中条山地区涑水杂岩新太古代烟庄正长花岗岩年龄及成因:对华北克拉通地壳演化的制约

Geochronology and Petrogenesis of Neoarchean Yanzhuang Syenogranites from Sushui Complex in the Zhongtiao Mountains: Implications for the Crustal Evolution of the North China Craton

太古宙末期钾质花岗岩的广泛发育是陆壳成熟和稳定化的重要标志,对了解早期陆壳的形成与演化具有重要的意义.发育于华北克拉通南缘中条山地区涑水杂岩中的烟庄正长花岗岩的形成年龄和成因还没有被很好地限定,构造背景还存在争议.对烟庄花岗岩进行了锆石U-Pb年代学和Hf同位素以及全岩地球化学和Nd同位素研究.烟庄花岗岩锆石SHRIMP U-Pb年龄为2 515±7 Ma.岩石具有高硅(SiO2=73.05%~74.85%)、高钾(K2O=4.46%~5.86%)、富碱(ALK=8.32%~9.36%)、贫钙(CaO=0.55%~0.98%)、低TFeO*(0.73%~1.28%)和MgO(0.31%~0.52%)的特征,A/CNK=1.01~1.04,为弱过铝质的钾玄系列.稀土总量变化较大(ΣREE=63.80×10-6~250.02×10-6)),轻重稀土元素分异明显((La/Yb)N=25.44~92.87),Eu异常变化较大(Eu/Eu*=0.47~0.79).岩石低Sr、Ba,富集Rb、Th、U等元素,亏损Nb、Zr、Y、Yb、Cr、Co、Ni等元素,具有较高的Rb/Sr、Rb/Ba和Sr/Yb比值以及较低Sm/Nd和Nd/Th比值,具有高分异I型花岗岩的特征.烟庄花岗岩具有0附近的全岩εNd(t)值,岩浆锆石具有正的εHf(t)值(2.85~3.66),两阶段Hf模式年龄为2 258~2 883 Ma,多数在2 600~2 883 Ma之间.结合其他方面研究,烟庄花岗岩具有同碰撞和后碰撞花岗岩的特征,推测为新生地壳在由挤压向伸展转换的构造背景下部分熔融所形成,可能有少量地幔物质添加.这期钾质花岗岩的形成,标志着华北克拉通太古宙末期强烈岩浆活动的结束以及稳定陆壳的形成.

The formation of the voluminous syenogranites of the late Neoarchean is an important mark of maturation and stabilization of continental crust, and play a vital role in understanding the formation and evolution of early continental crust.However, the formation age and genesis of the Yanzhuang syenogranite in the Sushui Complex in the southern margin of the North China Craton are not well defined, and the tectonic setting remains controversial. This paper presents the zircon U-Pb ages and Hf isotopes as well as whole rock element and Nd isotope compositions of the Yanzhuang syenogranites. SHRIMP dating of zircon from the granite yields an age of 2 515±7 Ma. The rocks are high in SiO2(73.05%-74.85%) and K2 O(4.46%-5.86%) and low in CaO(0.55%-0.98%), total FeO(0.73%-1.28%) and MgO(0.31%-0.52%), with K2 O+Na2 O and A/CNK at 8.32%-9.36% and 1.01-1.04, respectively. They show variations in REE contents(ΣREE=63.8×10-6-250.02×10-6), with relative enrichment of LREE to HREE((La/Yb)N=25.44-92.87) and somewhat negative Eu anomaly(Eu/Eu*=0.47-0.79). The rocks are low in Sr and Ba, and high in Rb, Th and U, with depletion in Nb, Zr, Y, Yb, Cr, Co and Ni. Thus they have high Rb/Sr,Rb/Ba and Sr/Yb ratios and low Sm/Nd and Nd/Th ratios, and show the characteristics of highly fractionated I type granite. The Yanzhuang syenogranite has whole-rock εNd(t) values of-1.09-0.89 and magmatic zircon εHf(t) values of 2.85-3.66, with Hf model TDM2 ages of 2 258-2 883 Ma(mainly 2 600-2 883 Ma). Combined with early work, this study indicates that the Yanzhuang syenogranite shows the feature of syn-collision and post-collision granites formed by partial melting of juvenile crust in a tectonic transition setting from compression to extension, probably with addition of a small amount of mantle material. The formation of voluminous syenogranites in this period marks the termination of the Archean intense magmatism and the stabilization of the North China Craton at the end of the Neoarchean.