Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex (Philippines) : A review

New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age. Radiometric dating of its plutonic and volcanic-hypabyssal rocks yielded middle Eocene ages. On the other hand, the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge – island arc affiliated Coto block of the ophiolite complex, together with isotopic age datings of its dikes and mafic cumulate rocks, also yielded Eocene ages. This offers the possibility that the Zambales Ophiolite Complex could have: (1) evolved from a Mesozoic arc (Acoje block) that split to form a Cenozoic back-arc basin (Coto block), (2) through faulting, structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or (3) through the interplay of slab rollback, slab break-off and, at a later time, collision with a microcontinent fragment, caused the formation of an island arc-related ophiolite block (Acoje) that migrated trench-ward resulting into the generation of a back-arc basin (Coto block) with a limited subduction signature. This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation

Secular Evolution of Continents and the Earth System

Understanding of secular evolution of the Earth system is based largely on the rock and mineral archive preserved in the continental lithosphere. Based on the frequency and range of accessible data preserved in this record, we divide the secular evolution into seven phases: (a) “Proto-Earth” (ca. 4.57–4.45 Ga); (b) “Primordial Earth” (ca. 4.45–3.80 Ga); (c) “Primitive Earth” (ca. 3.8–3.2 Ga); (d) “Juvenile Earth” (ca. 3.2–2.5 Ga); (e) “Youthful Earth” (ca. 2.5–1.8 Ga); (f) “Middle Earth” (ca. 1.8–0.8 Ga); and (g) “Contemporary Earth” (since ca. 0.8 Ga). Integrating this record with knowledge of secular cooling of the mantle and lithospheric rheology constrains the changes in the tectonic modes that operated through Earth history. Initial accretion and the Moon forming impact during the Proto-Earth phase likely resulted in a magma ocean. The solidification of this magma ocean produced the Primordial Earth lithosphere, which preserves evidence for intra-lithospheric reworking of a rigid lid, but which also likely experienced partial recycling through mantle overturn and meteorite impacts. Evidence for craton formation and stabilization from ca. 3.8 to 2.5 Ga, during the Primitive and Juvenile Earth phases, likely reflects some degree of coupling between the convecting mantle and a lithosphere initially weak enough to favor an internally deformable, squishy-lid behavior, which led to a transition to more rigid, plate like, behavior by the end of the early Earth phases. The Youthful to Contemporary phases of Earth, all occurred within a plate tectonic framework with changes between phases linked to lithospheric behavior and the supercontinent cycle.Peter A. Cawood, Priyadarshi Chowdhury, Jacob A. Mulder, Chris J. Hawkesworth, Fabio A. Capitanio, Prasanna M. Gunawardana, and Oliver Nebe

Stratigraphy and detrital zircon U-Pb-Hf isotope provenance of the Faro Peak formation, Central Yukon: implications for the Early Jurassic evolution of the Northern Canadian Cordillera

Late Triassic to Early Jurassic plate convergence and crustal thickening along the Cordilleran margin led to exhumation of the Intermontane terranes and subsequent deposition of multiple syntectonic stratigraphic assemblages in northwestern Canada. The Faro Peak formation is exposed in central Yukon along the Vangorda fault, the local suture between the Yukon-Tanana and Slide Mountain terranes, and constrains the timing and spatial extent of Early Jurassic tectonic exhumation. The Faro Peak formation unconformably overlies Yukon-Tanana terrane basement rocks (Snowcap assemblage) and unnamed Triassic strata (formerly lower member of the Faro Peak formation) and consists of Sinemurian to Toarcian massive sandstone and pebble to boulder conglomerate units. Field stratigraphic and detrital zircon U-Pb-Hf isotope studies indicate that the Faro Peak formation was locally sourced from Late Triassic to Early Jurassic arc- to syn-collisional intrusive rocks and mid- to upper Paleozoic arc and marine sedimentary successions. Snowcap assemblage rocks were recycled into the overlying Faro Peak formation and mostly consist of quartz-mica schist and quartzite units with Cryogenian and older maximum depositional ages and Precambrian detrital zircon grains that indicate northwestern Laurentian provenance. The Faro Peak formation was deposited in an isolated, structural basin by sediment gravity flows along the proto-Vangorda fault and separated from coeval, syn-tectonic deposition in the Whitehorse trough of southern Yukon by a regional drainage divide