Origin of mafic microgranular enclaves (MMEs) and their host rocks of the Cretaceous Xiaojiang- Liangnong granitic complexes in the Southeast Coast Magmatic Belt, S China
Resource
Terrestrial, Atmospheric and Oceanic Sciences, 20(3), 481-500
Journal
Terrestrial Atmospheric and Oceanic Sciences
Pages
481
Date Issued
2009
Date
2009
Author(s)
Hsieh, Pei-Shan
Chen, Cheng-Hong
Yen, Chiung-Mei
Lee, Chi-Yu
Abstract
Cre ta ceous Late Yanshanian (LY) magmatism pro duced large amounts of I-type granitoids in the South east Coast Mag matic Belt (SCMB). I-type granitoids from Xiaojiang-Liangnong com plexes (N Zhejiang) in the north ern part of this belt are char ac ter ized by con tain ing abun dant mafic microgranular en claves (MMEs). On the ba sis of pe trog ra phy and min er al ogy, two types of MMEs are rec og nized. One (Type 1), en closed in the granodiorite, is com posed of am phi bole, high-Ti tab u lar bi o tite, plagioclase, K-feld spar, and quartz. Us ing the Al-in-am phi bole geobarometer, a shal low or i gin (4 -8 km) of am phi boles is sug gested. The other (Type 2), en closed in al kali feld spar gran ite, is am phi bole-free and com posed of low-Ti acicular bi o tite, plagioclase, K-feld spar, and quartz. Geo chem is try of ma jor and trace el e ments seems to re flect two dif fer ent evolv ing trends for these host granitoids. The Sr-Nd iso to pic fea tures in di cate that all the stud ied sam ples vary in a nar row range of Isr (0.7078 to 0.7082) and eNd (T) (-5.6 to -8.3), ex cept the Type 2 en claves and hosts that show slightly more de pleted com po si tions (Isr = 0.7073 to 0.7075 and eNd (T) = -5.0 to -6.0). U-Pb zir con ages ob tained are 109.6 0.9 Ma for the granodiorite and 113.5 1.1 Ma for the al kali feld spar gran ite, with 103.2 0.9 Ma for the Type 2 MMEs. In her ited ages of 117.0 2.0 Ma and 119.8 1.1 Ma seem to pres ent in the for mer two sam ples. Sim i lar i ties of min eral chem is try and iso to pic com po si tion among the MMEs-host pairs as well as the youn ger age of MMEs sug gest that MMEs of Xiaojiang-Liangnong com plexes most likely rep re sent mix ing/min gling prod ucts formed as a con se quence of the in tru sion of ba saltic magma into the host granitoids un der dif fer ent cool ing con di tions. Judg ing from the pres ence of in her ited zir con ages, the com po si tion gap be tween high-Ti and low-Ti bi o tite in granodiorite and al kali feld spar gran ite, and lower zir con sat u ra tion tem per a tures for the host granitoids (cal cu lated as 787C and 763C, re spec tively, for these two rock types), or i gin of the LY I-type granitoids in the Xiaojiang-Liangnong com plexes is re lated to par tial melt ing of dif fer ent sources, with the preceding alkali feldspar granite derived from more quartzofeldspathic and later granodiorite, from more mafic sources.
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journal article
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