藏南冈底斯南缘程巴岩体高Sr/Y花岗闪长岩和包体形成机制及Sr-Nd-Hf同位素制约   总被引：1，自引：0，他引：1  

尚振  曾令森  高利娥  高家昊  陈福坤  侯可军  王倩  郭春丽 《地质通报》2016,35(1):71-90

程巴岩体位于藏南冈底斯岩基东段南缘,由花岗闪长岩、细粒闪长质包体等组成。测得的锆石U-Pb年龄可以代表岩石的形成年龄,即花岗闪长岩形成年龄为29.40±0.18Ma与29.42±0.25Ma,细粒闪长质捕虏体形成年龄为30.02±0.15Ma。花岗闪长岩具有较高的Si O2(65.2%~66.2%)、K2O(3.2%~4.0%),较低的铁(TFe O=3.2%~4.0%)和Mg O(约2%),同时具有高Sr(774×10-6~813×10-6)、低Y(9.9×10-6~11.2×10-6)、高Sr/Y值(63.4~82.2)等特征;闪长质包体表现出较低的Si O2(53%~56.1%)和K2O(1.5%~3.2%),较高的铁(TFe O=6.1%~8.1%)、Mg O(4.0%~6.2%)和Na2O/K2O≥2,同时具有负Eu异常(Eu/Eu*=0.432~0.804)。2种岩性都富集LREE及LILE,亏损HREE及HFSE,具有较高且一致的εHf(t)值(+1.1~+6.2)和全岩εNd(t)值(-2.9~-5.9)。以上数据表明,花岗闪长岩与细粒闪长质包体由同一岩浆分离结晶形成,花岗闪长岩经历磷灰石和角闪石的分离结晶,其高Sr/Y值为岩浆分离结晶的结果,并不代表原始岩浆组分。  相似文献   

Petrology,geochemistry and thermobarometry of the northern area of the Flamenco pluton,Coastal Range batholith,northern Chile. A thermal approach to the emplacement processes in the Jurassic andean batholiths     

《Journal of South American Earth Sciences》2016

The Flamenco pluton is part of a N–S alignment of Late Triassic to Early Jurassic intrusive belt comprising the westernmost part of the Coastal Range batholith in northern Chile. The Jurassic-Cretaceous voluminous magmatism related to subduction in the western active continental margin of Gondwana is emplaced in the predominantly metasedimentary Paleozoic host-rocks of the Las Tórtolas formation, which in the northern area of the Flamenco pluton present an intense deformation, including the Chañaral mélange.Geochemically, the Flamenco pluton shows a wide compositional variability (SiO₂ between 48wt % and 67wt %). Gabbros, Qtz-diorites and tonalites, mesocratic and leucocratic granodiorites are classified as calc-alkaline, calcic, magnesian and metaluminous magmatism. Flamenco granitoids define cotectic linear evolution trends, typical of magmatic fractionation processes. Geochemical trends are consistent with magmas evolved from undersaturated and low-pressure melts, even though the absence of transitional contacts between intrusive units precludes in-situ fractionation. Although some granodioritic samples show crossed geochemical trends that point to the compositional field of metasediments, and large euhedral prismatic pinnite-biotite crystals, typical Crd pseudomorph, are observed in contact magmatic facies, geochemical assimilation processes are short range, and the occurrence of host-rocks xenoliths is limited to a few meters from the pluton contact.A thermal approach to the emplacement process has been constrained through the thermobarometric results and a 2D thermo-numerical model of the contact aureole. Some Qtz-diorites and granodiorites located in the north area of the pluton exhibit granulitic textures as Hbl-Pl-Qtz triple junctions, poikiloblastic Kfs and Qtz recrystallization. The Hbl–Pl pairs have been used for the thermobarometric study of this metamorphic process, resulting granoblastic equilibrium temperatures between 770 and 790 °C, whereas Hbl–Pl pairs in domains that preserve the original igneous textures yield temperatures above 820 °C. This is characteristic of self-granulitization processes during the sequential emplacement of composite batholiths.In addition, the thermal modeling was used in order to compare the expected and observed thermal contact aureole of the intrusive body. Model P-T conditions have been established between 3 and 4 kbars (extracted from the thermobarometric results), and temperatures between 1159 °C (liquidus temperature for a tonalitic composition) and 992 °C (fixed at the rheological threshold of a 50% crystal fraction). The thermal modeling estimates a homogeneous contact aureole, where the established temperatures for the melting reactions in the host-rocks are located at distances between 200 and 650 m from the magma chamber boundary, whereas the temperatures for Crd stabilization extend 1500 m far from the contact in the case of the emplacement at liquidus temperatures and 4 kbars. According to field observations, the contact aureole presents a scarce development in the northern area of the Flamenco pluton, with few migmatite outcrops and less than 1 Km in thickness for Crd-schists. However, in the southern contact, partially melted rocks are described at distances up to 2 km from the Flamenco pluton boundary.The processes of self-granulitization and the differences between the observed and calculated (by the thermal modeling of one single pulse) contact aureole suggests a process of incremental emplacement for the Flamenco pluton, by accretion of magmatic pulses from north to south (in its current position), where the thermal maturity reached through the repeated magmatic intrusion generates a more extensive area of high-grade metamorphism.  相似文献   

