Terrane

About: Terrane is a research topic. Over the lifetime, 11025 publications have been published within this topic receiving 442596 citations. The topic is also known as: tectonostratigraphic terrane.

Geology and Tectonic Evolution of the Archean North Pilbara Terrain,Pilbara Craton, Western Australia

Abstract: Results from a multidisciplinary geoscience program since 1994 are summarized for the North Pilbara terrain of the Pilbara Craton. Major findings include the recognition of three separate terranes with unique stratigraphy, geochronological, and structural histories; the ca. 3.72 to 2.85 Ga East Pilbara granite-greenstone terrane, the ca. 3.27 to 2.92 Ga West Pilbara granite-greenstone terrane, and the <3.29 Ga Kuranna terrane in the southeast. These are separated by two late, dominantly clastic sedimentary basins deposited within tectonically active zones; the ca. 3.01 to 2.93 Ga Mallina basin in the west and the undated Mosquito Creek basin in the east. The oldest supracrustal rocks are the ca. 3.51 to 3.50 Ga Coonterunah and ca. 3.49 to 3.31 Ga Warrawoona Groups in the East Pilbara granite-greenstone terrane, deposited on fragments of older sialic crust to 3.72 Ga. The Warrawoona Group is subdivided into three main (ultra)mafic-felsic volcanic cycles including from base to top, the Talga Talga (3.49–3.46 Ga), Salgash (3.46–3.43 Ga), and newly defined Kelly (3.43–3.31 Ga) Subgroups. These dominantly basaltic rocks include chert beds containing Earth’s oldest stromatolites and are interbedded with significant felsic volcanics erupted intermittently from 3.49 to 3.43 Ga during emplacement of sheeted sodic granitoid sills. Estimates of autochthonous stratigraphic thickness range from 9 to 18 km. Deformation involved extensional growth faulting, local folding, and tilting of greenstones away from synvolcanic granitoid domes. Rapid partial convective overturn of upper and middle crust occurred at 3.32 Ga during voluminous potassic felsic magmatism, followed by deposition of the Budjan Creek Formation at 3.31 Ga. Granitoid plutonism at ca. 3.29 Ga in the Kuranna terrane preceded deposition of ultramafic through felsic volcanics and chert in the West Pilbara granite-greenstone terrane (3.27–3.25 Ga Roebourne Group) and western margin of the East Pilbara granite-greenstone terrane (3.26–3.24 Ga Sulphur Springs Group). Geochemical and isotopic data suggest that volcanism resulted from plume-related rifting of the East Pilbara granite-greenstone terrane, which was accompanied by granitoid plutonism and deformation. Following this was ca. 100 m.y. of relative quiescence during which locally economic concentrations of banded iron-formation and siliciclastics of the Gorge Creek Group were deposited in the East Pilbara granite-greenstone terrane. Thereafter, geologic events are more consistent with microplate tectonics, commencing with deformation at 3.15 Ga followed by deposition of 3.13 to 3.11 Ga bimodal volcanics in the West Pilbara granite-greenstone terrane (Whundo Group), which have juvenile Nd isotope signatures and thus may represent either a rift or island-arc succession. Basaltic rocks and minor felsic tuff were deposited in the East Pilbara granite-greenstone terrane at 3.06 Ga and possibly in the West Pilbara granite-greenstone terrane (Regal Formation). At 3.02 Ga, the Whundo and Roebourne Groups share a common history of deposition of banded iron-formation and granitoid plutonism across the Sholl shear zone, suggesting accretion at, or immediately preceding, this time. This was followed by deposition in the Mallina basin of the volcanic Whim Creek Group at 3.01 Ga, possibly as an arc, and then the 2.97 to 2.93 Ga volcanic Bookingarra (west) and clastic De Grey (east) Groups during periods of intracontinental rifting interspersed with compression and granitoid intrusion. The geochemistry of 2.95 Ga high Mg diorites (sanukitoids) indicates a previous episode of subduction during either the Whundo or Whim Creek Groups or both. Final events include emplacement of ultramafic-mafic layered intrusions (2.925 Ga in the West Pilbara granite-greenstone terrane), local shearing and lode Au mineralization (2.92 Ga in the West Pilbara granite-greenstone terrane, 2.90 Ga in the Mosquito Creek basin, 2.89 Ga in the East Pilbara granite-greenstone terrane), and intrusion of fractionated, Sn-Ta-Li-bearing granites to 2.85 Ga (East Pilbara granite-greenstone terrane).

