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Ke C.H.,Chinese Academy of Geological Sciences | Wang X.X.,Chinese Academy of Geological Sciences | Li J.B.,Changan University | Qi Q.,Institute of Resource Survey and Assessment | Qi Q.,China University of Geosciences
Acta Petrologica Sinica | Year: 2012

LA-ICP-MS U-Pb dating for the granites from the Taoguanping and Xigou plutons in the Mahe Mo deposit in the North Qinling yields concordant ages of 157 ± IMa ( NSWD =13) and 153 ± IMa ( NSWD = 14) respectively indicating that the two plutons were formed at late Jurassic. The Mahe Mo deposit is closely related to the two plutons. Therefore these ages may suggest the Mo deposit formed at Late Jurassic appreciably later than 157 ∼ 153Ma. The granites from the Taoguanping and Xigou plutons are characterized by high in silica (68.12% -76.33%) and alkali (Na2O + K2O =6.35% -10.38%) with the A/CNK of 0.85 -1.14 and lager variation of K 20/Na20 (0.91-1.89) , showing that they are metaluminous or weakly peraluminous and high-K calc-alkaline series. The Taoguanping and Xigou granites are enriched in U, Pb, Hf, but depleted in Rb, Ba, K, Sr and P. The REE patterns are characterized by enrichment in LREE with weak negative abnormal of Eu ( 0.5-0.9 ) , but a few samples have weak positive Eu anomalies (1.05 to 1.08). The granites are similar to the molybdenum deposits related granites in the southern margin of the North China Block in enriched in SiO 2 and Na2O + K2O.However, these granites are lower in SiO2 ,Na2O + K2O and higher in CaO and MgO than the granites in the southern margin of the North China Block. It may be one reason that the Mahe Mo deposit is not as larger as the deposits in the southern margin of the North China Block. Source


Qi Q.J.,Institute of Resource Survey and Assessment | Wang X.X.,Chinese Academy of Geological Sciences | Ke C.H.,Chinese Academy of Geological Sciences | Li J.B.,Changan University
Acta Petrologica Sinica | Year: 2012

The Laoniushan granitoid complex is located in the southern margin of North China Block.Field work and LA-ICP-MS zircon dating suggest that this complex consists of Late Triassic (Indosinian) and Late Jurassic ( Yanshanian) granitoids. The rock types of the Indosinian granitoids are adamellite, quartz diorite and coarse-grained biotite monzogranite with ages of 223 ± IMa, 223 ± IMa and 214 ± IMa, respectively. The Yanshanian granitoids are mid-coarse-grained, mid-grained biotite monzogranite and finegrained biotite monzogranite with ages of 152 ±lMa and 146Ma, respectively. The Indosinian adamellite and quartz diorite are low in SiO2 but rich in A12O3 and Na2O + K2O, showing Shoshonite series and metaluminous I-type granite: coarse-grained biotite monzogranite are rich in SiO2, A12O3 and Na2O + K2O, but poor in MgO with the features of high-K calc-alkalic series and metaluminous to peraluminous I-type granite. The Yanshanian biotite monzogranite with high SiO2, A12O 3 and Na2O + K2O also show the nature of high-K calc-alkalic series and metaluminous I-type granite. From Late Triassic to Late Jurassic SiO2 content of these granitoids increase, but MgO, CaO and Na2O decrease. The total REE contents of the granitoids are very high, especially LRRE, suggesting obvious LRRE and HRRE fractionation, and weakly negative Eu anomalies. The granitoids of Indosinian and Yanshanian are all rich in large ion lithophile elements (K, Rb, Ba, Sr) , and relative depleted in high-field strength elements (Nb, Ta, P). The Indosinian granitoids with ε/Nd (t) = -11.3- -14.87, tDM = 1.7 ∼ 1.9Ga, ε/Hf(t) = -9.57-25.11 ,tDM2 = 1863-2841Ma, and the Yanshanian ε/Nd (t) = -13.32- -16.83, tDM = 1.7-1.9Ga, ε/Hf(t) = -18.28- -24.79, tDM2 =2360 -2767 Ma, indicate that their sources are dominated by old crust component related to the Archaean Taihua Group and the sources of the Indosinian granitoids is with more juvenile component contributed. Source


Ke C.H.,Chinese Academy of Geological Sciences | Wang X.X.,Chinese Academy of Geological Sciences | Li J.B.,Changan University | Yang Y.,China University of Geosciences | And 2 more authors.
Acta Petrologica Sinica | Year: 2013

Zircon U-Pb LA-ICPMS dating for the Xiaxie and Mulonggou granitoid plutons from the southern margin of the North China block yield 154 ±2Ma (2a, N = 16) and 151 ± IMa (2σ, N = 15), respectively. These granitoids are metaluminous or weakly peraluminous and high-K calc-alkaline or shoshonite series with A/CNK = 0. 75 ∼ 1. 04, Na2 O + K2 O = 6. 15 % ∼ 8. 42 %, K2 O/Na2 O = 0. 77 ∼2. 29. They are riched in LILE, e. g. LREE, Rb, Ba, K, Pb, Sr and depleted in HFSE, e. g. HREE, Zr, Hf, Ta, Nb, P, Ti with weak negative abnormal of Eu (δ5Eu = 0. 85 ∼ 0. 99). Whole rocks Sr-Nd compositions of the granitoids are characterized by ISr = 0. 708676 ∼0. 711480 and εNd(t) = -22 ∼ - 16. 1 with Nd model ages of 2. 37Ga to 2. 96Ga. The granitoids show a large variation in zircon Hf compositions with εHf(t) = -27. 8 ∼ - 18. 4 and two-stage model ages of 2. 37Ga to 2. 96Ga. Geochemistry and Sr-Nd-Hf isotopic compositions of the granitoids suggest that they are derived from an ancient continental crust such as the Archaean Taihua Group, but the zircon Hf compositions and the mafic magmatic enclaves in the granitoids may imply that juvenile component contribute to their formation. Acording to the petrography and regional geological features, the juvenile component are mainly mantle related material. Therefore, the formation of these granitoids could be interpreted as mixing/mingling of an underplated mantle-derived magma and its induced crustal-melted magma in a deep crust. Source


