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Zn-Rich Spinel in Association with Quartz in the Al-Rich Metapelites from the Mashan Khondalite Series, NE China

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Zn-Rich Spinel in Association with Quartz in the Al-Rich Metapelites from the Mashan Khondalite Series, NE China Journal of Earth Science, Vol. 25, No. 2, p. 207–223, April 2014 ISSN 1674-487X Printed in China DOI: 10.1007/s12583-014-0428-4 Zn-Rich Spinel in Association with Quartz in the Al-Rich Metapelites from the Mashan Khondalite Series, NE China Xinzhuan Guo*1, Akira Takasu2, Yongjiang Liu3, Weimin Li3 1. Institute for Study of the Earth’s Interior, Okayama University, Misasa, Tottori-ken 682-0193, Japan 2. Department of Geoscience, Shimane University, Matsue 690-8504, Japan 3. College of Earth Sciences, Jilin University, Changchun 130061, China ABSTRACT: Al-rich metapelites from the Mashan khondalite series are characterized by the assem- blage Spl+Grt+Sil+Crd+Bt+Pl (An72)+Kfs+Quartz+graphite. Large amounts of spinel+quartz assem- blages occur as inclusions in garnet and prismatic sillimanite in the Al-rich metapelites of the Mashan complex, NE China. The chemical composition of spinel is characterized by Zn-rich (XZn=0.33–0.40. * * 2+ 3+ 3+ XZn=Zn/Zn+Mg+Fe ) (Fe =Fe +Fe ) and Fe rich (up to 0.31 p.f.u.). The characteristic chemical composition and the mineral association indicated that the formation of spinel and quartz assemblage may be due to the breakdown of Zn-rich staurolite. The geothermobarometers studies show that the peak temperature of the Mashan complex is around 820 ℃ and the peak pressures is 8.0 kbar. The Mashan complex shows a typical orogen style P-T path. KEY WORDS: Al-rich metapelites, Mashan complex, khondalite, spinel+quartz, granulite. 1 INTRODUCTION composition analysis and petrographical studies. The tempera- The Mashan khondalite series in the Mashan complex, ture of the peak metamorphism was confirmed to be much NE China, are characterized by graphite-bearing, Al-rich and lower than that of the UHT metamorphism (usually higher than phosphorus-bearing, and are mainly composed of Al-rich pelitic 900 ℃). rocks, felsic rocks and calc-silicate rocks. These rocks have been intruded by syn- and post-tectonic granitic rocks. Partial 2 GEOLOGICAL SETTINGS melting and migmatization are widely developed in the Mashan The Jiamusi Massif lies east of the Paleozoic Central khondalite series. Previous petrological studies showed that the Asian Orogenic belt (CAOB), located between the Siberian and Mashan khondalite series underwent granulite facies metamor- the North China cratons (Sengör et al., 1993) (Fig. 1), limited phism and were characterized by a tight clockwise P-T path by the Mudanjiang fault to the west, the Jiayi fault to the north- with peak temperatures of 850 ℃ and pressures of 7.4 kbar west, the Dunmi fault to the southeast and the Tongjiang fault (Jiang, 1992). to the east. In this study, we focused on the Al-rich metapelites of the The Jiamusi Massif is composed of two complexes: the Mashan khondalite series. Large amounts of spinels together Mashan complex of ~500 Ma in metamorphic age (Wilde et al., with quartz occurred as inclusions in peak mineral assem- 2000) and metamorphosed Jurassic accretionary Heilongjiang blages, such as garnet, sillimanite and K-feldspar in the Al-rich complex (Wu et al., 2007). Most geologists believe the Mashan metapelites. Spinel+quartz mineral assemblage is potential as complex is the basement and the Heilongjiang complex is the the ultra-high-temperature (UHT) metamorphism indicator. A cover. SHRIMP-U/Pb zircon ages of the Mashan complex re- lot of studies in the past two decades have reported such min- ported by Wilde et al. (2003, 2000, 1999), Wilde and Wu eral assemblage in the granulite-facies rocks (Sato et al., 2009; (2001) suggested that the Mashan complex was once associated Shimizu et al., 2009; Barbosa et al., 2006; Morimoto et al., with a Late Pan-African orogenic belt, which included parts of 2004; Sarkar et al., 2003; Sengupta et al., 1999; Waters, 1991). East Antarctica, Western Australia, Sri Lanka and India, and Here, the genesis of the spinel+quartz and the metamorphic possibly also portions of Madagascar, Tanzania and Kenya evolution were investigated through detailed chemical (Wilde et al., 1999), within the reconstructed Gondwana land. Two prograde metamorphic zones are recognized in the *Corresponding author:[email protected] Mashan complex: the granulite facies belt and the amphibolites © China University of Geosciences and Springer-Verlag Berlin belt. Al-rich metapelites of the granulite facies belt is located in Heidelberg 2014 the Xi Mashan, Liumao, Sandaogou and Didao. The distribu- tion of the metamorphic belt is independent of the depth. Manuscript received July 21, 2013. Spinel+quartz bearing metapelites were sampled from Manuscript accepted January 12, 2014. Guo, X. Z., Takasu, A., Liu, Y. J., et al., 2014. Zn-Rich Spinel in Association with Quartz in the Al-Rich Metapelites from the Mashan Khondalite Series, NE China. Journal of Earth Science, 25(2): 