Early Arc Volcanism and the Ophiolite Problem: A Perspective from Drilling in the Western Pacific

Abstract: Marine geologic studies and Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) transects of the intraoceanic Izu-Bonin-Mariana (IBM) forearcs have generated several important new ideas about the origin and evolution of these terranes. The first, and most striking, is the recognition that the initial phases of volcanism in these subduction zones developed nearly synchronously in the middle to late Eocene over a zone up to 300 km wide and thousands of kilometers long. This early, or “infant,” arc volcanism was characterized by the eruption of very depleted boninitic and arc tholeiitic lava compositions and occurred in extensional environments (as evidenced by dikes on Chichi-jima in the Bonin Islands). This infant arc volcanism was built on, or displaced, the pre-existing oceanic crust and had igneous production rates much higher than those of mature arcs—eruption rates on the order of those in slow-spreading ridges. This initial arc volcanism is unlike that developed during the “normal” or mature phases of arc activity and is a plausible mechanism for developing supra-subduction zone ophiolites. In fact, the duration of volcanism, volcanic and plutonic rock compositions, and structural setting in the IBM forearc are virtually identical to those in the Troodos ophiolite. The exposure of Eocene arc basement immediately adjacent to the axis of the Mariana-Bonin Trench requires some subduction erosion since the Eocene. However, if the Eocene basement did form by unusual, voluminous volcanism in an extensional environment, the required amount of erosion may only be 20 to 50 km; the vertical tectonics of the forearc indicate there has been little erosion of the forearc since the Oligocene. There is also clear evidence of minor, episodic, post-Eocene incorporation of older Pacific plate sediments and crustal fragments into the outer forearc. These forearcs are structurally and compositionally complex, and are clearly direct products of subduction, rather than just trapped pieces of oceanic crust. They have geological and geochemical similarities to supra-subduction zone ophiolites like those in Troodos and Oman and represent a previously unappreciated type of crustal construction. They are, in fact, the closest crustal analog to supra-subduction zone ophiolites that has been found in any modern geologic environment

Archean Accretion and Crustal Evolution of the Kalahari Craton—the Zircon Age and Hf Isotope Record of Granitic Rocks from Barberton/Swaziland to the Francistown Arc

Abstract: U^Pb and Lu^Hf isotope analyses, obtained by laser ablation-sector field-inductively coupled plasma-mass spectrometry on zircon grains from 37 granitoid samples indicate that the Kalahari Craton consists of at least five distinct terranescBarberton South (BS), Barberton North (BN), Murchison^Northern Kaapvaal (MNK), Limpopo Central Zone (LCZ), and Francistowncwhich underwent different crustal evolutions, and were successively accreted at c. 3� 23 Ga, 2� 9 Ga and 2� 65^2� 7 Ga. The investigated granitoids were emplaced over a period of c. 1.5 billion years, and are exposed along a c. 1000 km long traverse from the Barberton Mountain Land/ Swaziland to the Francistown arc complex, Botswana. The presented datasets reveal that most granitoids of the BS (3� 45^3� 10 Ga), MNK (2� 93^2� 67 Ga), Francistown (2� 70^2� 65 Ga) and LCZ terranes (3� 2^2� 03 Ga) show near-chondritic to subchondritic eHft (BS ¼ ^1� 7t oþ 0� 5; MNK ¼ ^3� 4t oþ 0� 7; Francistown ¼ ^0� 5t oþ 1� 1; LCZ ¼ ^12� 4t o ^1 � 8), indicating that crustal recyclingcperhaps by mixing of an older crust with a depleted mantle reservoircplayed an important role during their formation and growth. Higher, superchondritic eHft values, as indicative for an important depleted mantle influence, were obtained only from some granitoids of the BN terrane (eHf3� 23Ga ¼þ 2� 5 � 0� 8), the Gaborone Granite Suite (eHf2� 80Ga ¼þ 2� 0 � 1� 6), and from a few detrital zircons from the Mahalapye complex of the Limpopo Belt. In addition, the datasets show that the internal Hf isotope variation of magmatic zircon domains from most granitoids is commonly less than � 1� 5 e-units, and only in rare cases up to � 3� 1 e-units. The rare significant eHft variations may be ascribed to incomplete mixing of different sources during magma crystallization. It is also shown that the combined approach of cathodoluminescence imaging with U^Pb and Lu^Hf isotope analysis provides a powerful tool to distinguish zircon domains formed and/or altered at different times.