂-typc monzogranites, with the lithospheric mantle progressively thinning and rifting to form A₁-type granites,such as syenogranites,in the Jietebutiao pluton.This further proves the important contribution of Late Paleozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang.     

The Geochemical and Zircon Trace Elements Characteristics of A-type Granitoids in Boziguoer,Baicheng County,Xinjiang

The Boziguoer A-type granitoids in Baicheng County,Xinjiang,belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks.The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite,an aegirine or arfvedsonite alkali feldspar granite,and a biotite alkali feldspar syenite.The major rock-forming minerals are albite,K-feldspar,quartz,arfvedsonite,aegirine,and siderophyllite.The accessory minerals are mainly zircon,pyrochlore,thorite,fluorite,monazite,bastnaesite,xenotime,and astrophyllite.The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55％ to 72.29％ with a mean value of 67.32％,Na2O＋K2O is high （9.85％-11.87％） with a mean of 11.14％,K2O is 2.39％-5.47％ （mean =4.73％）,the K2O/Na2O ratios are 0.31-0.96,Al2O3 ranges from 12.58％ to 15.44％,and total FeOT is between 2.35％ and 5.65％.CaO,MgO,MnO,and TiO2 are low.The REE content is high and the total SREE is （263-1219） ppm （mean =776 ppm）,showing LREE enrichment and HREE depletion with strong negative Eu anomalies.In addition,the chondrite-normalized REE patterns of the alkaline granitoids belong to the ＂seagull＂ pattern of the right-type.The Zr content is （113-1246） ppm （mean =594 ppm）,Zr＋Nb＋Ce＋Y is between （478-2203） ppm with a mean of 1362 ppm.Furthermore,the alkaline granitoids have high HFSE （Ga,Nb,Ta,Zr,and Hf） content and low LILE （Ba,K,and Sr） content.The Nb/Ta ratio varies from 7.23 to 32.59 （mean =16.59） and the Zr/Hf ratio is 16.69-58.04 （mean =36.80）.The zircons are depleted in LREE and enriched in HREE.The chondrite-normalized REE patterns of the zircons are of the ＂seagull＂ pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly.The Boziguoer A-type granitoids share similar features with A1-type granites.The average temperature of the granitic magma was estimated at 832-839℃.The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature,anhydrous,and low oxygen fugacity conditions.     

滇西保山地块中-新生代岩浆作用及其构造意义

保山地块上的中-新生代岩浆活动以蚌渺岩体和桦桃林岩体为代表,蚌渺岩体岩石类型为石英二长岩、二长花岗岩,锆石U-Pb年龄为83~85Ma,桦桃林岩体为二云母花岗岩,锆石U-Pb年龄为60~66 Ma,表明该地区在晚白垩世和古新世发生了两次不同的岩浆作用。蚌渺岩体和桦桃林岩体都以全碱含量高为特征,K₂O/Na₂O>1,桦桃林岩体属于高钾钙碱性系列,蚌渺岩体更加倾向于钾玄岩系列。它们的铝饱和指数A/CNK的值均大于1.1,属铝过饱和系列。这两个岩体岩石总体上富集大离子亲石元素和Pb,亏损高场强元素。蚌渺岩体较桦桃林岩体明显富集轻稀土元素[(La/Yb)_N=65.2~67.2],而桦桃林岩体较蚌渺岩体显示明显的负Eu异常(δEu=0.17~0.35)。2个岩体中3件样品41个测点的锆石ε_Hf(t)值变化范围较大(-15.8~-1.1),蚌渺岩体和桦桃林岩体的Hf同位素地壳模式年龄分别集中于2.0~1.2Ga和2.0~1.5Ga。全岩锆饱和温度蚌渺高于桦桃林,说明这两个岩体源区岩石的熔融程度不同。这些地球化学特征指示中-新生代花岗岩类为S型花岗岩,主要来源于古元古代-中元古代地壳物质的重熔,并不同程度地混入了幔源物质。保山地块、腾冲地块和拉萨地体在中-新生代存在几乎同期的岩浆活动,但保山地块与拉萨地体由于岩石地球化学特征不同,不存在对比性,而与腾冲地块存在共同点。保山地块与腾冲地块上的中-新生代岩浆作用与新特提斯洋的闭合和印欧大陆的碰撞息息相关。     