Ke C.-H.,Chinese Academy of Geological Sciences | Wang X.-X.,Chinese Academy of Geological Sciences | Yang Y.,China University of Geosciences | Qi Q.-J.,Institute of Resource Survey and Assessment | And 3 more authors.
Geology in China | Year: 2012

The Nantai Mo polymetallic deposit is a typical porphyry-skarn deposit in North Qinling Mountains, the magmatic rocks in this deposit include granite-porphyry, quartz porphyry veins and explosion breccia, and there occur porphyry-type and skarn-type Mo polymetallic mineralizations within and around the granite porphyry body. The granite-porphyry from the Nantai Mo polymetallic deposit is dated at (151±l)Ma (N=12, NSWD =0.32)by using zircon U-Pb LA-ICPMS. Six molybdenites samples from the deposit yield Re-Os isotope model ages ranging from (146±2)Ma to (151±2)Ma,with an weighted average of (148.8±1.7)Ma (N=12, NSWD =0.84). The granite age and the metallogenic age are consistent with each other within the error limits, suggesting that the Nantai Mo polymetallic deposit was formed in the late Jurassic period, consistent with the formation epoch of the main porphyry-skarn type molybdenum deposits on the southern margin of North China Block. The zircon Hf isotope composition of the granite -porphyry has a large variation, with initial ratios of 176Hf/177Hf ranging from 0.281 864 to 0.282 454,εHf (t) from -28.8 to -7.9, and two-stage model ages from 2654Ma to 1506Ma. These data suggest that granite -porphyry was probably derived form several sources dominated by curstal materials with the addition of small amouts of mande materials, and the old crust was dominated by the contribution of juvenile components. Therefore, the source of the metallogenic material for the Nantai Mo polymetallic deposit was probably the same as that of the granite. Source


Wang X.,Chinese Academy of Geological Sciences | Wang T.,Chinese Academy of Geological Sciences | Ke C.,Chinese Academy of Geological Sciences | Yang Y.,China University of Geosciences | And 4 more authors.
Journal of Asian Earth Sciences | Year: 2015

Voluminous Late Mesozoic granitoids and the world's largest Mo deposits occur in the East Qinling. This paper presents the results of Nd-Hf isotopic mapping for the Late Mesozoic granitoids (155-105 Ma) and demonstrates their constraint on the basements and distribution of the Mo deposits in the East Qinling. This isotopic map, made by 98 (21 new and 77 published) whole-rock Nd isotopic and 29 (7 new and 22 published) average zircon Hf isotopic data, shows large variations of whole-rock εNd(t) values from -22.1 to -1.5, and the correspondingly Nd model ages (TDM(Nd)) from 2.83 to 0.79 Ga, and zircon εHf(t) values from -26.3 to +0.1 and two-stage Hf model ages (TDM2(Hf)) from 2.86 to 0.96 Ga. Three regions of variations have been identified from north to south: (a) εNd(t) values range from -22.1 to -10.9 with TDM(Nd) of 2.82-1.47 Ga, and εHf(t) values 26.3 to -13.5 with TDM2(Hf) 2.86-2.04 Ga; (b) εNd(t) values -13.9 to -1.5 with TDM(Nd) 2.02-0.79 Ga, and εHf(t) values -16.2 to +0.1 with TDM2(Hf) 1.96-0.96 Ga; and (c) εNd(t) values -6.3 to -4.5 with TDM(Nd) 1.28-1.12 Ga, and εHf(t) values -1.0 to -0.3 with TDM2(Hf) 1.25-1.22 Ga, respectively. The three regions approximately correspond to the three different terranes, the southern margin of the North China Block (NCB), the North Qinling Belt (NQB) and the South Qinling Belt (SQB), respectively. These demonstrate that the granitoids in the different terranes have distinct sources and their sources change from old to more juvenile from the north (southern margin of the NCB) to the south (SQB). These also reveal the distinct basements for the terranes in Late Mesozoic. The southern margin of the NCB contains widespread Neoarchaean to Paleoproterozoic basement, the NQB comprises Archaean to Neoproterozic basement and the SQB Mesoproterozic to Neoproterozic basement. All these suggest that the three terranes underwent different tectonic evolution and the continental crust of the East Qinling were mainly formed during Archaean to Neoproterozic, different from a typical accretion orogen. The old sources of the granitoids and basements of the terranes constrain the distribution, scale and number of the Mo mineralization and deposits. Mo mineralization is closely related to the small granitic bodies with old continental component sources and Mo deposits are mainly hosted by the terranes with oldest basement. The scale and number of the Mo mineralization and deposits decreased from the southern margin of the NCB to SQB. © 2014 Elsevier Ltd. Source

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