Lorin Davies

Bio: Lorin Davies is an academic researcher. The author has contributed to research in topics: Cretaceous & Crust. The author has an hindex of 2, co-authored 3 publications receiving 39 citations.

Mesozoic Paleo-Pacific Subduction Beneath SW Borneo: U-Pb Geochronology of the Schwaner Granitoids and the Pinoh Metamorphic Group

Abstract: The Schwaner Mountains in southwestern Borneo form a large igneous province with a complex magmatic history and poorly known tectonic history. Previously it was known that Cretaceous granitoids intruded metamorphic rocks of the Pinoh Metamorphic Group assumed to be of Paleozoic age. Jurassic granitoids had been reported from the southern Schwaner Mountains. Most ages were based on K-Ar dating. We present new geochemistry, zircon U-Pb and 40Ar/39Ar age data from igneous and metamorphic rocks from the Schwaner Mountains to investigate their tectono-magmatic histories. We subdivide the Schwaner Mountains into three different zones which record rifting, subduction-related and post-collisional magmatism. The Northwest Schwaner Zone (NWSZ) is part of the West Borneo Block which in the Triassic was within the Sundaland margin. It records Triassic to Jurassic magmatism during early Paleo-Pacific subduction. In contrast, the North Schwaner Zone (NSZ) and South Schwaner Zone (SSZ) are part of the SW Borneo (Banda) Block that separated from NW Australia in the Jurassic. Jurassic granitoids in the SSZ are within-plate (A-type) granites interpreted to have formed during rifting. The SW Borneo (Banda) Block collided with eastern Sundaland at c. 135 Ma. Following this, large I-type granitoid plutons and arc volcanics formed in the NWSZ and NSZ between c. 90 and 132 Ma, associated with Cretaceous Paleo-Pacific subduction. The largest intrusion is the c. 110 to 120 Ma Sepauk Tonalite. After collision of the East Java-West Sulawesi (Argo) Block, subduction ceased and post-collisional magmatism produced the c. 78 to 85 Ma Sukadana Granite and the A-type 72 Ma Sangiyang Granite in the SSZ. Rocks of the Pinoh Metamorphic Group mainly exposed in the NSZ, previously assumed to represent Paleozoic basement, contain abundant Early Cretaceous (110 to 135 Ma) zircons. They are interpreted as volcaniclastic sediments that formed contemporaneously with subduction-related volcanic rocks of the NSZ subsequently metamorphosed during intrusion of Cretaceous granitoids. There are no igneous rocks older than Cretaceous in the NSZ and older than Jurassic in the SSZ and there is no evidence for a continuation of a Triassic volcanic arc crossing Borneo from Sundaland to the east.

Cretaceous Crust in SW Borneo : Petrological, Geochemical and Geochronological Constraints from the Schwaner Mountains

Abstract: New geochronological data from SW Borneo indicate that supposed basement rocks of the Pinoh Metamorphic Group are Cretaceous rather than Palaeozoic as accepted until now. They are intruded by Cretaceous granites in the Schwaner Mountains. The Southern Schwaner Zone (SSZ) intrusives are granites and alkali-granites. Petrological data and major and trace element compositions indicate that they are within-plate granitoids (WPG) with a mix of Sand I-type characteristics. U-Pb ages of zircons from SSZ granitoids record magmatism at c. 185 Ma and c. 75 Ma. Granitoid rocks from the Northern Schwaner Zone (NSZ) are I-type tonalites and diorites. Trace element compositions indicate an arc magmatic character. U-Pb ages of zircons from Schwaner granitoids demonstrate that NSZ magmatism took place from c. 120 Ma to c. 80 Ma. Unmetamorphosed and metamorphosed volcanic rocks from the NSZ are tuffs, ignimbrites, and lavas of intermediate to acid composition. Trace element compositions indicate a volcanic arc character and they chemically resemble the NSZ granitoids. U-Pb ages of zircons record volcanism from c. 130 Ma. Metamorphic rocks (the Pinoh Metamorphic Group) are pelitic schists and hornfelses, with occasional quartzites and metabasites. Major element geochemistry points to an igneous protolith. Trace element plots suggest volcanogenic sediments which chemically resemble the NSZ granitoids. All metamorphic rocks contain Cretaceous zircons. Their ages overlap with zircons from volcanic and plutonic rocks, suggesting that rocks of the Pinoh Metamorphic Group were derived from a volcanogenic protolith which was subjected to thermal metamorphism related to granitoid intrusion. * Royal Holloway, University of London ** Research School of Earth Sciences, The Australian National University, Canberra WPG magmatism at c. 185 Ma is considered to mark extensional rifting of a SW Borneo block from the northern margin of Australia. This block moved northwards during the Cretaceous forming an intraoceanic arc above a subduction zone in the early Cretaceous which provided the source of the NSZ arc granitoids. The block docked with Sundaland at about 90 Ma.