207–223, doi:10.1007/s12583-014-0428-4 208 Xinzhuan Guo, Akira Takasu, Yongjiang Liu and Weimin Li Figure 1. Geological sketch map of the Jiamusi Massif (a), modified from Wilde et al. (2003). (b) Geotectonic map of the east- ern Asia. CAOB, Central Asia Orogenic belt. Al-rich pelitic rocks (located in Xi Mashan, Sandaogou and clude sillimanite, K-feldspar, garnet, plagioclase, and quartz Liumao) (Fig. 2). Foliation of the Al-rich pelitic rocks is clearly and the minor minerals include biotite, muscovite, chlorite, defined by compositional layes of various rock types, and ilmenite and spinel. Strong lepidoblastic foliations are defined lineation is defined by biotite grains and prismatic sillimanite. by prismatic sillimanite. The garnet porphyroblasts are coarse-grained (2–6 mm), and contain fibrous sillimanite, 3 PETROGRAPHY fine-grained sillimanite, plagioclase, quartz, biotite, spinel and The Al-rich pelitic rocks are sub-divided into Spl-bearing ilmenite. The fibrous sillimante inclusions in garnet and the Grt-Sil schist, Spl-free Grt-Sil gneiss, Grt-free Sil schist and prismatic sillimanite in the matrix belong to different genera- Grt-Crd-Sil schist. All the pelitic schists show strong lepido- tions. blastic foliations defined by prismatic sillimanite. Weak folia- Spinels occur as inclusions in garnet, sillimanite, tions are developed by biotite in the pelitic gneiss. The mineral K-feldspar and biotite (Figs. 3a, 3b, 3f, and 3h). Spinels always assemblages in the Al-rich metapelites are summarized in Table contacts with the biotite and the quartz (Figs. 3a, 3c, 3d, 3e and 1. Mineral abbreviations are referred from Kretz (1983). 3g). In some case, some fine-grained spinels directly contact with the quartz with a sharp boundary (Figs. 3c, 3d and 3g). In 3.1 Spl-Bearing Grt-Sil Schist some case, biotite grains occur as inclusions in the spinel (Fig. This type of rock outcrops in Sandaogou and Xi Mashan. 3c). The differences between samples MS3-3 and SL06-4 are: (1) Myrmekitic and granophyric intergrowths are common the volume fractions of biotite and sillimanite in the MS3-3 are along the boundary between K-feldspar and plagioclase, with much lower than those of the latter; (2) biotites in the former quartz present as vermicular blebs within plagioclase, which only occur as the retrograde minerals. The major minerals in- could be elucidated as in situ partial melting at the peak Zn-Rich Spinel in Association with Quartz in the Al-Rich Metapelites from the Mashan Khondalite Series, NE China 209 130°30'E N Liumao Xi Mashan Mashan Graphite Quaternary schist 45°11'E Tertiary Sillimanite gneiss Cretaceous Marble Jurassic Cordierite Sandaogou gneiss Faults Gneiss/ Sample granulite 0 2 km localities Granitoid/ migmatite Figure 2. Simplified geological map of Xi Mashan, Sandaogou and Liumao. Sample localities are marked by stars. This map is modified after Wilde et al. (1999). Table 1 Mineral assemblages in the metapelites from the Mashan complex Classification Sample No. Mineral assemblage Spl-bearing Grt-Sil schist MS3-3, SL06-4 Grt+Sil+Bt+Spl+Kfs+Pl+Ms+Chl+Qtz±Il± Rt Spl-free Grt-Sil gneiss LG25-3, SL06-7 Grt+Sil+Bt+Kfs+Ms+Pl+Qtz+Il±Rt Grt-free Sil schist SL06-6 Sil+Bt+Kfs+Ms+Qtz±Il±Rt Grt-Crd-Sil schist SL06-1, SL06-2 Grt+Crd+Sil+Pl+Kfs+Bt+Ms+Qtz+Il+Rt Note: MS. Xi Mashan; LG. Liumao; SL. Sandaogou. conditions. This type of rock shows mesoperthitic texture with 3.3 Grt-Free Sillimanite Schist exsolution lamellae of Na-feldspar within the core of host The garnet-free sillimanite schists (ubiquitously outcrop K-feldspar. But the exsolution texture is rare in the rim of alkali in the Sandaogou) display a lepidoblastic fabric defined by feldspar. prismatic sillimanite. The major minerals include K-feldspar, Some garnet porphyroblasts have been pulled apart and plagioclase, quartz, graphite and prismatic sillimanite. The partly surrounded by biotite, which is partly altered to chlorite minor minerals include muscovite, biotite, and illmenite. The and muscovite. The altered biotite also grows along the cracks foliation is well developed by prismatic sillimanite. K-feldspar, of the garnet. The late retrograde metamorphism, replacement prismatic sillimanite and plagioclase define the peak metamor- of sillimanite by muscovite and the chloritization of the matrix phic assemblage. This type of rock is typically different from minerals, is common in this type of rock. the other metapelites by a lack of garnet. The retrograde textures in this type of rock are common. 3.2 Spl-Free Grt-Sil Gneiss Some plagioclase grains have almost been overprinted by Spinel-free garnet-sillimanite gneiss (sampled from Liu- muscovite. Some sillimanite grains are pulled apart, with retro- mao) is characterized by less amount of sillimanite than grade muscovite growing along the cracks. spinel-bearing garnet-sillimanite schist. The major minerals include quartz, K-feldspar, graphite, garnet, biotite and silli- 3.4 Grt-Crd-Sil Schist manite. Ilmenite, rutile and monazite occur as accessory miner- Grt-Crd-Sil schist sampled from the Sandaogou silli- als.
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