An in situ zircon Hf isotopic,U-Pb age and trace element study of banded granulite xenolith from Hannuoba basalt： Tracking the early evolution of the lower crust in the North China craton

Backscattered electron images, in situ Hf isotopes, U-Pb ages and trace elements of zircons in a banded granulite xenolith from Hannuoba basalt have been studied. The results show that the banded granulite is a sample derived from the early lower crust of the North China craton. It is difficult to explain the petrogenesis of the xenolith with a single process. Abundant information on several processes, however, is contained in the granulite. These processes in-clude the addition of mantle material, crustal remelting, metamorphic differentiation and the delamination of early lower crust. About 80% of zircons studied yield ages of 1842 ±40 Ma, except few ages of 3097-2824 Ma and 2489-2447 Ma. The zircons with ages older than 2447 Ma have high εHf (up to +18.3) and high Hf model age (2.5-2.6 Ga), indicating that the primitive materials of the granulite were derived mainly from a depleted mantle source in late Archean. Most εhf of the zircons with early Proterozoic U-Pb age vary around zero, but two have     

Mantle xenoliths from Late Cretaceous basalt in eastern Shandong Province： New constraint on the timing of lithospheric thinning in eastern China

Studies of mantle xenoliths hosted in both the Cenozoic alkali basalt and the Early Paleozoic kimberlite suggest that part of the subcontinental lithosphere as thick as more than 100 km has been lost from the Early Paleozoic to Cenozoic[1—8]. Neither the scale and mechanism nor the accurate timing of the lithospheric thinning has been precisely constrained[7-12]. One of the reasons for this is that there are only a few Mesozoic basalts cropped out, especially, few containing mantle-derived …     

Thermodynamic evolution of lithosphere of the North China craton： Records from lower crust and upper mantle xenoliths from Hannuoba

Lithospheric thinning in East China attracts much attention of geologists. In many cases where a lithospheric thinning is inferred, the trigger for instability is a preced-ing episode of crustal thickening by the continental colli-sion[1]. Lithospheric processes (e.g. lithospheric thinning) could be recorded by the thermal history of the lower crustal and upper mantle xenoliths. Xu et al.[2] suggested that the cooling (from >1200 to 850℃) recorded by spinel harzburgite from Northeast China …     

SHRIMP U-Pb zircon dating for lamprophyre from Liaodong Peninsula： Constraints on the initial time of Mesozoic lithosphere thinning beneath eastern China

It is undebated fact that the lithospheric mantle beneath eastern China was considerably thinned during the Mesozoic time. However, it has no adequate evidence for the exact timing when the lithosphere thinning started. The Liaodong Peninsula is located in the eastern segment of the North China Craton and is one of the important domains to explore the event of lithosphere thinning. SHRIMP U-Pb zircon dating and geochemical study were carried out for the lamprophyre dike swarm that intruded into the magnesite ore-beds in the Dashiqiao Formation of Paleoproterozoic Liaohe Group at the Huaziyu magnesite ore district, Liaodong Peninsula. The results indicate that these lamprophyre dikes were intruded in late Jurassic （155±4 Ma） and show some geochemical characteristics of potassic magmas. It is now accepted that the lithosphere thinning took place in the late Mesozoic, and the peak thinning stage occurred in early Cretaceous （130-120 Ma）. Considering the potassic mafic magmatism marking the onset of the lithospheric thinning, we therefore suggest that the studied late Jurassic potassic lamprophyre dike swarm could imply that the late Jurassic is the time that lithosphere thinning started.     

Finding of Neoproterozoic （～775 Ma） magmatism recorded in metamorphic complexes from the North Qilian orogen： Evidence from SHRIMP zircon U-Pb dating

The Qilian Mountain is considered a part of the Cen- tral Orogenic Belt of China[1]. The Central Orogenic Belt of China, extending for a distance of about 4000 km long in the E-W direction from the east coast west- ward through the mainland China all the …     

Geochemistry and zircon U-Pb ages of granulite xenolith from Tuoyun basalts, Xinjiang： Implications for the petrogenesis and the lower crustal nature beneath the southwestern Tianshan

The continental lithosphere growth mainly includes the horizontal accretion at the plate boundaries and vertical accretion within the plate[1]. Mafic magmatic materials, as the products of crust-mantle interaction[2,3], became more and more important in studying the formation and evolu- tion of the lower crust. The previous geologic researcheson Tianshan, extending nearly 2500 km from east to west, and the neighbor area were mainly focused on the Paleozoic collision structure[4 ― 6], Mesozoi…     

Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance

The Huashanguan rapakivi pluton in Zhongxiang,Hubei Province,China,is the first discovered Proterozoic rapakivi pluton in the Yangtze block.Based on field and petrographical observations,a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton.Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts.Alkali feldspars and quartz had two or more generations.Petrochemically,the Huashanguan rapakivi granites were characterized as having high values of Si,K,Fe,Th,U,La,Ga,Ce,Sm and LREE,low values of Ca,Mg,Sr,Nb,Y and HREE,and a negative Eu anomaly.These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites,and had an affinity to A-type granites.LA-ICP-MS U-Pb zircon dating also was conducted.The dating yielded a 207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2),which represents the age of the pluton emplacement.The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton,and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation.The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block.These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.     

SHRIMP U-Pb zircon geochronology of granulites at Rimana （Southern Tibet） in the central segment of Himalayan Orogen

TheCenozoicHimalayanorogenisimportantinun-derstandingcontinentaldynamicprocesses.Lowercrustal,high-grademetamorphicrockshaverecentlybeendiscov-eredinNamcheBarwaandParmir,i.e.therespectivere-gionsofeasternandwesternsyntaxisoftheorogen[1—4].Eclogitesthatunderwentgranulite-faciesmetamorphismhaverecentlybeenreportedintheCadaareatotheeastofMountEverestinthecentralsegmentoftheHimalayanorogen[5].WiththehelpofthegeologicalsurveyofDing-gyeCountyandChentangSheets(scale1︰250000),high-pressuremafic…     

辽东矿洞沟地区四张磙子古元古代花岗岩识别及意义

为深入研究辽宁盖州四张磙子花岗岩的形成时代、地质特征及意义,通过锆石LA-ICP-MS U-Pb定年系统和X射线荧光光谱仪,对四张磙子花岗岩进行年龄测试和主微量元素分析.锆石定年结果表明,四张磙子花岗岩侵位年龄为(1 871.2±9.3)Ma,属于古元古代产物.主微量元素结果表明,四张磙子花岗岩与矿洞沟正长岩及闪长岩的Si O2与K2O及Na2O基本呈现正相关,与Ti O2,Al2O3,TFe2O3,Ca O,Mg O,M n O呈负相关,表明3种岩体可能具有亲缘关系.结合前人研究,认为四张磙子花岗岩与矿洞沟正长岩、闪长岩可能具有同一岩浆来源,四张磙子花岗岩为古元古代侵位的花岗岩体.     

滇西新生代赋矿斑岩及花岗岩包体的锆石年代和稀土特征的地质意义

滇西地区沿金沙江—哀牢山断裂带广泛发育新生代富碱斑岩及相关多金属矿床.以六合正长斑岩中与暗色深源包体共存花岗岩包体和马厂箐赋矿斑状花岗岩为研究对象,开展岩相学和LA-ICP-MS锆石U-Pb年代学研究及锆石稀土元素分析.研究表明,六合花岗岩浆活动起始时间约为(42.8士1.6)Ma B.P.,包体结晶成岩时间与主岩(正长斑岩)年龄一致(38.63 Ma B.P.±0.52 MaB.P.);马厂箐含矿富碱岩浆起始活动时间约为(38.51士0.52)MaB.P.,结晶成岩时间为(35.80士0.20)Ma B.P..结合花岗岩包体的液态不混溶现象和锆石稀土元素特征分析,初步揭示研究区富碱岩浆起源、演化及成岩成矿作用过程为:来自交代富集地幔源区的硅不饱和富碱岩浆伴随互不混溶含矿地幔流体同步上升运移;该富碱岩浆以其底劈作用和地幔流体交代作用引发地壳深熔形成长英质岩浆.此后的2类岩浆过程分为2部分:一是富碱岩浆直接捕获少量长英质岩浆以不混溶方式继续同步运移至地壳结晶成岩,形成含花岗岩包体的硅不饱和富碱斑岩;二是富碱岩浆与长英质岩浆发生同化混染形成混合岩浆运移至地壳,其中所含不混溶含矿地幔流体伴随其结晶成岩进行自交代蚀变,形成硅过饱和的赋矿斑状花岗岩.     

Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.