40Ar/39Ar ages of the high-P/T metamorphic rocks of the Heilongjiang Complex in the Jiamusi Massif, northeastern China

Abstract

The Heilongjiang Complex in northeastern China is composed mainly of alternating blueschists and pelitic schists which underwent high -P/T type metamorphism of the epidote blueschist facies. Phengites in the pelitic schists from two areas in the Heilongjiang Complex yielded

Newly discovered garnet-barroisite schists from the Heilongjiang Complex in the Jiamusi Massif, northeastern China

“…The mode of occurrence and petrographic characteristics are similar to those of the garnet -barroisite schists described in this paper (Sengan, 1985;Nishimura, 1998). Additionally, the metamorphic ages of the Suo belt are also similar to or slightly younger than those of the Heilongjiang Complex (145 -175 Ma; Li et al, 2009). Before the Japan Sea opened at ~ 15 Ma (Otofuji and Matsuda, 1983), the Heilongjiang high -P/T metamorphic rocks probably continued to the south.…”

“…), suggesting high -P metamorphic conditions. Blueschist facies metamorphic rocks in the Heilongjiang Complex yielded phengite 40 Ar/ 39 Ar ages of 161 -175 Ma and 145 -146 Ma (e.g., Wu et al, 2007;Li et al, 2009), probably suggesting multiple events of metamorphism and exhumation for high -P type metamorphic rocks.…”

“…The peak metamorphic conditions of the blueschists exposed in the Mudanjiang and Yilan areas were suggested as T = 350 -450 °C on the basis of the temperature range of the epidote -blueschist facies conditions and P = 6 -7 kbar using the b 0 values of phengites (Bai et al, 1988); however, the estimation of pressure by the b 0 value of phengite is unreliable (Massonne and Schreyer, 1987). Recently, Li et al (2009) reported blueschists exposed in the Yilan area that consist of glaucophane, phengite, epidote, albite, chlorite, titanite, and quartz. Phengites have high Si contents (Si = 6.70 -6.90 p.f.u.…”

U-Pb and 40Ar/39Ar age constrains on protolith and high-P/T type metamorphism of the Heilongjiang Complex in the Jiamusi Massif, NE China

“…Ar phengite age reported from the Luobei district, and it is similar to those obtained from Mudanjiang (164.8 ± 0.8 Ma; Li et al, 2009). In addition, phengites in the garnet -barroisite schist (423YJ -1) from the Yilan district do not show a plateau age, but a saddleshaped apparent age distribution ranging from 182.5 ± 0.8 Ma to 196.2 ± 1.0 Ma with a total gas age of 189.8 ± 0.8 Ma was obtained (Fig.…”

“…Previous age data compiled by Li et al (2009) and recent age dating (Zhou et al, 2009;Zhao and Zhang, 2011) suggest that the high -P/T metamorphic rocks of the Heilongjiang Complex were formed by Jurassic subduction metamorphism.…”