Palaeocurrents and provenance of the Mae Rim Formation, Northern Thailand: implications for tectonic evolution of the Chiang Mai basin

Abstract

The Chiang Mai basin is the largest of a zone of rift basins that define the Northern Thailand Basin and Range Province. This province lies within the Shan Thai block of NW Indochina that extruded out of the India–Asia collision. The Mae Rim Formation crops out along the western side of the Chiang Mai basin. Detachment faults border the Mae Rim Formation on the west and north and juxtapose it against the high-grade Western Ranges metamorphic complex and its low-grade cover of Palaeozoic Shan-Thai rocks. Understanding the age and tectonic relationships between rifting, detachment faulting, ductile shear, uplift and exhumation of the Western Ranges metamorphic complex is critical to understanding the underlying deformational mechanisms that accompanied Indochina's extrusion. To better understand the palaeogeography of the Chiang Mai basin and its relationship to the Western Ranges metamorphic complex, several partial sections were measured, and palaeocurrent and clast-composition data from the Mae Rim Formation were collected. Poorly organized, immature conglomerates of the Mae Rim Formation probably represent alternating debris flows, sheet-flood, and braided channel deposits. The Mae Rim Formation probably accumulated in range-front alluvial fans, and graded rapidly into lacustrine deposits within the buried central part of the Chiang Mai basin. Except for the youngest strata, where gneissic clasts predominate, virtually all clasts in the Mae Rim Formation came from the low-grade metasedimentary rocks that form the cover of the Western Ranges metamorphic complex. Imbricated clasts indicate eastward palaeocurrents away from the metamorphic complex. Most of the Mae Rim Formation accumulated during the uplift of the Western Ranges but before erosion had breached the detachment fault. These new data suggest a tectonic history for the Chiang Mai basin that involved distinct phases of extension from late Oligocene to Quaternary, with at least two intervening periods of basin inversion.

P–T–t constraints on the development of the Doi Inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt, northern Thailand

“…A low-angle detachment fault separates the Doi Suthep dome from overlying Lower Paleozoic strata and from Tertiary fanglomerate of the Mae Rim Formation. Field relations show clearly that the complex was being actively exhumed during deposition of the Mae Rim Formation, inferred to have been in the late Oligocene to early Miocene (Rhodes et al, 2005). Singharajwarapan and Saengsrichan (1999) described similar lithological units and field relations in the upper part of the paragneiss sequence in the Mae Wang area between Doi Inthanon and Doi Suthep (Fig.…”

“…Garnet is notably lacking in the semipelitic gneiss, other than in rare schistose pelitic layers, whereas it is more common in injected mylonitic granite, aplite, and pegmatite. A few layers within the Macdonald et al (1993) and Rhodes et al (2005). Also shown are the locations of dating samples and samples used for pressure (P)-temperature (T) estimation.…”

Geological Model of Mae Tang-Mae Ngad Diversion Tunnel Project, Northern Thailand

“…These thrust faults were predominated by at least five times of inversion in Li Basin. Moreover, [27] and [44] showed evidence of regional basin inversion resulting in folding, some reactivation of normal faults as thrusts in Chiang Mai basin and the vicinity. The inversion events related to geological structure along tunnel alignment at road cut near Mae Ping river (km 14 + 900), and Mae Rerm reservoir (km 19 + 500) that are the tectonic impact by thrust faults lied near E-W trending ( Figure 5).…”

Floodplain sediment from a 100-year-recurrence flood in 2005 of the Ping River in northern Thailand

“…2). The Ping River basin is underlain by older Paleozoic gneissic granites, Paleozoic sediments and volcanics, Mesozoic granitic rocks, and Tertiary continental basin-fill sediments (Hess and Koch, 1979;Rhodes et al, 2005). The lowlands are underlain by alluvial fan, terrace, and floodplain deposits (Margane and Tatong, 1999).…”