Key points:1. The shrinking-plate hypothesis predicts subtle differences in azimuths of right-lateral versus left-lateral transform faults 2. Transform-fault azimuths observed globally indicate a statistically significant difference between right-lateral and left-lateral faults 3. Transform faults do not precisely parallel plate motion, thus validating inferred quantifiable plate non-rigidity AbstractThe rigid-plate hypothesis implies that oceanic lithosphere does not contract horizontally as it cools (hereinafter "rigid plate"). An alternative hypothesis, that vertically averaged tensional thermal stress in the competent lithosphere is fully relieved by horizontal thermal contraction (hereinafter "shrinking plate"), predicts subtly different azimuths for transform faults. The size of the predicted difference is as large as 2.44° with a mean and median of 0.46° and 0.31° respectively and changes sign between right-lateral-(RL-) and left-lateral-(LL-) slipping faults. For the MORVEL transform fault data set, all six plate pairs with both RL-and LL-slipping faults differ in the predicted sense, with the observed difference averaging 1.4°±0.9° (95% confidence limits.), which is consistent with the predicted difference of 0.9°. r, the sum-squared normalized misfit to global transform fault azimuths is minimized for γ = 0.8 ±0.4 (95% confidence limits) where γ is the fractional multiple of the predicted difference in azimuth between the shrinking-plate (γ = 1) and rigidplate (γ = 0) hypotheses. Thus observed transform azimuths differ significantly between RLslipping and LL-slipping faults, which is inconsistent with the rigid-plate hypothesis, but consistent with the shrinking-plate hypothesis, which indicates horizontal shrinking rates of 2% Ma -1 for newly created lithosphere, 1% Ma −1 for 0.1-Ma-old lithosphere, 0.2% Ma −1 for 1-Ma-old lithosphere, and 0.02% Ma −1 for 10 Ma-old-lithosphere, which are orders of magnitude higher than the mean intraplate seismic strain rate of ~10 −6 Ma −1 (5 × 10 −19 s −1 ).

Detailed facies analysis and morphotectonic investigations of the Malin River's alluvial fan in the western Ganga Plain, India, reveal that the morphology of the fan is largely tectonically controlled whereas the sedimentary processes are mainly climatically controlled. The sedimentation occurred in two distinct evolutionary cycles which are separated by a time gap. The older cycle deposited thick gravelly units up to the distal-fan area, whereas the sediment fill of the younger cycle is gavel-dominated in the proximal-fan area, gravel-sand dominated in the middle-fan area and sand-mud dominated in the distal-fan area. The gravels of the older cycle were emplaced by intense sediment gravity flows during periods of strengthened monsoon and steeper regional gradient. During the younger cycle, the proximal to distal parts of the fan were dominated by different sedimentary processes. This was a time of relatively weaker monsoon and gentler regional slopes, when gravels could travel only up to the middle-fan area. The gravels in the proximal-fan area have mainly been deposited by sediment gravity flows and channel processes; in the middle-fan area channel processes, sheetfloods and sediment gravity flows have been the main sedimentary processes; and in the distal-fan area fluvial processes of channel migration and overbank deposition have been the main sedimentary processes.

Using global multiresolution topography, we estimate new transform‐fault azimuths along the Cocos‐Nazca plate boundary and show that the direction of relative plate motion is 3.3° ± 1.8° (95% confidence limits) clockwise of prior estimates. The new direction of Cocos‐Nazca plate motion is, moreover, 4.9° ± 2.7° (95% confidence limits) clockwise of the azimuth of the Panama transform fault. We infer that the plate east of the Panama transform fault is not the Nazca plate but instead is a microplate that we term the Malpelo plate. With the improved transform‐fault data, the nonclosure of the Nazca‐Cocos‐Pacific plate motion circuit is reduced from 15.0 mm a−1 ± 3.8 mm a−1 to 11.6 mm a−1 ± 3.8 mm a−1 (95% confidence limits). The nonclosure seems too large to be due entirely to horizontal thermal contraction of oceanic lithosphere and suggests that one or more additional plate boundaries remain to be discovered.

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