Multi-scale, diverse origin inherited fabrics in rifts: A discussion through the lens of Cenozoic rifting in Thailand and comparison with other rift basins

Abstract

Inherited fabrics in all rifts can be broadly viewed as affecting different scales of features in particular: regional rift location, rift mode, boundary faults and secondary faults. In rifts developed in relatively cold lithosphere (e.g. East African Rift) inherited fabrics are predominantly old (Precambrian), widely separated in time from rifting. Rift location is strongly linked to where lithospheric mantle strength is reduced by deep mantle processes. Conversely, in Thailand (SE Asia) Cenozoic rifting developed in hot lithosphere (upper plate of major subduction zones), inherited fabrics comprise a highly diverse range of types (folds, thrusts in Phanerozoic sequences, gneiss domes, granite plutons, metamorphic foliations, strike-slip faults) that formed primarily during the Triassic (Indosinian Orogeny), Late Cretaceous and Paleogene. The orogenic development of gneiss domes in Thailand has parallels with Caledonian structures below the northern North Sea rifts. Rift location is controlled by the area of weakest crust, i.e. the Indosinian Paleotethys suture zone. Rift mode in Thailand varies from wide to narrow to core complex not only in response to crustal conditions (temperature, thickness), but also to local magmatism and fabric inheritance (major Indosinian detachment zones). The wealth of fabrics in Thailand influenced the location, dip direction, dip value, strike orientation, propagation and linkage history, fault length-displacement characteristics, fault population size distribution and map-view patterns of normal faults. Fabric influence on Thailand's rift basins is important to identify for a variety of reasons including: 1) as an extra factor to crustal thickness and geothermal gradient that influences rift mode, 2) as a major control on rift location, 3) as means of explaining atypical fault patterns in rift basins, and thereby supporting an extensional origin, rather than an escape-tectonics related strike-slip origin, 4) as a major influence on the characteristics of individual rift basins and how structures of economic importance have developed. 5) Causing fault populations to evolve in a variety of ways during the rift initiation phase. The Cenozoic rifts of Thailand provide insights into the influence of inherited fabrics on rifting that represent near opposite end-member lithospheric conditions to the EAR.