On Correlational Properties for Volcanic Earthquakes Associated with Asamayama (Japan), 1983–2005

To a first approximation, earthquakes directly associated with volcanic activity may be studied as point-stochastic processes. The earthquakes associated with B-type (movements located at 1 km or shallower) eruptive activity in the caldera of Asamayama differ in correlational properties from concurrent deep-seated seismic activity (A-type, located deeper than approximately 1 km). A-type activity occurs either in the form of independently distributed intervals between events or as dependently distributed intervals which are most appropriately analysed in contiguous sub-samples (“windows”). The cross correlations between the magnitudes of A-type earthquakes and depth of events for three periods from 1983 to 2005 may be of significance for interpreting aspects of the volcanic history of Asamayama. The lag-1 serial correlation coefficient for the A-type sequence from 1983 to 1990 is not significantly different from zero. In the case of the sets for 1991–2002 and 2003–2005, the coefficients are small but not zero. The difference is in part, at least, probably due to the well-known confounding effect of trending as opposed to true serial correlation between successive events. The serial correlation coefficient for the B-type crater sequence is not significant. The novel aspect of the present study concerns the relationship between depth of A-type earth movements and magnitude of associated shocks.     

Petrogenesis and tectonic setting of the Queershan composite granitic pluton,eastern Tibetan Plateau: Constraints from geochronology,geochemistry and Hf isotope data

The Queershan composite granitic pluton is located in the north of the late Paleozoic Yidun arc collision-orogenic belt, eastern Tibetan Plateau. The main rock types are coarse-grained porphyritic alkalic-monzonite granite with minor fine-grained porphyritic monzogranite and granodiorite distributed in the eastern and southwestern regions. Here we report their zircon U-Pb ages and geo- chemical data. The intrusive contact relations indicate that granodiorite was formed earlier than the alkalic-monzonite granite(105.9±1.3 Ma) and monzogranite(102.6±1.1 Ma). These suggest that the Queershan composite granitic pluton was formed through three-stage magmatic events. The alkalic-monzonite granite(105.9±1.3 Ma) and monzogranite(102.6±1.1 Ma) are characterized by high SiO2(73.5%–77.7%), K2O+Na2O(6.9%–8.5%), Ga/Al ratios(2.6–3.4) and low Al2O3(11.8%–14.5%), CaO(0.25%–1.5%), MgO(0.18%–0.69%), negative Ba, Sr and Eu anomalies, showing A-type granite affinities. The granodiorite exhibits lower SiO2, P2O5 and K2O+Na2O contents, but higher Al2O3, CaO and MgO contents than alkalic-monzonite granite and monzogranite, showing I-type granite affinity. 176Hf/177 Hf ratios of the alkalic-monzonite granite and the monzogranite are 0.282692–0.282749 and 0.282685–0.282765, respectively, and with similar ?Hf(t) values(?0.56 to 1.43 and ?0.87 to 1.90 respectively). They also present similar TDM2 model ages(1.04–1.22 and 1.07–1.2 Ga respectively), indicating they may be sourced from a similar rock source, mostly like Kangding Complex. The homogeneity of the Hf isotopic compositions and the absence of the MMEs demonstrate that little depleted mantle materials have contributed to the source. We propose that the Mesoproterozoic crust materials of the Yangtze Craton exist beneath the Yidun arc terrane and support it was a dismembered part of the Yangtze Craton. The A-type granites of Queershan composite granitic pluton are most probably related to the closure of the Bangong-Nujiang Tethys ocean.