Nature and origin of Triassic igneous activity in the Western Qinling Orogen: the Wenquan composite pluton example   总被引：6，自引：0，他引：6  

Kun-Feng Qiu  Hao-Cheng Yu  Zong-Yang Gou  Zhi-Lu Liang  Jia-Lin Zhang  Rui Zhu 《International Geology Review》2018,60(2):242-266

The Western Qinling has been acknowledged to witness superimposed orogeny including north subduction of Paleotethys ocean and collision between North China and South China blocks; however, the precise timing constraints on transition of tectonic regime are remaining enigmatic. The Wenquan composite batholith comprising five phases and mafic enclaves is an ideal example to unlock this puzzle. The host granitoids are felsic, metaluminous to peraluminous, and high-K calc-alkaline to shoshonitic suite with I-type affinity. The mafic enclaves, however, are intermediate, and high-K calc-alkaline to shoshonitic. Zircon ages of multiple phases indicate an episodic growth lasting nearly 30 million years ranging from 238, 228, 218 to 208 Ma, consistent to Triassic igneous activity recording a transition regime from a subduction setting to a syn-collision setting and a post-collision setting in Western Qinling. Lead isotopes of whole-rock and K-feldspar at Wenquan and Lu-Hf isotopes of zircons separated from biotite monzogranite porphyry, porphyritic monzogranite, monzogranite porphyry, and hosted mafic enclaves suggest that the heat and the hot mafic melt initiated by the break-off of the northward subducting South China block lithosphere triggered partial melting of the Mesoproterozoic subcontinental lithospheric mantle to produce mafic magmas, and the underplated mafic magmas caused partial melting of the shallow subducted Mesoproterozoic lower crust generating granitic magmas at Wenquan. Combined our field observations and petrology study with a holistic review on previous geochronological and geochemical data of Triassic granitoids throughout the Western Qinling, we in this contribution proposed that the Triassic igneous activity in the Western Qinling corresponding to superimposed orogeny evolved from the northward subduction of Palaeotethys ocean (250–235 Ma) through syn-collision (228–215 Ma) to post-collision (215–185 Ma) between the North China and South China blocks.  相似文献   

Identification of Magma Mixing: A Case Study of the Daocheng Batholith in the Yidun Arc     