The palaeogeography of Sundaland and Wallacea since the Late Jurassic

Abstract: The continental core of Southeast (SE) Asia, Sundaland, was assembled from Gondwana fragments by the Early Mesozoic. Continental blocks rifted from Australia in the Jurassic [South West (SW) Borneo, East Java-West Sulawesi-Sumba], and the Woyla intraoceanic arc of Sumatra, were added to Sundaland in the Cretaceous. These fragments probably included emergent areas and could have carried a terrestrial flora and fauna. Sarawak, the offshore Luconia-Dangerous Grounds areas, and Palawan include Asian continental material. These probably represent a wide accretionary zone at the Asia-Pacific boundary, which was an active continental margin until the mid Cretaceous. Subduction ceased around Sundaland in the Late Cretaceous, and from about 80 Ma most of Sundaland was emergent, physically connected to Asia, but separated by deep oceans from India and Australia. India moved rapidly north during the Late Cretaceous and Early Cenozoic but there is no evidence that it made contact with SE Asia prior to collision with Asia. One or more arc-India collisions during the Eocene may have preceded India-Asia collision. The arcs could have provided dispersal pathways from India into SE Asia before final suturing of the two continents. During the Late Cretaceous and Early Cenozoic there was no significant subduction beneath Sumatra, Java and Borneo. At about 45 Ma Australia began to move north, subduction resumed and there was widespread rifting within Sundaland. During the Paleogene east and north Borneo were largely submerged, the Makassar Straits became a wide marine barrier within Sundaland, and West Sulawesi was separated from Sundaland but included land. By the Early Miocene the proto-South China Sea had been eliminated by subduction leading to emergence of land in central Borneo, Sabah and Palawan. Australia-SE Asia collision began, eliminating the former deep ocean separating the two continents, and forming the region now known as Wallacea. The microplate or terrane concept of slicing fragments from New Guinea followed by multiple collisions in Wallacea is implausible. Neogene subduction drove extension and fragmentation of Wallacea that caused both subsidence of deep marine basins and elevation of land; bathymetry changed very rapidly, especially during the Pliocene, but the detailed palaeogeography of this region remains uncertain.

Tectonic Evolution of Sundaland

Abstract: Sundaland, the continental core of SE Asia, is a heterogeneous collage of continental blocks and volcanic arcs bounded by narrow suture zones that represent the remnants of ancient ocean basins. All the continental blocks of Sundaland were derived directly or indirectly from the Arabia-India–Australia margin of eastern Gondwana by the opening and closure of three successive ocean basins, the Palaeo-Tethys (Devonian-Triassic), Meso-Tethys (Permian-Cretaceous) and Ceno-Tethys (Jurassic-Cretaceous), and assembled by the closure of these ocean basins. Core Sundaland comprises a western Sibumasu block and an eastern Indochina–East Malaya block with an island arc terrane, the Sukhothai Island Arc, sandwiched between. The Palaeo-Tethys is represented by the Changning–Menglian, Chiang Mai-Chiang Rai, Chanthaburi and Bentong–Raub Suture Zones that form the boundary between Sibumasu and the Sukhothai Arc. The Indochina block was derived from Gondwana in the Devonian when the Palaeo-Tethys opened. The Sukhothai Arc formed on the margin of Indochina in the Carboniferous, and then separated by back-arc spreading in the Permian. The Jinghong, Nan–Uttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Sibumasu Terrane separated from Gondwana in the late Early Permian when the Meso-Tethys opened and collided with the Sukhothai Arc and Indochina in the Middle-Late Triassic. The Cathaysian West Sumatra block possibly represents a part of the Sukhothai Arc and was emplaced by strike-slip tectonics outboard of Sibumasu in the Triassic. The West Burma Block was already attached to Sundaland before the Late Triassic and is likely a disrupted part of Sibumasu. East Java-West Sulawesi and South West Borneo are tentatively identified as the missing “Argoland” and “Banda” blocks which must have separated from NW Australia in the Jurassic and subsequently accreted to SE Sundaland in the Cretaceous.

Southeast Asia: New Views of the Geology of the Malay Archipelago

Abstract: Southeast (SE) Asia is surrounded by subduction zones causing intense seismicity and volcanic activity Subduction has been the principal tectonic driver of collisions that caused the growth of continental SE Asia, and most recently the collision of Australia with SE Asia The western part of SE Asia, Sundaland, is a heterogeneous and weak region, reflecting processes that can be observed today in the east, where there are subduction zones in different stages of development A close relationship between subduction rollback and extension has caused dramatic elevation of land, exhumation of deep crust, and spectacular subsidence of basins, observable with remotely acquired images and seismic and multibeam data obtained from oil exploration New dating indicates that subsidence and uplift occurred at high rates during short time intervals Laboratory studies, modeling, and reconstructions provide valuable insights, but field-based studies continue to present surprises and new discoveries essential for interp