Seafloor spreading magnetic anomalies south off Sri Lanka

Abstract

Results obtained from compilation and reinterpretation of about 21,200 line km of bathymetry, magnetic and satellite gravity data between 10°S to 10°N latitudes and 75 to 90°E longitudes south off Sri Lanka are presented here. Magnetic data and the synthetic seafloor spreading model reveal the presence of Mesozoic anomaly sequence M11 through M0 south of Sri Lanka. The oldest magnetic anomaly M11 (134 Ma) occurs between 110 and 140 km away from the Sri Lankan coast. The seafloor created during the Early Cretaceous is estimated to have evolved with variable half-spreading rates ranging from 5.5 to 1.53 cm/yr. The trends of the fracture zones inferred from the offsets in the magnetic anomalies have been constrained using the satellite gravity mosaic. The Cretaceous Magnetic Quiet Zone (CMQZ, 121-84 Ma) crust between the isochrons M0 and A34 has an unequal width and widens from about 170 km in the west (80°E longitude) to about 500 km towards east (85°E longitude). Plate reconstruction models for 160 (Fit), 134 (M11), 121 (M0) and 84 Ma (A34) are generated under the constraints of newly identified magnetic anomaly isochrons and fracture zones. The mismatch in the A34 reconstruction is attributed to the emplacement of the Ob, Lena and Marion Dufresne seamounts at the spreading ridge axis and/or the frequent ridge jumps in the Middle Cretaceous during the major plate reorganization.

Repeat ridge jumps associated with plume-ridge interaction, melt transport, and ridge migration

“…Mid‐ocean ridge jumps associated with plume‐ridge interaction are observed near current and former locations of many hot spots including Iceland [ Hardarson et al , 1997; Jóhannesson , 1980], the Galapagos [ Wilson and Hey , 1995], Ascension [ Brozena and White , 1990], Shona [ Small , 1995], Shatsky Rise [ Nakanishi et al , 1999], Louisville [ Géli et al , 1998; Small , 1995], and along the Ninety‐East Ridge [ Desa et al , 2006; Krishna et al , 1995; Krishna and Rao , 2000; Small , 1995]. In Figure 5c, we compare the trend predicted by equations (20a) and (20b) to observed values of t jump / t age and Δ X and inferred values of q max at four hot spots: Ascension, Iceland (since ∼16 Ma), Galapagos (at 10 Ma), and Louisville.…”

“…Ridge jumps are predicted to occur below any one curve for a given q max . Data are from Breivik et al [2006], Brozena and White [1990], Desa et al [2006], Géli et al [1998], Hardarson et al [1997], Krishna et al [1995], Krishna and Rao [2000], LaFemina et al [2005], Mjelde et al [2008], Nakanishi et al [1999], Sæmundsson [1974], Small [1995], and Wilson and Hey [1995].…”

“…At many locations including Iceland since ∼16 Ma [ Hardarson et al , 1997; Jóhannesson , 1980], Shatsky Rise [ Nakanishi et al , 1999], and along the Ninety‐East Ridge [ Desa et al , 2006; Krishna et al , 1995; Krishna and Rao , 2000], proximal ridge segments often jump repeatedly toward the hot spot as the rest of the plate boundary migrates away from the hot spot. Alternatively, the hot spot might capture a ridge segment through asymmetric spreading, such as at the Galapagos between ∼5 and ∼2.5 Ma during which the ridge remained fixed with the hot spot without resolvable discrete ridge jumps [ Hey , 1977; Wilson and Hey , 1995].…”

Thermochronological dating of brittle structures in basement rocks: A case study from the onshore passive margin of SW Sri Lanka

“…The dispersal of Gondwana started during the Permo‐Carboniferous with the opening of intracontinental rift basins [e.g., Biswas , 1999; Catuneanu et al , 2005], and extension culminated during Jurassic – Cretaceous times. Seafloor anomalies within the Mozambique Basin (M25, 158 Ma) and south of Sri Lanka (M11, 134 Ma) document oceanic crust formation during the separation of the Madagascar/India/Sri Lanka block, East Africa and East Antarctica [e.g., Salman and Abdula , 1995; Desa et al , 2006]. Following the initial opening of the proto Indian Ocean, the India/Sri Lanka/Seychelles block sheared off Madagascar and started to move northward, as recorded by late Cretaceous to middle Eocene episodes of seafloor spreading [e.g., Desa et al , 2006] and late Cretaceous volcanism [ Storey et al , 1995].…”

Structural and tectonic interpretation of geophysical data along the Eastern Continental Margin of India with special reference to the deep water petroliferous basins

“…Different views persist on the timing of breakup and rifting between India and east Antarctica and based on magnetic anomaly identifications it ranges between 132 Ma (Ramana et al, 1994;Desa et al, 2006) and 120 Ma (Gopala Rao et al, 1997). Observation of M2 to M9 anomalies and identification of fossil ridge in the Enderby basin of east Antarctica (Gaina et al, 2003) suggests younger magnetic lineations of M1 and M0 in the Bay of Bengal.…”