Ruigang Zhang  Xue Gao  Liqiang Yang 《地球科学进展》2018,33(10):1058-1074

The Daocheng batholiths, located in the east of the Yidun arc, consist of granite, granodiorite and K-feldspar granite. Abundant massive mafic microgranular enclaves (MMEs) mainly developed within the granodiorite and K-feldspar granite, and they have clear contacts with the hosted granites. The MMEs are characterized by the quartz eye structure, quenched apatite, and plagioclases phenocrysts with obvious oscillatory zones. Petrographical studies on MMEs and host granites, zoned plagioclase and whole-rock geochemical analysis were carried out to identify the presence of magma mixing. Combined with the previous studies on the whole-rock Sr-Nd-Hf isotopic signatures, the petrogenesis of Daocheng batholith was discussed. The zoned plagioclases from MMEs have An contents varying between 29 and 44, while those from the host granites have An contents of 21~50. The compositional variations and corrosion structure of plagioclase are probably related to magma mixing. Geochemically, the MMEs have relatively low SiO₂ contents (56.34~60.91wt%), high Al₂O₃ contents of 16.06~17.98wt%, and are enriched in magnesium and iron, belonging to metalumnious series (A/CNK=0.82~0.98). The Daocheng batholith belongs to high-K calc-alkaline series, which have high alkaline contents (Na₂O+K₂O=6.25~7.79wt%) and low CaO contents (1.40~3.22wt%). Furthermore, both the MMEs and hosted granites are enriched in LILEs (K, Rb and Pb) and LREEs and depleted in HFSEs (Nb, Ta, Zr, Hf, P and Ti), showing affinities of typical arc magmas. Compared with the host granites, the MMEs are characterized by lower (La/Yb)_N ratios of 1.99 to 2.46, and much more obvious Eu depletions (Eu/Eu^*=0.30~0.50). The host granites have Rb/Sr ratios ranging from 1.0 to 1.9, and they are consistent with the crust-derived materials (Rb/Sr>0.5). Their Zr/Hf ratios range from 27.5 to 36.9, which are close to the transitional Zr/Hf ratios between mantle-and crust-derived materials. This indicates that the formation of Daocheng batholith is genetically related to the mixing between mantle-and crust-derived materials. In addition, the relatively low silica contents and high Mg# values, and the linear patterns of MgO, Al₂O₃ and Fe₂O₃ with SiO₂ contents from the MMEs and host granites, show that the formation of MMEs is genetically related to magma mixing. Overall, the parent magmas of Daocheng granites are derived from the partial melting of Late Triassic arc lower crust, with the input of minor mantle-derived materials. The MMEs are generated by the mixing of the mafic magma with felsic magma.  相似文献   

西藏南拉萨地体尼木地区侏罗纪花岗岩地球化学与岩石成因     

赵书槿  赵志丹  唐演  齐宁远  孙昊  刘栋  王青  朱弟成 《岩石学报》2021,37(11):3464-3478

冈底斯岩基是新特提斯洋北向俯冲和印度-欧亚大陆碰撞的重要岩浆记录,尼木地区位于冈底斯岩基中部。本文报道了尼木地区寄主二长花岗岩和辉长质包体的锆石U-Pb年代学、元素地球化学和锆石Hf同位素。锆石U-Pb定年结果表明,寄主花岗岩（197~190Ma）和包体（195Ma）同期侵位,形成于早侏罗纪。寄主二长花岗岩为弱过铝质高钾钙碱性系列岩石,富集轻稀土和K、U、Sr等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,锆石ε_Hf（t）值为+13.9~+16.0,其可能来源于初生地壳的部分熔融;辉长质包体为准铝质钙碱性系列岩石,具有与寄主岩相似的稀土和微量元素分配特征,锆石ε_Hf（t）值为+13.8~+16.0,其可能代表了侏罗纪形成的新生下地壳,即寄主岩石的岩浆源区;结合前人研究,本文认为尼木地区的寄主花岗岩和暗色包体可能与新特提斯洋北向俯冲引起的地幔和初生地壳的部分熔融有关。  相似文献   

