207Pb/206Pb determination of zircons by laser probe-inductively coupled plasma mass spectrometry

Laser probe_inductively coupled plasma mass spectrometry (LP_ICP_MS) was used to determine 207 Pb/ 206 Pb ratios in single zircon grains. A Nd∶YAG laser operating at 1 064 nm and a Fisons_VG PQII Turbo ICP_MS were employed. For the known zircons, the 207 Pb/ 206 Pb results of LP_ICP_MS are close to the thermal ionization mass spectrometry (TIMS) results. The spatial resolution of this method is 40-50 μm and the sensitivities for lead isotopes are about 300-400 cps/ppm. The precision of 207 Pb/ 206 Pb ratio is 0.3%-4% and depends on the lead concentration of the sampling pits. LP_ICP_MS provides a simple, rapid and economic method for zircon 207 Pb/ 206 Pb determination.     

Petrogenesis and significance of the Hongshan syenitic pluton,South Taihang: zircon SHRIMP U-Pb age, chemical compositions and Sr-Nd isotopes

The Hongshan syenitic pluton (South Taihang) is mainly made up of hornblende syenite and minor granite. SHRIMP zircon dating yields a U-Pb age of 135±2.7 Ma for the emplacement of the pluton, while biotite Rb-Sr isotopic data give an isochron of 120. 3±2.4 Ma. Hongshan syenites show low silica, high alkalis and LILE such as Sr, and exhibit negligible Eu anomalies or slightly positive anomalies in the REE patterns. The syenites show quite enriched isotopic compositions with Isr from 0.7052 to 0. 7102 and εNd(t) from -7.5 to - 11.1. Petrogenesis of the pluton can be that partial melting of an enriched lithospheric mantle gave birth to an alkali basaltic magma, which subsequently underplated in the lower crust and experienced a coupled fractionation of ferromagnesian phases like pyroxene and hornblende and minor (<10 %) contamination of lower continental crust, producing the Hongshan syenites that partially e-volved into granite through combined fractionation of hornblende and feldspar. Our data are not in agreement with a previous model that the syenites originated from melting of lower crust in a thickened crust circumstance, and thus do not support the speculation of "East China Plateau" in the Mesozoic.     

Zircon U-Pb ages of olivine pyroxenite xenolith from Hannuoba: Links between the 97—158 Ma basaltic underplating and granulite-facies metamorphism

U-Pb zircon dating by LA-ICP-MS andSHRIMP for one olivine pyroxenite yields complex agepopulations including Mesozoic ages of 97-158 Ma and 228±8.7 Ma, Early Paleozoic ages of 418--427 Ma, Paleoprotero-zoic age of 1844±13 Ma, Neoarchean age of 2541±54 Ma andmiddle Archean age of 3123±4.4 Ma. The 97--158 Ma and228±8.7 Ma zircons show typical igneous oscillatory zona-tion in CL images, suggesting two episodes of magmaticevents. Overlapping of the 97-158 Ma ages with that ofgranulite xenoliths indicates that the Mesozoic granu-lite-facies metamorphism was induced by heating from thebasaltic underplating at the base of the lower crust. Bothprocesses lastcd at least from about 158 to 97 Ma. Ages of 418--427 Ma could be records of the subduction of Mongoliaoceanic crust under the North China craton. Ages of 1.84 Ga,2.54 Ga and 3.12 Ga correspond to the three importantcrust-mantle evolutionary events in the North China craton,and imply preservation of Precambrian lower crust in thepresent-day lower crust.     

Fluid inclusions hidden in coesite-bearing zircons in ultrahigh-pressure metamorphic rocks from southwestern Sulu terrane in eastern China

Fluidinclusionstudiesarepowerfultoolsfordeci-pheringthefluidevolutionandfluid-rockinteractionin-volvingultrahigh-pressure(UHP)metamorphismofcrustalrocksatmantledepths.Thecompositionandprop-ertiesoffluidinclusionscanreflectthephysico-chemicalconditionsofthefluidsduringplatesubduction,UHPmetamorphismandexhumation.However,UHPmeta-morphicrockscommonlyexperiencedconsiderablede-compressionrelatedtotherapidexhumationprocess.Thishascausedtheinternalpressureoftheinclusionstrappedinthemetamorphicmin…     

Zircon U-Pb SHRIMP dating of the Yematan batholith in Dulan,North Qaidam,NW China

The Yematan batholith crops out over 120 km^2 in the North Qaidam ultrahigh pressure (UHP) metamorphic belt. It consists of granodiorite, monzogranite and biotite granite and forms an irregular intrusion into Neoproterozoic gneiss that has undergone Caledonian UHP metamorphism. Zircons from the Yematan granodiorite yield a SHRIMP U-Pb age of 397 3 Ma. These granitic rocks have geochemical characteristics intermediate between I- and S-type granites, and are post-collisional. We suggest that the Yematan granitic rocks were formed during the last exhumation event of the North Qaidam UHP belt.     

Zircon U-Pb dating for the earliest Neoproterozoic mafic magmatism in the southern margin of the North China Block

Geological records of Neoproterozoic magmaticevents have recently been identified in the central Phanerozoic orogenic belts of China[1]. In regions of east Qinling orogen[2], Dabie-Sulu orogen[3], north Qaidam Basin orogen[4―6], and southwest Tarim Basin…     

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 …     

SHRIMP zircon U-Pb dating for subduction-related granitic rocks in the northern part of east Junggar, Xinjiang

A great deal of studies have recently devoted to the Central Asian orogenic belt (CAOB). Some of the studies have proposed that CAOB is a tectonic frame ofcomplex mosaic fragments, link of multiple suture zone and mountain-basin coupling, and has undergon…     

SHRIMP U-Pb zircon dating for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya and its implications

The Tethyan Himalaya is located between the In-dus-Yarlung Zangbo suture zone to the north and HigherHimalayan crystallines to the south, paleogeographicallybelonging to the northern margin of “Greater India”. TheSangxiu Formation is used to define a series of specialstrata with rich volcanic interbeds, and is only distributedto the southeast of Yangzuoyong Co within 200 km×50 km along the eastern part of central Tethyan Hima-laya[1]. Based on overlapped relationships of strata andfos…     

SHRIMP zircon U-Pb geochronology of Indosinian granites in Hunan Province and its petrogenetic implications

The structure, magmatism and sedimentation within the South China Block (SCB) related to the Indosinian Orogeny had attracted considerable attention since De-prat[1] and Fromagat[2] proposed the “Indosinian move-ment” based on two unconformities between Pre-Norian and Pre-Rhaetian during Triassic in Vietnam. However, Indosinian tectonic evolution of the SCB has been long debated[3―6]. Some researchers believed that the compli-cated structure-magmatism-sedimentation within the SCB w…