Tracing Argoland in eastern Tethys and implications for India-Asia convergence

Incremental accretion of continental fragments from East Gondwana to Eurasia resulted in the growth of Asia and rise of the Tibetan Plateau, yet its detailed evolution remains uncertain. Argoland, a continental fragment that rifted from NW Australia during the Late Jurassic, played a key role in the initial opening of the Indian Ocean and the evolution of eastern Tethys. However, its present identity remains elusive, with East Java-West Sulawesi currently assumed to be the most likely option. To constrain the missing Argoland and its role in India-Asia convergence, we report new detrital zircon data from Sulawesi, Indonesia, and West Burma, Myanmar, and synthesize literature results from relevant regions in Southeast Asia, which (>15,000) reveal age profiles of West Sulawesi, the central Sulawesi metamorphic belt, and southeast Borneo comparable to that of Bird’s Head, New Guinea, whereas age patterns of West Burma and East/West Java are similar to those of NW Australia. Notably, the most dominant age populations in NW Australia are rarely detected in Sulawesi and Borneo. These observations, combined with previous geological records and recent paleomagnetic data, suggest that West Burma is the mysterious Argoland, opposing the currently favored East Java-West Sulawesi model, with East Java and West Sulawesi probably having originated from NW Australia and Bird’s Head, respectively. We estimate an average northward motion of ∼6−8 cm/yr for West Burma, which split from NW Australia to approach the equator during ca. 155−95 Ma, shedding new light on the reconstruction and breakup of northern East Gondwana, progressive building of Southeast Asia, and India-Asia convergence.

Dendrobium sagin (Orchidaceae: Epidendroideae), a new species from the Bird’s Head Peninsula, West New Guinea

With about a dozen species, Dendrobium section Fugacia Smith (1905: 343) is one of the smaller but also one of the more distinctive clades within the large genus Dendrobium Swartz (1799: 82) (Schuiteman 2014). The plants have unbranched, tufted, clavate and usually distinctly angular stems of several internodes, of which only two or three of the uppermost ones carry a non-sheathing leaf. The inflorescences are subsessile and one- or few-flowered and arise singly from the swollen upper internodes. Flowers are ephemeral, generally opening early in the morning, often before sunrise, and withering in the afternoon. Unusually in Dendrobium, the lip is mobile and delicately hinged to the short column-foot, a character-state more commonly found in the sister genus Bulbophyllum Thouars (1822: t. 3). The lip is often broader than long and can be broadly obreniform in outline.