变泥质岩的深熔作用与具铈（Ce）负异常熔体的成因   总被引：6，自引：0，他引：6  

曾令森  Mihai  DUCEA  Jason  SALEEBY 《岩石矿物学杂志》2005,24(5):425-430

对美国加州南Sierra Nevada岩基中一个典型的中生代变质表壳岩及其混合岩带进行了详细的野外观察和元素地球化学研究。研究发现:在持久(约为150Ma)的花岗岩侵位作用下,早白垩世变泥质岩发生达角闪岩相的中高级变质作用和部分熔融,导致Isabella混合岩的形成;浅色体具有和变泥质岩及混合岩近平行的REE分布模式,但浅色体的LREE含量相对较低;和变泥质岩相似,混合岩中的浅色体具有显著的Ce负异常。野外观测、岩相观察及元素地球化学特征表明,浅色体显著的Ce负异常是继承了原岩的Ce负异常特征,而不是由于副矿物(磷灰石、独居石或锆石)的差异溶解或结晶分异作用造成的。早白垩世变泥质岩(浅色体的原岩)主要由泥质及沙质海相沉积物组成,局部夹基性火山灰和火山碎屑,形成于与大陆岛弧密切相关的浅海环境。原岩的Ce负异常反映了较还原的浅海沉积环境。具有Ce负异常浅色体的产出表明,如果俯冲带上的沉积岩在俯冲过程中发生部分熔融作用并且所产生的熔体参与大洋型岛弧岩浆作用,最终可以导致具有Ce异常的基性岩浆生成。  相似文献   

SHRIMP ziron U-Pb geochronology of early Mesozoic felsic igneous rocks from the southern Lancangjiang and its tectonic implications   总被引：5，自引：0，他引：5  

Peng Touping  Wang Yuejun  Fan Weiming  Liu Dunyi  Shi Yuruo  Miao Laicheng 《中国科学D辑(英文版)》2006,49(10):1032-1042

The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzonitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean ²⁰⁶Pb/²³⁸U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean ²⁰⁶Pb/²³⁸U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (∼230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic ²⁰⁶Pb/²³⁸U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of development of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.  相似文献   

SHRIMP zircon U-Pb geochronology of early Mesozoic felsic igneous rocks from the southern Lancangjiang and its tectonic implications   总被引：1，自引：0，他引：1  

PENG Touping  WANG Yuejun  FAN Weiming  LIU Dunyi  SHI Yuruo  MIAO Laicheng 《中国科学D辑(英文版)》2006,49(10)

The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzo nitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean 206Pb/238U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean 206Pb/238U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (~230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic 206Pb/238U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of devel- opment of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.  相似文献   

冀东都山花岗岩基及相关花岗斑岩脉SHRIMP锆石U-Pb法定年及其意义   总被引：22，自引：1，他引：22  

罗镇宽  苗来成  关康  裘有守  Y.M.Qiu  N.J.McNaughton  D.I.Groves 《地球化学》2003,32(2):173-180

都山花岗岩体是冀东地区最大的花岗岩基,在其周边产有众多与其有关的“卫星”岩体和岩脉。采用先进的SHRIMP定年方法,测得都山花岗岩基的206Pb/238U年龄为(223±2)Ma,其东侧三家金矿区成矿前花岗斑岩脉的年龄为(222±4)Ma,二者在误差范围内一致,花岗岩基和花岗斑岩脉可视为同一次岩浆活动的产物。这种晚古生代末—早中生代印支期的花岗岩在华北克拉通北缘广泛分布,显示它是一次重要的构造-岩浆事件的产物。根据岩石化学和微量元素特征及有关判别图,都山等印支期花岗岩可能属中朝板块与西伯利亚板块碰撞造山作用的后碰撞花岗岩。花岗斑岩脉中发现有新太古代的继承锆石,表明花岗斑岩的部分源岩为区内新太古代八道河岩群变质岩。都山花岗岩与花岗斑岩脉同时、同源,推测其源岩也有部分为新太古代结晶基底的变质岩。花岗岩与区内金矿化有较大的时差,两者不存在直接的成因联系,仅表明成矿晚于早中生代印支期。  相似文献   

浙江景宁花岗岩基的解体划分及其演化     

王天德  曹金用 《地质通报》1998,(4)

根据同源岩浆演化的观点,运用岩石谱系单位的划分方法,将景宁花岗岩基解体,划分为９个单元,归并成２个超单元。岩体定位方式为断裂扩张型。  相似文献