Petrogenesis of Early Cretaceous intrusions in the Sulu ultrahigh-pressure orogenic belt, east China and their relationship to lithospheric thinning
Petrogenesis of Early Cretaceous intrusions in the Sulu ultrahigh-pressure orogenic belt, east China and their relationship to lithospheric thinning
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DOI：
10.1016/j.chemgeo.2005.07.006
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发表时间：
2005-11
期刊：
影响因子：
3.9
通讯作者：
Jin-Hui Yang;Fu-Yuan Wu;Sun‐Lin Chung;S. Wilde;M. Chu;C. Lo;B. Song
中科院分区：
文献类型：
--
作者：
Jin-Hui Yang;Fu-Yuan Wu;Sun‐Lin Chung;S. Wilde;M. Chu;C. Lo;B. Song
摘要对苏鲁造山带两套晚中生代基性-长英质岩浆岩进行了年代学、地球化学、全岩Sr-Nd和锆石Hf同位素分析，探讨了它们的岩石成因及其构造意义。石九所二长花岗岩SHRIMP锆石206pb /238U年龄为127±2 Ma，角闪石锆石40ar /39Ar年龄为123.5±0.4 Ma。该岩体基性包裹体的SHRIMP锆石206pb /238U年龄为124±3 Ma，角闪石40ar /39Ar年龄为124.2±0.4 Ma，表明基性包裹体与寄主二长花岗岩在同一时期结晶。全岩40ar /39Ar测年结果表明，岩脉就位年龄为111.2±0.1 Ma。二长花岗岩低MgO和Cr，高Na2O， Sr-Nd-Hf同位素数据(87Sr/86Sr>0.7085, Nd（t)= - 20.5, Hf(t)= - 22.5 ~ - 56.6）符合晚太古宙至古元古代下地壳的演化特征，并有地幔物质参与。高Nd(t)和Hf(t)值的同代基性包体的存在表明，石九所岩体的形成过程中存在岩浆混合和幔源物质的参与。侵入二长花岗岩的基性岩脉具有超古典岩石特征。其地球化学特征为高MgO （Mg#高达75）和高Cr（高达1233 ppm），低TiO2（1.11 ~ 1.24 wt.%）和总Fe2O3(8.33 ~ 9.09 wt.%)，富集LILEs（如Rb、Ba、Sr）和lree，亏缺HFSE（如Nb、Ta和Ti），初始87sr /86Sr比值为0.7076 ~ 0.7078,Nd(t)值为负（- 17.6 ~ - 18.2），表明它们来源于含角闪石的难熔岩石圈地幔。石昌—方子二长—二长岩的锆石SHRIMP U-Pb年龄为~ 122 Ma。这些岩石的Sr、Nd和Hf同位素组成(初始值87sr /86Sr=0.7083 ~ 0.7088, Nd（t)=−16.5 ~−17.7,Hf(t)=−20.4）与附近石酒所岩体的基性岩脉相似，表明它们来源于同一源区。高Rb和HREE、低Sr和Ba以及强烈的负Eu异常表明，单黄道宙岩浆是由辉石和斜长石为主的岩浆分馏形成的，这些岩浆来源于富集的地幔源。综上所述，苏鲁造山带早白垩世岩浆活动与苏鲁地区特征性超高压变质岩的晚三叠世俯冲或剥蚀作用无关；相反，它们是在伸展环境下的幔壳相互作用的结果，很可能是由早白垩世华北克拉通东部岩石圈地幔的广泛移除引起的。
Geochronological, geochemical, whole-rock Sr–Nd and zircon Hf isotopic analyses have been carried out on two suites of Late Mesozoic mafic to felsic magmatic rocks in the Sulu orogenic belt (east-central China) with the aim of characterizing their petrogenesis and tectonic implications. The Shijiusuo monzogranite has a SHRIMP zircon206Pb/238U age of 127±2 Ma and an40Ar/39Ar age on hornblende of 123.5±0.4 Ma. A mafic enclave from this pluton has a SHRIMP zircon206Pb/238U age of 124±3 Ma and a hornblende40Ar/39Ar age of 124.2±0.4 Ma, indicating coeval crystallization of the mafic enclaves and host monzogranite. Whole rock40Ar/39Ar dating gives an emplacement age of 111.2±0.1 Ma for the mafic dikes. The monzogranites have low MgO and Cr, high Na2O, and Sr–Nd–Hf isotopic data (87Sr/86Sr>0.7085, ɛNd(t)=−20.5 and ɛHf(t)=−22.5 to −56.6) consistent with derivation from Late Archean to Paleoproterozoic lower crust with involvement of mantle materials. The presence of coeval mafic enclaves with high ɛNd(t) and ɛHf(t) values indicates magma mixing and involvement of mantle-derived materials in the generation of the Shijiusuo pluton. The mafic dikes that intrude the monzogranite have characteristics of ultrapotassic rocks. Their geochemical features, such as high MgO (Mg# up to 75) and Cr (up to 1233 ppm), low TiO2(1.11–1.24 wt.%) and total Fe2O3(8.33–9.09 wt.%), enrichment in LILEs (e.g., Rb, Ba, Sr) and LREEs, and depletion in HFSE (e.g., Nb, Ta and Ti), together with initial87Sr/86Sr ratios of 0.7076–0.7078 and negative ɛNd(t) values (−17.6 to −18.2), indicate they were derived from an amphibole-bearing, refractory lithospheric mantle. The Shichang–Fangzi monzodioritic to monzonitic rocks have zircon SHRIMP U–Pb ages of ∼122 Ma. These rocks have Sr, Nd and Hf isotopic compositions (initial87Sr/86Sr=0.7083–0.7088, ɛNd(t)=−16.5 to −17.7 and ɛHf(t)=−20.4) similar to the mafic dikes in the nearby Shijiusuo pluton, indicating they were derived from a common source. High Rb and HREE, low Sr and Ba and strongly negative Eu anomalies indicate that the monzodioritic magmas resulted from pyroxene- and plagioclase-dominated fractionation of magma derived from an enriched mantle source. Taken together, these features indicate that Early Cretaceous magmatism in the Sulu orogenic belt was not related to Late Triassic subduction or exhumation of the ultrahigh-pressure metamorphic rocks that characterize the Sulu region; instead they resulted from mantle–crust interaction in an extensional setting, most likely induced by widespread removal of lithospheric mantle in the eastern North China Craton during the Early Cretaceous.